Dubai Metro Project

8/10/2019 Dubai Metro Project

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DUBAI RAPID LINK CONSORTIUM

WS Atkins & Partners Overseas

Dubai Metro ProjectRED LINE

Viaducts Design Basis Report

November 2007


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ATKINS

Date: 7 November 2007

Document No.: DM001-E-ACW-CVI-DR-DCC-310001Page 2 of 64

DUBAI METRO PROJECT

VIADUCT - DESIGN BASIS REPORT

W S Atkins & Partners

Overseas

Verification Ref:

Revision StatusOriginated

By

Checked

ByVerified By Issued By Date Issued Issued To

A DraftM.Badcock

A. Shaw J. Baber M.Badcock29 July2005

JT MetroJV

B Draft

M.

Badcock A. Shaw J. Baber M.Badcock

5 August

2005

JT Metro

JV

C WorkingM.Badcock

A. Shaw J. Baber M.Badcock12August2005

JT MetroJV

DForComment

M.Badcock

A. Shaw J. Baber M.Badcock15August2005

JT MetroJV

A1-01P Draft G. Ziadat A. Shaw J. Baber G.Ziadat30 Nov2005

JT MetroJV

A1-02AForApproval

G. Ziadat A. Shaw J. Baber G.Ziadat30 Dec2005

JT MetroJV

B1-02B Draft M Chubb C Hendy

A5Forapproval

M Chubb C Hendy G.Ziadat J.Sundaram24 July2006

JT MetroJV

A6Forapproval

J.P.SagarJ.Sundaram

J.Sundaram7 Nov2007

JT MetroJV


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DUBAI METRO PROJECT Dubai Rapid Link

DUBAI RAPID LINK CONSORTIUMDUBAI 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 updateB1-05B

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. UnedaAPPROVED

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

CONTRACTORS DOCUMENT No.: DOCUMENT No.:

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

REVISION

A6


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DUBAI METRO PROJECT ATKINS



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 designof 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 coversthe 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 tensionedsegmental construction by the span by span method from an overhead gantry.

Twin Span Continuous. Two span continuous U-section decks constructed using posttensioned segmental construction by the span by span method from an overheadgantry and the stitching of both spans together to form a continuous structure.

Three Span Continuous. Three span continuous structures comprising a combinationof U-section and Box-section precast post tensioned segmental decks, erected bycrane using the balanced cantilever method.

Station spans. Three or four span continuous U-section decks constructed using posttensioned segmental construction by the span by span method from an overheadgantry and the stitching of both spans together to form a continuous structure

Single Track Decks. Simply supported U-section decks constructed using precast posttensioned 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 reinforcedinsitu concrete decks of variable geometry.

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

1.4 The viaduct substructures will generally comprise reinforced concrete piers with widerpier caps to support the deck and reinforced concrete abutments. Pier heads forsimple, twin spans, station spans and some special spans are constructed usingprecast thin reinforced concrete shells infilled with insitu concrete and prestressed instages. For single track spans and 3-span continuous internal piers pierheads are ofinsitu reinforced concrete. Piers and abutments will be founded on large diameterbored 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 approachesto 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 BasisReport (Ref. 1).

1.6 Stray current and civil earthing systems will be provided on the viaducts but theserequirements are subject to a separate Design Basis Report (Ref 2).

1.7 The Designer has obtained the Engineers agreement to use BS5400 as the designcode for the viaducts instead of AASHTO LFRD subject to the Engineer retaining theright to refer to AASHTO general requirements. This agreement is documented in theEngineers Comments on the Viaducts Design Basis Review Doc No DM001-E-ACW-CV1-DR-DCC-310001-D.

1 MATERIALS

2.1 ConcreteThe following concrete grades will be used

Structural Element Grade (fc) Grade (fcu) E (short term)CylinderStrength

CubeStrength

Modulus of Elasticity

SuperstructuresPrecast - 3 SpanPrecast 44/44 straightPrecast 44/44 curvedPrecast 36m curvedPrecast Type 1 station deckPrecast OtherInsitu continuity stitches:

Precast 44/44 straightPrecast 44/44 curvedType 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/mm

2

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/mm

2

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/mm

2

36 kN/mm2

34 kN/mm2

Piercaps and Bearing Plinths 40 N/mm2 50 N/mm

2 34 kN/mm

2

Pier Columns (3-span internalpiers)

40 N/mm2 50 N/mm

2 34 kN/mm

2

Other Pier Columns 32 N/mm2 40 N/mm

2 31 kN/mm

2

Abutment walls, Bases and PileCaps

32 N/mm2 40 N/mm

2 31 kN/mm

2

Piles 32 N/mm

2

* 40N/mm

2

* 31 kN/mm

2

Table 2.1 Concrete strengths

* Allowance has been made for the loss of strength due to placement of the concrete underdrilling fluid. Design strength, fcuof 50 and 40 N/mm

2

is the characteristic strength before and afterplacement respectively.The long term modulus of elasticity shall be taken as half the short term modulus whereappropriate.Where required by design constraints a higher concrete grade may be used. The higher gradeshall 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

/ C

The following table provides the design crack widths and nominal covers to be used in theDesign and specified for construction. The nominal design crack widths and nominal design covervalues specified are based on BS5400 Pt.4 Tables 1 and 13 respectively:

StructuralElement

Environment Nominal Design Nom.Specified

NominalDesign

Crack width Cover Cover

SuperstructuresPrecast - 3 Span

Precast OtherInsitu Structures

Considered for allthese decks asSevere to Very

Severe

0.20 mm0.20 mm0.20 mm

40 mm40 mm50 mm

35 mm35 mm

35 mm

Piercaps andBearing Plinths

Severe to VerySevere

0.20 mm 50 mm 35 mm

Pier Columns Severe to VerySevere

0.20 mm 50 mm 40 mm

Pier Bases andPile 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 bean intermediate classification between a severe and very severe environment. Thebenefits of the concrete coating system will be ignored in the design. A tanking systemwill 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 waterproofingsystem For the piles the concrete will be of a low permeability C50 concrete mixapproved by the Engineer. In addition 125mm cover is specified throughout its length anda 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 asprayed 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 ReportTR49, 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 thebest use of the available concrete capacity.

Exposed concrete surfaces (decks, pier and abutment stems) shall be treated with anelastomeric 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 withthe 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 coatingwill 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 DesignationCharacteristicStrength

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 duringthe

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 () 0.20

Wobble coefficient (k)* 0.0010 /m

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

Relaxation (after 1000hr at 20C & 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 shallbe limited to 75% of the guaranteed ultimate tensile strength (GUTS). The jacking forceis to account for any jack losses.

Relaxation losses will be adjusted for 28C 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

TendonSize

NoStrands

Application Duct DiameterInternal/External

MinimumBreakingLoad

AnchorageBearing Size(mm)

4T15 4 3 Span Deck(transverse)

45/50 mm 1043 kN 150 x 150

12T15 12 Simple, SingleTrack, Special , 2Span and 3 SpanDecks

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 31022T15 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 elastomericbearings. The continuous span structures will use only sliding pot bearings.

Elastomeric bearings will be in accordance with BS 5400 Part 9, 1983 and the followingshear 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 isexpected in all cases, the bearings shall be fitted with an interfacing chequered plate toprovide a minimum coefficient of friction of 0.5 between mating surfaces. Thisattachment shall be capable of carrying the entire transverse load.

Pot bearings will be provided with a PTFE sliding surface and will be designed andspecified 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 galvanisedchequered cover plate will be provided across the gap in the emergency walkways. Thisplate will be fixed on one side and will not be recessed into the concrete surface but willbe detailed to avoid becoming a tripping hazard to passengers and maintenancepersonnel.

2.7 Segmental Joints

The joints between the match cast precast concrete deck segments shall be formed withshear and location keys during precasting and filled using an appropriate epoxy glueduring 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 inAppendix 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 areasas earthquake loading and rail dynamic factors.

The load combinations used in the design are given in Section 3.23 and provided inAppendix 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 beassumed:

Material Description Characteristic Density (kN/m3)

Reinforced concrete 24.5Concrete

Mass concrete 22.0

Steel Structural, Prestressed andOrdinary 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 arenot structural elements but are permanent. The major part of the superimposed deadloading is the weight of the trackform plinths. Details can be seen in Appendix E. Theremainder of the loading is the equipment on the deck, and details of these are providedin Appendix F. The allowance per m run of deck is as follows for each deck type:


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Description Mainline (TwinTrack) Load

Mainline (SingleTrack) 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 toR=2000m)+

35.0 17.3 59.9

Total (Canted Track toR=250m)+

39.9 19.6 -

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

+ For simple twindeck spans additional trackform weights shall be added to account forcamber and alignment vertical curvature where the deck is precast on flat long-line bedsas follows (Maximum vertical curvature of R=1250m is assumed until span arrangementsand alignment are fixed) :

Table 3.2 Superimposed dead loading

The allowance per m run of deck for station structure are:

DescriptionT1 & T2 Stations

(Twin Track) LoadT3 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 2.01.0 1.0

Miscellaneous equipment 2.0 1.0 1.0

Total 67.044.0 38.0

Table 3.3 Superimposed dead loading on viaduct deck 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 TrackformAverage Weight dueto Camber

0.3 0.4 0.8 1.2

Additional TrackformAverage Weight dueto Vertical Curvature

3.0 3.9 5.0 12.2

Maximum (notadditive)

3.0 3.9 5.0 12.2

Table 3.4 Additional trackform weights for Simple twintrack 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 twintrack decks precaston flat long line beds.

Description



0.15 0.2 0.4 0.6

Additional TrackformAverage Weight dueto 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 precaston 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 Linewill start to operate with 3 car trains, which will be upgraded to 4 then 5 car trains aspatronage increases.The variable sized trains operating on the Green Route will use the Red Route fromUnion 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 thescheme. 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 configurationsspecific to this scheme are given in Appendix C. The choice of vehicle and position ofthe vehicle will be chosen to produce the most adverse effect on the structure. Theassumed axle load for all train axles is 140 kN. This is based on the AW4 load case ofgross vehicle weight including the maximum passenger capacity.

The loading from maintenance vehicles and low loaders carrying equipment requiredalong 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 appliedto the vertical train loading for longitudinal design, except for the simply supported spanswhere they are to be derived by dynamic analyses for the respective span lengths. Asstated 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 DesignSpeed shall be taken as 100 kph.

For transverse design, the recommendations of BS 5400 Part 2 Cl 8.2.3.2 for RL Loadingwill be applied. This gives a dynamic factor of 1.2, which needs to be increased to 1.4 forthe design of the floor slab supporting just a single track. These values are to be verifiedusing 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 axlelocations in accordance with the recommendations of BS 5400 Part 2

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

For twin tracked decks carrying traffic in opposite directions, consideration should begiven to braking forces from one train and traction forces from another, actingsimultaneously to maximise the longitudinal loading on a deck. Additionally

consideration should be given to braking or traction acting in opposite directions toproduce rotational effects. Allowance is also made for one train pushing or pulling abroken down train.

3.7 Centrifugal Forces (CF)

When the track is curved, centrifugal load will be considered. The centrifugal forceacting radially 1.8m above rail level will be determined in accordance with Cl 8.2.9 of BS5400 Part 2, assuming a maximum design speed of 100 kph, reducing with cant and adistributed load of 33 KN/m based on actual train loading. For calculation of f value thestatement for L greater than 2.88m and v t less than 120km/h will be amended to for Lgreater than 2.88m and vtgreater than 120km/h as corrected in BD37/01.


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

For sections of track with radius in plan less than 400 m, the design speed for calculationof centrifugal forces shall be reduced as follows:

Plan radius 400 m, design speed = 100 kphPlan radius = 350 m, design speed = 90 kphPlan radius = 300 m, design speed = 80 kphSpeeds 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 forRL Loading. A single 100 kN nominal load is required to be taken horizontally at raillevel at right angles in either direction to the track at a point to cause the most severeeffect.

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 forRL Loading. Lurching results from temporary transfer of part of the railway vertical liveloads 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 verticaltrain 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 memberssupport two tracks. This variation in distribution of the vertical train loads is onlyconsidered for local transverse design of the track support element. This variation doesnot require consideration in the longitudinal direction.

Lurching can be ignored for elements supporting more than two tracks. It may also notbe required for elements supporting two tracks providing that a Finite Element Analysisis carried out to demonstrate the actual transverse behaviour.

3.10 Derailment Loading (DF)

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

The design of the trackform plinths falls outside the scope of this report, as the worksare part of the trackwork, rather than structure. Account will be taken of the transfer ofthese loads from the trackform into the structure and down through to the supports, pierand 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 thetrack plinths and by the deck upstands. Therefore, this loading is not applicable as thedisplacements proposed are not possible and the derailment effect is only the horizontalload component caused by the tilting of the train.

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

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

The maximum eccentricity of a derailed train from the tracks will be assumed to be250mm 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 beconsidered.

A load of 4 kN/m2

shall be applied on the upper surface of the deck upstands (emergencywalkways) within the handrails. As this is an emergency condition of a broken downtrain, this will only be considered in conjunction with a static unloaded train (nopassengers and no dynamic impact factor) located on the track adjacent to the loadedemergency walkway. Rail loadings on any remaining tracks will be unaltered.

For loaded lengths greater than 30m the pedestrian loading will be reduced inaccordance 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 theloads from the Platform Screen Doors, accounting for pressure from crowd, and airpressure 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 DubaiInternational Airport for the period of 1984 to 2001 shows a maximum recorded range of7.4C to 47.5C.

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

A positive temperature gradient of 20C and a reverse temperature difference of 10Cshall 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 momentgenerated by this gradient will be considered, the axial effects will be determined by thetemperature changes mentioned above. Temperature gradient effects shall only beconsidered 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 15C and a reverse temperature difference of7.5C shall be considered to reflect the short term nature of the construction condition.

The positive temperature gradient cannot co-exist with the maximum temperature riseand the reverse temperature gradient cannot occur with the maximum temperature falland these combinations shall not be considered.

In the stations, the decks are enclosed by the station structures and therefore will not besubjected to the above temperature gradients in the operating condition after constructionof the stations has been completed.

As the effects of peak rise and fall temperatures are a long term phenomenon, an elasticmodulus of 75% of the short elastic modulus will be used for the temperature rise and fallanalysis. 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% ofthe applied permanent vertical load. When considering the differential friction frombearings either side of fixed pier(s) the friction on one side will be taken as 5% and on theother side 2.5%. These values will be confirmed upon availability of test data from thechosen bearing supplier / manufacturer. This assumes that both bearings are replaced atthe 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 andthe 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 duringconstruction 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 thebearings on either side of the pier cap for the U- section decks. A differential settlementof 1mm will be considered in the transverse direction post construction, for the railalignment.

Combinations of differential settlement movements shall be considered on one or morepiers 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 usedin 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 assuminga mean hourly wind speed of 30 m/s. This corresponds to a 3 second gust speed of45m/sec on the standard span decks. Wind loads shall be determined on the deck, piersand rail vehicle. In addition, the wind loading on the Type 2 Stations will be carried by theshared substructure. Maximum wind load to be applied to the train travelling on the deckis 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 lower1m masked by the deck. For wind with Live Load, the train design has been based on amaximum operating gust wind speed of 32 m/s. This value shall be adopted in the designfor a loaded structure.

Wind loading shall be applied in the transverse (PT), longitudinal (PL) and vertical (PV)directions in the following combinations:

PTalone

PTin combination with PV

PLalone

0.5PT in combination with PL 0.5PV

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

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 inFigure 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 LRFDfor Seismic Loading. Refer to Section 4 of this report for further information.

Seismic loading will not be considered during construction.


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For decks (and pier caps) with headroom less than 0.4m above the minimum headroomrequirement, vehicle collision loads on the superstructure will be considered. Theheadroom is measured over the carriageway and adjacent verges and should includeallowance 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 less than 0.40 m than minimumrequirement

The structure will be checked to ensure adequate capacity at the ultimate limit state onlyfor 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 theserviceability 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 beconstructed by overhead gantry. The temporary loading from the various gantries to beused on the scheme will be defined by the subcontractors appointed to undertake thedeck construction. These loads will include the effects of the most severe loading

configuration carrying deck precast elements and the unloaded case when the gantry issubject to high winds. These gantries also travel over the 3-span continuous decks insome locations and their loads need to be considered in the design. 3- span continuousbridges are all erected in balanced cantilever. Some spans however are erected using adeck-mounted mobile traveller with a maximum weight of 40 tonnes. Its loads also needto be considered in these bridge designs. Segments are mostly delivered at ground levelbut in some location where access is difficult some segments are delivered over the deckusing special transporters. These loads and their effects on permanent works need to bechecked. When there are no specific construction loads, a load of 0.5 kN/m is consideredon the 3-span balanced cantilever and 1.25 kN/m

2has been considered for all the other

precast Viaducts.


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Appendix B. Moments, shears, axial loads derived from the design loads are to bemultiplied by a further load factor f3 to obtain the design load effects. f3values will betaken 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 coexistenteffect, f3 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 of0.6 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, wherethe alignment is straight or curved down to a radius greater than 2000m. Where thealignment is curved between horizontal radii of 250m to 2000m these dimensions are3.3525m and 1.6763m respectively. The only variations occur at Rashidiya and NakheelStations 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 (platformedge 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 upstands.

On the approaches to the stations, transitions will be required to accommodate thevariation in upstand separation. Also transitions are required to accommodate thevariations 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 profileto the deck. A 1 in 100 fall will be maintained on the top surface of the deck upstandsoutside stations. The height of the rail level (lower rail on radius) will be a minimum of400mm above the crown of the deck floor slab on the viaduct centreline and the insideedge of the deck upstands will be 1095mm above rail level. For simple and twin spandecks the deck will be cast and erected at constant gradients over vertically curvedsections of the alignment. The deck level will be lowered to ensure a minimum trackformdepth 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 obstaclesbelow rail viaduct.

3.27 Fire Resistance

The viaduct components within the station buildings will be designed to have a designresistance 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 beallowed for in the design. The following maximum tolerances for the bored piles will beallowed 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 foundationsolution, 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 carriedout in accordance with AASHTO LRFD. The site is classed as Zone 2 with anacceleration coefficient (A) of 0.12. The structures shall be considered as essentialbridges, as defined in AASHTO LRFD Article 3.10.3. A project wide site-specific seismichazard assessment is currently being carried out and the seismic acceleration coefficientobtained from this will be utilised in design, on approval by the Engineer.

The Site Coefficients shall be determined in accordance with AASHTO LFRD Article3.10.5 on the basis of the relevant geological profile and geotechnical data for thefoundations. Based on the available data it is anticipated that, in general, Soil ProfileTypes I or II will be appropriate for the majority of the route. The Site Coefficients for SoilProfile 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 inaccordance 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 ofvibration will be determined by modeling individual piers using the computer programLUSAS, or similar. An example of a typical model is included in Appendix J. The analysiswill 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 thecomputer software REPUTE or similar. As the response may be non-linear, initial runswill be based on assumed seismic pile forces and if these are exceeded it may benecessary to modify the soil stiffnesses and equivalent cantilever properties.

The pile/soil springs analysis will be based on linear elastic springs to representing therestraint of the soil. On completion of the analysis it will be necessary to check themaximum horizontal earth pressures and if they exceed the passive limit then the springswill 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 thehorizontal earth pressures between the piles using the factors given in DIN 4014, Cl7.4.3.

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

3/2

m

sm =

where:

Tm= period of vibration of the mthmode (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 ElasticSeismic Response Coefficient, Csm and the equivalent mass of the structure. This willinclude the deck, pier crosshead, pier and pile cap self weights and the superimposeddead 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 beincluded. Horizontal seismic design forces will be considered to be acting at the centroidof each individual mass.

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

Substructure Element R

Pier Crosshead 2.0Pier 2.0Pile Caps and Piles 1.0

Table 4.1 Seismic Response Factors

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

Load Case Applied Forces

Load Case 1 1.0FL+ 0.3FTLoad 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 axisof the viaduct

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

Generally, the plastic capacity of the base of a pier multiplied by an overstrength factor of1.3 will be used to design the foundations, in accordance with AASHTO LRFD Article3.10.9.4.3f. This approach is likely to result in foundation design forces, which are lowerthan the Elastic Seismic Design Forces and will provide a more economical design.


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Pier longitudinal reinforcement shall only be spliced outside of the potential plastic hingezones. The minimum height of pier plastic hinges is defined in AASHTO LRFD Article5.10.11.4.1e.

4.4 Dynamic Analysis

The dynamic analysis of the straight sections of simply supported spans will be carriedout in accordance with Clause 4.7.3 of AASHTO LRFD for multi-span bridges withregular spans provided they meet the span ratio and pier stiffness segments eventhough the number of spans will exceed 6. A single mode elastic analysis uniform loadmethod will be used.

Other structures will be design using a multimode dynamic analysis. The presence of therails 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 weldedrunning rails are continuous over the deck expansion joints. The interaction occursbecause the rails are directly connected to the decks by base plate fittings fixed to thecontinuous reinforced concrete support plinths, which are monolithic with the deck. Theforces in the rails have a significant effect on the service performances of both the deckand the track.

The analysis of the rail/structure interaction takes two forms, the local analysis of the railspanning the expansion joint between two decks, and the global analysis to consider thedistribution 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 trackworkdesign.

The temperature range of the continuous welded rail (CWR) is assumed to be relative toits neutral setting temperature of 40C + or 3C and the maximum and minimum railtemperatures which are assume to be +75C and +3C respectively. This gives CWRextreme ranges of +38C and -40C.

The RSI temperature range is governed by the change of structure temperature relativeto deck temperature at the time of installation of the rail. Based on the air temperaturerange given in Section 3.12 the maximum and minimum deck temperatures are assumedto be +55C to +5C. It is further assumed that th e rails are fixed to the deck at decktemperatures between +20C and 40C which gives max imum and minimum temperatureranges of + 35C and 35C . This corresponds with the UIC 774 3R Clause 1.4.2requirements of maximum and minimum bridge temperatures ranges of +/- 35C.

The effect of introduction of a break in the rail by an accident or for maintenancepurposes 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 checkedagainst the recommendations in the International Union of Railways technical standardUIC 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. nolocal analysis will be undertaken for a seismic event.

In addition absolute and relative displacement checks will be carried out against the UIC774-3 requirements for braking and acceleration and deck end rotation due to verticalloading. The relative deflection across adjacent decks at rail locations will be limited to3 mm.

Checks will be made for the stresses introduced into the rails due to the end rotations ofthe decks, the differential vertical movements due to the compressibility of the bearingsand the eccentricity of the end of the deck from the centreline of the bearings, and thevariation in the expansion joint gap due to temperature, shrinkage and creep effects. Thevalues of these various movements will be determined for the various deck types andforwarded 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 toexamine the longitudinal load distribution. These will be modelled as separate memberswith spring members connecting them together to represent the base plates. Thisidealisation is not used for dynamic analysis see section 4.4. A sketch of a typicalmodel is included in Appendix I.

Pandrol track fixings will be used and the slip resistance have been established bytesting. The displacement u0 at the beginning of plastic zone is 0.65mm for the unloadedcase and 0.55mm for the loaded case; and the resistance of the rails, k, to longitudinalmovement relative to the track plinth is assumed to be 30kN/m for an unloaded track and54kN/m for a loaded track.

For lengths of simply supported spans, the interaction due to deck temperature changewill 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 lengthswill be analysed using a simple elastic 2D model of at least 5 spans either side of thedesign pier in order to quantify the forces on the bearings and piers. This will also beused for vertical load effects and traction and braking and seismic loading. The resultswill be compared with the Capita Symonds previous analytical work described in theirRail Structure Interaction Report and the requirements of UIC 774-3. The allowableincreased rail stresses shall be 92 N/mm

2in both tension and compression.

This work will be extended to apply to lengths of viaduct spans between fixed piers usingsimple methods. The work will then be calibrated using a non-linear analysis model ofsimple 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 itsneighbour.

For areas of horizontal curvature radial forces applied to the piers resulting from thelongitudinal analyses shall also be considered.

The complex track arrangements at Rashidiyah and Nakheel stations shall also bemodelled 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 breatherjoints 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 fullCWR forces will be considered.


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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 thisinformation the design will be based on consideration of the limited ground conditioninformation provided at tender.

The Illustrative Design shows viaduct structures with piers supported on alternatives ofsingle, twin and four pile foundations. The piles will extend through the overlying sandinto the weak rock to provide the required load bearing capacity. It is noted that othermethods 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 butthese will be located close to the ground surface and will not require significantdewatering. Therefore there will be a limited settlement risk to surrounding buildings andstructures adjacent to the elevated alignment.

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

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

Assessing liquefaction potential, defining water table level, particle sizedistribution 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 rockquality through pilot holes and hence determining required pile lengths and rocksocket lengths. Insitu tests or dilatometer tests will be used in test pile boreholesin the weak rock for correlation with Unconfined Compression Tests.

Obtaining design data from preliminary laboratory testing on bore hole samplesand CPTs and using it to provide design information for use in determiningappropriate 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 carriedout in general accordance with BS 8004 and standard reference books such as Bowlesand 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. Wherepiled foundations are to be used and liquefaction potential is indicated the design willdetermine whether the material is replaced or treated. Alternatively the pile foundation willbe designed to resist the loading from liquefaction effects. Piled foundations will befeasible throughout the elevated alignment. Pile foundation are to be analysed using theproprietary computer software REPUTE or similar. The stiffness profile adopted for thedesign will be appropriate for the design case:- static stiffness profile for normal loads anddegradated small strain stiffness values for the earthquake loading.

Where piled foundations are to be used, insufficient shaft shear stress or bearing will beprovided from the overlying soils. It is a requirement of Section 7.2.4.2 of the ParticularSpecification that piles shall be extended to form sockets in the weak rock. A rock socketof 4 times the pile diameter is proposed for piles up to 1.5m diameter. For piles greaterthan 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 bebored cast in place concrete piles.

Foundations for the structures may be formed of single piles or groups formed of fourpiles. It is anticipated that all pile diameters will be large (greater than 1.0m), in order toresist the design forces. It is envisaged that drilling fluid such as good quality bentoniteor similar approved will be used to maintain bore stability and that as a minimum, casingswill be required through the loose sand in the near surface. Pile reinforcement will berequired 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: Preliminarydesign based on the preliminary parameters presented herein using theoreticalcorrelations with UCS values. A correlation following Horvath and Kenney (1979) is

adopted as this has been shown to give good correlations for the materials encounteredin Dubai. The design would then be modified based on the actual capacities obtainedfrom 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 ofthe overall design basis verification.

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

Normal EQ Construction Loads (Temp)

End Bearing NOT PERMITTEDSkin 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 settlementsof all the rock sockets will be limited particularly if good basal cleanliness is achievedduring construction. A failure criterion for working pile tests is presented as a residualsettlement of only 6mm after unloading in the Particular Specification. Theappropriateness 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 timesthe 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 groundmotions. For the bridges the AASHTO LRFD method (Cl 3.10) is to be used, as describedin Section 4. . The bridges are considered as essential under Cl. 3.10.3. and are to bedesigned 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 basedon the AASHTO LFRD, Sections 3.10 and 4.7.4.1 and 4.7.4.3. The site coefficient is to bedetermined based on Cl. 3.10.5.

Seismic earth pressure coefficients developed for all the horizontal accelerationsdescribed above after the approach of Mononobe

5and Okabe

6are presented in the table

below. The values assume vertical sides to substructures and horizontal surface on the

active side of thewall.

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: Ingeneral the design of retaining walls will allow for and take account of a small outwarddisplacement to reach the active state in the retained fill. In these cases the dynamicactive earth pressure will be calculated by using a horizontal coefficient khequal to halfthe maximum ground acceleration (in g) of the design earthquake, in conjunction with theMononobe Okabe method.

Table 7.1 Seismic Active Earth Pressure Coefficients for use in


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Substructure Design

Table 7.2 Seismic Passive Earth Pressure Coefficients for use in SubstructureDesign

7.5.2 Liquefaction

The silty sand is assessed in the Systra Geotechnical Report as having significantliquefaction potential. A quantitative analysis based on fines content, SPT values andpredicted earthquake magnitude based on 0.15g, concludes that 10% of the investigatedsilty 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/orCPT data will be utilized to assess the liquefaction potential. The method has beendeveloped further by the National Center for Earthquake Engineering Research and waspresented by Idriss to the Institution of Civil Engineers in 2002. The original Seedliquefaction relationship of N60value and critical CSR (Cyclic Stress Ratio) can now bedetermined for materials with 35% fines. Additionally, theIdriss paper contains relationships for Stress Reduction Factor (rd) with depth andMagnitude Scaling Factor (MSF) to allow the calculation of critical CSR for liquefaction

kh kv / (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 11.0500 0 0.5 6.243 6.767 7.357 8.022 8.777 9.639 10.628 11.771

kh kv / (1-kv)KAE

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 anearthquake magnitude value of M = 6.0 which is appropriate for the Dubai area. TheJapanese Roads Association liquefaction assessment method will also be used forcomparison.

For piles extending through potentially liquefiable layers to the weak rock, considerationwill 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 thepeak inertial loading. When negative skin friction is considered it shall be treated as anaddition to the working load. Ground improvement may be considered to improve lateralstability.

7.6 Ground Improvement

An assessment of the potential for liquefaction and hence the density, stiffness andstrength 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 forground improvement as part of the development and choice of foundation options.Reference is made to CIRIA C573, 2002, A guide to ground treatment. Groundimprovement 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 islikely to be a cost effective option. It is anticipated that stone columns could be usedwhere 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 usedfor the station approach embankment and the at grade stations as the soil permeability ishigh.

Extensive Vibro-compaction is presented in the illustrative design for the deepfoundations. Vibro-compaction is not suitable where the fines content of the soil is greaterthan 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 beused 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 methodswhere treatment areas are extensive (typically 5000m

2). This process is also less efficient

when the water table is very high and would cause large ground-borne vibrationspotentially incompatible with built-up areas.

7.7 Chemical Aggressiveness of Ground

The Systra Geotechnical Report indicates that concrete design shall be in accordancewith CIRIA Special Publication 31 and section 9.2.3.2 of their report states that foundationconcrete is to have 100mm cover to reinforcement based on results of sulphate andchloride 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 fortanking/membrane and minimum reinforcement cover of 40 to 50mm.

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

Due to the aggressive environmental and ground conditions the requirements of BS 8004regarding concrete cover to underground construction shall be taken into account in thedesign 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 beignored 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 effectswill be determined from the 2D models and the transverse effects and distribution oflongitudinal stresses and loads will be determined by 3D modelling. The critical positionof 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 beeither formed of shell finite elements or solid brick finite elements. The analysis will bebased on gross un-cracked section properties, transformed to take account of variationsin material stiffnesses where appropriate.

Analysis of the pile caps will be undertaken either by the strut/tie model, or by standardbending theory.

8.2 Prestressed Concrete Design

The design of internally prestressed concrete structures and members will be carried outin accordance with BS5400: Part 4. Externally prestressed structures, elements and theirassociated prestress where used on the viaducts shall be designed to therecommendations of BD 58/94 - Design Manual for Roads & Bridges: Design ofconcrete highway bridges and structures with external and unbonded prestressing.

For the 3 span continuous bridge decks it is intended that any external prestressing orpartially external prestressing is replaced with internal prestressing. This is in order toovercome the problems associated with providing this form of prestressing in spanswhich are partially box girder and partially U shape in section. This approach, combinedwith 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 nonpresence of any deck surfacing or ballast, we believe will obviate the need to provide foradditional 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 theremaining Load Combinations as per Clause 4.2.2 of BS5400 Pt4:1990. The stresslimitations for prestressed concrete for in-service conditions will be as follows:

Position Load Combination 1 Load Combinations Maximum2,3,4 and 5 Compression*

Maximum Tension Maximum TensionSegmental Joints No Tension No Tension 0.4 fcu

Within ReinforcedConcrete Section

No Tension0.36fcu 0.4 fcu

Pier Cap No Tension0.36fcu 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 Cl6.3.2

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 theviaducts where external prestressing is used.

For ultimate shear, the precast segmental deck will be treated as monolithic except thatthe shear friction at segment joints needs to be checked in accordance with Cl. 6.3.4.6 ofBS5400 Pt4: 1990.

8.5 Reinforced Concrete Design

Design and detailing of reinforced concrete structures and elements on the viaductssection 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 thetransverse direction. Concrete cover and crack width limitations shall be as per section2.1 above.

8.6 Creep, Shrinkage, Differential Settlement and Temperature Difference

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

Where the effects of differential settlement, temperature difference and creep andshrinkage of concrete are considered at the ultimate limit state, stress limitations at theserviceability limit state will not be considered, in accordance with BS5400 Pt4 Clause4.1.1.3,

Creep redistribution of moments and shears within continuous decks will be taken intoaccount at both the serviceability and ultimate limit states.

8.7 Moment Rounding

Where prestressed concrete members are continuous over intermediate supports, theserviceability bending moment over the support will be reduced by the method outlinedby Guyon in his book, Limit State Design of Prestressed Concrete, Volume 2, TheDesign 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, theangle 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 loadwill 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 useof specialist proprietary software such as ADAPT-ABI.

For manual calculation, design load effects will be calculated from the formula:

MFinal(t) = (e-(t)

MAs-built) + (1 - e-(t)

) MMonolithic

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

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

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

(t)

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

The long term creep calculations are to be undertaken for year 2050 (t =16,500 days). Itis assumed that the age of the precast deck segments when incorporated into the workswill 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 effectsof fatigue for repeated cycles of live loading. The number of load cycles will be based ona life of 120 years.

Account will be taken for any welding of the reinforcement, for example for stray currentcollection.

8.10 Dispersal on Wheel Point Loads

Concentrated wheel loads applied to the rail will be distributed both longitudinally by thecontinuous rail to more than one base plate, and transversely by the width of the baseplate.

It is assumed that only two-thirds of the concentrated load from one wheel will be appliedto one base plate and the remaining one-third will be transmitted by the two base plateseither 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 theunderside 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 wheelloads to the structure.

8.11 Early Thermal Crack Control

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

Short-term fall in temperature values T1given in Table 1of BD 28/87 shall be increasedby 10C 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 1990Model Code recommendations, based on an average annual ambient temperature of28C.

Account will be taken of the maximum cement content, the most adverse environmentalconditions, the formwork type and the duration any external restraint is applied. Theduration of any external restraint is particularly important with precast elements, wherethe 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 tothe top of the piers. These effects are additional secondary moments caused by thedeflection 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 5400Part4. The P-delta moments will be added to the foundation forces as well as for the pierdesign.


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APPENDIX A

SCHEDULE OF DESIGN STANDARDS


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Schedule of Design Standards to be used in the Design

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 Structureswith 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 RoadsDubai Municipality Drainage System Design Criteria


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Walkway loading shall be considered in conjunction with an unloaded train on the adjacent trackand 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 inthe SLS stress checks.


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APPENDIX D

RAIL CLEARANCES


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PLEASE REFER TO THE VIADUCT STRUCTURAL GAUGE DRAWINGS


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APPENDIX E

DIMENSIONS OF TYPICAL DECKSECTIONS 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 I

TYPICAL GLOBAL RAIL/STRUCTUREINTERACTION MODEL


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APPENDIX J

TYPICAL EARTHQUAKE INERTIALOADING ANALYSIS MODEL


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