DUBAI RAPID LINK CONSORTIUM -...

DUBAI RAPID LINK CONSORTIUM

WS Atkins & Partners Overseas

Dubai Metro Project

RED LINE

Viaducts Design Basis Report

November 2007

ATKINS

Date: 7 November 2007 Document No.: DM001-E-ACW-CVI-DR-DCC-310001

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DUBAI METRO PROJECT

VIADUCT - DESIGN BASIS REPORT

W S Atkins & Partners Overseas

Verification Ref:

Revision Status Originated By

Checked By

Verified By Issued By Date Issued Issued To

A Draft M. Badcock A. Shaw J. Baber M.Badcock

29 July 2005

JT Metro JV

B Draft M. Badcock

A. Shaw J. Baber M.Badcock 5 August 2005

JT Metro JV

C Working M. Badcock A. Shaw J. Baber M.Badcock

12 August 2005

JT Metro JV

D For Comment

M. Badcock A. Shaw J. Baber M.Badcock

15 August 2005

JT Metro JV

A1-01P Draft G. Ziadat A. Shaw J. Baber G.Ziadat 30 Nov 2005

JT Metro JV

A1-02A For Approval

G. Ziadat A. Shaw J. Baber G.Ziadat 30 Dec 2005

JT Metro JV

B1-02B Draft M Chubb C Hendy

A5 For approval

M Chubb C Hendy G.Ziadat J.Sundaram 24 July 2006

JT Metro JV

A6 For approval J.P.Sagar

J. Sundaram J.Sundaram

7 Nov 2007

JT Metro JV

DUBAI METRO PROJECT Dubai Rapid Link

DUBAI RAPID LINK CONSORTIUM DUBAI METRO PROJECT OFFICE

Contract No.: DM001 CDRL No.: Project Title: DUBAI METRO

CDRL Title:

Document Title:

Viaduct – Design Basis Report

Revision History A6 7/11/07 Atkins update for approval A5 21/7/06 Atkins update for approval A3 23/6/06 Atkins update B1-05B

23-05-06 Atkins internal update A1 28-12-05 For Approval D 15-8-05 First Issue Signed below Signed below

MARK DATE DESCRIPTION RAIL CIVIL

Project Director T. Uneda APPROVED

Deputy Project Director S. Sasaki

Checked By (QA/QC Manager)

Checked By (Safety Manager)

Checked By Checked By (Project Manager)

Checked By Checked By (Design Manager)

Prepared By Prepared By

DATE DATE 21 July 2006

RAIL SYSTEM CIVIL JV

CONTRACTOR’S DOCUMENT No.:

DOCUMENT No.:

DM001/E-ACW-CVI-DR-DCC-310001

REVISION

A6

DUBAI METRO PROJECT ATKINS


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CONTENTS 1. INTRODUCTION 5 2. MATERIALS 6 3. DESIGN CRITERIA 11 4. EARTHQUAKE DESIGN 24 5. RAIL/STRUCTURE INTERACTION 28 6. DEFORMATIONS 30 7. GEOTECHNICAL 32 8. DESIGN METHODS 38 APPENDICES A. SCHEDULE OF DESIGN STANDARDS 43 B. LOAD COMBINATIONS 45 C. DESIGN RAIL VEHICLES 47 D. RAIL CLEARANCES 49 E. DECK SECTION AND TRACKFORM DIMENSIONS 52 F. EQUIPMENT ON DECK 56 G. MOMENT ROUNDING AT SUPPORTS 59 H. DIFFERENTIAL TEMPERATURE GRADIENT 61 I. TYPICAL GLOBAL RAIL/STRUCTURE INTERACTION MODEL 63 J. TYPICAL EARTHQUAKE INERTIA LOADING ANALYSIS MODEL 65



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INTRODUCTION

1.1 This design basis report sets out the parameters and assumptions used in the design of the viaduct structures for the Dubai Metro project.

1.2 This report is to be applied to the design of the viaducts for the Red Route and covers

the viaduct decks, piers, abutments and foundations, but excludes the trackform. 1.3 The viaduct superstructures consist of the following forms: Simple Spans. Simply supported U-section decks constructed using post tensioned

segmental construction by the ‘span by span’ method from an overhead gantry. Twin Span Continuous. Two span continuous U-section decks constructed using post

tensioned segmental construction by the ‘span by span’ method from an overhead gantry and the stitching of both spans together to form a continuous structure.

Three Span Continuous. Three span continuous structures comprising a combination

of U-section and Box-section precast post tensioned segmental decks, erected by crane using the balanced cantilever method.

Station spans. Three or four span continuous U-section decks constructed using post

tensioned segmental construction by the ‘span by span’ method from an overhead gantry and the stitching of both spans together to form a continuous structure

Single Track Decks. Simply supported U-section decks constructed using precast post

tensioned segments erected by the ‘span by span’ method from an overhead gantry (similar to Simple Spans)

Special Structures. Simply Supported and continuous post tensioned or reinforced

insitu concrete decks of variable geometry.

Segments are cast either using long line or short line moulds. Straight simply supported, twin spans and Station spans with a horizontal radius below 2000m are generally cast flat and straight using long line moulds and erected as a series of straight chords between piers. Curved spans are cast wider than straight spans using short line moulds to follow the horizontal curvature down to 300 m radius for twin tracks and 250m radius for single tracks, but cast as a series of straight chords for vertical alignment to simplify construction. 3-span continuous deck segments are cast with a constant width to follow both the horizontal and curved alignments using short line moulds. Minimum vertical curve radius is 1250m.

1.4 The viaduct substructures will generally comprise reinforced concrete piers with wider

pier caps to support the deck and reinforced concrete abutments. Pier heads for simple, twin spans, station spans and some special spans are constructed using precast thin reinforced concrete shells infilled with insitu concrete and prestressed in stages. For single track spans and 3-span continuous internal piers pierheads are of insitu reinforced concrete. Piers and abutments will be founded on large diameter bored pile foundations.

1.5 This report does not consider the at grade sections on the approaches to the viaducts,

or the embankments retained by retaining walls behind the abutments. Consequently, this report does not cover the requirements for transition structures on the approaches to the viaducts. Measures to control differential movements and the effects of



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variations in structural support stiffness are described in a separate Design Basis Report (Ref. 1).

1.6 Stray current and civil earthing systems will be provided on the viaducts but these

requirements are subject to a separate Design Basis Report (Ref 2). 1.7 The Designer has obtained the Engineer’s agreement to use BS5400 as the design

code for the viaducts instead of AASHTO LFRD subject to the Engineer retaining the right to refer to AASHTO general requirements. This agreement is documented in the Engineer’s Comments on the Viaducts Design Basis Review Doc No DM001-E-ACW-CV1-DR-DCC-310001-D.

1 MATERIALS 2.1 Concrete

The following concrete grades will be used

Structural Element Grade (fc’) Grade (fcu) E (short term) Cylinder

Strength Cube Strength

Modulus of Elasticity

Superstructures Precast - 3 Span Precast 44/44 straight Precast 44/44 curved Precast 36m curved Precast Type 1 station deck Precast – Other Insitu continuity stitches: Precast 44/44 straight Precast 44/44 curved Type 1 station deck Insitu Structures

48 N/mm2

48 N/mm2 56 N/mm2 48 N/mm2 48 N/mm2 40 N/mm2

48 N/mm2 56 N/mm2 48 N/mm2 40 N/mm2

60 N/mm2 60 N/mm2 70 N/mm2 60 N/mm2 60 N/mm2 50 N/mm2

60 N/mm2 70 N/mm2 60 N/mm2 50 N/mm2

36 kN/mm2

36 kN/mm2 38 kN/mm2 36 kN/mm2 36 kN/mm2 34 kN/mm2

36 kN/mm2 38 kN/mm2 36 kN/mm2 34 kN/mm2

Piercaps and Bearing Plinths 40 N/mm2 50 N/mm2 34 kN/mm2 Pier Columns (3-span internal piers)

40 N/mm2 50 N/mm2 34 kN/mm2

Other Pier Columns 32 N/mm2 40 N/mm2 31 kN/mm2 Abutment walls, Bases and Pile Caps 32 N/mm2 40 N/mm2 31 kN/mm2

Piles 32 N/mm2* 40N/mm2* 31 kN/mm2

Table 2.1 Concrete strengths

* Allowance has been made for the loss of strength due to placement of the concrete under drilling fluid. Design strength, fcu of 50 and 40 N/mm2

is the characteristic strength before and after placement respectively. The long term modulus of elasticity shall be taken as half the short term modulus where appropriate. Where required by design constraints a higher concrete grade may be used. The higher grade shall be recorded in the design calculations and final drawings.



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Unit weight of reinforced concrete See Section 3.2

Coefficient of Thermal Expansion 10.8 x 10-6

/ ºC The following table provides the design crack widths and nominal covers to be used in the Design and specified for construction. The nominal design crack widths and nominal design cover values specified are based on BS5400 Pt.4 Tables 1 and 13 respectively: Structural Element

Environment Nominal Design Nom. Specified

Nominal Design

Crack width Cover Cover

Superstructures Precast - 3 Span Precast – Other Insitu Structures

Considered for all these decks as Severe to Very

Severe

0.20 mm 0.20 mm 0.20 mm

40 mm 40 mm 50 mm

35 mm 35 mm 35 mm

Piercaps and Bearing Plinths

Severe to Very Severe

0.20 mm 50 mm 35 mm

Pier Columns Severe to Very Severe

0.20 mm 50 mm 40 mm

Pier Bases and Pile Caps

Severe 0.20 mm 100 mm 45 mm

Piles Severe 0.20mm 125 mm 45 mm

Table 2.2 Design crack widths and concrete cover The environment for the piers and abutment walls above the maximum ground water level, along with all the above ground concrete, including the decks, are assumed to be an intermediate classification between a severe and very severe environment. The benefits of the concrete coating system will be ignored in the design. A tanking system will be applied to the pile cap below ground level in order to provide added protection. This will be in addition to the cover requirements given above.

The pier and abutment bases, are to be waterproofed with a proprietary waterproofing system For the piles the concrete will be of a low permeability C50 concrete mix approved by the Engineer. In addition 125mm cover is specified throughout its length and a severe environment is assumed for crack width and nominal design cover calculation. Up to 3 m above ground level (or top of column) columns shall also be coated with a sprayed water proofing membrane to minimise evaporation of water from exposed concrete surface and upward draw of saline water from below ground.

This clarifies the approach to be taken with Tables 1 and 13 of BS 5400 Part 4. It is proposed to use the recommendations of the Concrete Society Technical Report TR49, “Design for High Strength Concrete” to allow for the increased concrete strength

above the 40 N/mm2

limit adopted in some clauses of BS 5400 Part 4. This makes the best use of the available concrete capacity. Exposed concrete surfaces (decks, pier and abutment stems) shall be treated with an elastomeric coating system, with a weather resistant top surface and a penetrating



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primer. The coating shall provide in-depth protection against corrosion associated with the ingress of chloride and sulphate ions, carbon dioxide and other air-borne acid gasses, and shall have the ability to allow water vapour to escape from the surface. The coating will be non-slip over the walkway on top of the deck edge beams.

2.2 Steel Reinforcement

Hot rolled reinforcement to BS 4449: 1997 will be specified with the following properties:

Type Designation Characteristic Strength

Elastic Modulus

Mild Steel R 250 N/mm2 200 kN/mm2

High Yield Deformed Type 2 T 460 N/mm2 200 kN/mm2

Table 2.3 Reinforcement types 2.3 Prestressing Steel

The prestressing steel shall be ASTM A416-85 seven-wire strand, relaxation class 2. Ducts to be galvanised steel. The requirements for the temporary prestressing applied to the segmental joints during the curing of the epoxy glue will be determined by the viaduct superstructure subcontractor.

The following parameters will be used in the design of the permanent prestressing:

Nominal diameter of strand 15.24 mm

Nominal cross-sectional area of strand 140 mm2

Ultimate tensile strength of strand 1860 N/mm2

Minimum Breaking Load of strand 260.7 KN

Elastic modulus (circa) 195,000 N/mm2

Coefficient of friction (µ) 0.20

Wobble coefficient (k)* 0.0010 /m

Wedge draw-in at anchorage 6 mm (max.)

Relaxation (after 1000hr at 20ºC & 70% of breaking load) 2.5 %

* The tendon support spacing shall be consistent with the assumed design



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wobble factor.

The force in the prestressing tendons at the anchorage immediately prior to lock-off shall be limited to 75% of the guaranteed ultimate tensile strength (GUTS). The jacking force is to account for any jack losses. Relaxation losses will be adjusted for 28°C and the % of breaking load after lock-off. None of the prestress tendons will be designed to be replaceable.

All the ducts will be grouted with cementitous grout.

2.4 Assumed Prestressing System Dimensions

Tendon Size

No Strands

Application Duct Diameter Internal/External

Minimum Breaking Load

Anchorage Bearing Size (mm)

4T15 4 3 Span Deck (transverse)

45/50 mm 1043 kN 150 x 150

12T15 12 Simple, Single Track, Special , 2 Span and 3 Span Decks

80/87 mm 3128 kN 250 x 250

13T15 13 3 Span Decks 95/102 mm 3389 KN 310 x 310 18T15 18 3 Span Decks 100/107mm 4693 kN 310 x 310 19T15 19 Pier Crossheads 100/107mm 4953 kN 310 x 310 22T15 22 Pier Crossheads 100/107mm 5735 kN 310 x 310

Table 2.4 Prestressing system details

2.5 Bearings

The bearings supporting the viaduct superstructures will be either pot or elastomeric bearings. The continuous span structures will use only sliding pot bearings. Elastomeric bearings will be in accordance with BS 5400 Part 9, 1983 and the following shear modulus values shall be provided:

G = 0.9 N/mm2

for static conditions (permanent loads)

G = 1.8 N/mm2

for short term loading conditions (live and earthquake loads)

The elastomer shall not have a nominal hardness value greater than 60.

Where transverse forces on elastomeric bearings exceed 10% of the vertical load, as is expected in all cases, the bearings shall be fitted with an interfacing chequered plate to provide a minimum coefficient of friction of 0.5 between mating surfaces. This attachment shall be capable of carrying the entire transverse load. Pot bearings will be provided with a PTFE sliding surface and will be designed and specified in accordance with BS 5400 Part 9, 1983. The corrosion protection system



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shall be in accordance with the Contract Specification. All bearings shall provide electrical isolation between the deck and substructure. 2.6 Expansion Joints

No cover plate will be provided across the gap between decks, but a galvanised chequered cover plate will be provided across the gap in the emergency walkways. This plate will be fixed on one side and will not be recessed into the concrete surface but will be detailed to avoid becoming a tripping hazard to passengers and maintenance personnel.

2.7 Segmental Joints

The joints between the match cast precast concrete deck segments shall be formed with shear and location keys during precasting and filled using an appropriate epoxy glue during erection.



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3 DESIGN CRITERIA 3.1 Design Standards

The design will be carried out in accordance with the technical standards listed in Appendix A. The design will be based on BS 5400 and the associated British Standards, with additional International Standards introduced to supplement the scope in such areas as earthquake loading and rail dynamic factors. The load combinations used in the design are given in Section 3.23 and provided in Appendix B.

3.2 Dead Loading (DL)

Dead loads will include the weights of the materials and parts of the structure that are structural and permanent in nature. The following unit weights of materials will be assumed:

Material Description Characteristic Density (kN/m3)

Reinforced concrete 24.5 Concrete

Mass concrete 22.0 Steel Structural, Prestressed and

Ordinary Reinforcement 77.0

Table 3.1 Dead loads

3.3 Superimposed Dead Loading (SDL)

Superimposed dead loads include all the weights of materials on the structure that are not structural elements but are permanent. The major part of the superimposed dead loading is the weight of the trackform plinths. Details can be seen in Appendix E. The remainder of the loading is the equipment on the deck, and details of these are provided in Appendix F. The allowance per m run of deck is as follows for each deck type:



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Description Mainline (Twin Track) Load

Mainline (Single Track) Load

Mainline (Turnout) Load

kN / m run / deck kN / m run / deck kN / m run / deck Trackform plinths (Straight)+ 23.0 16.9 48.0 Trackform plinths (Canted)+ 27.9 15.4 - Running rails and fixings 2.9 1.5 3.9 Third rail, supports & fixings 1.0 0.5 1.0 Cables trays and cables 5.9 2.9 5.9 Handrails 0.6 0.6 0.6 Soffit lighting* 1.2 - - Miscellaneous equipment 0.4 0.3 0.5 Total (Straight Track to R=2000m)+ 35.0 17.3 59.9

Total (Canted Track to R=250m)+ 39.9 19.6 -

* Soffit lighting only applies to simple and 2 span continuous twin track decks for 6.23 km of twin track viaduct, the location of which is yet to be agreed with the Client.

+ For simple twin–deck spans additional trackform weights shall be added to account for camber and alignment vertical curvature where the deck is precast on flat long-line beds as follows (Maximum vertical curvature of R=1250m is assumed until span arrangements and alignment are fixed) :

Table 3.2 Superimposed dead loading The allowance per m run of deck for station structure are: Description

T1 & T2 Stations (Twin Track) Load

T3 Stations

(Single Track – Middle ) Load

T3 Stations

(Single Track - Side) Load

kN / m run / deck

kN / m run / deck

kN / m run / deck

Trackform plinths (Straight)

30.8

16.9

16.9

Platform Finishes 14.5 14.8 11.2

Platform Screen Doors 5.0 5.0 2.5

Running rails and fixings 2.9 1.5 1.5

Third rail, supports , fixings 1.0 0.5 0.5

Cables trays and cables 8.0 4.0 4.0

Handrails 0.75 0.75 0.75

Soffit lighting / Cladding 2.0 1.0

1.0

Miscellaneous equipment 2.0 1.0 1.0

Total 67.0 44.0

38.0

Table 3.3 Superimposed dead loading on viaduct dec k for overground stations

(excluding concourse level loads in Type 2 stations )



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Description 28m Span 32m Span 36m Span 44m Span

kN / m run / deck kN / m run / deck kN / m run / deck kN / m run / deck Additional Trackform Average Weight due to Camber

0.3 0.4 0.8 1.2

Additional Trackform Average Weight due to Vertical Curvature

3.0 3.9 5.0 12.2

Maximum (not additive)

3.0 3.9 5.0 12.2

Table 3.4 Additional trackform weights for Simple twin–track decks precast

on flat long line beds.

Description


0.38 0.5 1.0 -


0.38 0.5 1.0 -

Table 3.5 Additional trackform weights for Station span twin–track decks precast

on flat long line beds.

Description


0.15 0.2 0.4 0.6

Additional Trackform Average Weight due to Vertical Curvature

1.5 1.95 2.5 6.1


1.5 1.95 2.5 6.1

Table 3.6 Additional trackform weights for Simple single-track decks precast

on flat long line beds. 3.4 Vertical Train Loading (VTL)

The Red Route is to operate with 5 car trains from the outset. However, the Green Line will start to operate with 3 car trains, which will be upgraded to 4 then 5 car trains as patronage increases. The variable sized trains operating on the Green Route will use the Red Route from Union Square to the Main Depot. There is also the possibility that the Green Line trains



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may use the remainder of the Red Route to the small depot at the south end of the scheme. It is therefore considered necessary to design the whole of the Red Route for 3, 4 and 5 car trains. Details of the maximum axle loads and spacing for the various train configurations specific to this scheme are given in Appendix C. The choice of vehicle and position of the vehicle will be chosen to produce the most adverse effect on the structure. The assumed axle load for all train axles is 140 kN. This is based on the AW4 load case of gross vehicle weight including the maximum passenger capacity. The loading from maintenance vehicles and low loaders carrying equipment required along the route will not be of a magnitude to be critical for the design.

3.5 Rail Vehicle Dynamic Impact Factor (DIF)

The American Concrete Institute technical design standard ACI 358.1R-92, Analysis and Design of Reinforced and Prestressed Concrete Guideway Structures (Chapter 3 - Loads, pg. 358. 1R-15), will be used for determination the dynamic factors to be applied to the vertical train loading for longitudinal design, except for the simply supported spans where they are to be derived by dynamic analyses for the respective span lengths. As stated in the code Cl.3.3.1.2 the DIF will not be applied to design of viaduct foundations. The maximum operating speed of the rolling stock will be taken as 90 kph and the Design Speed shall be taken as 100 kph. For transverse design, the recommendations of BS 5400 Part 2 Cl 8.2.3.2 for RL Loading will be applied. This gives a dynamic factor of 1.2, which needs to be increased to 1.4 for the design of the floor slab supporting just a single track. These values are to be verified using a Finite Element Analysis.

3.6 Longitudinal Rail Forces (braking and traction) (LF)

The longitudinal rail forces at rail level are applied parallel with the tracks at the axle locations in accordance with the recommendations of BS 5400 Part 2

The positions of the driving/braking axles are given in Appendix C. The Traction force per axle is 27.5 kN and Braking force per axle is 20.0 kN, based on loads supplied by the DURL Rail System Designer. ( Note: MHI to provide a basis for these figures)

For twin tracked decks carrying traffic in opposite directions, consideration should be given to braking forces from one train and traction forces from another, acting simultaneously to maximise the longitudinal loading on a deck. Additionally consideration should be given to braking or traction acting in opposite directions to produce rotational effects. Allowance is also made for one train pushing or pulling a broken down train.

3.7 Centrifugal Forces (CF)

When the track is curved, centrifugal load will be considered. The centrifugal force acting radially 1.8m above rail level will be determined in accordance with Cl 8.2.9 of BS 5400 Part 2, assuming a maximum design speed of 100 kph, reducing with cant and a distributed load of 33 KN/m based on actual train loading. For calculation of “f” value the statement “ for L greater than 2.88m and vt less than 120km/h” will be amended to “for L greater than 2.88m and vt greater than 120km/h” as corrected in BD37/01.



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Where there are twin tracks, centrifugal loading should be considered from rolling stock on both tracks.

For sections of track with radius in plan less than 400 m, the design speed for calculation of centrifugal forces shall be reduced as follows: Plan radius ≥ 400 m, design speed = 100 kph Plan radius = 350 m, design speed = 90 kph Plan radius = 300 m, design speed = 80 kph Speeds for intermediate radii may be interpolated.

3.8 Nosing (Hunting Forces) (NF)

The nosing load shall be determined in accordance with Cl 8.2.8 of BS 5400 Part 2 for RL Loading. A single 100 kN nominal load is required to be taken horizontally at rail level at right angles in either direction to the track at a point to cause the most severe effect. For multi track decks only one load is required to be applied.

3.9 Lurching (LU)

Lurching effects should be determined in accordance with Cl 8.2.7 of BS 5400 Part 2 for RL Loading. Lurching results from temporary transfer of part of the railway vertical live loads from one rail to another, the total track load remaining unaltered.

To account for lurching effects on single and two track structures, 0.56 of the vertical train load should be considered as acting on one rail concurrently with 0.44 of the vertical train load on the other rail. This redistribution of load need only be considered on one track where members support two tracks. This variation in distribution of the vertical train loads is only considered for local transverse design of the track support element. This variation does not require consideration in the longitudinal direction. Lurching can be ignored for elements supporting more than two tracks. It may also not be required for elements supporting two tracks providing that a Finite Element Analysis is carried out to demonstrate the actual transverse behaviour.

3.10 Derailment Loading (DF)

The derailment containment is generally provided by the trackform support plinths and the walkway upstand, which restrain the train transversely and prevent it from derailing off the tracks. No load cases will be considered therefore for a train displaced transversely off the track as this displacement will be minimal and the stability of the deck is not an issue.

The design of the trackform plinths falls outside the scope of this report, as the works are part of the trackwork, rather than structure. Account will be taken of the transfer of these loads from the trackform into the structure and down through to the supports, pier and foundations.

The derailment loading in BS 5400 Part 2 applies a series of displaced vertical loads,



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but no horizontal loads. In our situation the train vehicles will be held in position by the track plinths and by the deck upstands. Therefore, this loading is not applicable as the displacements proposed are not possible and the derailment effect is only the horizontal load component caused by the tilting of the train.

Consequently, it is proposed to use the derailment loading from the American Concrete Institute technical design standard ACI 358.1R-92, Analysis and Design of Reinforced and Prestressed-Concrete Guideway Structures. The loading from Cl 3.5.2 of ACI 358 shall be applied to the deck upstands.

The horizontal derailment load applied to the deck upstands will be taken as 50% of the maximum car weight applied to a 5m length of deck at axle level. For the most heavily loaded car which has 4 axles of 140 kN each, this amounts to a nominal force of 280 kN applied over a 5m length.

The maximum eccentricity of a derailed train from the tracks will be assumed to be 250mm and this should be considered in conjunction with the horizontal derailment load.

3.11 Walkway and Platform Loading (WL)

In the Station viaducts Platform loading of 5kN/m2, over 3m width per web shall be considered.

A load of 4 kN/m2

shall be applied on the upper surface of the deck upstands (emergency walkways) within the handrails. As this is an emergency condition of a broken down train, this will only be considered in conjunction with a static unloaded train (no passengers and no dynamic impact factor) located on the track adjacent to the loaded emergency walkway. Rail loadings on any remaining tracks will be unaltered. For loaded lengths greater than 30m the pedestrian loading will be reduced in accordance with Cl 7.1.1 and 7.2.1 of BS 5400 Part 2.

Loads on the deck upstands which constitute part of the station platforms will include the loads from the Platform Screen Doors, accounting for pressure from crowd, and air pressure from ventilation, air conditioning and the passing trains. 3.12 Temperature (TC, TD)

The temperature range from the records of recording station No 41194 at Dubai International Airport for the period of 1984 to 2001 shows a maximum recorded range of 7.4ºC to 47.5ºC.

Provisions shall be made for stresses and movements resulting from uniform temperature expansion / contraction. A temperature rise of +43°C and a temperature fall of -32°C shall be considered.

A positive temperature gradient of 20ºC and a reverse temperature difference of 10°C shall be considered between the top and bottom surfaces of the deck for both the U-Section and Box-girder decks, as shown in Appendix H. Only the effects of the moment generated by this gradient will be considered, the axial effects will be determined by the temperature changes mentioned above. Temperature gradient effects shall only be considered at the seviceability state under load combination 3 with a partial safety factor



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of 0.6, as shown in Appendix B. During construction, a positive gradient of 15ºC and a reverse temperature difference of 7.5ºC shall be considered to reflect the short term nature of the construction condition. The positive temperature gradient cannot co-exist with the maximum temperature rise and the reverse temperature gradient cannot occur with the maximum temperature fall and these combinations shall not be considered. In the stations, the decks are enclosed by the station structures and therefore will not be subjected to the above temperature gradients in the operating condition after construction of the stations has been completed.

As the effects of peak rise and fall temperatures are a long term phenomenon, an elastic modulus of 75% of the short elastic modulus will be used for the temperature rise and fall analysis. The short term elastic modulus will be used for the temperature gradients.

3.13 Bearing Friction (BF)

The maximum coefficient of friction for the sliding pot bearings shall be taken as 5% of the applied permanent vertical load. When considering the differential friction from bearings either side of fixed pier(s) the friction on one side will be taken as 5% and on the other side 2.5%. These values will be confirmed upon availability of test data from the chosen bearing supplier / manufacturer. This assumes that both bearings are replaced at the same time. The minimum friction shall be taken as 0.5%.

3.14 Differential Settlement (DS)

The design longitudinal differential settlement between any adjacent piers will be:

• between piled foundations 5mm • between any piers with spread foundations 15mm • between a pier with a piled foundation and a pier with spread foundation 20mm.

These values will be confirmed based on the findings of the Ground Investigation and the actual viaduct loading.

Note it is generally not proposed to use spread foundations on any continuous structures. Differential settlements are not considered in the design of any simply supported structures. The short term settlement of the pad foundations from the loading during construction is not considered as it will be built out in the simple spans. In the transverse direction, a construction tolerance of 2mm will be assumed between the bearings on either side of the pier cap for the U- section decks. A differential settlement of 1mm will be considered in the transverse direction post construction, for the rail alignment. Combinations of differential settlement movements shall be considered on one or more piers to produce the most adverse effect on the deck and piers.

Differential settlements between the stations and viaduct shall be established based on



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serviceability requirements and the capacity of the interface movement joints. Differential settlement is a long term effect and a long term elastic modulus will be used in the design, equal to half the short term modulus.

3.15 Wind Loading (WL)

The wind loading shall be determined in accordance with BS 5400 Part 2 1978 assuming a mean hourly wind speed of 30 m/s. This corresponds to a 3 second gust speed of 45m/sec on the standard span decks. Wind loads shall be determined on the deck, piers and rail vehicle. In addition, the wind loading on the Type 2 Stations will be carried by the shared substructure. Maximum wind load to be applied to the train travelling on the deck is to be based on a maximum gust speed of 115km/hr. The height of the rail vehicle is assumed to be 3.84m above the rail level, with the lower 1m masked by the deck. For wind with Live Load, the train design has been based on a maximum operating gust wind speed of 32 m/s. This value shall be adopted in the design for a loaded structure. Wind loading shall be applied in the transverse (PT), longitudinal (PL) and vertical (PV) directions in the following combinations:

PT alone

PT in combination with ± PV

PL alone 0.5PT in combination with PL ± 0.5PV

In determining the maximum and minimum wind gust speeds the following values will be adopted:

K1, coefficient for return period = 1.0, for a return period of 120 years and K1 = 0.85 for the reduced return period applicable to the construction period

K2, hourly speed factor is to be taken from Table 2 of BS5400 Part 2.

S1, funnelling factor = 1.0

S2, gust factor to be taken from Table 2.

The deck will be assumed to of the single box or slab, with sloping sides type as shown in Figure 3 of BS 5400 Part 2.

3.16 Earthquake Loading (EL)

Earthquake loading is not included in BS 5400, so reference is made to AASHTO LRFD for Seismic Loading. Refer to Section 4 of this report for further information. Seismic loading will not be considered during construction.



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3.17 Collision Loads from Road Vehicles (CL)

Collision of road vehicles with the deck and the piers will be considered in accordance with the UK Highways Agency technical document BD 60/04, The Design of Highway Bridges for Vehicle Collision Loads. Bridge supports within the central reservation or a verge/footway adjacent to a highway shall be designed for collision loads. Bridge supports within 4.5m of the edge of a major carriageway will be designed for impact loading as follows:

Load normal to the Load parallel to the Point of application to the adjacent carriageway adjacent carriageway Pier

Main load At the most severe point component between 0.75m and 1.5m 500 kN 1000 kN above the adjacent carriageway or ground level

Residual At the most severe point load between 1m and 3m above component 250 kN 500 kN the adjacent carriageway or ground level

Table 3.7 Collision forces for piers within 4.5m of a carriageway

Bridge supports greater than 4.5m from the edge of a major carriageway with a safety fence, or adjacent to a minor road will be designed for the requirements of BS 5400 Part 2 Cl 6.9, as follows:

Load normal to the Load parallel to the Point of application to the adjacent carriageway adjacent carriageway Pier

Main load 150 kN 50 kN 0.75m above the adjacent component carriageway or ground level

Residual 100 kN 100 kN 3m above the adjacent load carriageway or ground level component

Table 3.8 Collision forces for piers more than 4.5m from a carriageway

The piers will be capable of resisting the main and residual load components acting simultaneously. Loads normal to the carriageway are to be considered separately from loads parallel to the carriageway.



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For decks (and pier caps) with headroom less than 0.4m above the minimum headroom requirement, vehicle collision loads on the superstructure will be considered. The headroom is measured over the carriageway and adjacent verges and should include allowance for any sag deflection of the structure, as given below:

Highway Minimum Headroom Minimum Headroom below For Roads crossing above which Collision Loads applied

Sheikh Zayed Road 6.0 m 6.4 m

Others 5.5 m 5.9 m

Table 3.9 Deck headroom clearance requirements.

Vehicle Collision Loads on the superstructure and pier caps are set out below:

Table 3.10 Deck collision loads if clearance is le ss than 0.40 m than minimum requirement

The structure will be checked to ensure adequate capacity at the ultimate limit state only for a likely and reasonable load path to transfer the impact loads to the bearings, supports and foundations, with consideration of each structural element in the load path. For elastomeric bearings the effects due to collision loads will be considered at the serviceability limit state with a load factor of 1.0.

3.18 Gantry, Transporter, Traveller and Construction Loading (GL)

The majority of the simply supported decks and two-span continuous decks are to be constructed by overhead gantry. The temporary loading from the various gantries to be used on the scheme will be defined by the subcontractors appointed to undertake the deck construction. These loads will include the effects of the most severe loading configuration carrying deck precast elements and the unloaded case when the gantry is subject to high winds. These gantries also travel over the 3-span continuous decks in some locations and their loads need to be considered in the design. 3- span continuous bridges are all erected in balanced cantilever. Some spans however are erected using a deck-mounted mobile traveller with a maximum weight of 40 tonnes. Its loads also need to be considered in these bridge designs. Segments are mostly delivered at ground level but in some location where access is difficult some segments are delivered over the deck using special transporters. These loads and their effects on permanent works need to be checked. When there are no specific construction loads, a load of 0.5 kN/m is considered on the 3-span balanced cantilever and 1.25 kN/m2 has been considered for all the other precast Viaducts.



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3.19 Shrinkage and Creep Effects (SE, CE)

Shrinkage and Creep effects will be calculated in accordance with the recommendations of the FIP-CEB 1990 Model Code and shall be considered as permanent load effects. The average relative humidity ratio will be taken as 70% and average annual mean temperature as 28°C. Shrinkage and creep factors will be calculated for individual structural elements with account taken of the member thickness, the age of the concrete when loaded and the nature and timing of the applied loading. The reinforced trackform plinths will be effectively discontinuous. Therefore the effects of differential shrinkage and creep of stress into these plinths will not be considered.

3.20 Bearing Replacement (BR)

The viaducts will be checked for the effects of the deck being jacked to facilitate the replacement of the bearings. Consideration will be given to the effects of the change in the support positions due to the transfer of loads to the jacks, and for the displacements to the continuous structures. The railway shall remain operational during the bearing replacement. The deck(s) at a pier will be jacked together to ensure there is no twist placed into the deck and for a pier with a deck expansion joint, to prevent any adverse effects to the continuous welded rail which spans the joint. The assumed maximum amount required to jack each bearing type is:

For replacement of a pot bearing 5mm For replacement of an elastomeric bearing 10mm

During the jacking operations considerations will be given to any changes to the articulation. Temporary transverse and longitudinal restraint may be required.

3.21 Buffer Loading

At the end of the viaduct beyond Rashidiya Station buffers will be provided at the end of the tracks.

The maximum horizontal load to be accommodated by the buffer stop is 960kN applied at 800mm above the top of rail level.

3.22 Earth Pressure

For the design of the abutments the earth pressure coefficients will be determined once the fill material to be used is known. See also Section 7.6 for seismic earth pressures.

3.23 Load Combinations

For the load combinations for both the serviceability and ultimate limit states refer to



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Appendix B. Moments, shears, axial loads derived from the design loads are to be multiplied by a further load factor γf3 to obtain the design load effects. γf3 values will be taken as 1.0 for the serviceability limit state and 1.1 for the ultimate limit state.

For column design, when calculating the beneficial effect of axial load as a coexistent effect, γf3 at ultimate limit state shall be taken as 1.0. 3.24 Drainage

The drainage system will accommodate a rainfall rate of 20mm/hr. A minimum velocity of 0.6 m/s will be assumed.

3.25 Clearances

The separation of the two tracks is constant at 3.320m and the distance from the centreline of the alignment to the centrelines of the tracks is a constant 1.660m, where the alignment is straight or curved down to a radius greater than 2000m. Where the alignment is curved between horizontal radii of 250m to 2000m these dimensions are 3.3525m and 1.6763m respectively. The only variations occur at Rashidiya and Nakheel Stations where the twin track layout is replaced by a more complicated multi track layout. The internal clearance widths between the inside faces of the deck upstands (platform edge in stations) are as follows:

Location Straight Track Curved Track (R>2000m) (R=250-2000m)

Outside Station 6.780m 7.100m

Inside Station 6.330m Not applicable

Table 3.11 Internal dimensions between deck upstan ds.

On the approaches to the stations, transitions will be required to accommodate the variation in upstand separation. Also transitions are required to accommodate the variations between straight and curved sections of track.

Details of the clearance requirements can be seen in Appendix D.

It is possible that additional internal width will be required at the crossover positions. The final required clearance width has yet to be determined.

3.26 Deck Profile

The 2,040mm height of the Illustrative Design will be retained along with the outer profile to the deck. A 1 in 100 fall will be maintained on the top surface of the deck upstands outside stations. The height of the rail level (lower rail on radius) will be a minimum of 400mm above the crown of the deck floor slab on the viaduct centreline and the inside edge of the deck upstands will be 1095mm above rail level. For simple and twin span decks the deck will be cast and erected at constant gradients over vertically curved sections of the alignment. The deck level will be lowered to ensure a minimum trackform depth of 400mm throughout. The lowering of the deck level on these span types shall be



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taken into account in setting out to see that adequate clearance is provided to obstacles below rail viaduct.

3.27 Fire Resistance

The viaduct components within the station buildings will be designed to have a design resistance period of 2 hours. This will include both the deck and the substructure.

3.28 Piling Tolerances

The additional load effects from the most severe application of the pile tolerances will be allowed for in the design. The following maximum tolerances for the bored piles will be allowed for in the design:

Positional tolerance ± 75mm (at pile head level) Verticality tolerance 1 in ± 100

The additional load effects are particularly significant with the mono-pile foundation solution, with the application of an additional bending moment.



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4 EARTHQUAKE DESIGN 4.1 Site Classification

The Particular Design Specification states that viaduct earthquake design shall be carried out in accordance with AASHTO LRFD. The site is classed as Zone 2 with an acceleration coefficient (A) of 0.12. The structures shall be considered as essential bridges, as defined in AASHTO LRFD Article 3.10.3. A project wide site-specific seismic hazard assessment is currently being carried out and the seismic acceleration coefficient obtained from this will be utilised in design, on approval by the Engineer.

The Site Coefficients shall be determined in accordance with AASHTO LFRD Article 3.10.5 on the basis of the relevant geological profile and geotechnical data for the foundations. Based on the available data it is anticipated that, in general, Soil Profile Types I or II will be appropriate for the majority of the route. The Site Coefficients for Soil Profile Type I and II are 1.0 and 1.2 respectively.

4.2 Loading 4.2.1 Inertia Loading

Seismic forces arising from inertial effects on the viaduct structures will be derived in accordance with AASHTO LRFD Articles 3.10, 4.7.4.1 and 4.7.4.3.

In general, the single mode elastic method will be used and the fundamental period of vibration will be determined by modeling individual piers using the computer program LUSAS, or similar. An example of a typical model is included in Appendix J. The analysis will model the pile supports either with equivalent cantilevers or complete piles with soil springs.

Equivalent cantilevers will be based on analysing the soil/structure interaction using the computer software REPUTE or similar. As the response may be non-linear, initial runs will be based on assumed seismic pile forces and if these are exceeded it may be necessary to modify the soil stiffnesses and equivalent cantilever properties.

The pile/soil springs analysis will be based on linear elastic springs to representing the restraint of the soil. On completion of the analysis it will be necessary to check the maximum horizontal earth pressures and if they exceed the passive limit then the springs will be adjusted accordingly. The mass of the piles will be neglected in the analysis as the soil liquification depths are expected to be small and the results will then be slightly conservative. For pile groups, the soil spring properties will take account of the shielding effect on the horizontal earth pressures between the piles using the factors given in DIN 4014, Cl 7.4.3. Further information on pile modeling is included in the Geotechnical Section.

The fundamental period will be used to obtain the Elastic Seismic Response Coefficient, Csm, from AASHTO LFRD Equation 3.10.6.1-1:



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A5.2T

AS2.1C

3/2m

sm ≤=

where: Tm = period of vibration of the mth mode (sec). A = acceleration coefficient specified in Section 7.5.1 below. S = site coefficient specified in Section 7.5.1 below. The horizontal seismic design forces will be determined from the product of the Elastic Seismic Response Coefficient, Csm and the equivalent mass of the structure. This will include the deck, pier crosshead, pier and pile cap self weights and the superimposed dead loading (SDL), specified in Section 3.3. In addition live loading from a single train of 33 kN/m, which represents the average axle loading given in Appendix C, will also be included. Horizontal seismic design forces will be considered to be acting at the centroid of each individual mass.

Elastic Seismic Design Forces, calculated as described above, will be divided by the following response factors, R, for the respective elements. This is based on AASHTO LRFD Table 3.10.7.1-1 and Article 3.10.9.3.

Substructure Element R Pier Crosshead 2.0 Pier 2.0 Pile Caps and Piles 1.0

Table 4.1 Seismic Response Factors

These inertial seismic design forces will be considered in both the longitudinal and transverse axis of the viaduct structure as appropriate. The following two inertial load cases will be considered in accordance with AASHTO LRFD Article 3.10.8.

Load Case Applied Forces Load Case 1 1.0FL + 0.3FT

Load Case 2 0.3FL + 1.0FT

Table 4.2 Seismic load combinations

where:

FL = member forces due to an earthquake in the direction of the longitudinal axis of the viaduct

FT = member forces due to an earthquake in the direction of the transverse axis of the viaduct

Generally, the plastic capacity of the base of a pier multiplied by an overstrength factor of 1.3 will be used to design the foundations, in accordance with AASHTO LRFD Article 3.10.9.4.3f. This approach is likely to result in foundation design forces, which are lower than the Elastic Seismic Design Forces and will provide a more economical design.



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Cracked sections will be assumed within the plastic zone at the base of the pier column. Therefore the stiffness of the pier section is taken as EI/2 which has the effect of practically reducing the Csm value by up to 10%.

In order to prevent a brittle shear failure, the piers will be designed for a shear force that corresponds to the overstrength moment of resistance in the plastic hinge zone at the base of the piers. To ensure that the plastic hinge zone is confined to the base of the pier, the flexural design of the pier above the plastic hinge will be based on bending moments which are consistent with the overstrength moment of resistance in the plastic hinge zone and the corresponding overstrength shear force.

Superstructure/Pier connection forces will be based on the lesser of the Elastic Seismic Design Forces divided by a response factor, R of 1.0 or the shear force that corresponds with the overstrength moment of resistance in the plastic hinge zone at the base of the pier.

4.2.2 Kinematic Loading

There is no requirement in AASHTO Seismic zone 2 to consider soil seismic interaction as these are deemed to be covered by the Zone 2 design requirements. Liquefaction of soil strata under seismic events is to be allowed for, as discussed in Section 7.6.2.

4.3 Reinforcement Detailing 4.3.1 General

Reinforcement detailing shall generally be in accordance with the requirements of BS 5400. However special requirements for seismic detailing will be derived from AASHTO LRFD.

4.3.2 Seismic Detailing

For bridges in Zone 2, the requirements of AASHTO LRFD Article 5.10.11.3 will apply. In particular there is a need to ensure that piers have some ductility capacity. This will be achieved by the provision of adequate transverse reinforcement in the potential plastic hinge zones, to prevent buckling of the longitudinal reinforcement and to provide confinement to the concrete core. It is considered that potential plastic hinge zones will be confined to the base of piers and top of piles. Transverse reinforcement for confinement will extend into the pile cap in accordance with AASHTO LRFD Article 5.10.11.4.3.

Detailing of laps and anchorages to the confining transverse reinforcement will make allowance for loss of concrete cover. Spiral reinforcement shall only be spliced in the potential plastic hinge zones at the base of piers by fully welded splices or by full-mechanical connections. Hoop reinforcement or cross-ties shall be anchored by seismic hooks, with the extension of the hooks located within the concrete core, as defined in AASHTO LRFD Articles 5.10.2.2 and 5.10.11.4.1d.



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Pier longitudinal reinforcement shall only be spliced outside of the potential plastic hinge zones. The minimum height of pier plastic hinges is defined in AASHTO LRFD Article 5.10.11.4.1e.

4.4 Dynamic Analysis

The dynamic analysis of the straight sections of simply supported spans will be carried out in accordance with Clause 4.7.3 of AASHTO LRFD for multi-span bridges with ‘regular’ spans provided they meet the span ratio and pier stiffness segments even though the number of spans will exceed 6. A single mode elastic analysis uniform load method will be used. Other structures will be design using a multimode dynamic analysis. The presence of the rails will be ignored in this analysis.



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5 RAIL/STRUCTURE INTERACTION

A rail structure interaction [RSI] analysis is required because the continuously welded running rails are continuous over the deck expansion joints. The interaction occurs because the rails are directly connected to the decks by base plate fittings fixed to the continuous reinforced concrete support plinths, which are monolithic with the deck. The forces in the rails have a significant effect on the service performances of both the deck and the track. The analysis of the rail/structure interaction takes two forms, the local analysis of the rail spanning the expansion joint between two decks, and the global analysis to consider the distribution of the longitudinal loading and interaction between the various substructures. The design of the rails and base plate fixings will be undertaken as part of the trackwork design. The temperature range of the continuous welded rail (CWR) is assumed to be relative to it’s neutral setting temperature of 40°C + or –3°C and the maximum and minimum rail temperatures which are assume to be +75°C and +3°C respectively. This gives CWR extreme ranges of +38°C and -40°C. The RSI temperature range is governed by the change of structure temperature relative to deck temperature at the time of installation of the rail. Based on the air temperature range given in Section 3.12 the maximum and minimum deck temperatures are assumed to be +55°C to +5°C. It is further assumed that th e rails are fixed to the deck at deck temperatures between +20°C and 40°C which gives max imum and minimum temperature ranges of + 35°C and – 35°C . This corresponds with the UIC 774 3R Clause 1.4.2 requirements of maximum and minimum bridge temperatures ranges of +/- 35°C.

The effect of introduction of a break in the rail by an accident or for maintenance purposes will be investigated at detailed design stage.

5.1 Local Behaviour

Checks for the stress in the rails will be made on the lengths of continuously welded rail, which span the expansion joints between two decks. In principle the rails will be checked against the recommendations in the International Union of Railways technical standard UIC 774-3, Track/Bridge Interaction, Recommendations for Calculations, 2nd Edition, dated October 2001. These checks are only to be carried for in service conditions, i.e. no local analysis will be undertaken for a seismic event.

In addition absolute and relative displacement checks will be carried out against the UIC 774-3 requirements for braking and acceleration and deck end rotation due to vertical loading. The relative deflection across adjacent decks at rail locations will be limited to 3 mm. Checks will be made for the stresses introduced into the rails due to the end rotations of the decks, the differential vertical movements due to the compressibility of the bearings and the eccentricity of the end of the deck from the centreline of the bearings, and the variation in the expansion joint gap due to temperature, shrinkage and creep effects. The values of these various movements will be determined for the various deck types and forwarded to Mitsubishi Heavy Industries for consideration in their trackwork design.



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5.2 Global Behaviour

The global behaviour will be analysed using a 2D model of both the structure and rail to examine the longitudinal load distribution. These will be modelled as separate members with spring members connecting them together to represent the base plates. This idealisation is not used for dynamic analysis – see section 4.4. A sketch of a typical model is included in Appendix I. Pandrol track fixings will be used and the slip resistance have been established by testing. The displacement u0 at the beginning of plastic zone is 0.65mm for the unloaded case and 0.55mm for the loaded case; and the resistance of the rails, k, to longitudinal movement relative to the track plinth is assumed to be 30kN/m for an unloaded track and 54kN/m for a loaded track. For lengths of simply supported spans, the interaction due to deck temperature change will be analysed using spreadsheets which calculate the force variations in the rail due to slip/stick of the track fixings. The out of balance effects of different adjacent span lengths will be analysed using a simple elastic 2D model of at least 5 spans either side of the design pier in order to quantify the forces on the bearings and piers. This will also be used for vertical load effects and traction and braking and seismic loading. The results will be compared with the Capita Symonds previous analytical work described in their Rail Structure Interaction Report and the requirements of UIC 774-3. The allowable increased rail stresses shall be 92 N/mm2 in both tension and compression. This work will be extended to apply to lengths of viaduct spans between fixed piers using simple methods. The work will then be calibrated using a non-linear analysis model of simple spans and combinations.

In the transverse direction, the presence of the continuously welded rails between decks will be ignored, so that each deck will be assumed to behave separately from its neighbour.

For areas of horizontal curvature radial forces applied to the piers resulting from the longitudinal analyses shall also be considered. The complex track arrangements at Rashidiyah and Nakheel stations shall also be modelled as special cases accordingly. 5.3 Global CWR Effects

The build up of CWR forces in the rail will be considered at points where rail breather joints are located and for the case of a rail break. Account will be made of the CWR temperature given above. For viaducts with horizontal curvature the effects of the radial forces arising from the full CWR forces will be considered.



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6 DEFORMATIONS

The deformations for permanent loads will be determined under the action of all permanent loads. The deformations due to the live loads will include the appropriate Dynamic Impact Factor. All the deformations are to be checked for nominal loading, i.e. with applied load factors of 1.0. The following limiting values for bridge deformation refer to the total deformations caused to the rails.

6.1 Vertical deflection at mid-span

The vertical deflection at mid-span will be limited to a Span/Deflection ratio given in the table below based on the advice in UIC 776-3. This assumes the provision of a reasonable level of passenger comfort for the multi-span viaducts for a Speed Range 1, up to 120 kph. Intermediate span values are to be interpolated from the table.

Span Table 3 Table 7 Span/Deflection Ratio ≤ 20m 450 0.65 690

≤ 25m 450 0.69 650 28m 660 0.72 920 30m 800 0.73 1,095 32m 800 0.75 1,065

33m 800 0.76 1,050

36m 800 0.80 1,000

≥ 54m 800 1.00 800

Table 6.1 Deflection limits The vertical deformations will be determined for the maximum number of trains possible on a structure and in the most severe locations. The total vertical deflection will be made up of the deflections of the deck, the deformation of the bearings, and the deflections of the pier caps.

6.2 Deck Twist

The deformation of the bridge will be checked to limit the twist applied to any of the tracks to 0.0025 radians. This is to be checked over a length of 3m and is equivalent to a maximum change of levels between rails of 7.5mm over this length.

6.3 End Deck Rotations

The total change in angle at the simply supported ends of a deck and the vertical movement caused at this end by its rotation are required to be determined by the Rail/Structure Interaction analysis. See Section 5 for further information. The check for these rotations will be undertaken by Mitsubishi Heavy Industries, as part of their trackwork design exercise and these fall outside the scope of this Design Basis Report. The total rotations and vertical movements will be made up of the residual long term effects of creep, shrinkage and foundation settlement after installation of the rails and the effects of the maximum number of trains possible on the deck in the most adverse locations.



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6.4 Deck Relative Displacements

The serviceability limit state cyclic movements in the vertical direction between contiguous deck ends (at expansion joints) will be limited to ± 3mm at the running rail centreline. In the ultimate limit state the deck shall be prevented from falling off the pier under seismic conditions. This is to be achieved by providing sufficient resistance in the support bearings to restrain the deck during a seismic event. In the longitudinal direction the stresses in the rail will be checked at the serviceability limit state under normal operating conditions (non-seismic). These effects will be checked by Mitsubishi Heavy Industries as part of their trackwork design from the results of the Rail/Structure Interaction analysis, see Section 5 for further information. At the ultimate limit state, the gap between decks will be sufficient to prevent pounding of the adjacent decks together.

6.5 Precamber

For the simply spans, two-span decks and station decks no precamber will be applied to the deck, with all spans being cast flat. Other viaduct decks may be built to a precamber so the sum of the anticipated deflections under dead load, superimposed dead load, differential shrinkage and prestress effects after long term conditions have occurred, should achieve the desirable profile. It is proposed to provide a permanent camber to the decks, up to an amount at midspan of the span divided by 1000, to improve the appearance, as recommended by UIC 776-3. It is proposed that the loading from the trains are excluded from the determination of the precambers, contrary to the proposal in the Station and Line, Particular Design Specification (document PS007-T-ALLI-CWK-TN-SYS-064803-B1). Additionally, the deflections of the deck will be determined for the trackwork to account for the long term movements which will occur following the installation of the track. This deflections will account for the effects of the application of the weight of the trackform, the differential shrinkage between the trackform plinths and for the deck, the ongoing creep in the deck and the weight of the equipment on the deck. It will be assumed that the rails will be installed between 1 and 18 months after the completion of the deck. Deflections will be determined for both dates and the trackwork installer will be expected interpolate between the figures provided to suit the actual delay from deck construction to trackwork installation. An assessment will be made on the sensitivity to the age of the deck segments when incorporated into the works when undertaking this analysis.

6.6 Horizontal Deck Deflections

Horizontal deck deflections shall be checked as per the requirements of UIC 776-3 Clause 7. The horizontal deformation of the bridge deck shall not cause a horizontal change of angle at a free end exceeding 3.5 milliradians or a change of radius of curvature that is less than 3500 m.



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7 GEOTECHNICAL

7.1 Overview

A detailed site investigation is proposed for the whole of the route. Prior to receipt of this information the design will be based on consideration of the limited ground condition information provided at tender.

The Illustrative Design shows viaduct structures with piers supported on alternatives of single, twin and four pile foundations. The piles will extend through the overlying sand into the weak rock to provide the required load bearing capacity. It is noted that other methods of providing a foundation may be considered, such as shallow pad foundations.

There will be a limited requirement for dewatering during the construction of the viaduct substructures. Shallow foundations and pile caps may require some local dewatering but these will be located close to the ground surface and will not require significant dewatering. Therefore there will be a limited settlement risk to surrounding buildings and structures adjacent to the elevated alignment.

Ground investigations shall be conducted at every foundation location before construction commences. The presence of existing structures and obstructions in the ground shall be investigated through survey, with the aim of recording and resolving conflicts prior to commencement of construction.

The key geotechnical issues at the pier and station locations are:

• Assessing liquefaction potential, defining water table level, particle size distribution and the requirement for any ground treatment resulting in the determination of suitable foundation types.

• For piled foundations, determining the local rock-head level, assessing rock quality through pilot holes and hence determining required pile lengths and rock socket lengths. Insitu tests or dilatometer tests will be used in test pile boreholes in the weak rock for correlation with Unconfined Compression Tests.

• Obtaining design data from preliminary laboratory testing on bore hole samples and CPT’s and using it to provide design information for use in determining appropriate foundation sizes.

7.2 Geotechnical Design Parameters Detailed design shall use the data in the site-specific Ground Investigation Reports. 7.3 Foundation Design

The choice of foundation at any location will be driven by the performance, feasibility, economics and programme. The design of foundations, shallow and deep, will be carried out in general accordance with BS 8004 and standard reference books such as Bowles and Tomlinson. The potential for liquefaction will be assessed using available data, supplemented by the data from the proposed site investigation when received.



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7.4 Pile Foundations A liquefaction assessment is required for the foundation design as stated above. Where piled foundations are to be used and liquefaction potential is indicated the design will determine whether the material is replaced or treated. Alternatively the pile foundation will be designed to resist the loading from liquefaction effects. Piled foundations will be feasible throughout the elevated alignment. Pile foundation are to be analysed using the proprietary computer software REPUTE or similar. The stiffness profile adopted for the design will be appropriate for the design case:- static stiffness profile for normal loads and degradated small strain stiffness values for the earthquake loading.

Where piled foundations are to be used, insufficient shaft shear stress or bearing will be provided from the overlying soils. It is a requirement of Section 7.2.4.2 of the Particular Specification that piles shall be extended to form sockets in the weak rock. A rock socket of 4 times the pile diameter is proposed for piles up to 1.5m diameter. For piles greater than 1.5m diameter a minimum penetration of 6m into the weak rock is considered appropriate. Section 7.1.1 of the specification requires that all piled foundations shall be bored cast in place concrete piles.

Foundations for the structures may be formed of single piles or groups formed of four piles. It is anticipated that all pile diameters will be large (greater than 1.0m), in order to resist the design forces. It is envisaged that drilling fluid such as good quality bentonite or similar approved will be used to maintain bore stability and that as a minimum, casings will be required through the loose sand in the near surface. Pile reinforcement will be required to extend into the rock sockets due to the nature of the design loadings.

The process for the development of the piled foundations is as follows: Preliminary design based on the preliminary parameters presented herein using theoretical correlations with UCS values. A correlation following Horvath and Kenney (1979) is adopted as this has been shown to give good correlations for the materials encountered in Dubai. The design would then be modified based on the actual capacities obtained from the preliminary pile test results and data from the pre-construction site investigation.

Pressure meter type testing will be used to investigate soil and rock properties as part of the overall design basis verification.

The factors of safety to be adopted in design are as follows:

Normal EQ Construction Loads (Temp) End Bearing NOT PERMITTED Skin Friction 2.5 1.25 2.0 Pull out 3.0 1.5 3.0

Design vertical and lateral deflections shall be commensurate with the form of structure. Permissible limits are to be determined based on the track requirements. The settlements of all the rock sockets will be limited particularly if good basal cleanliness is achieved during construction. A failure criterion for working pile tests is presented as a residual settlement of only 6mm after unloading in the Particular Specification. The appropriateness of this limit is to be reviewed after the preliminary pile testing.

For piles the average compressive stress under working load shall not exceed 0.3 times the concrete compressive strength calculated on the total cross section.



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7.5 Seismic Design and Liquefaction Assessment 7.5.1 Seismic Design

All structures are to be designed and constructed to resist the effects of seismic ground motions. For the bridges the AASHTO LRFD method (Cl 3.10) is to be used, as described in Section 4. . The bridges are considered as essential under Cl. 3.10.3. and are to be designed based on Seismic Zone 2 for an acceleration coefficient (A) of 0.12.

The design approach for bridges shall follow the Client requirements noted above based on the AASHTO LFRD, Sections 3.10 and 4.7.4.1 and 4.7.4.3. The site coefficient is to be determined based on Cl. 3.10.5.

Seismic earth pressure coefficients developed for all the horizontal accelerations described above after the approach of Mononobe5 and Okabe6 are presented in the table below. The values assume vertical sides to substructures and horizontal surface on the active side of the wall.

Mononobe and Okabe derived active and passive earth pressures are presented below. The ratio of vertical acceleration (kv) to horizontal acceleration (kh) is taken to be 0.5: In general the design of retaining walls will allow for and take account of a small outward displacement to reach the active state in the retained fill. In these cases the dynamic active earth pressure will be calculated by using a horizontal coefficient kh equal to half the maximum ground acceleration (in g) of the design earthquake, in conjunction with the Mononobe Okabe method.

Table 7.1 Seismic Active Earth Pressure Coefficien ts for use in



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Substructure Design

Table 7.2 Seismic Passive Earth Pressure Coeffici ents for use in Substructure Design

7.5.2 Liquefaction

The silty sand is assessed in the Systra Geotechnical Report as having significant liquefaction potential. A quantitative analysis based on fines content, SPT values and predicted earthquake magnitude based on 0.15g, concludes that 10% of the investigated silty sand below the water table is potentially liquefiable to a depth of 15m.

The recent liquefaction assessment methods of Seed and Idriss based on SPT and/or CPT data will be utilized to assess the liquefaction potential. The method has been developed further by the National Center for Earthquake Engineering Research and was presented by Idriss to the Institution of Civil Engineers in 2002. The original Seed liquefaction relationship of N60 value and critical CSR (Cyclic Stress Ratio) can now be determined for materials with <5% fines, 15% fines and >35% fines. Additionally, the Idriss paper contains relationships for Stress Reduction Factor (rd) with depth and Magnitude Scaling Factor (MSF) to allow the calculation of critical CSR for liquefaction

kh kv δ/Φ (1-kv)KPE

33° 34° 35° 36° 37° 38° 39° 40°

0.22 0.11 0 2.583 2.704 2.833 2.968 3.112 3.264 3.425 3.596

0.15 0.075 0 2.849 2.977 3.113 3.257 3.409 3.570 3.741 3.922

0.05 0.025 0 3.214 3.353 3.501 3.656 3.821 3.995 4.180 4.376

0 0 0 3.392 3.537 3.690 3.852 4.023 4.204 4.395 4.599

0.22 0.11 0.5 4.431 4.823 5.263 5.760 6.325 6.970 7.711 8.568

0.15 0.075 0.5 5.019 5.452 5.940 6.490 7.115 7.829 8.649 9.596

0.05 0.025 0.5 5.839 6.333 6.888 7.515 8.227 9.039 9.972 11.050

0 0 0.5 6.243 6.767 7.357 8.022 8.777 9.639 10.628 11.771

kh kv δ/Φ (1-kv)K AE

33° 34° 35° 36° 37° 38° 39° 40°

0.22 0.11 0 0.413 0.399 0.385 0.371 0.358 0.345 0.333 0.321

0.15 0.075 0 0.367 0.354 0.341 0.328 0.316 0.304 0.293 0.282

0.05 0.025 0 0.316 0.303 0.291 0.280 0.268 0.257 0.247 0.236

0 0 0 0.295 0.283 0.271 0.260 0.249 0.238 0.228 0.217

0.22 0.11 0.5 0.401 0.388 0.375 0.362 0.350 0.339 0.327 0.316

0.15 0.075 0.5 0.347 0.335 0.323 0.312 0.301 0.290 0.280 0.270

0.05 0.025 0.5 0.290 0.279 0.268 0.258 0.248 0.238 0.229 0.220

0 0 0.5 0.267 0.256 0.246 0.236 0.227 0.217 0.208 0.199



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with varying maximum earthquake magnitude. The assessment will be carried out for an earthquake magnitude value of M = 6.0 which is appropriate for the Dubai area. The Japanese Roads Association liquefaction assessment method will also be used for comparison.

For piles extending through potentially liquefiable layers to the weak rock, consideration will be given to the effects of negative skin friction due to settlement of the upper layers. The peak loading due to liquefaction is not expected to occur at the same time as the peak inertial loading. When negative skin friction is considered it shall be treated as an addition to the working load. Ground improvement may be considered to improve lateral stability.

7.6 Ground Improvement

An assessment of the potential for liquefaction and hence the density, stiffness and strength of the overlying silty Sand shall be made as part of the foundation design. This pre-construction assessment shall then be used to determine if there is a requirement for ground improvement as part of the development and choice of foundation options. Reference is made to CIRIA C573, 2002, A guide to ground treatment. Ground improvement could take the form of:

Preloading compaction with or without vertical drains

Dynamic compaction by heavy tamping

Vibro-Compaction

Vibro-Stone columns replacement

Compaction grouting

Excavation and replacement

Where there is limited depth of liquefiable materials, full excavation and replacement is likely to be a cost effective option. It is anticipated that stone columns could be used where there is potential for liquefaction or where capacity and stiffness are inadequate. The grid of the stone columns shall be determined according to the bearing capacity, settlement requirements and liquefaction potential reduction. Preloading could be used for the station approach embankment and the at grade stations as the soil permeability is high.

Extensive Vibro-compaction is presented in the illustrative design for the deep foundations. Vibro-compaction is not suitable where the fines content of the soil is greater than 20% and is best suited when fines content is less than 10%, whereas vibro-replacement techniques are feasible for all fines contents. Vibro-compaction could be used to increase the SPT N60 to above 20 where the fines content permits. Dynamic compaction is only likely to be more cost-effective than the aforementioned methods where treatment areas are extensive (typically 5000m2). This process is also less efficient when the water table is very high and would cause large ground-borne vibrations potentially incompatible with built-up areas.

7.7 Chemical Aggressiveness of Ground

The Systra Geotechnical Report indicates that concrete design shall be in accordance with CIRIA Special Publication 31 and section 9.2.3.2 of their report states that foundation concrete is to have 100mm cover to reinforcement based on results of sulphate and chloride determination on samples of water and soil/rock recovered during the ground



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investigation.

CIRIA SP31, Table 13 indicates that for concrete that is in ground that is permanently saturated (class d(ii) or d(iv)) minimum cement content is in the range 320 to 400 kg/m3, maximum water/cement ratio in the range 0.50 to 0.42, a potential requirement for tanking/membrane and minimum reinforcement cover of 40 to 50mm.

Sulphate and chloride test results have been analysed for each line to BRE Special Digest 1, Concrete in Aggressive Ground. The current available data is relatively sparse and therefore the design criteria shall be re-evaluated based on additional groundwater and soil testing from the pre-construction phase Site Investigation.

Due to the aggressive environmental and ground conditions the requirements of BS 8004 regarding concrete cover to underground construction shall be taken into account in the design in order to achieve a minimum design life of 100 years.

A concrete coating system will be adopted in addition to the concrete cover requirements. This will extend to 5m below existing ground level. Skin friction on the piles will be ignored in this zone.



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8 DESIGN METHODS 8.1 Computer Modelling for Evaluation of Load Effects

The viaduct decks will be modelled with both 2D and 3D models. The longitudinal effects will be determined from the 2D models and the transverse effects and distribution of longitudinal stresses and loads will be determined by 3D modelling. The critical position of the rail vehicles will be determined by a 2D influence line analysis. The 2D models will be simple line beam models and the 3D models of the decks will be either formed of shell finite elements or solid brick finite elements. The analysis will be based on gross un-cracked section properties, transformed to take account of variations in material stiffnesses where appropriate. Analysis of the pile caps will be undertaken either by the strut/tie model, or by standard bending theory.

8.2 Prestressed Concrete Design The design of internally prestressed concrete structures and members will be carried out in accordance with BS5400: Part 4. Externally prestressed structures, elements and their associated prestress where used on the viaducts shall be designed to the recommendations of BD 58/94 - Design Manual for Roads & Bridges: Design of concrete highway bridges and structures with external and unbonded prestressing. For the 3 –span continuous bridge decks it is intended that any external prestressing or partially external prestressing is replaced with internal prestressing. This is in order to overcome the problems associated with providing this form of prestressing in spans which are partially box girder and partially U shape in section. This approach, combined with cambering for the deck deflections, which are likely to be small for these medium- span continuous bridges, and the reduced risk of increase in dead load due to non presence of any deck surfacing or ballast, we believe will obviate the need to provide for additional future external prestressing, as proposed in AASHTO LRFD Cl C5.14.2.3.8c. 8.3 Serviceability Limit State for Prestressed Concrete

The decks are considered as Class 1 for Load Combination 1 and Class 2 for the remaining Load Combinations as per Clause 4.2.2 of BS5400 Pt4:1990. The stress limitations for prestressed concrete for in-service conditions will be as follows:

Position Load Combination 1 Load Combinations Maximum 2,3,4 and 5 Compression* Maximum Tension Maximum Tension

Segmental Joints No Tension No Tension 0.4 fcu

Within Reinforced Concrete Section

No Tension 0.36√ fcu

0.4 fcu

Pier Cap No Tension 0.36√ fcu

0.4 fcu

* For loading in bending.



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Table 8.1 Stress limits for prestressed concrete

Allowable stresses during construction shall be in accordance with BS5400 part 4 Cl 6.3.2

8.4 Ultimate Limit State for Prestressed Concrete

The ultimate loads will be determined by a linear elastic analysis of the structure.

The requirements of BD 58/94 shall be implemented in structures or elements on the viaducts where external prestressing is used. For ultimate shear, the precast segmental deck will be treated as monolithic except that the shear friction at segment joints needs to be checked in accordance with Cl. 6.3.4.6 of BS5400 Pt4: 1990. 8.5 Reinforced Concrete Design Design and detailing of reinforced concrete structures and elements on the viaducts section shall be carried out to the requirements of BS5400 Part 4: Clause 5. The viaduct concrete decks will be designed as a reinforced concrete section in the transverse direction. Concrete cover and crack width limitations shall be as per section 2.1 above. 8.6 Creep, Shrinkage, Differential Settlement and Temperature Difference

The effects due to creep, shrinkage, differential settlement and temperature difference will generally be considered at the serviceability limit state design but will be excluded from the ultimate limit state checks. Other temperature effects will be considered for both serviceability and ultimate limit states.

Where the effects of differential settlement, temperature difference and creep and shrinkage of concrete are considered at the ultimate limit state, stress limitations at the serviceability limit state will not be considered, in accordance with BS5400 Pt4 Clause 4.1.1.3, Creep redistribution of moments and shears within continuous decks will be taken into account at both the serviceability and ultimate limit states.

8.7 Moment Rounding

Where prestressed concrete members are continuous over intermediate supports, the serviceability bending moment over the support will be reduced by the method outlined by Guyon in his book, “Limit State Design of Prestressed Concrete, Volume 2, The Design of the Member”. Details on the method of reduction are given in Appendix G. For reinforced concrete members, or prestressed members at the ultimate limit state, the angle of spread of the support up to the neutral axis is assumed to be zero.

8.8 Time Dependent Effects



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The time dependent creep redistribution effects of the dead load and the prestress load will be calculated in accordance with the FIP-CEB 1990 Model Code.

For twin span and station decks the time dependent effects will de determined by the use of specialist proprietary software such as ADAPT-ABI. For manual calculation, design load effects will be calculated from the formula:

MFinal(t) = (e-Ø(t)

MAs-built ) + (1 - e-Ø(t)

) MMonolithic

MFinal(t) Long term bending moment, shear force or axial force at time t after completion of structure

MAs-built Sum of elastic stage construction bending moment, shear force

or axial force

MMonolithic Bending moment, shear force or axial force induced in the structure if the loading is applied instantaneously to the complete structure

Ø(t)

Creep factor at time t, appropriate to the nature and time of application of the applied loads

The long term creep calculations are to be undertaken for year 2050 (t =16,500 days). It is assumed that the age of the precast deck segments when incorporated into the works will vary in age from 28 days to 1 year.

8.9 Fatigue

All the elements of the viaducts subject to railway loading will be checked for the effects of fatigue for repeated cycles of live loading. The number of load cycles will be based on a life of 120 years. Account will be taken for any welding of the reinforcement, for example for stray current collection.

8.10 Dispersal on Wheel Point Loads Concentrated wheel loads applied to the rail will be distributed both longitudinally by the continuous rail to more than one base plate, and transversely by the width of the base plate. It is assumed that only two-thirds of the concentrated load from one wheel will be applied to one base plate and the remaining one-third will be transmitted by the two base plates either side. The base plates are assumed to be 200mm (along line of rail) by 350mm (normal to rail) and spaced at 600mm centres. A dispersal of 1 horizontally to 1 vertically through the structural concrete from the underside of the base plate through the concrete track plinth to the neutral axis of the



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floor slab will be assumed for determination of the patch area for application of the wheel loads to the structure.

8.11 Early Thermal Crack Control

The determination of the minimum area of reinforcement to control early age thermal effects will be in accordance with the recommendations of BD 28/87 Early Thermal Cracking of Concrete, incorporating Amendment No.1, 1989.

Short-term fall in temperature values T1 given in Table 1of BD 28/87 shall be increased by 10°C to account for the higher ambient and conc rete placing temperatures in Dubai. Shrinkage strain in Clause 5.6 shall be calculated in accordance with CEB-FIP 1990 Model Code recommendations, based on an average annual ambient temperature of 28°C.

Account will be taken of the maximum cement content, the most adverse environmental conditions, the formwork type and the duration any external restraint is applied. The duration of any external restraint is particularly important with precast elements, where the external restraint is removed when the segment is removed from the mould.

8.12 P-Delta Buckling Effects

P-delta effects are to be included for all significant lateral load or sway effects applied to the top of the piers. These effects are additional secondary moments caused by the deflection of the pier and will be quantified using a non-linear analysis. The analysis will be used as an alternative to the slenderness moments given in BS 5400 Part4. The P-delta moments will be added to the foundation forces as well as for the pier design.



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APPENDIX A

SCHEDULE OF DESIGN STANDARDS



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Schedule of Design Standards to be used in the Desi gn

BS 5400 Steel Concrete and Composite Bridges Part 1; 1988 General Statement Part 2; 1978 Specification for Loads Part 4; 1990 CP for Design of Concrete Bridges Part 9; 1983 Bridge Bearings Part 10; 1980 CP for Fatigue BS 5930; 1999 Site Investigations BS 6031; 1981 Earthworks BS 8002; 1994 Earth Retaining Structures BS 8004; 1986 Foundations UIC 774-3 R Track/Bridge Interaction: Recommendations for

Calculations (2nd

Edition) UIC 776-1 R Loads to be considered in Railway Bridge Design

(4th

Edition)

UIC 776-3 R Deformation of Bridges (1st

Edition)

BD 28/87 Early Thermal Cracking of Concrete (Published by the Highways Agency, England)

BD 58/94 The Design of Concrete Highway Bridges and Structures with External and Unbonded Prestressing. (Published by the Highways Agency, England)

BD 60/04 Design of Highway Bridges for Vehicle Collision Loads (Published by the Highways Agency, England)

CS Technical Report TR49 Design for High Strength Concrete (Published by the UK Concrete Society in 1998)

AASHTO LRFD Bridge Design Specifications -3rd

Edition Dubai Municipality Geometric Design Manual for Dubai Roads Dubai Municipality Drainage System Design Criteria



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APPENDIX B

LOAD COMBINATIONS



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Walkway loading shall be considered in conjunction with an unloaded train on the adjacent track and normal train loading on the other track where appropriate. Shrinkage and creep shall be included in the ULS with a partial factor of 1.2 unless included in the SLS stress checks.



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APPENDIX C

DESIGN RAIL VEHICLES



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APPENDIX D

RAIL CLEARANCES



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PLEASE REFER TO THE VIADUCT STRUCTURAL GAUGE DRAWIN GS



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APPENDIX E

DIMENSIONS OF TYPICAL DECK SECTIONS WITH TRACKFORM



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TYPICAL SECTION - STRAIGHT



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TYPICAL SECTION - CURVED



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TYPICAL SECTION – SINGLE TRACK, STRAIGHT



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TYPICAL SECTION – SINGLE TRACK, CURVED



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APPENDIX F

EQUIPMENT ON DECK



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APPENDIX G

MOMENT ROUNDING AT SUPPORTS



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APPENDIX H

DIFFERENTIAL TEMPERATURE GRADIENT



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APPENDIX I

TYPICAL GLOBAL RAIL/STRUCTURE INTERACTION MODEL



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APPENDIX J

TYPICAL EARTHQUAKE INERTIA LOADING ANALYSIS MODEL



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