DNV HSLC rules Pt.3 Ch.2 - Hull Structural Design, Steel

RULES FORCLASSIFICATION OF

HIGH SPEED, LIGHT CRAFT ANDNAVAL SURFACE CRAFT

STRUCTURES, EQUIPMENT

PART 3 CHAPTER 2

HULL STRUCTURAL DESIGN, STEELJULY 1999This booklet includes the relevant amendments and corrections shown in the July 2010 version of Pt.0 Ch.1 Sec.3.

CONTENTS PAGE

Sec. 1 Structural Principles ................................................................................................................... 5Sec. 2 Materials and Material Protection ............................................................................................ 11Sec. 3 Manufacturing, Inspection, Testing.......................................................................................... 14Sec. 4 Hull Girder Strength ................................................................................................................. 15Sec. 5 Steel Plating and Stiffeners ...................................................................................................... 17Sec. 6 Steel Webframes and Girder Systems ...................................................................................... 20Sec. 7 Steel Pillars and Pillar Bulkheads ............................................................................................ 23Sec. 8 Welding and Weld Connections............................................................................................... 25Sec. 9 Direct Strength Calculations .................................................................................................... 30Sec. 10 Buckling Control ...................................................................................................................... 32

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CHANGES IN THE RULES

GeneralThe present edition of the rules includes additions and amendmentsdecided by the Board in June 1999, and supersedes the January 1991edition of the same chapter.The rule changes come into force as described below.This chapter is valid until superseded by a revised chapter. Supple-ments will not be issued except for an updated list of minor amend-ments and corrections presented in Pt.0 Ch.1 Sec.3. Pt.0 Ch.1 isnormally revised in January and July each year.Revised chapters will be forwarded to all subscribers to the rules.Buyers of reprints are advised to check the updated list of rule chap-ters printed in Pt.0 Ch.1 Sec.1 to ensure that the chapter is current.

Significant editorial changes adopted July 2010Taking effect immediately

• Sec.7 Steel Pillars and Pillar Bulkheads— In item B201 the definition of σE has been corrected.

Main changes adopted July 1999

Coming into force 1 January 2000

• General— During the development of the rules for naval surface craft, a

general update of Pt.3 Ch.2 "Hull Structural Design, Steel" wasfound to be necessary.

— The intention has been to obtain the same format and layout inthis chapter as in Ch.3 "Hull Structural Design, Aluminium".

— In addition, parts of the Rules for Classification of Ships, Pt.3Ch.1 "Hull Structural Design, Ships with length 100 meters andabove" have been included.

• Sec.1 Structural Principles— Existing subsections B and C are replaced by new B to E and are

expanded.— A new subsection G on superstructures and deckhouses is added.— Existing sub-sections E to H have been replaced by new sub-sec-

tions H to K and are expanded.

• Sec.2 Materials and Material Protection— Item B100 is amended.— Subsection C is renumbered B200 and is expanded.— Items B300 and B400 are added.— Previous subsection D is renamed and renumbered C.

— A new item C300 is added.— Existing subsections E and F are replaced by new D and E and

are expanded.

• Sec.3 Manufacturing, Inspection and Testing— Item A101 is amended.— Item A104 is added.— Item B100 is amended and new items B200 to B400 are added.— New subsections C to E are added.— Previous C200 is renumbered E200.

• Sec.4 Hull Girder strength— Item B200 is amended.— Subsection D is renamed.— Item D101 is amended.— Item D104 is added.

• Sec.5 Steel Plating and Stiffeners— Item A200 is amended.— Item A300 is added.— Subsections B and C are completely rewritten.

• Sec.6 Steel Webframes and Girder Systems— Item A200 is expanded.— Previous A300 to A400 is replaced with new A300.— Subsection B is completely rewritten.

• Sec.7 Steel Pillars and Pillar Bulkheads— Item B200 is expanded.— Subsection C is rewritten.

• Sec.8 Welding and Weld Connections— Subsections A and B are completely rewritten.— Items C101, C103, C106, C201 and Fig.7 are amended.

• Sec.9 Design Calculations— Item A101 is expanded.— Items C201, C302 and D203 are amended.

• Sec.10 Buckling Control— Item H200 is amended.

Corrections and ClarificationsIn addition to the above stated rule amendments, some detected errorshave been corrected, and some clarifications have been made in theexisting rule wording.

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Amended, Rules for High Speed, Light Craft and Naval Surface Craft, July 1999see Pt.0 Ch.1 Sec.3 July 2010 Pt.3 Ch.2 Contents –

CONTENTS

SEC. 1 STRUCTURAL PRINCIPLES ........................... 5

A. General...................................................................................5A 100 The scantling reduction.....................................................5

B. Bottom Structures .................................................................5B 100 Longitudinal stiffeners ......................................................5B 200 Longitudinal girders..........................................................5B 300 Engine room......................................................................5B 400 Double bottom ..................................................................5B 500 Bilge keel ..........................................................................5B 600 Bottom transverses and girders .........................................5B 700 Docking.............................................................................5

C. Side Structure........................................................................5C 100 Stiffeners ...........................................................................5C 200 Side transverses and stringers ...........................................5C 300 Cross ties ...........................................................................5

D. Deck Structure.......................................................................6D 100 Plating ...............................................................................6D 200 Stiffeners ...........................................................................6D 300 Bulwarks ...........................................................................6

E. Flat Cross Structure..............................................................6E 100 General ..............................................................................6E 200 Stiffeners ...........................................................................6

F. Bulkhead Structures .............................................................6F 100 Transverse bulkheads........................................................6F 200 Corrugated bulkheads .......................................................6F 300 Supporting bulkheads........................................................7

G. Superstructures and Deckhouses.........................................7G 100 Definitions.........................................................................7G 200 End bulkheads of superstructures anddeckhouses,

and exposed sides in deckhouses ......................................7

H. Structural Design in General ...............................................7H 100 Craft arrangement .............................................................7H 200 Continuity and transition of local members......................7

I. Some Common Local Design Rules.....................................7I 100 Definition of span .............................................................7I 200 End connection of stiffeners .............................................7I 300 End connections of girders................................................7I 400 Effective flange of girders.................................................8I 500 Effective web of girders....................................................8I 600 Stiffening of girders ..........................................................8I 700 Girder tripping brackets ....................................................9I 800 Reinforcement at knuckles................................................9

J. Support of Equipment and Outfitting Details....................9J 100 Heavy equipment, appendages etc. ...................................9J 200 Welding of outfitting details to hull................................10

K. Structural Aspects not Covered by the Rules...................10K 100 Deflections ......................................................................10K 200 Local vibrations ..............................................................10

SEC. 2 MATERIALS AND MATERIAL PROTECTION.................................................... 11

A. General.................................................................................11A 100 Introduction.....................................................................11A 200 Material certificates.........................................................11

B. Hull Structural Steel ...........................................................11B 100 General ............................................................................11B 200 Material designations and material factors .....................11B 300 Basic requirements..........................................................11B 400 Material at cross-joints....................................................11

C. Alternative Structural Materials .......................................11C 100 Aluminium ......................................................................11C 200 Connections between steel and aluminium.....................11

C 300 Stainless steel ..................................................................12

D. Corrosion Protection.......................................................... 12D 100 General ............................................................................12D 200 Specification and documentation of coating...................12D 300 Application of coating.....................................................12D 400 Provisions to avoid galvanic corrosion ...........................12D 500 Specification and documentation of cathodic

protection ........................................................................12D 600 Interactions with other electrical systems .......................13

E. Deck Composition .............................................................. 13E 100 General ............................................................................13

SEC. 3 MANUFACTURING, INSPECTION, TESTING ............................................................ 14

A. General ................................................................................ 14A 100 Basic requirements..........................................................14

B. Inspection ............................................................................ 14B 100 Non-destructive testing ...................................................14B 200 Magnetic particle testing.................................................14B 300 Radiographic testing .......................................................14B 400 Ultrasonic examination ...................................................14

C. Extent of Examination ....................................................... 14C 100 General ............................................................................14

D. Acceptance Criteria for NDT............................................ 14D 100 Acceptance criteria..........................................................14

E. Testing ................................................................................. 14E 100 Tanks...............................................................................14E 200 Closing appliances ..........................................................14

SEC. 4 HULL GIRDER STRENGTH .......................... 15

A. General ................................................................................ 15A 100 Introduction.....................................................................15

B. Vertical Bending Strength................................................. 15B 100 Hull section modulus requirement ..................................15B 200 Effective section modulus...............................................15B 300 Hydrofoil on foils............................................................15B 400 Longitudinal structural continuity...................................15B 500 Openings .........................................................................15

C. Shear Strength.................................................................... 16C 100 Cases to be investigated ..................................................16

D. Cases to be Investigated..................................................... 16D 100 Inertia induced loads .......................................................16

E. Transverse Strength of Twin Hull Craft.......................... 16E 100 Transverse strength .........................................................16E 200 Allowable stresses...........................................................16

SEC. 5 STEEL PLATING AND STIFFENERS .......... 17

A. General ................................................................................ 17A 100 Introduction.....................................................................17A 200 Definitions.......................................................................17A 300 Allowable stresses...........................................................17

B. Plating ................................................................................. 17B 100 Minimum thickness.........................................................17B 200 Formulae .........................................................................18B 300 Bottom and bilge plating.................................................18B 400 Sea inlets and other openings..........................................18

C. Stiffeners ............................................................................. 18C 100 Formulae and evaluations ...............................................18C 200 Bulkhead stiffeners other than longitudinals ..................19C 300 Machinery casings ..........................................................19C 400 Weather deck hatch covers. Shell doors .........................19

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Rules for High Speed, Light Craft and Naval Surface Craft, July 1999 Amended,Pt.3 Ch.2 Contents – see Pt.0 Ch.1 Sec.3 July 2010

SEC. 6 STEEL WEBFRAMES AND GIRDER SYSTEMS............................................................ 20

A. General ................................................................................ 20A 100 Introduction.....................................................................20A 200 Definitions.......................................................................20A 300 Allowable stress ..............................................................20

B. Web Frames and Girders................................................... 20B 100 General ............................................................................20B 200 Strength requirements .....................................................20B 300 Minimum thicknesses and geometrical ratios .................21B 400 Weather deck hatch covers. Shell doors .........................21B 500 Doors in watertight bulkheads ........................................22

SEC. 7 STEEL PILLARS AND PILLAR BULKHEADS ..................................................... 23

A. General ................................................................................ 23A 100 Introduction.....................................................................23A 200 Definitions.......................................................................23

B. Pillars ................................................................................... 23B 100 Arrangement of pillars ....................................................23B 200 Pillar scantlings ...............................................................23B 300 Pillars in tanks .................................................................24

C. Supporting Bulkheads........................................................ 24C 100 General ............................................................................24

SEC. 8 WELDING AND WELD CONNECTIONS..... 25

A. General ................................................................................ 25A 100 Introduction.....................................................................25A 200 Welding particulars .........................................................25

B. Types of Welded Joints ...................................................... 25B 100 Butt joints ........................................................................25B 200 Lap joints and slot welds.................................................25B 300 Tee or cross joints ...........................................................25

C. Load Based Weld Scantlings ............................................. 26C 100 Joints of abutting webs or plates .....................................26C 200 Steel and weld support of stiffeners to girders................27C 300 Steel and weld end connections of longitudinals ............28C 400 Weld end connections of stiffeners in general ................28C 500 End connections of girders, pillars and cross ties ...........28

D. Minimum Weld Scantlings ................................................ 29D 100 Minimum fillet weld .......................................................29

SEC. 9 DIRECT STRENGTH CALCULATIONS...... 30

A. General.................................................................................30A 100 Introduction.....................................................................30A 200 Application......................................................................30

B. Plating ..................................................................................30B 100 General ............................................................................30

C. Stiffeners..............................................................................30C 100 General ............................................................................30C 200 Calculation procedure .....................................................30C 300 Loads...............................................................................30C 400 Allowable stresses...........................................................30

D. Girders .................................................................................30D 100 General ............................................................................30D 200 Calculation methods........................................................30D 300 Design load conditions....................................................31D 400 Allowable stresses...........................................................31D 500 Allowable deflections .....................................................31

SEC. 10 BUCKLING CONTROL................................... 32

A. General.................................................................................32A 100 Definitions.......................................................................32

B. Longitudinal Buckling Load..............................................32B 100 Longitudinal stresses.......................................................32

C. Transverse Buckling Load.................................................32C 100 Transverse stresses..........................................................32

D. Plating ..................................................................................32D 100 Plate panel in uni-axial compression ..............................32D 200 Plate panel in shear .........................................................33D 300 Plate panel in bi-axial compression and shear ................33

E. Stiffeners in Direction of Compression.............................34E 100 Lateral buckling mode ....................................................34E 200 Torsional buckling mode ................................................34E 300 Web and flange buckling ................................................35

F. Stiffeners Perpendicular to Direction of Compression ...35F 100 Moment of inertia of stiffeners .......................................35

G. Elastic Buckling of Stiffened Panels..................................35G 100 Elastic buckling as a design basis ...................................35G 200 Allowable compression...................................................35

H. Girders .................................................................................36H 100 Axial load buckling.........................................................36H 200 Girders perpendicular to direction of compression.........36H 300 Buckling of effective flange............................................36H 400 Shear buckling of web.....................................................36

DET NORSKE VERITAS

Amended, Rules for High Speed, Light Craft and Naval Surface Craft, July 1999see Pt.0 Ch.1 Sec.3 July 2010 Pt.3 Ch.2 Sec.1 –

SECTION 1 STRUCTURAL PRINCIPLES

A. GeneralA 100 The scantling reduction101 The scantling reductions for high speed and light craftstructures compared to the Rules for Classification of Ships arebased on:

— thorough corrosion protection of steel, carried out underindoor conditions

— a certain stiffener spacing reduction ratio

s = chosen spacing in mmsr = basic spacing= 2 (240 + L) mm in general, including tank bulk-

heads= 760 mm for other bulkheads

— longitudinal framing in bottom and strength deck— extended global longitudinal and local buckling control— a sea and weather service restriction.

B. Bottom StructuresB 100 Longitudinal stiffeners101 Single bottoms as well as double bottoms are normallyto be longitudinally stiffened.102 The longitudinals should preferably be continuousthrough transverse members. If they are to be cut at transversemembers, e.g. at watertight bulkheads, brackets connecting theends of the longitudinals are to be fitted or welds are to be di-mensioned accordingly.103 Longitudinal stiffeners in slamming area should have ashear connection to transverse members.

B 200 Longitudinal girders201 Web plates of longitudinal girders are to be continuousin way of transverse bulkheads.202 Manholes or other openings should not be positioned atends of girders without due consideration being taken of shearloading.

B 300 Engine room301 In way of thrust bearings additional strengthening is tobe provided.302 Under the main engine, girders extending from the bot-tom to the top plate of the engine seating are to be fitted.303 Engine holding down bolts are to be arranged as near aspractical to floors and longitudinal girders.

B 400 Double bottom401 In case a double bottom is fitted, the following and 402and 403 apply. Manholes are to be cut in the inner bottom,floors and longitudinal girders to provide access to all parts ofthe double bottom. The vertical extension of lightening holesis not to exceed one half of the girder height in general. Man-holes in the inner bottom plating are to have reinforcementrings. Manholes are not to be cut in the floors or girders in wayof pillars.

402 In double bottoms with transverse stiffening, longitudi-nal girders are to be stiffened at every transverse frame.403 The longitudinal girders are to be satisfactory stiffenedagainst buckling.

B 500 Bilge keel501 The bilge keel and the flat bar to which it is attached, isnot to terminate abruptly. Ends are to be tapered, and internalstiffening is to be provided. Butts in the bilge keel and the flatbar are to be well clear of each other and of butts in the shellplating.The bilge keel and flat bar are to be of the same materialstrength as the bilge strake to which they are attached.

B 600 Bottom transverses and girders601 For rise of floor > 45 ° the case with unsymmetrical sideforce from sea pressure may have to be investigated, and theefficiency of the support of floors is to be examined.

B 700 Docking701 A centre girder is normally to be fitted for docking pur-poses.702 For craft of special design and for large craft, the dock-ing arrangement plan, giving calculated forces from the dock-ing blocks is to be submitted for information.Structure in way of docking blocks is to be evaluated for thegiven docking forces.

C. Side StructureC 100 Stiffeners101 The craft’s sides may be longitudinally or verticallystiffened.

Guidance note: It is advised that longitudinal stiffeners are used near the bottomand strength deck.

---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

102 Where the craft’s sides are longitudinally stiffened anddepending upon the area under consideration, the continuity ofthe longitudinals is to be as required for the bottom and decklongitudinals, respectively.

C 200 Side transverses and stringers201 For weather deck stringer plate along wide hatch open-ing, the following may have to be investigated above ordinaryside stringer requirements:

— combined deflection of stringer and hatch coaming atweather tightening level, when subjected to side and decksea pressure

— continuity of inner flange at hatch ends.

202 For web rings supporting deckhouses or deck equip-ment, reinforcements for the associated static and dynamicloads may be required.

C 300 Cross ties301 Cross ties may be regarded as effective for side verticalwhen:

— the cross tie extends from side to side

ssr----

DET NORSKE VERITAS

Rules for High Speed, Light Craft and Naval Surface Craft, July 1999 Amended,Pt.3 Ch.2 Sec.1 – see Pt.0 Ch.1 Sec.3 July 2010

— the cross tie is supported by other structure which may beconsidered rigid when subject to the maximum expectedaxial loads in the cross tie

— the load condition may be considered symmetrical with re-spect to the cross tie.

302 Cross ties and panting beam scantlings are to be deter-mined as for deck pillars, where the deck load is to be substi-tuted by the load on the supported side. Bending stress andsuspended bending deflection of slender cross ties may have betaken into account.

D. Deck StructureD 100 Plating101 If the end bulkhead of a long superstructure is locatedwithin 0.5 L amidships, the stringer plate is to be increased inthickness for a length of 3 m on each side of the superstructureend bulkhead. The increase in thickness is to be 20 %.102 If hatch opening corners of streamlined shape are notadopted, the thickness of deck plates in strength deck at hatchcorners is to be increased by 25 %.The longitudinal extension of the thicker plating is not to beless than 1.5 R and not more than 3 R on both sides of the hatchend. The transverse extension outside line of hatches is to be atleast 2 R.R = corner radius.103 The seam between the thicker plating at the hatch cornerand the thinner plating in the deck area between the hatches isto be located at least 100 mm inside the point at which the cur-vature of the hatch corner terminates.

D 200 Stiffeners201 Decks taking part of the longitudinal strength are nor-mally to be longitudinally stiffened. Where main stresses are inthe transverse direction, the deck may be transversely stiff-ened.202 Longitudinals should preferably be continuous throughtransverse members. If they are to be cut at transverse mem-bers, e.g. at watertight bulkheads, brackets connecting the endsof the longitudinals are to be fitted.

D 300 Bulwarks301 The thickness of the bulwark plates is not to be less thanrequired for the side plating in a superstructure in the same po-sition.302 Where bulwarks on exposed decks form wells, ampleprovision is to be made for freeing the deck for water

E. Flat Cross StructureE 100 General101 Flat cross structure is horizontal structure above water-line like bridge connecting structure between twin hulls, etc.102 The cross structure should be arranged with the possibil-ity for inspection of all parts of the structure.

E 200 Stiffeners201 Flat cross structure taking part of the longitudinalstrength are normally to be longitudinally stiffened. Wheremain stresses are in the transverse direction, the flat crossstructure may be transversely stiffened.202 Where the cross structure is transversely stiffened, trans-verse bulkheads and frames are to be continuous through lon-

gitudinal bulkheads.

F. Bulkhead Structures

F 100 Transverse bulkheads101 Number and location of transverse watertight bulkheadsare to be in accordance with the requirements given in Ch.1Sec.1.102 The stiffening of the upper part of a plane transversebulkhead is to be such that the necessary transverse bucklingstrength is achieved.

F 200 Corrugated bulkheads201 Longitudinal and transverse bulkheads may be corrugat-ed.202 The lower and upper ends of corrugated bulkheads andthose boundaries of vertically corrugated bulkheads connectedto ship sides and other bulkheads are to have plane parts of suf-ficient width to support the adjoining structures.203 For corrugated bulkheads the following definition ofspacing applies (see Fig.1):

s = s1 for section modulus calculations. = 1,05 s2 or 1,05 s3 for plate thickness calculations in

general.= s2 or s3 for plate thickness calculation when 90 degrees

corrugations.

Fig. 1Corrugated bulkhead

Section modulus and thickness formulae as for plane bulk-heads may be used.204 Unless the buckling strength is proved satisfactory bydirect stress calculation the following additional requirementsapply to corrugated bulkheads (where t and s2 and s3 are takenin same units):

Intermediate values are obtained by linear interpolation. For acorrugated bulkhead with a section modulus greater than re-quired, the required thickness may be multiplied by:

Zrule required section modulus. May be taken at section inquestion based upon a direct stress calculation

S2

S 3

S1

ts250------ when

s2s3---- 0 5,==

ts270------ when

s2s3---- 1 0,≥=

ZruleZactual-----------------

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F 300 Supporting bulkheads301 Bulkheads supporting decks are to be regarded as pillars.The compressive loads and buckling strength are to be calcu-lated as given in Sec.7 C.

G. Superstructures and DeckhousesG 100 Definitions101 Superstructure is defined as a decked structure on thefreeboard deck, extending from side to side of the craft or withthe side plating not inboard of the shell plating more than 4 %of the breadth (B).102 Deckhouse is defined as a decked structure above thestrength deck with the side plating being inboard of the shellplating more than 4 % of the breadth (B).Long deckhouse - deckhouse having more than 0.2 L of it’slength within 0.4 L amidships.Short deckhouse - deckhouse not defined as a long deckhouse.

G 200 End bulkheads of superstructures anddeckhouses, and exposed sides in deckhouses201 For deckhouse stiffeners the scantlings need not begreater than required for between deck frames with equivalentend connections.202 Front stiffeners are to be connected to deck at both endswith a connection area not less than:

a = 0.07 l s p (cm 2) Side and after end stiffeners in the lowest tier of erections areto have end connections.203 In long deckhouses, openings in the sides are to havewell rounded corners. Horizontal stiffeners are to be fitted atthe upper and lower edge of large openings for windows.Openings for doors in the sides are to be substantially stiffenedalong the edges.204 For hull girder strength in way of rows of openings, seeSec.4.

H. Structural Design in GeneralH 100 Craft arrangement101 The craft arrangement is to take into account:

— continuity of longitudinal strength, including horizontalshear area to carry a strength deck along

— transverse bulkheads or strong webs— web/pillar rings in the engine room— twin hull connections— superstructures and deckhouses:

— direct support— transitions

— deck equipment support— multi-deck pillars in line, as practicable— external attachments, inboard connections.

H 200 Continuity and transition of local members201 Attention is drawn to the importance of structural conti-nuity in general.202 Structural continuity is to be maintained at the junctionof primary supporting members of unequal stiffness by fittingwell rounded brackets. Brackets are not to be attached to un-supported plating. Brackets are to extend to the nearest stiffen-er, or local plating reinforcement is to be provided at the toe of

the bracket.203 Gradual taper or soft transition is especially important inhigh speed steel craft, to avoid:

— stress corrosion and fatigue in heavy stressed members— impact fatigue in impact loaded members.

204 Sufficient transverse strength is to be provided by meansof transverse bulkheads or girder structures.205 Web frames are to be continuous around the cross sec-tion i.e. floors, side webs and deck beams are to be aligned andconnected. Intermediate floors may be used.206 In superstructures and deckhouses aft, the front bulk-head is to be in line with a transverse bulkhead in the hull be-low or be supported by a combination of partial transversebulkheads, girders and pillars. The after end bulkhead is also tobe effectively supported. As far as practicable, exposed sidesand internal longitudinal and transverse bulkheads are to be lo-cated above bulkheads and/or deep girder frames in the hullstructure and are to be in line in the various tiers of accommo-dation. Where such structural arrangements in line are not pos-sible, there is to be other effective support.207 Where practicable, deck pillars are to be located in linewith pillars above or below. Pillars are to be supported by rigidhull structures.208 Below decks and platforms, strong transverses or longi-tudinal girders are to be fitted between verticals and pillars, sothat rigid continuous structures are formed.

I. Some Common Local Design RulesI 100 Definition of span101 The effective span of a stiffener (l) or girder (S) dependson the design of the end connections in relation to adjacentstructures. Unless otherwise stated the span points at each endof the member, between which the span is measured, is to bedetermined as shown in Fig.2. It is assumed that brackets areeffectively supported by the adjacent structure.

I 200 End connection of stiffeners201 Normally all types of stiffeners (longitudinals, beams,frames, bulkhead stiffeners) are to be connected at their ends.In special cases, however, sniped ends may be allowed.202 Bracketless end connections may be applied for longitu-dinals and other stiffeners running continuously through gird-ers (web frames, transverses, stringers, bulkheads etc.),provided sufficient connection area is arranged for.203 Stiffeners with sniped ends may be allowed where dy-namic loads are small and where vibrations are considered tobe of small importance, provided the thickness of plating sup-ported by the stiffener is not less than:

l = stiffener span in m S = stiffener spacing in mp = pressure on stiffener in kN/m2.

I 300 End connections of girders301 Normally, ends of single girders, or connections be-tween girders forming ring systems, are to be provided withbrackets. Brackets are generally to form a radius or be wellrounded at their toes. The free edge of the brackets are to bestiffened.Bracketless connections may be applied provided adequate

t 1 25, l 0 5, s–( ) s pf1

-------------------------------- (mm)=

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support of the adjoining faceplates is arranged for.The brackets shown in Fig.3 ALT. II and ALT. III are normallyconsidered better than the basic design. Other brackets may beaccepted after special consideration.

Fig. 2Span points

I 400 Effective flange of girders401 The section modulus of the girder is to be taken in ac-cordance with particulars as given in the following. Structuralmodelling in connection with direct stress analysis is to bebased on the same particulars when applicable. Note that suchstructural modelling will not reflect the stress distribution at lo-cal flange cut-outs or at supports with variable stiffness overthe flange width. The local effective flange, which may be ap-plied in stress analysis, is indicated for construction details invarious Classification Notes on "Strength Analysis of HullStructures".402 The effective plate flange area is defined as the cross-sectional area of plating within the effective flange width.Continuous stiffeners within the effective flange may be in-cluded. The effective flange width be is determined by the fol-lowing formula:

be = C b (m)

C = as given in Table I1 for various numbers of evenlyspaced point loads (r) on the span

b = the sum of the plate flange width on each side of girder,normally taken to be half the distance from the nearestgirder or bulkhead

a = the distance between points of zero bending moments

= S for simply supported girders= 0.6 S for girders fixed at both ends

r = number of point loads.

403 For plate flanges having corrugations parallel to thegirder, the effective width is as given in 402. If the corruga-tions are perpendicular to the direction of the girder, the effec-tive width is not to be taken greater than 10 % of the valuederived from 402.

I 500 Effective web of girders501 The web area of a girder is to be taken in accordancewith particulars as given in 502 and 503. Structural modellingin connection with direct stress analysis is to be based on thesame particulars when applicable.502 Holes in girders will generally be accepted provided theshear stress level is acceptable and the buckling strength is suf-ficient. Holes are to be kept well clear of end of brackets andlocations where shear stresses are high.503 For ordinary girder cross sections the effective web areais to be taken as:

Aw = 0.0 1 hn tw (cm2)

hn = net girder height in mm after deduction of cut-outs inthe cross section considered

= hnl + hn2.

If an opening is located at a distance less than hw/3 from thecross section considered, hn is to be taken as the smaller of thenet height and the net distance through the opening. See Fig.4.

I 600 Stiffening of girders601 The web plate of transverse vertical girders are to bestiffened where:

hw > 90 tw (mm)

tw = web thickness in mmhw = web height in mm

with stiffeners of maximum spacing: s = 90 t w (mm)

within 20 % of the span from each end of the girder and wherehigh shear stresses appear.Elsewhere stiffeners are required where:

hw > 140 tw (mm) with stiffeners of maximum spacing:

s = 140 t w (mm)for girders supporting other girders, the end requirements mayhave to be applied all over the span.

Table I1 Values of Ca/b 0 1 2 3 4 5 6 ≥7

C (r > 6) 0.00 0.38 0.67 0.84 0.93 0.97 0.99 1.00C (r = 5) 0.00 0.33 0.58 0.73 0.84 0.89 0.92 0.93C (r = 4) 0.00 0.27 0.49 0.63 0.74 0.81 0.85 0.87C (r < 3) 0.00 0.22 0.40 0.52 0.65 0.73 0.78 0.80

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Fig. 3Bracket design

602 the web plate is to be especially stiffened at openingswhen the mean shear stress exceeds 60 f1 N/mm2.

I 700 Girder tripping brackets701 The spacing value, ST, of tripping brackets is normallynot to exceed the values given in Table I2 which is valid forgirders with symmetrical face plates. For others, the spacingwill be especially considered.

Tripping brackets are furthermore to be fitted near the toebracket, near rounded corner of girder frames and in way ofcross ties.702 The tripping brackets are to be fitted in line with longi-

tudinals or stiffeners, and are to extend the whole height of theweb plate. The arm length of the brackets along the longitudi-nals or stiffeners, is not to be less than 40 % of the depth of theweb plate, the depth of the longitudinal or stiffener deducted.The requirement may be modified for deep transverses.

Fig. 4Effective web area in way of opening

703 Tripping brackets on girders are to be stiffened by aflange or stiffener along the free edge if the length of the edgeexceeds:

0.06 tt (m)thickness in mm of tripping brackets.The area of the stiffening is not to be less than:

10 lt (cm2)

lt = length in m of free edge.

The tripping brackets are to have a smooth transition to adjoin-ing longitudinals or stiffeners exposed to large longitudinalstresses.704 Girders with unsymmetrical face plates are to have trip-ping brackets spaced not more than 10 times the width of faceplate, maximum 1.5 metres.

I 800 Reinforcement at knuckles801 Whenever a knuckle in a main member (shell, longitudi-nal bulkhead, etc.) is arranged, it is important to have someform of stiffening fitted at the knuckle to transmit the trans-verse force.

J. Support of Equipment and Outfitting DetailsJ 100 Heavy equipment, appendages etc.101 Whether the unit to be supported is covered by classifi-cation or not, the forces and moments at points of attachmenthave to be estimated and followed through hull reinforcementsin line, through craft girder and pillar systems until the forcesare safely carried to the craft’s side or bulkheads taking into ac-count the hull stresses that already exist.102 Doublers should be avoided normal to a tensile force.

Table I2 Spacing between tripping bracketsGirder type ST (m)Bottom and deck transversesStringers and vertical webs in generalLongitudinal girders in general

0.02 bfmaximum 6

Longitudinal girders in bottom and strengthdeck for L > 50 m within 0.5 L amidshipsStringers and vertical webs in tanksand machinery spacesVertical webs supporting single bottomgirders and transverses

0.014 bfmaximum 4

If the web of a strength member forms an angle with the perpendicular to the craft’s side of more than 10 °, ST is not to exceed 0.007 bf.bf = flange breadth in mm

tw

hn2

lshn

a<hw/3hw

hn1

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Fig. 5Span points

J 200 Welding of outfitting details to hull201 Generally connections of outfitting details to the hull areto be such that stress-concentrations are minimized and weld-ing to high stressed parts are avoided as far as possible.Connections are to be designed with smooth transitions andproper alignment with the hull structure elements. Termina-tions are to be supported.202 Equipment details such as clips for piping, support ofladders, valves, anodes etc. are to be kept clear of the toe of

brackets, edges of openings and other areas with high stresses.Connections to the top flange of girders and stiffeners are to beavoided, if not well smoothened. Preferably, supports for out-fittings are to be welded to the stiffener web.203 All materials welded to the hull shell structure are to beof ship quality steel, or equivalent, preferably with the samestrength group as the hull structure the item is welded to.

K. Structural Aspects not Covered by the Rules

K 100 Deflections101 Rule requirements to minimum moment of inertia ormaximum deflection under load are limited to structures inway of hatches and doors and some other special cases.102 Deflection problems in general are left for the designer’sconsideration.

K 200 Local vibrations201 The evaluation of structural response to vibrationscaused by impulses from engine and propeller blades are notcovered by classification, but the builder is to provide relevantdocumentation.

Guidance note:IMO HSC Code:3.4 Cyclic loads, including those from vibrations which canoccur on the craft should not:

.1 impair the integrity of structure during the anticipatedservice life of the craft or the service life agreed withthe Administration;

.2 hinder normal functioning of machinery and equip-ment; and

.3 impair the ability of the crew to carry out its duties.


Upon request such evaluation may be undertaken by the Soci-ety.

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SECTION 2 MATERIALS AND MATERIAL PROTECTION

A. GeneralA 100 Introduction101 In this section requirements regarding the application ofvarious structural materials as well as protection are given.

A 200 Material certificates201 Rolled steel for hull structures is normally to be suppliedwith Det norske Veritas’ material certificates in compliancewith the requirements given in Pt.2.202 Requirements for material certificates for forgings, cast-ings and other materials for special parts and equipment arestated in connection with the rule requirements for each indi-vidual part.

B. Hull Structural SteelB 100 General101 Where the rules for material grade in this section are de-pendent on plate thickness, the requirements are based on thethickness as built.

B 200 Material designations and material factors201 Hull materials of various strength groups will be re-ferred to as follows:

— NV-27 denotes high strength structural steel with yieldpoint not less than 265 N/mm2.



— NV-40 denotes high strength structural steel with yieldpoint not less than 390 N/mm2

— NV420 denotes extra high strength structural steel withyield point not less than 420 N/mm2.






Normal, high strength and extra high steel may also be referredto as NS-steel, HS-steel and EHS-steel respectively.202 Hull materials of various grades will be referred to asfollows:A, B, D and E denotes NS-steel grades. AH, DH and EH denotes HS-steel grades. HS-steel may alsobe referred to by a combination of grade and strength group. Inthat case the letter H is substituted by one of the numbers indi-cated in 201, e.g. A 36-steel.AEH, DE, EEH and FEH denote EHS-steel grades. EHS-steelmay also be referred to by a combination of grade and strengthgroup. In this case the letters EH is substituted by one of thenumbers indicated in 201, e.g. D 550-steel.203 The material factor f1, which may be included in the var-ious formulae for scantlings and in expressions giving allowa-

ble stresses, is dependent on strength group as follows:

— For NV-NS: f1 = 1,00— For NV-27: f1 = 1,08— For NV-32: f1 = 1,28— For NV-36: f1 = 1,39— For NV-40: f1 = 1,43— For NV 420: f1 = 1.75— For NV 460: f1 = 1.92— For NV 500: f1 = 2.08— For NV 550: f1 = 2.29— For NV 620: f1 = 2.58— For NV 690: f1 = 2.88

For a 34-steel (with yield point not less than 335 N/mm2) thematerial factor may be taken as f1 = 1.35.

B 300 Basic requirements301 For a thickness more than 15 mm special considerationwill be made with respect to material grade, according to theRules for Classification of Ship Pt.3 Ch.1 Sec.2 Table B1.

B 400 Material at cross-joints401 In important structural cross-joints where high tensilestresses are acting perpendicular to the plane of the plate, spe-cial consideration will be given to the ability of the plate mate-rial to resist lamellar tearing. For a special test, see Pt.2 Ch.2Sec.1.

C. Alternative Structural MaterialsC 100 Aluminium101 Aluminium structures are to be designed and built ac-cording to Pt.3 Ch.3.102 In designing a combined steel and aluminium structure,the difference in modulus of elasticity and coefficient of ex-pansion must be taken into account.

C 200 Connections between steel and aluminium201 If there is risk of galvanic corrosion, a non-hygroscopicinsulation material is to be applied between steel and alumini-um.202 Aluminium plating connected to a steel boundary bar isas far as possible to be arranged on the side exposed to mois-ture.203 Direct contact between exposed wooden materials, e.g.deck planking, and aluminium is to be avoided.204 Bolts with nuts and washers are either to be of stainlesssteel or cadmium plated or hot galvanized steel. The bolts arein general to be fitted with sleeves of insulating material. For superstructures and deckhouses, the spacing is normallynot to exceed 4 times the bolt diameter.205 In case of rolled bi-metallic connections, high tensileforces normal to the bi-metallic contact surface should beavoided.206 For earthing of aluminium superstructures and deck-houses to steel craft, see Pt.4 Ch.8.

C 300 Stainless steel301 For clad steel and solid stainless steel due attention is tobe given to the reduction of strength of stainless steel with in-

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creasing temperature. For austenitic stainless steel and steelwith clad layer of austenitic stainless steel the material factorf1 included in the various formulae for scantlings and in ex-pressions giving allowable stresses is given in 302 and 303.302 For austenitic stainless steel the material factor f1 can betaken as:

σf = yield stress in N/mm2 at 0.2 % offset and temperature+ 20 °C (σ 0,2).

t = cargo temperature in °C.

For end connections of corrugations, girders and stiffeners thefactor is due to fatigue not to be taken greater than:

f1 = 1.21 – 3.2 (t – 20) 10 -3

303 For clad steel the material factor f1 can be taken as:

σf = yield stress in N/mm2 at 0.2 % °C (σ0,2).σfb = yield strength in N/mm2 of base materialt = cargo temperature in °C

f1 is in no case to be taken greater than that given for the basematerial in B203. The calculated factor may be used for the to-tal plate thickness.304 For ferritic-austenitic stainless steel the material factorwill be especially considered in each case.

Guidance note:For ferritic-austenitic stainless steels with yield stress 460 N/mm2, the following material factor will normally be accepted:

f1 = 1.6 at + 20 °C= 1.36 at + 85 °C

For end connection of corrugations, girders and stiffeners thefactor should due to fatigue not be taken greater than:

f1 = 1.39 at + 20 °C= 1.18 at + 85 °C

For intermediate temperatures linear interpolation may be ap-plied for the f1 factor.


D. Corrosion ProtectionD 100 General101 All steel surfaces except in tanks for oil for the craft’suse are to be protected against corrosion by paint of suitablecomposition or other effective coating. Inner bottom and decksfor dry cargoes will be especially considered.102 In way of other materials (e.g. propellers), provisions areto be made to avoid galvanic corrosion.

D 200 Specification and documentation of coating201 A coating specification including steel surface prepara-tion and coating application procedure is to be presented forapproval. The builder is to present documentation of steel sur-face treatment and coating application in accordance with theapproved specification.202 Specifications for coating including antifouling shallstate details of:

— metal surface cleaning and treatment before application of

primer coat, including welds and edges— build-up of the coating system with individual coats in-

cluding the thickness of individual and final coating— curing times and overcoating intervals— acceptable temperatures of air and metal surface and dry-

ness/humidity conditions during above mentioned opera-tions

— thicknesses of individual and final coating.

D 300 Application of coating301 The minimum cleanliness standard of steel for coatingapplication is normally blast cleaning to Sa 2,5 according toSIS 055900, near-white according to SSPC-SP10, or an equiv-alent standard.302 Shop primers applied over areas which will subsequent-ly be welded, are to be of a quality accepted by the Society ashaving no detrimental effect on the finished weld.See "Registers of Approved Manufacturers and Type Ap-proved Products".303 Coating systems are to be compatible with any previous-ly applied shop primer. Proper cleaning of any primer or inter-mediate coating which has been exposed to the yardatmosphere for some time is necessary before application ofthe next coat.304 The requirement for dry conditions during all essentialsteps of blast cleaning and coating applications is normallythat:

— the steel surfaces are to be minimum 3 °C above the dewpoint.

— the air humidity is at a maximum of 85 %.

D 400 Provisions to avoid galvanic corrosion401 Acceptable provisions are either one of or a combinationof:

— coating of water/moisture exposed surfaces (mandatoryaccording to 101)

— electrical insulation of different metals from each other— cathodic protection.

Guidance note:Full electrical insulation of e.g. the propeller from the hull mightbe difficult. Electrical contact between the propeller and the hullmay be established when the propeller is idle.


402 External cathodic protection of steel hulls in addition tothe coating can be obtained with aluminium or zink sacrificialanodes or impressed current.403 If impressed current systems are applied, precautions areto be taken to avoid overprotection by means of anode screenand overprotection alarm.

D 500 Specification and documentation of cathodic pro-tection501 Specifications of cathodic protection systems shall statedetails of:

— areas to be protected— current density demand— anode material and manufacturer— anode mass, distribution and total number— calculation of service life and estimated protective poten-

tial to be obtained.

Guidance note:The current density demand will vary dependent on the speed ofthe hull, the speed of the propeller, etc.


f1 3 9, t 20–650

-------------+⎝ ⎠⎛ ⎞ σf 4 15,– t 20–( ) 220+ 10 3–

=

f11 67, σf 1 37, t–

1000---------------------------------------- 41 5, σfb

0 7,– 1 6,+–=

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502 For documentation of instrumentation and automation,including computer based control and monitoring, see Pt.4Ch.9 Sec.1.503 The designed service life of cathodic protection systemsis normally to be at least 5 years.504 An acceptable criterion of efficient cathodic protectionis that it is found successful at annual survey, i.e. that no cor-rosion has occurred.Potential measurements may be required when considered nec-essary. The protective potential for steel hull surfaces in cleansea water is – 800 mV versus the Ag/AgCl reference electrode.The limit for overprotection is –1050 mV at the same condi-tions.

D 600 Interactions with other electrical systems601 Stray DC currents may impose rapid electrolytic corro-sion damages to hulls and are to be avoided.

Due consideration should be made to the above when utilizingonshore electrical current connection.

Guidance note:Other stray DC current sources may be railways, cranes, cables,unproperly grounded welding machines, etc.


E. Deck Composition

E 100 General101 Deck compositions are subject to type approval. Theyare to be of an elastic, non-hygroscopic material. Deck compo-sitions for application in cargo areas are to be suitably rein-forced.

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SECTION 3 MANUFACTURING, INSPECTION, TESTING

A. GeneralA 100 Basic requirements101 Welding of important structures, machinery installationsand equipment are to be carried out by qualified welders usingapproved welding procedures and welding consumables, seePt.2 Ch.3.102 For welding ambient temperature and welding details,see Sec.8.103 Shot blasting, priming and coating is to be carried outunder indoor conditions. For coating specification and docu-mentation, see Sec.2.104 For craft with a length greater than 50 m a non-destruc-tive testing (NDT) plan is to be submitted for approval.

B. InspectionB 100 Non-destructive testing101 Welds are to be subjected to visual survey and inspec-tion, as fabrication proceeds. NDT is to be performed accord-ing to established procedures and if required, qualified for thework.102 All testing is to be carried out by qualified personnel.The NDT operators are to be qualified according to a recog-nised certification scheme accepted by the Society. The certif-icate is to state clearly the qualifications as to whichexamination method and within which category the operator isqualified.

B 200 Magnetic particle testing201 Magnetic particle testing shall be carried out as specifiedin the approved procedures.

B 300 Radiographic testing301 Radiographic testing shall be carried out as specified inthe approved procedures.302 Processing and storage are to be such that the filmsmaintain their quality throughout the agreed storage time. Theradiographs shall be free from imperfections due to developprocessing.

B 400 Ultrasonic examination401 Ultrasonic testing shall be carried out as specified in theapproved procedures. Ultrasonic examination procedures shallcontain sketches for each type of joint and dimensional rangeof joints which clearly show scanning pattern and probes to beused.402 The examination records shall include the imperfectionposition, the echo height, the dimensions (length), and thedepth below the surface and, if possible, the defect type.

C. Extent of ExaminationC 100 General101 All welds are to be subjected to 100 % visual examina-tion. In addition to the visual examination at least 2 to 5 % ofthe total welded length is to be tested by magnetic particle ex-amination and/or radiographic examination. For highlystressed areas the extent of examination may be increased.102 If defects are detected, then the extent of the examina-tion shall be increased to the satisfaction of the surveyor.

D. Acceptance Criteria for NDTD 100 Acceptance criteria101 All welds shall show evidence of good workmanship.The quality shall normally comply with ISO 5817 quality levelC, intermediate. For highly stressed areas more stringent re-quirements, such as ISO level B, may be applied.

E. TestingE 100 Tanks101 Protective coating systems may be applied before watertesting.All pipe connections to tanks are to be fitted before testing. Ifengine bed plates are bolted directly on the inner bottom plat-ing, the testing of the double bottom tank is to be carried outwith the engine installed.102 All tanks are, unless otherwise agreed, to be tested witha water head equal to the maximum pressure to which the com-partment may be exposed. The water head is no case to be lessthan to top of air pipe or to a level h0 above the top of tank, ex-cept where partial filling alone is prescribed.

h0 = 0.03 L – 0.5 (m) minimum 1 generally.= pressure valve opening pressure when exceeding the

general value.

E 200 Closing appliances201 Inner and outer doors below the waterline are to be hy-draulically tested.202 Weathertight and watertight closing appliances not sub-jected to pressure testing, are to be hose tested. The nozzle in-side diameter is to be 12.5 mm and the pressure at least 250 kN/mm2 at the nozzle. The nozzle should be held at a distance ofmaximum 1.5 m from the item under test.Alternative methods of tightness testing may be considered.203 All weathertight/watertight doors and hatches are to befunction tested.

DET NORSKE VERITAS


SECTION 4 HULL GIRDER STRENGTH

A. GeneralA 100 Introduction101 In this section requirements for longitudinal and trans-verse hull girder strength is given. In addition, buckling controlaccording to Sec.10 may be required.102 Longitudinal strength has generally to be checked forthe craft types and sizes mentioned in the introduction to Ch.1Sec.3.103 For new designs (prototypes) of large and structurallycomplicated craft (e.g. multi-hull types) a complete 3-dimen-sional global analysis of the transverse strength, in combina-tion with longitudinal stresses, is to be carried out.104 Buckling strength in bottom and deck may, however,have to be checked also for the other craft. For this purpose for-mulae for estimate of section modulus to deck and bottombased on bottom and deck cross sectional areas have been giv-en in Ch.1 Sec.3 A700.

B. Vertical Bending StrengthB 100 Hull section modulus requirement101 The section modulus is calculated as follows:

M = the longitudinal midship bending moment in kNmfrom Ch.1 Sec.3.

σ = 175 f1 N/mm2 in general.

When σ is taken greater than 175 N/mm2, the bottom structureis to be assessed with respect to fatigue.

Guidance note:Simultaneous end impacts over a hollow are considered less fre-quent, and giving lower moments than the crest landing. Simul-taneous end impacts need not be investigated if deck bucklingresistance force is comparable to that of the bottom.


B 200 Effective section modulus201 When calculating the moment of inertia and sectionmodulus of the midship section, the effective sectional area ofcontinuous longitudinal strength members is in general to betaken as the net area after deduction of any openings. Superstructures which do not form a strength deck are not tobe included in the net section. This applies also to deckhousesand bulwarks.202 The effect of openings are assumed to have longitudinalextensions as shown by the shaded areas in Fig.1, i.e. insidetangents at an angle of 30 ° to each other. Example for trans-verse section III:

bIII = b’ + b” + b’”

Fig. 1Effect of openings

203 For twin hull vessels the effective breadth of wide deckswithout longitudinal bulkhead support will be especially con-sidered.

B 300 Hydrofoil on foils301 For hydrofoils the sections in way of the foils are to beconsidered, in addition to the calculations for the midship sec-tion.

B 400 Longitudinal structural continuity401 The scantling distribution of structures participating inthe hull girder strength in the various zones of the hull is to becarefully worked out so as to avoid structural discontinuitiesresulting in abrupt variations of stresses.402 At ends of effective continuous longitudinal strengthmembers in deck and bottom region large transition bracketsare to be fitted.

Guidance note: Height to length ratio of the transition brackets is to be 1: 4 orbetter.


B 500 Openings501 A keel plate for docking is normally not to have open-ings. In the bilge plate, within 0.5 L amidships, openings are tobe avoided as far as practicable. Any necessary openings in thebilge plate are to be kept clear of a bilge keel.502 Openings in strength deck are as far as practicable to belocated well clear of craft’s side and hatch corners.503 Openings in strength members should generally have anelliptical form. Larger openings in deck may be accepted with

Z Mσ----- 103⋅ cm3( )=

b'

30o

b''

b'''

I II

b3

III

b2

b1

DET NORSKE VERITAS


well rounded corners and are to be situated as near to the craft’scentreline as practicable.504 For corners with rounded shape the radius is not to beless than:

r = 0.025 Bdk (m)Bdk = breadth of strength deck.r needs not be taken greater than 0.1 b (m) where b = breadthof opening in m. For local reinforcement of deck plating at cir-cular corners, see Rules for Classification of Ships Pt.3 Ch.1Sec.5 E400.505 Edges of openings are to be smooth. Machine flame cutopenings with smooth edges may be accepted. Small holes areto be drilled.506 Studs for securing small hatch covers are to be fastenedto the top of a coaming or a ring of suitable thickness weldedto the deck. The studs are not to penetrate the deck plating.

C. Shear StrengthC 100 Cases to be investigated101 If doors are arranged in the craft’s side, the required sec-tional area of the remaining side plating will be especially con-sidered.102 If rows of windows are arranged below the strengthdeck, sufficient horizontal shear area must be arranged to carrydown the midship tension and compression.103 For the cases in 101 and 102 and for other locations withdoubtful shear area, the allowable shear stress may be taken as:

D. Cases to be InvestigatedD 100 Inertia induced loads101 Transversely framed parts of the forebody are to bechecked for the axial inertia forces given in Pt.3 Ch.1 Sec.3A700 as follows:

FL = Δ al (kN)

al = maximum surge acceleration, not to be taken as lessthan:

.

The height distribution of stresses will depend on instantane-ous forward immersion and on height location of cargo.102 Bottom structure in way of thrust bearings may need tobe checked for the increased thrust when the craft is retarted bya crest in front.103 Allowable axial stress and associated shear stresses willbe related to the stresses already existing in the region.104 For passenger craft, a separate analysis is to be per-formed to investigate the structural consequence when subject-ed to the collision load as given in the International Code ofSafety for High-Speed Craft, 4.3.3 (see Ch.7 Sec.1 B300).

Guidance note:Inertia forces from collision deceleration should be consideredfor shear and buckling in the foreship area, and for the forces act-ing on the supporting structure for cargo.


E. Transverse Strength of Twin Hull CraftE 100 Transverse strength101 The twin hull connecting structure is to have adequatetransverse strength related to the design loads and momentsgiven in Ch.1.102 When calculating the moment of inertia, and sectionmodulus of the longitudinal section of the connecting struc-ture, the effective sectional area of transverse strength mem-bers is in general the net area with effective flange afterdeduction of openings.The effective shear area of transverse strength members is ingeneral the net web area after deduction of openings.

E 200 Allowable stresses201 The equivalent stress is defined as:

σx = total normal stress in x-directionσy = total normal stress in y-directionτ = total shear stress in the xy-plane

By total stress is meant the arithmetic sum of stresses from hullgirder and local forces and moments.202 The following total stresses are normally acceptable:

— Normal stress: σ = 160 f1 (N/mm2)

— Mean shear stress: τ = 90 f1 (N/mm2)

— Equivalent stress: σe = 180 f1 (N/mm2)

allowable shear stress allowable bending stress3

-----------------------------------------------------------=

0,4 g for VL

------- 5≥

0,2 g for VL

------- 3≤

linear interpolation of al for 3 VL

------- 5< <

σc σx2 σy

2 σxσy 3τ2+( )–+=

DET NORSKE VERITAS


SECTION 5 STEEL PLATING AND STIFFENERS

A. GeneralA 100 Introduction101 In this section the general requirements for plate thick-nesses and local strength of stiffeners in single skin panels aregiven.102 For buckling control, see Sec.10.

A 200 Definitions201 Symbols:L, B, D, T, CB, see Ch.1 Sec.1.

t = rule thickness in mm of platingZ = rule section modulus in cm3 of stiffenerss = stiffener spacing in m, measured along the plat-

ingfor corrugations, see Sec.1 Dfor wash bulkhead section modulus calculationss may be reduced according to size and locationof openings

sr = basic stiffener spacing= 2 (240 + L) (mm) in general

= 760 mm for watertight bulkheads, cargo holdbulkheads and superstructure and deckhousebulkheads

l = stiffener span in m, measured along the topf-lange of the member. For definition of spanpoint, see Sec.1 F100. For curved stiffeners lmay be taken as the cord length

σ = nominal allowable bending stress in N/mm2.due to lateral pressure

p and psl = design pressure in kN/m2 as given in Ch.1 Sec.2.To be calculated at load point as defined in Ch.1Sec.2 A

ZA = midship section modulus in cm3 as built at deckor bottom, respectively

ZR = rule midship section modulus in cm3.

A 300 Allowable stresses301 Maximum allowable bending stresses in plates and stiff-eners are to be according to Table A1.

B. PlatingB 100 Minimum thickness101 The thickness of the structures is in general not to be lessthan:

t0 and k according to Table B1

Table A1 Allowable bending stresses (Continued)Item Plate Stiffener

Within0.4 L

Within0.1 Lfrom

AF/FP

Within0.4 L

Within0.1 Lfrom

AP/FP(N/mm2)

Bottom, slamming loads 160 f1 150 f1Bottom, sea load: 120 f1 160 f1 160 f1- longitudinals, ZA = ZR 1) 95 f1- longitudinals, ZA ≥ 2 ZR 1) 160 f1- transverse beams 160 f1Side, slamming load 160 f1 160 f1Side, sea load:Longitudinal stiffening 180 f1 160 f1- at neutral axis 2) 180 f1- at deck or bottom 2) 120 f1- 0.25 D above and below neutral axis 2)

160 f1

Transverse stiffening, 160 f1 160 f1

- at neutral axis 2) 160 f1- at deck or bottom 2) 120 f1Deck:Longitudinal stiffening 120 f1 180 f1 160 f1- ZA = ZR 1) 95 f1- ZA ≥ 2 ZR 1) 160 f1Transverse stiffening 120 f1 160 f1 160 f1Flat cross structurelongitudinal bulkhead:

160 f1 150 f1

Longitudinal stiffening 160 f1- at neutral axis 2) 160 f1- at deck or bottom 2) 120 f1Transverse stiffening 160 f1 160 f1- at neutral axis 2) 140 f1- at deck or bottom 2) 120 f1Transverse tank bulkhead 160 f1 160 f1Collision bulkhead 160 f1 160 f1Watertight bulkhead 220 f1 220 f1Watertight doors 135 f1Superstructure/deckhouse, side/front

160 f1 160 f1

Superstructure/deckhouse deck 160 f1Shell doors 135 f11) For ZR < ZA < 2 ZR σ-values may be varied linearly.2) Between specified regions σ-values may be varied linearly.

Table B1 Values of t0 and kItem t0 kShell plating: Keel 1) 7.0 0.05

Bottom, bilge, side, sea in-lets and other openings 2)

5.0 0.04

Strength deck Weather and cargo decks 4.5 0.025Accommodation deck 4.5 0.025

Plating of decks below strength deck

Cargo deck 4.0 0.02Accommodation deck 4.0 0.02

Plating of decks above strength deck

Weather exposed parts of first tier superstructure decks and deckhouse tops

4.0 0.02

Accommodation 4.0 0.02

t t0 kL+( ) ssr---- mm( )=

ssr---- is not to be taken less than 0.5 or greater than 1.0.

DET NORSKE VERITAS


B 200 Formulae201 The thickness requirement corresponding to lateral pres-sure or impact is given by:

σ as given in Table A1.202 The following extended formula for thickness of platingexposed to lateral pressure may be used when relevant:

ka = correction factor for aspect ratio of plate field= (1.1– 0.25 s/l)2= maximum 1.0 for s/l = 0.4= minimum 0.72 for s/l = 1.0

kr = (1– 0.5 s/r)= correction factor for curved plates

r = radius of curvature in mm.

B 300 Bottom and bilge plating301 Plating in way of rudder bearings, shaft brackets etc.may have to be increased.

B 400 Sea inlets and other openings401 Location, see Sec.4 B.402 Sea inlet boxes are to have scantlings of plating and stiff-eners as required for boundaries of tanks, but based on bottomshell sea pressure and half the surplus of the slamming pressureabove the sea pressure.403 For minor sea connections, see Pt.4 Ch.6 Sec.4.

C. StiffenersC 100 Formulae and evaluations101 The section modulus requirement corresponding to lat-eral pressure or impact is given by:

p or psl from Ch.1 Sec.2

l = span of the member in ms = spacing in m σ = nominal allowable stress due to lateral pressure, see

Table A1m = bending moment factor depending on the degree of end

constrains and type of loading, see also Sec. 6 TableB1.

The m-values are normally to be as given in Table C1.The m-values may have to be increased after special consider-

ation or rotation/deflection at supports or variation in lateralpressure.The m-values may be reduced, provided acceptable stress lev-els are demonstrated by direct calculations.

102 The formula given in 101 is to be regarded as the re-quirement about an axis parallel to the plating. As an approxi-mation, the requirement to standard section modulus forstiffeners at an oblique angle with the plating may be obtainedif the formula in 101 is multiplied by the factor:

α = angle between the stiffener web plane and the planeperpendicular to the plating

For α-values less than 15 ° corrections are normally not nec-essary.103 When several members are equal, the section modulusrequirement may be taken as the average requirement for eachindividual member in the group. However, the requirement forthe group is not to be taken less than 90 % of the largest indi-vidual requirement.104 The geometric properties of stiffeners (section modulusZ and in some cases moment of inertia I) may be calculated di-rectly from the given dimensions in connection with the effec-tive plate flange.Effective plate flange may normally be taken equal to the stiff-ener spacing.Z and I may also be obtained from published tables and curves.Equal angles should be avoided for full bending due to reducedeffective free flange by torsional stresses, and tripping effects.105 The thickness of web and flange is not to be less than:

tweb for flats = 1/15 x flat depth.tweb for other sections = 1/50 x web depth, provided net

shear area ≥ 0,075 lsp.

Bulkhead plating Tank bulkheads and water-tight bulkheads

5.0 0.025

First tier of superstructure ends and exposed sides

5.0 0.01

Other structures Structure not mentioned above

2.5

1) The thickness of the keel plate is in no case to be less than that of the adjacent bottom plate.

2) The thickness of the bilge plate is not to be less than that of the adjacent bottom and side plates whichever is the greater.

t15 8, s p or p s l

σ-------------------------------------- (mm)=

t15 8, kakrs p or p s l

σ------------------------------------------------- (mm)=

zml2s p or p s l( )

σ------------------------------------- cm3( )=

Table C1 Values of mItem mContinuous longitudinal members 85Non-continuous longitudinal members 100Transverse members 100Vertical members, ends fixed 100Vertical members, simply supported 135Bottom 85Bottom, transverse members 100Sides, longitudinal members 85Sides, vertical members 100Decks, longitudinal members 85Decks, transverse members 100Watertight bulkhead stiffeners, fixed ends 65Watertight bulkhead stiffeners, fixed one end (lower) 85Watertight bulkhead stiffeners, fixed one end (upper) 75Watertight bulkhead stiffeners, simply supported ends 125Watertight bulkhead horizontal stiffeners, fixed ends 85Watertight bulkhead horizontal stiffeners, simplysupported ends

125

Tank bulkheads, fixed ends 100Tank bulkheads, simply supported ends 135Deckhouse stiffeners 100Casing stiffeners 100Weather deck hatch covers 125Shell doors 125Doors in watertight bulkheads 125

1αcos

------------

DET NORSKE VERITAS


tflange = 1/15 x flange width from web.

C 200 Bulkhead stiffeners other than longitudinals201 The end attachment of the stiffeners is to comply withthe following requirements:For tank, cargo hold and collision bulkheads: Bracket to be fit-ted at both ends according to Sec.1 I200.For transverse watertight bulkheads, brackets are normally tobe fitted at both ends. Brackets may be omitted, however, onthe condition that the distance from top of the bulkhead to thelower end of the span is less than 6 s.202 For cargo hold centre line partial bulkheads, which arenot pillar bulkheads, see Sec.7, the following apply:Section modulus requirement for stiffeners:

Z = 2 l2 s (cm3)

The distance between stiffeners is not to be greater than 2frame spacings.

C 300 Machinery casings301 The section modulus of stiffeners is not to be less than:

Z = 3 l2 s (cm3)

l = length of stiffeners in m, minimum 2.5 m.

302 Casings supporting one or more decks above are to beadequately strengthened, see Sec.7.

C 400 Weather deck hatch covers. Shell doors401 In addition to the section modulus requirement, accord-ing to 100, the moment of inertia is not to be less than:

I = 1.7 Z l (cm4).

DET NORSKE VERITAS


SECTION 6 STEEL WEBFRAMES AND GIRDER SYSTEMS

A. GeneralA 100 Introduction101 In this section the general requirements for simple gird-ers in single skin structures are given. Procedures for the cal-culations of complex girder systems are given in Sec.9.

A 200 Definitions201 SymbolsL, B, D, T, CB, see Ch.1 Sec.1.

Z = rule section modulus in cm3 of stiffeners andgirders

s = stiffener spacing in m, measured along the plat-ing

l = stiffener span in m, measured along the topf-lange of the member. For definition of spanpoint, see Sec.1 F100. For curved stiffeners lmay be taken as the cord length

S = girder span in m. For definition of span point,see Sec.1 F100

b = breadth of load area in m. b may be determinedby Table A1

σ = nominal allowable bending stress in N/mm2 dueto lateral pressure

p and psl = design pressure in kN/m2 as given in Ch.1 Sec.2.To be calculated at load point as defined in Ch.1Sec.2 A

τ = nominal allowable shear stress in n/mm.2P = design axial force in kNAW = rule web area in cm2.A = rule cross sectional area in cm2.tw = web thickness in mmhw = web height in mmbf = flange breadth in mm.

A 300 Allowable stress301 Maximum allowable bending stresses and shear stressesin web frames and girders are to be according to Table A2.

B. Web Frames and GirdersB 100 General101 The requirements for section modulus and web area giv-en in 200 are applicable to simple girders supporting stiffenersor other girders exposed to linearly distributed lateral pressure.It is assumed that the girder satisfies the basic assumptions ofsimple beam theory and that the supported members are ap-proximately evenly spaced and similarly supported at bothends. Other loads will have to be especially considered.102 When boundary conditions for individual girders are notpredictable due to dependence of adjacent structures, directcalculations according to the procedures given in Sec.9 D willbe required.

B 200 Strength requirements201 The section modulus for girders subjected to lateralpressure is not to be less than:

σ = according to Table A2m = bending moment factor. m-values in accordance with

203 may be applied.

202 The effective web area of girders subjected to lateralpressure is not to be less than:

ks = shear force factorks - values in accordance with 203 may be applied

a = number of stiffeners between considered section andnearest support

r = average point load in kN from stiffeners between con-sidered section and nearest support

τ = according to Table A2.

The a-value is in no case to be taken greater than:

n = number of supported stiffeners on the girder span.

The web area at the middle of the span is not to be less than 0.5AW.203 The m - and ks- values referred to in 201 and 202 may becalculated according to general beam theory. In Table B1 m -and ks - values are given for some defined load and boundaryconditions. Note that the greatest m-value is to be applied forsimple girders. For girders where brackets are fitted or theflange area has been partly increased due to large bending mo-ment, a smaller m-value may be accepted outside the strength-ened region.

Table A1 Breadth of load areaFor ordinary girders b = 0.5 (l1 + l2.) (m)

l1 and l2are the spans in m of the sup-ported stiffeners

For hatch side coamings B = 0.2 (B1 - b2) (m)B1 = breadth of craft in m measured at the middle of the hatchwayb2 = breadth of hatch in m measured at the middle if the hatchway

For hatch end beams b = 0.4 b3 (m)b3 = distance in m between hatch and end beam and nearest deep transverse girder or transverse bulkhead

Table A2 allowable stressWeb frames and girders

Bending stress(N/mm2)

Shear stress(N/mm2)

Longitudinal girders Sec.5 Table A1 90 f1Hatch covers and shell door girders

135 f1 80 f1

Girders for watertight doors 200 f1Other girders 160 f1 90 f1Watertight bulkheads1) 220 f1 120 f11) For flooding loads

Table B1 Values of m and ksLoad and boundary

conditionsBending moment andshear force factors

Positions 1m1ks1

2m2–

3m3ks3

1Support

2Field

3Support

Z mS2 b pσ

-------------------- cm3( )=

Aw10 ksS b p a r–( )

τ------------------------------------------- cm2( )=

n 1+4

------------

DET NORSKE VERITAS


204 The m and ks values referred to in 201 and 202 are nor-mally to be as given in Table B2 for various structural items.

205 Girders supporting other girders or a pillar are to have asection modulus:

P = force from supported girder or pillar (kN)m = 5.5 for force at half-span with half restrained endsσ = as given in Sec.5 Table A1 for continuous longitudinal

girders = 160 for other girders = 220 for watertight bulkheads, except the collision

bulkhead, when the flooding load is applied

The effective web area is not to be less than:

ks = shear factor= 0.55 for P approximately at half-span

τ = as in 103.

For girders also laterally loaded, the value of Z and Aw are tobe added to the lateral load requirements in 201 and 202.

B 300 Minimum thicknesses and geometrical ratios301 The minimum thickness of web plates and brackets willbe related to web depth and web stiffeners spacing as describedin Sec.1 I600.302 Girder flanges are to have a thickness not less than 1/30of the flange width when the flange is symmetrical, and notless than 1/15 of the flange width when the flange width isasymmetrical. And for bottom transverses a width not less than1/20 of the distance between tripping brackets (side girders).

B 400 Weather deck hatch covers. Shell doors401 Girders, including edge stiffeners, supporting cover ordoor stiffeners are to have a section modulus as given by 201.In addition the moment of inertia is not to be less than:

I = 1.7 Z l (cm 4).402 To ensure sufficient packing pressure for the whole dis-tance between the securing devices, the moment of inertia ofthe side elements of the covers is to be at least:

I = 6 pl a4 (cm 4).for cover edges connected to a rigid hatch coaming and

I = 12 pl a4 (cm 4).between cover edges of equal stiffness both deflecting underthe packing pressure

pl = packing line pressure along edges in N/mm, minimum5 N/mm

a = spacing in m of bolts or other securing devices.

403 For edge stiffeners supporting cover or door stiffenersbetween securing devices, the moment of inertia is to be in-creased corresponding to the extra force.404 The design force for securing bolts and other closing de-vices of doors opening inwards, their supporting members andsurrounding structure is given by:

F = k A p 10 3 + a pl (N)

k = fraction of A supported by bolt or deviceA = area of door in m2.

p is normally to be calculated at the midpoint of A.

a = spacing of bolts in mpl = packing line pressure in N/mm. For calculation pur-

pose, however, the packing pressure is not to be takenless than 5 N/mm.

405 Net bolt area for each bolt is not to be less than:

F is as calculated in 404.

s = 125f1e =σf = minimum upper yield stress in N/mm2, not to be taken

greater than 70 % of the ultimate tensile strengthe = 0.75 for σf > 235

= 1.0 for σf < 235

406 The maximum stresses in closing devices of other typesthan bolts are:Normal stress:

σ = 120 f1e (N/mm2)Shear stress:

τ = 80 f1e (N/mm2)407 For hatch covers carrying deck cargo, special calcula-

850.50 42 85

0.50

0.38 70 1250.63

0.50 125 0.50

650.30 43 100

0.70

0.20 60 1350.80

0.33 130 0.67

Table B2 Values of m and ks for various structural itemsItem m ksBottom: Web frames

FloorsLongitudinal girders

100100100

0.630.630.63

Side: Longitudinal girdersWeb frames, upper endWeb frames, lower endsDeck girders

100100100100

0.540.540.720.63

Bulkhead: Horizontal girdersVertical girders, upper endVertical girders, lower end

100100100

0.540.540.72

Z 1000 P Smσf1

--------------------- cm3( )=

Aw10 ks P

τ f1----------------- cm2( )=

Ac0 01, Fσ f1e

---------------- cm2( )=

σf235---------⎝ ⎠

⎛ ⎞e

DET NORSKE VERITAS


tions will be required, both for the downward and upward re-action forces and for horizontal sliding forces.

B 500 Doors in watertight bulkheads501 The permanent set, which is allowed for watertight bulk-heads, is not allowed for watertight doors due to the leakageproblem.502 Girders, including edge stiffeners, supporting door stiff-eners are to have a section modulus as given in 201. In addi-tion, edge stiffeners of doors are to have a moment of inertianot less than:

I = 8 pe d4 (cm4)

d = distance between closing devices in m, to be measuredalong the door edge

pe = packing line pressure along edges, not to be taken lessthan 5 N/mm or

= pe, whichever is the greaterp = watertight bulkhead design pressure, as given in Ch.1

Sec.2

b = load breadth, normally taken as h/3 or w/2, whicheveris the less.

h and w are height and width of door in m.503 For edge stiffeners supporting main door stiffeners be-tween securing devices, the moment of inertia is to be in-creased corresponding to the extra force.504 Securing devices are to be designed for the load actingalso on the opposite side of where they are positioned. Allow-able stresses in securing devices are as follows:Normal stress:

σ = 180 (N/mm2)Shear stress:

τ = 120 (N/mm2)Bolt tension stress in way of threads:

σ = 190 f 1e (N/mm2)f1e as given in 405.

DET NORSKE VERITAS


SECTION 7 STEEL PILLARS AND PILLAR BULKHEADS

A. GeneralA 100 Introduction101 In this section requirements for pillars and bulkheadstiffeners, substituting pillars, are given.

A 200 Definitions201 Symbols:L, B, D, T, CB, see Ch.1.

t = thickness in mm of platings = stiffener spacing in m, measured along the plating

= 2 (240 + L) (mm)l = length of pillars, cross ties, bulkhead stiffeners etc. be-

tween effective supports normal to their axis in mI = smallest moment of inertia in cm4, including 20 x t

plating each side of bulkhead stiffenerA = cross-sectional area in cm2, including 20 x t plating

each side of bulkhead stiffeneri =p = design pressure as given in Ch.1.

B. PillarsB 100 Arrangement of pillars101 Where practicable, deck pillars are to be located in linewith pillars above or below. Otherwise beams or girders indeck in way will have to be reinforced.102 Pillars or equivalent supports are to be arranged belowdeckhouses, windlasses, winches and other heavy weights.103 The engine room casing is to be supported.104 Doublers are to be fitted on deck and inner bottom, ex-cept in tanks where doublers are not allowed. Brackets may beused instead of doublers.105 Structural reinforcement below pillars will be consid-ered in the individual cases.

B 200 Pillar scantlings201 The cross sectional area of members subjected to com-pressive loads is not to be less than:

η =

P = axial load in kN as given for various strength membersin 202 and 203. Alternatively, P may be obtained fromdirect stress analysis

l = length of member in mi = radius of gyration in cm

k = 0.7 in general= 0.6 when design loads are primarily dynamic

σc =

=

σE =σF = minimum upper yield stress of materialE = modulus of elasticity for steel = 210 000 N/mm2.

The formula given for σE is based on hinged ends and axialforces only.If, in special cases, it is verified that one end can be regardedas fixed, then the value of σE may be multiplied by 2.If it is verified that both ends can be regarded as fixed, the val-ue of σE may be multiplied by 4.In case of eccentric force, additional end moments or addition-al lateral pressure, the strength member is to be reinforced towithstand bending stresses.202 The nominal axial force in pillars is normally to be takenas:

P = n F

n = number of decks above pillar. In case of a large numberof decks (n > 3), a reduction in P will be consideredbased upon special evaluation of load redistribution

F = the force contribution in kN from each deck above andsupported by the pillar in question given by:

F = p AD (kN)

p = design pressure on deck as given in Ch.1 Sec.2AD = deck area in m2 supported by the pillar, normally taken

as half the sum of span of girders supported, multipliedby their loading breadth. For centre line pillars sup-porting hatch end beams, (see Fig.1 and Fig.2):

= =

b1 = distance from hatch side to craft’s side.

203 The nominal axial force in cross ties and panting beamsis normally to be taken as:

P = e b p (kN)

e = mean value of spans in m on both sides of the cross tieb = load breadth in mP = the larger of the pressures in kN/m2 on either side of

the cross tie (e.g. for a side tank cross tie, the pressurehead on the craft’s side may be different from that onthe longitudinal bulkhead)

IA---- = radius of gyration in cm

A 10 Pη σc----------- cm2( )=

k

1 li-+⎝ ⎠

⎛ ⎞----------------, minimum 0.3

σE when σEσF2

------ N mm⁄ 2( )<

σF 1σF

4σE----------–⎝ ⎠

⎛ ⎞ when σEσF2

------>

π2E i100 l-----------⎝ ⎠

⎛ ⎞ 2N mm2⁄( )

4 A1 A2+( )b1B----- when transverse beams

4 A3 A4 A5+ +( )b1B----- when longitudinals

DET NORSKE VERITAS


Fig. 1Deck with transverse beams

Fig. 2Deck with longitudinals

B 300 Pillars in tanks301 Hollow pillars are not accepted.302 Where the hydrostatic pressure may give tensile stressesin the pillars and cross members, their sectional area is not tobe less than:

A = 0,07 Adk pt (cm2)(The formula may be used also for tension control of pantingbeams and cross ties in tanks.)

Adk = deck or side area in m2 supported by the pillar or crossmember

pt = design pressure, p in kN/m2 giving tensile stress in thepillar

Doubling plates at ends are not allowed.

C. Supporting BulkheadsC 100 General101 Bulkheads supporting decks are to be regarded as pillars.Compressive loads are to be calculated based on supporteddeck area and deck design loading.102 Buckling strength of stiffeners are to be calculated as in-dicated in Sec.10 E101, assuming a plate flange equal to 40 xthe plate thickness when calculating IA, A and i.Local buckling strength of adjoining plate and torsional buck-ling strength of stiffeners are to be checked.

DET NORSKE VERITAS


SECTION 8 WELDING AND WELD CONNECTIONS

A. GeneralA 100 Introduction101 In this section requirements related to welding and vari-ous connection details are given.

A 200 Welding particulars201 Welding of important hull parts is to be carried out byapproved welders, only.202 Welding at ambient air temperature of –5 °C or below,is only to take place after special agreement.203 The welding sequence is to be such that the parts may,as far as is possible, contract freely in order to avoid cracks inalready deposited weld runs. Where a butt meets a seam, thewelding of the seam should be interrupted well clear of thejunction and not be continued until the butt is completed.Welding of a butt should continue past the open seam, and theweld then chipped out, so that the seam can be welded straightthrough.204 Welding procedures and welding consumables ap-proved for the type of connection and parent material in ques-tion, are to be used. See "Register of Type Approved ProductsNo.2, Welding Consumables".

B. Types of Welded JointsB 100 Butt joints101 For panels with plates of equal thickness, the joints arenormally to be butt welded with edges prepared as indicated inFig.1.102 For butt welded joints of plates with thickness differenceexceeding 4 mm, the thicker plate is normally to be tapered.The taper is generally not to exceed 1: 3. After tapering, theend preparation may be as indicated in 101 for plates of equalthickness.103 All types of butt joint are normally to be welded fromboth sides. Before welding is carried out from the second side,unsound weld metal is to be removed at the root by a suitablemethod.104 Butt welding from one side only will be permitted afterspecial consideration where a backing run is not practicable orin certain structures when the stress level is low.

B 200 Lap joints and slot welds201 Various types of overlapped joints are indicated in Fig.2.Type "A" (lap joint) is normally not to be used in primarystructures. Provided the dynamic stress levels are low, lapjoints may be accepted on special considerations. Type "B"(slot weld) may be used for connection of plating to internalwebs, where access for welding is not practicable. For size ofslot welds, see C103.

Fig. 1Manually welded butt joint edges

Fig. 2Lap joints and slot welds

B 300 Tee or cross joints301 The connection of girder and stiffener webs to plate pan-el as well as plating abutting on another plate panel, is normal-ly to be made by fillet welds as indicated in Fig.3.

DET NORSKE VERITAS


Fig. 3Tee or cross joints

Where the connection is highly stressed or otherwise consid-ered critical, the edge of the abutting plate may have to be bev-elled to give deep or full penetration welding. Where theconnection is moderately stressed, intermittent welds may beused. With reference to Fig.4, the various types of intermittentwelds are as follows:

— chain weld— staggered weld— scallop weld (closed). For size of welds, see C102.

Fig. 4Intermittent welds

302 Double continuous welds are required in the followingconnections irrespective of the stress level:

— weathertight, watertight and oiltight connections— connections in foundations and supporting structures for

machinery— all connections in after peak— connections in rudders, except where access difficulties

necessitate slot welds— connections at supports and ends of stiffeners, pillars,

cross ties and girders— centre line girder to keel plate— water jet duct structure and structure adjacent to the water

jet duct.

303 Where intermittent welds are accepted, scallop weldsare to be used in tanks for water ballast, cargo oil or fresh wa-ter. Chain and staggered welds may be used in dry spaces andtanks arranged for fuel oil, only.

C. Load Based Weld ScantlingsC 100 Joints of abutting webs or plates101 The throat thickness of double continuous fillet welds isnot to be less than:

C = weld factor given in Table C1t0 = net thickness in mm of abutting plate

For plate thicknesses (tn) above 22 mm, t0 may be sub-stituted by 0.5 (22 + tn)

f = 1,36 for NV-NS and weld deposit yield strength ≥ 355N/mm2

=

fpm = material factor f1 as defined in Sec.2 C200 for plates tobe joined

fw = material factor for weld deposit=

sfw = yield strength in N/mm2 of weld deposit, not to be tak-en higher than 1.5 times the yield strength of the mate-rial to be welded

102 The throat thickness of intermittent fillet welds, whenpermitted according to B302, is not to be less than:

C, t0 and f are as given in 101.

d = distance, in mm, between successive welds, see Fig.4l = length, in mm, of weld fillet, not to be less than 75 mm

If the required t exceeds:

— 0.6 t0 for chain and scallop weld— 0.75 t0 for staggered weld

Table C1 Weld factor CItem 60 % of

spanAt

endsStiffeners, frames, beams, longitudinals to shell, deck or bulkhead plating

0.16 0.26

Web plates of girders

To plating 0.26 0.43To flange 0.16 0.26

Webs of girders supporting other girders,— to the plating— to the flange

0.430.26

Bulkheadboundaryconnections

Tank and watertight bulkheads 0.52Pillar bulkheads 0.16Superstructure end, deckhouse external and machinery casing bulkheads to deck below

0.52

Strength deck to shell

0.68

Weather or tank decks to shell

0.52

Hatch coam-ing to strength deck

At corners 0.68Elsewhere 0.52

Weather hatch coaming top profile to coaming 0.52Sea inlets 0.68Scuppers and discharges to deck and shell 0.52

tC t0

f--------- (mm)=

fw

fpm------------ in other cases

σfw235---------⎝ ⎠

⎛ ⎞0 75,

tt0 d C

f l-------------- (mm)=

DET NORSKE VERITAS


intermittent weld cannot be applied. In addition, in the slam-ming area the ratio d/s should not exceed:

— 1.25 forward of amidships— 1.7 aft of amidships.

103 Fillets welds in slots are to have a throat thickness asgiven by the formula in 102 with:

t0 = net thickness of adjoining web plated = distance between slotsl = length of slots

Slots are to have a minimum length of 75 mm and, normally, awidth of twice the plate thickness. The ends are to be wellrounded, see Fig.2. The distance d between slots is not to ex-ceed 3 l, maximum 250 mm.104 When K-weld is used in a heavily shear loaded tee orcross joint, e.g. unsymmetrical or symmetrical bulkhead gird-ers, the visible throat thickness after welding may be reducedby the depth of the bevelling.105 When fillet weld, K-weld or full penetration weld is usedin an axially loaded cross joint, the visible throat thickness, seeFig.5, is not to be less than:

C =

σ = calculated maximum tensile stress in abutting plate inN/mm2, minimum 70

r = root face in mmt0 = net thickness in mm of abutting platefw = as given in B101.

Fig. 5Axially loaded cross joint

106 Full penetration welds are in any case to be used in thefollowing connections:

— shaft brackets to reinforced shell structure

— rudder side plating to rudder stock and other importantconnection areas of rudders, rudder suspension members,propeller ducts etc.

— end brackets of hatch side coamings to deck and coamingand other heavily shear loaded spots

— crane pedestal if abutting to upper deck plating— penetrating type edge reinforcements or pipe penetrations

to strength deck (including sheer strake) and bottom plat-ing within 0.6 L amidships, when transverse dimension ofopening exceeds 300 mm

— fatigue critical parts of water jet ducts, where grinding ofwelds may become necessary in order to have sufficientfatigue strength.

C 200 Steel and weld support of stiffeners to girders201 Stiffeners may be connected to the web plate of girdersin the following ways:

— welded directly to the web plate on one or both sides of thestiffener

— connected by single- or double-sided lugs— with stiffener or bracket welded on top of stiffener— a combination of the above.

In slamming areas, areas of vibration induced by the water jetimpeller or propeller, tanks, car decks and other special loca-tions, at least one side of the stiffener web should be connect-ed. In locations with great shear stresses in the web plate, a dou-ble-sided connection is normally required. A double-sidedconnection may be taken into account when calculating the ef-fective web area.202 The steel connection area at supports of stiffeners is nor-mally not to be less than:

ao = c k (l – 0.5 s) s p (cm2)

c = factor as given in Table C2k = 0.125 for pressure acting on stiffener side and for slam-

ming pressure= 0,1 for other pressure acting on opposite side

l = span of stiffener in ms = spacing between stiffeners in mp = design pressure in kN/m2

203 Various standard types of connections are shown inFig.6. Other types of connection will be considered in eachcase.204 Connection lugs are to have a thickness not less than theweb plate thickness.205 Weld area is not to be less than:

a = 0.85 a0 (cm2).

tC t0fw

--------- (mm)=

0 27, σ200--------- 0 34,–⎝ ⎠

⎛ ⎞ rt0----+

ROOT FACE r

VISIBLE THROAT THICKNESS t

ABUTTING PLATE THICKNESS to

σ

σ

Table C2 c-factorsType ofconnection(see Fig.6)

Stiffener/bracket on top of stiffenerNone Single-

sidedDouble-

sideda 1.00 1.25 1.00b 0.90 1.15 0.90c 0.80 1.00 0.80

"a" without stiffener web con-nection

1.50 1.25

DET NORSKE VERITAS


Fig. 6End connections

C 300 Steel and weld end connections of longitudinals301 Longitudinals, if broken on each side of a bulkhead, areto be connected by a continuous bracket through the bulkhead.302 The weld area of brackets to longitudinals as well as thesteel area of bracket through bulkhead is not to be less than thesectional area of the longitudinal. Brackets are to be connectedto bulkhead by a double continuous weld.303 When for L < 50 m and for larger craft outside 0.5 Lamidships the bracket may be welded to each side of the bulk-head, the cross joint welding is to satisfy 105.304 When no longitudinal on opposite side, see 400.

C 400 Weld end connections of stiffeners in general401 The connection between stiffener and bracket is in gen-eral to be so designed that the effective section modulus is notreduced below the requirement for the stiffener.402 When the plating supported by stiffener is continuousbeyond end of span, see Fig.7, the weld area restraining thefree edge of stiffener is not to be less than:

Z = net section modulus of stiffener in cm3

h = stiffener height in mmk = 15 in general = 25 for connections restraining the lower end of lower

side frames

= 10 for ’tween deck frames carried through the deck andoverlapping the underlying bracket

403 Lower ends of peak frames are also to be connected tothe floors by a weld area not less than:

a = 0.105 l s p (cm2)l, s and p = as given in 202.

Fig. 7End connections

404 When the plating supported by stiffener terminates at theend of span, see Fig.7, e.g. deck at side, bulkhead at circumfer-ence, the weld area of the bracket arms is not to be less than:

tb = net thickness in mm of bracket.Z = net section modulus of stiffener in cm3.

C 500 End connections of girders, pillars and cross ties501 The weld connection area of bracket to adjoining girdersand of bracket and girder to other structural parts may be basedon directly calculated normal and shear stresses. Double con-tinuous welding is to be used. Where large tensile stresses areexpected, welding according to 105 is to be applied.502 The end connections of simple girders are to satisfy therequirements for section modulus given for the girder in ques-tion. For brackets overlap welded to rolled sections the formu-lae of 402 and 404, as relevant, may be used.Where high shear stresses in web plates, double continuousboundary fillet welds are to have throat thickness not less than:

τ = calculated shear stress in N/mm2

t0 = net thickness of abutting platefw = as given in A200.

503 End connection of pillars and cross ties are to have aweld area not less than:

A = load area in m2 for pillar or cross tiep = design pressure in kN/m2 as given for the structure in

questionfw = as given in A200

a kZh

------- cm2( )=

Minimum weld area 10 ssr---- cm2

=⎝ ⎠⎛ ⎞

a 0 4, Ztb cm2( )=

tτ t0

200fw--------------- (mm)=

a k A pfw

------------- cm2( )=

DET NORSKE VERITAS


k = 0.05 when pillar in compression only= 0.14 when pillar in tension.

D. Minimum Weld ScantlingsD 100 Minimum fillet weld101 In no case the throat thickness of double continuous fil-let welds is to be taken less than given in Table D1.

102 For intermittent fillet weld, the throat thickness is not tobe less than 3.5 mm. For maximum thickness of intermittentweld, see C103.

Table D1Plate thickness(web thickness) t0(mm)

Minimum throat thickness (mm)Arc welding

with covered elec-trodes

Gas shieldedarc welding

t0 ≤ 4 2.04 < t0 ≤ 6.5 3.0 2.56.5 < t0 ≤ 8 3.0t0 > 8 0.21 t0, minimum 3.25

DET NORSKE VERITAS


SECTION 9 DIRECT STRENGTH CALCULATIONS

A. GeneralA 100 Introduction101 In the preceding sections the scantlings of the variousprimary and secondary hull structures (girder systems, stiffen-ers, plating) have been given explicitly, based on the designprinciples outlined in Ch.1 Sec.1. In some cases direct strengthor stress calculations have been referred to in the text. Thebackground and assumptions for carrying out such calculationsin addition to or as a substitute to the specific rule requirementsare given in this section. Load conditions, allowable stressesand applicable calculation methods are specified. It is also referred to Ch.9 which specifies requirements for di-rect calculations procedures of hydrodynamic and strengthanalyses as well as requirements for local finite element mod-els which are applicable for the local analyses as described inthis section.

A 200 Application201 The application of direct stress analysis is governed by: Required as part of rule scantling determination. In such caseswhere simplified formulations are not able to take into accountspecial stress distributions, boundary conditions or structuralarrangements with sufficient accuracy, direct stress analysishas been required in the rules. As alternative basis for the scantlings. In some cases directstress calculations may give reduced scantlings, especiallywhen optimization routines are incorporated.

B. PlatingB 100 General101 Normally direct strength analysis of laterally loadedplating is not required as part of rule scantling estimation.102 Buckling control of plating subjected to large in planecompressive or shear stresses is specified in Sec.10.

C. StiffenersC 100 General101 Direct strength analysis of stiffeners may be requested inthe following cases:

— stiffeners affected by supports with different deflectioncharacteristics

— stiffeners subject to large bending moments transferredfrom adjacent structures at supports.

102 Buckling control of stiffeners subjected to large axial,compressive stresses is specified in Sec.10.

C 200 Calculation procedure201 The calculations are to reflect the structural response ofthe 2 or 3 dimensional structure considered.Calculations based on elastic beam element models or finite el-ement analyses may normally be applied, with due attention to:

— boundary conditions— shear area and moment of inertia variations— effective flange

— effects of bending, shear and axial deformations— influence of end brackets.

C 300 Loads301 The local lateral loads are to be taken as specified inCh.1 Sec.2 for the structure in question.302 The magnitude and sign of hull girder stress acting si-multaneously, will have to be decided in each case. It is alsoreferred to Ch.9, which gives guidance for how this is to bedone.303 For double bottom and other cofferdam type structures,a cofferdam bending moment and a shear force induced stiff-ener bending moment may have to be considered at the sametime.

C 400 Allowable stresses401 The allowable stress level is as given in Table C1.

402 Stiffeners are in no case to have web and flange thick-nesses less than given in Sec.5 C for the structure in question.

D. GirdersD 100 General101 For girders which are parts of a complex 2- or 3-dimen-sional structural system, a complete structural analysis mayhave to be carried out to demonstrate that the stresses are ac-ceptable when the structure is loaded as described in 300.102 Calculations as mentioned in 101 may have to be carriedout for:

— bottom structures— side structures— deck structures— bulkhead structures— transverse frame structures in monohull craft supporting

deckhouses, containers and other permanent or cargomasses subject to tripping

— strength of deck along wide hatches, see Sec.6 B— other structures when deemed necessary by the Society.

D 200 Calculation methods201 Calculation methods or computer programs applied areto take into account the effects of bending, shear, axial and tor-sional deformations.The calculations are to reflect the structural response of the 2-or 3-dimensional structure considered, with due attention toboundary conditions.For systems consisting of slender girders, calculations based

Table C1 Maximum allowable stresses

Nominal local bendingstress

General σ = 180 f1 N/mm2

Watertight bulk-heads, except col-lision bulkhead

σ = 245 f1 N/mm2

Combined local bendingstress/girder stress/extremelongitudinal stress

σ = 230 f1 to 265 f1N/mm2, see reference in D405

Nominal shear stress

General τ = 90 f1 N/mm2

Watertight bulk-heads, except col-lision bulkhead

τ = 120 f1 N/mm2

DET NORSKE VERITAS


on beam theory (frame work analysis) may be applied, withdue attention to:

— shear area variation— moment of inertia variation— effective flange.

202 For rise of floor bottoms, shear in the bottom plating willresist vertical deflection of the keel, with a releasing effect onthe longitudinal girder, which may be taken into account.203 For deep girders, bulkhead panels, bracket zones, etc.where results obtained by applying the beam theory are unreli-able, finite element analysis, see Ch.9, or equivalent methodsare to be applied.204 Acceptable calculation methods are outlined in Classifi-cation Notes.

D 300 Design load conditions301 The calculations are to be based on the loads at designlevel as given in Ch.1. Except for monohull horizontal acceler-ations, which are given in the Rules for Classification of ShipsPt.3 Ch.1 Sec.4 B (extreme values).Horizontal accelerations may also be based on a hydrodynamicanalysis as described in Ch.9.For sea-going conditions realistic combinations of external andinternal dynamic loads and inertia forces are to be considered.The mass of deck structures may be neglected when less than5 % of the applied loads are in the vertical direction.

D 400 Allowable stresses401 The equivalent stress is defined as:

σe =σx = normal stress in x-directionσy = normal stress in y-directionτ = shear stress in the xy-plane

402 For girders in general, the following stresses are normal-ly acceptable:Normal stress:σ = 160 f1 N/mm2.Mean shear stress:

τ = 90 f1 N/mm2 for girders with one plate flangeτ = 100 f1 N/mm2 for girders with two plate flangesEquivalent stress:σe = 180 f1 N/mm2. 403 For girders on watertight bulkheads:

— σ and σe may be increased by 60 f1 N/mm2.— τ may be increased by 30 f1 N/mm2.

except for the collision bulkhead.404 For transverse structures and partial longitudinal struc-tures supporting deckhouses, containers etc. in the rolling andpitching conditions:

— σ and σe may be increased by 50 f1 N/mm2.— τ may be increased by 25 f1 N/mm2.

when extreme horizontal accelerations have been applied.405 For girders subjected to hull girder stresses, the follow-ing additional requirement applies:σe = 90 f1 N/mm2.plus maximum allowable longitudinal stress according toSec.4 B101 or maximum allowable transverse stress accordingto Sec.4 E202. The actual longitudinal or transverse stress in the girder is tak-en from the calculations in Sec.4.406 In compression, the buckling stress may be decisive. SeeSec.10.

D 500 Allowable deflections501 For deflections in general, see Sec.1 H.502 For weather deck hatch coamings, the horizontal deflec-tion at weather tightening level should not exceed 25 mm, un-less tightness at a greater deflection may be proved.503 For weathertight and watertight hatches and doors, therelative deflection of cover and hull coamings in the pressuredirection should not result in leakage due to loss of packingpressure.504 Deflection limits of girders and coamings of covers anddoors themselves are found in Sec.5 and Sec.6 in terms of amoment of inertia requirement.

σx2 σy

2 σxσy 3τ2+–+

DET NORSKE VERITAS


SECTION 10 BUCKLING CONTROL

A. General

A 100 Definitions101 Symbols

t = thickness in mm of platings = shortest side of plate panel in ml = longest side of plate panel in m

= length in m of stiffener, pillar etc.E = modulus of elasticity of the material

= 2.06 · 105 N/mm2 for steelσel = the ideal elastic (Euler) compressive buckling stress in

N/mm2

σf = minimum upper yield stress of material in N/mm2,may be taken as 235 N/mm2 for normal strength steel.For higher strength steel, see Sec.2 B

τel = the ideal elastic (Euler) shear buckling stress in N/mm2

τf = minimum shear yield stress of material in N/mm2

=

σc = the critical compressive buckling stress in N/mm2

τc = the critical shear stress in N/mm2

σa = calculated actual compressive stress in N/mm2

τa = calculated actual shear stress in N/mm2

η =

z n = vertical distance in m from the baseline or deckline tothe neutral axis of the hull girder, whichever is relevant

za = vertical distance in m from the baseline or deckline tothe point in question below or above the neutral axis,respectively.

102 Relationships:

Guidance note:When the required σc or τc is known, the necessary σel or τelwill from the above expressions of the Johnson-Ostenfeld rela-tionship be:

KJ—O from Fig.1 or from the formula:


Fig. 1Johnson-Ostenfeld K-factor

B. Longitudinal Buckling LoadB 100 Longitudinal stresses101 See Pt.3 Ch.1 Sec.3 A700.

C. Transverse Buckling LoadC 100 Transverse stresses101 Transverse hull stresses in compression may occur from:

— transverse loads and moments in twin hull craft, see Pt.3Ch.1 Sec.3 B

— supports of craft’s side structure, Sec.5 and Sec.6.

D. PlatingD 100 Plate panel in uni-axial compression101 The ideal elastic buckling stress may be taken as:

For plating with longitudinal stiffeners (in the direction ofcompression stress):

For plating with transverse stiffeners (perpendicular to thecompression stress):

σf

3-------

stability (usage) factor σaσc-----

τaτc----==

σc σel when σelσf2-----

σf 1σf

4σel-----------–⎝ ⎠

⎛ ⎞ when σelσf2----->=

<=

τc τel when τelτf2----

τf 1τf

4τel----------–⎝ ⎠

⎛ ⎞ when τelτf2---->=

<=

σelσc

KJ O–-------------- and τel

τcKJ O–--------------==

KJ O– 1σc or τc

0 5 σf or τf( ),--------------------------------- 1–⎝ ⎠

⎛ ⎞ 2–=

0.9

0.7

0.5

0.3

0.1

0.5 0.6 0.7 0.8 0.9 1.0

K J - O

σc / σf

τc / τf

or

Forσcσf----- 0 5 KJ O– 1=, ,<

σel 0 9, k E t1000s--------------⎝ ⎠

⎛ ⎞ 2N mm2⁄( )=

k kl8 4,

ψ 1 1,+------------------- for 0 ψ 1≤ ≤( )= =

DET NORSKE VERITAS


c = 1.21 when stiffeners are angles or T-sections= 1.10 when stiffeners are bulb flats= 1.05 when stiffeners are flat bars. For double bottom

panels the c-values may be multiplied by 1.1.ψ = the ratio between the smaller and the larger compres-

sion stress assuming linear variation, see Fig.2.

The above correction factors are not valid for negative ψ-val-ues.The critical buckling stress is found from A102.102 The critical buckling stress is to be related to the actualcompression stresses as follows:

σa = calculated compression stress in plate panels. With lin-early varying stress across the plate panel, σa is to betaken as the largest stress

η = 1.0 for deck, side, single bottom and longitudinal bulk-head plating

= 0.9 for bottom and inner bottom plating in double bot-toms

= 1.0 for locally loaded plate panels where an extremeload level is applied

= hG for locally loaded plate panels where a normal loadlevel is applied (e.g. plating acting as effective flangefor girders)

ηG =

Fig. 2Buckling stress correction factor

ps and pd = static and dynamic parts of p.103

Guidance note:The resulting thickness requirement, before elastic buckling, willbe:

— With stiffeners in direction of compression stress:

σc according to 102KJ—O from Fig.1.

— With stiffeners perpendicular to compressionve stress:

c according to 101.---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

104 For elastic buckling, see G.

D 200 Plate panel in shear201 The ideal elastic buckling stress may be taken as:

kt =

The critical shear buckling stress is found from A102.202 The critical shear stress is to be related to the actualshear stresses as follows:

η = 0.90 for craft’s sides and longitudinal bulkheads sub-jected to hull girder shear forces

= 0.95 % ηG for local panels in girder webs when nomi-nal shear stresses are calculated (τa = Q/A).

= ηG for local panels in girder webs when shear stressesare determined by finite element calculations or simi-lar.

ηG as given in 101.Guidance note:The resulting thickness requirement will be:

τc according to 202KJ—O from Fig.1.


D 300 Plate panel in bi-axial compression and shear301 For plate panels subject to bi-axial compression and inaddition to in-plane shear stresses the interaction is given by:

σax = compression stress in longitudinal direction (perpen-dicular to stiffener spacing s)

σay = compression stress in transverse direction (perpendic-ular to the longer side l of the plate panel)

σcx = critical buckling stress in longitudinal direction as cal-culated in 100

σcy = critical buckling stress in transverse direction as calcu-lated in 100.

τa and τcare as given in 200.

ηx, ηy = 1.0 for plate panels where the longitudinal stress σa(as given in Pt.3 Ch.1 Sec.3 A700) or other extremestress is incorporated in and constitutes a major partof σax or σay

k ks c 1 sl--⎝ ⎠

⎛ ⎞ 2+

22 1,

ψ 1 1,+------------------- for 0 ψ 1≤ ≤( )= =

σcσaη-----≥

ps 0 5 pd,+

ps pd+---------------------------

( )Cσσ ≤

ψσ

t 1 17 sσc

KJ O–-------------- (mm),=

t 2 33, s

1 sl--⎝ ⎠

⎛ ⎞ 2+

----------------------σc

cKJ O–----------------- (mm)=

τel 0 9,( )ktEt

1000s--------------⎝ ⎠

⎛ ⎞ 2N mm2⁄( )=

5 34, 4 sl--⎝ ⎠

⎛ ⎞ 2+

τcτaη----≥

t 2 33 sτc

ktKJ O–

------------------- (mm),=

σaxηxσcxq------------------ K

σaxσayηxηyσcxσcyq----------------------------------

σayηyσcyq------------------⎝ ⎠

⎛ ⎞n

1≤+–

DET NORSKE VERITAS


= 0,95 ηG in other cases.ηG as given in 101.

K = c β a

c and a are factors given in Table B1.

β =

n = factor given in Table B1.

ηt = h as given in 200.Only stress components acting simultaneously are to be insert-ed in the formula.For plate panels in structures subject to longitudinal stresses,such stresses are to be directly combined with local stresses tothe extent they are acting simultaneously and for relevant loadconditions. Otherwise combinations based on statistics may beapplied.

Guidance note:Shear in combination with:— uni-axial compression may be written:

and with— bi-axial compression, approximately:

For bi-axial compression alone q = 1.---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

E. Stiffeners in Direction of CompressionE 100 Lateral buckling mode101 The ideal elastic lateral buckling stress may be taken as:

i =

IA = moment of inertia in cm4 about the axis perpendicularto the expected direction of buckling

A = cross-sectional area in cm2.

When calculating IA and A, a plate flange equal to 0.8 timesthe spacing is included for stiffeners. The critical bucklingstress is found from A102. The formula given for σel is basedon hinged ends and axial force, only. Continuous stiffeners

supported by equally spaced girders are regarded as havinghinged ends when considered for buckling. In case of eccentricforce, additional end moments or additional lateral pressure,the strength member is to be reinforced to withstand bendingstresses.102 For longitudinals and other stiffeners in the direction ofcompression stresses, the critical buckling stress calculated in101 is to be related to the actual compression stress as follows:

σa = calculated extreme compression stress, or ordinary lo-cal load stress divided by ηG from D100

η = 0.85 for continuous stiffeners= 1– ηb, maximum 0.85, for single-span stiffeners

ηb =

Guidance note:The resulting maximum allowable slenderness will be:

σc = according to 102.

KJ—O from Fig.1.


E 200 Torsional buckling mode201 For longitudinals and other stiffeners in the direction ofcompression stresses, the ideal elastic buckling stress for thetorsional mode may in general be calculated from formulae inRules for Classification of Ships Pt.3 Ch.1 Sec.14.202 The critical buckling stress as found from 201 and A102is not to be less than:

σa = calculated extreme compression stress, or ordinary lo-cal load stress divided by ηG from D100

η = 0.85 in general. = 0.8 when the adjacent plating is allowed to buckle in

the elastic mode, according to G.

Guidance note:FlatsTo avoid torsional buckling the height of flats should not exceed:

tw = thickness of web in mmσc = according to 202

KJ—O from Fig.1.

Flanged profiles

Minimum flange breadth may be taken as:For symmetrical flanges:

Table B1 Factors a, c and n c a n

1,0 < l/s < 1,5 0,78 – 0,12 1,01,5 ≤ l/s < 8 0,80 0,04 1,2

1000st--

σfE-----

q 1τa

ηττc-----------⎝ ⎠

⎛ ⎞2

–=

σaxσcx-------- or

σayσcy-------- ηx or ηy( ) q≤

σaxηxσcx--------------- 1 1,

σayηyσcy--------------- 0 8,

ηxηy------------

σaxσcx--------

σayσcy-------- q≤–+

σel 10 E

100 li-⎝ ⎠

⎛ ⎞ 2--------------------- N mm2⁄( )=

IAA-----

σcσaη-----≥

simultaneous bending moment at midspanbending capacity.

-----------------------------------------------------------------------------------------------------

100 li- 1435

KJ O–

σc--------------=

σcσaη-----≥

hw tw245

σcKJ O–--------------

------------------- (mm)=

1hwbf------ 3:< <

DET NORSKE VERITAS


For unsymmetrical flanges:

σc = according to 202KJ—O = according to Fig.1hw = height of web in mm.


E 300 Web and flange buckling301 The σel-value required for the web buckling mode maybe taken as:

tw, hw=web thickness and height in mm

302 The ideal elastic buckling stress of flange of angle andT- stiffeners may be calculated from the following formula:

tf = flange thickness in mmbf = flange width in mm for angles, half the flange width for

T-sections.

303 The critical buckling stress σc found from A102 is notto be less than as given in 202.

Guidance note:

— For web thickness, see plating with stiffener in direction ofcompression stress, D103.

Flange width from web:

σc = according to 202KJ—O = according to Fig.1.


F. Stiffeners Perpendicular to Direction of Com-pression

F 100 Moment of inertia of stiffeners101 For stiffeners supporting plating subjected to compres-sion stresses perpendicular to the stiffener direction, the mo-ment of inertia of the stiffener section (including effectiveplate flange) is not to be less than:

l = span in m of stiffeners = spacing in m of stiffenerst = plate thickness in mm

σel =

σc =

σa = actual extreme compression stress, or ordinary localload stress divided by ηG from D100

KJ—O = according to Fig.1.

G. Elastic Buckling of Stiffened PanelsG 100 Elastic buckling as a design basis101 Elastic buckling may be accepted for plating betweenstiffeners when:

— plating

— η σc of stiffener in direction of compression > η σel ofplatingη σc from E and A102. To be multiplied by η G for ordi-nary local loadη σel from D and A102

— there are no functional requirements prohibiting the de-flections

— extreme loads are used in the calculations.

Guidance note:The torsional buckling mode of flats may be taken as:


G 200 Allowable compression201 The allowable compression force in the panel may be in-creased from:

PA = 0.1 ηp σel (Ap + As) (kN)to:

PA = 0.1 ηp σel (Ap + As)+

ηp, ηs = η for plating and stiffener from D and E. ηs to bemultiplied by ηG for ordinary local load

σel σc = for plating and stiffener, respectively, from D and E.Ordinary effective flange is to be used for stiffeners

Ap, As = area of plating and stiffener in cm2.

= fraction of Ap participating in the post-bucklingstress increase

=

σu = ultimate average stress of plating

=

202 For transversely stiffened plating (compression stressperpendicular to longest side l of plate panel) is:

bf 3lσc

KJ O–-------------- (mm)=

bf 2lσc

KJ O–-------------- (mm)=

σel 3 8, Etwhw------⎝ ⎠

⎛ ⎞2

N mm2⁄( )=

σel 0 38, Etfbf----⎝ ⎠

⎛ ⎞2

N mm2⁄( )=

bf tf245

σcKJ O–--------------

------------------- (mm)<

I0 09, σaσel l4s

t------------------------------------ cm4( )=

σcKJ O–--------------

σa0 85,------------

σelσf2----- i.e. σel σc=,<

σel 0 385, Etwhw---------⎝ ⎠

⎛ ⎞2

N mm2⁄( )=

0· 1 ηsσc ηpσel–( )beb-----Ap As+⎝ ⎠

⎛ ⎞ (kN)

beb-----

σ σel–uσ σel–f-----------------

σel 1 0 375σfσel------- 2–⎝ ⎠

⎛ ⎞,+

DET NORSKE VERITAS


c =

As = 0

resulting in:PA = 0.1 ηp σu Ap (kN).

203 σu may be substituted for σel when calculating bi-axialcompression and shear in D300.

H. GirdersH 100 Axial load buckling101 For lateral, torsional, web and flange buckling, see E.

H 200 Girders perpendicular to direction of compres-sion201 For transverse girders supporting longitudinals or stiff-eners subject to axial compression stresses, the ideal elasticbuckling stress may be taken as:

The critical buckling stress σc is found from A102.

S = span in m of girderl = distance in m between girderss = spacing in m of stiffenersIa = moment of inertia of stiffener in cm4

Ib = moment of inertia of transverse girder in cm4

t = plate thickness in mmta = equivalent plate thickness of stiffener area in mm

(smeared out thickness of stiffener).

202 The critical buckling stress found from 201 and A102 isnot to be less than:

σa = calculated compression stressη = 0.75.

H 300 Buckling of effective flange301 Plating acting as effective flange for girders which sup-port crossing stiffeners should have a satisfactory bucklingstrength.302 Compression stresses arising in the plating due to localloading of girders are to be less than ηG x critical bucklingstrength, see 303. When calculating the compression stress thesection modulus of the girder may be based on a plate flangebreadth equal to the distance between girders (100 % effectiveflange).ηG as given in D100.303 The critical buckling strength is given in D101 andA102, when l = span of stiffener or distance from girder tobuckling stiffener parallel to the girder, if any.304 Elastic buckling of deck plating may be accepted afterspecial consideration. Reference is made to G.The additional PA and the corresponding additional momentcapacity, will, however, refer to a girder section with effectivewidth of deck plating = be.

H 400 Shear buckling of web401 See D200, for constant shear force over l.

Guidance note:For variable shear force over l of panel considered, a reduced lmay be considered in formula.


σu σel 1 cσfσel------- 2–⎝ ⎠

⎛ ⎞+=

0 75,ls-- 1+------------

σel 4 12, π2

S2 t ta+( )-----------------------

IaIbsl

----------- N mm2⁄( )=

σcσaη-----≥

DET NORSKE VERITAS

DNV HSLC rules Pt.3 Ch.2 - Hull Structural Design, Steel

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Transcript of DNV HSLC rules Pt.3 Ch.2 - Hull Structural Design, Steel