Part 4 - Steel Unit Structures, May 1999

Rules andRegulations forthe Classificationof a FloatingOffshore Installationat a Fixed Location

Part 4Steel Unit Structures

May 1999

Lloyd’s Register of Shipping100 Leadenhall StreetLondon EC3A 3BP

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© Lloyd’s Register of Shipping 1999Registered office: 71 Fenchurch Street, London EC3M 4BS

Offshore part 4 tpA4 7/6/99 16:11 (Black plate)

In providing services, information or advice neither Lloyd’s Register of Shipping (hereinafter referred to as LR) nor any of its officers, employeesor agents warrants the accuracy of any information or advice supplied. Except as set out herein, neither LR nor any of its officers, employees oragents (on behalf of each of whom LR has agreed this clause) shall be liable for any loss, damage or expense whatever sustained by any persondue to any act, omission or error of whatsoever nature and howsoever caused of LR, its officers, employees or agents or due to any inaccuracyof whatsoever nature and howsoever caused in any information or advice given in any way whatsoever by or on behalf of LR, even if held toamount to a breach of warranty. Nevertheless, if any person, who is party to the agreement pursuant to which LR provides any service, uses LR’sservices or relies on any information or advice given by or on behalf of LR and suffers loss, damage or expense thereby which is proved to havebeen due to any negligent act, omission or error of LR, its officers, employees or agents or any negligent inaccuracy in information or advice givenby or on behalf of LR, then LR will pay compensation to such person for his proved loss up to but not exceeding the amount of the fee (if any)charged by LR for that particular service, information or advice.

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Ships Disclaimer 5/6/99 1:52 pm Page 1 (Black plate)

Lloyd’s Register of Shipping

PART 1 REGULATIONS

1A GUIDELINES FOR CLASSIFICATION USING RISKASSESSMENT TECHNIQUES TO DETERMINEPERFORMANCE STANDARDS

2 MANUFACTURE, TESTING AND CERTIFICATION OFMATERIALS

3 FUNCTIONAL UNIT TYPES AND SPECIALFEATURES

4 STEEL UNIT STRUCTURES

5 MAIN AND AUXILIARY MACHINERY

6 CONTROL AND ELECTRICAL ENGINEERING

7 SAFETY SYSTEMS, HAZARDOUS AREAS AND FIRE

8 CORROSION CONTROL

9 CONCRETE UNIT STRUCTURES

© Lloyd's Register of Shipping, 1999. All rights reserved.

Except as permitted under current legislation no part of this work may be photocopied,stored in a retrieval system, published, performed in public, adapted, broadcast,transmitted, recorded or reproduced in any form or by any means, without the priorpermission of the copyright owner. Enquiries should be addressed to Lloyd's Register ofShipping, 100 Leadenhall Street, London, EC3A 3BP.

Rules and Regulations for the Classification of a Floating Offshore Installation at a Fixed Location, May 1999

Part Contents Part 4Page i

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CHAPTER 1 GENERAL

2 MATERIALS

3 STRUCTURAL DESIGN

4 STRUCTURAL UNIT TYPES

5 PRIMARY HULL STRENGTH

6 LOCAL STRENGTH

7 WATERTIGHT AND WEATHERTIGHT INTEGRITY AND LOAD LINES

8 WELDING AND STRUCTURAL DETAILS

9 ANCHORING AND TOWING EQUIPMENT

10 STEERING ARRANGEMENTS

11 QUALITY ASSURANCE SCHEME (HULL)

APPENDIX A FATIGUE – S-N CURVES, JOINT CLASSIFICATION AND STRESS CONCENTRATION FACTORS


Chapter Contents Part 4Page iii

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ContentsRules and Regulations for the Classification of a Floating Offshore Installation at a Fixed Location, May 1999

Part 4Page v


CHAPTER 1 GENERAL

Section 1 Rule application1.1 General1.2 Loading1.3 Advisory services1.4 Intact and damage stability

Section 2 Direct calculations2.1 General2.2 Equivalents

Section 3 National and International Regulations3.1 International Conventions3.2 International Association of Classification Societies (IACS)3.3 International Maritime Organization (IMO)

Section 4 Information required4.1 General4.2 Plans and supporting information4.3 Calculations and data4.4 Specifications4.5 Plans to be supplied to the unit

Section 5 Definitions5.1 General

Section 6 Inspection, workmanship and testing6.1 Inspection6.2 Workmanship6.3 Acceptance testing on completion

CHAPTER 2 MATERIALS

Section 1 Materials of construction1.1 General1.2 Steel1.3 Aluminium

Section 2 Structural categories2.1 General2.2 Column-stabilized and tension-leg units2.3 Self-elevating units2.4 Surface-type units2.5 Buoys, deep draught caissons, turrets and miscellaneous

structures

Section 3 Design temperature3.1 General

Section 4 Steel grades4.1 General

CHAPTER 3 STRUCTURAL DESIGN

Section 1 General1.1 Application

Section 2 Design concepts2.1 Elastic method of design2.2 Limit state method of design2.3 Plastic method of design2.4 Fatigue design

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Part 4Page vi


Section 3 Structural idealization3.1 General3.2 Geometric properties of section3.3 Determination of span point3.4 Grouped stiffeners

Section 4 Structural design loads4.1 General4.2 Definitions4.3 Load combinations4.4 Gravity and functional loads4.5 Buoyancy loads4.6 Wind loads4.7 Current loads4.8 Orientation and wave direction4.9 Wave loads4.10 Inertia loads4.11 Mooring loads4.12 Snow and ice loads4.13 Marine growth4.14 Hydrostatic pressures4.15 Deck loads4.16 Accidental loads4.17 Fatigue design4.18 Other loads

Section 5 Number and disposition of bulkheads5.1 General5.2 Self-elevating units5.3 Column-stabilized units5.4 Buoys and deep draught caissons5.5 Tension-leg units5.6 Protection of tanks carrying oil fuel and lubricating oil

CHAPTER 4 STRUCTURAL UNIT TYPES

Section 1 Column-stabilized units1.1 General1.2 Air gap1.3 Structural design1.4 Upper hull structure1.5 Columns1.6 Lower hulls1.7 Main primary bracings1.8 Bracing joints1.9 Lifeboat platforms

Section 2 Sea bed-stabilized units2.1 General2.2 Air gap2.3 Operating conditions2.4 Corrosion protection

Section 3 Self-elevating units3.1 General3.2 Air gap3.3 Structural design3.4 Hull structure3.5 Deckhouses3.6 Structure in way of jacking or elevating arrangements3.7 Leg wells3.8 Leg design3.9 Unit in the elevated position3.10 Legs in field transit conditions3.11 Legs in ocean transit conditions3.12 Legs during installation conditions



Part 4Page vii


3.13 Stability in-place3.14 Sea bed conditions3.15 Foundation fixity3.16 Bottom mat3.17 Independent footings3.18 Lifeboat platforms

Section 4 Surface-type units4.1 General4.2 Structural design4.3 Fatigue design4.4 Sloshing analysis4.5 Fore end structure4.6 Aft end structure4.7 Machinery spaces4.8 Topside structure

Section 5 Buoy units5.1 General5.2 Environmental considerations5.3 Water depth5.4 Design environmental conditions5.5 Environmental loadings5.6 Structural design5.7 Buoy structure5.8 Topside structure5.9 Lifeboat platforms5.10 Fatigue

Section 6 Tension-leg units6.1 General6.2 Air gap6.3 Loading and environmental considerations6.4 Structural design6.5 Tension-leg materials6.6 Tension-leg design6.7 Tension-leg permissible stresses6.8 Tension-leg fatigue design6.9 Tension-leg foundation design6.10 Piled foundations6.11 Suction piled foundations6.12 Gravity foundations6.13 Mechanical components6.14 Monitoring in service6.15 Tether replacement

Section 7 Deep draught caisson units7.1 General7.2 Air gap7.3 Environmental loadings7.4 Model testing7.5 Structural design7.6 Caisson structure7.7 Topside structure7.8 Lifeboat platforms7.9 Fatigue7.10 Corrosion protection

CHAPTER 5 PRIMARY HULL STRENGTH

Section 1 General requirements1.1 General1.2 Structural analysis1.3 Primary structure1.4 Connections and details1.5 Stress concentration



Part 4Page viii


Section 2 Permissible stresses2.1 General

Section 3 Buckling strength of plates and stiffeners3.1 Application3.2 Symbols3.3 Elastic critical buckling stress3.4 Scantling criteria

Section 4 Buckling strength of primary members4.1 Application4.2 Symbols4.3 Scantling criteria

Section 5 Fatigue design5.1 General5.2 Fatigue life assessment5.3 Fatigue damage calculations5.4 Joint classifications and S-N curves5.5 Cast or forged steel5.6 Factors of safety on fatigue life

CHAPTER 6 LOCAL STRENGTH

Section 1 General requirements1.1 General

Section 2 Design heads2.1 General2.2 Symbols2.3 Stowage rate and design heads

Section 3 Watertight shell boundaries3.1 General3.2 Column-stabilized and tension-leg units3.3 Self-elevating units3.4 Buoys and deep draught caissons

Section 4 Decks4.1 General4.2 Deck plating4.3 Deck stiffening4.4 Deck supporting structure4.5 Deck openings

Section 5 Helicopter landing areas5.1 General5.2 Plans and data5.3 Arrangements5.4 Landing area plating5.5 Deck stiffening and supporting structure5.6 Stowed helicopters5.7 Bimetallic connections

Section 6 Decks loaded by wheeled vehicles6.1 General6.2 Deck plating6.3 Deck stiffeners6.4 Deck girders and transverses6.5 Hatch covers6.6 Securing arrangements



Part 4Page ix


Section 7 Bulkheads7.1 General7.2 Symbols7.3 Watertight and deep tank bulkheads7.4 Watertight flats, trunks and tunnels7.5 Watertight void compartments7.6 Mud tanks7.7 Non-watertight bulkheads

Section 8 Double bottom structure8.1 Symbols and definitions8.2 General8.3 Self-elevating units8.4 Other unit types

Section 9 Superstructures and deckhouses9.1 General9.2 Symbols9.3 Definition of tiers9.4 Erections on self-elevating units9.5 Erections on other unit types9.6 Deck plating9.7 Deck stiffening9.8 Deck girders and transverses9.9 Strengthening at ends and sides of erections9.10 Unusual designs9.11 Aluminium erections9.12 Fire protection

Section 10 Bulwarks and other means for the protection of crew andother personnel

10.1 General requirements10.2 Construction of bulwarks subject to wave loading10.3 Guard rail construction10.4 Helicopter landing area10.5 Freeing arrangements10.6 Deck drainage

CHAPTER 7 WATERTIGHT AND WEATHERTIGHT INTEGRITY AND LOAD LINES

Section 1 General1.1 Application1.2 Plans to be submitted

Section 2 Definitions2.1 General2.2 Freeboard2.3 Weathertight2.4 Watertight2.5 Position 1 and Position 22.6 Drainage waterline2.7 Intact stability waterline2.8 Down flooding

Section 3 Installation layout and stability 3.1 Control rooms3.2 Damage zones

Section 4 Watertight integrity4.1 Watertight boundaries4.2 Tank boundaries4.3 Boundary penetrations4.4 Internal openings related to damage stability4.5 External openings related to damage stability4.6 Strength of watertight doors and hatch covers4.7 Weathertight integrity related to stability



Part 4Page x


Section 5 Load lines5.1 General5.2 Column-stabilized and tension-leg units5.3 Self-elevating units5.4 Deep draught caissons and buoy units5.5 Weathertight integrity

Section 6 Miscellaneous openings6.1 Small hatchways on exposed decks6.2 Hatchways within enclosed superstructures or ‘tween decks6.3 Hatch coamings6.4 Manholes and flush scuttles6.5 Companionways, doors and access arrangements on weather

decks6.6 Side scuttles, windows and skylights

Section 7 Tank access arrangements and closing appliances in oilstorage units

7.1 Materials7.2 Tank access hatchways in oil storage areas7.3 Enlarged cargo tank access openings7.4 Miscellaneous openings7.5 Access to spaces other than oil storage tanks7.6 Equivalents7.7 General access to spaces in the oil storage area

Section 8 Ventilators8.1 General8.2 Coamings8.3 Closing appliances

Section 9 Air and sounding pipes9.1 General9.2 Height of air pipes9.3 Closing appliances

Section 10 Scuppers and sanitary discharges10.1 General10.2 Closing appliances10.3 Closing appliances on surface-type units10.4 Rubbish chutes and similar discharges10.5 Materials for valves, fittings and pipes

CHAPTER 8 WELDING AND STRUCTURAL DETAILS

Section 1 General1.1 Application1.2 Symbols

Section 2 Welding2.1 General2.2 Welding consumables and equipment2.3 Welding procedures2.4 Impact test requirements2.5 Approval of welders2.6 Workmanship and inspection2.7 Butt welds2.8 Lap connections2.9 Closing plates2.10 Stud welding2.11 Fillet welds2.12 Welding of primary structure2.13 Welding of primary and secondary member end connections2.14 Welding of aluminium alloys2.15 Welding of tubular members



Part 4Page xi


Section 3 Secondary member end connections3.1 General3.2 Symbols3.3 Basis for calculation3.4 Scantlings of end brackets3.5 Arrangements and details

Section 4 Construction details for primary members4.1 General4.2 Symbols4.3 Arrangements4.4 Geometric properties and proportions4.5 Web stability4.6 Openings in the web4.7 End connections4.8 Primary member ring systems

Section 5 Structural details5.1 Continuity and alignment5.2 Arrangements at intersections of continuous secondary and

primary members5.3 Openings5.4 Sheerstrake and bulwarks5.5 Fittings and attachments, general5.6 Bilge keels and ground bars5.7 Other fittings and attachments

Section 6 Fabrication tolerances6.1 General

CHAPTER 9 ANCHORING AND TOWING EQUIPMENT

Section 1 Anchoring equipment1.1 General1.2 Equipment number1.3 Determination of equipment1.4 Anchors1.5 High holding power anchors1.6 Chain cables1.7 Arrangements for working and stowing anchors and cables1.8 Testing of equipment

Section 2 Towing arrangements and equipment2.1 General2.2 Strength2.3 Self-propelled units

CHAPTER 10 STEERING ARRANGEMENTS

Section 1 Rudders and steering gears1.1 General

Section 2 Fixed and steering nozzles2.1 General2.2 Nozzle structure2.3 Nozzle stock and solepiece2.4 Ancillary items

Section 3 Tunnel thrust unit structure3.1 Unit wall thickness3.2 Framing3.3 Watertightness



Part 4Page xii


CHAPTER 11 QUALITY ASSURANCE SCHEME (HULL)

Section 1 General1.1 Definitions1.2 Scope of the Quality Assurance Scheme

Section 2 Application2.1 Certification of the fabrication yard

Section 3 Particulars to be submitted3.1 Documentation and procedures3.2 Amendments

Section 4 Requirements of Parts 1 and 2 of the Scheme4.1 General4.2 Policy statement4.3 Responsibility4.4 Management Representative4.5 Quality control and testing personnel4.6 Resources4.7 The Quality Management System4.8 Regulatory requirements4.9 Control of drawings4.10 Documentation and change control4.11 Purchasing data and receipt4.12 Owner-supplied material4.13 Identification and traceability4.14 Fabrication control4.15 Control of inspection and testing4.16 Indication of inspection status4.17 Inspection, measuring and test equipment4.18 Non-conforming materials and corrective action4.19 Protection and preservation of quality4.20 Records4.21 Internal audit and management review4.11 Training4.23 Sampling4.24 Sub-contracted personnel, services and components

Section 5 Additional requirements for Part 2 of the Scheme5.1 Quality System procedures5.2 Quality Plans5.3 Material supplier approval5.4 Identification and traceability5.5 Fabrication control5.6 Control of inspection and testing5.7 Control of non-conforming materials and corrective action5.8 Records5.9 Training5.10 Sub-contracted personnel, services and components

Section 6 Initial assessment of fabrication yard6.1 General

Section 7 Approval of the fabrication yard7.1 General

Section 8 Maintenance of approval8.1 General

Section 9 Suspension or withdrawal of approval9.1 General



Part 4Page xiii


APPENDIX A FATIGUE – S-N CURVES, JOINT CLASSIFICATIONAND STRESS CONCENTRATION FACTORS

Section A1 GeneralA1.1 Application

Section A2 Fatigue design S-N curvesA2.1 Basic design S-N curvesA2.2 Modification to basic S-N curvesA2.3 Treatment of low stress cyclesA2.4 Treatment of high stress cycles

Section A3 Fatigue joint classificationA3.1 General

Section A4 Stress concentration factorsA4.1 GeneralA4.2 Summary of details includedA4.3 Transverse/circumferential butt weldA4.4 Longitudinal butt weldA4.5 Axial stiffener weldA4.6 Cope holes in stiffenersA4.7 Conical/tubular intersection weldsA4.8 Ring stiffener weldsA4.9 Surface attachment weldsA4.10 Unreinforced/ring reinforced penetrations – GeneralA4.11 Circular penetrationA4.12 Elliptical penetrationA4.13 Rectangular penetration with full radius endsA4.14 Rectangular penetration with corner radiusA4.15 Gusset stiffener terminationA4.16 Column to pontoon jointsA4.17 Bracing to column jointsA4.18 Bracing to bracing jointsA4.19 Cruciform joint


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1Lloyd’s Register of Shipping


Part 4, Chapter 1Sections 1 & 2

SECTION 1Rule application

1.1 General

1.1.1 The Rules, in general, apply to steel units of allwelded construction. The use of other materials in thestructure wil l be special ly considered. For concretestructures see Part 9. The Rules apply to the unit typesdefined in Parts 1 and 3. Units of unconventional design willreceive individual consideration based on the generalstandards of the Rules.

1.2 Loading

1.2.1 The Rules are framed on the understanding thatunits will be properly loaded and operated. Units are to beoperated in accordance with an Operations Manual which isto contain all the necessary information for the safe loadingand operation of the unit, see Pt 3, Ch 1,3.

1.2.2 For surface-type units, loading guidanceinformation may be required by means of a Loading Manual,see Pt 1, Ch 2,1.

1.3 Advisory services

1.3.1 The Rules do not cover certain technicalcharacteristics such as stability, trim, vibration, dockingarrangements, etc. The Committee cannot assumeresponsibility for these matters, but is willing to advise uponthem on request.

1.4 Intact and damage stability

1.4.1 New units will be assigned class only after it hasbeen demonstrated that the level of intact and damagestability is adequate, see Pt 1, Ch 2,1.

1.4.2 For classif ication purposes, the minimumrequirements for watertight and weathertight integrity are tocomply with Chapter 7.

Section

1 Rule application

2 Direct calculations

3 National and International Regulations

4 Information required

5 Definitions

6 Inspection, workmanship and testing

General

SECTION 2Direct calculations

2.1 General

2.1.1 Direct calculations may be specifically requiredby the Rules or may be submitted in support of alternativearrangements and scantlings. When requested, LR mayundertake calculations on behalf of designers and makerecommendations.

2.2 Equivalents

2.2.1 In addition to cases where direct calculations arespecifically required by the Rules, LR will consider alternativearrangements and scantlings which have been derived bydirect calculations in lieu of specific Rule requirements. Alldirect calculations are to be submitted for examination.

2.2.2 Where direct calculat ion procedures areemployed supporting documentation is to be submitted forappraisal and this is to include details of the following:• Calculation methods, assumptions and references.• Loading.• Structural modelling.• Design criteria and their derivation, e.g. permissible

stresses, factors of safety against plate panel instability,etc.

2.2.3 LR will be ready to consider the use of Builders’programs for direct calculations in the following cases:(a) Where it can be established that the program has

previously been satisfactorily used to perform a directcalculation similar to that now submitted.

(b) Where sufficient information and evidence of satisfactoryperformance is submitted to substantiate the validity ofthe computation performed by the program.

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SECTION 4Information required

4.1 General

4.1.1 In general, the plans and information required tobe submitted are given in 4.2.

4.1.2 Requirements for addit ional plans andinformation for functional unit types are given in Part 3.

4.1.3 Plans are generally to be submitted in triplicate,but only one copy of supporting documents and calculationswill be required.

4.2 Plans and supporting information

4.2.1 Plans covering the following items are to besubmitted for approval, as relevant to the type of unit:• Bilge keel details.• Bracings and associated primary structure.• Corrosion control scheme.• Deck structures including pillars and girders.• Double bottom construction.• Engine room construction.• Equipment and supports.• Erection sequence.• Footings, pads or mats.• Fore and aft end construction.• Helideck.• Ice strengthening.• Leg structures and spuds.• Loading manuals, preliminary and final.• Machinery seatings.• Main hull or pontoon structure.• Masts and derrick posts.• Materials and grades.• Midship sections showing longitudinal and transverse

material• Penetrations and attachments to primary structure.• Quality control and non-destructive testing procedures.• Riser support structures• Rudder, stock, tiller and steering nozzles.• Shell expansion.• Stability columns.• Stern frame and propeller brackets.• Structural bulkheads and flats.• Structure in way of jacking or elevating arrangements.• Superstructures and deckhouses.• Support structures for cranes, masts, derricks, flare

towers and heavy equipment.• Tank boundaries and overflows.• Tank testing procedures and schedules.• Temporary anchoring equipment.• Towing arrangements and equipment.• Transverse and longitudinal sections showing scantlings.• Watertight sub-division.• Watertight and oiltight bulkheads and flats.• Watertight and weathertight doors and hatch covers.• Welding details and procedures.


General

2 Lloyd’s Register of Shipping


SECTION 3National and International Regulations

3.1 International Conventions

3.1.1 The Committee, when authorized, will act onbehalf of Governments and, if requested, LR will certifycompliance in respect of National and International StatutorySafety and other requirements for offshore units.

3.1.2 In satisfying the Load Line Conventions, thegeneral structural strength of the unit is required to besufficient for the draught corresponding to the freeboards tobe assigned. Units built and maintained in accordance withLR’s Rules and Regulations possess adequate strength tosatisfy the Load Line Conventions.

3.2 International Association of ClassificationSocieties (IACS)

3.2.1 Where applicable, the Rules take into accountunified requirements and interpretations established by IACS.

3.3 International Maritime Organization (IMO)

3.3.1 Attention is drawn to the fact that Codes ofPractice issued by IMO contain requirements which areoutside classif ication as defined in these Rules andRegulations.


4.2.2 The following supporting plans and documentsare to be submitted:• General arrangements showing decks, profile and

sections indicating all major items of equipment andmachinery.

• Calculation of equipment number.• Capacity plan.• Cross curves of stability.• Cross curves of allowable V.C.G.• Design deck loading plan.• Dry docking plan.• Operations Manual, see Pt 3, Ch 1,3.• Tank sounding tables.• Wind heeling moment curves.• Lines plan or equivalent.

4.3 Calculations and data

4.3.1 The following calculations and information are tobe submitted where relevant to the unit type and its design:• Proposed class notations, operating areas and modes

of operation, list of operating conditions statingproposed draughts.

• Design environmental criteria applicable to each mode,including wind speed, wave height and period, or sea-state/wave energy spectra (as appropriate), waterdepth, tide and surge, current speed, minimum airtemperature, ice and snow loads, sea bed conditions.

• A summary of weights and centres of gravity of lightshipitems.

• A summary of all items of deadweight, deckstores/supplies, fuel, fresh water, drill water, bulk andsack storage, crew and effects, deck loads (actual, notdesign allowables), riser, guideline, mooring tensions,hook or derrick loads and ballast schedules. Thesummary should be given for each operating condition.

• Details of distributed and concentrated gravity and livedesign loadings including crane overturning moments.

• Tank content data, and design pressure heads.• Details of tank tests, model tests, etc.• Strength and fatigue calculations.• Calculation of hull girder still water bending moment

and shear force as applicable.• Calculation of midship section modulus.• Stability calculations for intact and damaged cases

covering a range of draughts to include all loadingconditions.

• Documentation of damage cases, watertight sub-division and limits for downflooding.

• Preliminary freeboard calculation.

4.4 Specifications

4.4.1 Adequate design specifications in appropriatedetail are to be submitted for information.

4.4.2 Specifications for the design and construction ofthe hul l and structure are to include materials,grades/standards, welding construction procedures andfabrication tolerances.

4.4.3 Specifications related to the unit’s proposedoperations are to include environmental criteria, modes ofoperation and a schedule of all model tests with reports onminimum air gap, motion predictions, mooring analysis, etc..

Lloyd’s Register of Shipping 3


General Part 4, Chapter 1Section 4

4.5 Plans to be supplied to the unit

4.5.1 The following plans and documents are to beplaced on board the unit, see Pt 3, Ch 1,2:• Operations Manual.• Loading Manual.• Construction Booklet.• Main scantlings plans.• Corrosion control system.

4.5.2 Where an OIWS (In-Water Survey) notation is tobe assigned, approved plans and information covering theitems detailed in Pt 3, Ch 1,2 are also to be placed on board.





SECTION 5Definitions

5.1 General

5.1.1 Rule length, L, in metres, for self-elevating unitsand semi-submersible units with twin lower hulls is to betaken as 97 per cent of the extreme length on the maximumdesign transit waterline measured on the centreline or on aprojection of the centreline, see Fig. 1.5.1.

5.1.2 The Rule length, L, for surface-type units is thedistance, in metres, on the summer load waterline from theforward side of the stem to the after side of the rudder postor to the centre of the rudder stock if there is no rudder post.L is to be not less than 96 per cent, and need not be greaterthan 97 per cent, of the extreme length on the summer loadwaterline. In ships with unusual stem or stern arrangementsthe Rule length, L, will be specially considered.

5.1.3 The Rule length for units with unconventionalform will be specially considered in relation to the transit oroperating waterlines.

5.1.4 Breadth, B, is the greatest moulded breadth, inmetres.

5.1.5 Depth, D, is measured, in metres, at the middleof the length, L, from the top of keel to top of the deck beamat side on the uppermost continuous deck.

5.1.6 Draught, T0, is the maximum design summeroperating draught, in metres, measured from top of keel.

5.1.7 Draught, TT, is the maximum design transitdraught, in metres, measured from top of keel.

5.1.8 The block coefficient, Cb, is the moulded blockcoefficient corresponding to the design draught T based onthe Rule length L and moulded breadth B as follows:

whereT = To for surface-type unitsT = TT for self-elevating and semi-submersible

units

Cb =moulded displacement m3 at draught T

LBT

5.1.9 In general, the forward perpendicular, F.P., is theperpendicular at the intersection of the waterline at thedraught T with the fore end of the hull. The aft perpendicular,A.P., is the perpendicular at the intersection of the waterlineat the draught T with the aft end of the hull, see also 5.1.2.

5.1.10 Amidships is to be taken as the middle of theRule length, L, measured from the forward side of the stem or hull.

5.1.11 Lightweight is defined as the weight of thecomplete unit with all its permanently installed machinery,equipment and outfit, including permanent ballast, spare partsnormally retained on board, and liquids in machinery andpiping to their normal working levels, but does not includeliquids in storage or reserve supply tanks, items ofconsumable or variable loads, stores or crew and their effects.

A.P. F.P.L1

TT

L = 0,97L1 in metres

TT = maximum transit draught, in metres, measured from top of keel 4407/74

Fig. 1.5.1Rule length for self-elevating units and

semi-submersible units with twin lower hulls


SECTION 6Inspection, workmanship and testing

6.1 Inspection

6.1.1 Adequate facilities are to be provided to enablethe Surveyor to carry out a satisfactory inspection of allcomponents during each stage of prefabrication andconstruction.

6.2 Workmanship

6.2.1 All workmanship is to be of good quality and inaccordance with good shipbuilding practice. Any defect is tobe rectified to the satisfaction of the Surveyor before thematerial is covered with paint, cement or other composition.The materials and welding are to be in accordance with therequirements of Part 2. The assembly sequence and weldingsequence are to be agreed prior to construction and are to beto the satisfaction of the Surveyor. Plates which have beensubjected to excessive heating while being worked are to besatisfactorily heat-treated before being erected in the hull.

6.2.2 Wood sheathing on decks. Where plateddecks are sheathed with wood, the sheathing is to beefficiently attached to the deck, caulked and sealed, to thesatisfaction of the Surveyor.

6.2.3 Rudder and sternframe. The final boring out ofthe propeller boss and sternframe skeg or solepiece, and thefit-up and alignment of the rudder, pintles and axles, are to becarried out after completing the major part of the welding ofthe after part of the unit. The contacts between the conicalsurfaces of pintles, rudder stocks and rudder axles are to bechecked before the final mounting.

6.3 Acceptance testing on completion

6.3.1 Hose testing. The items listed in Table 1.6.1 areto be hose tested to the satisfaction of the Surveyor.

6.3.2 Pressure testing. The items listed in Table 1.6.2are to be subjected to the appropriate test head using water,or, alternatively, a combination of water and air. Any item notsubjected to a complete pressure test, see 6.3.6, is to beleak tested in accordance with 6.3.3.

6.3.3 Leak testing is required on al l f i l let weldconnections on tank boundaries. This test is also required onerection welds on tank boundaries excepting welds made byautomatic processes. Selected locations of automaticerection welds and pre-erection manual or automatic weldsmay be required to be similarly tested at the discretion of theSurveyor taking account of the quality control proceduresoperating in the yard. This test is carried out by applying asoapy water solution to the weld being tested while the tankis subjected to an air pressure of 0,14 bar (0,14 kgf/cm2). Itis recommended that the air pressure in the tank is raised to0,21 bar (0,21 kgf/cm2), with a minimum number ofpersonnel in the vicinity of the tank, and then lowered to thetest pressure prior to inspection. Leak testing is to be carriedout before a protective coating is applied.

6.3.4 When a preservative coating is to be applied tothe internal structure of a tank, the water testing may takeplace after the application of the preservative, provided thatthe structure is carefully examined to ensure that all weldingand structural stiffening is completed prior to the applicationof the coating, excluding prefabrication primers. The causeof any discolouration or disturbance of the coating is to beascertained, and any deficiencies repaired. The attachmentof fittings to oil-tight surfaces should be completed beforetanks are tested.

6.3.5 Pressure testing may be carried out afloat wheretesting using water is undesirable in dry-dock or on thebuilding berth. The testing afloat is to be carried out byseparately filling each tank and cofferdam to the test head.For units with crude oil storage tanks, the testing afloat is tobe carried out by separately filling each tank and cofferdamto the test head given in Table 1.6.2.

6.3.6 In lieu of the complete pressure testing requiredby 6.3.2, a combination of a leak test and water pressure testmay be adopted but full details of the proposed testingarrangements are to be submitted for approval. The leak testis generally to be carried out on each tank while the unit is onthe building berth or dry-dock.

6.3.7 Trial trip and operational tests. The itemslisted in Table 1.6.3 are to be tested on completion of theinstallation or at sea trials. For positional mooring systems,see Pt 3, Ch 10.




Table 1.6.1 Hose testing requirements

Item

• Watertight doors and hatch covers, in place

• Watertight bulkheads,tunnels, flats, recesses andmain bracings

• Weathertight doors andother weathertight closing appliances

• Weathertight steel hatch covers

Requirements

Pressure at least 2,0 bar (2,0 kgf/cm2) atmaximum distance of 1,5 mfrom item under test, orequivalent





Table 1.6.3 Trial trip and operational tests

Item Requirement

Watertight doors andhatch covers

Windlass ondisconnectable units

Steering gear, main andauxiliary ondisconnectable units

Bilge suctions in dryspaces, and handpumps in peak spaces

To be operated under workingconditions

An anchoring test is to be carried outin the presence of the Surveyor

The test should demonstrate that thewindlass with brakes, etc.,functions satisfactorily, and that thepower to raise anchor can bedeveloped and satisfies the Rulerequirements

For Rule requirements, see Ch 9,1.7

To be tested under workingconditions, to the satisfaction of theSurveyors,to demonstrate that theRule requirements are met

For Rule requirements, seePt 5, Ch 18

To be tested under working conditionsto the satisfaction of the Surveyors

Table 1.6.2 Testing requirements

Deep tanks, bunkers, peaktanks (including closingarrangements)

Water ballast tanks and doublebottom tanks

Scupper and discharge pipesin way of tanks

Peak bulkheads not formingboundaries of tanks

Double plated rudders andnozzles

Watertight doors and hatchcovers

Storage tanks and cofferdams(or void spaces)

Pump-rooms, shell plating inway

Pump-room bulkheads notforming tank boundaries

Head of water representing the maximum pressure which could beexperienced in service, or to a 2,45 m head above the highest pointof the tank, or to the top of the overflow, whichever is the greater,but is to be not less than 2,0ρ m above the top of the tank whereρ is the relative density (specific gravity) of any intended liquid in thetank

As for deep tanks

As for deep tanks

Peaks to be filled with water to the level of the maximum transitwaterline

2,45 m head, and rudder should normally be tested while laid on itsside

Each appliance is to be tested to a head of water equivalent to themaximum design pressure head h4 for the watertight boundaryplating as defined in Table 6.7.1 in Chapter 6. The test should benormally be carried out before the door or hatch cover is fitted tothe unit. No leakage is permitted from appliances fitted withrubber gaskets.

As for deep tanks, but is to be not less than 2,0 ρ m above the top ofthe tank, where ρ is the relative density (specific gravity) of theintended liquid, or 12,0pv m (12,0pv m) above the top of the tankswhere pv is the maximum positive pressure/vacuum relief valvesetting, in bar (kgf/cm2)

To be carefully examined with the unit afloat

––

0,14 bar (0,14 kgf/cm2)

As for deep tanks

As for deep tanks

––

0,20 bar (0,20 kgf/cm2) andarrangements made to ensure thatno pressure in excess of 0,30 bar(0,30 kgf/cm2) can be applied

Not applicable

bar (0,14 kgf/cm2)

––

0,14 bar (0,14 kgf/cm2)Alternative methods of testing will be

considered

All unit types, where appropriate

Units with crude oil bulk storage tanks

Item to be tested Pressure testing requirements Leak testing requirements – air pressure




Part 4, Chapter 2Section 1

SECTION 1Materials of construction

1.1 General

1.1.1 The Rules relate in general to the construction ofsteel units, although consideration will be given to the use ofother materials. For the use of aluminium alloys, see 1.3.

1.1.2 The materials used in the construction of the unitare to be manufactured and tested in accordance with therequirements of Part 2. Materials for which provision is notmade therein may be accepted, provided that they complywith an approved specification and such tests as may beconsidered necessary, see also Pt 3, Ch 1,4.

1.1.3 For concrete structures, see Pt 9, Ch 4.

1.2 Steel

1.2.1 Steels having a yield stress not less than 265 N/mm2 (27,0 kgf/mm2) are regarded as higher tensilesteels.

1.2.2 When higher tensi le steel is used in theconstruction of the unit the local scantlings determined fromthe Rules for steel plating, stiffeners and girders, etc., may bebased on a k factor determined as follows:

or 0,66, whichever is the greaterwhere

σo = specified minimum yield stress, of the highertensile steel in N/mm2 (kgf/mm2)

k = 1,0 for mild steel with a minimum yield stressof 235 N/mm2 (24 kgf/mm2)

1.2.3 When higher tensile steel is used in the primarystructure of surface type units the determination of the hullgirder section modulus is to be based on a higher tensile steelfactor k determined in accordance with Pt 3, Ch 2 of theRules for Ships.

1.2.4 For the application of the requirements of 1.2.2special consideration wil l be given to steel where σo > 355 N/mm2 (36 kgf/mm2). Where such steel grades areused in areas which are subject to fatigue loading thestructural details are to be verified using fatigue designassessment methods.

1.2.5 Where steel castings or forgings are used formajor structural components, they are to comply with Pt 2,Ch 4 or Ch 5, as appropriate.

k = 235σo

k = 24σo

Section

1 Materials of construction

2 Structural categories

3 Design temperature

4 Steel grades

Materials

1.3 Aluminium

1.3.1 The use of aluminium alloy is permitted forsuperstructures, deckhouses, hatch covers, helicopterplatforms, or other local components on board offshore units,except where stated otherwise in Pt 3, Ch 1,4.5.

1.3.2 Except where otherwise stated, equivalentscantlings are to be derived as follows:

Plating thickness:

ta =

Section modulus of stiffeners:Za = Zs ka c

where c = 0,95 for high corrosion resistant alloy= 1,0 for other alloys

ka =

ta = thickness of aluminium platingts = thickness of mild steel plating

Za = section modulus of aluminium stiffenerZs = section modulus of mild steel stiffenerσa = 0,2 per cent proof stress or 70 per cent of the

ultimate strength of the material, whichever isthe lesser.

1.3.3 In general, for welded structure, the maximumvalue of σa to be used in the scantlings derivation is that ofthe aluminium in the welded condit ion. However,consideration wil l be given to using unwelded valuesdepending upon the weld line location, or other heat affectedzones, in relation to the maximum applied stress on themember (e.g. extruded sections).

1.3.4 A comparison of the mechanical properties forselected welded and unwelded alloys is given in Table 2.1.1.

1.3.5 Where strain hardened grades (designated Hxxx)are used, adequate protection by coating is to be provided toavoid the risk of stress corrosion cracking.

1.3.6 The use of aluminium alloy for primary structurewill be specially considered.

245σa

ts ka c



Materials



Table 2.1.1 Minimum mechanical properties for selected aluminium alloys

Alloy Condition0,2% proof stress Ultimate tensile strength

N/mm2 N/mm2

Unwelded Welded Unwelded Welded(see Note 4) (see Note 4)

5083 O/H111 125 125 275 275

5083 H112 125 125 275 275

5083 H116/H321 215 125 305 275

5086 O/H111 100 95 240 240

5086 H112 125 95 250 240(see Note 2) (see Note 2)

5086 H116/H321 195 95 275 240

5754 O/H111 80 80 190 190

6005A T5/T6 Extruded: Open Profile 215 100 260 160(see Note 1) Extruded: Closed Profile 215 100 250 160

6061 T5/T6 Rolled 240 125 290 160(see Note 1) Extruded: Open Profile 240 125 260 160

Extruded: Closed Profile 205 125 245 160

6082 T5/T6 Rolled 240 125 280 190Extruded: Open Profile 260 125 310 190Extruded: Closed Profile 240 125 290 190

NOTES1. These alloys are not normally acceptable for application in direct contact with sea-water.2. See also Table 8.1.4 in Pt 2, Ch 8.3. The mechanical properties to be used to determine scantlings in other types and grades of aluminium alloy manufactured to national or

proprietary standards and specifications are to be individually agreed with LR, see also Pt 2, Ch 8,1.1.5.4. Where detail structural analysis is carried out, ‘Unwelded’ stress values may be used away from heat affected zones and weld lines, see

also 1.3.3.


SECTION 2Structural categories

2.1 General

2.1.1 All structural components of the unit may begrouped into structural categories taking into account thefollowing aspects:(a) Applied loading, stress level and the associated stress

pattern.(b) Critical load transfer points and stress concentrations.(c) Consequence of failure.

2.1.2 The structural categories can be summarized asfollows:(a) Special structure:

Primary structural elements which are in way of criticalload transfer points and stress concentrations.

(b) Primary structure:Structural elements essential to the overall integrity ofthe unit.

(c) Secondary structure:Structural elements of less importance than primarystructure, failure of which would be unlikely to affect theoverall integrity of the unit.

2.1.3 For the structural categories of supportingstructures of drilling plant and production and process plant,see Pt 3, Ch 7,2.2 and Ch 8,2.2 respectively.

2.2 Column-stabilized and tension-leg units

2.2.1 In general the structural members of column-stabilized and tension-leg units are to be grouped into thefollowing structural categories:(a) Special structure:

(i) The plating of decks, heavy flanges, shell boundaries and bulkheads of the upper hull orplatform which form ‘box’ or ‘I’ type supportingstructure in way of critical load transfer points andwhich receive major concentrated loads.

(ii) The shell plating in way of the intersections ofvertical columns with platform decks and upperand lower hulls.

(iii) End connections and major intersections ofprimary bracing members.

(iv) Critical load transfer by ‘through’ material used atconnections of vertical columns, upper platformdecks and upper or lower hulls which aredesigned to provide proper alignment andadequate load transfer.

(v) External brackets, portions of bulkheads, flats,and frames which are designed to receiveconcentrated loads at intersections of majorstructural members.

(b) Primary structure:(i) The plating of decks, heavy flanges, shell

boundaries and bulkheads of the upper hull orplatform which form ‘box’ or ‘I’ type supportingstructure except where the structure is consideredas special application.

(ii) The shell plating of vertical columns, lower andupper hulls, and diagonal and horizontal braces.

(iii) Bulkheads, flats or decks, stiffeners and girderswhich provide local reinforcement or continuity ofstructure in way of intersections, except areaswhere the structure is considered as specialapplication.

(iv) Main support structure to cantilevered helicopterdecks and lifeboat platforms.



Materials Part 4, Chapter 2Section 2

(v) Heavy substructures and equipment supports,e.g. drillfloor substructure, crane pedestals,anchor line fairleads and their supporting structure, see also 2.1.3.

(vi) Riser support structure.(c) Secondary structure:

(i) Upper platform decks or decks of upper hulls,except areas where the structure is consideredas primary or special application.

(ii) Bulkheads, stiffeners, flats or decks and girdersin vertical columns, decks, lower hulls, diagonaland horizontal bracing, which are not consideredas primary or special application.

(iii) Helicopter platforms and deckhouses.(iv) Lifeboat platforms.

2.3 Self-elevating units

2.3.1 In general, the structural members of self-elevating units are to be grouped into the fol lowingcategories:(a) Special structure:

(i) Vertical leg structures in way of intersections withindividual footings or with the mat structure.

(ii) Intersections of lattice type leg structures whichincorporate novel construction, including the useof steel castings.

(b) Primary structure:(i) The plating of bulkheads, decks and shell

boundaries of the main hull or platform which in combination form ‘box’ or ‘I’ type mainsupporting structure.

(ii) External plating of cylindrical legs.(iii) Plating of all components of lattice-type legs.(iv) Jack-house supporting structure.(v) External shell plating of footings and mats and

structural components which receive initial transfer of loads from the leg structures.

(vi) Internal bulkheads and girders of supportingstructure of footings and mats which aredesigned to distribute major concentrated oruniform loads into the structure.

(vii) Main support structure to cantilevered helicopterdecks and lifeboat platforms.

(viii) Heavy substructures and equipment supports,e.g. drillfloor substructure, drilling cantilevers andcrane pedestals, see also 2.1.3.

(c) Secondary structure:(i) Deck and shell boundaries of the main hull or

platform, except where the structure is consid-ered as primary application.

(ii) Internal bulkheads, decks stiffeners and girders ofthe main hull structure, except where the structureis considered as primary structure.

(iii) Internal diaphragms, girders or stiffeners in cylindrical legs.

(iv) Internal bulkheads, stiffeners and girders of footings and bottom mat supporting structures,except where the structure is considered primaryor special application.

(v) Helicopter platforms and deckhouses.(vi) Lifeboat platforms and walkways.





2.4 Surface-type units

2.4.1 In general, the structure of ship and barge-typeunits are to be grouped into the fol lowing structuralcategories:(a) Special structure:

(i) Structure in way of critical load transfer points which are designed to receive major concentrated loads in way of mooring systems,including yokes and similar structures, andsupports to hawsers to mooring installationsincluding external hinges, complex padeyes,brackets and supporting structures.

(b) Primary structure:(i) Strength deck, raised quarter deck and shell

plating of the main hull.(ii) Longitudinal bulkheads, bulkheads in way of

drilling wells and shell boundaries of circumturretwell bulkheads.

(iii) Main support structure to cantilevered helicopterdecks and lifeboat platforms.

(iv) Heavy substructures and equipment supports,e.g. integrated support stools to process plant,drill floor substructure, crane pedestals, anchorline fairleads and chain stoppers for positionalmooring systems and their supporting structures,see also 2.1.3.

(v) Turret bearing support structure.(vi) Swivel stack support structure.(vii) Supporting structures to external turrets.(viii) Riser support structures.

(c) Secondary structure:(i) Bulkheads, stiffeners, decks including poop deck

and forecastle deck, flats, etc., except where thestructure is categorized as Special or Primarystructure. For topside plant supporting structures, see also 2.1.3.

(ii) Helicopter platforms and deckhouses.(iii) Lifeboat platforms, walkways, guard rails, minor

fittings and attachments, etc.

2.4.2 Material classes for individual areas of the hullstructure are also to comply with Pt 3, Ch 2,2 of LR’s Rulesand Regulations for the Classification of Ships (hereinafterreferred to as the Rules for Ships).

2.5 Buoys, deep draught caissons, turrets andmiscellaneous structures

2.5.1 In general, the structure of buoys, deep draughtcaissons, turrets, and other miscellaneous structuresincluded in Pt 3, Ch 2 are to be grouped into the followingstructural categories:(a) Special structure:

(i) Structure in way of critical load transfer points which are designed to receive majorconcentrated loads including external brackets,portions of bulkheads, flats and frames.

(ii) Intersections of structures which incorporatenovel construction including the use of steel castings.

(iii) Complex padeyes.(iv) Highly stressed structural elements of anchor-line

attachments.(v) Bearings and structure at the base of mooring

towers.(b) Primary structure: The following structural members

are categorized as primary, except when the structureis considered as special application:(i) External shell plating of buoys, deep draught

caissons, turrets and subsea modules.(ii) Strength decks of buoys and deep draught

caissons.(iii) Truss structure supporting decks on deep

draught caissons.(iv) Miscellaneous structures:

• Support stools to process plant• Bearing support structure• Swivel stack support structure• Turntable construction• Chain tables• Riser support structure• Hawser support structure• Yoke and mooring arm construction• Mooring towers

(v) Main support structures to cantilevered helideckand lifeboat platforms.

(vi) Heavy substructures and equipment supports,e.g. crane pedestals, anchor line fairleads forpositional moorings,chain stoppers and theirsupporting structures.

(c) Secondary structure:(i) Bulkheads, stiffeners, decks, flats, etc., except

where the structure is categorized as Special orPrimary structure. For topside structures, seealso 2.1.3.

(ii) Helicopter platforms and deckhouses.(iii) Lifeboat platforms, walkways, guard rails and

minor fittings and attachments, etc.


SECTION 3Design temperature

3.1 General

3.1.1 The minimum design temperature (MDT) is areference temperature used as a criterion for the selection ofthe grade of steel to be used in the structure and is to bedetermined in accordance with Pt 3, Ch 1,4.

3.1.2 The MDT is not to exceed the lowest servicetemperature of the steel as appropriate to the position in thestructure.

3.1.3 A design temperature of 0°C is general lyacceptable for determining the steel grades for structurewhich is normally underwater, see also 4.1.4.

3.1.4 For column-stabilized units of conventionaldesign, the lower hulls need not normally be designed for adesign temperature lower than 0°C.

3.1.5 The internal structure of all units is normallyassumed to have the same design temperature as theadjacent external structure unless defined otherwise.

3.1.6 Internal structures in way of permanently heatedcompartments need not normally be designed fortemperatures lower than 0°C.



Materials Part 4, Chapter 2Sections 3 & 4

SECTION 4Steel grades

4.1 General

4.1.1 The grades of steel to be used in the structureare, in general, related to the thickness of the material, thestructural category and the MDT. The grades of steel to beused in the construction of the unit are to be determined fromTable 2.4.1, see also 4.1.5 and Section 2.

4.1.2 Special consideration will be given to the use ofhigher tensile steel grades with a minimum yield stressgreater than 390 N/mm2, e.g. legs of self-elevating units.

4.1.3 Plate material used at primary connectionswhere the principal loads from service or welding stresses areimposed perpendicular to the plate thickness will be requiredto have steel grades with suitable through-thicknessproperties in accordance with Pt 2, Ch 3,8.

4.1.4 Steel grades for units required to operate insevere ice condit ions wil l be special ly considered.Temperature gradient calculations may be required to assessthe design temperature of the structure, see also Pt 3, Ch 6,2.

4.1.5 Minor structural components such as guard rails,walkways and ladders, etc., are, in general, to beconstructed of Grade A steel, unless requested otherwise byLR.





Table 2.4.1 Thickness limitations (in mm) of hull structural steels for various application categories and designtemperatures

Structuralcategory

Required steelgrade

Maximum thickness (mm) for various temperatures

Secondary

Primary

Special

ABDE

AHDHEHFHAQDQEQFQ

ABDE

AHDHEHFHAQDQEQFQ

ABDE

AHDHEHFHAQDQEQFQ

0°C –10°C –20°C –30°C –40°C –50°C

30 20 10 X X X40 30 20 X X X50 50 45 35 25 1550 50 50 50 45 3540 30 20 10 X X50 50 45 35 25 1550 50 50 50 45 3550 50 50 50 50 5040 25 10 X X X50 45 35 25 15 X50 50 50 45 35 2550 50 50 50 50 45

10 X X X X X25 10 X X X X45 40 30 20 10 X50 50 50 40 30 2025 10 X X X X45 40 30 20 10 X50 50 50 40 30 2050 50 50 50 50 4020 X X X X X45 35 25 15 X X50 50 45 35 25 1550 50 50 50 45 35

X X X X X X15 X X X X X30 20 10 X X X50 45 35 25 15 X15 X X X X X30 20 10 X X X50 45 35 25 15 X50 50 50 50 40 30X X X X X X25 15 X X X X50 40 30 20 10 X50 50 50 40 30 20

NOTES1. X indicates no application.2. Thicknesses greater than those shown in this Table may be specially considered by LR.3. The substitution of materials considered to be equivalent to the grades shown, or steels of different strength levels, may be specially

considered by LR.4. The interpolation of thicknesses for intermediate temperatures may be considered.5. Steel grades are to comply with the requirements given in Part 2. Q grades refer to quenched and tempered steels as defined in Pt 2, Ch 3.6. Steel grades for bolted structural components will be specially considered.





Section

1 General

2 Design concepts

3 Structural idealization

4 Structural design loads

5 Number and disposition of bulkheads

Structural Design

SECTION 2Design concepts

2.1 Elastic method of design

2.1.1 In general, the approval of the primary structureof the unit will be based on the elastic method of design andthe permissible stresses in the structure are to be based onthe minimum factors of safety defined in Chapter 5. Whenspecifically requested, LR will consider other design methods.

2.2 Limit state method of design

2.2.1 When the l imit state method of design isproposed for the structure the design methods, loadcombinations and partial factors are to be agreed with LR.

2.3 Plastic method of design

2.3.1 When the plastic method of design based on theultimate strength is proposed for the structure, the loadfactors are to be in accordance with an acceptable Code ofPractice, see Part 3, Appendix A.

2.4 Fatigue design

2.4.1 All units are to be capable of withstanding thefatigue loading to which they are subjected. The minimumdesign fatigue life of a unit is to be 20 years or as otherwisespecified by the Owner if greater, see Ch 5,5.

SECTION 1General

1.1 Application

1.1.1 This Chapter indicates the general designconcepts and loading and the general principles adopted inapplying the Rule structural requirements given in this Part.

1.1.2 General definitions of span point, derivation ofgeometric properties of section and associated effective areaof attached plating are given in this Chapter.

1.1.3 Additional requirements relating to functional unittypes are also dealt with under the relevant unit type given inPart 3.

1.1.4 General principles of subdivision andrequirements for cofferdams are given in this Chapter.


3.2.2 The effective geometric properties of rolled orbuilt sections may be calculated directly from the dimensionsof the section and associated effective area of attachedplating. Where the web of the section is not normal to theattached plating, and the angle exceeds 20°, the propertiesof the section are to be determined about an axis parallel tothe attached plating.

3.2.3 The geometric properties of rolled or builtstiffener sections and of swedges are to be calculated inassociation with effective area of attached load bearingplating of thickness tp mm and of width 600 mm or 40tp mm,whichever is the greater. In no case, however, is the width ofplating to be taken as greater than either the spacing of thestiffeners or the width of the flat plating between swedges,whichever is appropriate. The thickness, tp, is the actualthickness of the attached plating. Where this varies, themean thickness over the appropriate span is to be used.

3.2.4 The effective section modulus of a corrugationover a spacing p is to be calculated from the dimensions and,for symmetrical corrugations, may be taken as:

where dw, b, tp, c and tw are measured, in mm, and are asshown in Fig. 3.3.1. The value of b is to be taken not greaterthan:

for welded corrugations

for cold formed corrugations

The value of θ is to be taken not less than 40°. The momentof inertia is to be calculated from:

3.2.5 The section modulus of a double plate bulkheadover a spacing b may be calculated as:

where dw, b, tp and tw are measured, in mm, and are asshown in Fig. 3.3.2.

Z = dw6000

6f btp + dw tw cm3

I = Z10

dw2

cm4

60tp k

50tp k

Z = dw6000

3btp + ctw cm3


Structural Design



SECTION 3Structural idealization

3.1 General

3.1.1 In general, the primary structure of a unit is to beanalysed by a three-dimensional finite plate element method.Only if it can be demonstrated that other methods areadequate, will they be considered.

3.1.2 The complexity of the mathematical modeltogether with the associated computer element types usedmust be sufficiently representative of all the parts of theprimary structure to enable accurate internal stressdistributions to be obtained.

3.1.3 Unless agreed otherwise, LR will perform anindependent structural analysis of the unit.

3.1.4 For derivation of local scantlings of stiffeners,beams, girders, etc., the formulae in the Rules are normallybased on elastic or plastic theory using simple beam modelssupported at one or more points and with varying degrees off ix ity at the ends, associated with an appropriateconcentrated or distributed load.

3.1.5 Apart from local requirement for web thicknessor flange thicknesses, the stiffener, beam or girder strength isdefined by a section modulus and moment of inertiarequirement.

3.2 Geometric properties of section

3.2.1 The symbols used in this sub-Section aredefined as follows:

b = actual width, in metres, of the load-bearingplating, i.e. one-half of the sum of spacingsbetween paral lel adjacent members orequivalent supports

f =2/3 but is not to exceed 1,0. Values of

this factor are given in Table 3.3.1l = overall length, in metres, of the primary

support member, see Fig. 3.3.3tp = thickness, in mm, of the attached plating.

Where this varies, the mean thickness overthe appropriate span is to be used.

0,3 lb

Table 3.3.1 Effective width factor

lb

0,51,01,52,02,53,0

f

0,190,300,390,480,550,62

lb

3,54,04,55,05,5

6 and above

f

0,690,760,820,880,941,00

NOTEIntermediate values to be obtained by linear interpolation.

b

tp

dw

p

tw 0,5bc

θ

4407/75

Fig. 3.3.1Corrugation geometry


3.2.6 The effective section modulus of a built sectionmay be taken as:

where a = area of the face plate of the member, in cm2

dw = depth, in mm, of the web between the insideof the face plate and the attached plating.Where the member is at right angles to a lineof corrugations, the minimum depth is to betaken

tw = thickness of the web of the section, in mmA = area, in cm2, of the attached plating, see

3.2.7. If the calculated value of A is less thanthe face area a, then A is to be taken as equalto a.

3.2.7 The geometric properties of primary supportmembers (i.e. girders, transverses, webs, stringers, etc.) areto be calculated in association with an effective area ofattached load bearing plating, A, determined as follows:(a) For a member attached to plane plating:

A = 10fbtp cm2

(b) For a member attached to corrugated plating and parallel to the corrugations:

A = 10btp cm2

See Fig. 3.3.1.(c) For a member attached to corrugated plating and at

right angles to the corrugations, A is to be taken asequivalent to the area of the face plate of the member.

3.3 Determination of span point

3.3.1 The effective length, le, of a stiffening member isgenerally less than the overall length, l, by an amount whichdepends on the design of the end connections. The spanpoints, between which the value of le is measured, are to bedetermined as follows:(a) For rolled or built secondary stiffening members, the

span point is to be taken at the point where the depthof the end bracket, measured from the face of thesecondary stiffening member is equal to the depth ofthe member. Where there is no end bracket, the spanpoint is to be measured between primary memberwebs. For double skin construction the span may bereduced by the depth of primary member web stiffener,see Fig. 3.3.3.

(b) For primary support members, the span point is to betaken at a point distant be from the end of the member,where

See also Fig. 3.3.3.

be = bb 1 – dwdb

Z = adw10

+ t w dw 2

6000 1 +

200 A – a200A + t w dw

cm3



Structural Design Part 4, Chapter 3Section 3

3.3.2 Where the stiffener member is inclined to a vertical or horizontal axis and the inclination exceeds 10°, thespan is to be measured along the member.

3.3.3 It is assumed that the ends of stiffening membersare substantially fixed against rotation and displacement. If thearrangement of supporting structure is such that this conditionis not achieved, consideration will be given to the effectivespan to be used for the stiffener.

3.4 Grouped stiffeners

3.4.1 Where stiffeners are arranged in groups of thesame scantling, the section modulus requirement of eachgroup is to be based on the greater of:• the mean head within the group; and• 90 per cent of the maximum head within the group.

tp

tw

tp b

dw

4407/76

Fig. 3.3.2Double plate bulkhead geometry





Span points

ds

ds

Span point

Span point

ds

ds

Span point

4407/77a

Fig. 3.3.3 Span points

db

be

bb

dw

l

Span pointSpan point

db

be

bb

dw

4407/77b

l


SECTION 4Structural design loads

4.1 General

4.1.1 The requirements in this Section define the loadsand load combinations to be considered in the overallstrength analysis of the unit and the design pressure heads tobe used in the Rules for local scantlings.

4.1.2 A unit’s modes of operation are to beinvestigated using realistic loading conditions, includingbuoyancy, gravity and functional loadings together withrelevant environmental loadings. Due account is to be takenof the effects of wind, waves, currents, motions (inertia),moorings, ice, and, where necessary, the effects ofearthquake, sea bed supporting capabilities, temperature,fouling, etc. Where applicable, the design loadings indicatedherein are to be adhered to for all types of offshore units.

4.1.3 The Owner/designer is to specify the modes ofoperation and the environmental conditions for which the unitis to be approved, see also Pt 1, Ch 2,2.

4.1.4 The design environmental criteria determining theloads on the unit and its individual elements are to be basedupon appropriate statistical information at the operatinglocation and have a return period (period of recurrence) of100 years for the most severe anticipated environment.Consideration will be given by the Committee to accepting areturn period of less than 100 years, when requested by anOwner, for units with a design life of 10 years or less. If a unitis restricted to seasonal operations in order to avoid extremesof wind and wave, such seasonal limitations must also be specified.

4.1.5 Model tests are to be carried out as necessaryand the tests are to include means of establishing the effectsof green water loading and/or slamming on the structurethrough video recordings of the model testing and bymeasurement of the following:• Relative motions.• Forces on local panels mounted at various locations on

exposed areas including bow areas of surface-typeunits and accommodation areas, see also Chapter 4and Pt 3, Ch 10,5.

4.1.6 When carrying out model tests, account is to betaken of the following:(a) The test programme and the model test facilities are to

be to LR’s satisfaction.(b) The relative directions of wind, wave and current are to

be varied as required to ensure that the most criticalloadings and motions are determined.

(c) The tests are to be of sufficient duration to establish lowfrequency motion behaviour.

4.1.7 The unit’s limiting design criteria are to beincluded in the Operations Manual, see Pt 3, Ch 1,3.

4.2 Definitions

4.2.1 Still water condition is defined as an idealcondition when no environmental loads are imposed on thestructure, e.g. no wind, wave or current, etc.




4.2.2 Gravity and functional loads are loads whichexist due to the unit’s weight, use and treatment in still waterconditions for each design case. All external forces whichare responses to functional loads are to be regarded asfunctional loads, e.g. support reactions and still waterbuoyancy forces.

4.2.3 Environmental loads are loads which are duedirectly or indirectly to environmental actions. All externalforces which are responses to environmental loads are to beregarded as environmental loads, e.g. mooring forces andinertia forces.

4.2.4 Accidental loads are loads which occur as adirect result of an accident or exceptional circumstances, e.g.loads due to collisions, dropped objects and explosions, etc.

4.3 Load combinations

4.3.1 The structure is to be designed for the mostunfavourable of all the following combined loading conditions:(a) Maximum gravity and functional loads.(b) Design environmental loads and associated gravity and

functional loads.(c) Accidental loads and associated gravity and functional

loads.(d) Design environmental loads and associated gravity and

functional loads after credible failures or accidents.(e) Maximum gravity and functional loads in a heeled

condition after accidental flooding.

4.3.2 Special requirements applicable to column-stabilized and self-elevating units are also defined in Chapter 4.

4.3.3 Permissible stresses relevant to the combinedloading conditions are given in Chapter 5.

4.4 Gravity and functional loads

4.4.1 All gravity loads, including static loads such asweight, outfit, stores, machinery, ballast, etc., and livefunctional loads from operating derricks, cranes, winches andother equipment are to be considered. Al l practicalcombinations of gravity and functional loads are to beincluded in the design cases.

4.5 Buoyancy loads

4.5.1 Buoyancy loads on all underwater parts of thestructure, taking account of heel and trim when appropriate,are to be considered.

4.6 Wind loads

4.6.1 Account is to be taken of the wind forces actingon that part of the unit which is above the still water level in alloperating conditions and of the following:(a) Consideration is to be given to wind gust velocities

which are of brief duration and sustained wind velocitieswhich act over intervals of time equal to or greater thanone minute. Different wind velocity averaging time intervals applicable to different structural categories tobe used in design calculations are shown in Table 3.4.1.

(b) Wind velocities are to be specified relative to a standardreference height of 10 m above still water level for eachoperating condition.





(c) The variation of wind velocity with height for each oper-ating condition may be determined from the followingexpression:

whereVH = wind velocity at specified height, in m/sVR = wind velocity at specified reference height HR,

in m/sH = specified height above sea level, in metres

HR = reference height, in metresn = power law exponent

for 3 second gust n = 0,077for 5 second mean n = 0,08for 15 second mean n = 0,09for 1 minute mean n = 0,125for 10 minute mean n = 0,13

4.6.2 The wind force is to be calculated for each partof the structure and is not to be taken less than:

F = Kw AV 2 Cs N (kgf)where

F = net force acting on any member or part of theunit. This includes the effect of any suctionon back surfaces

Kw = 0,613 (0,0625)A = project area of all exposed surfaces in upright

or heeled position, in m2

V = wind velocity, in m/s, see 4.6.1Cs = shape coefficient as given in Table 3.4.2.

VH = VR ( HHR

)n

4.6.3 When calculating wind forces the followingprocedures should be considered:(a) Shielding may be taken into account when a member

or structure lies closely enough behind another to havea significant effect. Procedures for determining theshielding effect and loading are to be acceptable to LR.

(b) Areas exposed due to heel, such as underdecks, etc.,are to be included using the appropriate shape coefficients.

(c) If several deckhouses or structural members, etc., arelocated close together in a plane normal to the winddirection the solidification effect is to be taken intoaccount. The shape coefficient may be assumed to be1,1.

(d) Isolated houses, structural shapes, cranes, etc., are tobe calculated individually, using the appropriate shapecoefficient.

(e) Open truss work commonly used for derrick towers,booms and certain types of masts may be approxi-mated by taking 30 per cent of the projected block areaof each side, e.g. 60 per cent of the projected blockarea of one side for double-sided truss work. Anappropriate shape coefficient is to be taken from Table 3.4.2.

4.6.4 For slender structures and components, theeffects of wind-induced cross-flow vortex vibrations are to beincluded in the design loading.

4.6.5 For slender structures sensitive to dynamic loads,the static gust wind force is to be multiplied by an appropriatedynamic amplification factor.

4.7 Current loads

4.7.1 In storm conditions, the current has two maincomponents: the tidal and wind driven components.Submitted information on currents is to include tidal and windinduced components and the variation of their profiles withwater depth, see 4.9.6 and 4.9.7.

Windspeedaveraging

time interval

3 second gust

5 second mean(sustained)

15 second mean(sustained)

1 minute mean(sustained)(see Note)

Structural category

Individual members and equipment securedto them

Part or whole of a structure whose greatesthorizontal or vertical dimension does notexceed 50 m

Part or whole of a structure whose greatesthorizontal or vertical dimension exceeds50 m

The whole structure of the unit regardless ofdimension for use with the maximumwave and current loads

NOTEIn no case is the one minute mean value to be taken less than25,8 m/s.

Shape Cs

Spherical 0,40Cylindrical 0,50Large flat surface (hull, deckhouse, smooth

under deck areas) 1,00Drilling derrick 1,25Wires 1,20Exposed beams and girders under deck 1,30Small parts 1,40Isolated shapes (cranes, booms, etc.) 1,50Clustered deck houses or similar structures 1,10

NOTEShapes or combinations of shapes which do not readily fall into thespecified categories will be subject to special consideration.

Table 3.4.1 Structural parts to be considered forwind loading

Table 3.4.2 Values of coefficient Cs


4.8 Orientation and wave direction

4.8.1 Loadings are to be assessed using sufficientwave headings and crest positions to determine the mostsevere loading on the unit. In addition to the design waveheight and period, the unit is to be designed to withstandshorter period waves of less height when these can inducemore severe loading on parts or the whole unit due todynamic effects, etc.

4.8.2 Where a unit is required to remain at a specificorientation in all operating conditions due to the nature of itsservice, account is to be taken of the maximum number ofwaves of all heights predicted for the design life of the unit.The long-term cumulative effect of forces is to be used inassessing the fatigue strength/life of the structure of the unit.

4.9 Wave loads

4.9.1 Design wave criter ia specif ied by theOwner/designer may be described either by means of designwave energy spectra or deterministic design waves havingappropriate shape, size and period. The following should betaken into account:(a) The maximum design wave heights specified for each

operating condition should be used to determine themaximum loads on the structure and principalelements. Consideration is to be given to waves of lessthan maximum height, where due to their period, theeffects on various structural elements may be greater.

(b) Wave lengths are to be selected as the most criticalones for the response of the structure or element to beinvestigated.

(c) An estimate is to be made of the probable waveencounters that the unit is likely to experience during itsservice life in order to assess fatigue effects on its structural elements.

(d) When units are to operate in intermediate or shallowwater, the effect of the water depth on wave heightsand periods and of refraction due to sea bed topogra-phy, is to be taken into account.

4.9.2 The forces produced by the action of waves onthe unit are to be taken into account in the structural design,with regard to forces produced directly on the immersedelements of the unit and forces resulting from heeledpositions or accelerations due to its motion. Theories usedfor the calculation of wave forces and selection of relevantcoefficients are to be acceptable to LR.

4.9.3 The wave forces may be assessed from tests ona representative model of the unit by a recognized laboratory,see 4.1.5 and 4.1.6.

4.9.4 Wave theories used for the calculation of waterparticle motions are to be acceptable to LR and when usingacceptable wave theories for wave force determination,reliable values of CD and CM which have been obtainedexperimentally for use in conjunction with the specific wavetheory are to be used. Otherwise published data are to beused.

4.9.5 Consideration is to be given to the possibility ofwave impact and wave induced vibration in the structure.

4.9.6 Where sea current acts simultaneously withwaves the effect of the current is to be included in the loadestimation.




4.9.7 The following methods may be used for loadestimation:(a) The forces on structural elements with dimensions less

than 0,2 of the wave length subject to drag/inertia loading due to wave and current motions can be calcu-lated from the Morison’s equation:

F = CD1/2ρ Au |u| + CM ρ Va

whereF = force per unit length of member

CD = drag coefficientρ = density of waterA = projected area of member per unit lengthu = component of the water particle velocity at

the axis of the member and normal to it(calculated as if the member were not there)

|u| = modulus of uCM = inertia coefficient

V = volume of water per unit lengtha = component of the water particle acceleration

at the axis of the member and normal to it(calculated as if the member were not there)

(b) Overall loading on an offshore structure is determinedfrom the summation of loads on individual members ata particular time. The proper values of CD and CM forindividual members to use with Morison’s equation willdepend on a number of variables, for example:Reynolds number, Keulegan-Carpenter number, inclination of the member to local flow and effectiveroughness of marine growth. Therefore fixed values forall conditions cannot be given. Typical values for circular cylindrical members, will range from 0,6 to 1,4for CD and 1,3 to 2,0 for CM. The values selected arenot to be smaller than the lower limits of these ranges.For inclined members the drag forces in Morison’sequation are to be calculated using the normal compo-nent of the resultant velocity vector.

(c) General values of hydrodynamic coefficients may beused in the Morison equation for the calculation of overall loading on the structure, namely:• For circular cylinders covered by hard marine

growth, CD is to be not less than 0,7.• For circular cylinders not covered by hard marine

growth, CD is to be not less than 0,6.• For circular cylinders, CM is to be not less than

1,7.If joint probability predictions of wave and current areincluded in the design procedure or if the conservatismis reduced in any part, consideration is to be given toincreasing the drag coefficient associated with marinegrowth.

(d) Diffraction theory is normally appropriate to determinewave loads where the member is large enough tomodify the flow field.

4.9.8 Account is to be taken of the increase of overallsize and roughness of submerged members due to marinegrowth when calculating loads due to wave and current, see 4.13.

4.10 Inertia loads

4.10.1 Dynamic loads imposed on the structure byaccelerations due to the units motion in a seaway are to beincluded in the structural design calculations. The dynamicloads may be obtained from model test results or bycalculation. The methods of calculation are to be acceptableto LR.





4.11 Mooring loads

4.11.1 Mooring loads are to be considered for unitsoperating afloat with positional mooring systems, see Pt 3,Ch 10. The following are to be considered:• The overall strength of the structure.• The local strength where the mooring line forces are

transmitted to the hull.

4.11.2 The support structure in way of mooringequipment is to be designed for the minimum designbreaking load of the mooring line, determined in accordancewith Pt 3, Ch 10.

4.12 Snow and ice loads

4.12.1 Consideration is to be given to the extent towhich snow and ice may accumulate on the exposedstructure under any particular weather conditions. The windresistance of exposed structural elements will be increasedby the growth of ice. Details of the thickness and distributionof accumulation are to be established and taken into accountin the design, see also Pt 3, Ch 6.

4.12.2 The increased loading caused by theaccumulation of snow and ice on any part of the structure isto be taken into account.

4.12.3 Values for the thickness, density and variationwith height of accumulated snow and ice are to be derivedfrom meteorological data acceptable to LR.

4.12.4 The overall distribution of snow and/or ice ontopside structure is to be taken as a thickness ti on the upperand windward faces of the deck structures or membersunder consideration, where ti is the basic thickness obtainedfrom the meteorological data. The distribution of ice onindividual members may be assumed to be as shown in Fig. 3.4.1.

4.12.5 It may be assumed that there is no increase ofdrag coefficient in the presence of ice.

4.12.6 The appropriate combinations of snow and iceloadings with other design environmental loads are to bespecially considered and agreed with LR. In general, extremesnow and ice loads are to be combined with otherenvironmental loads corresponding to the design five yearreturn criteria for the unit.

4.13 Marine growth

4.13.1 Marine growth will increase the weight and theoverall dimensions of submerged members and alter theirsurface characteristics. These effects will increase the loadsapplied to the structure. The thickness of marine growthtaken into account in the design is to be stated in theOperations Manual and the design limit is not to be exceededin service.

4.14 Hydrostatic pressures

4.14.1 The pressure head to be used as the basis forthe design of internal spaces is to be the greatest of thefollowing:(a) For tanks, the maximum head during normal operation.(b) For shell boundaries, the hydrostatic head due to

external pressure arising from the sea, taking maximumwave crest elevation in both operating and survivalconditions with a minimum head of 6 m on semi-submersible units.

(c) For watertight boundaries, the head measured to theworst damage waterline, see Chapter 7.

(d) The minimum design pressure heads for local strengthare to be in accordance with Chapter 6.

4.14.2 Where testing the tank involves pressure headsin excess of those derived in 4.14.1, the excess may betaken into account by the use of a load factor applied to thedesign head. Where this is done, it is to be clearly stated inthe calculations.

4.15 Deck loads

4.15.1 The maximum design uniform and concentrateddeck loads for all areas of the unit in each mode of operationare to be taken into account in the design. The minimumdesign deck loads for local strength are to be in accordancewith Chapter 6.

4.16 Accidental loads

4.16.1 Collision loads imposed by attending vesselswhich may be approaching, mooring or lying alongside theunit are to be considered in the design. The unit is to bedesigned to withstand accidental impacts between attendingvessels and the unit and be capable of absorbing the impactenergy.

4.16.2 The kinetic energy to be considered is normallynot to be less than:• 14 MJ for sideway collision;• 11 MJ for bow or stern collision;corresponding to an attending vessel of 5000 tonnesdisplacement with impact velocity 2 m/s.

4.16.3 A reduced impact energy may be accepted uponspecial consideration taking into account the environmentaldesign criteria.

4.16.4 The energy absorbed by the unit during acollision impact will be less than or equal to the total impactkinetic energy, depending on the relative stiffnesses of therelevant parts of the unit and the impacting ship/unit and alsoon the mode of collision and ship/unit operation. Thesefactors may be taken into account when considering theenergy absorbed by the unit, see also Ch 4,1 and Ch 4,3 forcolumn-stabilized and self-elevating units respectively.

ti2

4407/78

ti2

ti2

ti2

ti2

ti2

Fig. 3.4.1Assumed distribution of ice on individual members for

calculation purposes


4.16.5 Collision is to be considered for all elements ofthe unit which may be hit by sideway, bow or stern collision.The vertical extent of the collision zone is to be based on thedepth and draught of attending ships/units and the relativemotion between the attending ships/units and the unit.

4.16.6 The accidental impact loads caused by droppedobjects from cranes are to be considered in the design of theunit when the arrangements of the unit are such that thefailure of a vital structure member could result in the collapseof the structure.

4.16.7 Critical areas for dropped objects are to bedetermined on the basis of the actual movement of craneloads over the unit.

4.16.8 The structural bulkheads protectingaccommodation areas are to be designed for accidental blastloading, see Pt 7, Ch 3, where applicable. The design blastpressures are to be defined by the Owners’ designers and areto comply with National requirements. Design calculations areto be submitted which may be based on elastic analysis orelastoplastic design methods, see also 4.16.9.

4.16.9 Units with slender members where the failure ofa single member could result in the overall collapse of theunit’s structure are to be considered for credible failure ofsuch members, see Ch 4.

4.16.10 When a National Administration has additionalrequirements for accidental loads these are to be taken intoaccount in the design loadings.

4.17 Fatigue design

4.17.1 Fatigue damage due to cyclic loading must beconsidered in the design of all unit types.

4.17.2 Fatigue design calculations are to be carried outin accordance with the analysis procedures and generalprinciples given in Ch 5,5 or other acceptable method.

4.17.3 The factors of safety on calculated fatigue life areto comply with Ch 5,5, but for the hull structure of surface-type units, see Ch 4.

4.18 Other loads

4.18.1 If attending ships/units are to be moored to theunit, the forces imposed by the moorings on the structure areto be taken into account in the design.

4.18.2 Other local loads imposed on the structure byequipment and mooring and towing systems are to beconsidered in the design of the structure.

4.18.3 When partial filling of tanks is contemplated inoperating conditions, the risk of significant loads due tosloshing induced by any of the vessel motions is to beconsidered. An initial assessment is to be made to determinewhether or not a higher level of sloshing investigation isrequired, using the procedure given in Pt 3, Ch 3,5 of theRules for Ships.



Structural Design Part 4, Chapter 3Sections 4 & 5

SECTION 5Number and disposition of bulkheads

5.1 General

5.1.1 The number and disposition of watertightbulkheads are to be arranged to ensure adequate strength andthe arrangements are to suit the requirements for subdivision,floodability and damage stability. They are also to be inaccordance with the requirements of the NationalAdministration in the country in which the unit is registeredand/or in which it is to operate, see Pt 1, Ch 2,1 and Chapter 7.

5.1.2 Where due to the design of a unit the spacing ofbulkheads is unusually great, the transverse strength of theunit is to be maintained by fitting suitable web framesbetween the bulkheads.

5.1.3 The number and arrangement of bulkheads onsurface-type units are also to comply with LR’s Rules forShips. The requirements of 5.3.3 are to be complied with.


5.2.1 The arrangement of longitudinal and transversebulkheads are to satisfy the overall strength requirementsgiven in Chapters 4 and 5 when the unit is in the elevatedposition and when afloat.

5.2.2 The number and arrangement of watertightbulkheads are to meet the requirements of damage stability.

5.2.3 Watertight bulkheads are to extend to theuppermost continuous deck.

5.3 Column-stabilized units

5.3.1 The arrangement of watertight bulkheads andflats are to be made effective to that point necessary to meetthe requirements of damage stability.

5.3.2 The arrangement of longitudinal and transversebulkheads in the upper and lower hulls and in columns are tosatisfy the overall strength requirements given in Chapters 4 and 5.

5.3.3 The subdivision and arrangement of bulkheadsand cofferdams on production and oil storage units are alsoto comply with Pt 3, Ch 3.

5.4 Buoys and deep draught caissons

5.4.1 The number and arrangement of structuralbulkheads are to satisfy the overall strength requirements inChapters 4 and 5. The requirements of 5.1.1 and 5.3.3 areto be complied with.

5.5 Tension-leg units

5.5.1 In general, the number and arrangement ofstructural bulkheads are to comply with 5.3.





5.6 Protection of tanks carrying oil fuel andlubricating oil

5.6.1 Tanks carrying oil fuel or lubricating oil are to beseparated by cofferdams from those carrying feed water orfresh water.

5.6.2 Lubricating oil compartments are also to beseparated by cofferdams from tanks carrying oil fuel.However, these cofferdams need not be fitted provided that:(a) Common boundaries of lubricating oil and fuel oil tanks

have full penetration welds.(b) The tanks are arranged such that the oil fuel tanks are

not generally subjected to head of oil in excess of thatin the adjacent lubricating oil tanks.

5.6.3 Where fitted, cofferdams are to be suitablyventilated.

5.6.4 If oil fuel tanks are necessarily located within oradjacent to the machinery spaces, their arrangement is to besuch as to avoid direct exposure of the bottom from rising heatresulting from an engine room fire, see SOLAS Reg. II-2/A,15.2.3.





Section

1 Column-stabilized units

2 Sea bed-stabilized units

3 Self-elevating units

4 Surface-type units

5 Buoy units

6 Tension-leg units

7 Deep draught caisson units

Structural Unit Types

1.3.2 The structure is to be designed to withstand thestatic and dynamic loads imposed on the unit in transit andsemi-submerged conditions. All relevant loads as defined inChapter 3 are to be considered and the permissible stressesdue to the overall and local load effects are to be inaccordance with Chapter 5. The minimum local scantlings ofthe unit are to comply with Chapter 6.

1.3.3 All modes of operation are to be investigated andthe relevant design load combinations defined in Ch 5,1.2 areto be complied with. The loading conditions applicable to acolumn-stabilized unit are shown in Table 4.1.1.

1.3.4 The overall strength of the unit is to be analyzedby a three-dimensional finite element method in accordancewith Ch 3,3.

1.3.5 In order to ensure adequate structuralredundancy after credible failure or accidents, the structure isto be investigated for loading condition (d) in Table 4.1.1 andis to be able to withstand the following failures withoutcausing the overall collapse of the unit’s structure:• The failure of any slender primary bracing member.• When the upper hull structure consists of heavy or box

girder construction the failure of any primary slendermember.

SECTION 1Column-stabilized units

1.1 General

1.1.1 This Section outlines the structural designrequirements of column-stabilized (semi-submersible) units asdefined in Pt 1, Ch 2,2. Additional requirements forparticular unit types related to the design function of the unitare given in Part 3.

1.1.2 Units which are required to operate while restingon the sea bed are also to comply with the requirements ofSection 2.

1.1.3 Production and oil storage units are to complywith the requirements of Pt 3, Ch 3. Columns and pontoonsdesigned for the storage of oil in bulk storage tanks are to bedouble hull construction, but a double bottom need not befitted in pontoon tanks except where required by the CoastalState Authority and/or the National Authority of the country inwhich the unit is registered.

1.1.4 If it is intended to dry-dock the unit, the bottomstructure is to be suitably strengthened to withstand theloadings involved. The proposed docking arrangement planand maximum bearing pressures are to be submitted.

1.2 Air gap

1.2.1 In all floating modes of operation, column-stabilized units are normally to be designed to have aclearance ‘air gap’ between the underside of the upper hulldeck structure and the highest predicted design wave crest.Reasonable clearance is to be maintained at all times takinginto account the predicted motion of the unit relative to thesurface of the sea. Calculations, model test results orprototype reports are to be submitted for consideration.

1.2.2 In cases where the unit is designed without aclearance air gap, the scantlings of the upper hull deckstructure are to be designed for wave impact forces, see also1.4.4.

1.3 Structural design

1.3.1 The general requirements for structural designare given in Chapter 3, but the additional requirements of thisSection are to be complied with.

Applicable loading conditionMode

(a) (b) (c) (d) (e)See See

Note 2 Note 2

Operating ✓ ✓ ✓ ✓ ✓

Survival ✓ ✓ ✓ ✓ ✓

Transit ✓ ✓ ✓ ✓ ✓

NOTES1. For definition of loading conditions (a) to (e), see Ch 3,4.3.2. For loading conditions (c) and (d) as applicable to a column-

stabilized unit, see 1.3.5 to 1.3.8.

Table 4.1.1 Design loading conditions


1.5.4 Internal column structure supporting mainbracings is in general not to be of a lesser strength than thebracing itself.

1.5.5 When bracing forces are designed to betransmitted to the column shell, the resulting column shellstresses are to be combined with the stresses due to thehydrostatic pressure and overall forces.

1.6 Lower hulls

1.6.1 Lower hulls or pontoons are to be designed foroverall bending, shear forces, and axial forces due to endpressure when combined with the local hydrostatic pressureas defined in Ch 3,4.14.

1.6.2 Irrespective of the tank loading arrangement, thescantlings of tanks are to be verified in both full and emptyconditions.

1.6.3 Columns are as far as practicable, to becontinuous through the plating of the lower hull deckstructure and be aligned and integrated with the internalbulkheads and/or side shell.

1.6.4 Where the column shell plating is intercostal withthe lower hull deck, the deck plating below the columns is tobe suitably increased and is to have steel grades withsuitable through-thickness properties, see Ch 2,4.1.3.

1.6.5 Particular attention should be given to the designof the local structure at the intersection of columns with lowerhulls and due account should be given to penetrations andstress concentrations.

1.7 Main primary bracings

1.7.1 Bracing members are to be designed towithstand the stresses imposed by the overall loading,together with local stresses due to wave, current andbuoyancy forces and, when applicable, hydrostatic pressure.

1.7.2 Bracings are in general to be made watertightand provided with adequate means of access to enableinternal inspection to be carried out when the unit is afloat.

1.7.3 Watertight bracings are to be designed for thehydrostatic pressure loads defined in Ch 3,4.14, and thescantl ings are to be verif ied against buckling due tocombined axial stresses and hoop stresses caused byexternal hydrostatic pressure. Ring stiffeners are to be fittedwhere necessary.

1.7.4 Attachments and penetrations to the shell ofbracings are to be avoided as far as practicable. I fattachments are unavoidable they are to be welded tosuitable doubler plates having well rounded corners.

1.7.5 Leak detection and drainage arrangements of watert ight bracings are to be in accordance with Pt 5, Ch 11,4.5.

1.7.6 The scantlings and arrangements of free-floodingbracings will be specially considered.


Structural Unit Types



1.3.6 The general requirements for investigatingaccidental loads are defined in Ch 3,4.16 but in the case of acolumn-stabilized unit collision loads against a column orpontoon will normally only cause local damage to thestructure and consequently loading condit ions (c) in Table 4.1.1 need not be investigated from the overall strengthaspects. The requirements for very slender columns will bespecially considered.

1.3.7 Accidental damage to a main bracing membermay result in complete failure of the bracing and consequentlyit is a class requirement that loading conditions (c) and (d) inTable 4.1.1 are investigated to ensure the overall integrity ofthe unit in the event of failure of an individual primary bracingmember.

1.3.8 The permissible stress levels after crediblefailures or accidents are to be in accordance with Chapter 5.

1.4 Upper hull structure

1.4.1 Decks and supporting grillage structures formingpart of the primary structure are to be designed to resist boththe overall and local loadings.

1.4.2 Openings in primary bulkheads and decks arenormally to be represented in the structural model. Bulkheadopenings in ‘tween decks are not, in general, to be fitted inthe same vertical line. When large bulkhead openings are cutin the structure which were not included in the structuralmodel, the bulkhead thickness is to be increased in way ofthe opening to compensate for the loss of shear area andstiffness.

1.4.3 When the primary deck structure consists ofheavy or box girder construction and the infill deck plating isconsidered to be secondary structure, only the main deckgirders and the secondary deck plating stiffeners need satisfythe buckling strength requirements given in Chapter 5. Theinfill deck plating thickness and its contribution to the overallstrength of the structure will be specially considered, see alsoCh 6,4.

1.4.4 When the upper hull structure is designed to bewaterborne for operational purposes the upper hull scantlingsare not to be less than those specified for shell boundaries ofself elevating units as defined in Ch 6,3.

1.4.5 Columns should be aligned and integrated withthe bulkheads in the upper hull structure. Particular attentionshould be given to the detail design at the intersection ofcolumns with the upper hull structure to minimize stressconcentrations.

1.5 Columns

1.5.1 Columns are to be designed to withstand theforces and moments resulting from the overall loadings,together with forces and moments due to wave loadings andinternal tank pressures.

1.5.2 In general, internal spaces within the columnsare to be designed for the pressure heads defined in Ch 3,4.14.

1.5.3 High local loads are also to be taken intoaccount in the overall design strength of the columns.


1.8 Bracing joints

1.8.1 Joints at the intersection of bracings or betweenbracings and columns are to be designed to transmit thebending, direct and shear forces involved in such a manneras to reduce, so far as possible, the risk of fatigue failure.Stress concentrations are to be minimized by good detaildesign and, in general, nominal stress levels are to be madelower than in the adjacent structure by increasing platethickness or suitably flaring the member ends, or both. Ringstiffeners or other welded attachments across the principalstress direction are to be avoided wherever possible in allregions of high stress. It this is not possible (e.g. whererequired to support bracket ends on otherwise unstiffenedplating), the weld is to have a smooth profile withoutundercutting. Continuity of strength is to be maintainedthrough the joint, and shear web plates and other axialstiffening members are to be made continuous.

1.8.2 Special attention is also to be given to thequalities of bracing details, e.g. openings, penetrations,stiffener ends, brackets and other attachments. The weldingprocedure is to be such as to minimize the risk of cracks,lack of penetration and lamellar tearing of the parent steel.

1,8.3 Joints depending upon transmission of tensilestresses through the thickness of the plating of one of themembers (which may result in lamellar tearing) are to beavoided wherever possible. Plate steel used in suchlocations shall have suitable through thickness properties.

1.9 Lifeboat platforms

1.9.1 The strength of lifeboat platforms is to be verifiedwith the unit in the upright condition and in the inclinedcondition at an angle corresponding to the worst damagewaterline, and at an inclined angle of 15° in any direction.

1.9.2 For calculation purposes, the weight of thelifeboat is to be taken as the weight when fully manned andequipped. The platform weight is to be taken as the steelweight plus the weight of davits and equipment. Symmetricaland unsymmetrical load cases are to be considered asappropriate, e.g. one lifeboat launched and the otherlowering. The design calculations are to be submitted forinformation.

1.9.3 The following dynamic load factors are to beincluded in the calculations:

Item: Factor:Platform weight 0,3 gLifeboat weight when stowed 0,3 gLifeboat weight when lowering 0,5 g

1.9.4 In the upright condition and in the inclinedcondition the permissible stresses are to comply with Ch 5,2.1.1, loadcase (a) and (b) respectively.

1.9.5 After installation of the lifeboats, testing is to becarried out to the satisfaction of LR’s Surveyors.



Structural Unit Types Part 4, Chapter 4Sections 1 & 2

SECTION 2Sea bed-stabilized units

2.1 General

2.1.1 This Section outlines the structural designrequirements of sea bed-stabilized units as defined in Pt 1, Ch 2,2. Additional requirements for particular unit typesrelated to the design function of the unit are given in Part 3.Self-elevating units are to comply with Section 3.

2.1.2 Units of this type are generally designed tooperate under normal operating environmental conditionsand severe storm conditions whilst resting on the sea bed.The design transit condition and design limitations are to bespecified by the Owner/designer.

2.1.3 The structural analysis and determination ofscantlings is to be on the basis of distribution of loadings andballast required to satisfy 2.1.2 and all units are to haveadequate reserve of bearing pressure on the supportfootings, pontoons or mats.

2.1.4 The requirements of Sections 1 and 3 are to becomplied with as applicable to the design of the unit.

2.1.5 The permissible stress levels in all operatingmodes are to comply with Chapter 5.

2.1.6 The minimum local scantlings are to comply withthe requirements of Chapter 6, but the bottom structureshould not be less than required for tank bulkheads inChapter 6 using the load head h4 equivalent to the maximumdesign bearing pressure. In general, bottom primarymembers supporting shell stiffeners are to be spaced notmore than 1,85 m apart and side girders or equivalent are tobe spaced 2,2 m apart. The buckling strength of the primarymember webs is to be in accordance with Chapter 5, see also 2.4.

2.2 Air gap

2.2.1 For on-bottom modes of operation, theclearance air gap between the underside of the deckstructure and the highest predicted design wave crest is tobe in accordance with 3.2.1. In transit conditions, the air gapis to be in accordance with 1.2. Calculations, model testresults or prototype reports are to be submitted forconsideration.

2.3 Operating conditions

2.3.1 Classif ication wil l be based upon theOwner/designer’s assumptions in operating the unit and thesea bed conditions. These assumptions are to be recordedin the Operations Manual. It is the responsibility of theoperator to ensure that actual conditions do not impose moresevere loadings on the unit.

2.3.2 Procedures and limitations for ballasting and re-floating the unit in order to avoid overstressing thestructure by static or dynamic loads are to be clearly definedin the Operations Manual, see Pt 3, Ch 1,3.





2.4 Corrosion protection

2.4.1 Where it is intended to operate at a fixed locationfor the design life of the unit, the structure which is below themud line or internal areas which are permanently flooded andcannot be inspected are to have their structure designed withadequate corrosion margins and protection.

2.4.2 The corrosion allowance for wastage and themeans of protection is to be to the satisfaction of LR and areto be agreed at the design stage.

2.4.3 The general requirements for corrosionprotection are to comply with Part 8.

SECTION 3Self-elevating units

3.1 General

3.1.1 This Section outlines the structural designrequirements of self-elevating units. Additional requirementsfor particular unit types related to the design function of theunit are given in Part 3.

3.1.2 A self-elevating unit is a floating unit which isdesigned to operate as a sea bed-stabilized unit in anelevated mode, see Pt 1, Ch 2,2.

3.1.3 Production units are to comply with therequirements of Pt 3, Ch 3 as applicable.

3.1.4 The structural analysis and determination ofprimary scantlings are to be on the basis of the distribution ofloadings expected in all modes of operation.

3.2 Air gap

3.2.1 When in the elevated position, the unit is to bedesigned to have a clearance air gap between the undersideof the hull structure and the highest predicted design wavecrest superimposed on the maximum surge height over themaximum mean astronomical tide. The minimum clearanceis not to be less than 1,5 m. Calculations, model test resultsor prototype reports are to be submitted for consideration.


3.3.1 The structure is to be designed to withstand thestatic and dynamic loads imposed upon it in transit,installation and elevated conditions. All relevant distributionsof gravity and variable loads are to be considered, as arestresses due to the overall and local effects, see Ch 3,4.

3.3.2 The permissible stresses are to be in accordancewith Chapter 5 and the minimum local scantlings of the unitare to comply with Chapter 6.

3.3.3 All modes of operation are to be investigated andthe relevant design load combinations defined in Ch 5,1.2 areto be complied with. The loading conditions applicable to aself-elevating unit are shown in Table 4.3.1.

Applicable loading conditionMode

(a) (b) (c) (d) (e)

Site installationand re-floating ✓

Operating ✓ ✓ ✓ ✓See See

Note 2 Note 2

Survival ✓ ✓

Transit ✓ ✓ ✓

NOTES1. For definition of loading conditions (a) to (e), see Ch 3,4.3.2. For loading conditions (c) and (d) as applicable to a self-

elevating unit, see 3.3.4 and 3.3.5.



3.3.4 The general requirements for investigatingaccidental loads are defined in Ch 3,4.16. In transitconditions, collision loads against the hull structure willnormally only cause local damage to the hull structure andconsequently loading conditions (c) and (d) in Table 4.3.1 neednot be investigated from the overall strength aspects. Whenin the elevated position, accidental damage to the legs is tobe considered in the design and the unit is to be capable ofabsorbing the energy of impact in association withenvironmental loads corresponding to the appropriate oneyear storm condition.

3.3.5 In general, for loading conditions (c) and (d) inTable 4.3.1, the level of impact energy absorbed by the localleg structure is not to be taken less than 2 MJ. If the unit isonly to operate in protected waters, as defined in Pt 1, Ch 2,2.4, the level of impact energy absorbed by the local legstructure may be reduced but should not be less than 0,5MJ. Collision loads will, in general, only cause local damageto one leg, but the possibility of progressive collapse andoverturning should be considered in the design calculationswhich should be submitted for consideration.

3.3.6 Fatigue damage due to cyclic loading is to beconsidered in the design of the legs of the unit for transit andelevated condit ions. Fatigue damage is consideredaccumulative throughout the unit’s design life. The extent ofthe fatigue analysis will be dependent on the mode and areaof operations, see Ch 5,5.

3.4 Hull structure

3.4.1 The hull is to be considered as a completestructure having sufficient strength to resist all inducedstresses while in the elevated position and supported by itslegs. All fixed and variable loads are to be distributed, by anaccepted method of rational analysis, from the various pointsof application to the supporting legs. The scantlings of thehull are then to be determined consistent with this loaddistribution.

3.4.2 Due account must be taken of loadings inducedin the transit condition from external sea heads, variable deckloads and legs.

3.5 Deckhouses

3.5.1 Deckhouses are to have sufficient strength fortheir size, function and location. Requirements for scantlingsare given in Ch 6,6.

3.5.2 Special consideration is to be given to thescantlings of deckhouses and deck modules which will notbe subjected to wave loading in any operating condition suchas units which are ‘dry towed’ to the operating location.

3.6 Structure in way of jacking or elevatingarrangements

3.6.1 Load carrying members in the jackhouses andframes which transmit loads between the legs and the hullare to be designed for the maximum design loads and are tobe so arranged that loads transmitted from the legs areproperly diffused into the hull structure. The scantlings ofjackhouses are not to be less than required for deckhouses inaccordance with Ch 6,6.



Structural Unit Types Part 4, Chapter 4Section 3

3.7 Leg wells

3.7.1 The scantl ings and arrangements of theboundaries of leg wells are to be specially considered and thestructure is to be suitably reinforced in way of leg guidestaking into account the maximum forces imposed on thestructure. The minimum scantlings of leg wells are to complywith Ch 6,3.3.

3.8 Leg design

3.8.1 Legs may be either shell-type or lattice-type.Independent footings may be fitted to the legs or legs may bepermanently attached to a bottom mat. Shell-type legs maybe designed as either stiffened or unstiffened shells.

3.8.2 Where legs are fitted with independent footings,proper consideration is to be given to the leg penetration ofthe sea bed and the end fixity of the leg.

3.8.3 Leg scantl ings are to be determined inaccordance with a method of rat ional analysis andcalculations submitted for consideration, see Ch 3,3.

3.8.4 For lattice legs, the slenderness ratio of the mainchord members between joints is not to exceed 40, or two-thirds of the slenderness ratio of the leg column as a whole,whichever is the lesser, unless it can be shown that acalculation taking into account beam-column effect, jointrigidity and joint eccentricity justifies a higher figure.

3.9 Unit in the elevated position

3.9.1 When computing leg stresses with the unit in theelevated position, the maximum overturning load andmaximum shear load on the unit, using the most adversecombination of applicable variable loadings together with theenvironmental design loadings, are to be considered with thefollowing criteria:(a) Wave forces: Values of drag coefficient, CD, and

inertia coefficient, Cm, vary considerably with Reynoldsnumber, Rn, and Keulegan-Carpenter number, Nk, andare to be carefully chosen to suit the individual circum-stances. In calculating the wave forces using acceptablewave theories, values as given in (i) to (iii) for the hydrody-namic coefficients CD and CM, for non-tubular membersof the leg chords may be used essentially in the drag dominated regime with post-critical Rn and high Nk.Otherwise more detailed information based on tests orpublished data are to be used.(i) Cylindrical chord members with protruding racks:

Drag coefficient,

For marine fouled members, CD calculated is tobe factored by 1,2.Inertia coefficient,

whereCd = the drag coefficient used for a smooth

cylinder memberCm = the inertia coefficient used for a cylinder

memberDE = pitch distance of the racks

CM = Cm Ag

Ac

CD = Cd +DE – DC

DC 2 sin θ





DC = nominal diameter of the cylindrical part ofthe member

Ag = the cross sectional area of the memberAc = the cross sectional area of the cylindrical

part of the memberθ = the angle between the flow direction and

the central line of the cross section alongthe racks

(ii) Triangular chord members:Drag coefficient, for smooth triangular members:CD = 1,6 θ = 0°CD = 1,4 θ = 45°CD = 1,8 θ = 90°CD = 1,7 θ = 135°CD = 1,3 θ = 180°For marine fouled members, the CD values are tobe factored by 1,2.Inertia coefficient, CM = 1,4where

θ = Relative approach angle of flow, 0° beingtowards the backplate and to becounted clockwise.

(iii) Other shapes of non-tubular members: CD, CMvalues should be assessed based on the relevant published data or appropriate tests. The tests should consider possible roughness,Keulegan-Carpenter and Reynolds numbersdependence.

(b) Dynamics: Due account of dynamics is to be taken incomputing leg stresses when this effect is significant.The following governing aspects are to be included:(i) The mass and mass distribution of the unit. This

includes structural mass, mass of equipment andvariable load on board, added mass due to thesurrounding water and marine growth, if applica-ble, etc.

(ii) The global unit structural stiffness. This includesstiffness contributions from the leg to hullconnections and the footing interface, if applica-ble.

(iii) The damping. This includes structural damping,foundation damping and hydrodynamic damping.

(c) Other considerations: Other considerations incomputing leg stresses include:(i) Forces and moments due to initial leg inclination

and lateral frame deflections of the legs.(ii) Bending moments at leg/hull connections due to

hull sagging under gravity loads.

3.10 Legs in field transit conditions

3.10.1 In f ield transit condit ions within the samegeographical area, legs are to be designed for accelerationforces caused by a 6° single amplitude of roll or pitch at thenatural period of the unit, plus, 120 per cent of the gravityforces caused by the legs’ angle of inclination, unlessotherwise verified by appropriate model tests or calculations.The legs are to be investigated for any proposed legarrangement with respect to vertical position during fieldtransit moves, and the approved positions are to be specifiedin the Operations Manual. Such investigation is to includestrength and stability aspects. Field transit moves may onlybe undertaken when the predicted weather is such that theanticipated motions of the unit will not exceed the designcondition.

3.10.2 The duration of a field transit move may be for aconsiderable period of time and should be related to theaccuracy of weather forecasting in the area concerned. It isrecommended that such a move should not normally exceeda twelve hour voyage between protected locations orlocations where the unit may be safely elevated. However,during any portion of the move, the unit should not normallyto be more than a six hour voyage to a protected location ora location where the unit may be safely elevated. Suitableinstructions are to be included in the Operations Manual.Where a special leg position is required for field moves thisposition is to be specified in the Operations Manual.

3.11 Legs in ocean transit conditions

3.11.1 In ocean transit conditions involving a move to anew geographical area, legs are to be designed foracceleration and gravity loadings resulting from the motionsin the most severe anticipated environmental transitconditions, together with corresponding wind moments.Calculation or model test methods may be used to determinethe motions. Alternatively, legs may be designed for theacceleration and gravity forces caused by a design criteria of20° single amplitude of roll or pitch at a 10 second period.For ocean transit conditions, it may be necessary to reinforceor support the legs, or to remove sections of them. Theapproved condition is to be included in the OperationsManual.

3.12 Legs during installation conditions

3.12.1 When lowering the legs to the sea bed, the legsare to be designed to withstand the dynamic loads whichmay be encountered by their unsupported length just prior totouching the sea bed and also to withstand the shock oftouching bottom while the unit is afloat and subject to wavemotions.

3.12.2 Instructions for lowering the legs are to be clearlyindicated in the Operations Manual. The maximum designmotions, bottom conditions and sea state while lowering thelegs are to be clearly stated. The legs are not to be loweredin conditions which may exceed the design criteria.

3.12.3 For units without bottom mats, all legs are tohave the capability of being preloaded to the maximumapplicable combined gravity plus overturning load. Theapproved preload procedure should be included in theOperations Manual.

3.12.4 Consideration is to be given to the loads causedby a sudden penetration of one or more legs duringpreloading.

3.13 Stability in-place

3.13.1 When the legs are resting on the sea bed, theunit is to have sufficient positive downward gravity loadingson the support footings or mat to withstand the overturningmoment of the combined environmental forces from anydirection, with a reserve against the loss of positive bearing ofany footing or segment of the area, for each design loadingcondition. The most critical minimum variable load conditionis to be considered for each loading direction and in no caseis the variable load to be taken greater than 50 per cent ofthe maximum and using the least favourable location of thecentre of gravity.


3.13.2 The safety factor against overturning is to be atleast 1,25 with respect to the rotational axis through thecentres of the independent footings at the sea bed. For a unitwith a mat type footing, the rotational axis is to be taken atthe maximum stressed edge of the mat.

3.13.3 For independent footings, the safety factoragainst sliding at the sea bed is to be related to the soilcondition, but in no case is the safety factor to be taken asless than 1,0.

3.14 Sea bed conditions

3.14.1 Classification will be based upon the designer’sassumptions regarding the sea bed conditions. Theseassumptions are to be recorded in the Operations Manual.

3.14.2 Full details of the sea bed at the operatinglocation are to be submitted to LR for review at the designstage. The effects of scouring on bottom mat bearingsurfaces and footings is to be considered, see 3.16.3.

3.15 Foundation fixity

3.15.1 For units with independent legs, foundation fixityshould not normally be considered for in-place strengthanalysis of the upper parts of the leg in way of the lowerguides unless justified by proper investigation of the footingand soil conditions.

3.15.2 For in-place analysis, the lower parts of the legwith independent footings are to be designed for a legmoment no less than 50 per cent of the maximum legmoment at the lower guides, together with the associatedhorizontal and vertical loads.

3.16 Bottom mat

3.16.1 When the legs are attached to a bottom mat, the scantlings of the mat are to be specially considered, but the permissible stress levels are to be in accordance withChapter 5. Particular attention is to be given to the attachment,framing and bracing of the mat in order that the loads from thelegs are effectively distributed into the mat structure.

3.16.2 Mats and their attachments to the bottom endsof the legs are to be of robust construction to withstand theshock load on touching the sea bed while the unit is afloatand subject to wave motions.

3.16.3 The effects of scouring on the bottom bearingsurfaces should be considered by the designer, with a stateddesign figure for loss of bearing area. The effects of skirt plates,where provided, may be taken into account, see also 3.14.1.

3.16.4 The minimum local scantl ings of the matstructures are to comply with 3.17.5 and 3.17.6.

3.17 Independent footings

3.17.1 Independent footings are to be designed towithstand the most severe combination of overall and localloadings to which they may be subjected, see also 3.16.3. In general, the primary structure is to be analyzed by a three-dimensional finite element method.




3.17.2 The complexity of the mathematical modeltogether with the associated element types is to besufficiently representative of all parts of the primary structureto enable internal stress distributions to be established.

3.17.3 The loading combinations considered are torepresent all modes of operation so that the critical designcases are established, and are to include, but not be limitedto, the following:(a) The maximum preload concentrated or distributed over

the area of initial contact.(b) The maximum preload uniformly distributed over the

entire bottom area.(c) The relevant preload distributed over contact areas

corresponding to intermediate levels of penetration, asrequired.

(d) The greatest leg load due to the specified environmentalmaxima applied over the entire bottom area, with thepressure varying linearly from zero at one end to twicethe mean value at the other end.

(e) The distribution in (d) applied in different directions,depending on structural symmetry, to cover all possiblewave headings.

(f) Where it is intended to move the unit without the footings being fully retracted, a special analysis of theleg to spudcan connections may be required.

3.17.4 The permissible stresses are to be based on thesafety factors for yield and buckling as defined in Ch 5,2.The preload cases may be considered as load case (a) in Ch5,2 while the loadings associated with the maximum stormcases may be taken as load case (b) in Ch 5,2.

3.17.5 The minimum local scantlings of the bottom shelland stiffening and other areas subjected to pressure loadingare to be determined from the formulae for tank bulkheadsgiven in Ch 6,7. The loadhead h4 should be consistent withthe maximum bearing pressure, determined in accordancewith 3.17.3 and the wastage allowance of the plating shouldbe not less than 3,5 mm, see also 3.17.6 and 3.17.7.

3.17.6 Where it is intended to operate at a fixed locationfor the design life of the unit, the footing/leg structure which isbelow the mud line or internal areas of the footings whichcannot be inspected are to have their structure designed withadequate corrosion margins and protection. The corrosionallowance for wastage and the means of protection are to beto the satisfaction of LR and are to be agreed at the designstage.

3.17.7 When the structure consists of compartmentswhich are not vented freely to the sea, the scantlings of theshell boundaries and stiffening are not to be less thanrequired for tank boundaries in Ch 6,7 using the load head h4not less than 1,4T0 m where T0 is defined in Ch 1,5.

3.17.8 Where the legs of the unit are made from steel withextra high tensile strength, special consideration is to be givento the weld procedures for the leg to footing connections.Adequate preheat should be used and the cooling rate shouldbe controlled. Any non-destructive examination of the weldsshould be carried out after a minimum of 48 hours haveelapsed after the completion of welding.






3.18.1 When self-elevating units are f i tted withcantilevered lifeboat platforms the strength of the platformsare to comply with 1.9. If the lifeboat platform can besubjected to wave impact forces in transit conditions, thescantlings are to be specially considered and details are to besubmitted for consideration by LR.

SECTION 4Surface-type units

4.1 General

4.1.1 This Section outlines the structural designrequirements of ship and barge-type units engaged inproduction and/or oil storage/offloading while permanentlymoored at offshore locations.

4.1.2 The Rules are also applicable to units whichnormally operate while moored at offshore locations butwhich are disconnectable in order to avoid extremeenvironmental conditions or hazards, see also Pt 4, Ch 3,4.

4.1.3 Units which operate as shuttle tankers willnormally be assigned class in accordance with the Rules forShips.

4.1.4 In general, the scantlings and arrangements ofunits with oil bulk storage tanks are to comply with Pt 4,Chapters 9 and 10 of the Rules for Ships, as applicable, andproduction units without oil bulk storage tanks are to complywith Pt 4, Ch 1 of the Rules for Ships. All aspects whichrelate to the specialized offshore function of the unit are to beconsidered on the basis of this Chapter. Double hullconstruction is to be used in the oil bulk storage tank area,but a double bottom need not be fitted except whererequired by the National Administrations in the area ofoperation and/or the country in which the unit is registered,as applicable.

4.1.5 The scantlings and arrangements of units with alimited number of tanks for the storage of flammable liquidshaving a flash point not exceeding 60̊C (closed cup test) willbe specially considered.

4.1.6 The class notations and descriptive notesapplicable to units classed in accordance with these Rulesare to be in accordance with Pt 1, Ch 2 and Pt 3, Ch 3,1 towhich reference should be made.

4.1.7 Additional requirements related to the designfunction of the unit are given in Part 3.

4.1.8 Turret structures, mooring arms and yokestructures, etc., are to comply with the requirements of Pt 3,Ch 2.


4.2.1 The general requirements for structural designare given in Chapter 3, but the additional requirements of thisSection are to be complied with.

4.2.2 The hull structure is to be designed to withstandthe static and dynamic loads imposed on the structure in alloperating conditions. All relevant loads as defined in Chapter 3are to be considered and the effects of partial and/or non-homogeneous loading in oil bulk storage tanks are to beconsidered. When considering the design loading conditionsthe Owner/designer is to take account of the requirements foron station tank inspection.


4.2.3 The assessment of environmental loads may bebased on the results of model tests and by suitable directcalculation methods of the actual loads on the hull at the site-specific location taking into account the following servicerelated factors:

• Site-specific environmental loads, see also 4.2.5.• Local mooring loads.• Ship orientation with wave loadings predominantly

from one direction.• Long-term service effects at a fixed location.• Range of tank loading conditions including empty

tanks required for on site surveys.

4.2.4 All modes of operation are to be investigated andthe relevant design load combinations defined in Ch 5,1.2 areto be complied with. The loading conditions applicable to asurface-type unit are shown in Table 4.4.1. Where it isintended to dry-dock a unit during its service life, this is to betaken into account at the design stage and the dockingcondition is to be submitted to LR for approval.


4.2.5 The longitudinal strength of the unit is to beinvestigated and the total stress from the combined effects ofwave loads, still water loads and mooring loads is not toexceed the permissible stress levels and requirementsdefined in Pt 3, Ch 4 of the Rules for Ships. When the site-specif ic wave bending moments and shear forcesdetermined by direct calculation exceed the values defined inthe Rules for Ships, special consideration will be given to thepermissible stresses.

4.2.6 When the site-specific wave bending momentsand shear forces in operating conditions are less than thevalues defined in Pt 3, Ch 4 of the Rules for Ships, theminimum requirements for longitudinal strength defined in theRules for Ships are to be complied with.

4.2.7 The minimum hull modulus in way of turret areasand other large openings is to satisfy the Rule requirementsfor longitudinal strength. When the turret is situated within0,5L amidships the minimum hull midship section modulusabout the transverse neutral axis at deck or keel is to bemaintained in way of the turret opening. Increases in platethicknesses are to take place gradually.



Structural Unit Types Part 4, Chapter 4Sections 4

4.2.8 On-station tank inspection conditions are to berestricted to reasonable weather as defined in Pt 1, Ch 2. Inthe tank inspection condition, the permissible wave bendingmoments and shear forces may be based on those definedfor short voyages in Pt 3, Ch 4,5 of the Rules for Ships. Tankinspection conditions are to be included in the unit’s loadingmanual and the limiting environmental criteria is to be definedin the Operations Manual.

4.2.9 The strength of the unit in the transit conditionand in the site-specific installation condition is to beinvestigated and submitted to LR for approval. For a turret-moored unit with a turret well opening, suitable precautionsare to be taken to prevent damage to the well structure intransit.

4.2.10 Disconnectable units, as defined in 4.1.2, willremain in class in the sail-away condition and the loadingconditions are to be submitted for approval.

4.2.11 The general requirements for investigatingaccidental loads are defined in Ch 3,4.16. In operatingconditions, collision loads against the hull structure willnormally only cause local damage to the hull structure andconsequently loading conditions (c) and (d) in Table 4.4.1need not be investigated from the overall strength aspects.

4.2.12 The scantlings of the primary structure of the oilbulk storage tank area are to be verified by direct calculationsbased on a three-dimensional finite plate element analysiscarried out in accordance with the procedures contained inLR’s ShipRight Structural Design Assessment (SDA)Procedure as applicable to oil tankers.

4.2.13 In addition to the requirements of 4.2.12, the hullstructure in way of the mooring turret area is to be verified bydirect calculation. In all cases, the structural analysis is toinclude a representative portion of the hull and tank structuretogether with the integration of the mooring system with theunit’s structure. Permissible stress levels are to be inaccordance with Chapter 5.

4.2.14 The structural analysis required by 4.2.13 is toinclude the following load combinations:(a) Turret loads.(b) Overall hull bending moments and shear forces.(c) Internal and external pressure loads corresponding to the

design tank loading conditions and range of operatingdraughts.

(d) Local deck loading due to green seas as applicable.

4.2.15 Turret bearings are to comply with Pt 3, Ch 2and the turret bearing support structure is to be integratedinto the hull structure and the local permissible stress levelsare to comply with Ch 5,2.

4.2.16 The boundary of circumturret well bulkheads areto be designed for the maximum forces imposed on thestructure. Where the boundary of circumturret wel lbulkheads are designed as r ing sti ffened shel ls, thepermissible stresses in the bulkhead for direct calculationsare to be in accordance with Ch 5,2 but the minimumscantlings of circumturret well bulkheads are to comply withthe requirements for tank bulkheads in Ch 6,7 using the loadhead measured from the point of consideration to the top ofthe well, but in no case is the well bulkhead plating to have athickness less than the unit’s side shell plating adjacent to thewell opening, whichever is the greater.

Mode Applicable loading condition

(a) (b) (c) (d) (e)

Site installation ✓

(see Note 3)

Operating and survival ✓ ✓ ✓ ✓ ✓

See SeeNote 2 Note 2

Tank inspection ✓ ✓

Transit ✓ ✓

(see Note 3)

NOTES1. For definition of loading conditions (a) to (e), see Ch 3,4.3.2. For loading conditions (c) and (d) as applicable to a surface-type

unit, see 4.2.11.3. For loading conditions (a) and (b), see 4.2.9.





4.2.17 Where the circumturret well bulkhead forms theboundary of oil bulk storage tanks the scantlings are also tocomply with Pt 4, Ch 9 of the Rules for Ships.

4.2.18 Hawse pipes used in the mooring system are tohave adequate strength for the imposed loads and whenlocated inside tanks are to be considered for sloshing forces.

4.3 Fatigue design

4.3.1 The general requirements for fatigue design andfactors of safety on fatigue life for supporting structures todrilling and process plant, flare towers, derricks and mooringstructures are to comply with Chapter 5.

4.3.2 The fatigue assessment of the hull structure ofship and barge-type units is to be verified in accordance withLR’s ShipRight Fatigue Design Assessment (FDA) Procedureas applicable to oil tankers or another acceptable standard.

4.3.3 The turret bearing support structures are to beassessed for fatigue damage due to cyclic loading inaccordance with Ch 5,5.

4.3.4 Fatigue calculations for the integration of themooring system within the unit’s hull structure are also to becarried out, see Pt 3, Ch 10.

4.4 Sloshing analysis

4.4.1 When the partial filling tanks are contemplated inoperating conditions, the sloshing loads on tank boundariesare to be assessed in accordance with Pt 3, Ch 3,5 of theRules for Ships. Full account is to be taken of the operatingrequirements on station with regard to the filling, transfer andexport operations for oil bulk storage tanks.

4.5 Fore end structure

4.5.1 An integrated approach to structural design is tobe used to determine the scantl ings of al l structuralcomponents affected by wave impact loading.

4.5.2 In general, the scantl ings of the fore endstructure are to comply with Pt 3, Ch 5 of the Rules for Ships.When determining the scantlings of the shell envelope of thefore end structure a nominal speed of 15 knots is normally tobe assumed for calculation purposes. The thickness offorecastle shell plating forward of 0,05L from the F.P. is not tobe less than the adjacent side shell plating. The forecastleside framing is to be fitted with standard Rule brackets attheir lower ends. The deck structure in way of the lower endof forecastle frame connections is to be specially considered.Welding is to comply with Pt 4, Ch 8.

4.5.3 In benign environments, consideration is to begiven to reducing the nominal speed defined in 4.5.2 but inno case is a nominal speed of less than 12 knots to be usedto determine Rule scantlings.

4.5.4 For units with unconventional forward ends andunits which may be subjected to loadings in excess of thenominal Rule pressure heads due to wave impact loading,the scantlings are to be specially considered. In extremelyharsh environments, a site-specific assessment is to becarried out to determine equivalent design pressure heads onthe shell envelope. When model tests are to be carried out, itis recommended that arrangements are made to measurebow impact wave pressures.

4.5.5 Where the loadings exceed those determined inaccordance with 4.5.2, direct calculation methods may beused to determine the local hull scantlings. The designmethodology is to be agreed with LR and the permissiblestress levels for stiffening members are to comply with Ch 5,2.1.1(b). Special consideration is to be given to areasof the structure where localized peak stresses occur. Localyielding may be permitted.

4.5.6 The strengthening of the bottom forward is to bespecially considered in relation to the actual forces determinedfrom model tests and/or direct calculations but the minimumrequirements of Pt 3, Ch 5,1.5 are to be complied with.

4.5.7 Where the structure is subjected to concentratedmooring loads from mooring arms or yokes, external turretsor mooring hawsers, etc., the scantlings and arrangementsare to be specially considered. Finite element analysis ofattachments to the hull is to be carried out to ensuresatisfactory stress distribution of the mooring loads into thehull structure. The permissible local stress levels are tocomply with Chapter 5.

4.6 Aft end structure

4.6.1 In general, the scantlings of the aft end structureare to comply with Pt 3, Ch 6 of the Rules for Ships.

4.6.2 The scantlings and arrangements of machineryspaces are to comply with the requirements of Pt 3, Ch 7 ofthe Rules for Ships.

4.6.3 For units permanently moored by the stern, thestructural arrangements and scantlings of all exposedstructure located in the aft end of the unit are to be speciallyconsidered and the requirements of 4.5 are to be compliedwith as applicable. The strengthening of the bottom structureare to be specially considered, see also 4.5.6.

4.7 Machinery spaces

4.7.1 In general, the scantlings of machinery spacesare to comply with Pt 3, Ch 7 of the Rules for Ships.

4.7.2 When main auxiliary machinery is fitted above the weather deck, the machinery is to be protected bydeckhouses in accordance with 4.8.1.

4.8 Topside structure

4.8.1 The minimum scantlings of superstructures anddeckhouses are to comply with the requirements of Pt 3, Ch 8 of the Rules for Ships. Bulwarks and guard rails are tocomply with Ch 6,10, but special consideration is to be givento the scantlings of bulwarks at the fore end or screensprotecting the swivel stack. In general, the scantlings ofbulwarks at the fore end are not to be less than required fordeckhouse fronts at the position under consideration.


4.8.2 For units with unconventional forward ends andunits which may be subjected to high deck loading in excessof the minimum Rule heads due to loading from green seas,adequate protection by means of bulwarks and break waterstructure are to be provided at the forward end and thescantlings of the structure and its under deck supports are tobe specially considered. Where necessary the loadings areto be determined by model tests.

4.8.3 The boundary bulkheads of accommodationspaces which may be subjected to blast loading inaccordance with Pt 7, Ch 3 are to be designed in accordancewith Ch 3,4 and permissible stress levels are to satisfy thefactors of safety given in Ch 5,2.1.1(c).

4.8.4 For units fitted with a process plant facility and/ordrilling equipment, the support stools and integrated hullsupport structure to the process plant and other equipmentsupporting structures including derricks and flare structures areconsidered to be classification items regardless of whether ornot the process/drilling plant facility is classed and the loadingsare to be determined in accordance with Pt 3, Ch 8,2.Permissible stress levels are to comply with Chapter 5.

4.8.4 Equipment supports are to take into account hulldeflections when considered necessary.

4.8.5 Units with a process plant facility which complywith the requirements of Pt 3, Ch 8 will be eligible for theassignment of the special features class notation PPF.

4.8.6 Units with a drilling plant facility which complywith the requirements of Pt 3, Ch 7 will be eligible for theassignment of the special features class notation DRILL.




SECTION 5Buoy units

5.1 General

5.1.1 This Section outlines the structural designrequirements of buoys of any shape or form. For deepdraught caissons, see Section 7.

5.1.2 Additional requirements for particular unit typesrelated to the design function of the unit are also given in Part 3.

5.1.3 The hull structure of buoy units is to be dividedinto watertight compartments and have adequate buoyancyand floating stability in all conditions defined in 5.6.2.

5.1.4 Venting arrangements are to be fitted to all tanksor floodable spaces to ensure that air is not trapped in anyoperating mode, see Pt 5, Ch 11.

5.1.5 Venting of void spaces is normally to comply withPt 5, Ch 11,4.5. Special consideration is to be given to smallvoid spaces.

5.1.6 Any spaces filled with foam or permanent ballastis to be specially considered with regard to the materials andtheir attachment to the structure.

5.1.7 Buoys used for the storage of oil in bulk storagetanks are to be of double hull construction. The requirementsof Pt 3, Ch 3 are to be complied with.

5.2 Environmental considerations

5.2.1 The Owner or designer is to specify theenvironmental criteria for which the installation is to beapproved. The extreme environmental conditions applicable tothe location are to be defined, together with all relevantoperating environmental limits. Full particulars are to besubmitted with sufficient supporting information to demonstratethe validity of the environmental parameters, see Ch 3,4.

5.2.2 A full list of operating and extreme environmentallimiting conditions is to be submitted. This is to include thefollowing cases, as applicable, and any other conditionsrelevant to the system under consideration:• Extreme survival storm condition.• Worst environmental conditions in which a ship/unit

may remain moored to an installation.• Worst environmental conditions in which the main

operating functions may be carried out (e.g. transferof product through riser).

• Worst environmental conditions in which a ship/unitmay moor on arrival at an off-loading installation.

• Worst environmental condit ions in which adisconnectable ship/unit may remain connected.

5.2.3 Environmental factors for mooring systems are tobe in accordance with Ch 3,10.





5.3 Water depth

5.3.1 The minimum and maximum still water levels atthe operating location are to be determined, taking fullaccount of the tidal range, wind and pressure surge effects.Data is to be submitted to show the variation in water depthin way of the installation. This data is to be referenced to aconsistent datum and is to include, where relevant, the waterdepth in way of each anchor or pile, gravity base orfoundation, pipeline manifold, and in way of the radius sweptby a ship/unit attached to the mooring installation.

5.4 Design environmental conditions

5.4.1 The design is to be considered for the followingenvironmental conditions:• Extreme storm survival condition.• Maximum connected condition, see 5.2.2.• Other conditions are to be considered as defined in

Table 4.5.1.

5.4.2 Extreme storm survival condition. In general,the individual environmental factors (wind, wave and current)are to have an average recurrence period of not less than100 years. The joint probability of occurrence of extremevalues of individual environmental factors is to be taken intoaccount where sufficiently accurate data exists.

5.4.3 Maximum connected conditions . Themaximum environmental condit ions during whichdisconnectable ships/units will remain connected to the buoy.

5.4.4 Account is also to be taken in the design of themaximum conditions during which particular operationalactivities or marine operations are intended to be carried out,e.g. production through risers, transfer of product, connectionto or disconnection from single-point mooring. Appropriatelimits are to be set and defined in the Operations Manual.

5.5 Environmental loadings

5.5.1 The environmental loading on the installation andits motion responses are to be determined and the dynamiceffects are to be considered, see Ch 3,4. Account is to betaken of the following:(a) Environmental loads and motions are to be established

by model testing and suitable calculation methods.(b) Satisfactory correlation between the calculation method

and representative model test results is to be demon-strated.

(c) The possibility of resonant motion is to be fully investigated taking second order wave forces into account.

(d) In determining environmental loads, account is to betaken of the effect of marine growth. Both increase inthe dimensions of submerged members and thechange in surface characteristics are to be considered.

(e) Shallow water effects are to be considered whereappropriate.


5.6.1 The general requirements for structural designare given in Chapter 3 but the additional requirements of thisChapter are to be complied with.

5.6.2 The structure is to be designed to withstand thestatic and dynamic loads imposed on the unit in transit(loadout), site-specific installation, survival and operatingconditions. All relevant loads as defined in Chapter 3 are tobe considered.

5.6.3 Account is to be taken of slam effects whencalculating wave loads in the splash zone.

5.6.4 Local forces from mooring lines and risers are tobe included in the analyses for normal operating conditions.

5.6.5 All bearings, guide rollers, etc. forming part of aturntable or other swivel arrangement associated with risers,moorings or pipeline systems on the buoy are to comply withthe requirements given in Pt 3, Ch 2,6.

5.6.6 Permissible stresses due to the overall and localeffects are to be in accordance with Chapter 5. The minimumlocal scantlings of the unit are to comply with Chapter 6.

5.6.7 All modes of operation are to be investigated andthe relevant design load combinations defined in Ch 5,1.2 areto be complied with. The loading conditions applicable tobuoy type units are shown in Table 4.5.1.

5.6.8 Although buoy units will not be classed duringtransit (loadout) and during the installation procedure at theoperating location, the transit condition and the site-specificinstallation condition are to be investigated and submitted to LR.

5.6.9 The general requirements for investigatingaccidental loads are defined in Ch 3,4.16. In operatingconditions, coll ision loads against the buoy structure will normally only cause local damage to the structure and consequently loading conditions (c) and (d) in Table 4.5.1need not be investigated from the overall strength aspects, see also Ch 3,4.16.


(a) (b) (c) (d) (e)

Site installation ✓ ✓

(see Note 3)


(see Note 2) See SeeNote 4 Note 4

Survival ✓ ✓

Transit (loadout) ✓ ✓

(see Note 3)

NOTES:1. For definition of loading conditions (a) to (e), see Ch 3,4.3.2. For operating conditions, the load cases are to include those

defined in 5.2.2 as applicable.3. For loading conditions (a) and (b) for installation and transit

conditions, see 5.6.8.4. For loading conditions (c) and (d) as applicable to buoy units,

see 5.6.9.



5.7 Buoy structure

5.7.1 Buoys are to be designed to withstand theforces and moments resulting from the overall loadingstogether with the forces and moments due to local loadingsincluding internal and external pressures.

5.7.2 In general, internal spaces within the buoy are tobe designed for the pressure heads defined in Ch 3,4.14.The minimum head on shell boundaries is not to be less than6 metres, see also 7.5.5.

5.7.3 The minimum scantlings of shell boundariesincluding moon pools are to comply with Ch 6,3.4.

5.7.4 The general requirements for watertight and tankbulkheads are to comply with Ch 6,7. The scantlings of theboundaries of internal watertight compartments adjacent tothe sea which are required for buoyancy and stability tosupport the structure are to comply with the requirements fortank bulkheads.

5.7.5 The supports for riser systems and mooringsystems are to comply with Chapter 6.


5.8.1 The scantlings of deck support structures whichare designed as a trussed space frame structure are to bedetermined by analysis. The requirements of Section 1.7 and1.8 are to be complied with as applicable.

5.8.2 The minimum scantlings of decks are to complywith Ch 6,4.

5.8.3 The scantl ings of superstructures anddeckhouses are to comply with Ch 6,9.


5.9.1 The strength of lifeboat platforms are to bedetermined in accordance with the requirements of 1.9.

5.10 Fatigue

5.10.1 The structure of buoys and highly stressedstructural elements of mooring line attachments, chainstoppers and supporting structures are to be assessed forfatigue damage due to cyclic loading.

5.10.2 The general requirements for fatigue design andthe factors of safety on fatigue life are to comply with Ch 5,5.




SECTION 6Tension-leg units

6.1 General

6.1.1 This Section outlines the structural designrequirements of tension-leg units as defined in Pt 1, Ch 2,2.Additional requirements for particular unit types related to thedesign function of the unit are given in Part 3.

6.1.2 The requirements of Section 1, for semi-submersible units, are to be complied with as applicable.

6.1.3 The term ‘tension-leg’ used in this Sectionincludes all the component parts of the pretensioned mooringsystem in one group and includes the top connections to theunit and the bottom connections to the sea bed foundation.Each unit will have a number of tension legs. Each tensionleg may be made up of individual tensioned cables ormembers which are referred to in this Section as ‘tethers’.

6.2 Air gap

6.2.1 Unless the upper hull structure is designed forwave impact a clearance ‘air gap’ of 1,5 metres between theunderside of the upper hull deck structure and the highestpredicted design wave crest is to be maintained duringoperation on station. Calculations, model test results orprototype reports are to be submitted for consideration.

6.2.2 In cases where the unit is designed without anadequate air gap in accordance with 6.2.1, the scantlings ofthe upper hull deck structure are to be designed for waveimpact forces. If the whole hull structure is waterborne thescantlings are to be specially considered but they are not tobe less than would be required for a surface-type unit.

6.3 Loading and environmental considerations

6.3.1 The Owner or designer is to specify theenvironmental criteria for which the installation is to beapproved. The extreme environmental conditions applicableto the location are to be defined, together with all relevantoperating environmental limits. Full particulars are to besubmitted with suff icient support ing information todemonstrate the validity of the environmental parameters,see Ch 3,4.

6.3.2 The environmental loading on the installation andits motion responses are to be determined and the dynamiceffects are to be considered, see Ch 3,4.

6.3.3 When determining the critical design loadings ontethers, realistic combinations of environmental loadings andunit response are to be taken into account. All loadings andunit motions are to be agreed with LR and the full range ofoperating draughts are to be considered.

6.3.4 Motions may be determined by a suitablecombination of model tests and calculation methods.

6.3.5 The possibility of resonant motions is to be fullyinvestigated taking a second order wave and wind forces intoaccount. The likelihood of the occurrence of rotational andvertical oscillations is to be particularly considered.





6.3.6 In determining environmental loads, account is tobe taken of the effect of marine growth. Both increase in thedimensions of submerged members and the change insurface characteristics are to be considered.

6.3.7 When carrying out model testing, the testprogramme and the model test tank facilities are to be to thesatisfaction of LR and account is to be taken of the following:• The relative directions of wind, wave and current are to

be varied as required to ensure that the most criticalloadings and motions are determined.

• The tests are to be of sufficient duration to establish lowfrequency motion behaviour.


6.4.1 The general requirements for structural designare given in Chapter 3, and the requirements of Section 1 forsemi-submersible units are to be complied with, exceptwhere modified by this Section.

6.4.2 The following effects are to be considered wheninvestigating loading conditions that could lead to fatigue ofthe structure, tension legs or foundations:• Variations of combined wave and current to ensure that

all damaging stress levels are likely to be included in theanalysis.

• Member loading including the effects of varying buoy-ancy and/or flooding due to wave motions in the splashzone.

• Cyclic loading due to wind and the operation ofmachinery, where significant.

• Still water loading condition at mean draft.

6.4.3 All modes of operation are to be investigated andthe relevant design load combinations defined in Ch 5,1.2 areto be complied with. The loading conditions applicable to atension-leg unit are shown in Table 4.6.1.

6.4.4 The permissible stresses are to be in accordancewith Chapter 5 and the minimum local scantlings of the unitare to comply with Chapter 6.

6.4.5 Although a tension-leg unit will not be classed inthe transit condition and during site installation, the transitcondition and the site specific installation condition are to beinvestigated and submitted to LR.

6.4.6 The general requirements for investigatingaccidental loads are defined in Ch 3,4.16. In operatingconditions, collision loads against the hull structure willnormally only cause local damage to the structure andconsequently loading conditions (c) and (d) in Table 4.6.1need not be investigated from the overall strength aspects,see also Ch 3,4.16.


6.5 Tension-leg materials

6.5.1 The materials used for tension-legs are to bespecially considered and the materials used are to complywith the following requirements:(a) The corrosion protection is to be adequate for the life of

the installation.(b) The materials and their attachments to the structure are

to be suitable for their purpose and have adequatefatigue life.

(c) The strength, elasticity and flexibility of the tension-legsare to be sufficient to accommodate the designextreme motions of the installation and the dynamicpatterns which may be encountered over the wholerange of environmental criteria.

(d) The material grades used for tension-legs, fittings andattachments to the structure are to have adequateresistance to brittle fracture.

6.5.2 Adequate test data is to be submitted to LR todemonstrate that the materials and fittings used for tension-legs will have adequate service life. The design philosophyrelating to the life and replacement of tension-legs and theirfittings is to be clearly stated at the design stage.

6.6 Tension-leg design

6.6.1 When reference to tension-legs is made in thissub-Section, the Rules apply to tethers constructed of wireropes, tubes or any other equivalent section.

6.6.2 The leg system is to be fail-safe in that failure of a single tension-leg member at any time during the life of the installation will not induce stress levels in any othertension-leg member that will produce fatigue failure in thatmember or its associated fittings in less than one yearassuming average winter conditions or induce increasedaccumulated fatigue damage to reduce significantly theoverall fatigue life of the system.


(a) (b) (c) (d) (e)


(see Note 3)


(see Note 2) See SeeNote 4 Note 4

Survival ✓ ✓

Transit (loadout) ✓ ✓

(see Note 3)

NOTES1. For definition of loading conditions (a) to (e), see Ch 3,4.3.2. For operating conditions, the load cases are to include those

defined in 5.2.2 as applicable.3. For loading conditions (a) and (b) for site installation and transit

conditions, see 6.4.5.4. For loading conditions (c) and (d) as applicable to tension-leg

units, see 6.4.6.


6.6.3 In general, each tension-leg is to be assembledfrom tether members of only one type and size. The fitting ofmaterials, having different elastic constants, in parallel loadcarrying components of a tension-leg will not normally beaccepted.

6.6.4 All leg tether members forming any one tension-leg are to be set to an approximate common tension.Suitable means of adjusting the tensions of the individualcomponents of each leg are to be provided at the upper endof each individual tether.

6.6.5 Means are to be provided for monitoring thetensions in tension-leg components.

6.6.6 The design is to be such that with suitableballasting the minimum tension in any tether can be adjustedto be not less than five per cent of the normal pretension. A lesser tension is not normally permitted. Where the Ownerrequests a relaxation of this requirement appropriate dynamicanalysis is to be carried out to evaluate the tether design.

6.6.7 No end terminal or other fitting associated withthe tension-legs is to be dependent upon the maintenance ofthe leg tension to retain it in place.

6.6.8 In general, all leg connections including pins,bearings, locks, etc., are to be arranged by positivelyactivated wedging systems, or otherwise, so that there areno slack fits or non-essential clearances. Screwed andbolted fittings are to be provided with positive lockingarrangements.

6.6.9 Arrangements are to be made to prevent kinkingand sharp bends in tether members in way of the end fittings.In determining the maximum angles that may be assumed bythe leg members in way of end fittings account is to be takenof the maximum extent of snaking or other dynamicdistort ions of the legs that could occur in extremeenvironmental conditions.

6.6.10 The effects of scuffing and wear of tethers withinrope guides, bell mouths and other systems due to themovement of leg components caused by motions of the unitare to be taken into account in the design.

6.6.11 The extreme maximum and minimum tetherloads, which determine the tether design requirements, are tobe calculated.

6.6.12 Tether misalignment where tethers are notcompletely vertical and parallel are to be taken into account.

6.6.13 The maximum tether load is to be determined atthe top of the tether with the unit at its minimum designstorm weight and with the highest water level. The calculationis to include the effects of the worst combination of thehorizontal centre of gravity position, wave loading, wind andcurrent loading, tether misalignment and dynamic responseand platform motions.

6.6.14 The minimum tether load is to be determined at the bottom of the tether with the unit at its maximumdesign storm weight and at the lowest water level. Thecalculation is to include the effects of the worst combinationof the horizontal centre of gravity position, wave loading, windand current loadings, tether misalignment and dynamicresponse, platform motions, catenary effects of tethers andthe design margin.




6.6.15 When calculating the minimum tether load a designmargin of five per cent of the nominal pretension is to be applied.

6.6.16 The unit with the most unfavourable combinationof weight, centre of gravity and buoyancy is to be capable ofsurviving the worst design damage condit ion. Therequirements for watertight and weathertight integrity are tocomply with Chapter 7.

6.6.17 After flooding of any compartment as required to satisfy 6.6.16, the requirements of 6.6.15 are to becomplied with.

6.6.18 Within a period of 12 hours from commencementof any accidental flooding, the loading of the unit is to beadjusted, as necessary, so that the tensions of all tethers attheir lower ends remain positive under the most unfavourableenvironmental conditions which could be expected to occur atthe location within a return period of not less than one year.The loading adjustment may be means of deballasting, and/orremoval, dumping or horizontal movement of deck loads.

6.7 Tension-leg permissible stresses

6.7.1 The maximum permissible stresses in steeltethers under the worst combination of steady and dynamicloadings are to comply with the following factors of safetybased on the tensile yield stress of the material:(a) With all tethers in a tension-leg group in operation:

• 1,67 for tension.• 1,43 for combined ‘comparative’ stress.

(b) With one tether in a tension-leg group non-operational:• 1,25 for tension.• 1,11 for ‘comparative’ stress.

6.8 Tension-leg fatigue design

6.8.1 In the design of tether components,consideration is to be given to the fatigue damage that willresult from cyclic stresses. A detailed fatigue analysis is to beperformed. The combined axial and bending stress is to bedetermined by dynamic analysis and is to consider variationsaround the tether circumference.

6.8.2 Where the tethers are bui lt up of variouscomponents such as screwed sections or chain link theeffect of many tether components being connected in seriesis to be adequately accounted for in the design fatigue life.

6.8.3 The fatigue l i fe of tethers and their endconnections and the factors of safety on the calculated designfatigue life are to comply with the requirements of Ch 5,5.

6.9 Tension-leg foundation design

6.9.1 The sea bed and soil conditions at the proposedlocations of the tension leg foundations is to be determined toprovide data for the design of the foundation system.Requirements for site investigation are contained in Chapter 12.





6.10 Piled foundations

6.10.1 This sub-Section applies to piles which are eitherdriven or drilled and grouted into the sea bed to provideresistance to axial, lateral and torsional loading. Piles installedby vibrating hammers are not recommended.

6.10.2 Piles are characterized by being relatively longand slender and having a length to diameter or width ratiogenerally greater than 10.

6.10.3 The pile design is to be approved by LR.

6.10.4 The pile is to be designed to provide sufficientultimate capacity to resist the maximum applied axial, lateraland torsional loads with appropriate factors of safety basedon a working stress design approach.

6.10.5 Table 4.6.2 defines the design case and factorsof safety to be used for piles for a tension-leg foundationsystem. Table 4.6.2 does not apply to axial capacity of pilesinstalled by vibrating hammers.

Table 4.6.2 Minimum factors of safety for piles for atension-leg foundation system

6.10.6 The factors of safety given in Table 4.6.2 areapplicable to pile groups for tension-leg foundation systems.Individual piles within a group are to achieve a minimumfactor of safety of 1,5.

6.10.7 The possible variation in inclination of the appliedloading to the pile is to be taken into account.

6.10.8 Consideration is to be given to the effects ofcyclic loading on pile capacity.

6.10.9 Consideration is to be given to long termchanges to soil stresses around the pile and upward creep.

6.10.10 Consideration is to be given to performingspecial tests, such as centrifuge model tests, to provide abetter understanding of pile behaviour.

6.10.11 The pi le response under axial, lateral andtorsional loading is to be determined to ensure thatdeflections and rotations remain within tolerable limits.

6.10.12 Consideration is to be given to the possibleformation of a posthole at the pile head and its effect on axial capacity.

6.10.13 Consideration is to be given to the possiblescouring of sea bed soils around the suction pile and itseffect on capacity.

6.10.14 No account shall be taken of soil suction at thepile tip or the effect of rate of loading.

6.10.15 Analysis of the pile/soil interaction response is totake into account the non-linear stress/strain behaviour of thefoundation soils and the stress history and cyclic loadingeffects on soil resistance. Allowance is to be made for theresponse of different soil types.

6.10.16 An acceptable basis for pi le design andinstallation is contained in Pt 3, Ch 12.

6.10.17 The pile is to have sufficient strength to accountfor axial and bending stresses due to extreme, operating andinstallation loading conditions in accordance with Pt 3, Ch 12.

6.10.18 Detai ls of the proposed method of pi leinstallation are to be submitted. Consideration is to be givento the tolerances associated with pile verticality.

6.10.18 Consideration is to be given to the provision of amonitoring system for the measurement of long term verticalmovements of the piles relative to the surrounding soil.

6.11 Suction piled foundations

6.11.1 This sub-Section applies to piles which areinstalled by suction to achieve the required penetration intothe sea bed to provide resistance to axial, lateral andtorsional loading. Suction is applied by creating a reducedwater pressure within the pile compared to the externalambient water pressure. Suction piles can be retrieved fromthe sea bed by reversing the suction process.

6.11.2 Suction piles are characterized by having a largediameter and a length to diameter ratio generally less thanthree and are essentially caisson type foundations.

6.11.3 The suction pile design is to be approved by LR.

6.11.4 The suction pile is to be designed to providesufficient ultimate capacity to resist the maximum appliedaxial, lateral and torsional loads with appropriate factors ofsafety based on a working stress design approach.

6.11.5 Table 4.6.3 defines the design case and factorsof safety to be used for suction piles for a tension-legfoundation system.

Table 4.6.3 Minimum factors of safety for suctionpiles for a tension-leg foundation system

6.11.6 Appropriate failure modes for the soil are to beconsidered when evaluating the ultimate capacity of suctionpiles. The installation tolerances are to be considered whenassessing failure modes for the soil.

6.11.7 The possible variation in inclination of the appliedloading to the suction pile is to be taken into account.

6.11.8 Consideration is to be given to the effects ofcyclic loading on suction pile capacity.

Factor of safetyDesign case

Axial loading Lateral loading

Operating 2,7 2,0

Extreme storm 2,0 1,5

Factor of safetyDesign case

Axial loading Lateral loading

Operating 2,7 2,0

Extreme storm 2,0 1,5


6.11.9 Consideration is to be given to long termchanges to soil stresses around the suction pile and upward creep.

6.11.10 Consideration is to be given to performingspecial tests, such as centrifuge model tests, to provide abetter understanding of suction pile behaviour.

6.11.11 The suction pile response under axial, lateral andtorsional loading is to be determined to ensure thatdeflections and rotations remain within tolerable limits.

6.11.12 Consideration is to be given to the possibleformation of a posthole at the pile head and its effect on axial capacity.

6.11.13 Consideration is to be given to the possiblescouring of sea bed soils around the suction pile and itseffect on capacity.

6.11.14 No account shall be taken of soil suction at thepile tip or the effect of rate of loading unless the suction pile isprovided with a cap and suction can be justified based onrate of loading and soil permeability.

6.11.15 Analysis of the suction pile/soil interactionresponse is to take into account the non-linear stress/strainbehaviour of the foundation soils and the stress history andcyclic loading effects on soil resistance. Allowance is to bemade for the response of different soil types.

6.11.16 An acceptable basis for suction pile design andinstallation is contained in Pt 3, Ch 12.

6.11.17 The suction pile is to have sufficient strength toaccount for the stresses due to extreme, operating andinstallation loading conditions in accordance with Pt 3, Ch 12. Where necessary, a detailed finite element stressanalysis is to be carried out.

6.11.18 Details of the proposed method of suction pileinstallation are to be submitted. Consideration is to be givento the tolerances associated with suction pile verticality andalso to the internal soil heave.

6.11.19 Consideration is to be given to the provision of amonitoring system for the measurement of long term verticalmovements of the suction piles relative to the surroundingsoil.

6.12 Gravity foundations

6.12.1 This sub-Section applies to gravity foundationswhich rely on their mass to provide resistance to vertical,lateral and torsional loading. Gravity foundations may beprovided with skirts which penetrate the sea bed to provideincreased lateral resistance.

6.12.2 The gravity foundation design is to be approvedby LR.

6.12.3 The gravity foundation is to be designed toprovide sufficient ultimate capacity to resist the maximumapplied vertical, lateral and torsional loads with appropriateload and material coefficients based on a load and resistancefactor design approach.

6.12.4 The material coefficient for soil is to be taken as1,25.




6.12.5 Appropriate load coefficients are to be speciallyconsidered for particular applications for tension-legfoundation systems.

6.12.6 Appropriate failure modes for the soil are to beconsidered when evaluating the ultimate capacity of gravityfoundations. The installation tolerances are to be consideredwhen assessing failure modes for the soil.

6.12.7 The possible variation in inclination of the appliedloading to the gravity foundation is to be taken into account.

6.12.8 Consideration is to be given to the effects ofcyclic loading on gravity foundation capacity.

6.12.9 Consideration is to be given to performingspecial tests, such as centrifuge model tests, to provide abetter understanding of gravity foundation behaviour.

6.12.10 The gravity foundation response under vertical,lateral and torsional loading is to be determined to ensurethat deflections and rotations remain within tolerable limits.

6.12.11 Consideration is to be given to the possiblescouring of sea bed soils around the gravity foundation andits effect on capacity.

6.12.12 No account shall be taken of soil suction or theeffect of rate of loading.

6.12.13 Analysis of the gravity foundation/soil interactionresponse is to take into account the nonlinear stress/strainbehaviour of the foundation soils and the stress history andcyclic loading effects on soil resistance. Allowance is to bemade for the response of different soil types.

6.12.14 An acceptable basis for gravity foundationdesign and installation is contained in Pt 3, Ch 12.

6.12.15 The gravity foundation is to have sufficientstrength to account for the stresses due to extreme,operating and installation loading conditions in accordancewith Chapter 12. Where necessary, a detailed finite elementstress analysis is to be carried out.

6.12.16 Details of the proposed method of gravityfoundation installation are to be submitted. Consideration isto be given to the tolerances associated with gravityfoundation inclination and orientation and skirt penetration, ifapplicable.

6.13 Mechanical components

6.13.1 Essential mechanical components are to bedesigned such that the components are capable of beingcondition monitored, repaired and/or replaced. Prototypetesting may be required for specialized components or noveldesign arrangements.

6.14 Monitoring in service

6.14.1 The tether system is to be suitably instrumentedand monitored in service to ensure that the system isperforming within design limitations.

6.14.2 Provision is to be made to monitor tether toptensions. In addition, it is recommended that the platformmean offset position and the upper and/or lower flexible jointangles of tethers are monitored.





6.15 Tether replacement

6.15.1 Tethers are to be inspected at Periodical Surveysand the Owner/designer is to prepare a planned procedurefor inspection, retrieval and replacement of tethers in theevent of damage or as part of a planned schedule.

6.15.2 The replacement procedures involved is to beclearly documented with regard to the retrieval method,equipment required and unit operations. The procedures areto be included in the unit’s Operations Manual.

6.15.3 It is recommended that an adequate number ofspare parts of tethers and mechanical fittings are supplied tothe unit and made available during its service life.

SECTION 7Deep draught caisson units

7.1 General

7.1.1 This Section outlines the structural designrequirements of deep draught caisson units and similarfloating installations as defined in Pt 1, Ch 2,2 but excludingother unit types defined in this Chapter.

7.1.2 Additional requirements for particular unit typesrelated to the design function of the unit are also given in Part 3.

7.1.3 The hull of caisson units are to be divided intowatertight compartments and have adequate buoyancy andfloating stability in all conditions defined in 7.5.2.

7.1.4 Watertight compartments which are to betemporarily flooded during site installation or in upendingconditions are to have tank bulkhead scantlings as requiredby Ch 6,7.

7.1.5 Venting arrangements are to be fitted to allfloodable spaces to ensure that air is not trapped in anyoperating mode or temporary condition.

7.1.6 Any spaces filled with permanent ballast are tobe specially considered with regard to the material and itsattachment to the structure.

7.1.7 Production and oil storage units are to complywith the requirements of Pt 3, Ch 3. Caissons designed forthe storage of oil in bulk storage tanks are to be of doublehull construction.

7.2 Air gap

7.2.1 In all floating modes of operation the unit is to bedesigned to have a clearance air gap between the undersideof the top side deck structure and the highest predicteddesign wave crest. Model test results are to be submitted forconsideration.

7.3 Environmental loadings

7.3.1 The Owner or designer is to specify theenvironmental criteria for which the installation is to beapproved. The extreme environmental conditions applicableto the location are to be defined, together with all relevantoperating environmental limits. Full particulars are to besubmitted with suff icient support ing information todemonstrate the validity of the environmental parameters,see Ch 3,4.

7.3.2 Although a deep draught caisson unit will not beclassed during transit and during the installation procedure atthe operating location, the specif ied l imit ing designenvironmental criteria for transit/loadout, upending, andmating conditions for which LR structural approval is requiredis to be clearly defined and submitted.

7.3.3 Environmental loads and motions are to beestablished for each mode of operation, including theupending condition, by suitable analysis. Model tests willnormally be required.


7.3.4 In determining environmental loads account is tobe taken of the effect of marine growth, see Ch 3,4.13.

7.4 Model testing

7.4.1 The test programme and the model test facilitiesare to be to LR’s satisfaction, see also Ch 3,4.

7.4.2 The relative directions of wind, wave and currentare to be varied as required to ensure that the most criticalloadings and motions are determined. The tests are to be ofsufficient duration to establish low frequency motionbehaviour.

7.4.3 Model tests are to clearly demonstrate that the airgap as required by 7.2.1 is maintained in all operating modes.


7.5.1 The general requirements for structural designare given in Chapter 3, but the additional requirements of thisChapter are to be complied with.

7.5.2 The structure is to be designed to withstand thestatic and dynamic loads imposed on the unit and thestructural analysis and determination of primary scantlingsare to be on the basis of the distribution of loadings expectedin all modes of operation and temporary conditions includingloadout, transportation, upending, lifting and mating asapplicable.

7.5.3 All relevant loads as defined in Chapter 3 are tobe considered and special attention is to be made indetermining vortex-induced action effects due to wind andsea currents. The arrangement and scantlings of helical plateattachments on the hull, where fitted to keep vortex inducedresponses at acceptable levels, are to be special lyconsidered. The shell plating in way of attachments is to beincreased.

7.5.4 Local forces from mooring lines and risers are tobe included in the analyses for normal operating conditions.

7.5.5 Where units have combined crude oil bulkstorage and ballast tanks which are intended to remain full inoperating conditions consideration is to be given to taking thedesign hydrostatic loading as the difference between externaland internal pressures subject to adequate safe guardsagainst accidental loading and agreed survey requirements.The corrosion wastage allowance in such tanks is to bespecially considered, see 7.10.

7.5.6 Permissible stresses due to the overall and localeffects are to be in accordance with Chapter 5. The minimumlocal scantlings of the unit are to comply with Chapter 6.

7.5.7 The relevant design load combinations defined inCh 5,1.2 are to be complied with. The loading conditionsapplicable to a caisson unit are shown in Table 4.7.1.





7.5.8 The overall strength of the unit is to be analyzedby a three-dimensional finite element method in accordancewith Ch 3,3.

7.5.9 Where the hull form incorporates a space frameor truss system of braces, the requirements of 1.7 and 1.8are to be complied with.

7.6 Caisson structure

7.6.1 Caissons are to be designed to withstand theforces and moments resulting from the overall loadingstogether with the forces and moments due to local loadingsincluding internal and external pressures.

7.6.2 In general, internal spaces within the caisson areto be designed for the pressure heads defined in Ch 3,4.14.The minimum head on shell boundaries is not to be less than6 m, see also 7.5.5.

7.6.3 The minimum scantlings of shell boundariesincluding moon pools are to comply with Ch 6,3.4.

7.6.4 The general requirements for watertight and tankbulkheads are to comply with Ch 6,7. The scantlings of theboundaries of internal watertight compartments adjacent tothe sea which are required for buoyancy and stability tosupport the structure are to comply with the requirements fortank bulkheads, see also 7.10.

7.6.5 Internal caisson structure supporting mainbracings is in general not to be of a lesser strength than thebracing itself.

7.6.6 The supports for riser systems and mooringsystems are to comply with Chapter 6.

Applicable loading condition Mode

(a) (b) (c) (d) (e)


upending/mating(see Note 2)


See SeeNote 3 Note 3

Survival ✓ ✓

Transit (Loadout) ✓ ✓

(see Note 2)

NOTES1. For definition of loading conditions (a) to (e), see Ch 3,4.3.2. For loading condit ions (a) and (b) for site instal lat ion

(upending/mating) and transit (loadout) conditions, see 7.3.2.3. For loading conditions (c) and (d) as applicable to caissons, see

the general requirements stated in 1.3.5 to 1.3.8 as applicable.






7.7.1 The scantlings of deck support structures whichare designed as a trussed space frame structure are to bedetermined by analysis. The requirements of 7.5.9 are to becomplied with.

7.7.2 The minimum scantlings of decks are to complywith Ch 6,4.

7.7.3 The scantl ings of superstructures anddeckhouses are to comply with Ch 6,9.


7.8.1 The strength of lifeboat platforms are to bedetermined in accordance with the requirements of 1.9.

7.9 Fatigue

7.9.1 The structure of deep draught caissons andhighly stressed structural elements of mooring l ineattachments, chain stoppers and supporting structures are tobe assessed for fatigue damage due to cyclic loading.

7.9.2 The general requirements for fatigue design andthe factors of safety on fatigue life are to comply with Ch 5,5.

7.10 Corrosion protection

7.10.1 The general requirements for corrosionprotection are to comply with Part 8.

7.10.2 In tanks referred to in 7.5.5 where due to designoperating procedures or in areas where it is not consideredpracticable to inspect internal spaces or replace corrosionprotection systems the structure is to be designed withadequate corrosion margins and protection for the service lifeof the caisson. The corrosion wastage allowance andprotection of all structural components are to be to thesatisfaction of LR and agreed at the design stage.

7.10.3 Where practicable, suitable inspection couponsor other inspection aids are to be incorporated into thestructure so that the degree of corrosion in inaccessiblespaces can be monitored during Periodical Surveys requiredby Part 1.





SECTION 1General requirements

1.1 General

1.1.1 This Section defines the overal l strengthrequirements of the unit and the permissible stresses in alloperating modes.

1.1.2 The design loads are to be in accordance withCh 3,4 and the design conditions are to be based on themost unfavourable combinations of gravity loads, functionalloads, environmental loads and accidental loads.

1.1.3 Specific requirements for structural unit types arealso defined in Chapter 4.

1.1.4 The local strength of the unit is to comply withthe requirements of Chapter 6.

1.1.5 The l imit ing design environmental andoperational conditions for each mode of operation is to bedefined by the Owner/designer and included in theOperations Manual, see Pt 3, Ch 1,3.

1.2 Structural analysis

1.2.1 A structural analysis of the primary structure of theunit is to be carried out in accordance with the requirements ofChapter 3 and the resultant stresses determined.

1.2.2 The loading conditions are to represent allmodes of operation and the critical design cases obtained.

1.2.3 The structure is to be analysed for the followingcombined load cases and the maximum design stressesobtained:(a) Maximum gravity and functional loads.(b) Design environmental loads and associated gravity and

functional loads.(c) Accidental loads and associated gravity and functional

loads.(d) Design environmental loads and associated gravity and

functional loads after credible failures or accidents.(e) Maximum gravity and functional loads in a heeled

condition after accidental flooding.

1.2.4 For the load cases applicable to all unit types,see also Chapter 4.

1.2.5 The permissible stress levels relevant to thecombined load cases defined in 1.2.3 are to be inaccordance with Section 2.

1.2.6 Special consideration is to be given to structuressubjected to large deformations.

Section

1 General requirements

2 Permissible stresses

3 Buckling strength of plates and stiffeners

4 Buckling strength of primary members

5 Fatigue design

Primary Hull Strength

1.3 Primary structure

1.3.1 Local stresses, including those due tocircumferential loading on tubular members, are to be addedto the primary stresses to determine total stress levels.

1.3.2 The scantlings are to be determined on the basisof criteria which combine, in a rational manner, the individualstress components acting on the various structural elementsof the unit. The stresses are to be determined usingminimum scantlings, i.e. no corrosion allowance included,see also Pt 3, Ch 1,5.

1.3.3 The critical buckling stress of structural elementsis to be considered in relation to the computed stresses, see Sections 3 and 4.

1.3.4 Fatigue damage due to cyclic loading is to beconsidered in the design of the unit in accordance withSection 5.

1.3.5 When computing bending stresses, the effectiveflange areas are to be determined in accordance with‘effective width’, concepts derived from accepted shear lagtheories and plate buckling considerations.

1.3.6 Where appropriate, elastic deflections are to betaken into account when determining the effects ofeccentricity of axial loading, and the resulting bendingmoments superimposed on the bending moments computedfor other types of loadings.

1.3.7 When computing shear stresses in bulkheads,plate girder webs or hull side plating, only the effective sheararea of the plate or web is to be considered. For girders, thetotal depth of the girder may be considered as the web depth.

1.3.8 Members of lattice-type structures may bedesigned in accordance with a recognized Code as definedin Part 3, Appendix A.

1.4 Connections and details

1.4.1 Special consideration is to be given to structuralcontinuity and connections of critical components of theprimary structure such as the following:• Bracing intersections and endings.• Columns to lower and upper hulls.• Jackhouses to deck.• Legs to mat or footings.• Turret areas.• Yokes and mooring arms.• Mooring line attachments.• Swivel stack supports.


SECTION 2Permissible stresses

2.1 General

2.1.1 For the combined load cases (a) to (e), asdefined in 1.2.3, the maximum permissible stresses of steelstructural members are to be based on the following factorsof safety unless otherwise specified:(a) Load case (a):

2,50 for shear (based on the tensile yield stress)1,67 for shear buckling (based on the shear buck-

ling stress)1,67 for tension and bending (based on the tensile

yield stress)1,67 for compression (based on the lesser of the

least buckling stress or the yield stress)1,43 for combined ‘comparative’ stress (based on

the tensile yield stress).(b) Load case (b):

1,89 for shear (based on the tensile yield stress)1,25 for shear buckling (based on the shear

buckling stress)1,25 for tension and bending (based on the tensile


least buckling stress or the yield stress)1,11 for combined ‘comparative’ stress (based on

the tensile yield stress).(c) Load cases (c), (d) and (e):

1,72 for shear (based on the yield stress)1,0 for shear buckling (based on the shear buck-

ling stress)1,0 for tension and bending (based on the tensile


least buckling stress or the yield stress).

2.1.3 For plated structures, the combined‘comparative’ stress is to be determined where necessaryfrom the formula:

where σx and σy are the combined axial and bendingstresses in the X and Y directions respectively; τ is thecombined shear stress due to torsion and/or bending in theX-Y plane.

2.1.4 When finite element methods are used to verifyscantlings, special consideration will be given to areas of thestructure where localized peak stresses occur.

2.1.5 Plastic design methods may be used for verifyingthe local structure in load cases (c) to (e), as defined in 1.2.3,see also Ch 3,2.

2.1.6 The buckling strengths of plates and stiffenersare to comply with Section 3.

2.1.7 The buckling strength for individual primarymembers subjected to axial compression and combined axialcompression and bending is to be in accordance withSection 4.

2.1.8 Permissible stress levels for latt ice-typestructures are to be determined as required by 1.3.8.

2.1.9 Permissible stresses in materials other than steelare to be specially considered.

σcc = σx 2 + σy

2 – σx σy + 3τ2


Primary Hull Strength



1.4.2 Critical joints depending upon the transmissionof tensile stresses through the thickness of the plating of oneof the members which may result in lamellar tearing are to beavoided wherever possible. Where unavoidable, platematerial with suitable through-thickness properties asrequired by Pt 2, Ch 3,8 is to be used.

1.4.3 Welding and structural details are to be inaccordance with Chapter 7.

1.5 Stress concentration

1.5.1 The effect of notches, stress raisers and localstress concentrations is to be taken into account in thedesign of load-carrying elements.


SECTION 3Buckling strength of plates and stiffeners

3.1 Application

3.1.1 The requirements of this Section apply to platepanels, and attached stiffeners subject to overall hullstructure compression and shear stresses. The maximumdesign values computed are to be determined in accordancewith 1.2.

3.1.2 For states of stress which cannot be defined byone single reference stress, the buckling characteristics areto be based on recognized interaction formulae.

3.2 Symbols

3.2.1 The symbols used in this Section are defined asfollows:

s = spacing of secondary stiffeners, in mm. In thecase of symmetrical corrugations, s is to betaken as b or c in Fig. 3.3.1 in Chapter 3,whichever is the greater

tp = thickness of plating, in mmE = modulus of elasticity, in N/mm2 (kgf/mm2)

= 206 000 N/mm2 (21 000 kgf/mm2) for steelS = spacing of primary members, in metres

σo = specified minimum yield stress, in N/mm2

(kgf/mm2)σA = computed design compressive stress, in

N/mm2 (kgf/mm2)σCRB = critical buckling stress in compression, in

N/mm2 (kgf/mm2), corrected for yieldingeffects

σE = elastic critical buckling stress in compression,in N/mm2 (kgf/mm2)

τA = computed design shear stress, in N/mm2

(kgf/mm2)τCRB = critical buckling stress in shear, in N/mm2

(kgf/mm2), corrected for yielding effectsτE = elastic critical buckling stress in shear, in

N/mm2 (kgf/mm2)

τo =

3.3 Elastic critical buckling stress

3.3.1 The critical buckling stress of plating is to bedetermined from Table 5.3.1.

3.3.2 The critical buckling stress of stiffeners is to bedetermined from Table 5.3.2.

3.4 Scantling criteria

3.4.1 The critical buckling stress in compression, σE orσCRB as appropriate, of plate panels and stiffeners as derivedfrom Tables 5.3.1 and 5.3.2 respectively is to satisfy thefollowing:

σE or σCRB ≥ FSC σA

whereFSC = factor of safety for compression in

accordance with 2.1.1 for the appropriateload case

σo

3



Primary Hull Strength Part 4, Chapter 5Section 3

3.4.2 The critical buckling stress in shear, τE or τCRB asappropriate, of plate panels as derived from Table 5.3.1(c), isto satisfy the following:

τE or τCRB ≥ FSS τA

whereFSS = factor of safety for shear buckl ing in

accordance with 2.1.1 for the appropriateload case.





Mode Elastic critical buckling stress, N/mm2 (kgf/mm2)

(a) Compression of plating with stiffeners parallel to compressive stress, see Note

(b) Compression of plating with stiffeners perpendicular to compressive stress, see Note

where c = 1,3 when plating stiffened by floors or deep girders

= 1,21 when stiffeners are built-up profiles or rolled angles

= 1,10 when stiffeners are bulb plates

= 1,05 when stiffeners are flat bars

(c) Shear, see Note

NOTEWhere the elastic critical buckling stress, as evaluated from (a), (b) or (c), exceeds 50 per cent of specified minimum yield stress of the material,the corrected critical buckling stresses in compression (σCRB) and shear (τCRB) are given by:

τ CRB = τo 1 – τo4τ E

N/mm2 kgf/mm 2

σ CRB = σo 1 – σo4σ E

N/mm2 kgf/mm 2

τ E = 3,6 1,335 + ( s1000S

) 2 E ( tp

s )2

σ E = 0,9c [ 1 + ( s1000S

) 2] 2 E ( tp

s )2

σ E = 3,6E ( tps )

2

Table 5.3.1 Elastic critical buckling stress of plating





Mode Elastic critical buckling stress, N/mm2 (kgf/mm2)

(a) Column buckling (perpendicular to plane of plating) without rotation of cross section, see Note 1

(b) Torsional buckling, see Note 1

(c) Web buckling, see Notes 1 and 3(flat bars are excluded)

Symbols and Parameters

dw = web depth, in mm

tw = web thickness, in mm. For webs in which the thickness varies, a mean thickness is to be used

bf = flange width, in mm

tf = flange thickness, in mm. For bulb plates, the mean thickness of the bulb may be used, see Fig. 5.3.1

At = cross-sectional area, in cm2, of stiffener, including attached plating, see Note 4

Ia = moment of inertia, in cm4, of stiffener, including attached plating, see Note 4

It = St.Venant's moment of inertia, in cm4, of stiffener (without attached plating)

= 10–4 for flat bars

= for built-up profiles, rolled angles and bulb plates

Ip = polar moment of inertia, in cm4, of profile about connection of stiffener to plating

= for flat bars

= for built-up profiles, rolled angles and bulb plates

Iw = sectorial moment of inertia, in cm6, of profile about connection of stiffener to plating

= for flat bars

= for ‘Tee’ profiles

= for ‘L’ profiles, rolled angles and bulb plates

K = 1,03C S4

E Iw 10

4

bf 3

dw 2

12 (bf + dw)2

tf bf 2

+2bfdw + 4dw 2

+ 3tw bf dw 10–6

t f bf 3

dw 2

12 10

–6

dw 3

tw 3

36 10

–6

dw 3

tw3

+ dw 2

bf tf 10–4

dw 3

tw3

10–4

13

dw tw 3 + bf tf

3 1 – 0,63 tfbf

10 –4

dw tw 3

3

σ E = 3,8E ( t wdw) 2

σ E =0,001 E Iw

Ip S 2 m2 + K

m2 + 0,385E It

Ip

σ E = 0,001E Ia

At S 2

Table 5.3.2 Elastic critical buckling stress of stiffeners (see continuation)





m is determined as follows:

C = spring stiffness exerted by supporting plate panel

=

kp = 1 – ηp, and is not to be taken less than zero. For built-up profiles, rolled angles and bulb plates, kp need not be taken less than 0,1

ηp = where σEp = elastic critical buckling stress (σE) of supporting plate derived from Table 5.3.1

All other symbols as defined in 3.2.1.

NOTES

1. Where the elastic critical buckling stress, as evaluated from modes (a), (b) or (c), exceeds 50 per cent of specified minimum yield stress of

the material, the corrected critical buckling stress in compression (σCRB) is given by:

2. Fig. 5.3.1 shows the dimensions of stiffeners.

3. For flanges on angles and T-sections of stiffeners, the following requirement is to be satisfied:

≤ 15 for angles, ≤ 30 for ‘Tee’ profiles,

where

t = flange thickness, in mm

4. The area of attached plating is to be calculated using actual spacing of secondary stiffeners.

bf

t

bf

t

σCRB = σo 1 – σo

4σE N/mm

2 kgf/mm

2

σAσEp

kpE tp 3

3s 1 +1,33kp dw tp

3

s tw 3

m K range

1 0 < K ≤ 42 4 < K ≤ 363 36 < K ≤ 1444 144 < K ≤ 4005 400 < K ≤ 9006 900 < K ≤ 1764m (m – 1)2 m2 < K ≤ m2 (m + 1)2

Table 5.3.2 Elastic critical buckling stress of stiffeners (conclusion)





twdw dw dw

tw

tp tp tp

tw

tftf

tf

bf

bf

bf

Flat bar

twdw

tpRolled angle

bf��

twA

tf

dw h

c

tpBulb plate

Built up‘Tee’ profile

Built up‘L’ profile

4407/79

bf = c + tw

A = area of bulb plate, in mm2

A – h twtf c

=

dw = h – tf

Fig. 5.3.1 Dimensions of stiffeners





SECTION 4Buckling strength of primary members

4.1 Application

4.1.1 The requirements of this Section are applicableto individual primary structural members which are subjectedto axial compression or combined axial compression andbending due to overall loading.

4.2 Symbols


σo, E as defined in 3.2.1σA = computed axial compressive stress, in

N/mm2 (kgf/mm2)σB = computed compressive stress due to

bending, in N/mm2 (kgf/mm2)FA = factor of safety for compression, in

accordance with 2.1.1FB = factor of safety for bending, in accordance

with 2.1.1FC = factor of safety for overall member buckling,

as determined from Table 5.4.2σCRB = critical overall member buckling stress, in

N/mm2 (kgf/mm2), as determined from Table 5.4.1

σC = local member critical buckling stress, inN/mm2 (kgf/mm2)

σPA = permissible axial compressive stress, inN/mm2 (kgf/mm2)

= whichever is the lesser

σPB = permissible compressive stress due tobending, in N/mm2 (kgf/mm2)

= whichever is the lesser

D = mean diameter of cylindrical shell, in mmt = thickness of cylindrical shell, in mm

4.3 Scantling criteria

4.3.1 Individual members are to be investigated foroverall critical buckling in accordance with Table 5.4.1 andalso for local buckling.

4.3.2 The local buckling of cylindrical shells eitherunstiffened or ring-stiffened, is to be investigated if theproportions of the shell conform to the following:

4.3.3 When individual primary structural members aresubjected to axial compression or combined axialcompression and bending the computed design stresses areto satisfy the following requirement:

σAσPA

+ σBσPB

≤ 1,0

Dt > E

9σo

σoFB

or σCFB

σoFA

or σCFA

or σCRBFC

Table 5.4.1 Overall member critical buckling stress

Table 5.4.2 Factors of safety for overall memberbuckling

Condition Member critical buckling stressσCRB, N/mm2 (kgf/mm2)

(a) When

(b) When

Symbols and parameters

σo, E as defined in 3.2.1l = unsupported length of member in metres

K = effective length factor to be generally taken as unity butwill be specially considered in association with endconditions

le = Kl = unsupported effective length of member in metresr = least radius of gyration of member cross section, in mm,

and may be taken as:

A = cross-sectional area of member, in cm2

I = least moment of inertia of member cross section, in cm4

λ = slenderness ratio and may be taken as:

η = 2π2Eσo

λ = 1000 ler

r = 10 IA

mm

π2E

λ2

λ ≥ η

σo – σo 2 λ2

4π2Eλ < η

Condition Factor of safety, FC

(1) For case (a) as defined in 2.1.1:

(a) When

(b) When 1,92

(2) For case (b) as defined in 2.1.1:

(a) When

(b) When 1,44

(3) For cases (c), (d) and (e) as defined in 2.1.1:

(a) When

(b) When 1,15

Symbols and parameters

FC as defined in 4.2.1λ and η as defined in Table 5.4.1

λ ≥ η

1,0 +0,15 λ

η λ < η

λ ≥ η

1,25 +0,19 λ

η λ < η

λ ≥ η

1,67 +0,25 λ

ηλ < η


SECTION 5Fatigue design

5.1 General

5.1.1 Fatigue damage due to cyclic loading is to beconsidered in the design of all unit types. The extent of thefatigue analysis will be dependent on the mode and area ofoperation.

5.1.2 Where any unit is intended to operate as an oilproduction, storage or accommodation unit at one locationfor an extended period of time, a rigorous fatigue analysis isto be performed using the long-term predict ion ofenvironment for that area of operation with the unit at theintended orientation. Due allowance is to be made of anyprevious operational history of the unit.

5.1.3 The two basic methods of fatigue analysisavailable are Deterministic Fatigue Analysis and SpectralFatigue Analysis. Both are acceptable to LR.

5.1.4 Factors which influence fatigue endurance andshould be accounted for in the design calculations include:• Loading spectrum.• Detail structural design.• Fabrication and tolerances.• Corrosion.• Dynamic amplification.

5.1.5 The following important sources of cyclic loadingshould be considered in the design:• Waves (including those which cause slamming and

variable-buoyancy effects).• Wind (especially when vortex shedding is induced, e.g.

on slender members).• Currents (where these influence the forces generated

by waves and/or induced vortex shedding).• Mechanical vibration (e.g. caused by operation of

machinery).

5.1.6 Where a fine mesh finite element analysis is carriedout to determine local geometric stress concentration factorsselection of associated S/N curves will be specially considered.Account is to be taken of fatigue stress direction relative tothe weld. In general, the element mesh size adjacent to theweld detail under consideration is to be of the order of thelocal plate thickness. Mesh arrangement and analysismethodology are to be agreed with LR.

5.2 Fatigue life assessment

5.2.1 Fatigue life assessment of all relevant structuralelements is required to demonstrate that structural connectionshave a fatigue endurance consistent with the planned life of theunit and compliance with the minimum requirements. Thefollowing structural elements are to be included:(a) Column-stabilized and tension-leg units:

• Bracing structure.• Bracing connections to lower hulls, columns and

decks.• Column connections to lower hulls.• Column connections to deck.• Mooring structure and associated hull structure

integration.• General structural discontinuities.




(b) Surface-type units:• Hull longitudinal stiffener connections to transverse

frames and bulkheads in the oil storage/ballasttank area.

• Hopper knuckle connections.• Main openings in the hull envelope.• Mooring structure and associated hull structure

integration.• General structural discontinuities in this primary

hull structure.(c) Self-elevating units:

• Lattice legs and connections to footings.• Leg support structure.• Raw water towers.

(d) Other unit types:• Special consideration will be given to the hull

structure of other unit types on the basis of thisSection.

(e) General: Hull, deck and supporting structure in way oftopside facilities, e.g:

• module support• process plant support stools• crane pedestal• flare structures• offloading station• drilling derrick and substructures

(f) General: Other structures subjected to significant cyclicloading.

5.2.2 Fatigue life is normally governed by the fatiguebehaviour of welded joints, including both main andattachment welds. Structure is to be detai led andconstructed to ensure that stress concentrations are kept toa minimum and that, where possible, components maydeform without introducing secondary effects due to localrestraints.

5.2.3 The minimum design fatigue life of a unit is to bespecified by the Owners, but is not to be less than 20 years,unless agreed otherwise with LR.

5.3 Fatigue damage calculations

5.3.1 The fatigue damage calculations are to be basedon the long term distribution of the applied stress ranges. Asufficient number of draughts and directions are to be included.

5.3.2 An appropriate wave spectrum is to be used andrepresentatives percentages of the total cumulative spectrumincluded for each direction under consideration. When usinga limited number of directions account is to be taken ofsymmetry within the structure.

5.3.3 Cumulative damage may be calculated byMiner’s summation:

wheres = number of stress range blocksni = actual number of cycles for stress range

block number ‘i’Ni = corresponding number of cycles obtained

from the relevant S-N curve for the detailunder consideration.

5.3.4 Cumulative damage for individual components isto take into account of the degree of redundancy,accessibility of the structure and also the consequence offailure.

∑i = 1

s niNi

≤ 1,0





5.3.5 Fatigue life estimation is normally to be based onthe Miner’s summation method given in 5.3.3, butconsideration will be given to the use of an appropriatefracture mechanics assessment.

5.4 Joint classifications and S-N curves

5.4.1 Acceptable joint classification and S-N curves forstructural details are contained in Appendix A.

5.4.2 Full penetration welds are normally to be usedfor all nodal joints (i.e. tubular brace to chord connections).For full penetration welded joints, fatigue cracking wouldusually be located at the weld toe. However, if partialpenetration welds have to be used where weld throat failureis a possibility, fatigue should be assessed using the ‘W’curve and a shear stress estimated at the weld root.

5.4.3 For nodal joints, the stress range to be used inthe fatigue analysis is the hot spot stress range at the weldtoe. For any particular type of loading (e.g. axial loading) thisstress range is the product of the nominal stress range in thebrace and the appropriate stress concentration factor (SCF).

5.4.4 The hot spot stress is defined as the greatestvalue around the brace/chord intersection of theextrapolation to the weld toe of the geometric stressdistr ibution near the weld toe. This hot spot stressincorporates the effects of overall joint geometry (i.e. therelative sizes of brace and chord) but omits the stressconcentrating influence of the weld itself which results in alocal stress distribution. Hence, the hot spot stress isconsiderably lower than the peak stress but provides aconsistent definition of stress range for the design S-N curve(curve ‘T’ shown in Appendix A). Stress ranges both for thebrace and chord sides are to be considered in any fatigueassessment.

5.4.5 For all other types of joint (e.g. welded stiffenersor attachments, including those at nodal joints) the jointclassifications and corresponding S-N curves are to take intoaccount the local stress concentrations created by the jointsthemselves and by the weld profile. The relevant stress rangeis then the nominal stress range which is to include any localbending adjacent to the weld under consideration. However,if the joint is also situated in a region of stress concentrationresulting from the gross shape of the structure this is to betaken into account.

5.4.6 In load-carrying partial penetration or fillet-welded joints, where cracking could occur in the weld throat,the relevant stress range is the maximum range of shearstress in the weld metal. For details which are particularlyfatigue sensitive, where failure could occur through the weld,full penetration welding is normally to be used.

5.4.7 Geometric stress concentrat ions may bedetermined from experimental tests, appropriate references,semi-empirical or parametric formulae or analytical methods(e.g. finite elements analysis).

5.4.8 Normal fabrication tolerances according to goodworkmanship standards as given by the Rules are consideredto be implicitly accounted for in the S-N curves.

5.5 Cast or forged steel

5.5.1 Fatigue life calculations for cast or forged steelstructural components are to include details of the fatigueendurance curve for the material taking account of theparticular environment, mean stress and the existence ofcasting defects, and the derivation of any stressconcentration factors.

5.6 Factors of safety on fatigue life

5.6.1 The minimum factors of safety on the calculatedfatigue life of structural components are to be in accordancewith Table 5.5.1. For mooring systems, see 5.6.2.

Table 5.5.1 Fatigue life factors of safety for structuralcomponents

5.6.2 The minimum factors of safety on the calculatedfatigue life of anchor lines and tether components of mooringsystems are to be in accordance with Table 5.5.2.

Table 5.5.2 Fatigue life factors of safety for anchorline and tether components

Fatigue life factor

Inspectable/repairable Consequence of failure

Non-substantial SubstantialSee Note 1

Yes, dry 1 2See Note 2

Yes, wet 2 4See Note 3

No 5 10

NOTES1. Substantial consequences of failure include, inter alia, loss of

life, uncontrolled outflow of hazardous or polluting products,collision, sinking. In assessing consequences, account shouldbe taken of the potential for progressive failure.

2. Includes internal and external structural elements andconnections which can be subjected to dry inspection and repair.

3. Includes external structural elements and connections situatedbelow the minimum operating draught of the unit or structurewhich can only be inspected during in-water surveys but dryrepairs could be carried out subject to special arrangementsbeing provided.

Inspectable/replaceable Fatigue life factor

Yes, dry 3

Yes, wet 5

No 10

NOTEAnchor line or tether components include chains, steel wire ropes,and associated fittings such as shackles, connecting links, ropesockets and terminations.





SECTION 1General requirements

1.1 General

1.1.1 All parts of the structure are to be designed towithstand the most severe combination of overall and localloadings to which they may be subjected. Permissiblestresses for direct calculation methods are to comply with therequirements of Chapter 5.

1.1.2 The local effects of the loadings listed in Ch 3,4are to be considered and all parts of the structure are to beexamined individually as necessary, and the calculationssubmitted. The minimum Rule scantlings of all structures arealso to comply with the requirements of this Chapter.

1.1.3 The design heads for local strength are to be inaccordance with Section 2.

1.1.4 The scantlings of machinery seatings are to bespecially considered. On self-propelled units full details ofpower, and RPM, etc. are to be submitted.

1.1.5 The connections to anchor points as defined inPt 3, Ch 10,10 and the structure in way of fairleads,chainstoppers, winches, etc., forming part of anchoring orpositional mooring systems are to be designed for a workingload equal to the breaking strength of the mooring oranchoring lines as applicable. Permissible stresses are to bein accordance with Ch 5,2.1.1(b). Supply boat moorings andsupport structures are to be designed on a similar basis.

1.1.6 Towing brackets and supporting structure are tobe designed for a working load equal to the breaking strengthof the towline in accordance with the requirements ofChapter 9.

1.1.7 The supporting structure in way of lifeboat davitsis to be designed for the dynamic factors defined in Ch 4,1.9and the permissible stress levels are to comply with loadcase(a) in Ch 5,2.1.1.

1.1.8 The supporting structure to turret bearings onsurface-type units are to comply with Ch 4,4.

Section

1 General requirements

2 Design heads

3 Watertight shell boundaries

4 Decks

5 Helicopter landing areas

6 Decks loaded by wheeled vehicles

7 Bulkheads

8 Double bottom structure

9 Superstructures and deckhouses

10 Bulwarks and other means for the protection of crew and other personnel

Local Strength

1.1.9 The scantlings of product swivels are to bedetermined in accordance with Pt 3, Ch 2,6.6 and thesupporting structure is to be integrated into the unit’s hullstructure and the local permissible stresses are to complywith Chapter 5.

1.1.10 The supporting structures to production andprocess plant are to comply with Pt 3, Ch 8.




Local Strength Part 4, Chapter 6Section 2

SECTION 2Design heads

2.1 General

2.1.1 This Section contains the local design heads andpressures to be used in the derivation of scantlings for decks,and bulkheads. Where scantl ings in excess of Rulerequirements are fitted the procedure to be adopted todetermine the permissible head/pressure is also given.

2.2 Symbols


L and D as defined in Ch 1,5hi = appropriate design head, in metresp = design loading, in kN/m2 (tonne-f/m2)

pa = applied loading, in kN/m2 (tonne-f/m2)C = stowage rate, in m3/tonne (see 2.3)

=

E = correction factor for height of platform

= but not less than

zero nor more than 0,147T = T0 or TT as defined in Ch 1,5 as appropriate

2.3 Stowage rate and design heads

2.3.1 The following standard stowage rates are to beused:(a) 1,39 m3/tonne for weather or general loading on decks.(b) 0,975 m3/tonne for tanks with liquid of density

1,025 tonne/m3 or less on tank bulkheads and forwatertight bulkheads. For liquid of density greater than1,025 tonne/m3 the corresponding stowage rates areto be adopted.

2.3.2 The design heads and permissible deck loadingare shown in Table 6.2.1. For helicopter landing areas, seeSection 5.

0,0914 + 0,003L

D – T – 0,15,

hip





Tab

le 6

.2.1

Des

ign

head

s an

d p

erm

issi

ble

dec

k lo

adin

gs

(SI u

nits

) (se

e co

ntin

uatio

n)

Sta

ndar

dP

erm

issi

ble

Equ

ival

ent

Str

uctu

ral i

tem

and

pos

ition

Com

pone

ntst

owag

e ra

teD

esig

n lo

adin

g p

,E

quiv

alen

t des

ign

head

hi

deck

load

ing

perm

issi

ble

head

,C

, in

m3 /

tonn

ein

kN

/m2

in m

etre

sin

kN

/m2

in m

etre

s

1.A

ll un

its,

exc

ept

as in

dic

ated

bel

ow

(a)

Wea

ther

dec

ks–

––

h 1–

–

(b)

Load

ing

for

min

imum

sca

ntlin

gs

(i) E

xpos

ed d

eck

All

stru

ctur

e1,

399,

0 +

14,

41E

1,28

+ 2

,04E

9,0

1,28

(c)

Spe

cifie

d de

ck lo

adin

g

(i) E

xpos

ed d

eck

All

stru

ctur

e1,

39p

a+

14,

41E

0,14

pa

+ 2

,04E

pa

0,14

pa

but n

ot le

ss th

an (a

) abo

ve

2.S

elf-

elev

atin

g a

nd s

urfa

ce-t

ype

units

(a)

Wea

ther

dec

k–

––

h 1–

–

(b)

Load

ing

for

min

imum

sca

ntlin

gs

(i) F

orw

ard

of 0

,075

Lfro

m F

.P.

Stif

fene

rs1,

3912

,73

1,8

8,5

1,2

Prim

ary

stru

ctur

e29

,64

+ 1

4,41

E4,

2 +

2,0

4E

(ii) B

etw

een

0,12

Lan

d 0,

075L

from

F.P

.S

tiffe

ners

1,39

10,6

11,

58,

51,

2P

rimar

y st

ruct

ure

22,5

9 +

14,

41E

3,2

+ 2

,04E

(iii)

Aft

of 0

,12L

from

F.P

.A

ll st

ruct

ure

1,39

9,0

+ 1

4,41

E1,

28 +

2,0

4E9,

01,

28

(c)

Spe

cifie

d de

ck lo

adin

g

2,47

pa

+ 1

4,41

E0,

35p

a+

2,0

4E(i)

For

war

d of

0,0

75L

from

F.P

.S

tiffe

ners

1,39

or a

s (a

) whi

chev

er is

larg

erp

a0,

14p

aP

rimar

y st

ruct

ure

3,5p

a+

14,

41E

0,5p

a+

2,0

4Eor

as

(a) w

hich

ever

is la

rger

1,98

pa

+ 1

4,41

E0,

28p

a+

2,0

4ES

tiffe

ners

or a

s (a

) whi

chev

er is

larg

er(s

eeN

ote

1)(ii

) Bet

wee

n 0,

12L

and

0,07

5Lfro

m F

.P.

Prim

ary

stru

ctur

e1,

39(s

eeN

ote

1)p

a0,

14p

a2,

67p

a+

14,

41E

0,38

pa

+ 2

,04E

or a

s (a

) whi

chev

er is

larg

er

(iii)

Aft

of 0

,12L

from

F.P

.A

ll st

ruct

ure

1,39

pa

+ 1

4,41

E0,

14p

a+

2,0

4Ep

a0,

14p

aor

as

(a) w

hich

ever

is la

rger




Local StrengthTa

ble

6.2

.1D

esig

n he

ads

and

per

mis

sib

le d

eck

load

ing

s (S

I uni

ts) (

conc

lusi

on)

Sta

ndar

dP

erm

issi

ble

Equ

ival

ent

Str

uctu

ral i

tem

and

pos

ition

Com

pone

ntst

owag

e ra

teD

esig

n lo

adin

g p

,E

quiv

alen

t des

ign

head

hi

deck

load

ing

perm

issi

ble

head

,C

, in

m3 /

tonn

ein

kN

/m2

in m

etre

sin

kN

/m2

in m

etre

s

3.O

ther

dec

ks –

all

unit

typ

es

(a)

Load

ing

for

min

imum

sca

ntlin

gs

(i) W

ork

area

s A

ll st

ruct

ure

1,39

9,0

h 2 1,28

––

(ii) S

tora

ge a

reas

All

stru

ctur

e1,

3914

,13

h 3 2,0

––

9,82

hh 4

(iii)

Dec

ks fo

rmin

g cr

own

of d

eep

tank

sA

ll st

ruct

ure

CC

h–

–(s

eeN

ote

2)(s

eeN

ote

2)

(iv)A

ccom

mod

atio

n de

cks

All

stru

ctur

e1,

398,

5h 5 1,

2–

–

(b)

Spe

cifie

d de

ck lo

adin

g

(i) A

ll ar

eas

All

stru

ctur

e1,

39p

a+

14,

41E

h 2, h

3 , h

5–

–bu

t not

less

than

(a) a

bove

0,14

pa

(c)

Sup

erst

ruct

ure

deck

s–

––

h 6–

–(s

eeN

ote

3)

(i) 1

st ti

er0,

9(ii

) 2nd

tier

All

stru

ctur

e–

–0,

6–

–(ii

i) 3r

d tie

r an

d ab

ove

0,45

(see

Not

e 4)

(d)

Wal

kway

s an

d ac

cess

are

asA

ll st

ruct

ure

1,39

4,5

h 7–

–0,

64

4. W

ater

tig

ht b

ulkh

ead

sA

ll st

ruct

ure

0,97

510

,07h

4h 4

(see

Tabl

e 6.

7.1)

––

5. D

eep

tan

k b

ulkh

ead

sA

ll st

ruct

ure

Cbu

t ≤0,

975

9,82

h 4h 4

C(s

eeTa

ble

6.7.

1)–

–

NO

TES

1.Th

e eq

uiva

lent

des

ign

head

is to

be

used

in c

onju

nctio

n w

ith th

e ap

prop

riate

form

ulae

in th

e R

ules

.2.

Whe

re h

equ

als

half

the

dist

ance

to th

e to

p of

the

over

flow

abo

ve c

row

n of

tank

.3.

For

fore

cast

le d

ecks

forw

ard

of 0

,12L

from

F.P

., se

ew

eath

er d

ecks

.4.

Whe

re th

e de

ck is

exp

osed

to th

e w

eath

er a

dd 2

,04E

to th

e de

sign

hea

d.






Tab

le 6

.2.1

Des

ign

head

s an

d p

erm

issi

ble

dec

k lo

adin

gs

(met

ric

unit

s) (s

ee c

ontin

uatio

n)

Sta

ndar

dP

erm

issi

ble

Equ

ival

ent

Str

uctu

ral i

tem

and

pos

ition

Com

pone

ntst

owag

e ra

teD

esig

n lo

adin

g p

,E

quiv

alen

t des

ign

head

hi

deck

load

ing

perm

issi

ble

head

,C

, in

m3 /

tonn

ein

tonn

e-f/

m2

in m

etre

sin

tonn

e-f/

m2

in m

etre

s

1. A

ll un

its

exce

pt

as in

dic

ated

bel

ow

(a)

Wea

ther

dec

ks–

––

h 1–

–

(b)

Load

ing

for

min

imum

sca

ntlin

gs

(i) E

xpos

ed d

eck

All

stru

ctur

e1,

390,

92 +

1,4

67E

1,28

+ 2

,04E

0,92

1,28

(c)

Spe

cifie

d de

ck lo

adin

g

(i) E

xpos

ed d

eck

All

stru

ctur

e1,

39p

a+

1,4

67E

1,39

pa

+ 2

,04E

pa

1,39

pa

but n

ot le

ss th

an (a

) abo

ve

2. S

elf-

elev

atin

g a

nd s

urfa

ce-t

ype

unit

s

(a)

Wea

ther

dec

k–

––

h 1–

–

(b)

Load

ing

for

min

imum

sca

ntlin

gs

(i) F

orw

ard

of 0

,075

Lfro

m F

.P.

Stif

fene

rs1,

391,

295

1,8

0,86

51,

2P

rimar

y st

ruct

ure

3,02

+ 1

,467

E4,

2 +

2,0

4E

(ii) B

etw

een

0,12

Lan

d 0,

075L

from

F.P

.S

tiffe

ners

1,39

1,08

1,5

0,86

51,

2P

rimar

y st

ruct

ure

2,30

+ 1

,467

E3,

2 +

2,0

4E

(iii)

Aft

of 0

,12L

from

F.P

.A

ll st

ruct

ure

1,39

0,92

+ 1

,467

E1,

28 +

2,0

4E0,

921,

28

(c)

Spe

cifie

d de

ck lo

adin

g

2,5p

a+

1,4

67E

3,5p

a+

2,0

4E(i)

For

war

d of

0,0

75L

from

F.P

.S

tiffe

ners

1,39

or a

s (a

) whi

chev

er is

larg

erp

a1,

39p

aP

rimar

y st

ruct

ure

3,5p

a+

1,4

67E

4,87

pa

+ 2

,04E

or a

s (a

) whi

chev

er is

larg

er

2,0p

a+

1,4

67E

2,78

pa

+ 2

,04E

(ii) B

etw

een

0,12

Lan

d 0,

075L

from

F.P

.S

tiffe

ners

1,39

or a

s (a

) whi

chev

er is

larg

erp

a1,

39p

aP

rimar

y st

ruct

ure

2,67

pa

+ 1

,467

E3,

71p

a+

2,0

4Eor

as

(a) w

hich

ever

is la

rger

(iii)

Aft

of 0

,12L

from

F.P

.A

ll st

ruct

ure

1,39

pa

+ 1

,467

E1,

39p

a+

2,0

4Ep

a1,

39p

aor

as

(a) w

hich

ever

is la

rger





Tab

le 6

.2.1

Des

ign

head

s an

d p

erm

issi

ble

dec

k lo

adin

gs

(met

ric

unit

s) (s

ee c

oncl

usio

n)

Sta

ndar

dP

erm

issi

ble

Equ

ival

ent

Str

uctu

ral i

tem

and

pos

ition

Com

pone

ntst

owag

e ra

teD

esig

n lo

adin

g p

,E

quiv

alen

t des

ign

head

hi

deck

load

ing

perm

issi

ble

head

,C

, in

m3 /

tonn

ein

tonn

e-f/

m2

in m

etre

sin

tonn

e-f/

m2

in m

etre

s

1. O

ther

dec

ks –

all

unit

typ

es

(a)

Load

ing

for

min

imum

sca

ntlin

gs

(i) W

ork

area

sA

ll st

ruct

ure

1,39

0,92

h 2–

–1,

28

(ii) S

tora

ge a

reas

All

stru

ctur

e1,

391,

44h 3

––

2,0

hh 4

(iii)

Dec

ks fo

rmin

g cr

own

of d

eep

tank

sA

ll st

ruct

ure

Cc

h–

–(s

eeN

ote

2)(s

eeN

ote

2)

(iv) A

ccom

mod

atio

n de

cks

All

stru

ctur

e1,

390,

865

h 5–

–1,

2

(b)

Spe

cifie

d de

ck lo

adin

g

(i) A

ll ar

eas

All

stru

ctur

e1,

39p

ah 2

, h3 ,

h5

––

but n

ot le

ss th

an (a

) abo

ve1,

39p

a

(c)

Sup

erst

ruct

ure

deck

sh 6

(see

Not

e 3)

(i) 1

st ti

er0,

9(ii

) 2nd

tier

All

stru

ctur

e–

–0,

6(ii

i) 3r

d tie

r an

d ab

ove

0,45

––

(see

Not

e 4)

(d)

Wal

kway

s an

d ac

cess

are

asA

ll st

ruct

ure

1,39

0,46

h 7–

–0,

64

4. W

ater

tig

ht b

ulkh

ead

sA

ll st

ruct

ure

0,97

5h 4

h 4–

–0,

975

see

Tabl

e 6.

7.1

5. D

eep

tan

k b

ulkh

ead

sA

ll st

ruct

ure

Cbu

t ≤0,

975

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SECTION 3Watertight shell boundaries

3.1 General

3.1.1 The requirements of Chapter 7 regardingwatertight integrity are to be complied with.

3.1.2 The minimum requirements for watertight shellplating and framing of column-stabilized units, tension-legunits, self-elevating units, buoys and deep draught caissonsare given in this Section.

3.1.3 The minimum requirements for watertight shellplating and framing of surface-type units are to comply withCh 4,4.

3.1.4 The Rules are in general applicable to shellplating with stiffeners fitted parallel to the hull bendingcompressive stress. When other stiffening arrangements areproposed, the scantlings are to be specially considered andthe minimum shell thickness is to satisfy the buckling strengthrequirements given in Chapter 5, but the minimumrequirements of this Section are to be complied with.

3.1.5 The shell plating thickness is to satisfy therequirements for the overall strength of the unit in accordancewith Chapters 4 and 5.

3.1.6 The scantlings of moonpool bulkheads will bespecially considered with regard to the maximum forcesimposed on the structure and the permissible stress levelsare to comply with Chapter 5.

3.1.7 The minimum scantlings of moonpool bulkheadson buoys and deep draught caissons are to comply with 3.4and the load head ho in the Table 6.3.5 is to be measured tothe top of the moonpool bulkhead.

3.1.8 The minimum scantlings of moonpool bulkheadson column-stabilized and tension-leg units are to comply with3.2.5, but not less than 9,0 mm.

3.1.9 The scantlings of turretcircum well bulkheads onsurface-type units are to comply with Ch 4,4.

3.1.10 When column structures or superstructuresextend over the side shel l of the unit, the sideshell/sheerstrake is to be suitably increased locally at theends of the structure.

3.1.11 On units fitted with two chines each side thebilge plating should not be less than required for bottomplating. When units are fitted with hard chines the shellplating is not to be flanged, but where the chine, is formed byknuckling the shell plating, the radius of curvature, measuredon the inside of the plate, is not to be less than 10 times theplate thickness. Where a solid round chine bar is fitted, thebar diameter is to be not less than three times the thicknessof the thickest abutting plate. Where welded chines areused, the welding is to be built up as necessary to ensurethat the shell plating thickness is maintained across the weld,see also Table 6.3.3.

3.1.12 The plating of swim ends is to have a thicknessnot less than that required for bottom shell plating.

3.1.13 Where a rounded sheerstrake is adopted theradius should, in general, be not less than 15 times the platethickness.




3.1.14 Sea inlets, or other openings, are to have wellrounded corners and, so far as possible, are to be kept clearof the bilge radius. Openings on, or near to, the bilge radiusare to be elliptical. The thickness of sea inlet box plating is to be the same as the adjacent shell, but not less than 12,5 mm. The ends of stiffeners should in general bebracketed and alternative proposals may be considered.

3.1.15 In general, secondary hull framing is to becontinuous and the end connections of sti ffeners towatertight bulkheads are to provide adequate fixity and, sofar as practicable, direct continuity of strength.

3.1.16 The end connections of secondary hull framingand primary members are also to comply with Chapter 8.

3.1.17 The lateral and torsional stability of stiffenerstogether with web and flange buckling criteria are to beverified in accordance with Ch 5,3.

3.1.18 Web frames supporting secondary hull framingare in general to be spaced not more than 3,8 m apart. Forunits which are also required to operate aground, see Ch 4,2.


3.2.1 When the external watertight boundaries ofcolumns, lower hulls and footings are designed with stiffenedplating, the minimum scantlings for shell plating, hull framingand web frames, etc., are to comply with Table 6.3.1, see also 3.2.3.

3.2.2 The scantlings determined from Table 6.3.1 arethe minimum requirements for hydrostatic pressure loads onlyand the overall strength is to comply with Chapter 4.

3.2.3 Where cross ties are fitted in columns or lowerhulls, the scantlings are to comply with 3.3.5 and 3.3.6 takingthe head hc as the pressure head ho in accordance withTable 6.3.1 as appropriate. Where cross ties are fitted insidetanks, the requirements of 3.3.4 are also to be complied with.

3.2.4 When the scantlings of primary web frames orgirders are determined by a frame analysis or where theboundaries of columns, lower hulls and footings are designedas shells either unstiffened or ring stiffened, the scantlingsmay be determined on the basis of an agreed analysis, see Ch 1,2. The minimum design loads are to be inaccordance with Chapter 3 and the permissible stresses areto comply with Chapter 5. The scantlings are not to be lessthan required by 3.2.1.

3.2.5 The minimum scantl ings of the externalwatertight boundaries of the upper hull structure are tocomply with Table 6.3.2.

3.2.6 The shel l plat ing and structure are to bereinforced in way of mooring fairleads, supply boat moorings,towing brackets and other attachments, see also Section 1.

3.2.7 Columns, lower hulls, footings and other areaslikely to be damaged by anchors, chain cables and wireropes, etc., are to be protected or suitably strengthened.

3.2.8 Openings are not permitted in the shel lboundaries of columns, lower hulls and footings except whenthey are closed with watertight covers fitted with closelyspaced bolts, see Chapter 7.





Table 6.3.1 Watertight shell boundaries for lower hulls and columns of column-stabilized units and tension-leg

Items and requirement Boundaries of lower hull or columns

(1) Shell plating thickness t =See also 3.1.5 but not less than 9,0 mm

(2) Hull framing:(a) Modulus Z = 8,5 skho le2 x 10–3 cm3

(b) Inertia I =

(3) Primary members: Web frames supporting framing:(a) Modulus Z = 8,5 kho S le2 cm3

(b) Inertia I =

Symbols

f = 1,1 – but not to be taken greater than 1,0

ho = load head in metres measured vertically as follows:(a) For shell plating the distance from a point one-third of the height of the plate above its lower edge to a point 1,4T0 above the

keel or to the bottom of the upper hull structure whichever is the lesser with a minimum of 6,0 m.(b) For hull framing and primary members, the distance from the middle of the effective length to a point 1,4T0 above the keel or

to the bottom of the upper hull structure whichever is the lesser with a minimum of 6,0 m.k = steel factor as defined in Ch 2,1le = effective length of member, in metres, as defined in Ch 3,3.3s = spacing of frames, in mmS = spacing or mean spacing of primary members, in metres

T0 = maximum operating draught, in metres, as defined in Ch 1,5

NOTES1. In no case are the scantlings in way of tanks to be less than the requirements given in Table 6.7.1 for tank bulkheads using the load

head h4.2. In no case are the scantlings to be less than the requirements given in Table 6.7.1 for watertight bulkheads using the load head h4.3. Where frames are not continuous they are to be fitted with end brackets in accordance with Ch 7,1.4 or equivalent arrangements provided.

s2500S

2,5

k le Z cm4

2,3

k le Z cm4

0,004sf ho k + 2,5 mm






3.3.1 The minimum scantlings of shell plating are tocomply with Table 6.3.3 and the secondary hull framing and primary members are to comply with Table 6.3.4, see also 3.3.4.

3.3.2 The shell plating thickness is to be suitablyincreased in way of high shear forces in way of drillingcantilevers and other concentrated loads.

3.3.3 The scantl ings and arrangements of theboundary bulkheads of leg wells will be specially consideredwith regard to the maximum forces imposed on the structure,and the permissible stress levels are to comply with Chapter 5. The minimum scantlings are to comply with Table 6.7.1 as a tank bulkhead with the load head h4measured to the upper deck at side. In no case is theminimum plating thickness to be less than 9 mm.

3.3.4 When cross ties are fitted inside pre-load tanks,the tensile stress in the cross ties and its end connections isnot to exceed 108 N/mm2 (11,0 kgf/mm2) at the test head,but the scantlings are also to comply with the requirements of3.3.5 and 3.3.6.

3.3.5 When cross ties are fitted to support shell webframes the scantlings of the web frames are to be determinedfrom Tables 6.3.4 and 6.7.1 and the area and least momentof inertia of the cross tie are to satisfy the following, see also3.3.6 and 3.3.7:

Ac ≥

where:bc = one-half the vertical distance in metres

between the centres of the bottom or deckwebs adjacent to the cross tie, see Fig. 6.3.1.

hc = vertical distance from the centre of the crosstie to deck, in metres, see Fig. 6.3.1.

lc = length of cross tie between the toes of thehorizontal brackets on the web frames at thecross tie, in metres

S = spacing of web frames, in metresle = span of web frames, see Fig. 6.3.1.Ic = least inertia of cross tie cross-section, in cm4

Ac = area of cross tie, in cm2

r = least radius of gyration of cross tie cross-section, in cm

=

be as defined in Ch 3,3.3.

3.3.6 The scantlings of the webs and flanges of crossties are to be checked for buckling by direct calculation.

Ic

Ac

0,82 bc hc S k

1 – 0,42 lc

r k

Table 6.3.2 Watertight shell boundaries of the upper hull of column-stabilized units and tension-leg units

Items and requirement Boundaries of upper hull

(1) Shell plating thickness general The greater of the following:

See also 3.1.5 (a) t =

(b) t =

but not less than 7,5 mm

(2) Bottom plating thickness between columns within outside of The greater of the following:

(a) t =column shell but not less than two web frame spaces

(b) t =

See also 3.1.5 but not less than 7,5 mm

(3) Shell stiffeners and primary webs, general To comply with Table 6.7.1 using the load head h4 below

(4) Shell stiffeners adjacent to columns as defined in (2):(a) Modulus Z = 8,5 skh4 le2 x 10–3 cm3

(b) Inertia I =

Symbols

Symbols as defined in Table 6.7.1, except as follows:h4 = load head, in metres, as defined in Table 6.7.1 for watertight bulkheads but not less than 6,0 m

sb = 470 + mm or 700, whichever is the smaller

s1 = s but is not to be taken less than sbW = greatest width or diameter of stability column, in metres

NOTEIn no case are the scantlings in way of tanks to be less than the requirements given in Table 6.7.1 for tank bulkheads using the load head h4.

L0,6

2,3

k le Z cm4

0,012s1 k

0,004sf h4k + 2,5 mm

W2

0,012s1 k

0,004sf h4k mm





3.3.7 Design of end connections of cross ties is to besuch that the area of the welding, including vertical brackets,where fitted, is to be not less than the minimum crosssectional area of the cross tie derived from 3.3.5. To achievethis, full penetration welds may be required and thickness ofbrackets may require further consideration. Attention is to begiven to the full continuity of area of the backing structure onthe transverses. Particular attention is also to be paid to thewelding at the toes of all end brackets on the cross tie.

Table 6.3.3 Shell plating self-elevating units

Location Thickness, in mm, see also 3.1.5

(1) Bottom shell plating The greater of the following:See Notes 1, 2 and 4

(a) t = 0,001s1 (0,043L + 10)

(b) t = 0,0052s1

(2) Bilge plating (framed) t as for (1)See Note 2

(3) Side shell platingSee Notes 1, 2, 3 and 4 (a) Above from base:

The greater of the following:(i) t = 0,001s1 (0,059L + 7)

(ii) t = 0,0042s1

(b) At upper turn of bilge (see Note 2):The greater of the following:(i) t = 0,001s1 (0,059L + 7)

(ii) t = 0,0054s1

(c) Between upper turn of bilge and from base:

The greater of the following:(i) t from (b)(i)(ii) t from interpolation between (a)(ii) and (b)(ii)

(4) Minimum plating tm = (6,5 + 0,033L)

Symbols

L, D, TT, as defined in Ch 1,5k = steel factor as defined in Ch 2,1s = spacing of secondary stiffeners, in mm

sb = 470 + mm or 700 mm whichever is the smaller

s1 = s, but is not to be taken less than sb

NOTES1. In no case is the shell plating to be less than tm.2. When no bilge radius is fitted and the unit is fitted with hard chines, the bottom shell thickness required by (1) is, in general, to be extended

up to from base, see 3.1.7.

3. The thickness of side shell need not exceed that determined from (1) for bottom shell when using the spacing of side shell stiffeners.4. In no case are the scantlings of tanks to be less than the requirements given in Table 6.7.1 for tank bulkheads using load head h4.

D4

L0,6

ks1sb

D2

1,2TT k

1k

1,4TT k

1k

D2

1,5TT k

1k





Table 6.3.4 Shell framing self-elevating units

Items and location Modulus

(1) Hull framing, see Note 1

(a) Bottom frames Z = 11,0 s k hT le2 x 10–3 cm3

(b) Side frames Z = 8,0 s k hT le2 x 10–3 cm3

(2) Primary members, see Note 1

(a) Bottom web frames supporting framing Z = 11,0 k hT S le2 cm3

(b) Side web frames supporting framing Z = 8,0 k hT S le2 cm3

Symbols

D and TT as defined in Ch 1,5hT = load head, in metres, and is to be taken as the distance from the middle of the effective length to a point 1,6TT above the keel or

to the upper deck at side whichever is the lesser but not less than 0,01L + 0,7k = steel factor as defined in Ch 2,1le = effective length of member, in metres, as defined in Ch 3,3.3s = spacing of frames, in mmS = spacing or mean spacing of primary members, in metres

NOTES1. In no case are the scantlings in way of tanks to be less than the requirements given in Table 6.7.1 for tank bulkheads using the load head

h4.2. In no case are the scantlings to be less than the requirements given in Table 6.7.1 for watertight bulkheads using the load head h4.3. Where frames are not continuous they are to be fitted with end brackets in accordance with Ch 7,1.4 or equivalent arrangements provided.

Fig. 6.3.1 Pre-load tank construction

Top of transverse or double bottom

2bc

h c

l el e h 4

b eb e

lc

4407/80





3.4 Buoys and deep draught caissons

3.4.1 Where the external watertight hull boundaries aredesigned with stiffened plating, the minimum scantlings forshell plating, hull framing and web frames supporting framingetc. are to comply with Table 6.3.5.

3.4.2 The scantlings determined from Table 6.3.5 arethe minimum requirements for hydrostatic pressure loads onlyand the overall strength is to comply with Chapter 4.

3.4.3 Where the scantlings of primary web frames aredetermined by a frame analysis or where the boundaries aredesigned as shells, either unstiffened or ring stiffened, thescantl ings are to be determined on the basis of anestablished analysis using the appropriate design pressureheads as defined in Chapter 3. The permissible stresses areto comply with Chapter 5. But the scantlings are not to beless than required by 3.4.1.

Table 6.3.5 Watertight shell boundaries of buoys and deep draught caissons

Items and requirement Shell boundaries, see Note 5

(1) Shell plating thickness t =See also 3.1.5. but not less than 9,0 mm

(2) Hull framing:(a) Modulus Z = 8,5 skho le2 x 10–3 cm3

(b) Inertia I =

(3) Primary members: Web frames supporting framing(a) Modulus Z = 8,5 kho S le2 cm3

(b) Inertia I =

Symbols

f = 1,1 – but not to be taken greater than 1,0

ho = load head in metres measured vertically as follows:(a) For shell plating the distance from a point one-third of the height of the plate above its lower edge to the top of the highest

predicted wave in the most unfavourable design situation or to a height 1,0m above the uppermost deck, whichever is the greaterwith a minimum of 6,0m, see Note 3.

(b) For hull framing and primary members, the distance from the middle of the effective length to the top of the highest predicted wavein the most unfavourable design situation or to a height 1,0m above the uppermost deck, whichever is the greater with a minimumof 6,0 m, see Note 3.

k = steel factor as defined in Ch 2,1le = effective length of member in metres as defined in Ch 3,3.3s = spacing of frames in mmS = spacing or mean spacing of primary members, in metres

NOTES1. In no case are the scantlings in way of tanks to be less than the requirements given in Table 6.7.1 for tank bulkheads using the load head

h4.2. In no case are the scantlings to be less than the requirements given in Table 6.7.1 for watertight bulkheads using the load head h4.3. For units defined in Pt 3, Ch 2 which are designed to follow the wave profile, ho need not exceed the distance measured to a height 1,0 m

above the uppermost deck or 6,0 m, whichever is the greater.4. Where frames are not continuous they are to be fitted with end brackets in accordance with Ch 7,1.4 or equivalent arrangements provided.5. The scantlings of shell boundaries derived from this table are to be suitably increased in way of tanks which cannot be inspected at normal

periodic surveys, see Ch 4,7.10.

s2500S

2,5

k le Z cm4

2,3

k le Z cm4

0,004sf ho k + 2,5 mm

3.4.4 The shell plating and hull framing are to bereinforced in way of mooring line attachments, mooringfairleads, supply boat moorings, towing brackets and otherattachments, see also Section 1.

3.4.5 Areas of the hull which may be damaged bychain cables or wire ropes are to be protected or suitablystrengthened.

3.4.6 Where cross ties are fitted to support shell webframes, the scantlings are to comply with 3.3.5 and 3.3.6taking the head hc as the pressure head ho in accordancewith Table 6.3.5.

3.4.7 Where cross ties are fitted inside tanks therequirements of 3.3.4 are to be complied with.





SECTION 4Decks

4.1 General

4.1.1 The design deck loadings for all unit types arenot to be less than those defined in Section 2.

4.1.2 The scantlings of deck structures for surface-type units are to comply with Ch 4,4.

4.1.3 The minimum scantlings of deck structures on column-stabilized units, tension-leg units, self-elevatingunits, buoys and deep draught caissons are to comply withthis Section.

4.1.4 The scantlings of deck structures are also tosatisfy the overall strength requirements in Chapter 4 and besufficient to withstand the actual local loadings plus anyadditional loadings superimposed due to overall frame action.The permissible stress levels are to comply with Chapter 5.

4.1.5 Where decks form watertight boundaries indamage stability conditions, the minimum scantlings are notto be less than required for watertight bulkheads given inSection 7.

4.1.6 For units fitted with a process plant facility and/ordrilling equipment, the support stools and integrated hullsupport structure to the process plant and other equipmentsupporting structures including derricks and flare structuresare considered to be classif ication items regardless of whether or not the process/drilling plant facility is classedand the loadings are to be determined in accordance with Pt 3, Ch 8,2. Permissible stress levels are to comply withChapter 5.

Table 6.4.1 Deck plating

Symbols Location Thickness, in mm, see also 4.2.2

NOTES1. The thickness derived in accordance with (1) is also to satisfy the buckling requirements of Chapter 5.2. On column stabilized units when the primary deck structure consists of box girders or equivalent structure and the deck plating

is considered as secondary structure only the thickness of the plating will be specially considered but in no case is the thickness to be less than 6,5 mm.

3. Where the local deck loading exceeds 43,2 kN/m2 (4,4 tonne-f/m2) the thickness of plating will be specially considered.

b = breadth of increased plating, in mm

f = but not to be taken

greater than 1,0k = steel factor as defined in 2.1.2s = spacing of deck stiffeners, in mm

s1 = s but is to be taken not less thanthe smaller of:

Af = girder face area, in cm2

K1 = 2,5 mm at bottom of tank= 3,5 mm at the crown of tank

L = length of unit, in metres, as defined in 1.5.1

S = spacing of primary members, in metres

ρ, h4 as defined in Table 6.7.1

470 + L0,6

mm or 700 mm

1,1 + s2500S

(1) Strength/weather deck See Notes 1 and 2

(2) Lower decks

(3) Platform decks

(4) In way of the crown or bottom of tanks

(5) Plating forming the upper flange ofunderdeck girders

The greater of the following:

(a) t = 0,001s1 (0,059L + 7)

(b) t = 0,00083s1but not less than (2)

t = 0,012s1but not less than 7,0 mm

t = 0,01s1but not less than 6,5 mm

t = 0,004sf

or as (1), (2) or (3) whichever is the greater but not less than 7,5 mm

t =

but not less than required by (1), (2), (3) or (4) as appropriateMinimum breadth, b = 760 mm

Af1,8k

ρ k h4

1,025 + K1

k

k

Lk + 2,5

1k

4.2 Deck plating

4.2.1 The requirements are in general applicable tostrength/weather deck plating with stiffeners fitted parallel tothe hull bending compressive stress. When other stiffeningarrangements are proposed, the scantlings will be speciallyconsidered, but the minimum requirements of Table 6.4.1 areto be complied with.

4.2.2 The minimum thickness of deck plating is tocomply with the requirements of Table 6.4.1, except fordecks in way of erections above the upper deck. Forerection decks, see Section 6.

4.2.3 The thickness of strength/weather deck plating isalso to be that necessary to satisfy the overall strengthrequirements of Chapters 4 and 5.

4.2.4 The deck plating thickness and supportingstructure in way of towing brackets, winches, masts, cranepedestals, davits and machinery items, etc., is to be suitablyreinforced, see also Section 1.

4.2.5 Where plated decks are sheathed with wood orapproved compositions, consideration will be given toallowing a reduction in the minimum plating thickness given inTable 6.4.1, see also 6.5.2.





4.3 Deck stiffening

4.3.1 The scantlings of deck stiffeners are to complywith the requirements of Table 6.4.2. Stiffeners fitted in wayof concentrated loads and heavy machinery items, etc., willbe specially considered.

4.3.2 The lateral and torsional stability of stiffenerstogether with web and flange buckling criteria are to beverified in accordance with Ch 5,3.

4.3.3 End connection of stiffeners to bulkheads are toprovide adequate fixity and, so far as practicable, directcontinuity of primary strength. In general deck stiffeners areto be continuous through primary support structure, includingbulkheads but alternative arrangements will be considered.The end connections of stiffeners are in general to be inaccordance with the requirements of Chapter 8.

4.4 Deck supporting structure

4.4.1 The minimum scantl ings of girders andtransverses supporting deck stiffeners are to comply with therequirements of Table 6.4.3.

4.4.2 Transverses supporting deck stiffeners are, ingeneral, to be spaced not more than 3,8 m apart.

4.4.3 The web thickness, stiffening arrangements andend connection of primary supporting members are to be inaccordance with Chapter 8.

4.4.4 Where a girder is subject to concentrated loads,such as pillars out of line, the scantlings are to be suitablyincreased. Also, where concentrations of loading on one sideof the girder may occur, the girder is to be adequatelystiffened against torsion.

4.4.5 Pillars are to comply with the requirements ofTable 6.4.4.

4.4.6 Pillars are to be fitted in the same vertical linewherever possible, and effective arrangements are to bemade to distribute the load at the heads and heels of all

pillars. Where pillars support eccentric loads, they are to bestrengthened for the additional bending moment imposedupon them.

4.4.7 Tubular and hollow square pillars are to beattached at their heads to plates supported by efficientbrackets, in order to transmit the load effectively. Doubling orinert plates are to be fitted to decks under the heels oftubular or hollow square pillars. The pillars are to have abearing fit and are to be attached to the head and heel platesby continuous welding. At the heads and heels of pillars builtof rolled sections, the load is to be well distributed by meansof longitudinal and transverse brackets.

4.4.8 Where pillars are not fitted directly above theintersection of bulkheads, equivalent arrangements are to beprovided.

4.4.9 In double bottoms where pillars are not directlyabove the intersection of the plate floors and girders, partialfloors and intercostels are to be fitted as necessary tosupport the pillars. Manholes are not to be cut in floors andgirders below the heels of pillars.

4.4.10 Where pillars are fitted inside tanks or underwatertight flats, the tensile stress in the pillar and its endconnections is not to exceed 108 N/mm2 (11,0 kgf/mm2) atthe test heads. In general, such pillars should be of builtsections, and end brackets may be required.

4.4.11 Pillars or equivalent structures are to be fittedbelow deckhouses, machinery items, winches, etc., andelsewhere where considered necessary.

4.4.12 The thickness of primary longitudinal andtransverse bulkheads supporting decks is to satisfy therequirements for the overall strength of the unit in accordancewith Chapters 4 and 5. When the bulkheads are to bewatertight the scantlings are also to comply with therequirements of Section 7.

4.4.13 The lateral and torsional stability of primarybulkhead stiffeners together with web and flange bucklingcriteria are to be verified in accordance with Ch 5,3.

Table 6.4.2 Deck stiffeners

Symbols Location Modulus, in cm3 Inertia, in cm4

NOTES1. The load heads h1, h2, h3 and h5 are to be determined from the maximum design uniform loadings and are not to be less than the minimum

design load heads given in Table 6.2.1.2. The web depth, dw, of stiffeners is to be not less than 60 mm.

dw = depth of stiffener, in mm, see Note 2h1 = weather head, in metresh2 = work area head, in metresh3 = storage head, in metresh4 = tank head, in metres, as defined in

Table 6.7.1h5 = accommodation head, in metresk = steel factor defined in Ch 2,1.2le = span point,in metres as defined in

Ch 3,3.3 but not less than 1,5 ms = spacing of stiffeners, in mmγ = 1,4 for rolled or built sections

= 1,6 for flat barsρ as defined in Table 6.7.1

(1) Weather decks

(2) Work areas

(3) Storage areas

(4) Accommodation decksand crew spaces

(5) In way of the crown orbottom of tanks

Z = 5,5s k h1 le2 x 10–3

Z = 5,5s k h2 le2 x 10–3

Z = 5,0s k h3 le2 x 10–3

Z = 4,5s k h5 le2 x 10–3

As (1), (2), (3) or (4)as applicable, or

whichever is the greater

0,0113ρ s k h4 le 2

γ

–

–

–

–

I =2,3

k le Z




Local Strength

4.4.14 When openings are cut in the primarylongitudinal and transverse bulkheads the openings are tohave well rounded corners and full compensation is to beprovided. All openings are to be adequately framed.

4.4.15 The minimum scantlings of non-watertight pillarbulkheads are to comply with the requirements of Table 6.4.5.

4.5 Deck openings

4.5.1 The corners of all deck openings are to beelliptical parabolic or well rounded and the free edges are tobe smooth. Large openings are to comply with 4.5.4 and4.5.5.

4.5.2 All openings are to be adequately framed.Attention is to be paid to structural continuity, and abruptchanges of shape, section or plate thickness are to beavoided.

4.5.3 Arrangements in way of corners and openingsare to be such as to minimize the creation of stressconcentrations. Openings in highly stressed areas of decks,having a stress concentration factor in excess of 2,4, willrequire edge reinforcements in the form of a spigot ofadequate dimensions, but alternative arrangements will beconsidered. The area of any edge reinforcement which maybe required is not to be taken into account in determining therequired sectional area of compensation for the opening.


4.5.4 When large openings are cut in highly stressedareas of decks, the corners of the openings are to beelliptical, parabolic or rounded, with a radius generally notless than 1/24 of the breadth of the opening. The minimumradius for large openings is to be 150 mm, provided the inneredge of the plating is stiffened by means of a coaming orspigot. Where the inner edge is unstiffened, the minimumradius is to be 300 mm.

4.5.5 Where the corners of large openings arerounded, the deck plating thickness is to be increased at thecorners of the openings.

4.5.6 Compensation will be required for deck openingscut in highly stressed areas.

4.5.7 All openings which are required to be madewatertight or weathertight are to have closing appliances inaccordance with the requirements of Chapter 7.

Table 6.4.3 Deck girders, transverses and deep beams

Symbols

h4 = tank head, in metres, as defined in Table 6.7.1k = steel factor as defined in Ch 2,1.2le = span point, in metres, defined in Ch 3,3.3

Hg = weather head h1 or work area head h2 or storage head h3 or accommodation head h5, in metres, as defined in Table 6.2.1 whicheveris applicable

S = spacing of primary members, in metresρ as defined in Table 6.7.1

Location and arrangements

(1) Girders and traverses in way of dry spaces:(a) Supporting point loads

(b) Supporting a uniformly distributed load

(2) Deep beams supporting deck girders in way of dryspaces:(a) Supporting point loads

(b) Supporting a uniformly distributed load

(3) Girders and transverses in way of the crown or bottomof tanks

Modulus, in cm3

Z to be determined from calculationsusing stress

and assuming fixed endsZ = 4,75k S Hg le2

Z to be determined from calculationsusing stress

and assuming fixed endsZ = 4,75k S Hg le2

Z = 11,7ρ k h4 S le2

123,5

k N/mm2

12,6

k kgf/mm2

123,5

k N/mm2

12,6

k kgf/mm2

Inertia, in cm4

I =2,5

k le Z

I =2,3

k le Z

I =1,85

k le Z





Table 6.4.4 Pillars

Symbols Parameter Requirement

b = breadth of side of a hollow rectangu-lar pillar or breadth of flange or webof a built or rolled section, in mm

dp = mean diameter of tubular pillars,in mm

k = local scantling higher tensile steelfactor, see Ch 2,1.2.1, but not lessthan 0,72

l = overall length of pillar, in metresle = effective length of pillar, in metres,

and is taken as 0,80lr = least radius of gyration of pillar cross-

section, in mm, and may be taken as:

Ap = cross-sectional area of pillar, in cm2

Hg as defined in Table 6.4.3I = least moment of inertia of cross-

section, in cm4

P = load, in kN (tonne-f), supported bythe pillar and is to be taken as:P = Po + Pabut not less than 19,62 kN (2 tonne-f)

Pa = load, in kN (tonne-f), from pillar orpillars above (zero if no pillars over)

Po = load, in kN (tonne-f), supported bypillar based on Hg

r = 10 IAp

mm

(1) Cross-sectional area of all types of pillar

(2) Minimum wall thickness of tubular pillars

(3) Minimum wall thickness of hollow rectan-gular pillars or web plate thickness of Ior channel sections

(4) Minimum thickness of flanges of angle orchannel sections

The greatest of the following:

(a) t =

(b) t =

(c) t = 5,5 mm where L < 90 m, or= 7,5 mm where L ≥ 90 m

dp

40 mm

t = P0,04dp – 0,5le

mm

P0,392dp – 4,9le

mm

The lesser of the following:

(a) t =

(b) t =

but to be not less thant = 5,5 mm where L < 90 m, or

= 7,5 mm where L ≥ 90 m

b55

mm

br600le

mm


(a) tf =

(b) tf = b18

mm

br200le

mm

(5) Minimum thickness of flanges of built orrolled I sections


(a) tf =

(b) tf = b36

mm

br400le

mm

NOTE

As a first approximation, Ap may be taken as and the radius of gyration estimated for a suitable section having this area.

If the area calculated using this radius of gyration differs by more than 10 per cent from the first approximation, a further calculation using theradius of gyration corresponding to the mean area of the first and second approximation is to be made.

k P9,32

k P0,95

See Note

Ap = k P

1,26 – 5,25 le

r k

cm2

Ap = k P

12,36 – 51,5 le

r k

cm2





Table 6.4.5 Non-watertight pillar bulkheads

RequirementParameterSymbols

dw, tp , b, c as defined in Ch 3,3.2r = radius of gyration, in mm, of

stiffener and attached plating

= for rolled, built

or swedged stiffeners

= for

symmetrical corrugations = spacing of stiffeners, in mmI = moment of inertia, in cm4, of

stiffener and attached platingA = cross-sectional area, in cm2,

of stiffener and attached plating

A1 =

As a first approximation A1may be taken as

A2 =

As a first approximation A2may be taken as

P, le as defined in Table 6.4.4

λ = bc

P3,92

P0,4

A2 = P

0,5 – 1,5 ler

cm2

P

4,9 – 14,7 ler

cm2

P9,32

P0,95

A1 = P

1,26 – 5,25 ler

cm2

P

12,36 – 51,5 ler

cm2

dw 3b + c12 (b + c)

mm

10 lA

mm

5,5 mm

1500 mm

75 mm

(a) Where A = A1

(b) When A = A2

(c) Where A is obtained by interpolation between A1 and A2

80 < st < 120

st ≥ 120

st ≤ 80

(a) Where A = A1

(b) When A = A2btp

> 750 λ leλ + 0,25 r

btp

≤ 750 λ leλ + 0,25 r

(1) Minimum thickness of bulkhead plating

(2) Maximum stiffener spacing

(3) Minimum depth of stiffeners orcorrugations

(4) Cross-sectional area (including plating) for rolled, built or swedgedstiffeners supporting beams, longitudinals, girders or transverses

(5) Cross-sectional area (including plating) for symmetrical corrugation




Local Strength

SECTION 5Helicopter landing areas

5.1 General

5.1.1 This Section gives the requirements for decksintended for helicopter operations.

5.1.2 Attention is drawn to the requirements ofNational and other Authorities concerning the construction ofhelicopter decks and the landing area arrangementsnecessary for helicopter operations.

5.1.3 Where helicopter decks are positioned so thatthey may be subjected to wave impacts, the scantlings are tobe considered in a realistic manner and increased to thesatisfaction of LR.

5.1.4 Where the landing area forms part of a weatheror erection deck, the scantlings are to be not less than thoserequired for decks in the same position.

5.2 Plans and data

5.2.1 Plans and data are to be submitted giving thearrangements, scantlings and details of the helicopter deck.The type, size and weight of helicopters to be used are alsoto be indicated.

5.2.2 Relevant details of the largest helicopters, forwhich the deck is designed, are to be stated in theOperations Manual.

5.3 Arrangements

5.3.1 The landing area is to comply with applicableRegulations with respect to size, landing and take-off sectorsof the helicopter, freedom from height obstructions, deckmarkings, safety nets and lighting, etc.

5.3.2 The landing area is to have an overall coating ofnon-slip material or other arrangements are to be provided tominimize the risk of personnel or helicopters sliding off thelanding area.

5.3.3 A drainage system is to be provided inassociation with a perimeter guttering system or slightlyraised curb to prevent spilled fuel falling on to other parts ofthe unit. The drains are to be led to a safe area.

5.3.4 A sufficient number of tie-down points are to beprovided to secure the helicopter.

5.4 Landing area plating

5.4.1 The deck plate thickness, t, within the landingarea is to be not less than:

t = t1 + 1,5 mmwhere

t1 =

α = thickness coefficient obtained from Fig. 6.6.1β = tyre print coefficient used in Fig. 6.6.1

= log10 P1 k2

s2 x 107

αs1000 k

mm

The plating is to be designed for the emergency landing casetaking:

P1 = 2,5 φ1 φ2 φ3 φ f γ Pw tonneswhereφ1, φ2, φ3 are to be determined from Table 6.6.1

f = 1,15 for landing decks over manned spaces,e.g., deckhouses, bridges, control rooms,etc.

= 1,0 elsewhereP = the maximum all up weight of the helicopter,

in tonnesPw = landing load, on the tyre print in tonnes;

for helicopters with a single main rotor, Pw, isto be taken as P divided equally between thetwo main undercarriagesfor helicopters with tandem main rotors, Pw,is to be taken as P distributed between allmain undercarriages in proportion to thestatic loads they carry

γ = 0,6 general ly. Factor to be special lyconsidered where the hel icopter deckcontributed to the overall strength of the unit

Other symbols used in this Section are defined in Section 6and in the appropriate sub-Section.

The tyre print dimensions specified by themanufacturer are to be used for the calculation. Where theseare unknown, it may be assumed that the print area is 300 x300 mm and this assumption is to be indicated on thesubmitted plan.

5.4.2 The plate thickness for aluminium decks is to benot less than:

t = 1,4t1 + 1,5 mmwhere t1 is the mild steel thickness as determined from 5.4.1.Where the deck is fabricated using extruded sections withclosely spaced stiffeners the plate thickness may bedetermined by direct calculations but the minimum deckthickness is to include 1.5mm wear allowance. If the deck isprotected by closely spaced grip/wear treads the wearallowance may be omitted.

5.4.3 For helicopters fitted with landing gear consistingof skids, the print dimensions specified by the manufacturerare to be used. Where these are unknown, it may beassumed that the print consists of a 300 mm line load at oneend of each skid, when applying Fig. 6.6.1.

5.5 Deck stiffening and supporting structure

5.5.1 The helicopter deck stiffening and the supportingstructure for helicopter decks are to be designed for the loadcases given in Table 6.5.1 in association with the permissiblestresses given in Table 6.5.2.

5.5.2 In addition to the requirements of 5.5.1, thestructure supporting helicopter decks is to be designed towithstand the loads imposed on the structure due to themotions of the unit. For self-elevating units, the motions arenot to be less than those defined for transit conditions in Ch 4,3.10 and 3.11. The stress levels are to comply withload case 3 in Table 6.5.2, see also 5.1.3.






Table 6.5.1 Design load cases for deck stiffening and supporting structure

Load cases

Load

Landing area Supporting structureSee Note 1

UDL HelicopterSee Note 2

Self weight Horizontal loadSee Note 2

(1) Overall distributed loading

(2) Helicopter emergency landing

(3) Normal usage

2(0,2)

0,2(0,02)

0,5(0,05)

–– –– ––

2,5Pf W 0,5P

1,5P W 0,5P + 0,5W

Symbols

P and f as defined in 5.4.1UDL = uniformly distributed vertical load over entire landing area, kN/m2 (tonne-f/m2)

W = structural weight of helicopter platform

NOTES1. For the design of the supporting structure for helicopter platforms applicable self weight and horizontal loads are to be added to the landing

area loads.2. The helicopter is to be so positioned as to produce the most severe loading condition for each structural member under consideration.

Table 6.5.2 Permissible stresses for deck stiffening and supporting structure

Load caseSee Table 6.5.1

(1) Overall distributed loading

(2) Helicopter emergency landing

(3) Normal usage

Permissible stresses, in N/mm2 (kgf/mm2)

Deck secondary structure (beams,

longitudinals,See Notes 1 and 2)

Primary structure(transverses, girders, pillars, trusses) All structure

ShearCombined bending and axialBending

147k

15k

147k

15k

Bending

3

0,6σc

0,9σc

0,6σc

Symbols

k = a material factor:= as defined in Ch 2,1.2 for steel members= ka as defined in Ch 2,1.3 for aluminium alloy members

σc = yield stress, 0,2% proof stress or critical compressive buckling stress, in N/mm2 (kgf/mm2), whichever is the lesser

NOTES1. Lower permissible stress levels may be required where helideck girders and stiffening contribute to the overall strength of the unit.

Special consideration will be given to such cases.2. When determining bending stresses in secondary structure, for compliance with the above permissible stresses, 100% end fixity may

be assumed.

245k

25k

220,5

k

22,5

k

176k

18k

147k

15k




Local Strength Part 4, Chapter 6Sections 5 & 6

5.5.3 For load cases (1) and (2) in Table 6.5.1 theminimum moment of inertia, I, of aluminium alloy secondarystructure stiffening is to be not less than:

where Z is the required section modulus of the aluminiumalloy stiffener and attached plating and ka as defined in Ch 2,1.3.

5.5.4 Where a grillage arrangement is adopted for theplatform stiffening, it is recommended that direct calculationprocedures be used.

5.5.5 When the deck is constructed of extrudedaluminium alloy sections, the scantlings will be speciallyconsidered on the basis of this Section.

5.6 Stowed helicopters

5.6.1 In addition to the requirements of 5.4 and 5.5,when arrangements are made to stow helicopters secured tothe deck in predetermined positions, the structure is to bedesigned for the local loadings which can occur duringnormal operations.

5.6.2 Local loads on the structure are to be based onthe maximum design under-carriage loadings specified by thehelicopter manufacturer multiplied by a dynamic amplificationfactor based on the predicted motions of the unit asapplicable. The self weight of the helicopter deck is to beincluded in the loadings imposed on the primary supportstructure. The permissible stress levels are to be inaccordance with load case 3 in Table 6.5.2.

5.6.3 When the minimum design air temperature of theunit is 0°C or below, then when considering the loadings in5.6.2 the helicopter deck is to be assumed loaded with auniformly distributed load of 0,5 kN/m2 (0,05 tonne-f/m2) torepresent wet snow or ice.

5.7 Bimetallic connections

5.7.1 Where aluminium alloy platforms are connectedto steel structures, details of the arrangements in way of thebimetallic connections are to be submitted.

I =5,25ka

Z le cm4

SECTION 6Decks loaded by wheeled vehicles

6.1 General

6.1.1 Where it is proposed to use wheeled vehiclessuch as fork lift trucks and mobile cranes on deck structures,the deck plating and the supporting structure are to bedesigned on the basis of the maximum loading to which theymay be subjected in service and the minimum scantlings areto comply with this Section. In no case, however, are thescantl ings to be less than would be required by theremaining requirements of this Chapter when the deck isconsidered as a weather deck or storage deck, asappropriate.

6.1.2 The vehicle types and axle loads, for which thevehicle-carrying decks including, where applicable, hatchcovers have been approved, are to be stated in theOperations Manual.

6.1.3 Details of the deck loading resulting from theoperation of wheeled vehicles are to be supplied by theShipbuilder or designer. These details are to include thewheel load, axle and wheel spacing, tyre print dimensionsand type of tyre for the vehicles.

6.1.4 For design purposes, where wheeled vehiclesare to be used for handling stores, etc., on storage decks orweather decks, the deck is to be taken as loaded with theappropriate design head, except in way of the vehicle.

6.2 Deck plating

6.2.1 The deck plate thickness, t, is to be not lessthan:

t = t1 + tc mmwhere

k = higher tensile steel factor, see Ch 2,1.2.tc = wear and wastage allowance determined

from Table 6.6.2

t1 =

P1 = corrected patch load obtained from Table 6.6.1α = thickness coefficient obtained from Fig. 6.6.1β = tyre print coefficient used in Fig. 6.6.1

= log10

6.2.2 Where it is proposed to carry tracked vehicles,the patch dimensions may be taken as the track printdimensions and Pw is to be taken as half the total weight ofthe vehicle. The wear and wastage al lowance from Table 6.6.2 is to be increased by 0,5 mm.

6.2.3 If wheeled vehicles are to be used on insulateddecks or tank tops, consideration will be given to thepermissible loading in association with the insulationarrangements and the plating thickness.

P1 k2

s2 x 107

αs1000 k

mm





Table 6.6.1 Corrected patch load calculation

au

v

s

s and a are panel dimensions, in mmu and v are print dimensions, in mm

40

36

32

28

24

20

16

12

8

4 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 3,6

NOTE: For intermediate values of v/s linear interpolation may be used

0,2

0,7

0,8

β

Line

load

v/s=

0,1

0,3

0,4

0,5

0,6

0,9

v/s

≥ 1,

0

α

4407/81

Fig. 6.6.1 Tyre print chart

Symbols Expression

a, s, u, and v as defined in Fig. 6.6.1n = tyre correction factor, see Table 6.6.3

Pw = load, in tonnes, on the tyre print. For closely spacedwheels the shaded area shown in Fig. 6.6.1 may be takenas the combined print

P1 = corrected patch load, in tonnesλ = dynamic magnification factor

φ1 = patch aspect ratio correction factorφ2 = panel aspect ratio correction factorφ3 = wide patch load factor

P1 = φ1φ2φ3 λ Pw

λ = (1 + 0,7n)

v1 = v, but > su1 = u, but > a

φ1 =2v1 + 1,1s

u1 + 1,1s

φ2 = 1,0 for u ≤ (a – s)

= for a ≥ u > (a – s)

= for u > a0,77 au

1

1,3 –0,3s

a – u

φ3 = 1,0 for v < s

= for

= for vs

≥ 1,51,2 sv

1,5 > vs

> 1,00,6 sv

+ 0,4





6.3 Deck stiffeners

6.3.1 The section modulus, Z, of deck stiffeners is tobe not less than that required for a weather deck or storagedeck as appropriate, nor less than the following, where forklift trucks are to be used:

Z = (0,375K1 Ple + 0,00125 K2hsle2) k cm3

where the values of K1 and K2 are given in Table 6.6.4h = normal load head on the deck, in metres, as

defined in Table 6.4.2P = total weight, in tonnes, of the vehicle divided

by the number of axles. Where distribution ofweight is not uniform, P is to be taken as themaximum axle load. For fork lift trucks thetotal weight is to be applied to one axle

le, k and s as defined in Section 4, Table 6.4.2.

6.4 Deck girders and transverses

6.4.1 Where the load on deck girders and transversesis uniformly distributed, the section modulus is to be not lessthan:

Z = 4,75bHg le2 k cm3

where b = mean width of plating supported by a deckgirder or transverse, in metres

Hg, le, k and s as defined in Section 4, Table 6.4.3.

6.4.2 Where the member supports point loads, with orwithout the addition of uniformly distributed load, the section

modulus is to be based on a stress of N/mm2

, assuming 100 per cent end fixity.12,6

k kgf/mm2

123,6k

6.5 Hatch covers

6.5.1 Where wheeled vehicles are to be used, thehatch cover plating is to be not less in thickness than thatrequired by 6.2, and the modulus of the stiffeners is to be notless than:

Z = (K3 P le + 0,00167K4hs le2) kwhere the values of K3 and K4 are given inTable 6.5.5 and P and h are defined in 6.3.1.

le, k and s as defined in Section 4, Table 6.4.2.In no case, however, are the scantlings of plating and stiffenersto be less than would be required as a normal deck hatchcover, in the position under consideration, see Chapter 7.

6.6 Securing arrangements

6.6.1 Details of the connections to the structure ofvehicle securing arrangements are to be submitted forapproval.

Wheel spacing

Stiffener spanK3 K4

0,10,20,30,40,50,60,70,80,9

11,9610,69

9,588,467,466,515,554,232,38

2,321,891,551,281,070,910,730,360,11

NOTEWheel spacing equals outer wheel to outer wheel on axles withmultiple wheel arrangements

Table 6.6.5 Load distribution factors K3 and K4

Location tc, in mm

Strength deck, weather decks, decks forming crown of tank, inner bottom 1,5

Internal decks elsewhere 0,75

Table 6.6.2 Wear and wastage allowance

Table 6.6.3 Tyre correction factor, n

Number ofPneumatic Solid Steel or

wheels intyres rubber tyres solid tyres

idealized patch

1 0,6 0,8 1,02 or more 0,75 0,9 1,0

Wheel spacing

Stiffener spanK1 K2

0,10,20,30,4

0,5 and greater

15,414,613,3511,810,1

1,891,8451,7301,551,30

NOTEWheel spacing equals outer wheel to outer wheel on axles withmultiple wheel arrangements

Table 6.6.4 Load distribution factors K1 and K2


SECTION 7Bulkheads

7.1 General

7.1.1 This Section is applicable to watertight and deeptank transverse and longitudinal bulkheads, watertight flats,trunks and tunnels of all units, except for bulkheads insurface-type oil storage units which are to comply with Ch 4,4. Requirements are also given for non-watertightbulkheads.

7.1.2 The requirements of this Section apply to avertical system of stiffening on bulkheads. They may also beapplied to a horizontal system of stiffening provided thatequivalent end support and alignment are provided.

7.1.3 The number and disposit ion of watert ightbulkheads are to be in accordance with Ch 3,5 and therequirements of Chapter 7 regarding watertight integrity areto be complied with.

7.1.4 The buckling requirements of Ch 5,4 are also tobe satisfied.

7.1.5 The height of the air and overflow pipes are to beclearly indicated on the plans submitted for approval and theload heads for scantlings are to be not less than thosedefined in Table 6.7.1.

7.2 Symbols

7.2.1 The following symbols are applicable to thisSection:

k = higher tensile steel factor, see Ch 2,1s = spacing of secondary stiffeners, in mmI = inert ia of st i ffening member, in cm4,

see Ch 3,3S = spacing or mean spacing of primary

members, in metresZ = section modulus of stiffening member, in cm3,

see Pt 3, Ch 3,3ρ = relative density (specific gravity) of liquid

carried in a tank, but is not to be taken lessthan 1,025.

7.3 Watertight and deep tank bulkheads

7.3.1 The scantlings of watertight and deeptankbulkheads are to comply with the requirements of Tables 6.7.1 to 6.7.3. Where tanks cannot be inspected atnormal periodic surveys the scantlings derived from thisSection are to be suitably increased, see Ch 4,7.10.

7.3.2 Where bulkhead stiffeners support deck girders,transverses or pillars over, the scantlings are to satisfy therequirements of Section 4.

7.3.3 The strength of bulkheads and flats which supportthe ends of bracings or columns will be specially considered.

7.3.4 In way of partially filled tanks, the scantlings andstructural arrangements of the boundary bulkheads are to becapable of withstanding the loads imposed by the movementof the liquid in those tanks. The magnitude of the predictedloadings, together with the scantling calculations may requireto be submitted, see also Ch 3,4.18.



Local Strength

7.3.5 In deep tanks, oil fuel or other liquids are to havea flash point of 60°C or above (closed cup test). Where tanksare intended for liquids of a special nature, the scantlings andarrangements will be specially considered in relation to theproperties of the liquid, see 7.3.6. For the scantlings of mudtanks, see 7.5.

7.3.6 Where tanks are intended for the storage of oilwith a flash point less than 60 ˚ C (closed cup test) thescantlings of bulkheads on surface-type units are to complywith Ch 4,4, but other unit types are to comply with thisSection. The minimum scantlings and arrangements on allunits are also to comply with Pt 3, Ch 3.

7.3.7 For cofferdams on units with oil storage tanks asdefined in 7.3.6 the separation of tanks and spaces are tocomply with Pt 3, Ch 3. Cofferdams are to be fitted betweentanks as necessary depending on the liquids stored. Ingeneral, cofferdams are to be fitted between tanks inaccordance with the requirements of Ch 3,5.

7.3.8 Where watertight bulkhead stiffeners are cut inway of watertight doors in the lower part of a bulkhead, theopening is to be suitably framed and reinforced. Wherestiffeners are not cut but the spacing between the stiffeners isincreased on account of watertight doors, the stiffeners at thesides of the doorways are to be increased in depth andstrength so that the efficiency is at least equal to that of theunpierced bulkhead, without taking the stiffness of the doorframe into consideration. Watertight recesses in bulkheadsare generally to be so framed and stiffened as to providestrength and stiffness equivalent to the requirements forwatertight bulkheads.

7.3.9 Wash bulkheads or divisions are to be fitted todeep tanks as required by Ch 7,4. The division bulkheadmay be intact or perforated as desired. If intact thescantlings are to be as required for boundary bulkheads. Ifperforated the plating thickness is not to be less than 7,5 mmand the modulus of the stiffeners may be 50 per cent of thatrequired for boundary bulkheads, using h4 measured to thecrown of the tank. The stiffeners are to be bracketed at topand bottom. The area of perforation is to be not less thanfive per cent nor more than 10 per cent of the total area ofthe bulkhead. Where brackets from horizontal girders on theboundary bulkheads terminate at the centreline bulkhead,adequate support and continuity are to be maintained.

7.3.10 The scantlings of end brackets fitted to bulkheadstiffeners are, in general, to comply with Chapter 8.

7.4 Watertight flats, trunks and tunnels

7.4.1 The scantlings and arrangements of watertightf lats, trunks and tunnels are to be equivalent to therequirements for watertight bulkheads or tanks as defined in7.3 as appropriate. The scantlings of shaft tunnels will bespecially considered. The scantlings at the crown or bottomof tanks are to comply with the requirements of Table 6.4.1.

7.4.2 Additional strengthening is to be fitted to tunnelsunder the heels of pillars, as necessary.





Local Strength

7.5 Watertight void compartments

7.5.1 In all units where watertight void compartmentsare adjacent to the sea the scantlings of the boundarybulkheads are to be determined from Table 6.7.1 forwatertight bulkheads but the scantlings are not to be lessthan required for tank bulkheads using the load head h4measured to the maximum operating draught of the unit.


Table 6.7.1 Watertight and deep tank bulkhead scantlings

Item and requirement Watertight bulkheads Deep tank bulkheads

(1) Plating thickness for plane, symmetrically corrugated and doubleplate bulkheads

(2) Modulus of rolled and built stiffeners,swedges, double plate bulkheads andsymmetrical corrugations

(3) Inertia of rolled and built stiffeners andswedges

(4) Symmetrical corrugations and doubleplate bulkheads

(5) Stringers or webs supporting vertical orhorizontal stiffening(a) Modulus

(b) Inertia

t =but not less than 5,5 mm0,004sf h4 k mm

Z = 5,5kh4S le2 cm3

––

Z = 11,7ρkh4S le2 cm3

I =2,5

k le Z cm4

Z = skh4 le 2

71γ ω1 + ω 2 + 2 cm3

In the case of symmetrical corrugations, s is to be taken as b or c in Fig. 3.3.1 in Chapter 3,whichever is the greater

In the case of symmetrical corrugations, s is to be taken as p, see also Note 2

Additional requirements to be complied with as detailed in Table 1.9.2

t =

nor less than 7,5 mm

0,004sf ρh4 k

1,025 + 2,5 mm

Z =ρskh4 le

2

22γ ω1 + ω 2 + 2 cm3

–– I =2,3

k le Z cm4

Symbols

s, S, I , k, ρ as defined in 7.2.1dw = web depth of stiffening member, in mm

f = but not to be taken greater than 1,0

h4 = load head, in metres measured vertically as follows:(a) For watertight bulkhead plating, the distance from a

point one-third of the height of the plate above itslower edge to a point 0,91 m above the bulkheaddeck at side or to the worst damage waterline,whichever is the greater

(b) For tank bulkhead plating, the distance from a pointone-third of the height of the plate above its loweredge to the top of the tank, or half the distance tothe top of the overflow, whichever is the greater

(c) For watertight bulkhead stiffeners or girders, thedistance from the middle of the effective length to apoint 0,91 m above the bulkhead deck at side or tothe worst damage waterline whichever is the greater

(d) For tank bulkhead stiffeners or girders, the distancefrom the middle of the effective length to the top ofthe tank, or half the distance to the top of the over-flow, whichever is the greater

le = effective length of stiffening member, in metres, and forbulkhead stiffeners, to be taken as l – e1 – e2 (see alsoFig. 6.7.1)

p = spacing of corrugations as shown in Fig. 3.3.1 in Chapter 3γ = 1,4 for rolled or built sections and double plate bulkheads

= 1,6 for flat bars= 1,1 for symmetrical corrugations of deep tank bulkheads= 1,0 for symmetrical corrugations of watertight bulkheads

ω, e = as defined in Table 6.7.3, see also Fig. 6.7.1

1,1 – s2500S

NOTES1. In no case are the scantlings of deep tank bulkheads to be less

than the requirements for watertight bulkheads where the boundary bulkheads of the tanks form part of the watertight sub-division of the unit to meet damage stability requirements,see Ch 3,5.

2. For self-elevating units and surface-type units, the bulkhead deckis to be taken as the freeboard deck.

3. For column-stabilized units, buoys and deep draught caissons,the bulkhead deck is, in general, to be taken as the uppermostcontinuous strength deck unless agreed otherwise with LR.

4. The scantlings of all void compartments adjacent to the sea arealso to comply with 7.5.1.

5. In calculating the actual modulus of symmetrical corrugations thepanel width b is not to be taken greater than that given by Ch 3,3.2.

6. For rolled or built stiffeners with flanges or face plates, the web

thickness is to be not less than whilst for flat bar

stiffeners the web thickness is to be not less than .dw

18 k

dw

60 k





Fig. 6.7.1Effective length and end constraint definitions for bulkheads

End of stiffener unattachedpermitted in upper tween decks only

End connections of thistype not permitted attank boundaries

ω2 = 0

ω1 = 0

le = l

1

1

(a)

3

2

le = l

Member B

ω1 = ZB or 1 for member flanges aligned

4,5M1

5

4

lω1 = 0 otherwise

ω2 = 1 for member flanges aligned

ω2 = 0 otherwise

ω1 = 1

ω2 = 1

Member B

Member A

Member A

(b) (c)

le

e1 = dA

7

6

7

l

a2

a1

le

ω2 = 1

e2 = βa2 or 0,1l for type

e2 = 0 for type

6

7

Bracket with full line

Bracket with dotted line

Floor

ω1 = 1

l

a2

a1 8

8

e1 = βa1 or 0,1l

le

ω1 = 1

ω2 = 1

e2 = βa2 or 0,1l

Member B

11

12 13

ω1 = or or 1,0δ.tbtm

tB

tf

te

δ.tetm

ω2 = or or 1,0δ.tftm

δ.tetm

lle = l le

Floors to be alignedunder flanges

Transverse stiffeners

Floors

10

ω1 = or 1,0δ.tetm

a2 e2 = αl or a2

ω2 = or or 1,0δ.tttm

δ.tftm

l le

a2

a1

14

14

ω1 = or or 1,0δ.tstm

δ.tetm

ω2 = or or 1,0δ.tstm

δ.tetm

e2 = αl or a2

e1 = αl or a1

(d) (e)

(f) (g) (h) 4407/82

To be considered as type 14where structural arrangementincludes stool





Table 6.7.2 Symmetrical corrugations and double plate bulkheads (additional requirements)

Deep tank bulkheadsWatertight bulkheadsType ofbulkhead ParameterSymbols

s, k as defined in 7.2.1b = panel width as shown in Fig. 3.3.1 in

Chapter 3d = depth, in mm, of symmetrical

corrugation or double plate bulkheadle as defined in Table 6.7.1

Aw = shear area, in cm2, of webs of doubleplate bulkhead

θ = angle of web corrugation to plane ofbulkhead

NOTES1. The plating thickness at the middle of span le of

corrugated or double plate bulkheads is toextend not less than 0,2 le m above mid-span.

2. Where the span of corrugations exceeds 15 m,a diaphragm plate is to be arranged at aboutmid-span.

3. See also Chapter 8.4. In calculating the actual modulus of symmetrical

corrugations the panel width b, is not to betaken greater than that given by Ch 3,3.2.

Symmetricallycorrugated, see alsoNotes 1 and 2

Double plate,see also Note 3

Not to exceed: Not to exceed:

at top, and at top and

at bottom bottom70 k

70 k 85 k

To be not less than: To be not less than:

cm2 at top, and cm2 at top, and

cm2 at bottom cm2 at bottom0,10Z

le

0,18Z

le

0,07Z

le

0,12Z

le

Not to exceed: at top, and

at bottom65 k

75 k

Not to exceed: at top, and

at bottom75 k

85 k

See also Note 4

d

d

Aw

bt

θ

st

dtw

––To be not less than:

39le mm

––To be not less than:

39le mm

To be not less than 40°





Table 6.7.3 Bulkhead end constraint factors (see continuation)

Type ω e µEnd connection, see Fig. 6.7.1

Rolled or built stiffeners and swedges

End of stiffeners unattached or attached to plating only1 0 0 ––

2 Members with webs and flanges (or bulbs) in line and attached atdeck or horizontal girder See also Note 1

Adjacent member of B of smallermodulus

The lesser of4,5ZB

M1 or 1,0 0 ––

Adjacent member B of same orlarger modulus 1,0 0 ––3

4 Member A within length l 1,0 dA1000

––Bracketless connection to

longitudinal member5 Member A outside length l 1,0 0 ––

6

Bracketed connection

To transversemember

1,0 The lesser ofβa or 0,1l ––Bracket extends to

floor

7 Otherwise 1,0 0 ––

8 To longitudinal member 1,0 The lesser ofβa or 0,1l ––

Symmetrical corrugations or double plate bulkheads

9 No longitudinal brackets 0 0 ––

Welded directly to deck – no bulkhead in line

10With longitudinal brackets and trans-

verse stiffeners supportingcorrugated bulkhead

0 ––The lesser ofδ tetm

or 1,0

11 Bulkhead B, having same section, inline

The least ofδtBtm

or δtetm

or 1,0 0 ––Welded directly to deck or girder

12Welded directly to tank top and

effectively supported by floors inline with each bulkhead flange,see also Note 2

Thickness at bottom same as that atmid-span

The least ofδtttm

or δtetm

or 1,0 0 ––

13 Thickness at bottom greater thanthat at mid-span

The least ofδtttm

or δtetm

or 1,0The lesser of

αl or a

The lesser oftttm

or tetm

14 Welded to stool efficiently supported by the unit’s structure

For deep tankbulkheads 1,0For watertightbulkheads the

least ofδtstm

or δtetm

or 1,0

The lesser ofαl or a

10ZsM2





7.6 Mud tanks

7.6.1 The scantlings of mud tanks are to be not lessthan those required for tanks using the design density ofmud. However, in no case is the relative density of wet mudto be taken as less than 2,2.

7.7 Non-watertight bulkheads

7.7.1 The scantlings of non-watertight bulkheadssupporting decks are to be in accordance with Table 6.4.5.

Table 6.7.3 Bulkhead end constraint factors (conclusion)

Symbols

s, l , ρ, k, as defined in 7.2.1a = height, in metres, of bracket or end stool or lowest

strake of plating of symmetrically corrugated or doubleplate bulkheads, see Fig. 6.7.1

dA = web overall depth, in mm, of adjacent member Ae = effective length, in metres, of bracket or end stool, see

Fig. 6.7.1ho = h4 but measured from the middle of the overall length l

le, p, h4 as defined in Table 6.7.1tf = thickness, in mm, of supporting floor

tm, te = thickness, in mm, of flange plating of corrugation ordouble plate bulkhead at mid-span or end, respectively

ts = thickness, in mm, of stool adjacent to bulkheadtB = thickness, in mm, of flange plating of member B

Subscripts 1 and 2, when applied to ω, e and a, refer to the topand bottom ends of stiffener respectively

M1 = for watertight bulkheads

= for deep tank bulkheads

M2 = for watertight bulkheads

= for deep tank bulkheads

In the case of symmetrical corrugations s = pZs = section modulus, in cm3, of horizontal section of stool

adjacent to deck or tank top over breadth s or p (asapplicable)All material which is continuous from top to bottom ofstool may be included in the calculation

ZB = section modulus, in cm3, of adjacent member Bα = a factor depending on µ and determined as follows:

where µ ≤ 1,0 α = 0

where µ > 1,0 α =

β = a factor depending on the end bracket stiffening andto be taken as:1,0 for brackets with face bars directly connected

to stiffener face bars0,7 for flanged brackets0,5 for unflanged brackets

δ = 1,0 generally

δ = for corrugated watertight bulkheads

η = lesser of 1,0 and for welded sections

η = lesser of 1,0 and for cold formed sections

µ = a factor representing end constraint for symmetricalcorrugation and double plate bulkheads

ξ = 1,0 where full continuity of corrugation webs isprovided at the ends

ξ = greater of 1,0 and (η + 0,333) where full continuity isnot provided

ω = an end constraint factor relating to the different typesof end connection, see Fig. 6.7.1

60tm k

b

50tm k

b

0,932 k

ξ

0,5 – 12µ + 2

ρ ho s l 2

22

ho s l 2

71

ρ h4 s le 2

22

h4 s le 2

71

NOTES1. Where the end connection is similar to type 2 or 3, but member flanges (or bulbs) are not aligned and brackets are not fitted, ω = 0.2. Where the end connection is similar to type 12 or 13, but a transverse girder is arranged in place of one of the supporting floors, special

consideration will be required.


SECTION 8Double bottom structure

8.1 Symbols and definitions

8.1.1 The symbols used in this Section are defined asfollows:L, T0 and TT as defined in Ch 1,5B as defined in Ch 1,5 but need not exceed B1

B1 = maximum distance between longitudinalbulkheads, in metres

dDB = Rule depth of centre girder, in mmdDBA = actual depth of centre girder, in mmhDB = head from top of inner bottom to top of

overflow pipe, in metresh4 = load head as defined in Table 6.7.1s = spacing of stiffeners, in mm.

8.2 General

8.2.1 In general, double bottoms need not be fitted innon-propelled units and column-stabilized units. Doublebottoms need not be fitted in oil storage units except whererequired by a National Administration. For surface-type units,see Ch 4,4.

8.2.2 Where double bottoms are f i tted on self-elevating units and other unit types, the scantlings are tocomply with this Section.

8.2.3 The requirements in this Section are, in general,applicable to double bottoms with stiffeners fitted parallel tothe hull bending compressive stress. When other stiffeningarrangements are proposed the scantlings will be speciallyconsidered, but the minimum requirements of this Section areto be complied with.

8.2.4 The arrangements of drainage wells, recessesand dump valves in the double bottom will be speciallyconsidered.

8.2.5 If it is intended to dry-dock the unit, girders andthe side walls of duct keels are to be continuous and thestructure is to have adequate strength to withstand the forcesimposed by dry-docking the unit.

8.2.6 Adequate access is to be provided to all parts ofthe double bottom. The edges of all holes are to be smooth.The size of the opening should not, in general, exceed 50 percent of the double bottom depth, unless edge reinforcementis provided. In way of ends of floors and fore and aft girdersat transverse bulkheads, the number and size of holes are tobe kept to a minimum, and the openings are to be circular orelliptical. Edge stiffening may be required in these positions.

8.2.7 Provision is to be made for the free passage ofair and water from all parts of tank spaces to the air pipesand suctions, account being taken of the pumping ratesrequired. To ensure this, sufficient air holes and drain holesare to be provided in all longitudinal and transverse non-watertight primary and secondary members. The drain holesare to be located as close to the bottom as is practicable,and air holes are to be located as close to the inner bottomas is practicable, see also Pt 3, Ch 8.



Local Strength


8.3.1 When a double bottom is fitted to a self-elevatingunit, the scantlings of the double bottom will be speciallyconsidered in accordance with Ch 4,3 but the generalrequirements of this Section are to be complied with.

8.3.2 The longitudinal extent of the double bottom willbe specially considered in respect of the design and safety ofthe unit but it should extend as far forward and aft as ispracticable. A double bottom need not be fitted in pre-loaddeep tanks or other wing deep tanks.

8.3.3 The depth of the double bottom at the centreline,dDB, is to be in accordance with 8.3.4 and the inner bottomis, in general, to be continued out to the unit’s side in such amanner as to protect the bottom to the turn of bilge. Whenpre-load wing deep tanks are fitted port and starboard, theinner bottom may be terminated at the deep tank logitudinalbulkheads.

8.3.4 The centre girder is to have a depth of not lessthan that given by:

dDB =

nor less than 650 mm. The centre girder thickness is to benot less than:

t =

nor less than 6,0 mm. The thickness may be determinedusing the value for dDB without applying the minimum depthof 650 mm.

8.3.5 Side girders are to be fitted below logitudinalbulkheads. In general, one side girder is to be fitted wherethe breadth, B, exceeds 14 m and two side girders are to befitted on each side of the centreline where B exceeds 21 m.Equivalent arrangements are to be provided wherelongitudinal bulkheads are fitted. The side girders are toextend as far forward and aft as practicable and are to have athickness not less than:

t =

nor less than 6,0 mm. In general, a vertical stiffener, having adepth not less than 100 mm and a thickness equal to thegirder thickness, is to be arranged midway between floors.

8.3.6 Watertight side girders are to have a platingthickness corresponding to the greater of the following:

(a)

(b) Thickness, t, as for deep tanks (see 7.2.1) using theload head h4 which in the case of double bottom tankswhich are inter-connected to side tanks or cofferdamsis not to be less than the head measured to the highestpoint of the side tank or cofferdam.

8.3.7 If the depth of the watertight side girdersexceeds 915 mm but does not exceed 2000 mm, the girdersare to be fitted with vertical stiffeners spaced not more than915 mm apart and having a section modulus not less than:

Z = 5,41dDBA2 hDB sk x 10–9 cm3

The ends of the stiffeners are to be sniped. Where thedouble bottom tanks are inter-connected with side tanks orcofferdams, or where the depth of the girder exceeds 2000 mm, the scantlings of watertight girders are to be notless than those required for deep tanks, see 7.2.1, and theends of the stiffeners are to be bracketed top and bottom.

t = 0,0075dDB + 2 k mm, or

0,0075dDB + 1 k mm

0,008dDB + 4 k mm

28B + 205 TT mm





Local Strength

8.3.8 Duct keels, where arranged, are to have athickness of side plates corresponding to the greater of thefollowing:

(a)

(b) Thickness, t, as for deep tanks, see 7.3, using the loadhead h4 which in the case of double bottom tankswhich are inter-connected to side tanks or cofferdamsis not to be less than the head measured to the highestpoint of the side tank or cofferdam.

8.3.9 The sides of the duct keels are, in general, to bespaced not more than 2,0 m apart. Where the sides of theducts keels are arranged on either side of the centreline orside girder, each side is, in general, to be spaced not morethan 2,0 m from the centreline or side girder. The innerbottom and bottom shell within the duct keel are to besuitably stiffened. The primary stiffening in the transversedirection is to be suitably aligned with the floors in theadjacent double bottom tanks. Where the duct keels areadjacent to double bottom tanks which are interconnectedwith side tanks or cofferdams, the stiffening is to be inaccordance with the requirements for deep tanks, see 7.3.Access to the duct keel is to be by watertight manholes ortrunks.

8.3.10 Inner bottom plating is, in general, to have athickness not less than:

t =

nor less than 6,5 mm.

8.3.11 The thickness of the inner bottom plating asdetermined in 8.3.10 is to be increased by 10 per cent inmachinery spaces but in no case is the thickness less than7,0 mm.

8.3.12 A margin plate, if fitted, is to have a thicknessthroughout 20 per cent greater than that required for innerbottom plating.

8.3.13 Where the double bottom tanks are commonwith side tanks or cofferdams, the thickness of the innerbottom plating is to be not less than that required for deeptanks, see 7.3, and the load head h4 is to be measured to thehighest point of the side tank or cofferdam.

8.3.14 Inner bottom stiffeners are in general to have asection modulus not less than 85 per cent of the Rule valuefor bottom shell stiffeners, see 3.3.1. When the inner bottomdesign loading is considerably less than 9,82TT kN/m2

(TT tonne-f/m2) the scantlings of the inner bottom stiffenerswill be specially considered. Where the double bottom tanksare inter-connected with side tanks or cofferdams, thescantlings are to be not less than those required for deeptanks, see 7.3.

0,00136 s + 660 k2 L TT 4

mm

t = 0,008dDB + 2 k mm, or

8.3.15 Plate floors are to be f i tted under heavymachinery items and under bulkheads and elsewhere at aspacing not exceeding 3,8 m. The thickness of non-watertight plate floors is to be not less than:

t =

nor less than 6,0 mm. The thickness need not be greaterthan 15 mm, but the ratio between the depth of the doublebottom and the thickness of the floor is not to exceed

. This ratio may, however, be exceeded if suitableadditional stiffening is fitted. Vertical stiffeners are to be fittedat each bottom shell stiffener, having a depth not less than150 mm and a thickness equal to the thickness of the floors.For units of length, L, less than 90 m, the depth is to be notless than 1,65L mm, with a minimum of 50 mm.

8.3.16 Watertight floors are to have thickness not lessthan:

(a) t =

(b) t =

whichever is the greater,but not to exceed 15 mm on floors of normal depth. Thethickness is also to satisfy the requirements for deep tanks(see 7.2.1) with the load head h4 measured to the highestpoint of the side tank, or cofferdam if the double bottom tankis inter-connected with these tanks. The scantlings of thestiffeners are to be in accordance with the requirements of7.2.1 for deep tanks, but in no case is the modulus to be lessthan:

Z = 5,41dDBA2 hDB sk x 10–9 cm3

Vertical stiffeners are to be connected to the inner bottomand shell stiffeners.

8.3.17 Between plate floors, transverse brackets havinga thickness not less than 0,009dDB mm are to be fitted,extending from the centre girder and margin plate to theadjacent longitudinal. The brackets, which are to be suitablystiffened at the edge, are to be fitted at every frame at themargin plate, and those at the centre girder are to be spacednot more than 1,25 m.

8.3.18 Where floors form the boundary of a sea inletbox, the thickness of the plating is to be the same as theadjacent shell, but not less than 12,5 mm. The scantlings ofstiffeners, where required are, in general, to comply with 7.3for deep tanks. Sniped ends for stiffeners on the boundariesof these spaces are to be avoided wherever practicable. Thestiffeners should be bracketed or the free end suitablysupported to provide alignment with backing structure.

8.4 Other unit types

8.4.1 Where a double bottom is fitted in the lower hullof column-stabilized units, tension-leg units, deep draughtcaissons or buoys, the scantlings of the double bottomstructure will be specially considered but the generalrequirements of 8.3 are to be complied with whereapplicable. The minimum scantlings of the double bottomstructure are to be in accordance with 8.4.2.

0,009dDB + 1 k mm, or

0,008dDB + 3 k mm, or

130 k

(0,009dDB + 1) k mm



8.4.2 The scantlings of tank boundaries are to complywith the requirements for tank bulkheads in Section 7 but theload head h4 is not to be taken less than the distancemeasured to T0. When the internal double bottomcompartment is a void space the scantlings of watertightboundaries are to comply with 7.5.1 and Table 6.7.1.

8.4.3 The boundaries of a sea inlet box is to complywith the requirements of 8.3.18.



Local Strength

SECTION 9Superstructures and deckhouses

9.1 General

9.1.1 The term ‘erection’ is used in this Section toinclude both superstructures and deckhouses.

9.1.2 This Section applies to erections on all types ofunits defined in Pt 3, Ch 2,2 except for erections on surface-type units which are to be in accordance with Ch 4,4. Unitswith a Rule length, L, greater than 150 m will be speciallyconsidered.

9.1.3 The scantlings of exposed bulkheads and decksof deckhouses are generally to comply with the requirementsof this Section, but increased scantlings may be requiredwhere the structure is subjected to local loadings greaterthan those defined in the Rules, see also 9.1.6. Where thereis no access from inside the house to below the freeboarddeck or into buoyant spaces included in stability calculations,or where a bulkhead is in a particularly sheltered location, thescantlings may be specially considered.

9.1.4 The scantlings of superstructures which form anextension of the side shell or which form an integral part ofthe unit’s hull and contribute to the overall strength of the unitwill be specially considered. The upper hull structure ofcolumn-stabilized units are to comply with Section 3.

9.1.5 Any exposed part of an erection which may besubject to immersion in damage stability conditions andwhich could result in down flooding is to have scantlings notless than required for watertight bulkheads given in Section 7.

9.1.6 The boundary bulkheads of accommodationspaces which may be subjected to blast loading inaccordance with Pt 7, Ch 3 are to comply with Ch 3,4 andpermissible stress levels are to satisfy the factors of safetygiven in Ch 5, 2.1.1 (c).

9.1.7 The scantlings of erections used for helicopterlanding areas are also to comply with Section 5.

9.1.8 For requirements relating to companionways,doors and hatches, see Chapter 7.





Local Strength

9.2 Symbols

9.2.1 The fol lowing symbols and definit ions areapplicable to this Chapter, unless otherwise stated:L, B, TT and Cb as defined in Ch 1,5.1.

b = breadth of deckhouse, at the positions underconsideration, in metres

k = higher tensile steel factor, see Ch 2,1.2le = span, of deck stiffeners, in metres, measured

between span points, see Ch 3,3.3ls = span, in metres, of erection stiffeners and is to

be taken as the ‘tween deck or house heightbut in no case less than 2,0 m

s = spacing of stiffeners, in metressb = standard spacing, in mm, of stiffeners, and is

to be taken as:(a) for 0,05L from the ends:

sb = 610 mm or that required by (b),whichever is the lesser

(b) elsewhere:sb = 470+1,67L mmbut forward of 0,2L from the forwardperpendicular sb is not to exceed 700 mm

B1 = actual breadth of unit at the section underconsideration, measured at the weather deck,in metres

D = moulded depth of unit, in metres, to theuppermost continuous deck

X = distance, in metres, between the afterperpendicular and the bulkhead underconsideration. When determining thescantl ings of deckhouse sides, thedeckhouse is to be subdivided into parts ofapproximately equal length not exceeding0,15L each, and X is to be measured to themid-length of each part

α = a coefficient given in Table 6.9.1

β =

=

Cb is to be taken not less than 0,6 nor greaterthan 0,8. Where the aft end of an erection isforward of amidships, the value of Cb used fordetermining β for the aft end bulkhead is tobe taken as 0,8

γ = vert ical distance, in metres, from themaximum transit waterline to the mid-point ofspan of the bulkhead stiffener, or the mid-point of the plate panel, as appropriate

δ = 1,0 for exposed machinery casings and

elsewhere, but in no case to

be taken less than 0,475λ = a coefficient given in Table 6.9.2

0,3 + 0,7 bB1

1,0 + 1,5 (XL

– 0,45

Cb + 0,2 )2

for XL

> 0,45

1,0 + (XL

– 0,45

Cb + 0,2 )2

for XL

≤ 0,45


9.3 Definition of tiers

9.3.1 The first, or the lowest tier, is an erection situatedon the freeboard deck on self-elevating units or on theuppermost strength deck of other unit types covered in thisSection. The second tier is the next tier above the lowest tier,and so on.

9.4 Erections on self-elevating units

9.4.1 The design pressure head, h, to be used in thedetermination of erection scantlings is to be taken as:

h = αδ (βλ – γ) m

9.4.2 In no case is the design pressure head to betaken as less than the following:(a) Lowest tier of unprotected fronts:

minimum h = 2,5 + 0,01L m(b) All other locations:

minimum h = 1,25 + 0,005L m

9.4.3 The plating thickness, t, of exposed lowest tierfronts is to be not less than:

t =

but in no case is the thickness to be less than 7,0 mm.

0,0036s kh mm

Table 6.9.1 Values of α

Position α

Lowest tier – unprotected front

Second tier – unprotected front

Third tierand above – unprotected front

All tiers – protected frontsAll tiers – sides

All tiers – aft end where aftof amidships

All tiers – aft end whereforward of amidships

2,0 + 0,0083L

1,0 + 0,0083L

0,7 + 0,001L – 0,8 XL

0,5 + 0,0067L

0,5 + 0,001L – 0,4 XL

Length L λ Expression for λin metres

20 0,8930 1,7640 2,5750 3,3460 4,0770 4,7680 5,4190 6,03

110 7,16130 8,18150 9,10

L ≤ 150 m

λ = L10

e– L300 – 1 – ( L

150)2

Table 6.9.2 Values of λ


9.4.4 The plating thickness, t, of side, aft end andupper tier fronts of all erections other than the sides oferections where these are an extension of the side shell, is tobe not less than:

t =but in no case is the thickness to be less than:(a) for the lowest tier:

t =

but not less than 5,0 mm(b) for the upper tiers:

t =

but not less than 5,0 mm

9.4.5 The modulus of stiffeners, z, on exposed lowesttier fronts is to be not less than:

z = 0,0044 hs ls2 k cm3

9.4.6 The modulus of stiffeners, z, on side, aft end andupper tier fronts of all erections, other than the sides oferections where these are an extension of the side shell is tobe not less than:

z = 0,0035 hs ls2 k cm3

9.4.7 The end connections of stiffeners are to be asgiven in Table 6.9.3.

9.4.8 Where the exposed side of an erection is closeto the side shell of the unit, the scantlings may be required toconform to the requirements for exposed bulkheads ofunprotected house fronts.

9.4.9 The scantlings of jackhouses will be speciallyconsidered, but are not to be less than the scantlings thatwould be required for an erection at the same location.

4,0 + 0,01L k mm

5,0 + 0,01L k mm

0,003s kh m



Local Strength

9.5 Erections on other unit types

9.5.1 Where the erection can be subjected to waveforces the scantlings of exposed ends and sides of erectionsare to comply with 9.4.

9.5.2 When the erection is not subjected to waveforces in any condition then the structure is to be suitable forthe maximum design loadings but the minimum scantlings ofexposed sides and ends of all erections is to be not lessthan:(a) for the lowest tier:

t = , but not less than

5,0 mm.(b)for the upper tiers:

t = , but not less than

5,0 mm.

9.5.3 The modulus of stiffeners, z, of exposed sidesand ends of all erections is to be not less than:

z = 0,0035 hs ls2 k cm3

where h = 1,25 + 0,005L m

9.5.4 The end connections of stiffeners not subjectedto wave loadings are to be as given in Table 6.9.4.

9.6 Deck plating

9.6.1 In general, the thickness of erection deck platingis to be not less than that required by Table 6.9.5.

4,0 + 0,01L k mm

5,0 + 0,01L k mm


Table 6.9.3 Self-elevating units stiffener endconnections

Table 6.9.4 Other unit types stiffener end connections

1. Front stiffeners of lower tiersand all stiffeners on lowertiers of exposed machinerycasings

2. Front stiffeners of upper tiers

3. Side stiffeners of lower tierswhere two or more tiers arefitted

4. Side stiffeners if only one tieris fitted, and aft endstiffeners of afterdeckhouses on deck towhich D is measured

5. Side stiffeners of upper tiers

6. Aft end stiffeners except ascovered by item 4

7. All stiffeners on exposedmachinery casings except ascovered by item 1

Bracketed

May be unattached

Bracketed unless stiffenermodulus is increased by 20 percent and ends are welded tothe deck all around

See Chapter 8.

May be unattached

May be unattached

Attached with 6,5 cm2 of weld

Position Attachment at top and bottom

Position Attachment at top and bottom

1. Side stiffeners of lower tierswhere two or more tiers arefitted

2. Side stiffeners if only one tieris fitted.

3. All other stiffeners

Bracketed unless stiffenermodulus is increased by 20 per cent and ends arewelded to the deck allaround

See Chapter 8.

May be unattached

L ≤ 100 m L > 100 m

Thickness of deck plating, in mm

Position

Top of first tiererection

Top of second tiererection

Top of third tierand above

4,5 + 0,02L kssb

5,0 + 0,02L kssb

5,5 + 0,02L kssb but

notlessthan5,0mm 6,5 ks

sb

7,0 kssb

7,5 kssb

NOTEFor units not subjected to wave loading, see 9.6.2.

Table 6.9.5 Thickness of deck plating




Local Strength

9.6.2 For erections not subjected to wave forces in anycondition, the thickness of erection deck plating for all tiersneed not exceed the requirements given in Table 6.9.5 forthird tier erections, using:

sb = 470 + 1,67L

9.6.3 When decks are fitted with approved sheathing,the thickness derived from Table 6.9.5 may be reduced by 10 per cent for a 50 mm sheaving thickness, or five per centfor 25,5 mm, with intermediate values in proportion. Thesteel deck is to be coated with a suitable material in order toprevent corrosive action, and the sheathing or composition isto be effectively secured to the deck. Inside erections thethickness may be reduced by a further 10 per cent. In nocase is the deck thickness to be less than 5,0 mm.

9.7 Deck stiffening

9.7.1 Deck stiffeners on erections are to have asection modulus, Z, not less than:

Z = 0,0048h6s le2k cm3, but in no case less than:Z = 0,025s cm3

where the load head, h6, is to be taken as not less than:on first tier decks 0,9 mon second tier 0,6 mon third tier decks and above 0,45 m

but where the deck can be subjected to weather loading theload, h6, is to be increased in accordance with therequirements given in Table 6.2.1.

9.7.2 When erection decks are subjected to specifiedloadings greater than the heads defined in 9.7.1 or aresubjected to concentrated loads, equivalent load heads areto be used.

9.8 Deck girders and transverses

9.8.1 The scantlings of deck girders and transverseson erection decks are to be in accordance with therequirements of Table 6.4.3, using the appropriate load head,Hg, determined from 9.7.1 or 9.7.2.

9.9 Strengthening at ends and sides of erections

9.9.1 Web frames or equivalent strengthening are tobe arranged to support the sides and ends of large erections.

9.9.2 These web frames should be spaced about 9 mapart and are to be arranged, where practicable, in line withwatertight bulkheads below. Webs are also to be arranged inway of large openings, boats davits and other points of highloading.

9.9.3 Arrangements are to be made to minimize theeffect of discontinuities in erections. All openings cut in thesides are to be substantially framed and have well roundedcorners. Continuous coamings or girders are to be fittedbelow and above doors and similar openings. Erections areto be strengthened in way of davits.

9.9.4 Adequate support under the ends of erections isto be provided in the form of webs, pillars, diaphragms orbulkheads in conjunction with reinforced deck beams.

9.9.5 At the corners of deckhouses and in way ofsupporting structures, attention is to be given to theconnection to the deck, and doublers or equivalentarrangements should generally be fitted.

9.10 Unusual designs

9.10.1 Where superstructures or deckhouses are ofunusual design, the strength is to be not less than thatrequired by this Section for a conventional design.

9.11 Aluminium erections

9.11.1 Where an aluminium al loy complying with Pt 2, Ch 8 is used in the construction of erections, thescantlings of these erections are to be increased (relative tothose required for steel construction) by the percentagesgiven in Table 6.9.6.

9.11.2 The thickness, t, of aluminium alloy members isto be not less than:

t = 2,5 + 0,022dw mm but need not exceed 10 mmwhere

dw = depth of the section, in mm.

9.11.3 The minimum moment of inertia, I, of aluminiumalloy stiffening members is to be not less than:

I = 5,25Z l cm4

Where l is the effective length of the member le or ls, inmetres, as defined in 9.2 and Z is the section modulus of thestiffener and attached plating in accordance with 9.4 and 9.5taking k as 1.

9.11.4 Where aluminium erections are arranged above asteel hull, details of the arrangements in way of the bimetallicconnections are to be submitted.

9.11.5 For aluminium alloy helicopter decks, see Section6.

9.12 Fire protection

9.12.1 Fire protection of aluminium alloy erections is tobe in accordance with the fire safety Regulations of theappropriate National Administration, see Pt 7, Ch 3.

9.12.2 Where it is proposed to use aluminium alloy foritems or equipment in hazardous areas, incendive sparkingmay constitute a risk and full details are to be submitted forconsideration.


Item Percentage increase

Fronts, sides, aft ends, unsheathed deck plating 20

Decks sheathed in accordancewith 9.6.3 10

Deck sheathed with wood, and on which the plating is fixed to the wood sheathing at the centre of each beam space Nil

Stiffeners and beams 70

Scantlings of small isolated houses Nil

Table 6.9.6 Percentage increase of scantlings


SECTION 10Bulwarks and other means for the protection of crew and other personnel

10.1 General requirements

10.1.1 Bulwarks or guardrails are to be provided at theboundaries of exposed weather and superstructure decksand deckhouses. Bulwarks or guardrails are to be not lessthan 1,0 m in height measured above sheathing, and are tobe constructed as required by 10,2 and 10,3. Considerationwill be given to cases where this height would interfere withthe normal operation of the unit.

10.1.2 The freeing arrangements in bulwarks are to bein accordance with 10.4.

10.1.3 Guardrails, as required by 10.1.1, are to consistof at least three courses and the opening below the lowestcourse is not to exceed 230 mm. The other courses are tobe spaced not more than 380 mm apart. Where practicable,a toe plate 150 mm high is to be fitted below the lowestcourse. In the case of units with rounded gunwales, theguard-rail supports are to be placed on the flat of the deck.

10.1.4 Satisfactory means, in the form of guardrails, life-lines, handrails, gangways, underdeck passageways or otherequivalent arrangements, are to be provided for theprotection of the crew in getting to and from their quarters,the machinery space and al l other parts used in thenecessary work of the unit. For units with production andprocess plant, see also Pt 7, Ch 3.

10.1.5 Where access openings are required in bulwarksor guardrails they are to be fitted with suitable gates and ingeneral chains are not to be used where a person could fallinto the sea.

10.1.6 Where gangways on a trunk are provided bymeans of a stringer plate fitted outboard of the trunk sidebulkheads (port and starboard), each gangway is to be asolid plate, effectively stayed and supported, with a clearwalkway at least 450 mm wide, at or near the top of thecoaming, with guard-rails complying with 10.1.3.

10.1.7 Where a National Administration have additionalrequirements for the protection of the crew or personnel onboard it is the Owners’ responsibility to comply with allnecessary Regulations.

10.2 Construction of bulwarks subject to wave loading

10.2.1 Plate bulwarks are to be stiffened by a strong railsection and supported by stays from the deck. The spacingof these stays forward of 0,07L from the forwardperpendicular is to be not more than 1,2 m on surface-typeunits and not more than 1,83 m on other unit types.Elsewhere, bulwark stays are to be not more than 1,83 mapart. Where bulwarks are cut to form a gangway or otheropening, stays of increased strength are to be fitted at theends of the openings. Bulwarks are to be adequatelystrengthened where required to support additional loads orattachments and in way of mooring pipes the plating is to bedoubled or increased in thickness and adequately stiffened.

10.2.2 Bulwarks should not be cut for gangway or otheropenings near the breaks of superstructures, and are also tobe arranged to ensure their freedom from main structuralstresses.



Local Strength

10.2.3 The section modulus, Z, at the bottom of thebulwark stay is to be not less than:

Z = (33,0 + 0,44L) h2s cm3

whereh = height of bulwark from the top of the deck

plating to the top of the rail, in metress = spacing of the stays, in metres, see 10.2.1.L = length of unit, in metres, but to be not greater

than 100 m.

10.2.4 In the calculation of the section modulus, onlythe material connected to the deck is to be included. Thebulb or flange of the stay may be taken into account whereconnected to the deck, and where, at the ends of the unit,the bulwark plating is connected to the sheerstrake, a widthof plating not exceeding 600 mm may also be included. Thefree edge of the stay is to be stiffened.

10.2.5 Bulwark stays are to be supported by, or to be inline with, suitable underdeck stiffening, which is to beconnected by double continuous fillet welds in way of thebulwark stay connection.

10.2.6 When the bulwarks are required to supportattachments or equipment for local operational or functionalloads they are to be suitably strengthened.

10.3 Guardrail construction

10.3.1 Guardrails are, in general, to be constructed inaccordance with a recognized Standard and the arrangementand spacing of guardrails are to comply with 10.1.3.

10.3.2 Stanchions are to be spaced not more than 1,5 m apart and the guardrails and their supports are to bedesigned to withstand a horizontal loading of 0,74 kN/mapplied at the top rai l . The permissible stresses inassociation with this loading are to satisfy the factors ofsafety given in Ch 5,2.1.1(a).

10.3.3 The stanchions and stays are to be supported bysuitable underdeck stiffening.

10.3.4 When guardrai ls are required to supportattachments for local operational or functional loads they areto be suitably strengthened.

10.4 Helicopter landing area

10.4.1 Safety nets are to be installed around the decklanding area extending at least 1500 mm out from theperimeter. The netting is to be of approved material and of aflexible nature.

10.4.2 The safety net is to be supported at its outeredge and intermediate supports are to be spaced about 1,9 m apart. The supports are to be designed to withstand aconcentrated load of 1,3 kN applied at any point on thesupports. The permissible stresses are to satisfy the factorsof safety given in Ch 5,2.1.1(a).





Local Strength

10.5 Freeing arrangements

10.5.1 Surface-type oil storage units are to have openrails for at least half the length of the exposed part of theweather deck. Alternatively, if a continuous bulwark is fitted,the minimum freeing area is to be at least 33 per cent of thetotal area of the bulwark. The freeing area is to be placed inthe lower part of the bulwark. Where superstructures areconnected by trunks, open rails are to be fitted for the wholelength of the exposed part of the freeboard deck.

10.5.2 For self-elevating units and on surface-type unitsexcept where the additional requirements of 10.5.1 apply therequirements of 10.5.3 to 10.5.18 are applicable.

10.5.3 Where bulwarks on the weather portions offreeboard or superstructure decks form wells, ampleprovision is to be made for rapidly freeing the decks of largequantities of water by means of freeing ports, and also fordraining them.

10.5.4 The minimum freeing area on each side of theunit, for each well on the freeboard deck or raised quarterdeck, where the sheer in the well is not less than the standardsheer required by the International Convention on Load Lines,1966, is to be derived from the following formulae:(a) where the length, l, of the bulwark in the well is 20 m or

less: area required = 0,7 + 0,035 l m2

(b) where the length, l, exceeds 20 m:area required = 0,07 l m2

NOTE

l need not be taken greater than 0,7LL, where LL is the loadline length of the unit in accordance with the InternationalConvention on Load Lines, 1966.

10.5.5 If the average height of the bulwark exceeds 1,2 m or is less than 0,9 m, the freeing area is to be increasedor decreased, respectively, by 0,004 m2 per metre of length ofwell for each 0,1 m increase or decrease in height respectively.

10.5.6 The minimum freeing area for each well on a firsttier superstructure is to be half the area calculated from 10.5.4.

10.5.7 Two-thirds of the freeing port area required is tobe provided in the half of the well nearest to the lowest pointof the sheer curve.

10.5.8 When the deck has little or no sheer, the freeingarea is to be spread along the length of the well.

10.5.9 In units with no sheer, the freeing area ascalculated from 10.5.4 is to be increased by 50 per cent.Where the sheer is less than the standard, the percentage isto be obtained by linear interpolation.

10.5.10 Where the length of the well is less than 10 m, orwhere a deckhouse occupies most of the length, the freeingport area will be specially considered but in general need notexceed 10 per cent of the bulwark area.

10.5.11 Where it is not practical to provide sufficientfreeing port area in the bulwark, credit can be given for bollardand fairlead openings where these extend to the deck.

10.5.12 Where a unit f i tted with bulwarks has acontinuous trunk or coamings, the requirements of 10.5.1 areto be complied with.

10.5.13 Where a deckhouse has a breadth less than 80per cent of the beam of the unit, or the width of the sidepassageways exceed 1,5 m, the arrangement is consideredas one well. Where a deckhouse has a breadth equal to ormore than 80 per cent of the beam of the unit, or the width ofthe side passageways does not exceed 1,5 m, or when ascreen bulkhead is fitted across the full breadth of the unit,this arrangement is considered as two wells, before and abaftthe deckhouse.

10.5.14 Adequate provision is to be made for freeingwater from superstructures which are open at either or bothends and from all other decks within open or partially openspaces in which water may be shipped and contained.

10.5.15 Suitable provision is also to be made for therapid freeing of water from recesses formed bysuperstructures, deckhouses and deck plant, etc., in whichwater may be shipped and trapped. Deck equipment is notto be stowed in such a manner as to obstruct unduly the flowof water to freeing ports.

10.5.16 The lower edges of freeing ports are to be asnear to the deck as practicable, and should not be more than100 mm above the deck.

10.5.17 Where freeing ports are more than 230 mm high,vertical bars spaced 230 mm apart may be accepted as analternative to a horizontal rail to limit the height of the freeingport.

10.5.18 Where shutters are fitted, the pins or bearingsare to be of a non-corrodible material, with ample clearanceto prevent jamming. The hinges are to be within the upperthird of the port.

10.6 Deck drainage

10.6.1 Adequate drainage arrangements by means ofscuppers are to be fitted as required by Ch 7,10.






SECTION 1General

1.1 Application

1.1.1 This Chapter gives the minimum classificationrequirements for watertight and weathertight integrity andload line application.

1.1.2 The requirements for intact and damage stabilityand the assignment of load lines are to be in accordance withPt 1, Ch 2,1.

1.1.3 The requirements in this Chapter may bemodif ied where necessary to take into account therequirements of the appropriate National Administrationresponsible for the intact and damage stability of the unit.

1.2 Plans to be submitted

1.2.1 The following plans are to be submitted forapproval:• Deck drainage, scuppers and sanitary discharges.• Ventilators and air pipes (including closing appliances).• Watertight doors and hatch covers (internal and

external) showing scantlings, coamings and closingappliances.

• Weathertight doors and hatch covers showing scantlings, coamings and closing appliances.

• Windows and side scuttles.• Schematic diagrams of local and remote control of

watertight and weathertight doors and hatch coversand other closing appliances.

• Location of control rooms.• Freeing arrangements.

Section

1 General

2 Definitions

3 Installation layout and stability

4 Watertight integrity

5 Load lines

6 Miscellaneous openings

7 Tank access arrangements and closing appliances in oil storage units

8 Ventilators

9 Air and sounding pipes

10 Scuppers and sanitary discharges

Watertight and Weathertight Integrity andLoad Lines

1.2.2 The following plans are to be submitted forinformation:• General arrangement.• Arrangement plan indicating the defined watertight

boundaries of spaces included in the buoyancy.• Arrangement plans of watertight doors and hatches.• Details of intact and worst damage stability waterlines

shown in elevations and plan views.• Freeboard plan showing the maximum design operating

draughts in accordance with Load Line Regulations andindicating the position of all external openings and theirclosing appliances.

• Location of down flooding openings.• Trim and stability booklet, see Pt 1, Ch 2.


2.7 Intact stability waterline

2.7.1 The intact stability waterline is the most severeinclined waterline to satisfy the range of intact stability definedin the applicable stability Regulations, see 1.1.2.

2.8 Down flooding

2.8.1 Down flooding means any flooding of the interiorof any part of the buoyant structure of a unit throughopenings which cannot be closed watertight or weathertight,as appropriate, in order to meet the intact or damage stabilitycriteria or which are required for operational reasons to be leftopen.

2.8.2 The down flooding angle is the least angle ofheel at which openings in the hull, superstructure ordeckhouses, which cannot be closed weathertight, immerseand allow flooding to occur.

2.8.3 Intact stability is to comply with Pt 1, Ch 2,1.





SECTION 2Definitions

2.1 General

2.1.1 The freeboard deck is normally the uppermostcomplete deck exposed to weather and sea, which haspermanent means of closing all openings in the weather part,and below which all openings in the sides of the unit are fittedwith permanent means of watertight closing. For semi-submersible units, see also 5.2.4.

2.2 Freeboard

2.2.1 Freeboard is the distance measured verticallydownwards amidships from the upper edge of the deck lineto the upper edge of the related load line.

2.3 Weathertight

2.3.1 A closing appliance is considered weathertight ifit is designed to prevent the passage of water into the unit inany sea conditions.

2.3.2 Generally, all openings in the freeboard deck andin enclosed superstructures are to be provided withweathertight closing appliances.

2.4 Watertight

2.4.1 A closing appliance is considered watertight if itis designed to prevent the passage of water in either directionunder a head of water for which the surrounding structure isdesigned.

2.4.2 Generally, all openings below the freeboard deckin the outer shell boundaries and in main watertight decksand bulkheads are to be fitted with permanent means ofwatertight closing.

2.4.3 When the Rules require closing appliances withclosely bolted covers, the pitch of the securing bolts is not toexceed five diameters.

2.5 Position 1 and Position 2

2.5.1 For the purpose of Load Line conditions ofassignment, there are two basic positions of hatchways,doorways and ventilators defined as follows:Position 1 – Upon exposed freeboard and raised

quaterdecks, and exposed superstructuredecks within the forward 0,25LL.

Position 2 – Upon exposed superstructure decks abaft theforward 0,25LL.

where LL = the load line length in accordance with theInternational Convention on Load Lines, 1966.

2.5.2 The application to column-stabilized units will bespecially considered, see 5.2.4.

2.6 Damage waterline

2.6.1 The damage waterline is the final equilibriumwaterline after damage defined in the applicable stabilityRegulations, see 1.1.2.


SECTION 3Installation layout and stability

3.1 Control rooms

3.1.1 Control rooms essential for the safe operation ofthe unit in an emergency are to be situated above zones ofimmersion after damage, as high as possible and as near acentral posit ion on the unit as is practicable. Therequirements for the central ballast control station on column-stabilized units are to be in accordance with Pt 6, Ch 1,2.8.

3.2 Damage zones

3.2.1 The extent of defined damage is to be inaccordance with the applicable damage stability Regulations.

3.2.2 All piping, ventilation ducts and trunks, etc.,should, where practicable, be situated clear of the defineddamage zones. When piping, ventilation ducts and trunks,etc., are situated within the defined extent of damage, theyare to be assumed damaged and positive means of closureare to be provided at watertight subdivisions to precludeprogressive flooding of other intact spaces, see also Pt 5, Ch 11,1.2.

3.2.3 In addition to the defined damages referred to in3.2.1, compartments with a boundary formed by the bottomshell of the unit are to be considered flooded individuallyunless agreed otherwise with LR.





SECTION 4Watertight integrity

4.1 Watertight boundaries

4.1.1 All units are to be provided with watertightbulkheads, decks and flats to give adequate strength and thearrangements are to suit the requirements for subdivision,floodability and damage stability.

4.1.2 The number and disposit ion of watert ightbulkheads are to comply with Ch 3,5.

4.1.3 The strength of watertight subdivisions are tocomply with Ch 6,7.

4.1.4 Surface-type units are to be fitted with a collisionbulkhead in accordance with LR’s Rules and Regulations forthe Classification of Ships (hereinafter referred to as the Rulesfor Ships).

4.2 Tank boundaries

4.2.1 Deep tanks for fresh water, fuel oil or any othertanks which are not normally kept filled in service are, ingeneral, to have wash bulkheads or divisions.

4.2.2 Tank bulkheads and watertight divisions are tohave adequate strength for the maximum design pressurehead in normal operating and damage conditions and thescantlings are to comply with Ch 6,7.

4.3 Boundary penetrations

4.3.1 Where internal boundaries are required to bewatertight to meet damage stability requirements, thenumber of openings in such boundaries is to be reduced tothe minimum compatible with the design and proper workingof the unit.

4.3.2 Where piping, including air and overflow pipes,ventilation ducts, shafting, electric cable runs, etc., penetratewatertight boundaries, arrangements are to be made toensure the watertight integrity of the boundary. Details of thearrangements are to be submitted for approval.

4.3.3 No openings such as manholes, watertightdoors, pipelines or other penetrations are to be cut in thecollision bulkhead of surface-type units, except as permittedby Pt 5, Ch 12,4.2.4.

4.3.4 Where pipelines or ducts serve more than onecompartment, satisfactory arrangements are to be providedto preclude the possibility of progressive flooding through thesystem to other spaces in the event of damage, see also 3.2.

4.3.5 Where piping systems and ventilation ducts aredesigned to watertight standards and are suitable for themaximum design pressure head in damage conditions, theyare to be provided with valves at the boundaries of eachwatertight compartment served.

4.3.6 Ventilation ducts which are of non-watertightconstruction are to be provided with valves where theypenetrate watertight subdivision boundaries.





4.3.7 Where valves are provided at watert ightboundaries to maintain watertight integrity in accordance with4.3.5 and 4.3.6, these valves are to be capable of beingoperated from a pump room or other normally mannedspace, a weather deck, or a deck which is above the finalwaterline after flooding. In the case of a column-stabilizedunit, this would be the central ballast control station. Valveposition indicators should be provided at the remote controlstation, weather deck or a normally manned space.

4.3.8 For self-elevating units, the ventilation systemvalves required to maintain watertight integrity should be keptclosed when the unit is afloat. Necessary ventilation in thiscase should be arranged by alternative approved methods.

4.4 Internal openings related to damage stability

4.4.1 The requirements for the operation, alarmdisplays and controls of watertight doors and hatch coversand other closing appliances are given in Pt 7, Ch 1,8.

4.4.2 Internal access openings fitted with appliancesto ensure watertight integrity, which are used during theoperation of the unit while afloat, are to comply with thefollowing:(a) Watertight doors and hatch covers which are frequently

used may normally be open provided the closing appliances are capable of being remotely controlledfrom a damage central control room on a deck which isabove any final waterline after flooding and are also tobe operable locally from each side of the bulkhead.Indicators are to be provided in the control room showing whether the doors are open or closed.

(b) The requirements regarding remote control in (a) maybe dispensed with for those doors or hatch coverswhich are normally closed, provided an alarm system(e.g. light signals) is arranged, showing personnel bothlocally and in the control room whether the closingappliances in question are open or closed. In addition,a notice to the effect that the closing appliance is to beclosed while afloat and is only to be used temporarily, isto be displayed locally.

(c) The closing appliances are to have strength, packingand means for securing which are sufficient to maintainwatertightness under the maximum design waterpressure head of the watertight boundary underconsideration.

4.4.3 Internal openings fitted with appliances to ensurewatertight integrity, which are to be kept permanently closedwhile afloat, are to comply with the following:(a) A notice to the effect that the opening is always to be

kept closed while afloat is to be attached to the closingappliances in question.

(b) Opening and closing of such closing appliances are tobe noted in the unit’s logbook, or equivalent.

(c) Manholes fitted with gaskets and closely bolted coversneed not be dealt with as under (a).

(d) The closing appliances are to have strength, packingand means for securing which are sufficient to maintainwatertightness under the maximum water pressurehead of the watertight boundary under consideration.

4.5 External openings related to damagestability

4.5.1 Where watertight integrity is dependent onexternal openings which are used during the operation of theunit while afloat, they are to comply with the following:(a) The lower edge of openings of air pipes (regardless of

their closing appliances) is to be above the final equilibrium damage waterline including wind heeleffects.

(b) The lower edge of ventilator openings, doors andhatches with manually operated means of weathertightclosures is to be above the final equilibrium damagewaterline including wind heel effects.

(c) Openings such as manholes fitted with gaskets andclosely bolted covers, and side scuttles and windows ofthe non-opening type with inside hinged deadlightsmay be submerged.

(d) Scuppers and discharges are to be fitted with closingappliances, see 7.2.

4.5.2 Where watertight integrity is dependent uponexternal openings which are permanently closed during theoperation of the unit while afloat, such openings are tocomply with the requirements of 4.4.3.

4.5.3 External watertight doors and hatch covers oflimited size which are used while afloat may be acceptedbelow the worst damage waterline, including wind heeleffects, provided they are on or above the freeboard deckand the closing appliances comply with the requirements of4.4.2(a) and (b).

4.6 Strength of watertight doors and hatchcovers

4.6.1 The symbols used in this sub-Section are asfollows:

d = distance between securing devices, in metres

f1 = but not greater than 1

hD = design pressure head, in metres, measuredvertically from the bottom of the door to theworst damage waterline plus 5 m

k = higher tensile steel factor as defined in Ch 2,1.2

ls = span of stiffener between support points, inmetres

s = spacing of stiffeners, in mmPI = packing line pressure along edges, in N/cm

(kgf/cm), but not less than 50 (5,1).

4.6.2 Closing appliances for internal and externalopenings are to have scantlings in accordance with this sub-Section and are to satisfy the requirements of 4.4 and 4.5respectively.

4.6.3 In general, watertight closing appliances are tobe designed to withstand the design pressure head fromboth sides of the appliance unless the mode of failure basedon the damage stability criteria can only result in one-sidedpressure loading.

4.6.4 The thickness of plating, t, subjected to lateralpressure in damage conditions is to be not less than:

t = but not less than 8 mm0,0048s fl hD k mm

1,1 – s2500ls



4.6.5 The section modulus, z, of panel stiffeners fittedin one direction and edge stiffeners is not to be less than:

z = 0,0065 s k hD ls2 cm3 but not less than 15 cm3

The section modulus of secondary panel stiffeners may alsobe determined from the above formula, but doors withstiffeners designed as grillages will be specially considered.

4.6.6 The moment of inertia, I, of edge stiffeners is ingeneral not to be less than:

I = 0,8PI d4 cm4 (8PI d4 cm4)

4.6.7 Securing devices for closing appliances are to bedesigned for water pressure acting on the opposite side ofthe appliance to which they are positioned, see also 4.6.3.

4.6.8 The strength of the bulkhead and deck framingin way of watertight closing appliances is to comply with therequirements of Ch 6,7.

4.6.9 Watert ight closing appl iances are to behydraulically tested in accordance with the requirements ofTable 1.6.2 in Chapter 1. In general, the test is to be carriedout before the appliance is fitted to the unit. The test pressureis to be applied separately to both sides of the appliance, see also 4.6.3.

4.6.10 After installation in the unit watertight closingappliances are to be hose tested in accordance with therequirements of Table 1.6.1 in Chapter 1, and functional testsare to be carried out to verify the satisfactory operation of theappliance, its control and alarm functions, as required by Pt 7, Ch 1,8.

4.7 Weathertight integrity related to stability

4.7.1 In general, external openings f i tted withappliances to ensure weathertight integrity of the unit whileafloat are not to submerge when the unit is inclined to anangle equal to the first intercept of the righting moment andwind heel ing moment arms in any intact or damagecondition.

4.7.2 In addit ion to the requirements of 4.7.1,openings on column-stabilized and tension-leg units are notto submerge within Zones A or B as shown in Fig. 7.4.1,except external openings fitted with appliances to ensureweathertight integrity which comply with the following maysubmerge:• Access openings which are permanently closed while

afloat and which comply with the requirements of 4.4.3.• Access openings which are used while afloat and which

comply with the requirements of 4.4.2.Where chain locker openings are situated within Zones A andB in Fig. 7.4.1, the chain locker is to be fitted with remotemeans to detect flooding and an installed dewatering systemin accordance with Pt 5, Ch 12,9.2.

4.7.3 External openings which would become whollyor partially submerged in meeting the stability area ratio andrange requirements are to be fitted with suitable weathertightclosing appliances.





Fig. 7.4.1Minimum weathertight integrity requirements for

column-stabilized and tension-leg units

��

4407/83

4 m

Final damage waterline

Initial waterline

A – 4 m zone of weathertightnessB – 7° zone of weathertightness, see also 5.2.6

A

B7°






SECTION 5Load lines

5.1 General

5.1.1 Any unit to which a load line is required to beassigned under the applicable terms of the InternationalConvention on Load Lines, 1966 (hereinafter referred to asLoad Line Convention), is to be subject to compliance withthe Convention, see 1.1.2. For semi-submersible units, seealso 5.2.

5.1.2 The requirements of the Load Line Convention,with respect to weathertightness and watertightness ofdecks, superstructures, deckhouses, doors, hatchwaycovers, other openings, ventilators, air pipes, scuppers, inletsand discharges, etc., are taken as a basis for all units in theafloat conditions.

5.1.3 The requirements for hatchways, doors andventilators are dependent upon the position on the unit asdefined in 2.5.

5.1.4 Units which cannot have freeboard computed bynormal methods laid down by the Convention will have thepermissible draughts determined on the basis of meeting theapplicable intact stability, damage stability and structuralrequirements for transit and operating conditions while afloat.In no case is the draught to exceed that permitted by theLoad Line Convention, where applicable.

5.1.5 All units are to have load line marks whichdesignate the maximum permissible draught when the unit isin the afloat condition. Such markings are to be placed atsuitable visible locations on the structure, to the satisfactionof LR. These marks, where practicable, are to be visible tothe person in charge of mooring, lowering or otherwiseoperating the unit.


5.2.1 Load lines for column-stabilized and tension-legunits are to be based on the following:• The strength of the structure.• The air gap between the maximum operating waterline

and the bottom of the upper hull structure.• The intact and damage stability requirements.

5.2.2 The conditions of assignment are to be based onthe requirements of the Load Line Convention. TheRegulations of the relevant National Administration are also tobe complied with, see 1.1.2.

5.2.3 In general, the heights of hatch and ventilatorcoamings, air pipes, door sills, etc., in exposed positions andall closing appliances are to be determined by considerationof both intact and damage stability requirements.

5.2.4 The freeboard deck and reference deck fromwhich the air gap is measured, is normally taken as thelowest continuous deck exposed to weather and sea, andwhich has permanent means of closing and below which allopenings are watertight and permanently closed at sea.

5.2.5 Side scuttles and windows, including those ofnon-opening type, or other similar openings, are not to befitted below the freeboard deck, as defined in 5.2.4.

5.2.6 In addition to the stability requirements in 4.7,the upper deck and the boundaries of the enclosed upperhull structure between the upper deck and the freeboarddeck are to be made weathertight.

5.2.7 Special consideration will be given to the positionof openings which cannot be closed in emergencies, such asair intakes for emergency generators.


5.3.1 Load lines and conditions of assignment for self-elevating units when afloat in transit conditions will be subjectto the applicable terms of the Load Line Convention. A loadline where assigned, is not applicable to self-elevating unitswhen resting on the sea bed, or when lowering to or raisingfrom such position. The Regulations of the relevant NationalAdministration are also to be complied with, see 1.1.2.

5.3.2 In general, the heights of hatch and ventilatorcoamings, air pipes, door sills, etc., in exposed positions andall closing appliances are also to be determined byconsideration of both intact and damage stability requirements.

5.4 Deep draught caissons and buoy units

5.4.1 The weathertight integrity of units which are notsubject to the requirements of the Load Line Convention willbe special ly considered on the basis of 5.5 and therequirements for both intact and damage stability.

5.5 Weathertight integrity

5.5.1 Closing arrangements for shel l , deck andbulkhead openings and the requirements for ventilators, airpipes and overboard discharges, etc., are to comply withSections 6 to 10.

5.5.2 The requirements of this Chapter conform,where relevant, with those of the Load Line Convention.Reference should also be made to any addit ionalrequirements of the National Authority of the country in whichthe unit is to be registered and to the appropriate Regulationsof the Coastal State Authority in the area where the unit is tooperate.

5.5.3 The closing appliances are in general to have astrength at least corresponding to the required strength ofthat part of the hull in which they are fitted.

5.5.4 The requirements for closing appliances ofhatches, doors, venti lators, air pipes, etc., and theirassociated coamings situated at such height as will notconstitute a danger to the weathertightness of the unit will bespecially considered.

5.5.5 In all areas where mechanical damage is likely, allair and sounding pipes, scuppers and discharges, includingtheir valves, controls and indicators, are to be well protected.This protection is to be of steel or other equivalent material.


SECTION 6Miscellaneous openings

6.1 Small hatchways on exposed decks

6.1.1 This sub-Section is appl icable to smallhatchways or access openings. For access arrangements tooil storage tanks, see Section 7.

6.1.2 The number and size of hatchways and otheraccess openings are to be kept to the minimum consistentwith the satisfactory operation of the unit.

6.1.3 The height and scantlings of coamings are to bein accordance with 6.3.

6.1.4 Hatch covers are to be of steel, weathertight andhinged. The means of securing are to be such thatweathertightness can be maintained in any sea condition.Where toggles are fitted, their diameter and spacing are to bein accordance with an ISO standard or equivalent.

6.1.5 Hinges are not to be used as securing devicesunless specially considered.

6.1.6 Small hatch cover scantlings and securingdevices are to be in accordance with Table 7.6.1 or with anacceptable standard.

Table 7.6.1 Hatch cover scantlings

6.1.7 Hatch covers of a greater size than those definedin Table 7.6.1 wil l have their scantl ings and closingarrangements specially considered.

6.1.8 When applicable, large hatch covers are to complywith the requirements of Pt 3, Ch 11 of the Rules for Ships.

6.1.9 Escape hatches are to be capable of beingopened from either side.

6.1.10 Small hatches, including escape hatches, are tobe situated clear of any obstructions.

6.1.11 Where portable plates are required in decks forunshipping machinery, or for other similar reasons, they maybe accepted provided they are of equivalent strength to theunpierced deck and are secured by gaskets and closelyspaced bolts at a pitch not exceeding five diameters.

6.2 Hatchways within enclosed superstructuresor ‘tween decks

6.2.1 The requirements of 6.1 are to be complied withwhere applicable.





6.2.2 Access hatches within a superstructure ordeckhouse in Position 1 or 2 need not be provided withmeans for closing if all openings in the surrounding bulkheadshave weathertight closing appliances.

6.3 Hatch coamings

6.3.1 The height of coamings of hatchways situated inPositions 1 and 2 closed by steel covers fitted with gasketsand clamping devices are to be not less than:• 600 mm at Position 1;• 450 mm at Position 2.

6.3.2 Lower heights than those defined in 6.3.1 maybe considered in relation to operational requirements and thenature of the spaces to which access is given.

6.3.3 Coamings with height less than given in 6.3.1may normally be accepted for column-stabilized and tension-leg units after special consideration, see also 6.3.4.

6.3.4 Coaming heights on all units are also to satisfy therequirements for intact and damage stability, see 4.5 and 4.7.

6.3.5 The thickness of the coamings is to be not lessthan the minimum thickness of the structures to which theyare attached, or 11 mm, whichever is the lesser. Stiffening ofthe coaming is to be appropriate to its length and height.Scantlings of coamings more than 900 mm in height will bespecially considered.

6.4 Manholes and flush scuttles

6.4.1 Manholes and flush scuttles fitted in Positions 1and 2, or within superstructures other than enclosedsuperstructures, are to be closed by substantial coverscapable of being made watertight. Unless secured by closelyspaced bolts, the covers are to be permanently attached.

6.5 Companionways, doors and access arrangements on weather decks

6.5.1 Companionways on exposed decks are to be ofequivalent construction, weathertightness and strength to adeckhouse in the same position and effectively secured tothe deck.

6.5.2 For access to spaces in the oil storage area onunits with tanks for the storage of oil in bulk, see Pt 3, Ch 3,2.11.

6.5.3 Access openings in:• bulkheads of enclosed superstructures;• deckhouses or companionways protecting openings

leading into enclosed superstructures or to spacesbelow the freeboard deck; and

• deckhouse on a deckhouse protecting an openingleading to a space below the freeboard deck

are to be fitted with doors of steel or other equivalentmaterial, permanently and strongly attached to the bulkheadand framed, stiffened and fitted so that the whole structure isof equivalent strength to the unpierced bulkhead, and weathert ight when closed. The doors are to be gasketed and secured weathert ight by means of clamping devices or equivalent arrangements, permanently attached to the bulkhead or to the door. Doorsare generally to open outwards and are to be capable ofbeing operated and secured from both sides. The sill heightsare to be as required by 6.5.4.

Size of hatch Plate Stiffeners Toggles(mm) (mm)

600 x 600 8,0 – 4

760 x 760 8,0 – 6

925 x 925 8,0 75 x 7,5 mm flat bar 7

1220 x 1220 10,0 75 x 7,5 mm flat bar 8


6.5.14 Where portable plates are required in casings forunshipping machinery, or for other similar reasons, they maybe accepted provided they are of equivalent strength to theunpierced bulkhead and are secured by gaskets and closelyspaced bolts at a pitch not exceeding five diameters.

6.5.15 The sill heights of accesses closed by coverswhich are secured by closely spaced bolts or otherwise keptpermanently closed at sea will be specially considered.

6.6 Side scuttles, windows and skylights

6.6.1 A plan showing the location of side scuttles andwindows is to be submitted. Attention is to be given to anyrelevant Statutory Requirements of the Coastal StateAuthority where the unit is to operate and/or the NationalAuthority of the country in which the unit is to be registered.

6.6.2 Side scuttles and windows together with theirglasses and deadlights, if fitted, are to be of an approveddesign or in accordance with a recognized National orInternational Standard.

6.6.3 The location of windows and side scuttles andthe provision of deadlights or storm covers on semi-submersible units will be specially considered in each case,see also 4.5.1(c) and 5.2.5.

6.6.4 Surface-type and self-elevating units, whenafloat, are to comply with the requirements of 6.6.5 to 6.6.22.

6.6.5 Side scuttles to spaces below the freeboarddeck, or to spaces within enclosed superstructures, are to befitted with efficient, hinged, inside deadlights and capable ofbeing effectively closed and secured watertight.

6.6.6 No side scuttle is to be fitted in such a positionthat its sill is below a line drawn parallel to the freeboard deckat side and having its lowest point 2,5 per cent of the breadthB above the load waterline corresponding to the summerfreeboard or 500 mm, whichever is the greater distance, see Fig. 7.6.1.

6.6.7 Windows and side scuttles are to be of the non-opening type where damage stability calculationsindicate that they would become immersed as result ofspecified damage.

6.6.8 Windows should not generally be fitted in endbulkheads of superstructures in Position 1.

6.6.9 If fitted in a deckhouse in Position 1, windowsare to be provided with strong, hinged, steel, weathertightstorm covers. However, if there is an opening leading belowdeck in this deckhouse, this opening is to be treated as beingon an exposed deck and is to be protected as required by6.1.4.

6.6.10 Side scutt les and windows at the shel l in Position 2, protecting direct access below, are to be providedwith strong permanently attached deadlights.

6.6.11 Side scutt les and windows at the shel l in Position 2, not protecting direct access below, are to beprovided with strong portable steel covers for 50 per cent of each size, with means for securing at each side scuttle and window.





Double doors are to be equivalent in strength to theunpierced bulkhead, and in Position 1, a centre pillar is to beprovided which may be portable.

6.5.4 The height of doorway si l ls above decksheathing, if f itted, is to be not less than 600 mm in Posit ion 1, and not less than 380 mm in Posit ion 2. For semi-submersible units, see 5.2.3.

6.5.5 Doorway sill heights on all units are also to satisfy the requirements for intact and damage stability, see 4.5 and 4.7.

6.5.6 Fixed lights in doors in Positions 1 and 2 are tocomply with the requirements for side scuttles as given in6.6.1 and 6.6.2. Hinged steel deadlights may be external.

6.5.7 Where access is provided from the deck aboveas an alternative to access from the freeboard deck, theheight of sill into a bridge or a poop is to be not less than 380 mm. The same requirement applies to deckhouses on thefreeboard deck. The sill height for doorways in a forecastle, ifprotecting a companionway, is to be 600 mm regardless ofwhether or not access is provided from above. If notprotecting a companionway, the sill height may be 380 mm.

6.5.8 Where closing appl iances of openings insuperstructures and deckhouses do not comply with 6.5.3,the interior deck openings are to be treated as if exposed onthe weather deck.

6.5.9 Where an access opening, in the top of adeckhouse situated on a raised quarterdeck, gives accessbelow the freeboard deck or to an enclosed superstructure,the closing appliances in the surrounding bulkheads are notrequired to be gasketed, provided the raised quarterdeck isat least standard height, and the deckhouse is at leaststandard superstructure height.

6.5.10 On surface-type oil storage units, direct accessfrom the freeboard deck to the machinery space throughexposed casings is not permitted except when 6.5.11applies. A door complying with 6.5.3 may, however, be fittedin an exposed machinery casing on these units provided thatit leads to a space or passageway which is of equivalentstrength to the casing and is separated from the machineryspace by a second weathertight door complying with 6.5.3.The outer and inner weathertight doors are to have sillheights of not less than 600 mm and 230 mm respectivelyand the space between is to be adequately drained bymeans of a screw plug or equivalent.

6.5.11 For surface-type oil storage units with freeboardsgreater than, or equal to, a Type B ship, inner doors are notrequired for direct access to the engine room.

6.5.12 If internal access is provided from a wheelhousein Position 2, or below, to spaces below the weather deckeither directly or through other spaces, the opening shouldbe protected by a hinged weathertight cover adequatelysecured, fitted on a coaming appropriate to its position, or byan equivalent arrangement, and the space adequatelydrained.

6.5.13 In way of a moonpool, where a working orplatform deck is provided below the weather deck, openingsin the surrounding bulkheads are to be kept to a minimum.Access or companionway openings are to be provided withweathert ight closing appl iances as for an exposedsuperstructure bulkhead, with 600 mm high coamings.


6.6.12 Side scuttles and windows set inboard from theshell in Position 2, protecting direct access below, are eitherto be provided with strong permanently attached deadlightsor, where they are accessible, strong permanently attachedexternal steel storm covers instead of internal deadlights.

6.6.13 Side scuttles and windows set inboard from theshell in Position 2, not protecting direct access below, do notrequire deadlights or storm covers.

6.6.14 In Position 2, cabin bulkheads and doors areconsidered effective between side scuttles or windows andaccess below.

6.6.15 Windows in the shell above Position 2 are to beprovided with strong portable internal storm covers for 25 percent of each size of window, with means of securing beingprovided at each window.

6.6.16 Where windows are permitted in an exposedbulkhead on the weather deck in the forward 0,25LL, strongexternal storm covers which may be portable and storedadjacent are to be provided.

6.6.17 Where the wheelhouse is in Position 2, in lieu ofstorm covers being provided for the wheelhouse windows, aweathertight cover, fitted to a coaming of not less than 230 mm in height around the internal stairway opening withinthe wheelhouse, may be accepted. If this arrangement isaccepted, adequate means of draining the wheelhouse are tobe provided.

6.6.18 If necessary, for practical considerations, thestorm covers may be in two parts.

6.6.19 Deckhouses situated on a raised quarter deckmay be treated as being in Position 2 as far as the provisionof deadlights is concerned, provided the height of the raisedquarter deck is equal to, or greater than, the standard height.





6.6.20 Skylights, where fitted, are to be of substantialconstruction and securely attached to their coamings. Theheight of the lower edge of opening and the scantlings of thecoaming are to be as required by 6.3 as appropriate. Thethickness of glasses in fixed or opening skylights is to beappropriate to their size and position as required for sidescuttles or windows. Glasses in any position are to beprotected from mechanical damage, and where fitted inPositions 1 or 2 (as defined in 2.5) are to be provided withrobust deadlights or storm covers permanently attached.

6.6.21 Laminated toughened safety glass may also beused for windows, but the total thickness will need to begreater than that required for the equivalent sized windowusing toughened safety glass. The equivalent thickness oflaminated toughened safety glass is to be determined fromthe following formula:

TL12 + TL2

2 + ........TLn2 = TS

2

where:n = number of laminatesTL = thickness of glass laminateTS = thickness of toughened safety glass

6.6.22 Rubber frames are not acceptable for windowsin Positions 1 and 2, and are not generally acceptable in anyother position in external casings. Any proposals to fit rubberframes are to be submitted for consideration. The proposedlocations, frame dimensions, glass thicknesses and theresults of any tests carried out are to be forwarded.

Line drawn parallel to freeboard deck on sidebelow which no sidescuttles are allowed

Summer load waterline or Timber summer loadwaterline if timber freeboards are assigned 2,5 per cent of breadth (B) or 500 mm

whichever is the greatest

Allowed

Not allowed

Freeboard deck

Fig. 7.6.1Acceptable positions of side scuttles






SECTION 7Tank access arrangements and closingappliances in oil storage units

7.1 Materials

7.1.1 Covers for access hatches, tank cleaning andother openings to oil storage tanks and adjacent spaces areto be manufactured from mild steel complying with Part 2.

7.1.2 Consideration will be given to the use of bronze,brass or other materials. However, aluminium alloy is not tobe used for the covers of any openings to tanks.

7.1.3 Synthetic materials will be considered, taking intoaccount their fire-resistance and physical and chemicalproperties in relation to the intended operating conditions.Details of the properties of the material, the design of thecover and the method of manufacture are to be submitted forapproval.

7.1.4 The hatch cover packing material is to becompatible with the stored liquids and is to be efficiently heldin place.

7.2 Tank access hatchways in oil storage areas

7.2.1 Attention is drawn to IMO Resolutionsconcerning safe access to, and working in, large tanks.

7.2.2 Oilt ight hatchways are to be kept to theminimum size required to provide reasonable access andventilation. Where tanks are large or subdivided by washbulkheads, additional hatchways may be required. Indetermining the size and location of hatchways,consideration should be given to the handling of materialsand staging for maintenance in the tank.

7.2.3 The size and location of hatchways are also totake into account access for personnel wearing breathingapparatus, and removal of injured personnel (possibly on astretcher) from the bottom of the tank.

7.2.4 The height of hatch coaming is to be not lessthan 600 mm, measured above the upper surface of thefreeboard deck, unless a lower height is permitted by theCoastal State Authority or the National Authority of thecountry in which the unit is to be registered.

7.2.5 Taking account of sheer and camber, the heightof any storage tank hatch coaming is to be such as to ensurethat the top of the hatch coaming is above the highest pointof the tank over which it is fitted.

7.2.6 The height of the coaming may be required to beincreased if this is shown to be necessary by damage stabilityregulations.

7.2.7 The thickness of the coaming plate is to be not less than 10 mm, but may be required to be increased,and edge stiffening fitted, where the coaming height exceeds600 mm.

7.2.8 Unstiffened plate covers are to be not less than12,5 mm in thickness, but if the area of the cover exceeds1,2 m2 this thickness may be required to be increased orstiffening fitted.

7.2.9 Unstiffened covers are to be secured byfastenings spaced not more than 600 mm apart on circularhatchways. On rectangular hatchways, the spacing offastenings is generally not to exceed 450 mm, and thedistance between hatch corners and adjacent fastenings is tobe not more than 230 mm.

7.2.10 The arrangement of fastenings on stiffenedhatchway covers and covers of special design will bespecially considered.

7.2.11 Where the cover is hinged, adequate stiffening ofthe coaming and cover in way of the hinge is to be provided.In general, hinges are not to be used as securing devices forthe cover.

7.2.12 Access openings are to have smooth edges andedge stiffening is also to be arranged in regions of high stress.

7.3 Enlarged cargo tank access openings

7.3.1 Proposals to fit enlarged cargo tank accessesclosed by bolted plate covers will be considered. Suchopenings may be of extended dimensions for ease of accessand evacuation of personnel, see 7.2.3, and may incorporatea smaller access hatch for normal use constructed asrequired by 7.2.

7.3.2 The plate cover is to be not less than 15 mm inthickness and is to be secured by closely spaced studs to aring of suitable dimensions, welded to the deck. The studsare not to penetrate the deck plating.

7.4 Miscellaneous openings

7.4.1 Small openings for tank cleaning, ullage andsimilar purposes may be closed by flush covers which are tobe not less than 12,5 mm in thickness and secured by studsnot more than 100 mm apart. Studs are to be arranged in aring of suitable width and thickness attached to the deck,and are not to penetrate the deck plating.

7.4.2 Small diameter holes provided for staging wiresare to be closed by plugs of an approved pattern. The plugsare to be provided with a thick washer of suitable materialwhich is also compatible with the stored liquids. Spare plugsequal to at least 10 per cent of the number of holes are to beprovided and maintained on board. If these openings arethreaded they are to be protected while in use with aprotective sleeve of suitable material.

7.4.3 Small openings are to be kept clear of otheraccess openings.

7.5 Access to spaces other than oil storage tanks

7.5.1 Access to clean ballast or dry tanks and tocofferdams may be either by access hatch or by manholegenerally complying with the preceding requirements.


7.6 Equivalents

7.6.1 Alternative access cover designs and securingarrangements will be considered on the basis of equivalenceto the above requirements and taking into account anyrelevant National Requirements.

7.7 General access to spaces in the oil storage area

7.7.1 The general requirements for access to spaceswithin the oil storage area are to comply with Pt 3, Ch 3,2.11.





SECTION 8Ventilators

8.1 General

8.1.1 Special care is to be taken in the design andpositioning of ventilator openings and coamings, particularlyin the region of the forward end of superstructures and otherpoints of high stress. The deck plating in way of thecoamings is to be efficiently stiffened.

8.1.2 Ventilators from deep tanks and tunnels passingthrough pontoons, columns and tween decks are to havescantlings suitable for withstanding the pressures to whichthey may be subjected, and are to be made watertight.

8.1.3 For height and location of oil storage tank ventoutlets, see Pt 5, Ch 14,4.

8.2 Coamings

8.2.1 The scantlings and height of ventilator coamingsexposed to the weather are to be not less than required byTable 7.8.1 but the thickness need not exceed that of theadjacent deck or bulkhead plating. In particularly exposedpositions, the height of the coamings and scantlings may berequired to be increased.

Table 7.8.1 Ventilator coaming requirements

8.2.2 For gooseneck ventilators, the coaming height isto be measured to the underside of the bend, this being thelowest point through which water on deck could pass freelyto spaces below.

8.2.3 Where wall vents are fitted with an internal bafflewhich rises above the lower edge of the exterior opening, thecoaming height is measured to the top of the baffle.

8.2.4 Venti lator coaming heights and closingappliances on all units are also to satisfy the requirements forintact and damage stability, see 4.5 and 4.7.

Feature Requirements

Height (measuredabove sheathing iffitted)

Thickness

Support

Symbols

tc = thickness of coaming, in mmhc = height of coaming, in mmδv = internal diameter of coaming, in mm

NOTEWhere the height of the ventilator exceeds that given in Item (1),the thickness given by (2) may be gradually reduced, above thatheight, to a minimum of 5,5 mm on column stabilised units and 6,5 mm on other units. The ventilator is to be adequately stayed.

(1) hc = 900 mm at Position 1(see 2.5)

hc = 760 mm at Position 2(see 2.5)

(2) tc = 5,5 + 0,01δ v mmwhere 7,5 mm ≤ tc ≤ 10,0 mm

(3) If hc > 900 mm the coaming is to be specially supported






8.3 Closing appliances

8.3.1 All ventilators will generally be required to beprovided with permanently attached steel weathertight coversunless:(a) the height of the coaming is greater than 4,5 m where

Table 7.8.2 requires a minimum height of 900 mm; or (b) the height of the coaming is greater than 2,3 m where

Table 7.8.2 requires a minimum height of 760 mm, see also 8.2.4.

8.3.2 On self-elevating units, it is recommended thatclosing appliances for ventilators situated on the freeboarddeck are fitted at or below the deck level.

8.3.3 Mushroom ventilators closed by a head revolvingon a centre spindle (screw down head) are acceptable inPosition 2, and also in sheltered positions in Position 1, butthe diameter is not to exceed 300 mm if situated within theforward 0,25LL on surface type units and self elevating units.

8.3.4 Mushroom ventilators with a fixed head andclosed by a screw down plate (screw down cover) may beaccepted in exposed positions within the forward 0,25LL onall units up to a diameter of 750 mm.

8.3.5 A ventilator head not forming part of the closingarrangements is to be not less than 5,0 mm thick on column-stabilized units and 6,5 mm thick on other units.

8.3.6 Wall ventilators (jalousies) may be acceptedprovided they are capable of being closed weathertight byhinged steel gasketed covers secured by bolts or toggles, orequivalent arrangements provided.

8.3.7 Fire dampers are not acceptable as ventilatorclosing appl iances unless they are of substantialconstruction, gasketed, and able to be secured weathertightin the closed position.

8.3.8 Reference should be made to 8.2.4 concerningdown flooding through ventilators which do not requireclosing appliances due to their coaming height being inaccordance with 8.3.1.

SECTION 9Air and sounding pipes

9.1 General

9.1.1 Air and sounding pipes are to comply with therequirements of Pt 5, Ch 12,11 and Ch 13,5.

9.1.2 Striking plates of suitable thickness, or theirequivalent, are to be fitted under all sounding pipes.

9.2 Height of air pipes

9.2.1 The height of air pipes from the upper surface ofdecks exposed to the weather, to the point where water mayhave access below, is normally to be not less than:• 760 mm on the freeboard deck;• 450 mm on the superstructure deck.These heights being measured above deck sheathing, wherefitted. For column-stabilized units, see 5.2.

9.2.2 Air pipes are generally to be led to an exposeddeck and are to be well protected from mechanical damage.

9.2.3 The exposed portion of air pipes is to be of steelor equivalent material of a thickness in accordance with Table 7.9.1.

Table 7.9.1 Air pipe thicknesses (steel)

9.2.4 Air pipes are also to satisfy the requirements forintact and damage stability, see 4.5 and 4.7.


9.3.1 All openings of air and sounding pipes are to beprovided with approved automatic type closing applianceswhich prevent the free entry of water and excessive pressureimposed on the tank.

9.3.2 Pressure/vacuum valves as required by Pt 5, Ch 13,4 may be accepted as closing appliances for oilstorage tanks.

Ext. dia t

80 mm and below 6,0 mm

165 mm and above 8,5 mm

NOTEThe thickness of pipes of intermediate diameters is to be obtainedby linear interpolation.


SECTION 10Scuppers and sanitary discharges

10.1 General

10.1.1 Scuppers sufficient in number and size toprovide effective drainage are to be fitted in all decks.

10.1.2 Scuppers draining weather decks and spaceswithin superstructures or deckhouses not fitted with efficientweathertight doors are to be led overboard.

10.1.3 Scuppers and discharges which drain spacesbelow the freeboard deck, or spaces within intactsuperstructures or deckhouses on the freeboard deck fittedwith efficient weathertight doors, may be led to the bilges inthe case of scuppers, or to suitable sanitary tanks in the caseof sanitary discharges. Alternatively, they may be ledoverboard provided that:(a) the freeboard on surface type units is such that the

deck edge is not immersed when the unit heels to 5 ˚ ;and

(b) the scuppers are fitted with means of preventing waterfrom passing inboard in accordance with 10.2.

10.1.4 Where a sewage system is fitted, the shellboundary valves on the discharge pipe from the effluenttank(s) and the by-pass system are to comply with 10.2.

10.1.5 Open bend weather deck scuppers are to be ofthickness in accordance with Table 7.10.1 but need notexceed the thickness of the adjacent structure, see also10.1.8.

Table 7.10.1 Weather deck scuppers

10.1.6 The minimum wall thickness of pipes notindicated in 10.1.5 is to be:• 4,5 mm for pipes of 155 mm external diameter or smaller;• 6,0 mm for pipes of 230 mm external diameter or greater.Intermediate minimum thicknesses are to be determined bylinear interpolation.

10.1.7 For the use of non-metallic pipe, see Pt 5, Ch 11,5.

10.1.8 Scuppers and discharge pipes should notnormally pass through oil fuel or oil storage tanks. Wherescuppers and discharge pipes pass, unavoidably, through oilfuel or oil storage tanks, and are led through the shell withinthe tanks, the thickness of the piping should be at least thesame thickness as Rule shell plating in way, derived from theappropriate Chapters, but need not exceed 19 mm.

10.1.9 Piping within tanks is to be tested in accordancewith Pt 5, Ch 11,8.

10.1.10 All piping is to be adequately supported.






10.2.1 Normally each separate overboard dischargefrom an enclosed space is to be fitted with an automatic non-return valve at the shell boundary. Where the inboard end ofa discharge is situated below the worst damage water line,the non-return valve is to be of a type which is effective at theworst expected inclination after damage, whatever theorientation, and is to have a positive means of closingoperable from a readily accessible position above thedamage water line. An indicator is to be fitted at the controlposition showing whether the valve is open or closed. For surface-type units, see 10.3.

10.2.2 The requirements for non-return valves areapplicable only to those discharges which remain open whilethe unit is afloat during normal operation. For dischargeswhich are closed while the unit is afloat, such as gravitydrains from tanks, a single screw down valve operated fromthe freeboard deck is considered to provide sufficientprotection. An indicator is to be fitted at the control positionshowing whether the valve is open or closed.

10.2.3 The non-return valve required by 10.2.1 is to bemounted directly on the shell and secured in accordance withPt 5, Ch 12,2.9. If this is impracticable, a short distancepiece of rigid construction may be introduced between thevalve and the shell.

10.2.4 Discharge piping situated between the sea leveland the bottom of the upper hull of semi-submersible unitsand below the bottom shell of the self-elevating units when inthe elevated position is to be of substantial construction, wellsecured and protected.

10.3 Closing appliances on surface-type units

10.3.1 The requirements of 10.2 are to be compliedwith where applicable.

10.3.2 In general, each separate overboard discharge isto be fitted with a screw-down non-return valve capable ofbeing operated from a position always accessible and abovethe freeboard deck. An indicator is to be fitted at the controlposition showing whether the valve is open or closed.

10.3.3 Where the vertical distance from the summerload waterline to the inboard end of the discharge pipeexceeds 0,01LL, the discharge may be fitted with twoautomatic non-return valves without positive means ofclosing, instead of the screw-down non-return valve,provided that the inboard valve is always accessible forexamination under service conditions.

10.3.4 Where the vertical distance from the summerload waterline to the inboard end of the discharge pipeexceeds 0,02LL , a single automatic non-return valve withoutpositive means of closing may be fitted, see Fig 7.10.1.

10.3.5 The requirements for non-return valves areapplicable only to those discharges which remain openduring the normal operation of the unit, see 10.2.2.

10.3.6 Scuppers and discharge pipes originating at anylevel which penetrate the shell either more than 450 mmbelow the freeboard deck or less than 600 mm above thesummer load waterline are to be fitted with an automatic non-return valve at the shell. This valve, unless required by 10.1.3,may be omitted provided the piping has a minimum wallthickness in accordance with Table 7.10.1, see also 10.1.8.

Ext. dia t

80 mm and below 7,0 mm

180 mm 10,0 mm

220 mm and above 12,5 mm

NOTEThe thickness of pipes of intermediate diameters is to be obtainedby linear interpolation.






10.3.7 If a valve is required by 10.1.3, this valve shouldpreferably be fitted as close as possible to the point of entryof the pipe into the tank. If fitted below the freeboard deck,the valve is to be capable of being controlled from an easilyaccessible position above the freeboard deck. Local controlis also to be arranged, unless the valve is inaccessible. An indicator is to be fitted at the control position showingwhether the valve is open or closed.

10.4 Rubbish chutes and similar discharges

10.4.1 Rubbish chutes and similar discharges should beconstructed of mild steel piping or plating of shell thickness.Other materials will be specially considered. Openings are tobe kept clear of the sheerstrake and areas of high stressconcentration.

10.4.2 Rubbish chute hoppers are to be provided with ahinged weathertight cover at the inboard end with aninterlock so that the discharge flap and hopper cover cannotbe open at the same time. The hopper cover is to besecured closed when not in use, and a suitable noticedisplayed at the control position.

10.4.3 Where the inboard end of the hopper on asurface-type unit is less than 0,01LL above the summer loadwaterline, a suitable valve with positive means for closing is tobe provided in addition to the cover and flap in an easilyaccessible position above the deepest design operatingwaterline. The valve is to be controlled from a positionadjacent to the hopper and provided with an open/shutindicator. The valve is to be kept closed when not in use, anda suitable notice displayed at the valve operating position.

10.5 Materials for valves, fittings and pipes

10.5.1 All shell fittings and valves required by 10.2 and10.3 are to be of steel, bronze or other approved ductilematerial; ordinary cast iron or similar materials are notacceptable. Materials are to satisfy the requirements of Part 2.

10.5.2 Al l these items, i f made of steel or otherapproved material with low corrosion resistance, are to besuitably protected against wastage.

10.5.3 The lengths of pipe attached to the shell fittings,elbow pieces or valves are to be of galvanized steel or otherequivalent approved material.






Fig. 7.10.1 Diagrammatic arrangement of discharge valves

Scupper from enclosed space

ANRV

Freeboard deck

F

One automatic non-return valve on shelloperated from above the freeboard deckfitted with controls and indicators

ANRV

Positive controlvalve

One automatic non-return valve in the linewith positive control valve on shelloperated from above the freeboard deck

OR

ANRV

Positive controlvalve

In manned machinery spaces one locally operated positive control valve on shell but with one automatic non-return valvein the line

OR

ANRV

LL = Load line length of ship

ANRV

Freeboard deck


Deepest seasonal load line

Two automatic non-return valves withoutpositive means of closing, one on shell and one always accessible under serviceconditions

OR

Positive control valve

ANRV

ANRV

If not practicable to fit inboard valve abovethe specified waterline then it can be accepted below provided positive controlvalve with indicators is fitted between the two automatic non-return valves in readilyaccessible position

Freeboard deck


ANRV

F

One automatic non-return valve withoutpositive means of closing

F more than 0,02LLF more than 0,01LL but less than 0,02LL

= Automatic non-return valve

= Positive control valve

= ANRV of screw-down type

F = Vertical distance between the inboard end of the dischargepipe and the summer load waterline or timber summer loadwaterline, if assigned.

F less than 0,01LL

F


ke





SECTION 1General

1.1 Application

1.1.1 This Chapter is applicable to all unit types andcomponents.

1.1.2 Requirements are given in this Chapter for thefollowing:(a) Welding connection details, defined practices and

sequence, consumables and equipment, procedures,workmanship and inspection.

(b) End connection scantlings and constructional details forlongitudinals, beams, frames and bulkhead stiffeners.

(c) Primary member proportions, stiffening and constructiondetails.

1.2 Symbols

1.2.1 Symbols are defined as necessary in eachSection.

Section

1 General

2 Welding

3 Secondary member end connections

4 Construction details for primary members

5 Structural details

6 Fabrication tolerances

Welding and Structural Details

SECTION 2Welding

2.1 General

2.1.1 The plans to be submitted for approval are toindicate clearly details of the welded connections of mainstructural members, including the type and size of welds. Thisrequirement includes welded connections to steel castings.The information submitted should include the following:• Whether weld sizes given are throat thicknesses or leg

lengths.• Grades and thicknesses of materials to be welded.• Location, types of joints and angles of abutting

members.• Reference to welding procedures to be used.• Sequence of welding of assemblies and joining up of

assemblies.

2.1.2 Structural arrangements are to be such as willallow adequate ventilation and access for preheating, whererequired, and for the satisfactory completion of all weldingoperations. Welded joints are to be so arranged as tofacilitate the use of downhand welding wherever possible.

2.1.3 The type and disposition of connections andsequences of welding are to be so planned that any restraintduring welding operations is reduced to a minimum.

2.1.4 The proposed sequence of welding is to beagreed with the Surveyor prior to construction.

2.1.5 Careful consideration is to be given to assemblysequence and overall shrinkage of plate panels, assemblies,etc., resulting from welding processes employed. Welding isto proceed systematically with each welded joint beingcompleted in correct sequence without undue interruption.Where practicable, welding is to commence at the centre of ajoint and proceed outwards or at the centre of an assemblyand progress outwards towards the perimeter so that eachpart has freedom to move in one or more directions.Generally, the welding of stiffener members includingtransverses, frames, girders, etc., to welded plate panels byautomatic processes should be carried out in such a way asto minimize angular distortion of the stiffener.

2.1.6 Special consideration is to be given to jointpreparation and welding sequence at intersections of specialand primary members with a view to minimising the risk oflamellar tearing in the plating. Proposed procedures are tobe agreed with LR prior to the commencement of fabrication.Material with adequate through thickness properties is to beutilized where necessary, see Pt 2, Ch 3,8.


2.2.4 Where the carbon equivalent (Ceq), calculatedfrom the ladle analysis and using the formula given below, is inexcess of 0,45 per cent, approved low hydrogen highertensile welding consumables and preheating are to be used.Where the carbon equivalent is above 0,41 per cent but is notmore than 0,45 per cent, approved low hydrogen highertensile welding consumables are to be used, but preheatingwill not generally be required except under conditions of highrestraint or low ambient temperature. Where carbonequivalent is not more than 0,41 per cent, any type ofapproved higher tensile welding consumables may be usedand preheating will not generally be required except as above.

Carbon equivalent, Ceq = C +

This formula is applicable only to steels which are basically ofthe carbon-manganese type containing minor quantities ofgrain refining elements, for example niobium, vanadium oraluminium. The proposed use of low alloy steels will besubject to special consideration.

2.2.5 Where the structure incorporates mild steel andhigher tensile steel, details of the welding arrangements andprocedures at the interchange joints are to be submitted forapproval in all cases where the chemical analysis of thehigher tensile steel requires that it be preheated.

2.2.6 The type and diameter of electrode or wire, thecurrent, voltage, rate of deposit and number of runs, etc., areto conform to those established in accordance with 2.3.Provision is to be made for checking the above parameters atthe welding area.

2.2.7 For the welding of aluminium alloys, see also2.14.

2.3 Welding procedures

2.3.1 Welding procedure tests are to be carried out toverify that the materials and methods prescribed in theProcedure Specification will produce weldments that areadequate for the intended appl ication and satisfyspecification requirements. The range of material thicknessqualified by a welding procedure test is to be 0,5t to 1,5t formultirun welding, where t is the thickness of the proceduretest piece. For single or two-run technique the range is 0,8tto 1,1t. Welding procedure specifications are to be submittedfor consideration by LR.

2.3.2 Welding procedure specifications are to containthe following minimum information:• Welding processes used.• Steel type and grade.• Details of edge preparation and joint fit up.• Material thickness and for pipe, the outside diameter.• Welding position.• Full details of welding consumables, parameters and

sequences.• Details of preheating and interpass temperatures and

post weld heat treatment (where applicable).• Codes of practice.• Treatment of tack welds.

2.3.3 Welding procedure qualification test pieces areto be prepared in each welding position to be encounteredduring construction, or, alternatively, 6G (H-L045) position.On completion of welding, including any necessary post weldheat treatment, procedure qualification test pieces are to besubjected to the non-destructive and destructive tests shownin Figs. 8.2.1, 8.2.2, 8.2.3, 8.2.4 and 8.2.5, as applicable.


Welding and Structural Details



2.1.7 Precautions are to be taken to screen andprewarm, as necessary, the general and local weld areas.Surfaces are to be dry and rapid cooling of welded joints is tobe prevented. Special attention is to be paid to preheatingwhen low hydrogen electrodes are used for higher tensilesteels on thick materials under high restraint or whenapplying small weld beads.

2.1.8 Consumables for tack welding should be of thesame grade as those used for the main weld. Generally, tackwelds are not to be applied in lengths of less than 30 mm formild steel grades and 50 mm for higher tensile steel grades.Care should be taken to ensure that tack welds, which are tobe retained as part of the finished weld, are clean and freefrom defects before being incorporated. Where tack weldsare to be removed, the Surveyors are to ensure that themethods adopted to remove them will not damage thematerial of the structure.

2.1.9 Special attention is to be given to the examinationof plating in way of all lifting eye plate positions to ensurefreedom from cracks and laminations. This examination is notrestricted to the positions where eye plates have beenremoved but includes the positions where lifting eye plates arepermanent fixtures.

2.1.10 Where prefabrication primers are applied overareas which will be subsequently welded, they are to be of aquality accepted by LR as having no significant deleteriouseffect on the finished weld, see Pt 8, Ch 3,2.

2.2 Welding consumables and equipment

2.2.1 Welding plant and appliances are to be suitablefor the purpose intended and are to be maintained in anefficient condition. Special care is to be taken in thedistr ibution, storage and handl ing of al l weldingconsumables. Condensation on the metal surface duringstorage and use should be avoided. Flux coated electrodesand submerged arc fluxes are to be stored under controlledconditions. Other welding consumables such as bare wireand welding studs are to be stored under dry conditions toprevent rusting. Effective facilities for the storage and use ofwelding consumables in accordance with the manufacturer’sinstructions are to be provided close to working areas.

2.2.2 All welding consumables are to be approved by LR and are to be suitable for the type of joint and grade ofmaterial, see Pt 2, Ch 11.

2.2.3 The following grades of consumables are to beused:For normal strength steels:

Grade 1 For welding Grade AGrade 2 For welding any combination of grades

other than Grade E to Grade EGrade 3 For welding any combination of grades.

For higher tensile steels:Grade 1Y For welding Grade AHGrade 2Y For welding any combination of grades

other than Grade EH to Grade EHGrade 3Y For welding any combination of grades.

For joints between steels of different grades or differentstrength levels the welding consumables may be of typesuitable for the lesser grade or strength being connected.The use of a higher grade of welding consumable may berequired at discontinuit ies or other points of stressconcentration.

Mn Cr + Mo + V Ni + Cu6 5 15

+ +


2.3.4 Charpy V-notch impact tests are to be carriedout in the weld metal, fusion line and heat affected zone inaccordance with 2.4.

2.3.5 Welding procedures and associated workmanshipstandards are to show that due consideration has been givento the avoidance of cracking, see also 2.2.4.

2.3.6 Where specific published recommendations forthe avoidance of hydrogen cracking have been followed, thesource is to be quoted in the Welding ProceduresSpecification (WPS).

2.4 Impact test requirements

2.4.1 Impact tests are required when the designtemperature is 0° or lower. Impact tests are not required forGrade A material.

2.4.2 For special and primary structure as defined inCh 2,2, the impact test temperature is to be derived from thedesign temperature and the material thickness by the use ofFig. 8.2.6. Secondary structure as defined in Ch 2,2 is alsoto be tested in accordance with Fig. 8.2.6 but the testtemperature need not be lower than the parent metal testtemperature as appropriate to the material grade being used.

2.4.3 Minimum energy absorption in the Charpy test isto be related to the minimum specified yield strength of thematerial according to Table 8.2.1. For materials of differentyield strengths to those covered by this Table, the minimumenergy absorption in Joules is, in general, to be one tenth ofthe specified minimum yield strength of the material inN/mm2.

2.4.4 Fabrications whose thicknesses exceed 65 mmare in general to be subjected to a post weld heat treatmentwhere practicable. Impact tests when required by 2.3.1 areto be made on specimens heat treated in the same manneras the fabrication. Test temperatures are to comply withTable 8.2.2 and the energy absorption requirements are to bein accordance with 2.3.3.



Welding and Structural Details Part 4, Chapter 8Section 2

Table 8.2.1 Charpy impact energy requirements for structural components for designtemperatures of 0°C and lower

Specified minimum yield Minimum required energystress not above absorption

N/mm2 J

235 27315 31355 34390 39

Fig. 8.2.1 Butt welds in plate

of weldCL

4407/84

For retests if necessary

Approximately 300 mm

G

G

G

H

G

E

E

F

F

D

Test requirementsA Visual examinationB Surface crack detectionC 100% radiographic examinationD Al-weld metal tensile tests (YS UTS R/E)E Two bend tests. Two side bends for thickness greater than 20 mm. In other cases one face and one rootF Two transverse tensile tests (UTS)G Four sets Charpy V-notch impact tests 1 set notched at centre of weld 1set notched at fusion line (F/L) 1set notched at F/L + 2 mm 1set notched at F/L + 5 mmH One macro specimen including hardness survey





Weld one sideor both sides asdetailed in procedure

100 mm

100

mm

4407/86

Test requirementsA Magnetic particle examinationB One macro specimen including hardness surveyC Fracture of each fillet through throat

Approved butt welding procedures will qualify for fillet welds made using the same consumables and welding parameters. Where fillet weld procedures are to be submitted then a test is to be performed as follows:

Fig. 8.2.3 Fillet welds

Fig. 8.2.2 Butt welds in pipe

D and E

G

F

D and E

500 mm approximately

4407/85

The diameter of the test piece is to be a minimum of where D

is the maximum diameter of pipe to be welded in construction

Test requirementsA Visual examinationB Surface crack detectionC 100% radiographic examinationD Two transverse tensile testsE Two bend tests. Two side bends for thickness greater than 20 mm. In other cases one face and one rootF Four sets Charpy V-notch impact tests 1 set notched at centre of weld 1 set notched at fusion line (F/L) 1 set notched at F/L + 2 mm 1 set notched at F/L + 5 mmG One macro specimen including hardness survey

D2





Edge preparation and fit up to be as detailed in welding procedure

400 mm approx.

500

mm

app

rox.

Smallest dihedral angleused in construction

4407/87

Test requirements

A Visual examinationB Surface crack detectionC 100% ultrasonic examinationD From acute angle one macro specimen including hardness survey

Fig. 8.2.4 T, K and Y connections

Notes to Figs. 8.2.1, 8.2.2, 8.2.3, 8.2.4 and 8.2.51. The results of hardness surveys will be assessed with

reference to the survey technique adopted and thematerials involved. Generally the Vickers diamondindenter is to be used with a load not exceeding 10 kg.

2. Alternative NDE procedures will be considered.

CL Specimen

CL Specimen

1 mm minimum

1 mm minimum

1 2 3 4

1 2 3 4

1st welded side

2nd welded side

Notch location:

1 Centre of weld2 On fusion line3 In HAZ, 2 mm from fusion line4 In HAZ, 5 mm from fusion line HAZ = heat affected zone

4407/88

Single-V butt weld

Single-V butt weld

Fig. 8.2.5 Orientation of weld test specimen

Post weldheattreatmentrequiredSee 2.3.4

Thickness mm10 25 30 45 65

Des

ign

tem

pera

ture

°C

Impact test not required

-10

-20

-40

0

10°C

20°C

40°C

60°C 4407/89

Fig. 8.2.6Impact test temperatures related to design temperature and thickness

NOTETemperatures written on the graph are those at which Charpy impactspecimens are to be tested. (Boundary lines form part of the lowergrade, i.e. with the higher test temperature). Do not extrapolate.





Charpy impact testThickness temperature related to design

mm temperature

up to 25 equal26 – 100 10°C below primary

and 20°C below special

NOTERequirements for components with thicknesses in excess of 100 mm are subject to agreement.

Table 8.2.2 Charpy impact test temperatures for postweld heat treated structural componentsfor design temperatures of 0°C and lower

2.6.4 The quality and workmanship of welding of allf i tt ings and attachments to the main structure, bothpermanent and temporary, are to be equivalent to those ofthe main hull structure. Special care is to be taken whenremoving attachments such as lifting eyeplates and lugs ofvarious types which have been used to maintain alignment ofstructure during welding operations. When complete removalof these attachments is required, it is recommended they beburned off at the top of the fillet weld connections and theremainder chipped and ground smooth. However, alternativemethods of removing these attachments will be considered.Any defects in the unit’s structure caused by this operationare to be prepared, efficiently welded and ground smooth soas to have a defect-free repair.

2.6.5 Al l joints are to be prepared, al igned andadjusted in accordance with the established joint design.The preparation of plate edges and joint fit are to be withinthe tolerances given in the qualified procedure specification.Excessive force is not to be used in fairing and closing thework. Means are to be provided to maintain the relevantpositions of the components during welding. Whereexcessive gaps exist between surfaces or edges to be joined,the corrective measures to be adopted are to be to thesatisfaction of the Surveyors and any welding involved is tobe in accordance with qualified procedures.

2.6.6 Tack welding should be kept to a minimum and,where used, is to be qualified equal to the finished welds, see also 2.1.8.

2.6.7 Welding procedures and associated workmanshipstandards are to show that due consideration has been givento the avoidance of cracking, see also 2.2.4.

2.6.8 The surfaces of all areas to be fused in welding,and all faying surfaces of partial penetration joints, are to beclean, dry and free from rust scale and grease. The surfacesand boundaries of each run of weld metal are to bethoroughly cleaned and freed from slag before the next run isapplied. Welding is to proceed systematically, each weldedjoint being completed in proper sequence without undueinterruption. Provision is to be made for checking the currentin the vicinity of the arc. Unless the procedure test hasdemonstrated that satisfactory fusion and penetration hasbeen obtained, the second side of joints completed fromboth sides is to be back gouged in accordance with thequalified procedure before depositing weld metal on thesecond side.

2.6.9 Where thermal cutting or arc-air gouging is to beused for preparing plates or weld grooves, consideration is to be given to the possibility of preheating being required to avoid cracking. The Surveyors may require writtenprocedures, confirmed by qualification tests in certain cases.

2.6.10 Where plate has been cut by shearing or thermalcutting and the edge is not subsequently to be fused inwelding, the need for removal of the effects of cutting is to be indicated on the plans. Where required, machining or grinding or heat treatment or a combination of thesetechniques is to be used.

2.6.11 Adequate protection is to be provided wherewelding is required to be carried out in exposed positions inwet, windy or cold weather. In cold weather (below 5 ˚ C)precautions are to be taken to preheat the weldment. Unlessotherwise agreed electric resistance heaters or otheradequately controlled method is to be used for all pre- andpost weld treatment.

2.5 Approval of welders

2.5.1 Welders and welding machine operators are tobe proficient in the work they are to perform. Prior to thecommencement of construction they are to have passed theapproval tests in accordance with the requirements of thisSection or, where otherwise agreed, in accordance with arecognized Code of Practice which meets theserequirements.

2.5.2 A welder who has successfully welded all testpieces undertaken during welding procedure approval testswill not normally be required to perform separate welderapproval tests for the processes and the positions coveredby the procedure tests.

2.5.3 Welders who have not used a particular processand equipment for a period exceeding six months are to beretested.

2.5.4 Welder approval tests utilizing the approvedwelding procedures are to be carried out in each weldingposition to be encountered during construction. For approvalof all positional welding the test piece is to be prepared in thefixed inclined position (5G or 6G), i.e. 45° to the horizontaland is to include welding in the overhead position. Forrestricted access type welding situations, the 6GR tests areto be utilized.

2.5.5 On completion, the test piece is to be examined.Visual examination is to be followed by either non-destructiveexamination (ultrasonic testing where radiography isinappropriate) and by bend testing of suitable specimens. A micro section is also to be prepared and examined for soundness. Alternative schemes of examination will be considered.

2.6 Workmanship and inspection

2.6.1 The general requirements for welding are tocomply with 2.1.

2.6.2 Technically competent and suitably qualifieddirection and control is to be provided to ensure effectivecontrol at all stages of sub-assembly, assembly and weldingoperations.

2.6.3 Where structural components are to beassembled and welded in works sub-contracted by Builders,the Surveyors are to inspect the Sub-contractor’s works toensure that compliance with the requirements of this Chaptercan be achieved.


2.6.12 Fairing, by linear or spot heating, to correctdistortions due to welding, is to be carried out usingapproved procedures in order to ensure that the properties ofthe material are not adversely affected. Visual examination ofall heat affected areas and welds in the vicinity is to becarried out to ensure freedom from cracking.

2.6.13 Effective arrangements are to be provided by theBuilder for the visual inspection of finished welds to enablethe Surveyor to ensure that all welding has been satisfactorilycompleted.

2.6.14 All finished welds are to be sound and free fromcracks and substantially free from lack of fusion, incompletepenetration, slag inclusion, porosity and other defects. The surfaces of welds are to be reasonably smooth andsubstantially free from undercut or overlap. Care is to betaken to ensure that the specified dimensions of welds havebeen achieved and that both excessive reinforcements andunder-fill of welds are avoided.

2.6.15 Welds are to be clean and free from paint at thetime of inspection.

2.6.16 In addition to visual inspection, all critical weldsand other welded joints are to be examined using any one ora combination of ultrasonic, radiographic, magnetic particle,eddy current, dye penetrant or other acceptable methodsappropriate to the configuration of the weld.

2.6.17 The method to be used for the volumetricexamination of the welds is the responsibility of the Builder.Radiography is generally to be used on butt welds of 15 mmthickness or less. Ultrasonic testing is acceptable for weldsof 15 mm thickness or greater and is to be used for theexamination of full penetration tee butt or cruciform welds orjoints of similar configuration.

2.6.18 Non-destructive examinations (NDE) are to bemade in accordance with approved written proceduresprepared by the Builder, which identify the method andtechnique to be used, the extent of the examination and theacceptance criteria to be applied. NDE for acceptancepurposes is to be carried out after final heat treatment, whereapplicable, and is not to be carried out until at least 48 hoursafter the weldment has cooled to ambient temperature.

2.6.19 Non-destructive examinations are to beundertaken by personnel qualified to the appropriate level ofcertification scheme recognized by LR.

2.6.20 Checkpoints examined at the pre-fabricationstage are to include ultrasonic testing on examples of thestop/start points of automatic welding and magnetic particleinspection of weld ends.

2.6.21 Checkpoints examined at the construction stageare generally to be selected from those welds intended to beexamined as part of the agreed quality control programme tobe applied by the Builder. The locations and numbers ofcheckpoints are to be agreed between the Builder and theSurveyor. Special attention is to be paid to the weldedconnections of primary bracings and their end connectionsand other structure defined as special in Ch 2,2.

2.6.22 Particular attention is to be paid to highlystressed items. Magnetic particle inspection is to be used atends of fillet welds, T-joints or crossings in main structuralmembers and at sternframe connections, where applicable.




2.6.23 Checkpoints for volumetric examination are to beselected so that a representative sample of welding isexamined.

2.6.24 Typical locations for NDE and the recommendednumber of checkpoints to be taken in surface-type andcolumn-stabilized units are shown in Tables 8.2.3 and 8.2.4respectively. For other unit types, the extent of NDE will bespecially considered in each case. Critical locations asidentified by LR’s ShipRight Fatigue Design Assessment andother relevant fatigue calculations are also to be consideredwhere applicable. A document detailing the proposed itemsto be examined is to be submitted by the Builder forapproval.

2.6.25 For the hull structure of units designed tooperate in low air/sea temperatures, the recommendedextent of non-destructive examination will be speciallyconsidered but is not to be less than that defined in Tables8.2.3 and 8.2.4 as applicable.

2.6.26 The Bui lder is to carry out random non-destructive examination at the request of the Surveyor.

2.6.27 Weld defect acceptance levels and fabricationtolerances are to be in accordance with good shipbuildingpractices and are to be agreed with LR before fabrication iscommenced. In general, the acceptance levels for welddefects are to be in accordance with Table 8.2.5 andfabrication tolerances are to comply with Section 6. It isimportant to ensure that compatibility exists between designcalculations and construction standards particularly in fatiguesensitive areas.

2.6.28 All defective sections of welds are to be repairedin accordance with an appropriate, qualified repair procedure,and re-inspected.

2.6.29 The recommended scope of weld inspection in 2.6.24 may require to be increased in the event of failuresin the Builder’s or Sub-contractor’s quality procedures, toensure appropriate corrective actions are being implemented.

2.7 Butt welds

2.7.1 Abrupt change of section is to be avoided whereplates of different thicknesses are to be butt welded. Wherethe difference in thickness exceeds 3 mm, the thicker plate tobe welded is to be prepared with a taper not exceeding 1 in 3or with a bevelled edge to form a welded joint proportionedcorrespondingly. Where the difference in thickness is lessthan 3 mm, the transition may be achieved within the width ofthe weld. Difference in thickness greater than 3 mm may beaccepted provided it can be proven by the Builder, throughprocedure tests, that the Rule transition shape can beachieved and that the weld profile is such that structuralcontinuity is maintained to the Surveyor’s satisfaction.

2.7.2 Where stiffening members are attached bycontinuous fillet welds and cross completely finished butt orseam welds, these welds are to be made flush in way of thefaying surface. Similarly, for butt welds in webs of stiffeningmembers, the butt weld is to be completed and generallymade flush with the stiffening member before the fillet weld ismade. The ends of the flush portion are to run out smoothlywithout notches or sudden change of section. Where theseconditions cannot be complied with, a scallop is to bearranged in the web of the stiffening member. Scallops are tobe of such size, and in such a position, that a satisfactoryweld can be made.





Recommended extent of testing, see Note 1

Structural Item Location Volumetric Magnetic particlecheckpoints checkpoints

Intersection of butts and seams Throughout: See Note 2 See Note 2of fabrication and section welds • hull envelope

• longitudinal and transverse bulkheads• inner bottom and hopper

Butt welds in plating Throughout 5%, see Note 3 5%, see Note 3

Seam welds in plating Throughout See Note 4 See Note 4

Butts in longitudinals • Hull envelope within 0,4L amidships 10% 10%• Hull envelope outside 0,4L amidships 5% 5%

Bilge keel butts Throughout 100% 100%

Structural items when made with full/partial Throughout 10%, see Note 5 10%, see Note 5penetration welding as follows:• hopper knuckles• sheerstrake to deck stringer• hatchways coaming to deck

Penetrations and attachments to hull, Throughout 100% 100%e.g. sea inlets, piping, anode supports

Moonpool integration structure Throughout See Note 2 See Note 2

Topside support structure connections Throughout 25%, see Note 6 25%, see Note 6to hull and hull structure in way

Flare stack and crane pedestal structure Throughout 50%, see Note 6 50%, see Note 6

Connections to deck Local 100% 100%

Other structural items Throughout See Note 4 See Note 4

Side shell butts, seams and intersection • Forward end See Note 7 See Note 7welds where vessel is strengthened for operations in ice. • Remainder See Note 8 See Note 8

Exposed shell butts, seams and Throughout See Note 8 See Note 8intersection welds where vessel is designed for low temperature operations

Local areas identified as fatigue sensitive, e.g. :• Identified bracket connections at Local – 25%

intersections of side shell longitudinals and transverse frames and bulkheads

• Key locations identified on turret Local 100% 100%moonpool integration structure

• Topside support stool welds to upper Local 100% 100%deck and underdeck welds in way

• Flare stack support welds to upper Local 100% 100%deck and underdeck welds in way

NOTES1. The diameter of each checkpoint is to be between 0,3 and 0,5

metres, and volumetric and magnetic particle checks are to becarried out unless indicated otherwise.

2. 10 per cent selection of butts and seams and 20 per cent atintersections. Particular attention is to be given in way of stops andstarts of automatic and semi-automatic welding during fabrication.

3. In addition to those at intersections.4. Random selection to the Surveyor’s satisfaction.5. Particular attention is also given to ends of bracket connections

where fitted.6. Particular attention to be given in way of weld intersections and

discontinuities at stops and starts positions.

7. 10 per cent selection of butts and seams and 30 per cent atintersections. Particular attention to be taken in way of stops andstarts of automatic and semi-automatic welding during fabrication.

8. 10 per cent selection of butts and seams and 25 per cent atintersections. Particular attention to be given in way of stops andstarts of automatic and semi-automatic welding during fabrication.

9. Agreed locations are not to be indicated on blocks prior to thewelding taking place, nor is any special treatment to be given atthese locations.

10. Particular attention is to be given to repair rates. Additional weldsare to be tested in the event that defects such as lack of fusion orincomplete penetration are repeatedly observed.

Table 8.2.3 Non-destructive examination of welds on surface-type units





Recommended extent of testing, see Note 9

Structural item Volumetric checkpoints Magnetic particle checkpoints

Bracing butt and seam welds 100% 100%

Bracing weld connections to:• columns• pontoons 100% 100%• upper hull• lower nodes

Attachments to bracings – 100%

Penetrations through bracings 100% 100%

Bracing shell attachment of diaphragms, gussets, stiffeners 100% 100%

Column shell butts and seams See Note 4 20%

Column weld connections to:• pontoons• upper hull 100% 100%• in way of anchor fairleads and sheaves

Internal column structure connections 5%, see Note 5 See Note 3

Pontoons, shell and bulkhead butts/seams See Note 4 20%

Internal pontoon structure 5%, see Note 5 See Note 3

Hull penetrations, subsea inlets, anode and attachments, 100% –piping connection supports, etc.

Bilge keel butts 100% 100%

Upper hull: Main bulkheads/deck girders See Notes 2 and 4 See Note 6

Strength decks and drill floor See Notes 2 and 4 See Note 7

In way of windlasses and mooring winches – 100%

Topside support structure connections to deck 25% 25%

Flare stack, crane pedestals and gusset connections to deck 100% 100%

Drill floor and derrick substructure See Notes 4 and 7 See Note 7

Helideck primary support 20% 20%

Helideck remainder See Note 8 –

Other items See Note 9 –

NOTES1. Back-up structure of the items in question is also to be included,

where applicable.2. 100 per cent in way of full penetration welding at end of

diaphragm plates, gussets, stiffeners, etc.3. 50 per cent in way of fillet welds around stiffener ends, notches,

cut-outs, drain hole openings, etc.4. 10 per cent selection of butts and seams, and 20 per cent at

intersections. Particular attention to be taken in way of stops andstarts of automatic and semi-automatic welding during fabrication.

5. 10 per cent random selection of butt welds, of pontoon andcolumn shell longitudinal stiffeners and transverse andlongitudinal bulkheads stiffeners.

6. 10 per cent random selection of fillet welds in way of stiffenerends, drain hole openings, cut-outs, notches, etc.

7. Girder and sub-structure butt welds 100 per cent UT; principalconnections to deck and main structure 100 per cent UT and100 per cent MPI.

8. Random spot checks to the Surveyor’s satisfaction.9. The diameter of each checkpoint is to be between 0,3 and 0,5 m,

and both volumetric and magnetic particle checks are to becarried out unless indicated otherwise.

Table 8.2.4 Non-destructive examination of welds on column-stabilized units





2.8 Lap connections

2.8.1 Overlaps are generally not to be used to connectplates which may be subjected to high tensile or compressiveloading and alternative arrangements are to be considered.Where, however, plate overlaps are adopted, the width of theoverlap is not to exceed four times nor be less than threetimes the thickness of the thinner plate and the joints are tobe positioned as to allow adequate access for completion ofsound welds. The faying surfaces of lap joints are to be inclose contact and both edges of the overlap are to havecontinuous fillet welds.

2.9 Closing plates

2.9.1 For the connection of plating to internal webs,where access for welding is not practicable, the closingplating is to be attached by continuous full penetration weldsor by slot fillet welds to face plates fitted to the webs. Slotsare to have a minimum length of 90 mm and a minimumwidth of twice the plating thickness, with well rounded ends.Slots cut in plating are to have smooth, clean and squareedges and should by spaced not more than 230 mm apartcentre to centre. Slots are not to be filled with welding. Forrudder closing plates, see Ch 10,1.1.1.

Special and primary structure

Undercut

Shrinkage grooves/ root concavities

Excess penetration

Misalignment

Crack / Lamellar tears

Lack of:• root fusion• side fusion• interrun fusion

• root penetration

Porosity:

• Individual pore

• Uniformly distributed porosity

Slag:

• Individual and parallel to weld axis

• Linear group

Permitted maximum

t = plate thicknessl = length of defect

W = width of defect

Symbols

NOTES1. LR is prepared to accept other International and Nationally recognized Standards relating to construction, welding and acceptance criteria.

Where it is intended to utilize such Standards, the acceptance of same should be agreed prior to commencement of construction.2. Special, primary and secondary structure are defined in Ch 2,2.3. Certain joints/weldments of special structure may need special consideration with reference to the degree of undercut allowable, if any.

Table 8.2.5 Weld defect acceptance level

Defect type

Secondary structure

Intermittent undercut is permitted, providedthe depth does not exceed 0,25 mm, seeNote 3.

Permitted in acute heel of Y connection welds provided slight

Permitted in heel of Y connnection weld

provided slight

but not greater than 3 mm

l = but not greater than 6 mm

W = 1,5 mm max.

Aggregate length not to exceed t in a length of 30t

t2

t4

Intermittent undercut is permitted, providedthe depth does not exceed 0,4 mm

Slight intermittent shrinkage grooves and rootconcavities permitted to a maximum depthof 1,2 mm

Slight lack of penetration permitted

3 mm for t ≤ 50 mm4,5 for t > 50 mm ≤ 75 mm6,0 mm for t > 75 mm

l = t but not greater than 25 mm

W = 1,5 mm max.

Aggregate length not to exceed t in a lengthof 12t

Maximum 3 mm

but not greater than 3 mm but not greater than 3 mm

Not permitted

Not permittedNot permittedNot permitted

Not permitted

t5

t10


2.10 Stud welding

2.10.1 Where permanent or temporary studs are to beattached by welding to main structural parts in areas subjectto high stress, the proposed location of the studs and thewelding procedures adopted are to be submitted forapproval. In general, studs are to be welded to the samestandard as the main structure.

2.11 Fillet welds

2.11.1 T-connections are generally to be made by filletwelds on both sides of the abutting plate. Where theconnection is highly stressed, deep penetration or fullpenetration welding may be required. Where full penetrationwelding is required, the abutting plate may be required to bebevelled.

2.11.2 Fillet welds are to be continuous in all locationsdefined in 2.11.11.

2.11.3 Intermittent welding may be used for secondarystructural items and in all areas where double continuouswelding is not defined in 2.11.11.

2.11.4 The throat thickness of fillet welds based on theweld factors given in Table 8.2.6 is to be determined asfollows:• Double continuous welding:

Throat thickness = tp x weld factor• Intermittent welding:

Throat thickness = tp x weld factor x

wheres = the length, in mm, of correctly proportioned

weld fillet, clear of end craters, and is to benot less than 75 mm

d = the distance between start positions ofsuccessive weld fillets, in mm

tp = plate thickness, in mm, on which weld filletsize is based, see Fig. 8.2.7.

2.11.5 The leg length of the weld is to be not less than x the specified throat thickness.

2.11.6 Weld sizes should be clearly defined as throatthickness or leg length on the plans submitted for approval.

2.11.7 Where an approved automatic deep penetrationprocedure is used, the weld factors given in Table 8.2.6 maygenerally be reduced by 15 per cent. Consideration may begiven to reductions of up to 20 per cent provided that theShipyard is able to consistently meet the following requirements:(a) Suitable process selection confirmed by welding

procedure tests covering both minimum and maximumroot gaps.

(b) Demonstrate, to the satisfaction of the Surveyor, that anestablished quality control system is in place.

2.11.8 The plate thickness, tp, to be used in the abovecalculation is generally to be that of the thinner of the twoparts being joined. Where the difference in thickness isconsiderable, the size of fillet will be considered.

2

ds




2.11.9 Where the thickness of the abutting member ofthe connection (e.g. the web of a stiffener) is greater than15 mm and exceeds the thickness of the table member (e.g.plating), the welding is to be double continuous and thethroat thickness of the weld is to be not less than thegreatest of the following: (a) 0,21 x thickness of the table member. The table

member thickness used need not exceed 30 mm.(b) 0,21 (0,27 in tanks) x half the thickness of the abutting

member. (c) As required by item 3 in Table 8.2.7.

2.11.10 Except as permitted by 2.11.9, the throatthickness of the weld is not to be outside the limits specifiedin Table 8.2.7.

Fig. 8.2.7 Weld types

t2

t1

tp = lesser of t1 or t2 Leg length

(a) Weld fillet dimensions

Throat thickness

150 mmmax.

(b) Staggered intermittent

s

150 mmmax.

(c) Chain intermittent

sd

d

150 mmmax.

sd

Depth of scallop not greaterthan 0,25dw or 75 mm, whichever is the lesser

Welding to be carriedround ends of all lugs

Radius not lessthan 25 mm dw

(d) Scalloped construction

NOTE s to be not less than 75 mm, in all cases 4407/90





Table 8.2.6 Weld factors (see continuation)

Item Weld factor Remarks

(1) General application:

(a) Shell boundaries of columns to lower and upper hulls

(b) Internal watertight or oiltight plate boundaries

(c) Non-tight plate boundaries

(d) Longitudinals, frames, beams, and other secondary members to shell, deck or bulkhead plating

(e) Panel stiffeners, etc.

(f) Overlap welds, generally

(g) Longitudinals of the flat-bar type to plating

except as required below

generally, but alternative proposals based on items 2 and 3 of Table 8.2.10 will be considered inspecific areas

in tanksin way of end connections

see 2.11.9

full penetration

0,34

0,13

0,100,130,21

0,10

0,27

(2) Bottom construction in general:

(a) Non-tight centre girder : • to keel • to inner bottom

(b) Non-tight boundaries of floors, girders andbrackets

(c) Connection of floors to inner bottom in way ofplane bulkheads, bulkhead stools, or corru-gated and double plate bulkheads supportedon inner bottom. The supporting floors are tobe continuously welded to the inner bottom

0,270,21

0,210,27

0,44

no scallops

in way of 0,2 x span at endsin way of brackets at lower end of main frame

weld size based on floor thickness;weld material compatible with floor material

(3) (a) Upper hull framing and hull framing on selfelevating and surface units:

(i) Webs of web frames and stringers:• to shell• to face plate

(ii) Tank side brackets to shell and inner bottom

(b) Primary hull framing and girders on lowerhulls, columns, caissons and buoys

0,160,13

0,34

to be in accordance with Table 8.2.8

(4) Decks and supporting structure:

(a) Strength deck plating to shell

(b) Other decks to shell and bulkheads (except where forming tank boundaries)

(c) Webs of cantilevers to deck and to shell inway of root bracket

(d) Webs of cantilevers to face plate

(e) Pillars: • fabricated• end connections• end connections (tubular)

(f) Girder web connections and brackets in wayof pillar heads and heels

(g) Primary deck girders and connectionsbetween primary members on column-stabilized and tension-leg units

0,21

0,44

0,21

0,100,34

full penetration

0,21

as shown in Table 8.2.8, but alternative proposals willbe considered

generally continuous

see Note 1

continuous

generally to comply with Table 8.2.8, but full penetrationwelding may be required






(5) Bulkhead and tank construction:

(a) Plane, double plate and corrugated watertightbulkhead boundary at bottom, bilge, inner bottom,deck and connection to shell plate, where fitted

(b) Shell plate connection to stool

(c) Plane, double plate and corrugated bulkheadboundaries in way of deep tanks:

• Boundary at bottom, bilge, inner bottom and deck

• Connection of stool and bulkhead to lower stool shelf plating

• Connection of stool and bulkhead plating to upper stool shelf plate

• Connection of bulkhead plating to hopper and topside tanks

• Connection of bulkhead plating to side shell

(d) Secondary members where acting as pillars

(e) Non-watertight pillar bulkhead boundaries

(f) Perforated flats and wash bulkhead boundaries

weld size to be based on thickness of bulkheadsplating;

weld materials to be compatible with bulkhead platingmaterials

weld size to be based on thickness of stool at junctionwith shelf plate;

weld material to be compatible with stool material

0,44

0,44

0,44

full penetration

0,44

0,440,34

0,13

0,13

0,10

(6) Structure in crude oil storage tanks in oil storage units:

(a) Longitudinals to shell

(b) Longitudinal of flat-bar type to plating

(c) Connections between primary structural members

(d) For connections of primary structure:• longitudinal bulkhead• transverse bulkhead

(e) Vertical corrugations to an inner bottom

(f) Non-tight bulkhead boundaries to plating

0,21

0,440,34

0,440,340,44

full penetration

0,21

for forward 0,3L

see 2.11.9

at bottomat deck

in accordance with Table 8.2.6

at deck, sides and longitudinal bulkheadat bottom

(7) Self-elevating units:

(a) Leg construction, general(b) Leg connections to footings or mats(c) Internal webs, girders and bulkheads in

footings and mats(d) Internal stiffeners in footings and mats(e) Jack houses, general(f) Bulkheads and primary structures in way of

leg wells

full penetrationfull penetration

0,440,340,44

0,44

see also 2.15 for tubular members

full penetration may be required



(8) Main bracings and ‘K’ joints, etc.:

(a) Ring frames, girders and stiffeners

(b) Shell boundaries and end connections includ-ing brackets, gussets and cruciform plates

full penetration

full penetration

generally, but alternative proposals may be considered

(9) Structure in machinery spaces:

(a) Centre girder to keel and inner bottom

(b) Floors to centre girder in way of engine, thrustand boiler bearers

(c) Floors and girders to shell and inner bottom

(d) Main engine foundation girders:• to top plate• to hull structure

(e) Floors to main engine foundation girders

(f) Brackets, etc., to main engine foundation girders

(g) Transverse and longitudinal framing to shell

0,27

0,27

0,21

deep penetration todepend on design

0,27

0,21

0,13

no scallops to inner bottom

edge to be prepared with maximum root 0,33tp deeppenetration, generally








(10) Construction in 0,25L forward on surface-typeunits:

(a) Floors and girders to shell and inner bottom

(b) Bottom longitudinals to shell

(c) Transverse and longitudinal side framing to shell

(d) Tank side brackets to frame and inner bottom

(e) Plating stringers to shell and frames

(f) Fore peak construction: all internal structure unless a greater weld factor is required

0,21

0,13

0,13

0,34

0,34

0,13

(11) After peak construction:

(a) All internal structure and stiffeners on after peak bulkhead 0,21 unless a greater weld factor is required

(12) Superstructure and deckhouses:

(a) Connection of external bulkheads to deck

(b) Forecastle framing to shell 0,15L forward

(c) Internal bulkheads

0,340,21

0,21

0,13

1st and 2nd tier erectionselsewhere

0,34 at end connections

(13) Hatchways and closing arrangements:

(a) Hatchways coamings to deck

(b) Hatch cover rest bar

(c) Hatch coaming stays to coaming

(d) Hatch coaming stays to deck

(e) Cleats and fittings

(f) Primary and secondary stiffening of hatch covers

0,34

0,16

0,13

0,21

0,44

0,10

0,44 at corners

full penetration welding may be required

0,13 for tank covers and where covers strengthened forloads over

(14) Steering control systems:

(a) Rudder:• Fabricated mainpiece and mainpiece to

side plates and webs• Slot welds inside plates• Remaining construction

(b) Fixed and steering nozzles:• Main structure• Elsewhere

(c) Fabricated housing and structure of thruster units, stabilizers, etc.:• Main structure• Elsewhere

0,440,440,21

0,440,21

0,10

0,440,21





2.11.11 Continuous welding is to be adopted in thefollowing locations, and may be used elsewhere if desired: (a) Boundaries of weathertight decks, platforms and

erections, including hatch coamings, companionwaysand other openings.

(b) Boundaries of tanks and watertight compartments.(c) All welding inside tanks and peak compartments. (d) Primary and secondary members to shell in lower hulls

and stability columns.(e) Primary and secondary members to main bracings,

trusses or ‘K’ joints.(f) Primary and secondary members to bottom shell in the

forward 0,3L on surface-type units.(g) Legs, footings, mats, jackhouse and leg well structures

on self-elevating units.(h) Primary and secondary members to plating in way of

end connections, and end brackets to plating in thecase of lap connections.

(j) Where 2.11.9 applies.(k) Other connections or attachments, where considered

necessary, and in particular the attachment of minorfittings to higher tensile steel plating.

(l) Fillet welds where higher tensile steel is used.(m) Forecastle shell framing in forward 0,2L.

2.11.12 Where intermittent welding is used, the weldingis to be made continuous in way of brackets, lugs andscallops and at the orthogonal connections with othermembers.

Table 8.2.6 Weld factors (conclusion)


(15) Miscellaneous structures, fittings and equipment:

(a) Rings and coamings for manhole type coversto shell on stability columns and lower hulls

(b) Rings for manhole type covers, to deck or bulkhead

(c) Frames of watertight and weathertight bulkhead doors

(d) Stiffening of doors

(e) Ventilator, air pipes, etc., coamings to deck

(f) Ventilator, etc., fittings

(g) Scuppers and discharges, to deck

(h) Masts, flare structures, crane pedestals, etc.,to deck

(j) Turret and swival supports

(k) Deck machinery seats to deck

(l) Process plant stools to deck

(m) Mooring equipment seats, fairleads and chainstoppers

(n) Bulwark stays to deck

(o) Bulwark attachment to deck

(p) Guard rails, stanchions, etc., to deck

(q) Bilge keel ground bars to shell

(r) Bilge keels to ground bars

(s) Fabricated anchors

full penetration

0,34

0,34

0,21

0,340,21

0,21

0,44

0,44

0,44

0,21

0,44

0,44

0,21

0,34

0,34

0,34

0,21

full penetration

generally, but alternative proposals may be considered

Load line Positions 1 and 2elsewhere



generally



0,34 in forward 0,15L on surface-type units

continuous fillet weld, minimum throat thickness 4 mm

light continuous or staggered intermittent fillet weld,minimum throat thickness 3 mm

NOTEWhere pillars are fitted inside tanks or under watertight flats, the end connection is to be such that the tensile stress in the weld does not exceed108 N/mm2 (11 kgf/mm2).

Table 8.2.7 Throat thickness limits

ItemThroat thickness, in mm

Minimum Maximum

(1) Double continuous welding 0,21tp 0,44tp

(2) Intermittent welding 0,27tp 0,44tpor 4,5

(3) All welds, overriding minimum: (a) Plate thickness tp ≤ 7,5 mm

• Hand or automatic welding 3,0 –• Automatic deep penetration

welding 3,0 –(b) Plate thickness tp > 7,5 mm

• Hand or automatic welding 3,25 –• Automatic deep penetration

welding 3,0 –

NOTES1. In all cases, the limiting value is to be taken as the greatest of

the applicable values given above.2. Where tp exceeds 25 mm, the limiting values may be calcu-

lated using a notional thickness equal to 0,5 (tp + 25) mm.3. The maximum throat thicknesses shown are intended only as a

design limit for the approval of fillet welded joints. Any weldingin excess of these limits is to be to the Surveyor’s satisfaction.





2.11.13 Where structural members pass through theboundary of a tank, and leakage into the adjacent spacecould be hazardous or undesirable, full penetration welding isto be adopted for the members for at least 150 mm on eachside of the boundary. Alternatively a small scallop of suitableshape may be cut in the member close to the boundaryoutside the compartment, and carefully welded all round.

2.12 Welding of primary structure

2.12.1 Weld factors for the connections of primarystructure are given in Table 8.2.8.

2.12.2 The weld connection to shell, deck or bulkheadis to take account of the material lost in the notch wherelongitudinals or stiffeners pass through the member. Wherethe width of notch exceeds 15 per cent of the stiffenerspacing, the weld factor is to be multiplied by:

2.12.3 Where direct calculation procedures have beenadopted, the weld factors for the 0,2 x overall length at theends of the members will be considered in relation to thecalculated loads.

2.12.4 The throat thickness limits given in Table 8.2.7are to be complied with.

2.13 Welding of primary and secondary memberend connections

2.13.1 Welding of end connections of primary membersis to be such that the area of welding is not less than thecross-sectional area of the member, and the weld factor is tobe not less than 0,34 in tanks or 0,27 elsewhere.

0,85 x stiffener spacinglength of web plating between notches

2.13.2 The welding of secondary member endconnections is to be not less than as required by Table 8.2.9.Where two requirements are given the greater is to becomplied with.

2.13.3 The area of weld, Aw, is to be applied to eacharm of the bracket or lapped connection.

2.13.4 Where a longitudinal strength member is cut at aprimary support and the continuity of strength is provided bybrackets, the area of weld is to be not less than the cross-sectional area of the member.

2.13.5 Where the secondary member passes through,and is supported by, the web of a primary member, the weldconnection is to be in accordance with 5.2.

2.13.6 The throat thickness limits given in Table 8.2.7are to be complied with.

2.14 Welding of aluminium alloys

2.14.1 Where welding of aluminium alloy is employed,the requirements given in this Section are to be complied withso far as they are applicable, with the following additions:(a) The joint edges and both sides of the plate at the joint

are to be wire brushed thoroughly, preferably usingpower-driven rotary brushes, immediately before welding is commenced.

(b) Parts are to be set up and welded in such a way thatcontraction stresses are kept to a minimum.

2.14.2 All welding is to be carried out using the metal-arc inert gas or tungsten inert gas arc welding processes,unless otherwise agreed.

2.14.3 Where it is proposed to use other weldingprocesses, details are to be submitted for approval.

Table 8.2.8 Connections of primary structure

Primary member face area, in cm2 Weld factor

In dry spacesIn tanks

To platingTo face plateTo platingTo face plate

Position,see Note 1

Not exceedingExceeding

30,0

65,0

95,0

130,0

30,0

65,0

95,0

130,0

At endsRemainder

At endsRemainder

At endsRemainder

At endsRemainder

At endsRemainder

0,210,10

0,210,13

0,340,27, see Note 2

0,340,27, see Note 2

0,440,34

0,270,16

0,340,27

0,44, see Note 30,34

0,44, see Note 30,34

0,44, see Note 30,34

0,210,10

0,210,13

0,210,16

0,270,21

0,340,27

0,210,13

0,210,16

0,270,21

0,340,27

0,44, see Note 30,34

NOTES1. The weld factors ‘at ends’ are to be applied for 0,2 x the overall

length of the member from each end, but at least beyond thetoes of the member end brackets. On vertical webs theincreased welding may be omitted at the top, but is to extend atleast 0,3 x overall length from the bottom.

2. Weld factor 0,34 in crude oil storage tanks.

3. Where the web plate thickness is increased locally, the weld sizemay be based on the thickness clear of the increase, but is to benot less than 0,34 x the increased thickness.

4. The final throat thickness of the weld fillet to be not less than0,34tp in crude oil storage tanks.


2.14.4 Welding consumables are to comply with therequirements of Pt 2, Ch 11,9, and are to be approved forspecific welds in the structures of mobile units.

2.14.5 Alloy grades which may contain more than 0,10 per cent copper, such as Grade 6061, are not normallyacceptable for use in direct contact with sea-water becauseof an inadequate resistance to corrosion.

2.14.6 Welding consumables are selected on the basisof corrosion resistance and strength. The 5083 and 5086alloys are normally welded using the 5356, 5556 or 5183consumables and the 6061 and 6082 alloys are usuallywelded using the 4043 consumable. Where consumables ofhigh magnesium are used, adequate protection by coating isto be provided to avoid risk of stress corrosion cracking.

2.14.7 Special care is to be taken in the distribution,storage and handling of all welding consumables. Aluminiumfiller metals should be kept in a heated dry storage area witha relatively uniform temperature. Condensation on the metalsurface during storage and use should be avoided. Fluxcoated electrodes and submerged arc fluxes are to be storedunder controlled conditions. Other welding consumablessuch as bare wire and welding studs are to be stored underdry conditions to prevent rusting. Effective facilities forprotecting consumables are to be provided close to workingareas.

2.14.8 Aluminium alloys are not required to be hardnessnor impact tested, otherwise testing and weld procedures areto be the same as required for steel in this Section.




2.15 Welding of tubular members

2.15.1 Welding is to comply with agreed Internationallyor Nationally accepted Codes such as AWS or API and allwelding, generally is to conform to the following:(a) All steel is to be joined by complete penetration groove

welds.(b) Unless single sided welding has been agreed for the

particular weld configuration, double sided welds are tobe used, wherever practicable.

(c) In lattice-type structures, a minimum weld attachmentlength at the cord of 1,5 times the brace wall thicknessis required at all locations. This is based on fatigueconsiderations.

(d) Care is to be taken to ensure the weld surface profile issmooth and blends with the parent material.

(e) Backing strips are not to be used unless speciallyagreed with LR.

(f) Root gaps are to be generally in the range of 3 to 6 mm.(g) Bevels are to be such that the included angle is in the

range 45° to 60°. However, when the dihedral angle isless than 45°, the included angle may be reduced asindicated for locations 4 and 5, see Fig. 8.2.9.

(h) Where saddle weld toe grinding has been agreed as amethod of improving fatigue life, at the locationsagreed, the grinding of the weld toe is to produce asmooth transition between the weld and the parentplate. The grinding should remove all defects, slaginclusions and any undercut. Overgrinding into theparent plate is not to exceed 2 mm or 0,05 times theplate thickness, whichever is less. The grinding toolshould preferably have a spherical head (e.g. a tung-sten carbide burr) and, in general, disk-grinders are tobe avoided except for initial heavy grinding. Any marksmade by rotation of the grinding tool are to be alignedwith the direction of stress. The surface of the mainbody of the weld may be dressed to produce a betterconcave profile if the as-welded profile is poor, see Fig.8.2.8 and Fig. 8.2.15. Care must be exercised in orderthat overgrinding does not excessively reduce the sizeof the attachment weld and in no case less than thatrequired by the Rules.

Table 8.2.9 Primary and secondary member end connection welds

Connection Weld area, Aw, in cm2 Weld factor

(1) Stiffener welded direct to plating

(2) Bracketless connection of stiffeners or stiffener lapped to bracket or bracket lappedto stiffener:(a) in dry space

(b) in tank

(c) main frame to tanks side bracket in 0,15L forward

(3) Bracket welded to face of stiffener and bracket connection to plating

(4) Stiffener to plating for 0,1 x span at ends, or in way of end bracket if that be greater

0,25As or 6,5 cm2

whichever is the greater

as (a) or (b)

––

––

1,4 Z

1,2 Z

0,34

0,27

0,34

0,34

0,34

0,34

Symbols

As = cross sectional area of the stiffener, in cm2

Aw = the area of the weld, in cm2, and is calculated as total length of weld, in cm x throat thickness, in cmZ = the section modulus, in cm2, of the stiffener on which the scantlings of the bracket are based, see Section 3.

NOTEFor maximum and minimum weld fillet sizes, see Table 8.2.7.





2.15.2 Locations 1, 2, 3, 4 and 5 are related to the localdihedral angle (the angle between the brace wall and chordwall). Transition from one detail to another is to be by gradualuniform level preparation and surface profile, see Fig. 8.2.9.

1

2

3

ItemStringer plate

thicknessmm

Weld type

t ≤ 15

15 < t ≤20

t > 20

Double continuous fillet weldwith a weld factor of 0,44

Single vee preparation toprovide included angle of 50°with root R ≤ 1/3t in conjunctionwith a continuous fi l let weldhaving a weld factor of 0,39

orDouble vee preparation toprovide included angles of 50°with root R ≤ 1/3t

Double vee preparation toprovide included angles of 50°with root R ≤ 1/3t but not toexceed 10 mm

NOTES1. Welding procedure, including joint preparation, is to be

specified. Procedure is to be qualified and approved forindividual Builders.

2. See also 2.11.13.3. For thickness t in excess of 20 mm the stringer plate may be

bevel led to achieve a reduced thickness at the weldconnection. The length of the bevel is, in general, to be basedon a taper not exceeding 1 in 3 and the reduced thickness is,in general, to be not less than 0,65 times the thickness ofstringer plate or 20 mm, whichever is the greater.

4. Alternative connection will be considered.

��R

50°

50°

Where t = thickness of stringer plate, in mm

Single vee preparation

Double vee preparation4407/91

or

50°

R

Fig. 8.2.8 Grinding of weld toe

Table 8.2.10 Weld connection of strength deck platingto shell/sheerstrake

Fig. 8.2.9 Local dihedral angle for weld profile locations





Fig. 8.2.10 Welding at location 1







Fig. 8.2.15 Weld grinding





SECTION 3Secondary member end connections

3.1 General

3.1.1 Secondary members, that is longitudinals,beams, frames and bulkhead stiffeners forming part of thehull structure, are generally to be connected at their ends inaccordance with the requirements of this Section. Where it isdesired to adopt bracketless connections, the proposedarrangements will be individually considered.

3.1.2 Where end connections are fitted in accordancewith these requirements, they may be taken into account indetermining the effective span of the member.

3.1.3 Where the section modulus of the secondarymember on which the bracket is based (see 3.3.2) exceeds2000 cm3, the scantl ings of the connection wil l beconsidered.

3.2 Symbols


a, b = the actual lengths of the two arms of thebracket, in mm, measured from the plating tothe toe of the bracket

bf = the breadth of the flange, in mmt = the thickness of the bracket, in mmZ = the section modulus of the secondary

member, in cm3.

3.3 Basis for calculation

3.3.1 Where a secondary member which contributesto the overall strength of the hull is cut at a primary supportand the continuity of strength is provided by brackets, thescantlings of the brackets are to be such that their sectionmodulus and effective cross-sectional area are not less thanthose of the member. Care is to be taken to ensure correctalignment of the brackets on each side of the primarymember.

3.3.2 In other cases to those stated in 3.3.1 thescantlings of the bracket are to be based on the modulus asfollows:(a) Bracket connecting stiffener to primary member:

modulus of the stiffener.(b) Bracket at the head of a main transverse frame where

frame terminates: modulus of the frame.(c) Brackets connecting lower deck beams or longitudinals

to the main frame in the forward 0,15L on surface units: modulus of the frame.

(d) Elsewhere: the lesser modulus of the members beingconnected by the bracket.

3.3.3 Typical arrangements of stiffener end bracketsare shown diagrammatically in Fig. 8.3.1.

Fig. 8.3.1 Diagrammatic arrangements of stiffener end brackets

b

a

a

b

a

b

a

b

a

b

4407/97


3.4 Scantlings of end brackets

3.4.1 The lengths, a and b, of the arms are to bemeasured from the plating to the toe of the bracket and areto be such that:(a) a + b ≥ 2,0l(b) a ≥ 0,8l(c) b ≥ 0,8lwhere

l =

but in no case is l to be taken as less than twice the webdepth of the stiffener on which the bracket scantlings are tobe based.

3.4.2 The length of arm of tank side brackets is to benot less than 20 per cent greater than that required above.

3.4.3 The thickness of the bracket is to be not lessthan as required by Table 8.3.1.

3.4.4 The free edge of the bracket is to be stiffenedwhere any of the following apply:(a) The section modulus, Z, exceeds 500 cm3.(b) The length of free edge exceeds 50t mm.(c) The bracket is fitted at the lower end of main transverse

side framing.

3.4.5 Where a flange is fitted, its breadth is to be notless than:

bf =

but not less than 50 mm

3.4.6 Where the edge is stiffened by a welded face flat,the cross-sectional area of the face flat is to be not less than:(a) 0,009bf t cm2 for offset edge stiffening.(b) 0,014bf t cm2 for symmetrically placed stiffening.

3.4.7 Where the stiffening member is lapped on to thebracket, the length of overlap is to be adequate to provide forthe required area of welding. In general, the length of overlapshould be not less than 10 mm, or the depth of stiffener,whichever is the greater.

Z

40 1 + Z1000

mm

90 2 Z14 + Z

– 1 mm




3.4.8 Where the free edge of the bracket is hollowedout, it is to be stiffened or increased in size to ensure that themodulus of the bracket through the throat is not less thanthat of the required straight edged bracket.

3.5 Arrangements and details

3.5.1 The arrangement of the connection between thestiffener and the bracket is to be such that at no point in theconnection is the modulus reduced to less than that of thestiffener with associated plating.

3.5.2 The design of end connections and theirsupporting structure is to be such as to provide adequateresistance to rotation and displacement of the joint.

Table 8.3.1 Thickness of brackets

Bracket Thickness,in mm

Limits

Minimumin mm

Maximumin mm

With edge stiffened:

(a) in dry spaces

(b) in deep tanks

(c) in storage tankregion of oilstorage units

Unstiffened brackets 5,5 + 0,25 Z

4,5 + 0,25 Z

4,5 + 0,25 Z

3,5 + 0,25 Z 6,5

7,5

7,5see Note

8,5see Note

12,5

13,5

13,5

14,5

NOTEMinimum thickness not to be less than compartment thickness givenin Pt 3, Ch 3, 2.15.





SECTION 4Construction details for primary members

4.1 General

4.1.1 The requirements for section modulus and inertia( i f appl icable) of primary members are given in theappropriate Chapter. This Section includes the requirementsfor proportions, stiffening and construction details for primarymembers in dry spaces and in tanks of all unit types.

4.1.2 The requirements of this Section may bemodified where direct calculation procedures are adopted toanalyse the stress distribution in the primary structure.

4.2 Symbols


dw = depth of member, in mmk = higher tensile steel factor, see Ch 2,1.2

tw = thickness of member web, in mmAf = area of member face plate or flange, in cm2

Sw = spacing of stiffeners on member web, ordepth of unstiffened web, in mm.

4.3 Arrangements

4.3.1 Primary members are to be so arranged as toensure effective continuity of strength, and abrupt changes ofdepth or section are to be avoided. Where members abut onboth sides of a bulkhead, or on other members, arrangementsare to be made to ensure that they are in alignment. Primarymembers in tanks are to form a continuous line of supportand, wherever possible, a complete ring system.

4.3.2 The members are to have adequate lateralstability and web stiffening and the structure is to bearranged to minimize hard spots and other sources of stressconcentration. Openings are to have well rounded cornersand smooth edges and are to be located having regard to thestress distribution and buckling strength of the panel.

4.3.3 Primary members are to be provided withadequate end fixity by end brackets or equivalent structure.The design of end connections and their supporting structureis to be such as to provide adequate resistance to rotationand displacement of the joint and effective distribution of theload from the member.

4.3.4 Where the primary member is supported by astructure which provides only a low degree of restraintagainst rotation, the member is generally to be extended forat least two frame spaces, or equivalent, beyond the point ofsupport before being tapered.

4.3.5 Where primary members are subject toconcentrated loads, particularly if these are out of line withthe member web, additional strengthening may be required.

4.4 Geometric properties and proportions

4.4.1 The geometric properties of the members are tobe calculated in association with an effective width ofattached plating determined in accordance with Ch 3,3.2.

4.4.2 The depth of the web of any primary member isin general to be not less than 2,5 times the depth of the cut-outs for the passage of secondary members, except wherecompensation is arranged to provide satisfactory resistanceto deflection and shear buckling in the web.

4.4.3 In general, the minimum thickness or area ofmaterial in each component part of the primary member is tocomply with the requirements of Table 8.4.1 but the minimumweb thickness of primary shell members in the lower hulls ofcolumn stabilized units and tension leg units is to be not lessthan 0,017Sw.

4.4.4 The minimum thickness or area of material ineach component part of the primary member is given in Table 8.4.1, see also 4.4.3.

4.4.5 Primary members constructed of higher tensilesteel are to comply with Table 8.4.1.

4.5 Web stability

4.5.1 Primary members of asymmetrical section are tobe supported by tripping brackets at alternate secondarymembers. If the section is symmetrical, the tripping bracketsmay be four spaces apart.

4.5.2 Tripping brackets are also to be fitted at the toesof end brackets and in way of heavy or concentrated loadssuch as the heels of pillars.

4.5.3 Where the ratio of unsupported width of faceplate (or flange) to its thickness exceeds 16:1, the trippingbrackets are to be connected to the face plate and onmembers of symmetrical section, the brackets are to be fittedon both sides of the web.

4.5.4 Intermediate secondary members may bewelded directly to the web or connected by lugs.

Item Requirement

(1) Member web plate, general,see Notes 1 & 2

(2) Member face plate

(3) Deck plating forming theupper flange of underdeckgirders

tw = 0,01Swbut not less than 7 mm in dry

spaces;and not less than 8 mm in tanks

or to satisfy item (2)

Plate thickness not less than:

, and 10 per cent

greater for side girders in way oflarge openings

Width of plate not less than700 mm

Af1,8k

mm

Af not to exceed dw tw150

cm2

NOTES1. For primary members having a web depth exceeding 1500 mm,

the arrangement of stiffeners will be individually considered, and stiffening parallel to the member face plate may be required.

2. Minimum thickness not to be less than compartment minimum thickness given in Pt 3, Ch 3, 2.15, see also 4.4.3.

Table 8.4.1 Minimum thickness of primary members


4.5.5 Where the depth of web of a primary girderincluded in the overall hull strength of the unit exceeds 55tw , additional longitudinal web stiffeners are to be fittedat a spacing not exceeding the value given. In cases wherethis spacing is exceeded, the web thickness is, in general, tobe suitably increased.

4.5.6 The arm length of unstiffened end brackets is notto exceed 100tw. Stiffeners parallel to the bracket face plateare to be fitted where necessary to ensure that this limit is notexceeded.

4.5.7 Web stiffeners may be flat bars of thickness, tw,and depth 0,1dw, or 50 mm, whichever is the greater.Alternative sections of equivalent moment of inertia may beadopted.

4.6 Openings in the web

4.6.1 Where openings are cut in the web, the depth ofopening is not to exceed 25 per cent of the web depth, andthe opening is to be so located that the edges are not lessthan 40 per cent of the web depth from the face plate. Thelength of opening is not to exceed the web depth or 60 percent of the secondary member spacing, whichever is thegreater, and the ends of the openings are to be equidistantfrom the corners of cut-outs for secondary members. Wherelarger openings are proposed, the arrangements andcompensation required will be considered.

4.6.2 Openings are to have smooth edges and wellrounded corners.

4.6.3 Cut-outs for the passage of secondary membersare to be designed to minimize the creation of stressconcentrations. The breadth of cut-out is to be kept as smallas practicable and the top edge is to be rounded, or thecorner radii made as large as practicable. The extent ofdirect connection of the web plating, or the scantlings of lugsor collars, is to be sufficient for the load to be transmittedfrom the secondary member.

4.7 End connections

4.7.1 End connections of primary members aregenerally to comply with the requirements of Section 3,taking Z as the section modulus of the primary member.

4.7.2 In no case is the depth of the end bracketmeasured from the face of the primary member to be lessthan the depth of the primary member. The two arm lengthsof the bracket are to be of approximately equal lengths.

4.7.3 The thickness of the bracket is to be not lessthan that of the primary member web. The free edge of thebracket is to be stiffened.

4.7.4 For connections between primary membersforming ring systems, see 4.8.

4.7.5 Where a deck girder or transverse is connectedto a vertical member on the shell or bulkhead, the scantlingsof the latter may be required to be increased to provideadequate stiffness to resist rotation of the joint.

k




4.7.6 Where a member is continued over a point ofsupport, such as a pillar or pillar bulkhead stiffener, thedesign of the end connection is to be such as to ensure theeffective distribution of the load into the support. Proposalsto f i t brackets of reduced scantl ings, or alternativearrangements, will be considered.

4.8 Primary member ring systems

4.8.1 Connections between primary members forminga ring system are to minimize stress concentrations at thejunctions. Integral brackets are generally to be radiused orwell rounded at their toes.

4.8.2 The arm length of the bracket, measured fromthe face of the member, is to be not less than the depth ofthe smaller member forming the connection, nor exceed 1,5 times the web depth. The two arm lengths of the bracketare to be of approximately equal lengths.

4.8.3 Where the end bracket is integral with the websof the members, and the face plate is carried continuouslyalong the edges of the members and the bracket, the fullarea of the largest face plate is to be maintained to the mid-point of the bracket and gradually tapered to the smaller faceplates. Butts in face plates are to be kept well clear of thetoes of brackets. Where a wide face plate abuts onto anarrower one, the taper is generally not to exceed 1 in 4.Where a thick face plate abuts against a thinner one, if thedifference in thickness exceeds 3 mm, the taper on thicknessis not to exceed 1 in 3.

4.8.4 The thickness of separate end brackets isgenerally to be not less than that of the thicker of the primarymember webs being connected. The bracket is to extend toadjacent tripping brackets, stiffeners or other support points.The toes of large brackets are to be well radiused. The freeedge of the bracket is to be stiffened and the arm lengths areto comply with 4.8.2.





SECTION 5Structural details

5.1 Continuity and alignment

5.1.1 The arrangement of material is to be such as willensure structural continuity. Abrupt changes of shape orsection, sharp corners and points of stress concentration areto be avoided.

5.1.2 Where members abut on both sides of abulkhead or similar structure, care is to be taken to ensuregood alignment.

5.1.3 Pillars and pillar bulkheads are to be fitted in thesame vertical l ine wherever possible, and elsewherearrangements are to be made to transmit the out of lineforces satisfactorily. The load at head and heel of pillars is tobe effectively distributed and arrangements are to be made toensure the adequacy and lateral stability of the supportingmembers.

5.1.4 Continuity is to be maintained where primarymembers intersect and where the members are of the samedepth, a suitable gusset plate is to be fitted.

5.1.5 End connections of structural members are toprovide adequate end fixity and effective distribution of theload into the supporting structure.

5.1.6 The toes of brackets, etc., should not land onunstiffened panels of plating. Special care is to be taken toavoid notch effects at the toes of brackets, by making the toeconcave or otherwise tapering it off.

5.1.7 Where primary and/or secondary members areconstructed of higher tensile steel, particular attention is to bepaid to the design of the end bracket toes in order tominimize stress concentrations. Sniped face plates which arewelded onto the edge of primary member brackets are to becarried well around the radiused bracket toe and are toincorporate a taper not exceeding 1 in 3. Where sniped faceplates are welded adjacent to the edge of primary memberbrackets, adequate cross-sectional area is to be providedthrough the bracket toe at the end of the snipe. In general,this area measured perpendicular to the face plate is to benot less than 60 per cent of the full cross-sectional area ofthe face plate, see Fig. 8.5.1.

5.2 Arrangements at intersections of continuous secondary and primarymembers

5.2.1 Cut-outs for the passage of secondary membersthrough the web of primary members, and the related collaring arrangements, are to be designed to minimize stressconcentrations around the perimeter of the opening and inthe attached hull envelope or bulkhead plating. The criticalshear buckling stress of the panel in which the cut-out ismade is to be investigated. Cut-outs for longitudinals will berequired to have double lugs in areas of high stress, e.g. inway of cross tie ends.

5.2.2 Cut-outs are to have smooth edges, and thecorner radii are to be as large as practicable, with a minimumof 20 per cent of the breadth of the cut-out or 25 mm,whichever is the greater. It is recommended that the webplate connection to the hull envelope or bulkhead should endin a smooth tapered ‘soft toe’. Recommended shapes ofcut-out are shown in Fig. 8.5.2, but consideration will begiven to other shapes on the basis of maintaining equivalentstrength and minimising stress concentration. Considerationis to be given to the provision of adequate drainage andunimpeded flow of air and water when designing the cut-outsand connection details.

5.2.3 Asymmetrical secondary members are to beconnected on the heel side to the primary member webplate. Additional connection by lugs on the opposite sidemay be required.

5.2.4 Symmetrical secondary members are to beconnected by lugs on one or both sides, as necessary.

5.2.5 The cross-sectional areas of the connections areto be determined from the proportion of load transmittedthrough each component in association with its appropriatepermissible stress.

5.2.6 In the lower hulls of column-stabilized units,where primary member webs are slotted for the passage ofsecondary members, web stiffeners are generally to be fittednormal to the face plate of the member to provide adequatesupport for the loads transmitted. The end of web stiffenersare to be attached to the secondary members.

5.2.7 Web stiffeners may be flat bars of thickness, tw,with a minimum depth of 0,08dw or 75 mm, whichever is thegreater. Alternative sections of equivalent moment of inertiamay be adopted. The direct stress in the web stiffeners is tobe determined in accordance with this sub-Section.

5.2.8 The total load P transmitted in the connection ofsecondary members to primary members is to be inaccordance with Table 8.5.1.

Bracket toe area

Faceplate area

4407/98

Fig. 8.5.1 Bracket toe construction





Fig. 8.5.2 Cut-outs and connections

Primarymember

web platestiffener

a (max. 40 mm)

tw

blt l

W

W

0,2W(min. 25 mm)

0,2W(min. 25 mm)

W

a (max. 40 mm)

Wt l W l

bl

For lug

bl

For direct connection

tw

Primarymember

web platestiffener

a (max. 40 mm)

tw

blt l

W

W

0,2W(min. 25 mm)

0,2W(min. 25 mm)

W

a (max. 40 mm)

Wt l Wl

bl

For lug

bl

For direct connection

4407/99

tw

(a) (b)

(c) (d)

max.150 mm

tw

max. 150 mm





Unit type Head, h1, in metres Total load, P, transmitted to connection

(1) Surface-type oil storage units h1 = load height, in metres, derived in accordance withthe following provisions, but to be taken as not

less than or (0.01L1 + 0,7) m, whichever is

the greater

For shell framing members:(a) With mid-point of span at base line,

h1 = 0,8D2

(b) With mid-point of span at a distance 0.6D2 abovebase line,h1 = f D2bf

(c) With mid-point of span intermediate between (a) (a) In general:and (b). The value of h1 is to be obtained by linear P = 10,06 Sw s1 h1 kNinterpolation between values from (a) and (b). (P = 1,025 Sw s1 h1 tonne-f)

(d) With mid-point of span higher than 0,6D2 above (b) For wash bulkheads:base line. The value of h1 is to be obtained by P = 11,77 Sw s1 h1 kNlinear interpolation between the values from (b) (P = 1,25 Sw s1 h1 tonne-f)and the values at the following points:(i) For framing members Zero value at the

located at and abaft level of the deck0,2L from the forward edge amidshipsperpendicular, seeFig. 10.5.2(a)

(ii) For framing members Value of f D2 (bf – 1)forward of cargo tank at the level 3 mregion, above the minimumsee Fig. 10.5.2.(b) bow height

determined fromCh 3,6

(iii) Intermediate values between locations (i) and(ii) are to be determined by linear interpolation.

For secondary stiffening members of transverse andlongitudinal bulkheads, and inner hull and inner bottom:h1 = distance from mid-point of span to top of

tank but need not exceed 0,8D2

(2) Column-stabilized Column and pontoon shell framing:and tension-leg units h1 = h0 in Table 6.3.1

(3) Self-elevating units Shell framing:h1 = hT in Table 6.3.4 In general:

P = 10,06 Sw s1 h1 kN(4) Buoys and deep Shell framing: (P = 1,025 Sw s1 h1 tonne-f)draught caissons h1 = h0 in Table 6.3.5

(5) For units in (2), (3) and (4) For secondary stiffening members of tank bulkheads:h1 = h4 in Table 6.7.1

NOTESbf = bow fullness factor for surface-type units,see Fig 8.5.4. To be taken as 1 for framing members located at and abaft 0,2L from

forward perpendicularf = load height factor at level 0,6D above base line, see Table 8.5.2h1 = load height, in metres (See also Fig. 8.5.3 for surface-type units)Sw = spacing of primary members in metress1 = spacing of secondary membersD2 = D in metres, but need not be taken greater than 1,6TL1 = L but need not be taken as greater than 190 m

Table 8.5.1 Total load transmitted to connection of secondary members (see continuation)

L156





Table 8.5.2 Load height factor, f, for surface type oil storage units

Unit depth, D, in metres

≤17,5 20 22,5 25 27,5 30

(1) Oil storage units with tankboundaries wholly within 0,6 0,6 0,582 0,556 0,535 0,517parallel mid-body

(2) Oil storage units with tankboundaries wholly or partially 0,7 0,685 0,685 0,628 0,6 0,557outside parallel mid-body

NOTEIntermediate values to be obtained by linear interpolation.

2937/01(a) (b)

0,6D

2 h1 = f D2

h1 = 0,8D2

h1 = f D2bf

h1 = f D2(bf - 1)

0,6D

2

h1 = 0,8D2

Fig. 8.5.3Load height diagrams for framing members on surface

type oil storage units (a) at and abaft 0,2L from theforward perpendicular and (b) forward of the oil

storage tank region

(b)

(a)

1. φ to be deduced at 0,025L aft of fore perpendicular

2. Aft of fore peak tank φ to be deduced at section being considered

3. For ships with a bulbous bow the angle φ is to be measured from the narrowest point of the bow between 0,6D from base and upper deck

Conditions for φ

Forecastle deck

Upper deck

Upper deck

Forepeak

F.P.

0,025L

0,6D

Bow fullness factorbf = 2,45 cos φ tan θbut not to be taken less than 1,0

CL

φ

θ

Fig. 8.5.4Illustration of bow fullness factor determination for

surface-type units





Table 8.5.3 Permissible stresses for surface-type oil storage units

Item Direct stress Shear stressin N/mm2 (kgf/mm2) (see Notes 1 and 2) in N/mm2 (kgf/mm2) (see Note 1)

Primary member web plate stiffener within147,2 (15,0) –

distance a of end (see Fig. 8.5.2)

98,1 (10,0)(double continuous fillet) –

Welding of primary member Butted147,2 (15,0)

web plate stiffener to(automatic deep penetration) –

secondary member

Lapped –83,4 (8,5)

(See Note 2)

Single – 68,6 (7,0)

Lug or collar plate and weld

Double – 83,4 (8,5)

NOTES1. The welding requirements of Section 2 and, where applicable 5.2.15, are also to be complied with.2. Where longitudinals are of higher tensile steel having a yield stress of 32kg/mm2 or more, these stresses are to be divided by the

factor 1,2 for application to side longitudinals above 0,3D2 from the base-line. For definition of D2 see Table 8.5.1.

Fig. 8.5.5Bilge keel construction

W

As close aspracticable

Hole diameter>– 25 mm and > W

Bilge keel

Shell plating

4407/100


5.2.9 This load is to be apportioned between theconnections as follows:(a) Transmitted through the collar arrangement:

where A1 is derived in accordance with 5.2.10 and

is not to be taken as greater than 0,25. The collarload factor, Cf, is to be derived as follows:

• Symmetrical secondary members:Cf = 1,85 for Af ≤ 18Cf = 1,85 – 0,0341 (Af – 18) for 18 < Af ≤ 40Cf = 1,1 – 0,01 (Af – 40) for Af > 40

• Asymmetrical secondary members:

Cf = 0,68 + 0,0224

where Af = the area, in cm2, of the primary member webstiffener in way of the connection includingbacking bracket, where fitted, see 5.2.12

bl = the length of lug or direct connection, in mm,as shown in Fig. 8.5.2. Where the lug ordirect connections differ in length, a meanvalue of bl is to be used

(b) Transmitted through the primary member web stiffener:P2 = P – P1 kN (tonne-f)

(c) Where the web stiffener is not connected to the secondary member, P1 is to be taken equal to P.

5.2.10 The effective cross-sectional area A1 of the collararrangements is to be taken as the sum of cross-sectionalareas of the components of the connection as follows (seealso Fig. 8.5.2):• Direct connection:

A1 = 0,01bl tw cm2

• Lug connection:A1 = 0,01f1 bl t1 cm2

wheref1 = 1,0 for symmetrical secondary member

connections

= but not greater than 1,0, for asymmetrical

secondary member connectionstw = thickness of primary member web, in mmtl = thickness, in mm, of lug connection, and is to

be taken not greater than the thickness of theadjacent primary member web plate

W = overall width of the cut-out, in mmW l = width for cut-out asymmetrical to secondary

member web, in mm

5.2.11 For surface-type units, the values Af and A1 areto be such that the stresses given in Table 8.5.3. are notexceeded. For other unit types, the direct stress in thevertical web stiffener and the shear stresses in the lug, collarplate and weld connections are to satisfy the factors of safetygiven in Ch 5, 2.1.1 (a).

5.2.12 Where a bracket is fitted to the primary memberweb plate in addition to a connected stiffener, it is to be arranged on the opposite side to, and in alignment with,the stiffener. The arm length of the bracket is to be not lessthan the depth of the stiffener, and its cross-sectional areathrough the throat of the bracket is to be included in thecalculation of Af.

140W l

b lAf

s1

Sw

P1 = P s1Sw

+ A14Cf Af + A1




5.2.13 In general, where the primary member stiffener isconnected to the secondary member, it is to be aligned withthe web of the secondary member, except where the faceplate of the latter is offset and abutted to the web, in whichcase the stiffener connection is to be lapped. Lappedconnections of primary member stiffeners to mild steel bulbplate or rolled angle secondary members may also bepermitted. Where such lapped connections are fitted,particular care is to be taken to ensure that the primarymember stiffener wrap around weld connection is free fromundercut and notches, see also 2.13.

5.2.14 Fabricated longitudinals having the face platewelded to the underside of the web, leaving the edge of theweb exposed, are not recommended for side shell andlongitudinal bulkhead longitudinals. Where it is proposed tofit such sections, a symmetrical arrangement of connection totransverse members is to be incorporated. This can beachieved by fitting backing brackets on the opposite side ofthe transverse web or bulkhead. The primary memberstiffener and backing brackets are to be lapped to thelongitudinal web, see 5.2.12.

5.2.15 In addition to the requirements of 5.2.1 to 5.2.12the weld area of the connections is to be not less than:• Connection of primary member stiffener to the

secondary member:Aw = 0,25Af or 6,5 cm2, whichever is the greater,

corresponding to a weld factor of 0,34 for thethroat thickness;

• Connection of secondary member to the web of theprimary member:

Aw = 0,5 corresponding to a weld factor of0,34 in tanks or 0,27 in dry spaces for thethroat thickness;

whereAw = weld area, in cm2, and is calculated as total

length of weld, in cm, multiplied by throatthickness, in cm

Af = cross-sectional area of the primary memberweb stiffener, in cm2, in way of connection

Z = the section modulus, in cm3, of thesecondary member.

5.2.16 Alternative arrangements will be considered onthe basis of their ability to transmit load with equivalenteffectiveness. Details of the calculations made and testingprocedures are to be submitted.

5.3 Openings

5.3.1 Manholes, lightening holes and other cut-outsare to be avoided in way of concentrated loads and areas ofhigh shear. In particular, manholes and similar openings arenot to be cut in vertical or horizontal diaphragm plates innarrow cofferdams or double plate bulkheads within one-thirdof their length from either end, nor in floors or double bottomgirders close to their span ends, or below the heels of pillars,unless the stresses in the plating and the panel bucklingcharacteristics have been calculated and found satisfactory.

5.3.2 Manholes, lightening holes and other openingsare to be suitably framed and stiffened where necessary.

5.3.3 Penetrations in main bracing members are to beavoided as far as possible. Details of essential penetrationsor openings in main bracing members are to be submitted forconsideration.

Z





5.3.4 Air and drain holes, notches and scallops are tobe kept at least 200 mm clear of the toes of end brackets andother areas of high stress. Openings are to be well roundedwith smooth edges. Details of scalloped construction areshown in Fig. 8.2.7. Closely spaced scallops are not permittedin higher tensile steel members. Widely spaced air or drainholes may be accepted, provided that they are of ellipticalshape, or equivalent, to minimize stress concentration andare, in general, cut clear of the weld connection.

5.4 Sheerstrake and bulwarks

5.4.1 Where an angled gunwale is fitted, the top edgeof the sheerstrake is to be kept free of all notches andisolated welded fittings. Bulwarks are not to be welded tothe top of the sheerstrake within the 0,5L amidships.

5.4.2 Where a rounded gunwale is adopted, thewelding of fairlead stools and other fittings to this plate is tobe kept to the minimum, and the design of the fittings is to besuch as to minimize stress concentration.

5.4.3 Arrangements are to ensure a smooth transitionfrom rounded gunwale to angled gunwale towards the endsof the ship.

5.4.4 At the ends of superstructures where the sideplating is extended and tapered to align with the bulwarkplating, the transition plating is to be suitably stiffened andsupported. Where freeing ports or other openings areessential in this plate, they are to be suitably framed and keptwell clear of the free edge.

5.5 Fittings and attachments, general

5.5.1 The quality of welding and general workmanshipof fittings and attachments as given in 5.6 and 5.7 are to be equivalent to that of the main hull structure. Visualexamination of all welds is to be supplemented by non-destructive testing as considered necessary by the Surveyor.

5.6 Bilge keels and ground bars

5.6.1 In general, bilge keels are to be attached to acontinuous ground bar as shown in Fig. 8.5.5. Butt welds inshell plating, ground bar and bilge keels are to be staggered.

5.6.2 The minimum thickness of the ground bar is tobe equal to the thickness of the bilge strake or 14 mm,whichever is the lesser.

5.6.3 The material grade and quality of the ground barare to be to the same standard as the shell plating to which itis attached.

5.6.4 The ground bar is to be connected to the shellwith a continuous fillet weld and the bilge keel to the groundbar with a light continuous or staggered intermittent filletweld.

5.6.5 Direct connection between ground bar buttwelds and shell plating, and between bilge keel butt weldsand ground bar, is to be avoided.

5.6.6 Bilge keels are to be gradually tapered at theends and arranged to finish in way of a suitable internalstiffening member. The taper should have a length to depthratio of at least 3 to 1.

5.6.7 For units over 65 m in length, holes are to bedrilled in the bilge keel butt welds. The size and position ofthese holds are to be as illustrated in Fig. 8.5.5. Where thebutt weld has been subject to non-destructive examinationthe stop hole may be omitted.

5.6.8 Bilge keels of a different design from that shownin Fig. 8.5.5 will be specially considered.

5.6.9 A plan of the bilge keels is to be submitted forapproval of material grades, welded connections and detaildesign.

5.7 Other fittings and attachments

5.7.1 Gutterway bars at the upper deck are to be soarranged that the effect of main hull stresses on them isminimized and the material grade and quality of the bar are tobe to the same standard as the deck plate to which it isattached.

5.7.2 Where attachments are made to roundedgunwale plates, special consideration will be given to therequired grade of steel taking into account the intendedstructural arrangement and attachment details. In general,the material grade and the quality of the attachment are to beto the same standard as the gunwale plates.

5.7.3 Minor attachments, such as pipe clips, staginglugs and supports, are generally to be kept clear of toes ofend brackets, corners of openings and similar areas of highstress. Where connected to asymmetrical stiffeners, theattachments may be in line with the web providing the filletweld leg length is clear of the offset face plate or flange edge.Where this cannot be achieved, the attachments are to beconnected to the web, and in the case of flanged stiffenersthey are to be kept at least 25 mm clear of the flange edge.On symmetrical stiffeners, they may be connected to the webor to the centreline of the face plate in line with the web.

5.7.4 Where necessary in the construction of the unit,lifting lugs may be welded to the hull plating but they are notto be slotted through. Where they are subsequentlyremoved, this is to be done by flame or mechanical cuttingclose to the plate surface, and the remaining material andwelding ground off. After removal the area is to be carefullyexamined to ensure freedom from cracks or other defects inthe plate surface.

5.7.5 Fitt ings and attachments to main bracingmembers are to be avoided as far as possible. Where theyare necessary, ful l detai ls are to be submitted forconsideration.

5.7.6 Where permanent or temporary studs are to beattached by welding the requirements of 2.10 are to becomplied with.


SECTION 6Fabrication tolerances

6.1 General

6.1.1 All fabrication tolerances are to be in accordancewith good shipbuilding practice and be agreed with LRbefore fabrication is commenced. Where appropriate,tolerances are to comply with a National Standard. Ingeneral, the tolerances for the fabrication of structuralmembers for the categories defined in Ch 2,2.1 are tocomply with the requirements of this Section.

6.1.2 For cylindrical members, the out of roundness isnot to exceed 0,5 per cent of the true mean radius or 25 mmon the true mean internal diameter, whichever is the lesser.

6.1.3 When measuring cylindrical members, the out ofroundness is to be measured always as a deviation from thetrue mean radius in order to avoid errors.

6.1.4 Cylindrical members are not to deviate fromstraightness by 3 mm or l mm, whichever is the greater,where l is the length of the member, in metres.

6.1.5 The misalignment of plate edges in butt welds isnot to exceed the lesser of the following values:• Special structure 0,1t or 3 mm• Primary structure 0,15t or 3 mm• Secondary structure 0,2t or 4 mmwhere t = thickness of the thinnest plate, in mm.

6.1.6 Misalignment of non-continuous plates such ascruciform joints is not to exceed the lesser of the followingvalues:• Special structure 0,2t or 4 mm• Primary structure 0,3t or 4 mm• Secondary structure 0,5t or 5 mmwhere t = thickness of the thinnest plate, in mm.

6.1.7 Plate deformation measured at the mid pointbetween stiffeners or support points is not to exceed thelesser of the following values:

• Special structure

• Primary structure or t mm

• Secondary structure or t mm

where s = stiffener spacing or unsupported panel width,in mm

t = plate thickness, in mm.

s80

s130

s200





ke





SECTION 1Anchoring equipment

1.1 General

1.1.1 For self-propelled disconnectable units to be assigned the figure (1) in the character of Classification,the anchoring equipment, (i.e. anchors, cables, windlass and winches, etc.) necessary for the unit during seagoingcondit ions is to be as required by this Section. TheRegulations governing the assignment of the figure (1) forequipment are given in Pt 1, Ch 2,2.

1.1.2 When the equipment f i tted to the unit isdesigned primari ly as positional mooring equipment,consideration will be given to accepting the proposedequipment as equivalent to the Rule requirements but only ifthe arrangements are such that it can be efficiently used asanchoring equipment.

1.2 Equipment number

1.2.1 The requirement for anchors, cables, wires andropes is to be based on an Equipment Number calculated asfollows:

Equipment Number =

where∆ = moulded displacement in transit condition, in

tonnesA1 = projected area perpendicular to wind direction

when at anchor, in m2

A2 = projected area parallel to wind direction whenat anchor, in m2

In calculating the areas A1 and A2:• masking effect can be taken into account for columns;• open trusswork of derricks, booms and towers, etc.,

may be approximated by taking 30 per cent of theblock area of each side, i.e. 60 per cent of the projectedarea of one side for double sided trusswork.

1.3 Determination of equipment

1.3.1 The basic equipment of anchors and cables is tobe determined from Table 9.1.1 and associated notes. Table 9.1.1 is based on the following assumptions:(a) The anchors will be high holding power anchors of an

approved design, see 1.5.(b) The chain cable will be in accordance with the require-

ments of 1.6.

1.3.2 Where the equipment is based on 1.1.2, thesizes of individual anchors are not to exceed the values givenin Table 9.1.1 by more than seven per cent unless the cablesizes are increased as appropriate.

∆23 + 2,5A1 + A2

10

Section

1 Anchoring equipment

2 Towing arrangements and equipment

Anchoring and Towing Equipment

1.3.3 Where the equipment is based on 1.1.2, theminimum cable strength is to be maintained and 1.7.6 is alsoto be complied with.

1.4 Anchors

1.4.1 Two anchors are to be fitted and arranged sothat they may be readily dropped should an emergencyoccur.

1.4.2 The mass of each anchor is to be as given in Table 9.1.1 except that one anchor may weigh seven percent less than the Table weight so long as the total weight ofthe two anchors attached to the cables is not less than twicethe tabular weight for one anchor.

1.4.3 Anchors are to be of approved design. Thedesign of all anchor heads is to be such as to minimize stressconcentrations, and in particular, the radii on all parts of castanchor heads are to be as large as possible, especially wherethere is a considerable change of section.

1.4.4 Positional mooring anchors of the type which aregenerally similar to conventional marine anchors but whichmust be specially laid the right way up, or which require thefluke angle or profile to be adjusted for varying types of seabed, will not normally be accepted as anchoring equipment inaccordance with these Rules.

1.4.5 If ordinary ship-type stockless bower anchors,not approved as high holding power anchors, are to be usedas Rule equipment the mass of each anchor is to be not lessthan 1,33 times that listed in Table 9.1.1 for the unit’sEquipment Number.

1.4.6 The requirements for manufacture, proof testingand identification of anchors are to be in accordance with Pt 2, Ch 10.

1.5 High holding power anchors

1.5.1 Anchors of designs for which approval is soughtas high holding power anchors are to be tested at sea toshow that they have holding powers of at least twice those ofapproved standard stockless anchors of the same mass.

1.5.2 If approval is sought for a range of sizes, then atleast two sizes are to be tested. The smaller of the twoanchors is to have a mass not less than one-tenth of that ofthe larger anchor, and the larger of the two anchors tested isto have a mass not less than one-tenth of that of the largestanchor for which approval is sought.

1.5.3 The tests are to be conducted on not less thanthree different types of bottom, which should normally be softmud or silt, sand or gravel, and hard clay or similarlycompacted material.



Anchoring and Towing Equipment



Diameter, in mm

Equipmentnumber

Stud link chain cable

Exceeding Notexceeding

EquipmentLetter

Grade U1 Grade U2 Grade U3

High holding power anchor mass,

in kgLength per

anchor,in metres

Table 9.1.1 Equipment – Anchors and chain cables

7090

110130150175205240280320360400450500550600660720780840910980

10601140122013001390148015701670179019302080223023802530270028703040321034003600380040004200440046004800500052005500580061006500690074007900840089009400

10000

ABCDEFGHIJKLMNOPQRSTUVWXYZA†B†C†D†E†F†G†H†I†J†K†L†M†N†O†P†Q†R†S†T†U†V†W†X†Y†Z†A*B*C*D*E*F*G*H*I*

140180230270310360430500590680770860970

108011901300144015801710185019902140229024702660284030403240344036703940421045004840518055105850623065306980743078808330878092509700

10 10010 60011 00011 60012 10012 70013 40014 10015 00016 00017 50018 50019 50020 50022 000

110110110110137,5137,5137,5137,5165165165192,5192,5192,5192,5220220220220220220247,5247,5247,5247,5247,5247,5275275275275275275302,5302,5302,5302,5302,5302,5330330330330330330357,5357,5357,5371,5371,5371,5371,5371,5371,5385385385385385385385

–––––––

20,522242426283030323436363840424446464850505254565860626466687073767878818487879092959797

100102107111114117122127132132

507090

110130150175205240280320360400450500550600660720780840910980

10601140122013001390148015701670179019302080223023802530270028703040321034003600380040004200440046004800500052005500580061006500690074007900840089009400

12,5141617,517,51920,52224262830323434363840424446485050525456586062646668707376788184848790929597

100102105107111111114117120124127132137142147152

141617,51920,52224262830323436384042444648505254565860626466687073767881848790929597

100102105107111114117120122124127130132

––––––––


1.5.4 The test should normally be carried out from atug, and the pull measured by dynamometer or derived fromrecently verified curves of tug rev/min against bollard pull. Ascope of 10 is recommended for the anchor cable, whichmay be wire rope for this test, but in no case should a scopeof less than six be used. The same scope is to be used forthe anchor for which approval is sought and the anchor thatis being used for comparison purposes.

1.5.5 High holding power anchors are to be of adesign that will ensure that the anchors will take effective holdof the sea bed without undue delay and will remain stable, forholding forces up to those required by 1.5.1, irrespective ofthe angle or position at which they first settle on the sea bedwhen dropped from a normal type of hawse pipe. In case ofdoubt, a demonstration of these abilities may be required.

1.6 Chain cables

1.6.1 The minimum sizes and lengths of chain cablesare to be as required by Table 9.1.1.

1.6.2 Chain cables may be of mild steel, special qualitysteel or extra qual ity steel in accordance with therequirements of Pt 2, Ch 10 and are to be graded inaccordance with Table 9.1.2.

1.6.3 Grade U1 material having a tensile stress of lessthan 400 N/mm2 (41 kgf/cm2) is not to be used in associationwith high holding power anchors. Grade U3 material is to beused only for chain 20,5 mm or more in diameter.

1.6.4 The form and proportion of links and shacklesare to be in accordance with Pt 2, Ch 10.

1.6.5 As an alternative to the chains listed in Table 9.1.1,consideration will be given to the use of the following:• Chain cables of Grades R3, R3S and R4 in accordance

with Pt 2, Ch 10,3.• Wire rope meeting the requirements of Part 2.In this case, the length and breaking strength of the wire ropewill be specially considered.



Anchoring and Towing Equipment Part 4, Chapter 9Section 1

1.7 Arrangements for working and stowinganchors and cables

1.7.1 A windlass or winch of sufficient power andsuitable for the type of cable is to be provided for each of theanchor cables. Where Owners require equipment significantlyin excess of Rule requirements, it is their responsibility tospecify increased windlass or winch power.

1.7.2 The windlasses or winches are to be securelyfitted and efficiently bedded to suitable positions on the unit.The structural design integrity of the bedplate is theresponsibility of the builder and windlass manufacturer.

1.7.3 The following performance criteria are to be usedas a design basis for the windlass:(a) The windlass is to have sufficient power to exert a

continuous duty pull over a period of 30 minutes of:36,79dc

2 N (3,75dc2 kgf) – for Grade U1 chain,

41,68dc2 N (4,25dc

2 kgf) – for Grade U2 chain,46,6dc

2 N (4,75dc2 kgf) – for Grade U3 chain,

where dc is the chain diameter, in mm.(b) The windlass is to have sufficient power to exert, over a

period of at least two minutes, a pull equal to thegreater of:(i) short term pull:

1,5 times the continuous duty pull as defined in1.7.3(a).

(ii) anchor breakout pull:

where:lc is length of chain cable per anchor, in metres,as given by Table 9.1.1Wa is the mass of high holding power anchor, inkg, is given in Table 9.1.1

(c) The windlass, with its braking system in action and inconditions simulating those likely to occur in service, isto be able to withstand, without permanent deformationor brake slip, a load, applied to the cable, given by:Kbdc

2 (44 – 0,08dc) N (kgf)where Kb is given in Table 9.1.3.

NOTE

The performance criteria are to be verified by means of shoptests in the case of windlasses manufactured on an individualbasis. Windlasses manufactured under LR’s Type ApprovalScheme will not require shop testing on an individual basis.

1,65Wa +14,2 lc dc

2

1000 kgf

16,24Wa +14,0 lc dc

2

100 N

Grade MaterialTensile strength

(kgf/mm2)N/mm2

Mild steelU1

(50 – 70)490 – 690Specialquality steel(wrought)

U2(a)

(50 – 70 )490 – 690Specialquality steel(cast)

U2(b)

(70 min.)690 min.Extra specialquality steelU3

Table 9.1.2 Anchoring equipment chain grades

(31 – 50)300 – 490

Table 9.1.3 Windlass braking factors

Cablegrade

Kb

Windlass usedin conjunction with

chain stopper

Chain stoppernot fitted

7,85 (0,8)4,41 (0,45)U1

11,0 (1,12)6,18 (0,63)U2

15,7 (1,6)8,83 (0,9)U3





1.7.4 Where shop testing is not possible and TypeApproval has not been obtained, calculations demonstratingcompliance with 1.7.3 are to be submitted together withdetailed plans and an arrangement plan showing thefollowing components:• Shafting.• Gearing.• Brakes.• Clutches.

1.7.5 During trials on board the unit, the windlassshould be shown to be capable of raising the anchor from adepth of 82,5 m to a depth of 27,5 m at a mean speed of notless than 9 m/min. Where the depth of water in the trial areais inadequate, suitable equivalent simulating conditions will beconsidered as an alternative.

1.7.6 The cable is to be capable of being paid out inthe event of a power failure.

1.7.7 Windlass performance characteristics specifiedin 1.7.3 and 1.7.5 are based on the following assumptions:• One cable lifter only is connected to the drive shaft.• Continuous duty and short term pulls are measured at

the cable lifter.• Brake tests are carried out with the brakes fully applied

and the cable lifter declutched.• The probability of declutching a cable lifter from the

motor with its brake in the off position is minimised.• Hawse pipe efficiency assumed to be 70 per cent.

1.7.8 An easy lead of the cables from the windlass orwinch to the anchors and chain lockers or wire storage drumis to be arranged. Where cables pass over or throughstoppers, these stoppers are to be manufactured from ductilematerial and be designed to minimize the probability ofdamage to, or snagging of, the cable. They are to becapable of withstanding without permanent deformation aload equal to 80 per cent of the Rule breaking load of thecable passing over them.

1.7.9 The chain locker is to be of a capacity and depthadequate to provide an easy direct lead for the cable into thechain pipes, when the cable is fully stowed. Chain or spurlingpipes are to be of suitable size and provided with chafing lips.If more than one chain is to be stowed in one locker then theindividual cables are to be separated by substantial divisionsin the locker.

1.7.10 Provision is to be made for securing the inboardends of the cables to the structure. This attachment shouldhave a working strength of not less than 63,7 kN (6,5 tonne-f) or 10 per cent of the breaking strength of thechain cable, whichever is the greater, and the structure towhich it is attached is to be adequate for this load. Attentionis drawn to the advantages of arranging that the cable maybe slipped in an emergency from an accessible positionoutside the chain locker.

1.7.11 Where wire rope cables are used, these are tobe stored on suitable drums. The lead to the drums is to besuch that the cables will reel onto the drums reasonablyevenly. If the drums are designed to apply the full winchhauling load to the cables then the arrangements, usingspooling gear or otherwise, are to ensure even reeling of thecables onto the drums.

1.7.12 Fair leads, hawsepipes, anchor racks andassociated structure and components are to be of amplethickness and of a suitable size and form to house theanchors efficiently, preventing, as much as practicable,slackening of the cable or movements of the anchor beingcaused by wave action. The plating and framing in way ofthese components are to be reinforced as necessary.Columns, lower hulls, footings and other areas likely to bedamaged by anchors, chain cables and wire ropes, etc., areto be suitably strengthened.

1.7.13 The design of the windlass is to be such that thefollowing requirements or equivalent arrangements willminimize the probability of the chain locker or forecastle beingflooded in bad weather:• a weathertight connection can be made between the

windlass bedplate, or its equivalent, and the upper endof the chain pipe;

• access to the chain pipe is adequate to permit thefitting of a cover or seal, of sufficient strength andproper design, over the chain pipe if the sea is liable tobreak over the windlass; and

• for column-stabilized units, see Ch 7, 4.7.2.

1.8 Testing of equipment

1.8.1 All anchors and chain cables are to be tested atestablishments and on machines recognized by LR andunder the supervision of LR’s Surveyors or other Officersrecognized by LR, and in accordance with Part 2.

1.8.2 Test certificates showing particulars of weights ofanchors, or size and weight of cable and of the test loadsapplied are to be furnished. These certificates are to be examined by the Surveyors when the anchors and cables areplaced on board the unit.

1.8.3 Steel wire ropes are to be tested as required by Part 2.


SECTION 2Towing arrangements

2.1 General

2.1.1 All non-self-propelled units which are to be wet-towed to their operating location are to be fitted withtowing brackets.

2.1.2 The design basis for the towing system and thedesign load for the towing brackets are to be submitted withthe structural plans required in Ch 1,4. The design load forthe towing system is not to be taken less than 75 tonne-f.

2.1.3 In general, each non-self-propelled unit is to befitted with two independent towing brackets which are to beposit ioned as far apart as practicable. Alternativearrangements will be considered.

2.2 Strength

2.2.1 The attachments to the unit as required by 2.1.3are to be designed for a towing direction of 0˚ to 90˚ offcentreline port and starboard.

2.2.2 The strength of towing brackets and theirsupporting structure are to be designed to the breakingstrength of the attached towing pendant determined inaccordance with 2.1.2. The permissible stresses in thetowing brackets and their supporting structure are to be inaccordance with Ch 5,2.1.1 (b).

2.3 Self-propelled units

2.3.1 Towing brackets are in general not required onself-propelled units for classification purposes.

2.3.2 Oil storage units which are disconnectable inorder to avoid hazards or extreme environmental conditionsmay require emergency towing arrangements in accordancewith IMO Resolution MSC 35(63) for oil tankers whenrequired by a National Administration. Where emergencytowing arrangements are required, plans of the system andstructural arrangements are to be submitted for approval.





ke





SECTION 1Rudders and steering gears

1.1 General

1.1.1 When units are self-propelled and are fitted withconventional rudders, the scantlings and arrangements are tocomply with the requirements of the applicable sections of Pt 3, Ch 13 of the Rules for Ships.

1.1.2 Where a non-conventional rudder is installed on self-propelled units, special consideration will be given tothe steering system so as to ensure that an acceptabledegree of reliability and effectiveness based on the Rules forShips is provided.

1.1.3 When a ship-type unit is to be converted and classed as an floating offshore installation and the rudderis inoperative, it is strongly recommended that the rudder is removed to prevent damage to the steering gear in storm conditions.

1.1.4 If the rudder is removed in accordance with1.1.3, the hull aperture is to be fitted with a suitable blankingplate and sealing arrangements to ensure watertight integrityof the hull and the scantlings and arrangements are tocomply with Chapter 7.

1.1.5 Where rudders are left in situ on ship-type units,positive locking devices of sufficient strength are to be fitted orstructural supports provided to prevent rudders movingviolently in storm or rough weather conditions. Plans,together with supporting design calculations, are to besubmitted for approval to show satisfactory capacity in theworst contemplated environmental conditions, see also Pt 5,Ch 18.

1.1.6 For ship-type units which are disconnectable toavoid severe environmental conditions, the locking devicesrequired by 1.1.5 are to be fitted on the steering gear.

1.1.7 When units are fitted with steering arrangementsconsisting of Azimuth thrusters, see 1.1.8 and 1.1.10. For tunnel thrusters, see Section 3.

1.1.8 The requirements for fixed and steering nozzleand thrust units are given in Section 2.

1.1.9 The requirements for steering gear and alliedsystems are given in Pt 5, Ch 18.

1.1.10 The requirements for azimuth thrusters are givenin Pt 5, Ch 17.

Section

1 Rudders and steering gears

2 Fixed and steering nozzles

3 Tunnel thrust unit structure

Steering Arrangements

SECTION 2Fixed and steering nozzles

2.1 General

2.1.1 The requirements for scantlings for fixed andsteering nozzles are given, for guidance only, in 2.2 to 2.4and Table 10.2.1.

Table 10.2.1 Nozzle construction requirements

Item Requirement

(1) Nozzle numeral

(2) Shroud plating in wayof propeller blade tips

(3) Shroud plating clearof blade tips, flareand cone plating, wallthickness of leadingand trailing edgemembers

(4) Webs and ring webs

(5) Nozzle stock

(6) Solepiece and strut

Symbols

NN = a numeral dependent on the nozzle requirementsP = power transmitted to the propellers, in kW

(H = power transmitted to the propellers, in shp)δp = diameter of the propeller, in metrests = thickness of shroud plating in way of propeller tips,

in mmtp = thickness of plating, in mm

tW = thickness of webs and ring webs in way of headbox andpintle support, in mm

NOTEThicknesses given are for mild steel. Reductions in thickness will beconsidered for certain stainless steels.

NN = 0,01Pδp(NN = 0,00736Hδp)

For NN ≤ 63ts = (11 + 0,1NN) mmFor NN > 63ts = (14 + 0,052NN) mm

tp = (ts – 7) mm but not lessthan 8 mm

As item (3) except in way of headboxand pintle support where:

tW = (ts + 4) mm

• Combined stresses in stock at lowerbearing

≤ 92,7 N/mm2 (9,45 kgf/mm2)

• Torsional stress in upper stock≤ 62,0 N/mm2 (6,3 kgf/mm2)

Bending stresses not to exceed70,0 N/mm2 (7,1 kgf/mm2)

1996 MOU – Pt 4, Ch 10 5/6/99 11:01 am Page 1 (Black plate)

2.3 Nozzle stock and solepiece

2.3.1 Stresses, derived using the maximum side loadon the nozzle and fin acting at the assumed centre of pressure, are not to exceed the values given in Table 10.2.1,in both the ahead and astern conditions.

2.4 Ancillary items

2.4.1 Using the Rule stock diameters and equivalentpintle reaction required to comply with the stress levels givenin Table 10.2.1, the scantlings of pintles, rudder couplingsand bearings are to be in accordance with Pt 3, Ch 13 of theRules for Ships.

2.4.2 Where it is proposed to use stainless steel asliners or bearings for rudder stocks and/or pintles, thechemical composition is to be submitted for approval.Synthetic rubber bearing materials are to be of a typeapproved by LR. When this type of l ining is used,arrangements to ensure an adequate supply of sea-water tothe bearing are to be provided.

2.4.3 Suitable arrangements are to be provided toprevent the steering nozzle from lifting.


Steering Arrangements Part 4, Chapter 10Section 2


2.1.2 The requirements, in general, apply to nozzleswith a numeral not greater than 200, see Table 10.2.1.Nozzles exceeding this value will be specially considered.

2.2 Nozzle structure

2.2.1 For basic scantl ings of the structure, see Table 10.2.1, in association with Fig. 10.2.1.

2.2.2 The shroud plating in way of the propeller tips isto be carried well forward and aft of this position, dueallowance being made on steering nozzles for the rotation ofthe nozzle in relation to the propeller.

2.2.3 Fore and aft webs are to be fitted between theinner and outer skins of the nozzle. Both sides of theheadbox and pintle support structure are to be connected tofore and aft webs of increased thickness. For thicknesses,see Table 10.2.1.

2.2.4 The transverse strength of the nozzle is to bemaintained by the fitting of ring webs. Two ring webs are tobe fitted in nozzles not exceeding 2,5 m in diameter. Nozzlesbetween 2,5 and 3,0 m in diameter are generally to have twofull ring webs and a half-depth web supporting the flare plating. The number of ring webs is to be increased asnecessary on nozzles exceeding 3,0 m in diameter. Wherering webs are increased in thickness in way of the headboxand pintle support structure in accordance with Table 10.2.1,the increased thickness is to be maintained to the adjacentfore and aft web.

2.2.5 Local stiffening is to be fitted in way of the topand bottom supports which are to be integrated with thewebs and ring webs. Continuity of bending strength is to bemaintained in these regions.

2.2.6 Fin plating thickness should be not less than thecone plating, and the fin should be adequately reinforced.Solid fins should be not less than 25 mm thick.

2.2.7 Care is to be taken in the manufacture of thenozzle to ensure its internal preservation and watertightness.Internal surfaces of nozzles are to be coated, and means fordraining the nozzle are to be provided. Testing is to becarried out in accordance with Table 1.6.2 in Chapter 1.

Fore and aftwebs

Ring web

Trailing edgemember

Coneplating

Ring webs

Shroud platingin way of propeller

Flareplating

Leading edgemember

FORE AND AFT SECTION ONMIDDLE LINE

TRANSVERSE SECTION

Shroudplating

4407/101

Fig. 10.2.1Nozzle arrangements


SECTION 3Tunnel thrust unit structure

3.1 Unit wall thickness

3.1.1 The wall thickness of the unit is, in general, to bein accordance with the manufacturer’s practice but is to benot less than either the thickness of the surrounding shellplating plus 10 per cent or 15 mm, whichever is greater.

3.2 Framing

3.2.1 The unit is to be framed to the same standard asthe surrounding shell plating.

3.2.2 The unit is to be adequately supported by meansof web frames, floors or bulkheads and be effectively builtinto the hull structure at its ends.

3.3 Watertightness

3.3.1 Thrust units are to be enclosed in suitablewatertight spaces to prevent flooding in the case of leakageor damage to the thrust unit.



Steering Arrangements Part 4, Chapter 10Section 3


ke





SECTION 1General

1.1 Definitions

1.1.1 Quality Assurance Scheme. LR’s QualityAssurance requirements for the hull construction of mobileoffshore units are defined as follows:

(a) Quality Assurance. All activities and functionsconcerned with the attainment of quality includingdocumentary evidence to confirm that such attainmentis met.

(b) Quality system. The organization structure, responsi-bilities, activities, resources and events laid down byManagement that together provide organized procedures (from which data and other records aregenerated) and methods of implementation to ensurethe capability of the fabrication yard to meet qualityrequirements.

(c) Quality programme. A documented set of activities,resources and events serving to implement the qualitysystem of an organization.

(d) Quality plan. A document derived from the qualityprogramme setting out the specific quality practices,special processes, resources and activities relevant to aparticular unit or series of similar units. This documentwill also indicate the stages at which, as a minimum,direct survey and/or system monitoring will be carriedout by the Classification Surveyor.

(e) Quality control. The operational techniques and activities used to measure and regulate the quality ofconstruction to the required level.

(f) Inspection. The process of measuring, examining,testing, gauging or otherwise comparing the item withthe approved drawings and the fabrication yard’s written standards including those which have beenagreed by LR for the purposes of classification of thespecific type of unit concerned.

Section

1 General

2 Application

3 Particulars to be submitted

4 Requirements of Parts 1 and 2 of the Scheme

5 Additional requirements for Part 2 of the Scheme

6 Initial assessment of fabrication yard

7 Approval of the fabrication yard

8 Maintenance of approval

9 Suspension or withdrawal of approval

Quality Assurance Scheme (Hull)

(g) Assessment. The initial comprehensive review of thefabrication yard’s quality systems, prior to the grantingof approval, to establish that all the requirements ofthese Rules have been met.

(h) Audit. A documented activity aimed at verifying byexamination and evaluation that the applicableelements of the quality programme continue to beeffectively implemented.

(j) Hold point. A defined stage of manufacture beyondwhich the work must not proceed until the inspectionhas been carried out by all the relevant personnel.

(k) System monitoring. The act of checking, on a regularbasis, the applicable processes, activities and associated documentation that the Fabricator’s qualitysystem continues to operate as defined in the qualityprogramme.

(l) Special process. A process where some aspects ofthe required quality cannot be assured by subsequentinspection of the processed material alone.Manufacturing special processes include welding, forming and the application of protective treatments.Inspection and testing processes classified as specialprocesses include non-destructive examination andpressure and leak testing.

1.2 Scope of the Quality Assurance Scheme

1.2.1 This Chapter specifies the minimum QualitySystem requirements for a fabrication yard to constructfloating offshore installations under LR’s Quality AssuranceScheme.

1.2.2 For the purposes of this Chapter of the Rules,‘construction (hull)’ comprises the primary bracings, columns,legs, footings and hull structure.

1999 FPFL – Pt 4, Ch 11 22/6/99 14:32 Page 1 (Black plate)

SECTION 3Particulars to be submitted

3.1 Documentation and procedures

3.1.1 Under either Part of the Scheme, the documen-tation to meet the requirements of Section 4 is to besubmitted. This documentation includes the Quality Manual,Quality Plans, documented procedures and work instructions.

3.1.2 Additionally, under Part 2 of the Scheme, thedocumentation to meet the requirements of Section 5 is to besubmitted for approval. Construction plans and all necessary particulars are also to be submitted for approval inaccordance with the relevant requirements of the Rules, see Pt 1, Ch 2,3.2.1.

3.2 Amendments

3.2.1 Any major changes to the documentation orprocedures required by Sections 4 or 5 are to be re-submitted.


Quality Assurance Scheme (Hull) Part 4, Chapter 11Sections 2 & 3


SECTION 2Application

2.1 Certification of the fabrication yard

2.1.1 LR will give consideration to a fabrication yard’sQuality Assurance System provided, at all times, there is fullcommitment by al l the Fabricator’s personnel to theimplementation and maintenance of this System. Onsatisfactory completion of assessment and audits, LR willissue a certificate of approval to the yard as indicated in2.1.2.

2.1.2 LR’s Quality Assurance Scheme comprises:Part 1 The requirements of the Quality System applicable

to fabrication yards operating a quality programmebut not necessarily constructing to LR’s Class.Certificates of approval valid for three years will beissued, with Intermediate Audits at intervals of sixmonths.

Part 2 The Quality System requirements applicable to floating offshore installations under construction toLR’s Class as part of the Special Survey. LR’sparticular requirements for construction of floatingoffshore installations to its Class, and the continuousinvolvement in the construction process by a combi-nation of direct survey and systems monitoring byLR’s Surveyors, are provided for by Part 2. WhereLR considers that there is a stage in construction atwhich a high degree of direct inspection by theSurveyors is desirable, this stage will be described on the Part 2Approval Certificate.

Certificates of approval for Part 2 will be valid for one year,and will be issued after satisfactory assessment/audit carriedout at a suitable stage during construction to LR’s Class.Part 1 certification will automatically be issued or re-issued asapplicable, on attainment of Part 2 approval.

2.1.3 The Quality System at a fabrication yard will beexamined for compliance with these Rules by the assessmentsand audits laid down in Sections 4, 5 and 6. Initial andperiodical approval of the System will be considered by the Committee on receipt of satisfactory assessment and audit reports.

2.1.4 Al l information and data submitted by aFabricator for approval under this Scheme and formaintenance of approval will be treated by LR in strictconfidence and will not be disclosed to any third partywithout the prior written consent of the Fabricator.

2.1.5 A list of fabrication yards approved under theScheme will be maintained and published by LR.


SECTION 4Requirements of Parts 1 and 2 of theScheme

4.1 General

4.1.1 The requirements of this Section are applicable tofabrication yards seeking approval under Part 1 and Part 2 ofthe Scheme.

4.2 Policy statement

4.2.1 A policy statement, signed by the chief executiveof the fabrication yard concerned, confirming the full commit-ment of all levels of personnel in the fabrication yard to theimplementation and sustained operation of quality assurancemethods is to be included in the Quality Manual.

4.3 Responsibility

4.3.1 Personnel responsible for functions affectingquality are to have defined responsibility and authority to identify, control and evaluate quality.

4.4 Management Representative

4.4.1 The Fabricator is to appoint a ManagementRepresentative, who is to be independent of other functionsunless specifically agreed otherwise by LR, and who is tohave the necessary authority and responsibility for ensuringthat the requirements of the Scheme are complied with.

4.4.2 The Management Representative is to have theauthority to stop production if serious quality problems arise.

4.5 Quality control and testing personnel

4.5.1 The Fabricator is to utilize quality control andtesting personnel whose performance and continued freedomof influence from production pressures is to be systematicallyconfirmed by the Management Representative.

4.6 Resources

4.6.1 Sufficient resources shall be provided by thefabrication yard to enable the requirements identified by theQuality Management System to be effectively implemented.

4.7 The Quality Management System

4.7.1 The Fabricator is to establish, document andmaintain an effective Quality Management System that willensure and demonstrate that materials and consumablesused, and working processes employed, conform to therequirements for hull construction.

4.7.2 Quality Manual. The basic documentation is tobe in the form of a Quality Manual which sets out the generalquality policies and which references the detailed procedures,standards, etc., and includes the requirements of 4.2 to 4.24and, where appropriate, 5.1 to 5.10.



Quality Assurance Scheme (Hull) Part 4, Chapter 11Section 4

4.7.3 Procedures. The Fabricator is to establish,document and maintain an adequate and defined control ofthe hull construction process comprising:(a) defined and documented controls, processes, proce-

dures, tolerances, acceptance/rejection criteria andworkmanship standards; and

(b) the provision of Quality Plans for each floating offshoreinstallation or series of similar units for the processesand procedures for manufacture, inspection and testinginvolved from receipt of material through to completionof the construction process.

4.7.4 Work instructions. The Fabricator is to developand maintain clear and complete documented work instructions for the processes and standards involved inconstruction. Such instructions are to provide directions tovarious levels of personnel.

4.8 Regulatory requirements

4.8.1 The Fabricator is to establish that the requirementsof all applicable Regulations are clearly specified and agreedwith the Owner/Classification Society/Regulatory Authority.These Regulations are to be made available for all functions thatrequire them and their suitability is to be reviewed.

4.8.2 The Fabricator is to establish a design verificationprocedure to ensure that the regulatory requirements havebeen incorporated into the design output.

4.9 Control of drawings

4.9.1 The Fabricator is to establish, document andmaintain a procedure for the submission to the ClassificationSociety and other regulatory bodies of all the necessary drawings required for approval sufficiently early and in such amanner that the requirements of the Classification Society andother regulatory bodies can be included in the design beforeconstruction commences. This procedure is to include aprovision which ensures that all amendments to approveddrawings are incorporated in the working drawings and thatdesign revisions are re-submitted for approval.

4.10 Documentation and change control

4.10.1 The Fabricator is to establish a procedure toensure that:(a) valid drawings, specifications, procedures, work

instructions and other documentation necessary foreach phase of the fabrication process are prepared;

(b) all necessary documents and data are made readilyavailable at all appropriate work, testing and inspectionlocations;

(c) all amended drawings and changes to documentationare processed in a timely manner to ensure inclusion inthe production process;

(d) records are maintained of amendments and changes todocumentation; and

(e) provision is made for the prompt removal or immediateidentification of all superseded drawings and documentation throughout the fabrication yard.





4.11 Purchasing data and receipt

4.11.1 The Fabricator is to maintain purchasing documents containing a clear description of the materialsordered for use in construction and the standards to whichmaterial must conform, and the identification and certification requirements.

4.11.2 For the requirements for receiving inspection ofpurchased items, see 4.15.

4.12 Owner-supplied material

4.12.1 The Fabricator is to have procedures for theinspection, storage and maintenance of Owner-suppliedmaterials and equipment.

4.13 Identification and traceability

4.13.1 The Fabricator is to establish and maintain aprocedure to ensure that materials and consumables used inthe construction process are identified (by colour-codingand/or marking as appropriate) from arrival at the fabricationyard through to erection in such a way as to enable the typeand grade to be readily recognized. The procedure is toensure that the Fabricator has the ability to identify material inthe completed unit and ensure traceability to the mill sheets.

4.14 Fabrication control

4.14.1 The Fabricator is to establish, document andmaintain suitable procedures to ensure that fabrication andconstruction operations are carried out under controlledconditions. Controlled conditions are to include:(a) clearly documented work instructions defining material

treatment, marking, cutting, forming, sub-assembly,assembly, erection, fitting of closing appliances, use offabrication aids and associated fit-up, weld preparation,welding and dimensional control procedures;

(b) criteria for workmanship and manufacturing tolerances.These are to be documented in a clear manner andmade available to the appropriate workforce, and are toinclude acceptance/rejection criteria; and

(c) documented instructions for the control of equipmentand machines used in fabrication. These are to bemade available to the appropriate workforce andsupplied to individuals where necessary.

4.14.2 The Fabricator is to establish and control welding, non-destructive examination and painting which arepart of the fabrication system, the equipment used in suchprocesses and the environment in which they are employed.Operators of these special processes are to be properly qualified. Details of these processes are to be included in therelevant Quality Plans.

4.14.3 A list of approved welding procedures is to bemaintained and made available to relevant personnel.Records of the results of testing for approval are also to bemaintained. Lists of appropriately qualified welders are to bemaintained. Procedures for distribution and recycling of welding consumables are to be implemented.

4.14.4 The Fabricator is to establish, document andmaintain adequate maintenance schedules and standards forall equipment associated with the construction process.

4.15 Control of inspection and testing

4.15.1 The Fabricator is to be responsible for ensuringthat all incoming plates, sections, castings, components,fabrications and consumables and other materials used in theconstruction process are inspected or otherwise verified asconforming to purchase order requirements.

4.15.2 The Fabricator is to provide an inspection systemat suitable stages of the fabrication process from the materialdelivery to the completion of construction. The inspectionsystem is to confirm and record the inspections carried out.

4.16 Indication of inspection status

4.16.1 The Fabricator is to establish and maintain asystem for identifying the inspection status of structuralcomponents at appropriate stages of the fabrication process.This may include the direct marking of components. Recordsof inspection and measurements are to be identifiable tocomponents to which they refer and be readily accessible toproduction and inspection personnel and to ClassificationSurveyors.

4.17 Inspection, measuring and test equipment

4.17.1 The Fabricator is to be responsible for thecontrol, calibration, and maintenance of the inspection,measuring and test equipment used in the fabrication andnon-destructive examination of the hull structure.

4.17.2 The calibration system is to allow traceabilityback to appropriate National Standards. Where these do notexist, the basis of calibration is to be defined.

4.18 Non-conforming materials and correctiveaction

4.18.1 The Fabricator is to establish and define proce-dures to provide for:(a) the clear identification and segregation from production

areas of all plates, sections, castings, components,fabrications, consumables and other materials whichdo not conform to the agreed specification; and

(b) the initiation of authorized corrective or alternativeaction.

4.19 Protection and preservation of quality

4.19.1 The Fabricator is to establish and maintain aprocedure to control handling and preservation processes forboth the material used in fabrication and the structuralcomponents at all stages of the fabrication process. Thisprocedure is to ensure conformance to specified require-ments and established standards.

4.19.2 Welding consumables are to be stored, handledand recycled according to maker’s recommendations.


4.20 Records

4.20.1 The Fabricator is to develop and maintain records that demonstrate achievement of the required quality and the effective operation of the Quality System. Records demonstrating sub-contractor achievement of these requirements are to be maintained. These records are to beretained and available for a defined period. These records areto include identification of materials and consumables used in fabrication, the number and class of defects found duringfabrication and information regarding corrective action taken. Records of particular processes (e.g. plate surface preparation, priming, marking, cutting, forming, accuracycontrol, non-destructive examination and audits) and all otherrecords pertaining to the operation of the Quality System arealso to be maintained.

4.21 Internal audit and management review

4.21.1 Internal audits of the performance of all aspectsof the systems relating to design, production and testing areto be carried out systematically by appointed staff andrecorded under the authority of the ManagementRepresentative. These staff members will not normally auditfunctions for which they are directly responsible.

4.21.2 Using data obtained from the audits and anyother available relevant information, management reviews areto take place at specified intervals or more frequently asdeemed necessary in order to review the performance of theQuality System.

4.21.3 The Fabricator is to establish, document andmaintain a procedure for corrective application of data feed-back from previous construction, including previous unitsduring the guarantee period.

4.21.4 The Fabricator is to establish, document andmaintain a procedure to provide for the analysis of departuresfrom manufacturing standards, steel material scrapped,reworked or repaired during the fabrication and constructionprocess in order to detect trends, investigate the cause todetermine the action needed to correct the processes andwork procedures, or to identify the further training of operators as appropriate.

4.21.5 Agreed improvements to the Quality System areto be implemented within a time scale appropriate to thenature of the improvement.

4.22 Training

4.22.1 The Fabricator is to establish and maintain asystem to identify training needs and ensure that all personnelinvolved in the fabrication, erection and quality-involved functions have adequate experience, training and qualifications.This requirement extends to sub-contractor personnel workingwithin the fabrication yard. Records are to be available to theClassification Surveyor.

4.23 Sampling

4.23.1 Any sampling processes used by the Fabricatorare to be in accordance with specified or StatutoryRequirements or to the satisfaction of the ClassificationSurveyor as applicable.




4.24 Sub-contracted personnel, services andcomponents

4.24.1 The requirements of the Scheme are applicable,as appropriate, to all sub-contractor personnel and sub-contracted services operating within the fabrication yard.

4.24.2 The requirements of the Scheme are not applicableto sub-contractor personnel or sub-contracted services operating at locations outside the fabrication yard. In thesecircumstances it will be necessary for inspections to be carriedout by the LR Surveyor using conventional survey methods.





SECTION 5Additional requirements for Part 2 of theScheme

5.1 Quality System procedures

5.1.1 The procedures detailed in 4.7 are to be submittedfor approval.

5.2 Quality Plans

5.2.1 Quality Plans for units which are to be classed byLR are to be submitted for approval well in advance ofcommencement of work, irrespective of any submissions thatmay have been made for similar units under Part 1 of theScheme. Such Quality Plans are to outline all of the manufacturing, testing and inspection operations to beperformed by the Fabricator and by which personnel they willbe carried out. The Quality Plans are then to be submitted tothe LR Surveyors who will indicate all the stages at which theywill perform system monitoring, carry out direct inspectionand participate in hold point inspections. These hold pointswill include, but not be limited to, the following:• Radiographs and other test records of non-destructive

examinations as required for Classification purposes,see Ch 8,2.5.

• The items described in Ch 1,6 relevant to the scope ofthis Chapter.

5.2.2 Notwithstanding what may have been agreed inthe Quality Plans, the LR Surveyors have the discretion toincrease their involvement, see also 8.1.5.

5.3 Material supplier approval

5.3.1 The Fabricator is to ensure that constructionmaterials and consumables used are selected from manufacturers who are approved by LR.

5.4 Identification and traceability

5.4.1 The procedure required by 4.13.1 is to besubmitted for approval.

5.5 Fabrication control

5.5.1 The information required by 4.14.1(b) will beexamined for acceptability.

5.5.2 Procedures for material treatment, forming, weldpreparation and welding are to be submitted for approval.

5.5.3 Procedures required by 4.14.3 are to be submit-ted to the LR Surveyors for approval.

5.6 Control of inspection and testing

5.6.1 The inspection stages incorporated into theScheme are to include specific checks for fit-up and weldingwhich are to be carried out at each sub-assembly, assembly,pre-erection and erection stage as well as self-checking by theoperator. The number of recorded checks at each stage willbe agreed with the LR Surveyor, after consideration of documentary evidence of quality being achieved. Repairs,where required, are to be effected after each check. CollatedQuality Control data to demonstrate the efficiency of the aboveself-check system are to be made available to the LR Surveyorby the Fabricator. The Quality Plans referred to in 4.7.3(b)provide the opportunity for the Fabricator and the LR Surveyorto consider the structural design and unit type fully in order todetermine the most efficient and effective inspection stages.

5.7 Control of non-conforming materials andcorrective action

5.7.1 All predetermined repair procedures are to beconsistent with the requirements of 4.7.3(a) and are to be tothe satisfaction of the LR Surveyor. Where a defect is found,whether by the LR Surveyor or through fabrication yardinspection, for which no agreed repair procedure exists,approval is to be obtained from the LR Surveyor before anycorrective action is effected.

5.8 Records

5.8.1 The fabrication yard is to make data available to the LR Surveyor, to demonstrate the efficiency of theinspection system, see 5.6.1.

5.9 Training

5.9.1 The competence of the welding operators, non-destructive examination and other personnel involved inspecial processes and inspection are to be to the satisfactionof the LR Surveyor.

5.10 Sub-contracted personnel, services andcomponents

5.10.1 The requirements of the Scheme are not applicableto those services operating at locations outside the fabricationyard. It will be necessary for inspections to be carried out by theLR Surveyor using conventional survey methods.

5.10.2 The methods of control for the requirements of4.24.1 are to be submitted to the LR Surveyor.


SECTION 6Initial assessment of fabrication yard

6.1 General

6.1.1 In the first instance, applications for approvalunder this Scheme wil l be considered on therecommendation of the local Surveyors.

6.1.2 Fabricators applying for approval to Part 1 of theScheme are required to submit the Quality Manual referencedin 3.2.1 for appraisal.

6.1.3 Fabricators applying for approval to Part 2 of theScheme are required to submit for appraisal the QualityManual referenced in 3.3.1 and if not already included in theQuality Manual, details of the following:• Construction standards, including tolerances,

accept/reject criteria and repair procedures.• The methods used for maintaining identification of

material from arrival through to erection of unit assemblies.

• The methods by which materials and consumables maybe traced back to the supplier and batch.

• Procedures for heat forming.• Procedures for the control of welding consumables.• Non-destructive examination procedures.• Test procedures.In addition, outline details of approved welding proceduresshould be submitted for information.

6.1.4 After receipt and appraisal of the documentation,an assessment of the fabrication yard is to be carried out bythe Surveyors to examine all aspects of the Quality Systemapplicable to construction.

6.1.5 The Surveyors wi l l review the qual ityarrangements proposed by the Fabricator at the Fabricator’syard. They may advise as to how the proposed QualitySystem might be improved and where it is consideredinadequate, advise how it might be revised to be acceptableto LR.

6.1.6 For assessment to Part 1 of the Scheme, theSurveyors will review the Quality System in association withthe quality documentation and will check that all aspects ofthe System are established and in accordance with therequirements of Section 3.

6.1.7 For assessment to Part 2 of the Scheme, theSurveyors wil l confirm that the requirements given in Section 3 have been fully implemented and are complied withby a detailed examination of work in progress and byconfirming that a satisfactory level of workmanship is beingconsistently achieved.




SECTION 7Approval of the fabrication yard

7.1 General

7.1.1 If the init ial assessment confirms that thefabrication yard’s quality arrangements are satisfactory, theCommittee will issue LR’s Quality Assurance ApprovalCertificate. Maintenance of approval will be subject to theprovisions of Section 6.

7.1.2 Approval by another organization will not beaccepted as sufficient evidence that the arrangements forconstruction comply with these requirements.





SECTION 8Maintenance of approval

8.1 General

8.1.1 For Part 2 of the Scheme, the arrangementsapproved at the fabrication yard are to be kept under reviewby the Surveyors to ensure that the approved Quality Systemis being maintained in a satisfactory manner. This is to becarried out by:• regular and systematic audits by the LR Surveyor; and• comprehensive Annual Audits. The audit team leader

will be formally nominated by LR.

8.1.2 Where a comprehensive audit cannot be carriedout due to lack of a current building programme to Class,demonstration that the requirements of Part 1 of the Schemeare being maintained may be confirmed by audit review atintervals of six months, normally by the local Surveyors.Where necessary a comprehensive triennial audit would becarried out by a Surveyor formally nominated by LR. Thedegree of reassessment for re-approval at therecommencement of building to LR’s Class would be at thediscretion of the Committee.

8.1.3 All documentation, including records, is to beavailable to the Surveyors.

8.1.4 Minor alterations in the approved proceduresmay be permitted provided that the Surveyors are advisedand their prior concurrence obtained. Major alterationswould need to be submitted for approval and may require anadditional audit.

8.1.5 In a fabrication yard constructing f loatingoffshore installations to LR’s Class, the following areapplicable:(a) The attending Surveyor is to be allowed access at all

reasonable times to all records pertaining to quality andto all parts of the fabrication yard involved in the implementation and maintenance of the QualityAssurance Programme.

(b) LR Surveyors are immediately to advise theManagement Representative of any matter pertaining tothe Quality System with which they are not satisfied.

(c) When minor deficiencies in the approved proceduresare discovered during audits, or if workmanship isconsidered unsatisfactory, the Surveyors will applymore intensive auditing and inspection.

(d) Notwithstanding any of the provisions of the QualitySystem, all work related to Classification of floatingoffshore installations with LR is to be to the satisfactionof the attending Surveyor.

SECTION 9Suspension or withdrawal of approval

9.1 General

9.11 When the Surveyors have drawn attention tosignificant faults or deficiencies in the Quality System or itsoperation and these have not been rectified within a period oftime acceptable to LR, the approval of the System, togetherwith the associated certification, will be withdrawn and thefabrication yard’s name deleted from the Approval List.

9.1.2 If a significant period of time elapses betweensuch withdrawal and any application for reinstatement, there-approval procedures, if agreed to by the Committee, mayrequire a restructuring of the Quality Management Systemand will always require a complete re-examination as for aninitial assessment.




Part 4, Appendix ASections A1 & A2

SECTION A1General

A1.1 Application

A1.1.1 This Appendix contains details of acceptabledesign S-N curves and joint classification. The detailscontained in this Appendix takes due account of the fatiguedata published in the UK HSE Guidance Notes for Design,Construction and Classification of Offshore Installations, 4thedition, 1990.

A1.1.2 All tubular joints are assigned Class T. Othertypes of joints are assigned Class B, C, D, E, F, F2, G or Wdepending upon:• geometric arrangements;• direction of applied stress; and• method of fabrication and inspection.

A1.1.3 Details of the design S-N curves are given inSection A2, joint classifications are given in Section A3.

A1.14 Guidance on the determination of global stressconcentration factors is given in Section A4.

Section

A1 General

A2 Fatigue design S-N curves

A3 Fatigue joint classification

A4 Stress concentration factors

Fatigue – S-N Curves, Joint Classification andStress Concentration Factors

SECTION A2Fatigue design S-N curves

A2.1 Basic design S-N curves

A2.1.1 The basic design curves consist of l inearrelationships between log(SB) and log(N). They are basedupon a statistical analysis of appropriate experimental dataand may be taken to represent two standard deviationsbelow the mean line. Thus the basic S-N curves are of theform:

log(N) = log(K1) – dσ – m log(SB)where

N = the predicted number of cycles to failureunder stress range SB

K1 = a constant relating to the mean S-N curved = the number of standard deviations below the

meanσ = the standard deviation of log N

m = the inverse slope of the S-N curve.The relevant values of these terms are shown in Table A2.1.Table A2.1 also shows the value of K2, where:

log(K2) = log (K1) – 2σwhich is relevant to the basic design curves (i.e. for d = 2).

A2.2 Modifications to basic S-N curves

A2.2.1 The factors listed in this sub-Section are to beconsidered when using the basic S-N curve.

A2.2.2 Unprotected joints in sea-water. For jointswithout adequate corrosion protection which are exposed tosea water the basic S-N curve is reduced by a factor of twoon life for all joint classes. NOTE

For high strength steels, i.e. σy >400 N/mm2, a penalty factorof two may not be adequate). In addition the correctionrelating to the numbers of small stress cycles is notapplicable.

1999 FPFL – Pt 4, Appendix 5/6/99 10:56 am Page 1 (Black plate)

A2.2.4 Weld improvement. For welded joints involvingpotential fatigue cracking from the weld toe, an improvementin strength by at least 30 per cent, equivalent to a factor of2,2 on life, can be obtained by controlled local machining orgrinding of the weld toe. This is to be carried out either witha rotary burr or by disc grinding. The treatment shouldproduce a smooth concave profile at the weld toe with thedepth of the depression penetrating into the plate surface toat least 0,5 mm below the bottom of any visible undercut,see Fig. A2.1, and ensuring that no exposed defects remain.The maximum depth of local machining or grinding is not toexceed 2 mm or five per cent of the plate thickness. In thecase of a multi-pass weld more than one weld toe may needto be dressed. Where toe grinding is used to improve thefatigue life of fillet welded connections, care should be takento ensure that the required throat size is maintained. Thebenefit of grinding is only applicable for welded joints whichare adequately protected from sea-water corrosion. Anycredit for other beneficial treatments should be justified. It isrecommended that no advantage for toe grinding should betaken at the initial design stage. Overall weld profiling ispreferred but no improvement in fatigue strength can beallowed unless accompanied by toe grinding. In the case ofpartial penetration welds, where failure may occur from theweld root, grinding of the weld toe cannot be relied upon togive an increase in strength.

A2.3 Treatment of low stress cycles

A2.3.1 Under constant amplitude stresses there is acertain stress range, which varies both with the environmentand with the size of any initial defects, below which anindefinitely large number of cycles can be sustained. In airand sea-water with adequate protection against corrosion,and with details fabricated in accordance with this Appendix,it is assumed that this non-propagating stress range (So) isthe stress corresponding to N = 107 cycles; relevant values ofSo are shown in Table A2.1.



Part 4, Appendix ASection A2


A2.2.3 Effect of plate thickness. The fatigue strengthof welded joints is to some extent dependent on platethickness, strength decreasing with increasing thickness.The basic S-N curves shown in Figs. A2.2 and A2.3 relate tothicknesses as follows:• Nodal joints (Class T) 32 mm• Non-nodal joints (Classes B-G) up to 22 mm.For joints of other thicknesses, correction factors on life orstress have to be applied to produce a relevant S-N curve.The correction on stress range is of the form:

S =1/4

whereS = the fat igue strength of the joint under

considerationSB = the fatigue strength of the joint using the

basic S-N curvet = the actual thickness of the member under

considerationtB = the thickness relevant to the basic S-N curve

Substituting the above relationship in the basic S-N curveequation in A2.1.1 and using the equation for log(K2) inA2.1.1 yields the following equation of the S-N for a jointmember thickness t:

log(N) = 1/4

A value of t = 22 mm should be used for calculatingendurance N when the actual thickness is less than 22 mm.NOTE

This gives a benefit for nodal joints with wall thicknesses inthe range of 22 to 32 mm.

logK2 – m log St Bt

SB t Bt

K1 Standard deviation SoClass K1 log10 loge m log10 loge K2 N/mm2

B 2,343 x 1015 15,3697 35,3900 4,0 0,1821 0,4194 1,01 x 1015 100

C 1,082 x 1014 14,0342 32,3153 3,5 0,2041 0,4700 4,23 x 1013 78

D 3,988 x 1012 12,6007 29,0144 3,0 0,2095 0,4824 1,52 x 1012 53

E 3,289 x 1012 12,5169 28,8216 3,0 0,2509 0,5777 1,04 x 1012 47

F 1,289 x 1012 12,2370 28,1770 3,0 0,2183 0,5027 0,63 x 1012 40

F2 1,231 x 1012 12,0900 27,8387 3,0 0,2279 0,5248 0,43 x 1012 35

G 0,566 x 1012 11,7525 27,0614 3,0 0,1793 0,4129 0,25 x 1012 29

W 0,368 x 1012 11,5662 26,6324 3,0 0,1846 0,4251 0,16 x 1012 25

T 4,577 x 1012 12,6606 29,1520 3,0 0,2484 0,5720 1,46 x 1012 53, see Note 1

NOTES1. Idealized hot spot stress2. For example, the T curve expressed in terms of log10 is:

log10(N) = 12,6606 – 0,2484d – 3log10(SB)

Table A2.1 Details of basic S-N curves


A2.3.2 When the applied fluctuating stress has varyingamplitude, so that some of the stress ranges are greater andsome less than So, the larger stress ranges will cause growthof the defect, thereby reducing the value of the non-propagating stress range below So. In time, an increasingnumber of stress ranges, below So can themselvescontribute to crack growth. The final result is an earlierfatigue failure than could be predicted by assuming that allstress ranges below So are ineffective.

A2.3.3 An adequate estimate of this behaviour can bemade by assuming that the S-N curve has a change ofinverse slope from m to m + 2 at N = 107 cycles. Thiscorrection does not apply in the case of unprotected joints insea-water.

A2.4 Treatment of high stress cycles

A2.4.1 For high stress cycles the design S-N curve fornodal joints (the T curve) may be extrapolated back linearly toa stress range equal to twice the material yield stress 2σy.

A2.4.2 An example of the high stress cycle limit for the T curve is given in Fig. A2.4.





A2.4.3 A similar procedure can be adopted for non-nodal joints (Classes B-G) where local bending or otherstructural stress concentrating features are involved and therelevant stress range includes the stress concentration.

A2.4.4 If, the joint is in a region of simple membranestress, then the design S-N curves may be extrapolated backlinearly to a stress range given by twice the tensile stresslimitations given in these Rules.

A2.4.5 For the Class W curve, extrapolation may bemade back as for the non-nodal joints but to a stress rangedefined by half the values given above (i.e. with reference toshear instead of tensile stress).

��

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��B

ADefect

Chord

Brace Depth of grindingshould be 0,5 mmbelow bottom of any visible undercut

BA

Defect

Chord

Brace

Depth of grindingshould be 0,5 mmbelow bottom of any visible undercut

Defect in chord

Defect in brace

4407/02

Grinding a weld toe tangentially to the plate surface as at A, will produce little improvement in strength. Grinding must extend below the plate surface, as at B, in order to remove toe defects.

Fig. A2.1 Weld improvements






1 00

0

100 10 10

410

510

610

710

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1

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Stress range, SB (N/mm2)

B C D E F F2 G W

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710

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Stress range, SB (N/mm2)

T

Fig

. A2.

3

Bas

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ts






1 00

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102

103

104

105

106

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Stress range, SB (N/mm2)T

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SECTION A3Fatigue joint classification

A3.1 General

A3.1.1 Fatigue joint classification details including noteson mode of failure and typical examples are given in Table A3.1.










Type number, description and notes on modeof failure

1.1 Plain steel

(a) In the as-rolled condition, or withcleaned surfaces but with no flame-cutedges of re-entrant corners.

(b) As (a) but with any flame-cut edgessubsequently ground or machined toremove all visible sign of the drag lines.

(c) As (a) but with the edges machine flame-cut by a controlled procedure to ensurethat the cut surface is free from cracks.

2.1 Full or partial penetration butt welds, orfillet welds.Parent or weld metal in members,without attachments built up of plates orsections, and joined by continuouswelds.

(a) Full penetration butt welds with the weldoverfill dressed flush with the surfaceand finish-machined in the direction ofstress, and with the weld proved freefrom significant defects by non-destructive examination.

(b) Butt or fillet welds with the welds madeby an automatic submerged or open arcprocess and with no stop-start positionswithin the length.

(c) As (b) but with the weld containing stop-start positions within the length.

Class explanatory comments

B Beware of using Class B for a memberwhich may acquire stress concentrationduring its life, e.g. as a result of rustpitting. In such an event Class C wouldbe more appropriate.

B Any re-entrant corners in flame-cutedges should have a radius greater thanthe plate thickness.

C Note, however, that the presence of a re-entrant corner implies the existence ofa stress concentration so that the designstress should be taken as the net stressmultiplied by the relevant stressconcentration factor.

B The significance of defects should bedetermined with the aid of specialistadvice and/or by the use of fracturemechanics analysis. The NDT techniquemust be selected with a view to ensuringthe detection of such significant defects.

C If an accidental stop-start occurs in aregion where Class C is requiredremedial action should be taken so thatthe finished weld has a similar surfaceand root profile to that intended.

D For situation at the ends of flange coverplates see joint Type 6.4.

Examples, including failure modes

TYPE 1 MATERIAL FREE FROM WELDING

Notes on potential modes of failure:

In plain steel, fatigue cracks initiate at the surface, usually either at surface irregularities or at corners of the cross-section. In weldedconstruction, fatigue failure will rarely occur in a region of plain material since the fatigue strength of the welded joints will usually be much lower.In steel with rivet or bolt holes or other stress concentrations arising from the shape of the member, failure will usually initiate at the stressconcentration.

4407/06

��

TYPE 2 CONTINUOUS WELDS ESSENTIALLY PARALLEL TO THE DIRECTION OF APPLIED STRESS


With the excess weld metal dressed flush, fatigue cracks would be expected to initiate at weld defect locations. In the as-welded condition,cracks might initiate at stop-start positions or, if these are not present, at weld surface ripples

General comments:(a) Backing strips:If backing strips are used in making these joints: (i) they must be continuous; and (ii) if they are attached by welding those welds must alsocomply with the relevant Class requirements (note particularly that tack welds, unless subsequently ground out or covered by a continuousweld, would reduce the joint to Class F, see joint 6.5).

(b) Edge distance:An edge distance criterion exists to limit the possibility of local stress concentrations occurring at unwelded edges as a result for example, ofundercut, weld spatter or accidental overweave in manual fillet welding (see also notes on joint Type 4). Although an edge distance can bespecified only for the ‘width’ direction of an element, it is equally important to ensure that no accidental undercutting occurs on the unweldedcorners of, for example, cover plates or box girder flanges. If it does occur is should subsequently be ground smooth.

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��Applied stress

��

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��

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Edge distance fromweld toe to edge offlange > 10 mm

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Table A3.1 Fatigue joint classification (see continuation)







3.1 Parent metal adjacent to or weld metal infull penetration butt joints welded fromboth sides between plates of equalwidth and thickness or where differencesin width and thickness are machined toa smooth transition not steeper than 1 in 4.

(a) With the weld overfill dressed flush withthe surface and with the weld provedfree from significant defects by non-destructive examination.

(b) With the welds made, either manually orby an automatic process, other thansubmerged arc, provided all runs aremade in the downhand position.

(c) Welds made other than in (a) or (b).

3.2 Parent metal adjacent to, or weld metalin, full penetration butt joints made on apermanent backing strip between platesof equal width and thickness or withdifferences in width and thicknessmachined to a smooth transition notsteeper than 1 in 4.


Note that this includes butt welds whichdo not completely traverse the member,such as circular welds used for insertinginfilling plates into temporary holes.

C The significance of defects should bedetermine with the aid of specialistadvice and/or by the use of fracturemechanic analysis. The NDT techniquemust be selected with a view to ensuringthe detection of such significant defects.

D In general, welds made by thesubmerged arc process, or in positionsother than downhand, tend to have apoor reinforcement shape, from the pointof view of fatigue strength. Hence suchwelds are downgraded from D to E.

E In both (b) and (c) of the corners of thecross-section of the stressed element atthe weld toes should be dressed to asmooth profile.Note that step changes in thickness arein general, not permitted under fatigueconditions, but that where the thicknessof the thicker member is not greater than1,15 x the thickness of the thinnermember, the change can beaccommodated in the weld profilewithout any machining. Step changes inwidth lead to large reductions in strength(see joint Type 3.3).

F Note that if the backing strip is filletwelded or tack welded to the memberthe joint could be reduced to Class G(joint Type 4.2).


TYPE 3 TRANSVERSE BUTT WELDS IN PLATES (i.e. essentially perpendicular to the direction of applied stress)Notes on potential modes of failure:

With the weld ends machined flush with the plate edges, fatigue cracks in the as-welded condition normally initiate at the weld toe, so that thefatigue strength depends largely upon the shape of the weld overfill. If this is dressed flush the stress concentration caused by it is removed andfailure is then associated with weld defects. In welds made on a permanent backing strip, fatigue cracks initiate at the weld metal/strip junctionand in partial penetration welds (which should not be used under fatigue conditions), at the weld root.Welds made entirely from one side, without a permanent backing, require care to be taken in the making of the root bead in order to ensure asatisfactory profile.

Design stresses:In the design of butt welds of Types 3.1 or 3.2 which are not aligned, the stresses must include the effect of any eccentricity. An approximate

method of allowing for eccentricity in the thickness direction is to multiply the normal stress by , where

e is the distance between centres of thickness of the two abutting members: if one of the members is tapered, the centre of the untapered thickness must be used; and

t is the thickness of the thinner member.With connections which are supported laterally, e.g. flanges of a beam which are supported by the web, eccentricity may be neglected.

1 + 3 et

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��

4407/11��

��

4407/12

t

e

�� 4407/13

No track welds

Table A3.1 Fatigue joint classification (continued)







3.3 Parent metal adjacent to, or weld metalin, full penetration butt welded jointsmade from both sides between plates ofunequal width, with the weld endsground to a radius not less than 1,25 times the thickness t.

4.1 Parent metal (of the stressed member)adjacent to toes or ends of bevel-butt orfillet welded attachments, regardless ofthe orientation of the weld to thedirection of applied stress and whetheror not the welds are continuous roundthe attachment.

(a) With attachment length (parallel to thedirection of the applied stress)≤ 150 mm and with edge distance≥ 10 mm.

(b) With attachment length (parallel to thedirection of the applied stress)> 150 mm and with edge distance≤ 10 mm.

4.2 Parent metal (of the stressed member) atthe toes or the ends of butt or filletwelded attachments on or within 10 mmof the edge or corners of a stressedmember and regardless of the shape ofthe attachment.

4.3 Parent metal (of the stressed member) atthe toe of a butt weld connecting thestressed member to another memberslotted through it.

(a) With the length of the slotted-throughmember, parallel to the direction of theapplied stress, ≤150 mm and with edgedistance ≥10 mm.

(b) With the length of the slotted-throughmember, parallel to the direction of theapplied stress, >150 mm and with edgedistance ≥10 mm.

(c) With edge distance <10 mm.


F2 Step changes in width can often beavoided by the use of shaped transitionplates, arranged so as to enable buttwelds to be made between plates ofequal width.Note that for this detail the stressconcentration has been taken intoaccount in the joint classification.

Butt welded joints should be made withan additional reinforcing fillet so as toprovide a similar toe profile to that whichwould exist in a fillet welded joint.

F The decrease in fatigue strength withincreasing attachment length is becausemore load is transferred into the longergusset giving an increase in stressconcentration.

F2

G Note that the classification applies to allsizes of attachment. It would thereforeinclude, for example, the junction of twoflanges at right angles. In suchsituations a low fatigue classification canoften be avoided by the use of atransition plate (see also joint Type 3.3).

Note that this classification does notapply to fillet welded joints (see jointType 5.1b). However it does apply toloading in either direction (L or T in thesketch).

F

F2

G


TYPE 4 WELDED ATTACHMENTS ON THE SURFACE OR EDGE OF A STRESSED MEMBERNotes on potential modes of failure:

When the weld is parallel to the direction of the applied stress, fatigue cracks normally initiate at the weld ends, but when it is transverse to thedirection of stressing they usually initiate at the weld toe; for attachments involving a single, as opposed to a double, weld cracks may alsoinitiate at the weld root. The cracks then propagate into the stressed member. When the welds are on or adjacent to the edge of the stressedmember the stress concentration is increased and the fatigue strength is reduced, this is the reason for specifying an ’edge distance’ in some ofthese joints (see also note on edge distance in joint Type 2).

r ≥ 1,25t

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t

�

��4407/15

Edge distance

��

��

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T

T

L

L

��4407/16

Edge distance

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5.1 Joint descriptionParent metal adjacent to cruciform jointsor T joints (member marked X insketches).

(a) Joint made with full penetration weldsand with any undercutting at the cornersof the member dressed out by localgrinding.

(b) Joint made with partial penetration orfillet welds with any undercutting at thecorners of the member dressed out bylocal grinding.

5.2 Parent metal adjacent to the toe of load-carrying fillet welds which are essentiallytransverse to the direction of appliedstress (member X in sketch).

(a) Edge distance ≥ 10 mm.

(b) Edge distance < 10 mm.

5.3 Parent metal at the ends of load-carryingfillet welds which are essentially parallelto the direction of applied stress, withthe weld end on plate edge (member Yin sketch).

5.4 Weld metal in load-carrying joints madewith fillet or partial penetration welds,with the welds either transverse orparallel to the direction of applied stress(based on nominal shear stress on theminimum weld throat area).


Member Y can be regarded as one witha non-load-carrying weld (see joint Type 4.1). Note that in this instance theedge distance limitation applies.

F

F2 In this type of joint, failure is likely tooccur in the weld throat unless the weldis made sufficiently large (see joint Type 5.4).

The relevant stress in member X shouldbe calculated on the assumption that itseffective width is the same as the widthof member Y.

F2 These classifications also apply to jointswith longitudinal weld only.

G

G

W This includes joints in which a pulsatingload may be carried in bearing, such asthe connection of bearing stiffeners toflanges. In such examples the weldsshould be designed on the assumptionthat none of the load is carried inbearing.


��Y X

��

Y X��Y X

��Y

X

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X

X

Edge distance

YX

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Y

XEdgedistance

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TYPE 5 LOAD-CARRYING FILLET AND T BUTT WELDS


Failure in cruciform or T joints with full penetration welds will normally initiate at the weld toe, but in joints made with load-carrying fillet or partialpenetration butt welds cracking may initiate either at the weld toe and propagate into the plate or at the weld root and propagate through theweld. In welds parallel to the direction of the applied stress, however, weld failure is uncommon, cracks normally initiate at the weld end andpropagate into the plate perpendicular to the direction of applied stress. The stress concentration is increased, and the fatigue strength istherefore reduced, if the weld end is located on or adjacent to the edge of a stressed member rather than on its surface.








6.1 Parent metal at the toe of a weldconnecting a stiffener, diaphragm, etc.,to a girder flange.

(a) Edge distance ≥10 mm (see joint Type 4.2).

(b) Edge distance <10 mm.

6.2 Parent metal at the end of a weldconnecting a stiffener, diaphragm, etc.,to a girder web in a region of combinedbending and shear.

6.3 Parent metal adjacent to welded shearconnectors.

(a) Edge distance ≥10 mm.

(b) Edge distance <10 mm (see Type 4.2).

6.4 Parent metal at the end of a partiallength welded cover plate, regardless ofwhether the plate has square or taperedends and whether or not there are weldsacross the ends.

6.5 Parent metal adjacent to the ends ofdiscontinuous welds, e.g. intermittentweb/flange welds, tack welds unlesssubsequently buried in continuous runs.

Ditto, adjacent to cope holes.

7.1 Parent material adjacent to the toes offull penetration welded nodal joints.


Edge distance refers to distance from afree, i.e. unwelded edge. In thisexample, therefore, it is not relevant

F as far as the (welded) edge of the webplate is concerned. For reason for edge

G distance see note on joint Type 2.

E This classification includes allattachments to girder webs.

F

G

G This Class includes cover plates whichare wider than the flange. However,such a detail is not recommendedbecause it will almost inevitably result inundercutting of the flange edge wherethe transverse weld crosses it, as well asinvolving a longitudinal weld terminatingon the flange edge and causing a highstress concentration.

E This also includes tack welds which arenot subsequently buried in a continuousweld. This may be particularly relevant intack welded backing strips.Note that the existence of the cope holeis allowed for in the joint classification,

F it should not be regarded as anadditional stress concentration.

T In this situation design should be basedon the hot spot stress as defined in Pt 3,Ch 5,5 (see also this Section forguidance on partial penetration welds).


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��Edge distance

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��

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��

4407/23�Edge distance

TYPE 7 DETAILS RELATING TO TUBULAR MEMBERS

��

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TYPE 6 DETAILS IN WELDED GIRDERS


Fatigue cracks generally initiate at weld toes and are especially associated with local stress concentrations at weld ends, short lengths of returnwelds, and changes of direction. Concentrations are enhanced when these features occur at or near an edge of a part (see notes on joint Type 4).

General comment:

Most of the joints in this section are also shown, in a more general form in joint Type 4, they are included here for convenience as being thejoints which occur most frequently in welded girders.







7.2 Parent metal at the toes of weldsassociated with small (≤150 mm in thedirection parallel to the applied stress)attachments to the tubular member.

As above, but with attachment length >150 mm.

7.3 Gusseted connections made with fullpenetration or fillet welds. (But note thatfull penetration welds are normallyrequired).

7.4 Parent material at the toe of a weldattaching a diaphragm or stiffener to atubular member.

7.5 Parent material adjacent to the toes ofcircumferential butt welds betweentubes.

(a) Welds made from both sides with theweld overfill dressed flush with thesurface and with the weld proved freefrom significant defects by non-destructive examination.

(b) Weld made from both sides.

(c) Weld made from one side on apermanent backing strip.

(d) Weld made from one side without abacking strip provided that fullpenetration is achieved.


F

F2

F Note that the design stress must includeany local bending stress adjacent to theweld end.

W For failure in the weld throat of filletwelded joints.

F Stress should include the stressconcentration factor due to overallshape of adjoining structure.

In this type of joint the stress shouldinclude the stress concentration factor toallow for any thickness change and forfabrication tolerances.

C The significance of defects should bedetermined with the aid of specialistadvice and/or by the use of fracturemechanics analysis. The NDT techniqueshould be selected with a view toensuring the detection of such significantdefects.

E

F

F2 Note that step changes in thickness are,in general, not permitted under fatigueconditions, but that where the thicknessof the thicker member is not greater than1,15 x the thickness of the thinnermember, the change can beaccommodated in the weld profilewithout any machining


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��

4407/29

�� 4407/28

��

4407/26








7.6 Parent material at the toes ofcircumferential butt welds betweentubular and conical section.

7.7 Parent material of the stressed memberadjacent to the toes of bevel butt or filletwelded attachments in a region of stressconcentration.

7.8 Parent metal adjacent to, or weld metalin, welds around a penetration throughthe wall of a member (on a planeessentially perpendicular to the directionof stress). Note that full penetrationwelds are normally required in thissituation.

7.9 Weld metal in partial penetration or filletwelded joints around a penetrationthrough the wall of a member (on aplane essentially parallel to the directionof stress).


Class and stress should be thosecorresponding to the joint type asindicated in 7.5, but the stress must alsoinclude the stress concentration factordue to overall form of the joint.

Class depends on attachment length(see Type 4.1) but stress should includethe stress concentration factor due tooverall shape of adjoining structure.

D In this situation the relevant stressshould include the stress concentrationfactor due to the overall geometry of thedetail.

W The stress in the weld should include anappropriate stress concentration factorto allow for the overall joint geometry.


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CEFF2

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ForF2

��

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Stress

��4407/33

X

XStress

Table A3.1 Fatigue joint classification (conclusion)


SECTION A4Stress concentration factors

A4.1 General

A4.1.1 The purpose of this Section is to provide someguidance for the determination of geometric stressconcentration factors for classified details, under the action ofaxial and shear loadings. Information relating to structuralfeatures commonly found in fatigue prone areas of typicalmobile offshore units is included.

A4.1.2 In general, any discontinuity in a stressedstructure results in a local increase in stress at thediscontinuity. The ratio of the peak stress at the discontinuityto the nominal average stress that would prevail in theabsence of the discontinuity is commonly referred to as thestress concentration factor (SCF). The peak stress (i.e.nominal stress x SCF) is normally used in conjunction with anappropriate S-N curve to derive the estimated fatigue life.

A4.1.3 The design weld S-N curves are given in Section A2 for the particular joint arrangements given inSection A3.

A4.1.4 For semi-submersible units, experience hasshown that the areas of minimum fatigue life are usually foundat the joints, stiffener terminations, penetrations in primarybracings and also at their junctions with hull, columns anddecks. For jack-up structures locations of minimum fatiguelife are usually found on the lattice legs and support structure.Other structures subjected to significant cylic loading alsorequire assessment.

A4.1.5 This Section does not contain guidance fortubular brace to chord connections (i.e. nodal joints). Stressconcentration factors may be determined from LR’s technicalreport Recommended Parametric Stress ConcentrationFactors or an equivalent standard.

A4.1.6 Consideration will be given to data derived fromappropriate alternative sources. For complex arrangements,a detailed analysis may be required.

A4.2 Summary of details included

A4.2.1 This Section highlights typical structural detailswhich are considered to be of importance from a fatigue lifepoint of view. The various structural details consideredinclude items which have been relatively free from problemsin-service in addition to those features which have proven tobe prone to defects in service.

A4.2.2 Listed in Table A4.1 are common structuraldetails/arrangements found on offshore installations togetherwith section numbers of this report where information onSCF’s may be found. These features would be subject toregular inspection during survey cycles.

A4.3 Transverse/circumferential butt weld

A4.3.1 The applicable S-N curve will depend on the typeof weld used. In general, only weld types corresponding to S-N curves for Classes C to E would normally be consideredsuitable for primary members. Welds made from one side,corresponding to S-N curves for Classes F and F2, are notnormal practice.





A4.3.2 Four types of arrangements could normally beexpected to define the range of joint geometries:(a) Equal plate thickness connection, no chamfer on parent

metal. Joint may include allowable fabrication misalign-ment.

(b) Unequal plate thickness connections, no chamfer onparent model. Joint may include allowable fabricationmisalignment.

(c) Unequal plate thickness connection, chamfer on thickness plate not to exceed slope of 1:3. Joint mayinclude allowable fabrication misalignment.

(d) Angular misalignment.

A4.3.3 The maximum fabrication axial misalignment forfatigue prone locations would normally be limited to thesmaller of 0,1 x t or 3 mm.where

t = thickness of thinner plateThe maximum angular misalignment would be limited to thesmaller of 0,001 x length of member or 3 mm. For thisguidance, it may be assumed that the effects of thesemaximum fabrication misalignments are included within theS-N classification.

A4.3.4 The general expression for the stressconcentration factor applicable for axial loading in a flat plateis:

SCF =

wheree = distance between the centrelines of the platest1 = thinner plate thicknesst2 = thicker plate thicknessf = variable factor to account for length ratio to

support points and support conditions, (neednot be taken as greater than 1,0)

n = power index, conservatively taken as 1,5

A4.3.5 The general expression for the stressconcentration factor applicable for axial loading and angularmisalignment is:

• SCF = for fixed ends

• SCF = for pinned ends

where

β =

t = plate thicknessL = distance to support point or reference planey = misalignmentσ = nominal axial stressE = Young’s modulus

NOTE that the tanh correction factor is always ≤1,0.

A4.3.6 For combined misalignment:

SCF (total) = SCF (axial) + SCF (angular) – 1

2Lt

3σ

E

1 +6yt

tanh β

β

1 +3yt

tanh

β2

β2

1 + 6et1

t1 n

t1 n + t2 n f






Description

Transverse/circumferential butt weld:

In flat plates and tubular members.

Welds essentially transverse to the direction of theapplied stress.

Longitudinal butt welds:

In the welds essentially parallel to the direction of theapplied stress.

Axial stiffener welds

Cope holes:

In members welded parallel to the direction of theapplied stress.

Circumferential butt welds:

Between tubular and conical sections.

Weld essentially transverse to the direction of theapplied stress.

Bracing diaphragm or ring stiffener welds

Welded attachments:

On the surface of a stressed member.

Section No.

A4.3

A4.4

A4.5

A4.6

A4.7

A4.8

A4.9

Detail

4407/34

4407/35

4407/36

4407/38

4407/37

4407/39

4407/40

Table A4.1 Summary of details and section members (see continuation)






Description

Ring reinforced penetration:

Through wall of bracing.

Penetration in flat plate.

Gusset stiffener end:

Smooth profile (weld toe ground).Abrupt profile.

Gusset stiffener:

Terminating at a ring stiffener or diaphragm.

Column to pontoon deck joint

Bracing to column joints:

Full penetration welds.

Bracing to bracing joints:

With stiffening.

Cruciform joint

Section No.

A4.10to

A4.14

A4.15

A4.15

A4.16

A4.17

A4.18

A4.19

Detail

4407/41

4407/42

4407/43

4407/44

4407/45

4407/46

4407/47

Table A4.1 Summary of details and section members (conclusion)






A4.3.7 The basic stress concentration factor (St) forthickness transitions in tubular members may be obtained

from Fig. A4.1 for ratios up to 60. Alternatively the

following equation may be used:

St =

wheret1 = brace thicknesst2 = stub thicknessR = brace radius

St = SCF for thickness transition• The total SCF should be obtained from the following

expression:

SCF = St x Smwhere

Sm =

e = distance between centrelines of plates• The effect of mismatches resulting from maximum

fabrication misalignments may be assumed to beincluded in the S-N curves which are based on experimental test results from welded specimens, seeA4.3.3. For ratios greater than 100, the SCF

formulation given in A4.3.4 may also be referred to.

A4.4 Longitudinal butt weld

A4.4.1 The applicable S-N curve will depend on thetype of weld used. In general only weld types correspondingto S-N curves for Classes B to D would normally beconsidered suitable for this location. Welds made from oneside are not normal practice.

A4.4.2 The stress distribution inherent in this type ofwelded joint is included in the classification assigned to thejoint. In general no additional geometric stress concentrationfactor would be required for this detail and the applied SCFmay be taken to be 1,0.

A4.4.3 If a gross geometric discontinuity exists in theregion of the weld (e.g. a penetrat ion or structuralattachment), then an appropriate SCF should be determinedto account for this.

A4.5 Axial stiffener weld

A4.5.1 The applicable S-N curve will depend on thetype of weld used. For normal fabrication when the weldmay contain stop/start positions within the length, the D classS-N curve is to be used. The S-N curve should bedowngraded to E Class for intermittent welding.

A4.5.2 The stress distribution inherent in this type ofwelded joint is included in the classification assigned to thejoint. In general, no additional geometric stress concentrationfactor would be required for this detail and the applied SCFmay be taken to be 1,0.

Dt1

1,0 + 6et1

1

1 + (t2t1)2,5

3 + R10t1

0,3

1,07 [1,0 + 0,1 3 + R10t1

tanh ( t2t1

– 1

Dt

A4.5.3 If a gross discontinuity exists in the region of theplate close to the weld (e.g. a penetration or structuralattachment), then an appropriate SCF should be determinedto account for this. Discontinuities such as cope holes andstiffener terminations are dealt with in later sections.

A4.6 Cope holes in stiffeners

A4.6.1 The applicable S-N curve will depend on thetype of weld however, for normal fabrication the F Class S-Ncurve is to be used.

A4.6.2 The presence of a standard small radius copehole is allowed for in the joint classification given above. Ingeneral, no additional geometric stress concentration factorwould be required for this detail and the applied SCF may betaken to be 1,0.

A4.6.3 If a gross geometric discontinuity exists in theregion of the weld (e.g. a penetrat ion or structuralattachment), then an appropriate SCF should be determinedto account for this.

1 2 3 4

2,0

1,9

1,8

1,7

1,6

1,5

1,4

1,3

1,2

1,1

1,0

SCF

Axial SCF

Moment SCF

D/t1 60

D/t1 60

D/t1 40

D/t1 40

D/t1 20

D/t1 20

t1

t2

Diameter = D

Member

31

Ratio of tube thickness t2 t1

4407/48

CL

Fig. A4.1SCF in tubulars due to wall thickness transition


A4.6.4 The S-N designation may be improved to the D Class by grinding flush the plate butt weld and eliminatingthe cope hole. An alternative improvement would be toprofile the cope hole. This may reduce the applicable SCF bya factor of around 1,5 from that used for the radius copehole. The applicable S-N designation would be revised to D Class. The weld should be full penetration and toe groundin way of the profiled cope hole to avoid possible failurethrough the weld throat.

A4.7 Conical/tubular intersection welds

A4.7.1 The applicable S-N curve will depend on thetype of weld used and whether junction stiffening is fitted. Ingeneral, only butt weld types corresponding to S-N curvesfor Classes C or E would normally be considered suitable forthis location. Butt welds made from one side, correspondingto S-N curves for Classes F and F2, are not normal practice.

A4.7.2 Circumferential stiffening welds should beassessed using the F Class S-N curve.

A4.7.3 Four different arrangements are addressed inA4.7.5 to A4.7.8. In each case plating/ring stiffenercentrelines are taken to occur at a single point (i.e. the effectof misalignment is not included).

A4.7.4 The following definitions are used in this sub-Section:

D = diameter of tubular membert1 = thickness of tubular membert2 = cone thicknessα = inclined angle of cone from cyl inder ( in

radians), typically 0 to 0,35.t = the smaller of t1 or t2.

A4.7.5 Unstiffened connection. The stress concentrationfactor may be taken as:

SCF =

A4.7.6 Connection fitted with internal ring stiffener.The stress concentration factor may be taken as:

SCF = (for the outer surface)

SCF = (for the inner surface)

A4.7.7 Connection fitted with internal bulkhead. Thestress concentration factor may be taken as:

SCF = (for the outer surface)

SCF = (for the inner surface)1 – 0,53 D

t tan α

1 + 0,53 D

t tan α

1 – 0,62 D

t tan α

1 + 0,62 D

t tan α

1 + 0,71 D

t tan α





A4.7.8 Connection fitted with internal ring/bulkheadand axial stiffeners.• The effect of closely spaced axial stiffeners (eight or

more) will be to reduce the value of the SCFs. In theabsence of alternative data this may be estimated byusing the formulations given in A4.7.5 to A4.7.7 andsubstituting an effective thickness (te) for t, where tegives the same local bending stiffness as the plate/axialstiffener combination.

• For widely spaced stiffeners (seven or less), the SCF willonly be reduced in way of the stiffener positions, atintermediate positions, in the absence of alternativedata, their effect should be neglected.

A4.8 Ring stiffener welds

A4.8.1 For normal fabrication, the F Class S-N curve isto be used.

A4.8.2 Two types of basic arrangements are addressedin A4.8.4 and A4.8.5.


D = diameter of tubular membert = thickness of tubular member

Ar = area of ring stiffenerte = effective thickness of plate/axial stiffener

combination.

A4.8.4 Tubular member with internal ring stiffener.The stress concentration factor may be taken as:

SCF =

A4.8.5 Tubular member with ring stiffener and axialstiffeners.• The effect of closely spaced axial stiffeners (eight or

more) will be to increase the cylinder stiffness with aresultant increase in the SCF. This may be estimated byusing the formulation given in A4.8.4 and substitutingan effective te for t, where te gives the same local bend-ing stiffness as the plate/axial stiffener combination.

• Alternatively, the SCF may be conservatively taken as1,0.

A4.9 Surface attachment welds

A4.9.1 This sub-Section covers small miscellaneousattachments to tubular members, such as those used forhandrails, anodes, pipe supports, etc. Load bearing mainstiffening members are not covered.

A4.9.2 The applicable S-N curve depends on the lengthof the attachment. Where the attachment length is less thanor equal to 150 mm, the F Class S-N curve should be used.Where the attachment length is greater than 150 mm, the F2 Class S-N curve should be used.

A4.9.3 The stress distribution inherent in this type ofwelded joint is included in the classification assigned to thejoint. In general, no additional geometric stress concentrationfactor would be required for this detail and the applied SCFmay be taken to be 1,0.

1 –0,5

1 +1,2 t 2

Ar D

t






A4.9.4 If a gross discontinuity exists in the region of theweld, e.g. a penetration, then an appropriate SCF should bedetermined to account for this.

A4.9.5 It is recommended that the attachment is keptbelow 150 mm whenever possible.

A4.10 Unreinforced/ring reinforced penetrations –General

A4.10.1 The applicable S-N curve will depend on thetype of weld used. For fat igue prone locations, ful lpenetration welding would normally be required and for thiscase the D Class S-N curve is generally applicable. Wherepartial penetration or fillet welds are used, weld stresses areto be assessed using the W Class S-N curve. Where theopening is in plain plate material (i.e. no welding around theopening) then the C Class S-N curve may be used.

A4.10.2 Location 1 is at the weld toe, location 2 isthrough the weld throat. When the ring is connected by a fullpenetration weld only location 1 is required to be considered.

A4.10.3 For most practical applications, for location 1, D Class S-N curve is appropriate and the design SCFs givenbelow may be used for the loading cases specif ied.However, for complex geometry arrangements and loadingsystems the F Class S-N curve may be relevant at certainlocations. The SCF would require to be specially considered.


D = diameter of circular openings (includingring/flange thickness)

R = or corner radius as appropriate

t = plate/tubular member thicknessf = stiffening ring/flange depthL = overal l length of penetrat ion ( including

ring/flange thickness)B = overall breadth of penetration (including

ring/flange thickness)tr = thickness of ring/flangeσ = nominal axial stress in plateq = nominal shear stress in plate

qw = shear stress in weldtw = weld throat thickness

A4.10.5 Four basic penetrat ion arrangements areaddressed below these are:• Circular, see A4.11.• Elliptical, see A4.12.• Rectangular with full radius ends, see A4.13.• Rectangular with corner radius, see A4.14.SCFs are given for locations 1 and 2 under the application ofaxial and shear loading. For location 2 the shear stress in theweld may be estimated from the following:

qw = (axial loading)

qw = (shear loading)SCFq t q

2 tw

SCFq t σ2 tw

D2

A4.10.6 The SCF will generally depend on the value ofthe equivalent cross-sectional area A of the reinforcementwhere

A = cross sectional area of reinforcementζ = efficiency factor determined from Figs. A4.2

to A4.8

For symmetric compact reinforcement .

Fig. A4.2 Symmetric reinforcement

Fig. A4.3 Unsymmetric reinforcement

A4.10.7 Stress concentration factors for penetrationswith a large aspect ratio will be specially considered.

A4.11 Circular penetration

A4.11.1 Location 1 under axial loading. The stressconcentration factor may be estimated from Fig. A4.9.

A4.11.2 Location 1 under shear loading. The stressconcentration factor may estimated from Fig. A4.13 for:

L = B = D

A4.11.3 Location 2 under axial loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.10.

A4.11.4 Location 2 under shear loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.11.

A = tr.f

A = ζ.A and

��

f

tr

t

R

h

h

4407/49

A = ζ.(2.h.tr)

ζ from Fig. A4.2 R = radius D

2

Symmetric reinforcement

��tr

t

R

h

Unsymmetric reinforcement

Α = ζ.h.tr

ζ from Fig. A4.2 to A4.6 (for h from 3 to 10)

tr

R = radius D

2

4407/50


A4.12 Elliptical penetration


A4.12.2 Location 1 under shear loading. The stressconcentration factor may be estimated from Fig. A4.13.

A4.12.3 Location 2 under axial loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.10 using B = D.

A4.12.4 Location 2 under shear loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.11 using B = D.

A4.13 Rectangular penetration with full radiusends


A4.13.2 Location 1 under shear loading. The stressconcentration factor may be estimated from Fig. A4.13.

A4.13.3 Location 2 under axial loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.10 using B = D.

A4.13.4 Location 2 under shear loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.11 using B = D.

A4.14 Rectangular penetration with corner radius

A4.14.1 Location 1 under axial loading. The stressconcentration factor may be estimated from Fig. A4.14(unreinforced), or the highest value from Figs. A4.12 andA4.16 (reinforced).

A4.14.2 Location 1 under shear loading. The stressconcentration factor may be estimated from Fig. A4.15(unreinforced), or the highest value from Figs. A4.13 andA4.17 (reinforced).

A4.14.3 Location 2 under axial loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.10 using 2Rc = D.

A4.14.4 Location 2 under shear loading. The shearstress in the weld may be estimated from A4.10.4, whereSCFq is taken from Fig. A4.11 using 2Rc = D.

A4.15 Gusset stiffener termination

A4.15.1 For fatigue prone locations full penetrationwelding would normally be required and for this case the F class S-N curve is to be used. Where partial penetration orfillet welds are used, weld stresses are to be assessed usingthe W class S-N curve for failure in the weld throat.

A4.15.2 Location 1 is at the weld toe, location 2 isthrough the weld throat. When the gusset stiffener weldadjacent to the termination is full penetration, only location 1need to be considered.





A4.15.3 Four arrangements are considered. Type (a) isnot recommended for fatigue sensitive locations:(a) Abrupt stiffener termination.(b) Soft profile stiffener termination.(c) Internal/external stiffener combination.(d) Gusset terminating at a ring stiffener.NOTE

Stress concentration factors are given for axial loading.

A4.15.4 The shear stress in the weld throat should betaken as the vector sum of the shear stresses in the weldmetal based on an effective throat dimension and on theassumption that none of the load is carried in bearingbetween parent metals, see Fig. A4.18. When calculating thestress range, the vector difference of the greatest and theleast vector sum stress may be used instead of the algebraicdifference.

A4.15.5 General definitions:D = tubular member diameter

As = nominal stiffener areat = tubular member thickness

A4.15.6 Abrupt stiffener termination, location 1. Thestress concentration factor may be estimated from Fig. A4.19.

A4.15.7 Abrupt stiffener termination, location 2. Theshear stress in the weld throat will depend on the actualgeometry and attachment weld and should be determined ona case basis.

A4.15.8 Soft profile stiffener termination, location 1.The stress concentration factor may be estimated from Fig. A4.20. Full penetration weld is recommended in way ofthe gusset termination.

A4.15.9 Internal/external stiffener terminations,location 1. The stress concentration factor may beestimated as follows:

SCFc = SCFa x Kcwhere

SCFc = stress concentration factor for stiffenercombination. (Not to be taken as less than1,0)

SCFa = stress concentration factor from Fig. A4.19 orFig. A4.20 as applicable

Kc = factor allowing for overlap of stiffeners (seeFig. A4.21)

A4.15.10 Internal/external stiffener terminations,location 2. For partial penetration or fillet welds, the shearstress in the weld throat will depend on the actual geometryand attachment weld and should be determined on a case bycase basis.

A4.15.11 Gusset stiffener terminating at a ring stiffener,location 1. The stress concentration factor may beestimated as follows:

SCFr = SCFa x 0,75where

SCFr = stress concentration factor including effect ofring stiffener (not to be taken as less than 1,0)

SCFa = stress concentration factor determined fromFig. A4.19.

The above SCF may be used irrespective of whether a rathole is present at the stiffener intersection or not.

A4.15.12 Gusset stiffener terminating at a ring stiffener,location 2. For partial penetration or fillet welds the shearstress in the weld throat will depend on the actual geometryand attachment weld and should be determined on a case by






1,0

5 10 100

2

3

4

6

5

8

10

20

30

50

ht r

4407/51

ζ

Rtr

Fig. A4.4 ζ for symmetric flange reinforcement

1,0

5 10010

4407/52R tr

ζ

1,0

0,5

0,25

0,15

0,10

0,05

0,025

0,010,0050,001

5001005025151052,51,5 t 3

tr( ) ( )tr 0,5

R

Fig. A4.5 ζ for unsymmetric flange reinforcement htr

= 3


case basis.





4407/53

10010

1,0

5Rtr

ζ

1,0

1,5

0,5

0,25

0,15

0,10

0,05

0,0250,010,005

0,001

5001005025151052,5 t 3

tr( ) ( )tr 0,5

R


= 4






4407/54

10010

1,0

5 Rtr

ζ

1,0

1,5

2,5

0,5

0,25

0,15

0,10

0,050,0250,010,005

0,001

t 3

tr( ) ( )tr 0,5

R500100502515105


= 5






4407/5510010

1,0

5Rtr

ζ

1,0

1,5

2,5

5,0

0,50,250,150,100,050,0250,01

10 15 25 50100 500 t 3

tr( ) ( )tr 0,5

R


= 10






4407/56

SCF

3

0 0,2 0,4 0,6 0,8 1,0

2

1

Α D.t

Typical range

σ

t

D

tr

Fig. A4.9 SCF for ring stiffened circular penetration in tubular member under axial/bending loads (location 1)






SCFτ

0,5 0,6 0,7 0,8 0,90

0,2

0,4

0,6

0,8

1,0

σ

t

D

tr

10

5

2

1

ft

4407/571– 2tr D

Fig. A4.10 SCF for ring stiffened circular penetration in tubular member under axial/bending loads (location 2)

0,5 0,6 0,7 0,8 0,9

2,0

1,6

1,2

0,8

0,4

0

t

D

tr

4407/58

SCFq

10

5

2

1

ft

1– 2tr D

q

q

Fig. A4.11 SCF for ring stiffened circular penetration in plate under shear load (location 2)






0 0,2 0,4 0,6 0,8 1,0

3,5

4,0

3,0

2,5

2,0

1,5

1,0

t

tr

4407/59

SCF

0,5

0,6

0,7

0,80,9

2,01,11,81,21,6

1,4

2.Α (L + B)t

Typical range

L

B

σ

LB

1,1

1,2

1,4

1,6

1,8

2,0

Fig. A4.12 SCF for ring stiffened elliptical penetration in tubular member under axial/bending loads (location 1)






0 0,2 0,4 0,6 0,8 1,0

7,0

8,0

6,0

5,0

4,0

3,0

2,0

1,0

0

t

tr

4407/60

SCF

1,71,81,92,0

1,6

1,5

1,4

1,3

1,2

1,11,0

2.Α (L + B)t

L

B

LB

q

q

Fig. A4.13 SCF for ring stiffened elliptical opening in plate under shear load






L

BR

σ

4407/610

1

2

3

4

5

6

7

8

21 3 4

SCF

RB

0,025

0,05

0,10

0,15

0,200,300,400,50

LB

Fig. A4.14 SCF for unreinforced rectangular opening in plate under axial load






L

BR

4407/62

0

2

4

6

8

10

12

14

0,40,2 0,6 0,8 1,0LB

SCF

RB

0,025

0,05

0,075

0,10

0,15

0,25

q

q

Fig. A4.15 SCF for unreinforced rectangular opening in plate under shear load






L

B

5

4

3

2

1

0 0,2 0,4 0,6 0,8 1,0 2.Α Bt 4407/63

L = B

t

tr

σ

SCF

0,10

0,15

0,20

0,25

0,35

0,50

R

RB

Fig. A4.16 SCF for ring reinforced square opening with rounded corners in plate under axial loading (location 1)






L

B L = B

t

8

7

6

3

2

4

5

1

0 0,2 0,4 0,6 0,8 1,0

2.Α B.t 4407/64

SCF

q

q

R

RB

0,1

0,15

0,20,50,25

0,35

Fig. A4.17 SCF for ring reinforced square opening with rounded corners in plate under shear load (location 1)






Fig. A4.18 Weld stress

4407/65

σN = PN

+ (PNe + M)

lt tl2

6 t = combined size of

effective weld throats

PN

e

EQEQ

PT

P

M

l

Vector sum stressσp = (σn2 + σt2)0,5

σt = Pt

lt

σmax = SCF x σ

σ

AsDt

0 0,2 0,4 0,6 0,8 1,0

1,6

2,0

SCF

Typical range

4407/66

1,2

Fig. A4.19 SCF for abrupt stiffener termination under axial/bending loads (location 1)






SCF

2,0

1,0

0

0 0,2 0,4 0,6 0,8 1,0

AsDt

σmax = SCF x σ

σ4407/67

typical range

Fig. A4.20 SCF for soft profile stiffener termination under axial/bending loads (location 1)






A4.16 Column to pontoon joints

A4.16.1 The applicable S-N curve will depend on theexact structural arrangement of these complex joints. In wayof critical locations it is unlikely that use of a Class higher than‘F’ could normally be justified. To determine the minimumfatigue life it would generally be necessary to examine severallocations in way of the joint.

A4.16.2 In general, SCFs for various locations within thejoint should be obtained by an appropriate method (e.g. finiteelement analysis (FEA), model testing) for each jointconfiguration.

A4.16.3 The most likely key problem areas would be inthe region of the column shell to pontoon deck connection atthe main transverse and longitudinal bulkheads. Particularattention to structural details and welding should be given inthese areas.

A4.16.4 From results of FEA of typical pontoon to columnconnections it is clear that local stress patterns aredependent on geometry and applied loading, however, theresults of the analyses indicates that for initial designpurposes in SCF of 2,0 may be assumed.

Internal

External

LInternal

External

L

CL

0,8 0,6 0,4 0,2 0 0,2

0,2

0,4

0,6

0,8

1,0

1,2

0,4 0,6 0,8

LD

Kc (internal)

4407/68

Fig. A4.21 SCF ‘ kc’ factor for internal/external stiffener combination under axial/bending loads (location 1)


A4.17 Bracing to column joints

A4.17.1 The applicable S-N curves will depend on theparticular detail being assessed and the type of weld used. Itwill normally be necessary to consider a number differentlocations to determine the overall minimum fatigue life of thejoint. A summary of typical details found at these joints isgiven in Fig. A4.22.

A4.17.2 A large variety of joint configurations andstructural arrangements are possible within this joint type.SCFs for the details requiring assessment are arrangementdependent, and suitable values for any proposed joint designshould be determined by appropriate methods (e.g. FEA,model testing).

A4.17.3 From results of FEA of typical bracing to columnjoints it is clear that local stress patterns are dependent ongeometry and applied loading.

A4.17.4 SCF data obtained from FEA of various jointarrangements are summarized for information in Table A4.4.For initial design purposes the following may be noted:(a) Equivalent SCFs related to use of the D class S-N

curve, for the various joint designs were between 2,0and 5,0.

(b) Most of the joints have been equivalent SCFs ofbetween 2,0 and 3,5.

(c) Joint geometries indicating equivalent SCFs in excessof 4,0 are not recommended.

A4.18 Bracing to bracing joints

A4.18.1 This Section only covers multi-stiffened tubularbracing joints and no nodal joints, see also A4.1.5.

A4.18.2 The applicable S-N curves will depend on theparticular detail being assessed and the type of weld used. Itwill normally be necessary to consider a number of differentlocations to determine the overall minimum fatigue life of thejoint. A summary of typical details found at multi-stiffenedtubular joints is given in Fig. A4.23.





A4.18.3 A variety of joint configurations and structuralarrangements are possible within this joint type. SCFs fordetails requiring assessment are arrangement dependent andsuitable values for any proposed joint design should bedetermined by appropriate methods (e.g. FEA, modeltesting).

A4.18.4 SCF data obtained from FEA of various jointarrangements are summarized for information in Table A4.3.

A4.19 Cruciform joint

A4.19.1 The applicable S-N curve will depend on thetype of weld used. For fat igue prone locations ful lpenetration welding would normally be required and for thiscase F class S-N curve is to be used. Parent metal adjacentto the toe of a fillet welded cruciform of ‘T’ joint is to beassessed using the F2 Class S-N curve. Where partialpenetration or fillet welds are used, weld stresses are to beassessed using the W Class S-N curve for failure in the weldthroat.

A4.19.2 The general joint geometry may be illustrated asgiven in Fig. A4.24.

A4.19.3 Location 1 is at the weld toe, Location 2 isthrough the weld throat.

A4.19.4 Definitions:

Member stiffness parameter:

whereE = Youngs modulusti = member thicknessLi = member unsupported lengthe = misalignment

ki =E (ti)3

3Li

Fig. A4.22 Details at brace to column connection

13

1

12

1410

15

115

6

8

7

2

4

9

3

Bracing

Column shell 4407/69

Table A4.2 Brace to column joint examples

SCFLocation S-N curve

(See Fig. A4.22) Low High

1 1,1 4,5 D2 1,1 5,0 D3 1,0 2,0 F4 1,0 2,0 F5 1,0 2,0 F6 1,0 2,0 F7 2,5 5,0 B/C8 1,0 1,5 D9 1,0 2,0 D10 1,0 2,0 D11 1,0 1,0 F12 1,0 1,2 F13 2,0 3,3 C/D14 1,5 2,0 D15 1,0 1,5 F






A4.19.5 Location 1 under axial loading. The stressconcentration factor may be estimated from:

SCF (member i) =

Where an element is unrestrained then Ki should be set atzero for that number.

A4.19.6 Location 2 under axial loading. The shearstress in the weld throat will depend on the actual geometryand attachment weld and should be determined on a case bycase basis, see A4.15.4.

1 + 6 eti ki

k1 + k2 + k3 + k4

Table A4.3 Stiffened tubular joint examples

SCFLocation S-N curve

(See Fig. A4.23) Low High

1 1,0 1,0 F2 1,0 1,0 D3 1,0 1,0 F4 1,8 3,5 B/C5 1,0 1,5 F6 1,5 2,5 D7 1,5 2,5 D

4407/70

Section A – A

Section B – B

Section C – CPlan

4

32

1

5

6

7

AA

B B

C

C

Fig. A4.23 Details at multi-stiffened tubular joint

Fig. A4.24

Continuous plate

1

3

2

4

e

4407/71


ke


© Lloyd’s Register of Shipping, 1999Published by Lloyd’s Register of Shipping

Registered office71 Fenchurch Street, London, EC3M 4BS

United Kingdom

1999 FPFL – Pt 4, Imprint 5/6/99 10:55 am Page 1 (Black plate)

Part 4 - Steel Unit Structures, May 1999

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Transcript of Part 4 - Steel Unit Structures, May 1999