design of railway structures to the structural eurocodes - part 1

Research ProgrammeEngineering

Design of railway structuresto the structural Eurocodes

Part 1

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1

List of Contents Page

Applicable British Standards, Eurocodes, National Annexes and Other Referenced Publications

Glossary

Summary S-1

Chapters and Appendices

1 Recommended Values where National Choice is Allowed in BS EN 1990:2002. 24

2 Recommended Values where National Choice is Allowed in Eurocodes, other than BS EN

1990:2002 + A1:2005. 33

3 Part 1 - Enhancement of Previous Studies 42

3.1 Load Comparison Factor 42

4 Comparison of Design Load Effects 43

4.1 Partial and Combination Factors 43 4.1.1 Eurocodes 43 4.1.2 British Standards 44 4.1.3 Deck Types 45

4.2 Variation of Load Classification Factor, α. 46

4.3 Variation of Dynamic Load Factor, Ф. 50

5 Live Load Surcharge on Substructures 53

5.1 Differences in Applied Actions 53

6 Longitudinal Actions 55

6.1 Traction 55

6.2 Braking 58

7 Accidental Actions 61

7.1 Derailment Effects 61

7.2 Collision Effects 64

8 Vertical Deformation and Rotation 66

9 Wind Effects 69

9.1 Wind - Ultimate Limit State 72 9.1.1 Summary of ULS Wind Combination Results 73

9.2 Wind - Serviceability Limit State 74 9.2.1 Summary of SLS Wind Combination Results 75

2

9.3 Discussion 76 9.3.1 Wind Only 76 9.3.2 Wind (Leading) and Railway Traffic 76 9.3.3 Railway Traffic (Leading) and Wind 77

10 Temperature Effects 78

10.1 Ultimate Limit State Actions 78

10.2 Serviceability Limit State Actions 79

10.3 Global Temperature Effects 80

10.4 Discussion 81

10.5 Thermal Gradient Effects 82 10.5.1 Temperature Only 82 10.5.2 Temperature Coexistent with Railway Loading, Temperature Leading Action

82 10.5.3 Temperature Coexistent with Railway Loading, Railway Loading Leading

Action 83 10.5.4 Conclusion 83

11 Groups of Loads 84

List of Figures

Figure 1: ULS Moments in Very Light Bridge Main Girder for Variation of α (Alpha) 47 Figure 2: ULS Moments in Medium Weight Bridge Main Girder for Variation of α (Alpha) 47 Figure 3: ULS Moments in Very Heavy Bridge Main Girder for Variation of α (Alpha) 48 Figure 4: ULS Shear in Very Light Bridge Main Girder for Variation of α (Alpha) 49 Figure 5: ULS Shear in Medium Weight Bridge Main Girder for Variation of α (Alpha) 49 Figure 6: ULS Shear in Very Heavy Bridge Main Girder for Variation of α (Alpha) 50 Figure 7: ULS Shear in Medium Weight Bridge Main Girder for Variation of Φ 52 Figure 8: ULS Shear in Very Heavy Bridge Main Girder for Variation of Φ 52 Figure 9: Comparison between Characteristic (Nominal) Traction Forces 57 Figure 10: Comparison between ULS Traction Forces 57 Figure 11: Comparison between Characteristic (Nominal) Braking Forces 59 Figure 12: Comparison between ULS Braking Forces 60 Figure 13: Comparison between Characteristic (Nominal) & ULS Longitudinal Train Forces 60 Figure 14: Design Moments due to Derailment Effects 62 Figure 15: Design Shears due to Derailment Effects 63 Figure 16: BS EN 1991-2 Table 6.11 Groups of Loads 84

List of Tables

Table 1: Documents and Standards Referenced Throughout the Study 7 Table 2: Recommended Values in BS EN 1991-1-1 33 Table 3: Recommended Values in BS EN 1991-2 35 Table 4: Alternative Values for Traction and Braking BS EN 1991-2 36 Table 5: Recommended Values in BS EN 1992-2 37 Table 6: Recommended Values in BS EN 1993-2 39 Table 7: Recommended Values in BS EN 1994-2 40 Table 8: Eurocode SLS Partial and Combination Factors used for Investigating α and Φ 43 Table 9: Eurocode ULS Partial and Combination Factors used for Investigating α and Φ 44 Table 10: Eurocode ACC Partial and Combination Factors used for Investigating α and Φ 44 Table 11: British Standards SLS Partial and Combination Factors used for Investigating α and Φ 45

3

Table 12: British Standards ULS Partial and Combination Factors used for Investigating α and Φ 45 Table 13: British Standards ACC Partial and Combination Factors used for Investigating α and Φ 45 Table 14: Comparison of ULS Bending Moments where α = 1,10 46 Table 15: Range of Factor Φ Considered in Study 51 Table 16: British Standards Live Load Surcharge Values and Partial Factors 53 Table 17: Eurocode Live Load Surcharge Values and Partial Factors 53 Table 18: Comparison of the Live Load Surcharge Effects on Typical Retaining Structures 54 Table 19: Comparison between Traction Forces 56 Table 20: Comparison between Braking Forces 58 Table 21: Derailment Loads 62 Table 22: Eurocode Collision Loading (Class A Structures) 64 Table 23: GC/RC5510 Collision Loading 65 Table 24: Comparison of Design Criteria for a Typical Pier in the Hazard Zone 65 Table 25: Comparison of Deflections for the Typical Decks Studied 66 Table 26: Summary of Deck Type 5 (Pre-stressed Concrete Beams) Deflections 66 Table 27: Eurocode ULS Partial and Combination Factors used for Wind Study 72 Table 28: British Standards ULS Partial and Combination Factors used for Wind Study 72 Table 29: Summary of ULS Wind Combination Results 73 Table 30: Eurocodes SLS Partial and Combination Factors used for Wind Study 74 Table 31: British Standards SLS Partial and Combination Factors used for Wind Study 74 Table 32: Summary of SLS Wind Combination Results 75 Table 33: Eurocode ULS Partial and Combination Factors used for Temperature Study 78 Table 34: British Standards ULS Partial and Combination Factors used for Temperature Study 79 Table 35: Eurocode SLS Partial and Combination Factors used for Temperature Study 79 Table 36: British Standards SLS Partial and Combination Factors used for Temperature Study 80 Table 37: Summary of Expansion and Contraction with T0 Specified (+/- 10°C) 80 Table 38: Summary of Expansion and Contraction with T0, not applied 81

4

Applicable British Standards, Eurocodes, National Annexes and Other Referenced Publications

Standard or Report Reference Title Date Published

BS 5400-1:1998 Incorporating

Amendment No. 1

Steel, concrete and composite

bridges — Part 1: General

statement

12 March 2003

BS 5400-2:2006 Steel, Concrete and Composite

Bridge Part 2: Specification for

Loads

September 2006

BS 5400-3:2000 Incorporating

Corrigendum No. 1

Steel, concrete and composite

bridges – Part3: Code of

practice for design of steel

bridges

May 2001

BS 5400-4:1990 Steel, concrete and

composite bridges —

Part 4: Code of practice for

design of

concrete bridges

June 1990

BS 5400-5:1979 Reprinted,

incorporating

Amendment No. 1

Steel, concrete and

composite bridges —


design of

composite bridges

May 1982

BS 5400-10:1980:1980

Incorporating Amendment No. I

Steel, concrete and

composite bridges -


fatigue

March 1999

BS 7608:1993

Incorporating

Amendment No. 1

Code of practice for

Fatigue design and

assessment of steel

structures

April 1993

BS 8002:1994 Code of practice for earth

retaining structures

April 1994

GC/RT5110 Design Requirements for

Structures

August 2000

GC/RT5112 Loading Requirements for the

Design of Bridges

May 1997

GC/RC5510 Recommendations for the

Design of Bridges

August 2000

NR/GN/CIV/025 The Structural Assessment of

Underbridges

June 2006

BS EN 1990:2002 Eurocode — Basis of Structural

Design

April 2002

DRAFT National Annex to BS

EN 1990:2002

UK National Annex to

Eurocode – Basis of Structural

Design

2006

BS EN 1991-1-1:2002 Eurocode 1: Actions on

Structures – Part 1-1: General

Actions – Densities, Self-

weight, Imposed Loads for

Buildings

April 2002

5

BS EN 1991-2:2003 Eurocode 1: Actions on

Structures – Part2: Traffic

Loads on Bridges

September 2003

BS EN 1991-1-3:2003 Eurocode 1 — Actions on

structures — Part 1-3: General

actions — Snow loads

July 2003


structures - Part 1-4: General

actions - Wind actions

April 2005


EN 1991-1-4:2005


Eurocode 1 - Part 1-4: General


June 2005



actions — Thermal actions

March 2004

National Annex to BS EN 1991-

1-5:2003


Eurocode 1 — Part 1-5: General

actions — Thermal actions

April 2007



actions — Accidental

actions

September 2006


EN 1991-2:2003


Eurocode 1: Actions on

Structures – Part2: Traffic

Loads on Bridges

Draft, dated 07/08/03.


1-3:2003



structures —

Part 1-3: General actions —

Snow loads

December 2005


EN 1991-1-4:2005



structures - Part 1-4: General


June 2005


1-5:2003



structures –

Part 1-5: General actions –

Thermal actions

April 2007

BS EN 1992-1-1:2004 Eurocode 2: Design of Concrete

Structures Part 1-1: General

Rules and Rules for Buildings

December 2004


1-1:2004


Eurocode 2: Design of Concrete



December 2005

BS EN 1992-2:2005 Eurocode 2: Design of Concrete

Structures Part 2: Concrete

Bridges Design and Detailing

Rules

December 2005

6


2:2005


Eurocode 2: Design of concrete

structures. Concrete bridges -

Design and detailing rules

December 2007

BS EN 1993-1-1:2005 Eurocode 3: Design of Steel

Structures - Part 1-1: General


May 2005


EN 1993-1-1:2005


Eurocode 3: Design of Steel



Undated Draft.


Structures - Part 1-5: Plated

Structural Elements

October 2006


Structures - Part 1-8: Design of

Joints

May 2005


Structures - Part 1-9: Fatigue

May 2005


EN 1993-1-9:2005



Structures Part 1-9: Fatigue

July 2007

BS EN 1993-2:2006 Eurocode 3: Design of Steel

Structures - Part 2: Steel

Bridges

October 2006


EN 1993-2:2006



Structures Part 2: Steel Bridges

May 2007

BS EN 1994-1-1:2004 Eurocode 4: Design of

composite steel and concrete


rules and rules for buildings

February 2005

BS EN 1994-2:2005 Eurocode 4 — Design of


structures — Part 2: General

rules and rules for bridges

December 2005


2:2005


Eurocode 4: Design of


structures – Part 2: General

Rules and rules for bridges

December 2007

BS EN 1997-1:2004 Eurocode 7: Geotechnical

Design Part 1: General Rules

December 2004

BS EN 1997-2:2007 Eurocode 7: Geotechnical

Design Part 2: Ground

Investigation and Testing

April 2007

ISBN No. 978-0-7277-3160-9 Designer‘s Guide to BS 1993-2

– C.R. Hendy and C.J.Murphy,

Series Editor Haig Gulvanessian

First Published 2007

7

ISBN No. 978-0-7277-3159-3 Designer‘s Guide to BS 1992-2

Eurocode 2: Design of Concrete

Structures Part 2; Concrete

Bridges – C.R. Hendy and D.A.

Smith, Series Editor Haig

Gulvanessian

First Published 2007

NETWORK RAIL REPORT Appraisal of Eurocode for

Railway Loading (by Scott

Wilson for Network Rail)

July 2003

T696 Appraisal of Eurocodes for

Railway Loading

January 2008

RSSB REPORT

13410/R01 Rev B

EN 1992 Design Criteria for

railway (by Gifford for RSSB)

May 2007

ERRI D216/RP1 ERRI Fatigue of Railway

Bridges, State of the Art Report

September 1999

96/48/EC Council Directive 96/48/EC on

the interoperability of the trans

European high-speed rail system

(referenced throughout this

document as the High Speed

TSI)

July 1996

2001/16/EC Directive 2001/16/EC of the

European Parliament and of the

Council on the interoperability

on the conventional rail system

(referenced throughout this

document as the Conventional

RailTSI)

March 2001

UIC776-3 1st Edition Deformation of Bridges January 1989

UIC776-1 5th Edition Loads to be considered in

railway bridge design

August 2006

Table 1: Documents and Standards Referenced Throughout the Study

8

Glossary

Terms

Term Document Item

ACC BS EN 1990:2002 Accidental design situation

British Standards Not Applicable The current British Standards

used in bridge design that

include the BS5400 suite of

standards and Network Rail and

Railway Group Standards

BS Not Applicable British Standard

EN Not Applicable Euronorm (Eurocode)

EQU BS EN 1990:2002 Limit state for loss of static

equilibrium of the structure or

any part of it considered as a

rigid body, where:

minor variations in the value

or the spatial distribution of

actions from a single source

are significant, and

the strengths of construction

materials or ground are

generally not governing.

FAT BS EN 1990:2002 Limit state for fatigue failure of

the structure or structural

members

GEO BS EN 1990:2002 Limit state for the failure or

excessive deformation of the

ground where the strengths of

soil or rock are significant in

providing resistance.

Mott MacDonald Not Applicable Mott MacDonald

NA Not Applicable National Annex

Nom Not Applicable Nominal (equivalent to

characteristic in BS )

RSSB Not Applicable Railway Safety and Standards

Board

Seismic BS EN 1990:2002 Seismic design situation

SLS Not Applicable Serviceability Limit State

STR BS EN 1990:2002 Limit state for internal failure or

excessive deformation of the

structure or structural members,

including footings, piles,

basement walls etc, where the

strength of construction

materials of the structure

governs.

TSI Not Applicable Technical Specification for

Interoperability (mandatory)

UIC Not Applicable International Union of Railways

ULS Not Applicable Ultimate Limit State

9

Characters

Character Standard Description

γfL BS 5400-2:2006 Partial factor for a load

γf3 BS 5400-3:2000

BS 5400-4:1990

BS 5400-5:1979

A factor that takes account of

inaccurate assessment of the

effects of loading, unforeseen

stress distribution in the

structure, and variations in

dimensional accuracy achieved

in construction.

γm BS 5400-3:2000

BS 5400-4:1990

BS 5400-5:1979

Partial factor for a material

property, also accounting for

model uncertainties and

dimensional variations

τl BS 5400-3:2000 Limiting shear strength of web

τy BS 5400-3:2000 Shear strength

φ BS 5400-3:2000 Aspect ratio of a web panel

mfw BS 5400-3:2000 Factor used in determining

limiting shear strength

MR BS 5400-3:2000 Limiting moment of resistance

MULT BS 5400-3:2000 Moment of resistance if lateral

torsional buckling is prevented

G BS EN 1990:2002 Partial factor for permanent

actions.

P BS EN 1990:2002 Partial factor for Pre-stressing

actions

Q BS EN 1990:2002 Partial factor for variable

actions

BS EN 1990:2002 Partial factor for the

combination of actions

α BS EN 1991-2:2003 Load classification factor

applied to characteristic loading

for railway lines carrying rail

traffic which is heavier or

lighter than normal rail traffic.

Φ BS EN 1991-2:2003 Dynamic factor which enhances

the static load effects under

Load Models 71, SW/0 & SW/2

Qvk BS EN 1991-2:2003 Value of Vertical point loads in

Load Models

qvk BS EN 1991-2:2003 Value of Vertical uniformly

distributed loads in Load

Models

γM BS EN 1992 (all)

BS EN 1993 (all)

BS EN 1994 (all)

Partial factor for a material

property, also accounting for

model uncertainties and

dimensional variations

Mcr BS EN 1993-1-1:2005 Elastic Critical Moment.

d0 BS EN 1993-1-8:2005 the hole diameter for a bolt

fub BS EN 1993-1-8:2005 ultimate tensile strength for bolt

fu BS EN 1993-1-8:2005 ultimate tensile strength

e1 BS EN 1993-1-8:2005 the end distance from the centre

of a fastener hole to the adjacent

10

end of any part, measured in the

direction of load transfer

p1 BS EN 1993-1-8:2005 the spacing between centres of

fasteners in a line in the

direction of load transfer

η BS EN 1994-1-1:2004 Degree of shear connection;

coefficient

11

Executive Summary

The commission to compare the design of railway structures in accordance with the Structural

Eurocodes and the current British Standards was awarded by RSSB to Mott MacDonald in August

2007. This report summarises Mott MacDonald‘s findings and experiences in using the Eurocodes.

Headline results are included in this summary section, along with outline details of the methodology

used in achieving the objectives set out below. The main text of the report provides more details of the

study and the principal outcomes. The appendices give a detailed breakdown of the work undertaken

including graphs and a comprehensive results summary. Calculations supporting the results and

conclusions reported were supplied to RSSB and may be available upon request. However, caution

must be used as many of the standards and national annexes have been revised since the draft versions

used in this study.

Objectives

The objectives of study T741, the design of railway structures to the Structural Eurocodes, are

summarised below:

Recommend values where national choice is permitted in BS EN 1990:2002.

Confirm the appropriateness of the recommended values in the Eurocodes, other than BS EN

1990, where national choice is permitted.

Complete and update earlier studies into the differences in actions (by other parties for

Network Rail and RSSB).

Compare the margin of capacity (utilisation) between the design of typical railway structural

elements to current British Standards and the Eurocodes.

Discuss significant differences between the current British Standards and the Eurocodes.

Provide a commentary on the lessons learned from using the Eurocodes.

Methodology

In achieving the majority of the study‘s objectives, the detailed design of selected details for a number

of typical railway bridges was undertaken. This enabled Mott MacDonald to determine a comparison

between the margin of capacity (utilisation) for a variety of bridge components and to identify issues

arising from design using the Eurocodes. The designs, to both the current British Standards and the

Structural Eurocodes, were augmented by a series of stand alone studies that included:

Investigating the sensitivity of varying the line classification factor, α, a factor for non-

standard railway loads.

Investigating the sensitivity of varying the dynamic factor, Φ, for railway loads in determining

shear effects.

Consideration of ‗Groups of Loads‘

Consideration of load effects not critical in designing the selected elements of the typical

structures (for example wind and temperature).

Investigating the differences in the approach to design for fatigue.

Design of Railway Structures to the

Structural Eurocodes

12

Summary of Study

The principal findings of the study are summarised in the table below. The results of design comparisons between the British Standards and the Eurocodes are

described and discussed in more detail in the main text. The number of typical structures considered was limited to six superstructures and a generic

substructure. Only the factors encountered during the design of the selected elements have been varied.

Description of Investigation Relevant Standards (refer to

list of references for dates of

publication)

Summary of Recommended Values, New Studies and Commentary

Recommending values where

national choice is permitted in

BS EN 1990:2002

BS EN 1990:2002 + A1:2005

(Annex A2)

Draft National Annex to BS EN

1990:2002 + A1:2005 (Annex

A2)

The values in the draft National Annex are recommended with the following

exceptions:

Table A2.4 (STR/GEO) (Set B) & (Set C), γQ,Sup for wind. Draft National Annex value

= 1,70. Recommended value = 1,50 to avoid over-design of wind-sensitive elements.

Table A2.4 (STR/GEO) (Set B), γG,Sup for superimposed loads. Draft National Annex

value = 1,20. Recommended value = 1,35 for ballast to ensure equivalent load effects

as current British Standards.

Confirming the appropriateness

of the recommended values in

the Eurocodes other than BS EN

1990 where national choice is

permitted.

Note only the factors considered

in the design of typical elements

agreed with RSSB have been

considered.

BS EN 1991-1-1:2002


1-1:2002

The values in the National Annex are recommended with the following exception:

cl. 5.2.3 (1), the lower characteristic value of the density of ballast. National Annex

value = 17kN/m3. Recommended value = 18kN/m

3 for design of structural elements.

Note that dynamic effects were not considered in this study and the recommended

value is generally taken as 17kN/m3 for dynamic analyses.

Typical bridge designs BS EN 1991-2:2003

Draft National Annex BS EN

1991-2:2003 dated 07/08/2003

The values in the draft National Annex are recommended.



13



publication)



National Annex BS EN 1992-

2:2005 dated 31/12/2007




1993-2:2006 dated 02/05/2007



National Annex not available

The values in the Eurocode are recommended.

Investigating the sensitivity of

varying the line classification

factor, α

BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

The use of α = 1,1 will be mandatory for the design of new railway structures

following the implementation of the Technical Specifications for Interoperability

(Conventional Rail and High Speed Infrastructure TSI). ULS assessment is

comparable with British Standards. SLS assessment will be more onerous but is

unlikely to result in significant changes in section sizes, quantities of reinforcement or

numbers of connectors. Uncertainty surrounding the validity of simple FAT

assessment: BS EN 1991-2:2003 states simple FAT assessment not valid if α > 1,0

(see Error! Reference source not found.).

Investigating the sensitivity of

varying the dynamic factor, Φ

BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

The use of Φ3 for calculating shear effects due to transient load is recommended. The

increased shear force due to the use of Φ3 combined with α = 1,1 will lead to higher

shear forces calculated in accordance with the Eurocodes compared with the current

British Standards. The increase is unlikely to result in significant changes in section

sizes or connection details.



14



publication)


Braking BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

BS5400-2:2006

The values in the current British Standard are recommended in the National Annex.

The characteristic braking forces in the BS are greater than the Eurocode values. A

maximum braking force of 6000kN is specified in the Eurocode. No such cut off exists

in the current British Standards. At ULS the differences are less and for loaded lengths

above 305m the Eurocode values are greater, until the maximum value is achieved.

Design to the current Eurocode values for loaded lengths <300m, will make the design

of substructures within the allowable horizontal movement limits, the design of

bearings resisting longitudinal forces and, ensuring lateral stability of substructures,

will be less onerous. Note that traction will govern the design of short and medium

spans (up to 30m using the current British Standard and, up to 45m using Eurocode).

Traction BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

The values in the current British Standard are recommended in the National Annex.

The characteristic traction forces in the BS are greater than the Eurocode values for

spans less than 14.7m. Above 14.7m the Eurocode characteristic values are greater.

The maximum characteristic traction force in the BS is 750kN compared with 1000kN

specified in the Eurocode. The differences in the ULS values are similar. Design to the

current Eurocode will make the design of, bearings resisting longitudinal forces,

ensuring lateral stability of substructures and, meeting the allowable horizontal

movement limits for substructures, less onerous for short spans (<15m) but more

onerous for medium spans (15m to 50m). Above 50m braking governs the design.

Derailment BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

The study indicates that Eurocode derailment loadings are more onerous than those

from current British Standards and that elements designed specifically to resist

derailment loading may require increased capacity. The study did not cover the local

effects of derailment loading and the associated effects on member sizes. However,

for the design of the typical bridges considered, member sizes were dictated by load

combinations for the Permanent/Transient design situations rather than from

derailment loading (Accidental design situation).



15



publication)


Collision with substructures BS EN 1991-2:2003 referring to

BS EN 1991-1-7:2006

There are potentially significant differences between the BSs and the EC, which will

be addressed by the National Annex to BS EN 1991-1-7 (Published December 2008).

The differences include the magnitude of the collision load, classification of structures

and hazard zones, and the rules of application.

The most significant differences arise from consideration of the appropriate impact

class, when impact shall be considered and, the magnitude of the equivalent impact

force.

Deformation under transient

railway actions

BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

UIC 776-3

GC/RT5110

GC/RC5510

The differences in the deformations of the steel structures studied were minimal and

attributed to the different partial factors on the actions.

The differences encountered were greater for the reinforced concrete structure. The

comparison factor was 1,15 for the vertical deformation and 1,12 for the rotation. This

is attributed to the difference in the short term modulus of elasticity specified in the

codes (for fcu = 50MPa, E = 34kN/mm2 in current British Standards compared with

37kN/mm2 in the Eurocodes), the different partial factors on the actions and, increased

effective, cracked section properties permitted by the Eurocode.

The comparison for the composite concrete and steel structure was 0,89 for the vertical

deformation and 1,041 for the rotation. This is attributed to the differences in the

modulus of elasticity specified in the codes (as above) and the different partial factors

on the actions.

Although there are differences, they should not result in any significant changes in

design or construction of railway structures.



16



publication)


Wind effects BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

BS EN 1991-1-4:2005


1991-1-4:2005

BS 5400-2:2006

The Eurocode basic wind velocity is lower than the current British Standard. The

environmental factors are similar resulting in a wind pressure that is marginally higher

than the Eurocode.

Wind only BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

BS EN 1991-1-4:2005


1991-1-4:2005

BS 5400-2:2006

The wind force coefficients and ULS partial factors are larger when calculated in

accordance with the Eurocode. The resulting wind force is therefore marginally greater

calculated in accordance with the Eurocode. Little change to the size and detailing for

elements designed primarily to resist wind actions is likely.



17



publication)


Wind coexistent with live load BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

BS EN 1991-1-4:2005


1991-1-4:2005

BS 5400-2:2006

The wind force coefficients, the wind area and the ULS partial factors are larger when

calculated in accordance with the Eurocode. The resulting wind force is greater

calculated in accordance with the Eurocode. The Eurocode includes a load

combination comprising maximum railway traffic actions plus wind. This may lead to

larger section sizes for elements primarily resisting traffic actions but that are

vulnerable to wind forces.

It is recommended that the partial factor γQ is 1,50 rather than the suggested 1,70 value

in the draft National Annex to avoid potential increased conservatism. (Note that since

the completion of this study, the UK national Annex recommends the value of partial

factor γQ is 1,70 if the characteristic value of wind actions which corresponds to 50

year return is used, or 1,45 if the characteristic value of wind actions for the required

return is calculated).

Global Temperature Effects BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

BS EN 1991-1-5:2003

Published National Annex BS

EN 1991-1-5:2003

BS 5400-2:2006

Values of the coefficient of thermal expansion (CTE) for concrete and composite

structures are different. There are also differences in the partial safety factors applied

for the limit states, where the Eurocode is marginally more conservative for an

equivalent temperature range.

In accordance with the Eurocode, where an installation temperature is not specified for

bearings and expansion joints, the temperature range should be modified by adding up

to a further 20 C to the range. Therefore the calculated Eurocode expansions and

contractions calculated are greater than those calculated in accordance with British

Standard, which is based on an assumed value of temperature at time zero.

Where temperatures are not modified in accordance with the Eurocode, the resulting

movements were similar to the current British Standard values.

It is recommended that the partial factors remain as the recommended values but that

the 20 C adjustment need not necessarily be made to the temperature range where

accurate consideration of the season when construction will take place has been made.

(Note that since the completion of this study, the UK national Annex recommends the

value of partial factor γQ is 1,55).



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publication)


Effect of temperature gradient BS EN 1991-2:2003


1991-2:2003 dated 07/08/2003

BS 5400-2:2006

The temperature gradients through the sections are the same in accordance with the

current British Standard and the Eurocode. However, the Eurocode is more

conservative as the applied partial factors on the thermal effects are greater than the

current British Standard.

The design situation involving coexistent railway load is similar at ULS but the

Eurocode is more conservative at SLS.

Although the effects of temperature gradients rarely govern the design of continuous

bridges at ULS, they often contribute significant components of stress that must be

accounted for at SLS. When combined with the greater stress from the coexistent

railway load, this will lead to changes in design of structural elements and connections

compared to the current British Standard and a more conservative design.

The Eurocode allows temperature effects to be combined with the railway traffic live

load and wind. No equivalent combination exists in the current British Standard. This

could lead to increases in element sizes for continuous bridges or integral (e.g. portal

frame) structures which are primarily designed to resist traffic actions but which are

vulnerable to wind and thermal actions.

Groups of loads BS EN 1991-2:2003


1991-2:2003

BS 5400-2:2006

The Eurocode combines individual components of railway traffic actions into Groups

of loads that can then be combined with appropriate other actions. Using specified

groups of loads as a single (multi-directional) action as an alternative to determining

the critical railway traffic actions individually may be more convenient to use and will

not result in any difference in details or margin of capacity for typical superstructures.

No advantage in using the groups of loads approach in design could be determined

when used with the factors in the UK National Annex to the Eurocode.



19



publication)


Comparison of the margin of

capacity (utilisation) for the

design of typical railway

structural elements to current

British Standards and the

Eurocodes

BS EN 1991-2:2003


1991-2:2003

BS 5400-2:2006

The summary is based on the study of the typical railway structures agreed with

RSSB. Only the differences between the design of the agreed details are summarised

in the following sections.

Steel plate girder structures BS EN 1993-2:2006

National Annex BS EN 1993-2

The results of the study indicate that designing details at SLS and ULS will be similar

whether designed in accordance with the Eurocode or British Standards. Designs in

accordance with the Eurocodes are generally less efficient (lower utilisation) than the

current British Standards . The Eurocode design of connections subject to HSFG bolt

shear tended to be more efficient (higher utilisation) than the British Standards but the

conclusions for HSFG bolt slip and bearing were less conclusive.

The calculation of buckling capacity of beams with partially effective lateral restraint

at ULS in accordance with the Eurocodes using non linear finite element buckling

analysis could, in theory, result in a marginally smaller section being adopted.

Designing sections subject to shear in accordance with the Eurocode will result in a

marginally smaller section size being required except when the effects of shear

buckling are considered.

Designing connections to satisfy the ULS and SLS (using HSFG bolts) requirements

with the Eurocodes may require a greater number of bolts or greater bolt spacing, and

hence larger connection plates and connection areas.

The assessment of fatigue susceptible details using the simple approach (no damage)

in the current British Standards and Eurocodes shows similar results for all but the

web shear fatigue assessment although fatigue is unlikely to govern the design of shear

resisting details. It is therefore concluded that the design details to resist fatigue would

be similar for most railway bridges designed to either the current British Standards or



20



publication)


the Eurocodes with little change in the margin of capacity for the majority of details

but an increase where fatigue of welds governs.

Calculating damage using the Miner sum approach shows the current British Standards

to be more conservative because of the sensitivity of calculating damage with SN

curves. Consideration of further detail types beyond the range studied is recommended

before conclusions can be made with regard to the Miner sum fatigue assessment

methods.

Changing the recommended partial factor values is not recommended.

Steel box girder structures BS EN 1993-2:2006

National Annex BS EN 1993-2

The calculation for the bending capacity of boxes at ULS in accordance with the

Eurocodes is more efficient. The differences are small and it is unlikely that section

sizes would change.

Designing sections subject to shear in accordance with the Eurocode will result in a

smaller section at ULS.

Designing connections to satisfy the ULS and SLS (using HSFG bolts) requirements

may require a greater number of bolts or greater bolt spacing, and hence larger

connection plates and connection areas.

Changing the proposed partial factor values is not recommended.



21



publication)


Composite steel and concrete

structures

BS EN 1994-1-1:2004, BS EN

1994-2:2005, National Annex

BS EN 1994-2:2005.

The calculation of the bending capacity of beams with fully effective lateral restraint at

ULS in accordance with the Eurocodes could result in a marginally larger section and

hence some increase in the margin of capacity.

Designing sections subject to shear in accordance with the Eurocode is unlikely to

result in a change of section or reduced margin of capacity at ULS.

Designing shear (stud) connections in accordance with the Eurocode may result in a

reduction in the number of shear connectors.

The design of reinforced concrete slabs spanning between longitudinal girders in

accordance with the Eurocodes is more onerous at ULS. Section sizes will have to

increase, stronger concrete be specified, and larger bars or more reinforcing bars be

used. The margin of capacity will be greater than designing to the current British

Standards.


Pre-stressed concrete structures BS EN 1992-1-1:2004, BS EN


BS EN 1992-2:2005.

The Eurocodes are generally more efficient (higher utilisation) than the British Codes

although this is dependent on the exposure condition of the bridge: if the bridge is

exposed to chlorides, both the Eurocodes and British Standards were found to produce

similar results.

If the bridge is not exposed to chlorides, the Eurocode provided more efficient results

with savings of approximately 10% in the number of tendons required.


Composite steel and concrete

structures – Filler Decks

BS EN 1994-1-1:2004, BS EN


BS EN 1994-2:2005.

Designing filler beam decks in accordance with the British Standards resulted in a

more efficient design (higher utilisation) at ULS and for fatigue. However, the

differences were small and unlikely to result in any change in section size of any

member.



22



publication)


Substructures BS EN 1997-1:2004 and

National Annex BS EN 1997-

1:2004

The Eurocodes are generally more onerous for design action DA1-1, but equivalent to

BS 8002:1994 for design action DA1-2. DA1-1 load combination applies a factor to

the permanent and variable actions, whilst DA1-2 applies factors to the materials and a

reduced factor to the variable actions. It is not anticipated that the change from British

codes to Eurocodes will have a significant impact upon the overall dimensions of

retaining walls.

Note that the design of piers in the impact zone may be more substantial in accordance

with the Eurocode where piers are supporting ‗Class A‘ structures and the impact

forces are greater than those in the British Standards

Differences in the approach to

fatigue assessment

BS EN 1992-1-1:2004

BS EN 1992-2:2005

BS EN 1993-1-1:2005

BS EN 1993-1-9:2005

BS EN 1993-2:2006

BS EN 1994-1-1:2004

BS EN 1994-2:2005

There are significant differences in the detail classes / categories, most notably where

fatigue failure across the throat of a weld is considered. In BS 5400-10:1980 the detail

is class W and the equivalent allowable stress for 2x106 cycles is 43MPa whereas the

BS EN 1993-1-9 detail category is 36. This will lead to larger weld details.

The current, draft National Annex to BS EN 1993-1-9 limits the number of detail

categories to the equivalent BS 5400-10:1980 classes to ensure the current margins of

safety are maintained. The margin of capacity may reduce in where designs are

undertaken in accordance with the Eurocodes.

There are significant differences in the S-N curves: The current British Standard is bi-

linear with no cut off limits (except where all stresses are below the non-propagating

level) whereas the Eurocodes are tri-linear with cut off limits. This leads to significant

differences in the calculated number of cycles to failure or damage.

The train types and mixes are not the same in the current British Standards and the

Eurocodes. It is recommended that the relevance of the Eurocode train types and

traffic mixes to the UK railway network is established from further studies. Such a

study should consider the design of fatigue susceptible details for typical railway

bridge structures subject to real trains, together with the application of the British



23



publication)


Standard and Eurocode traffic mixes.

The workmanship levels to the British Standards are set out in BS 5400-6, 7 & 8. The

workmanship requirements for the Eurocodes are set out in BS EN 1090 and BS EN

13670, but these documents have yet to be published and before a final conclusion on

the effect of designing to the Structural Eurocodes can be made, this document must

be reviewed. The draft National Annex limits a number of the detail categories for this

reason.

Simple Method (no damage

calculation)

Despite the differences in the values for the various k and λ factors, where the partial

safety factor γMf recommended in the National Annex is used, and where the detail

class/category and load are constant, typically the utilisation factor BS/EN = 1,10, i.e.

the utilisation (i.e. action / resistance) in accordance with the British Standards is

greater.

It was concluded that where the detail classes are comparable, the simple approach in

accordance with the current British Standards gives reasonably similar results to the

Eurocode and the design details and the margin of capacity will not be significantly

different compared to the current British Standards.

Miner Sum Method (damage

calculated)

The damage calculted fatigue assessment, based on the Miner sum approach, is the

same in the current British Standards and the Eurocodes. However, the traffic

attributes and S-N curves differ and have a significant influence on the damage

calculation, as demonstrated in the study of the different deck types.



24

1 Recommended Values where National Choice is Allowed in BS EN 1990:2002.

The following tables indicate all of the factors in BS EN 1990:2002 + A1:2005 where national choice

is allowed. The table details the values specified in the Eurocode, the values suggested in the draft

national annex and those recommended as a result of this study. Differences between the National

Annex and recommended values are highlighted.

A commentary follows the table giving further background considerations applied in determining the

recommended values and to highlight the differences between the recommended values and the values

specified in UIC leaflet UIC776-1 6th edition.

All references are to BS EN 1990:2002 + A1:2005 and Draft National Annex to BS EN 1990:2002 +

A1:2005

Description Clause Eurocode

Value

National Annex

Value

Recommended Value

Design working life A.2.1 (1) Note 3 100 years Text refers to

table National

Annex.A.2.1 but

no value is

given.

120 years in

National Annex

BS EN 1991-

2:2003.

120 years.

Values of ψ factors A2.2.6(1) NOTE 1 See separate table

Values of γ factors A2.3.1 Table

A2.4(A) NOTES 1

and 2

See separate table

Choice between 6.10

and 6.10a/b

A2.3.1 Table

A2.4(B) NOTE 1.

Not Given Equation 6.10 Equation 6.10

Values of γ and factors A2.3.1 Table

A2.4(B) NOTE 2

See separate table

Values of γSd A2.3.1 Table

A2.4(B) NOTE 4

Not Given 1,15 1,10 – 1,15 is

reasonable for most

situations though

specifying a value to

reduce γQ or γG would

result in a reduction in

the safety margin

Values of γ factors A2.3.1 Table A2.4

(C)

See separate table



25


A1:2005


Value

National Annex

Value

Recommended Value

Design values in Table

A2.5 for accidental

design situations, design

values of accompanying

variable actions and

seismic design situations

A2.3.2(1) 1,0 1,0

The impact

forces given in

BS 1991-1-7

should be

adjusted to

ensure that the

partial factor can

be set to unity.

1,0

Design values of actions

for use in accidental and

seismic combinations of

actions

A2.3.2 Table A2.5

NOTE

1,0 1,0 1,0

Alternative γ values for

traffic actions for the

serviceability limit state

A2.4.1(1) NOTE 1

(Table A2.6)

1,0 1,0 1,0

Infrequent combination

of actions

A2.4.1(1) NOTE 2 Not Given 1,infq factors

need not be used 1,infq not relevant for

railway bridges

Serviceability

requirements and criteria

for the calculation of

deformations

A2.4.1(2) Not Given Serviceability

requirements

and criteria

given in A.2.4.2

and A.2.4.3 may

be modified if

appropriate for

the individual

project.

Serviceability

requirements and

criteria given in

A.2.4.2 and A.2.4.3

are for road bridges

and footbridges.

Combination rules for

snow loading on railway

bridges

A2.2.4(1) Snow need

not be

considered

To be completed Snow need not be

considered apart from

execution.

Maximum wind speed

compatible with rail

traffic

A2.2.4(4) BS EN 1991-

1-4

To be

completed.

40m/s (gust) in

National Annex

BS EN 1991-1-4

25m/s limit for

fundamental wind

gives the equivalent

peak velocity pressure

as 40m/s wind gust to

BS 5400-2:2006 for

most situations.

Current British

Standards do not

impose any limit, for

operational reasons.

Deformation and

vibration requirements

for temporary railway

bridges

A2.4.4.1(1) NOTE

3

Not given. Not given Not considered in this

study



26


A1:2005


Value

National Annex

Value

Recommended Value

Peak values of deck

acceleration for railway

bridges and associated

frequency range

A2.4.4.2.1(4)P γbt = 3,5 m/s2

γdf = 5 m/s2

Not given Not considered in this

study

Limiting values of deck

twist for railway bridges

A2.4.4.2.2 – Table

A2.7 NOTE

t1 = 4,5mm

t2 = 3,0mm

t3 = 1,5mm


study

Limiting values of the

total deck twist for

railway bridges

A2.4.4.2.2(3)P tT is

7,5mm/3m.


study

Vertical deformation of

ballasted and non

ballasted railway bridges

A2.4.4.2.3(1) Not given Not given Not considered in this

study

Limitations on the

rotations of non

ballasted bridge deck

ends for railway bridges


study

Additional limits of

angular rotations at the

end of decks


study

Values of αi and ri

factors

A2.4.4.2.4(2) –

Table A2.8 NOTE

3

α1= 0,0035;

α2 = 0,0020;

α3 = 0,0015;

r1 = 1700;

r2 = 6000;

r3 = 14000;

r4 = 3500;

r5 = 9500;

r6 = 17500


study

Minimum lateral

frequency for railway

bridges

A2.4.4.2.4(3) The

recommended

value is:

fh0 = 1,2 Hz


study

Requirements for

passenger comfort for

temporary bridges


study



27

All references to BS EN 1990:2002 + A1:2005 and Draft National Annex to BS EN 1990:2002 + A1:2005

Values of ψ factors (A2.2.6(1) NOTE 1)

Actions

BS EN 1990:2002 National

Annex

Recommended

ψ0 ψ1 ψ2 ψ0 ψ1 ψ2 ψ0 ψ1 ψ2

Individual

components of

traffic actions

LM71

1 track

2 tracks

3 tracks

0,80

0,80

0,80

0,80

0,70

0,60

0

0

0

To be suggested

as part of this

study

0,80

0,80

0,80

0,80

0,70

0,60

0

0

0

SW/0

1 track

2 tracks

3 tracks

0,80

0,80

0,80

0,80

0,70

0,60

0

0

0

To be suggested

as part of this

study

0,80

0,80

0,80

0,80

0,70

0,60

0

0

0

SW/2 0 1,00 0 Not considered

in this study Not considered in

this study

Unloaded Train 1,00 - - Not considered

in this study

Not considered in

this study

HSLM 1,00 1,00 0 Not considered

in this study

Not considered in

this study

Traction Individual components of traffic actions in design situations

where the traffic loads are considered as a single (multi-

directional) leading action and not as groups of loads should

use the same factors as those adopted for the associated

vertical loads.

Braking

Centrifugal forces

Interaction forces*

Nosing forces 1,00 0,80 0 To be suggested

as part of this

study

1,00 0,80 0

Non public footpath loads 0,80 0,50 0 Not considered


this study

Real trains 1,00 1,00 0 Not considered

in this study

Not considered in

this study

Hz earth pressure#

1 track

2 tracks

3 tracks

0,80

0,80

0,80

0,80

0,70

0,60

0

0

0

To be suggested

as part of this

study

0,80

0,80

0,80

0,80

0,70

0,60

0

0

0

Aerodynamic effects 0,80 0,50 0 Not considered

in this study

Not considered in

this study

Main traffic

actions

(groups of

loads)

The groups of load are factored as the components that form the groups and are not listed

here. Refer to section 11 for further explanation.

Other

operating

actions

Aerodynamic effects 0,80 0,50 0 Not considered

in this study

Not considered in

this study

Maintenance loading for

non public footpaths

0,80 0,50 0 Not considered


this study

Wind forces Fwk 0,75 0,50 0 To be suggested

as part of this

study

0,75 0,50 0



28

All references to BS EN 1990:2002 + A1:2005 and Draft National Annex to BS EN 1990:2002 + A1:2005

Values of ψ factors (A2.2.6(1) NOTE 1)

Actions

BS EN 1990:2002 National

Annex

Recommended

ψ0 ψ1 ψ2 ψ0 ψ1 ψ2 ψ0 ψ1 ψ2

Fw** (maximum wind force

with traffic action)

1,00 0 0 To be suggested

as part of this

study

1,0 0 0

Thermal

actions

Tk 0,60 0,60 0,50 To be suggested

as part of this

study

0,60 0,60 0,50

Snow loads QSn,k (during execution) 0,80 - 0 To be suggested

as part of this

study

Snow need not be

considered apart

from execution.

Execution

loads

Qc 1,00 - 1,00 Not considered

in this study

Not considered in

this study

* Interaction forces due to deformation under vertical traffic loads

# Horizontal earth pressure due to traffic load surcharge



29

All references to BS EN 1990:2002 + A1:2005and Draft National Annex to BS EN 1990:2002 +

A1:2005

Design values of actions (EQU) (Set A)

Actions BS EN 1990:2002 National Annex Recommended

G,sup G,inf G,sup G,inf G,sup G,inf

Concrete self weight 1,05 0,95 1,05 0,95 1,05 0,95

Steel self weight 1,05 0,95 1,05 0,95 Not considered in

this study

Super-imposed dead 1,05 0,95 1,05 0,95 1,05 0,95

Weight of soil 1,05 0,95 1,05 0,95 1,05 0,95

Hydrostatic effects 1,00 0,95 1,00 1,00 1,00 1,00

Self weight of other

materials listed in BS EN

1991-1-1:2002, Tables

A.1-A.6

1,05 0,95 1,05 0,95 1,05 0,95

Prestressing P as defined in the

relevant design

Eurocode.

P as defined in the

relevant design

Eurocode or for the

individual project and

agreed with the

relevant authority

Not considered in

this study

Rail traffic actions 1,45 (0 where

favourable)

Non

given

(0 where

favourable) 1,45 (0

where

favoura

ble)

Wind actions 1,50 (0 where

favourable)

1,70 (0 where

favourable) Not considered in

this study

Thermal actions 1,50 (0 where

favourable)

1,50 (0 where

favourable) Not considered in

this study

The National Annex recommends that NOTE 2 is ignored, i.e. there is a different set of factors to

check uplift on continuous bridges. THIS HAS NOT BEEN CONSIDERED IN THIS STUDY.

Only a limited number of structures have been considered. The values recommended are based on

engineering judgement.



30

All references to BS EN 1990:2002 + A1:2005 and Draft National Annex to BS EN 1990:2002 +

A1:2005

Design values of actions (STR/GEO) (Set B)



Concrete self weight 1,35 1,00 1,35 0,95 1,35 0,95

Steel self weight 1,35 1,00 1,20 0,95 1,20 0,95

Super-imposed dead 1,35 1,00 1,20 0,95 1,35 (for

ballast)

0,95

Weight of soil 1,35 1,00 1,35 0,95 1,35 0,95

Hydrostatic effects 1,35 1,00 1,00 1,00 1,00 1,00



1991-1-1:2002, Tables

A.1-A.6

1,35 1,00 1,35 0,95 1,35 0,95

Creep and shrinkage 1,35 1,00 1,35 0,00 1,35 0,00

Settlement (linear

analysis)

1,20 1,00 1,20 0,00 1,20 0,00

Settlement (nonlinear

analysis)

1,35 1,00 1,35 0,00 Not considered in this

study

Prestressing γP as defined in the

relevant design

Eurocode or for the

individual project

and agreed with the

relevant authority

γP as defined in the

relevant design

Eurocode or for the

individual project and

agreed with the

relevant authority


relevant design Eurocode

or for the individual

project and agreed with the

relevant authority

Rail traffic actions 1,45 0 where

favourable

Not

given

(0 where

favourable)

1,45 (0 where

favourable)

Earth pressure 1,50 1,00 Not

given

Not given 1,50 1,00

Wind actions

No traffic actions

applied simultaneously

with wind

1,50

0 where

favourable

1,70

(0 where

favourable)

1,50

(0 where

favourable)

Traffic actions applied

simultaneously with

wind

1,50 0 where

favourable

1,50 (0 where

favourable)

Thermal actions 1,50 0 where

favourable

1,50 (0 where

favourable)

1,50 (0 where

favourable)



31

All references to BS EN 1990:2002 + A1:2005 and National Annex to BS EN 1990:2002 + A1:2005

Design values of actions (STRGEO) (Set C)



Concrete self weight 1,00 1,00 1,35 0,95 Too few examples

considered to

recommend values.

Engineering judgement

and limited work

conclude National

Annex values

reasonable.

Steel self weight 1,00 1,00 1,20 0,95

Super-imposed dead 1,00 1,00 1,20 0,95

Weight of soil 1,00 1,00 1,35 0,95

Hydrostatic effects 1,00 1,00 1,00 1,00



1991-1-1:2002, Tables

A.1-A.6

1,00 1,00 1,35 0,95

Creep and shrinkage 1,00 1,00 1,35 0,00

Settlement (linear

analysis)

1,00 1,00 1,20 0,00

Settlement (nonlinear

analysis)

1,00 1,00 1,35 0,00

Prestressing γP as defined in the



project and agreed with

the relevant authority




project and agreed with

the relevant authority

Rail traffic actions 1,25 (0 where

favourable)

Not given (0 where

favourable)

1,25 (0 where

favourable)

Horizontal earth pressure 1,30 (0 where

favourable)

Not given Not given 1,30 (0 where

favourable)

Wind actions

No traffic actions

applied

simultaneously with

wind

1,50

(0 where

favourable)

1,70

(0 where

favourable)

1,50

(0 where

favourable)

Traffic actions applied

simultaneously with

wind

1,50 (0 where

favourable)

1,50 (0 where

favourable)

Thermal actions 1,30 (0 where

favourable)

1,50 (0 where

favourable) 1,50 (0 where

favourable)



32

Commentary:

The following summarises the discussions between Mott MacDonald and RSSB in determining the

recommended values in the preceding tables:

The values of the combination factors ψ0 and ψ1 for wind actions specified in BS EN

1990:2002 + A1:2005 are recommended. Mott MacDonald initially suggested that a reduced

partial factor (γQ) should be considered to account for the reduced probability of maximum

traffic occurring when the wind action is the leading action. In this case the maximum wind

action need only be applied together with a reduced (80% recommended) value for the

coexistent traffic actions. For combination 2 loads, BS 5400-2:2006 reduces γfL for the wind

load from 1,40 to 1,10 in such an event and γfL for the railway loads to 1,20. BS EN

1990:2002 + A1:2005, Table A2.3 (Note 2) states that where wind forces act simultaneously

with traffic actions, the wind force ψ0FWk should be taken as no greater than FWk** (where the

fundamental wind velocity is limited to a value compatible with the limiting wind speed for

train operations). This might be taken to imply that the traffic action is always the leading

action, which may not always be the case. Clause A2.2.4 (4) of BS EN 1990:2002 + A1:2005

places this restriction on wind velocity regardless of whether wind is an accompanying action

or not. In respect of the value to be adopted for the partial factor (γQ) for wind, it was

accepted that by reverting to the values recommended in the National Annex to BS EN

1990:2002 + A1:2005, there will be an increase in wind actions but for most railway bridge

designs, this combination will not normally govern the design (it is more likely to govern for

the design of long spans such as cable supported structures.)

The action due to snow has been determined and is less than the characteristic walkway

actions for a typical, single track deck (3,50m wide). It is concluded that the Eurocode

recommendation, that snow can be neglected for all but very special structures or

environments, is followed, noting that it may need to be considered during execution.

Values of the combination factors ψ0 and ψ1 for thermal actions were initially recommended

as 1,30 in line with BS 5400-2:2006. However, it is accepted that by reverting to the values

recommended in BS EN 1990:2002 + A1:2005, whilst there will be an increase in thermal

actions for most railway bridge designs, this combination will not govern the design for

typical railway structures, with the exception of structures with continuous spans.

UIC776-1 5th edition incorporates many aspects of BS EN 1990:2002 + A1:2005 for railway

bridge loading. UIC776 Tables 1, 2 and 3 summarise the suggested combinations and partial

factors. There are differences that are worthy of highlighting and may require discussion:

Recommended values of ψ factors for railway bridges (BS EN 1990:2002 + A1:2005, Table

A2.3), Wind forces, FWk. Suggested values for ψ0 = 0,75. Values in UIC776-1 5th edition are

ψ0 = 0,60.

Ultimate limit state, equilibrium (EQU) (BS EN 1990:2002 + A1:2005, Table A2.4(A) (Set

A), permanent, direct actions (all). Suggested values for γGj = 1,05 or 0,95. Values in

UIC776-1 are γGj = 1,1 or 0,90 generally or γGj = 1,15 or 0,85 if loss of equilibrium could

result in multiple fatalities.

Ultimate limit state, equilibrium (EQU) (BS EN 1990:2002 + A1:2005, Table A2.4(A) (Set

A), permanent, indirect actions (settlement and differential settlement). Suggested values for

γGset = 1,35 if non linear analysis undertaken, or γGset = 1,20 if linear analysis undertaken.

Values in UIC776-1 are γGset = 1,35.

Ultimate limit state, resistance (STR/GEO) (BS EN 1990:2002 + A1:2005, Table A2.4(B) (Set

B). Suggested values for γGj (self weight of steel) = 1,20 or 1,00. Values in UIC776-1 are γGj

(self weight of steel) = 1,35 or 1,00.



33

2 Recommended Values where National Choice is Allowed in Eurocodes, other than BS EN 1990:2002 + A1:2005.

The following tables provide a summary of the values and factors considered in the study where

national choice is allowed in Eurocodes other than BS EN 1990:2002 + A1:2002. The table details the

value specified in the Eurocodes, the suggested value in the draft National Annex and the

recommended value following the work undertaken for this study. Differences between the

recommended values and National Annex values are highlighted.

A commentary follows the table to give further background information in determining the

recommended values and to facilitate further discussion.

All references to BS EN 1991-1-1:2002 and National Annex to BS EN 1991-1-1:2002 dated 30th

December 2005


Value

National Annex

Value

Recommended

Value

the upper characteristic

value of the density of

ballast

5.2.3 (1) 20,0kN/m3 21 kN/m

3 21 kN/m

3

the lower characteristic

value of the density of

ballast

5.2.3 (1) Not given 17 kN/m3 18 kN/m

3

the nominal depth of

ballast

5.2.3 (2) ±30 %

irrespective of

ballast depth

±30 % should be

applied only to the

top 300 mm

±30 % should be

applied only to the

top 300 mm

Table 2: Recommended Values in BS EN 1991-1-1



34

All references to BS EN 1991-2:2003 and National Annex BS EN 1991-2:2003 dated 3rd

August

2007


Value

National Annex

Value

Recommended

Value

Alternative load

models for railway

bridges

6.1 (2) Alternative

models may be

specified

See Table 3 See Table 3

Load on a walkway if

it supports a cable

route

6.3.7 (2) Pedestrian,

cycle and

general

maintenance

loads, qfk =

5kN/m2

Greater of 1 kN/m or

the actual weight of

the cables

Not considered in

this study

Maintenance load for

the design of local

elements.

6.3.7 (3) Qk = 2,0kN

applied to

square of

200mm

Greater of Qk

= 2,0 kN applied to a

circular area

of 100mm diameter,

or a point load of 1

kN.

Not considered in

this study

Handrail loading 6.3.7 (4)

Horizontal

forces taken as

category B and

C1 EN 1991-1-

1

Greater of

0,74 kN/m or a

horizontal force

of 0.5 kN applied at

any point to the top

rail.

Not considered in

this study

Values of factor 6.3.2 (3)P 1,0

(recommended

for international

lines)

1,1

Alternative values of

may be

determined for the

individual project.

1,1 is mandatory

for design of new

bridges (TSI

requirements: Refer

to documents

referenced in Table

1)

Choice of dynamic

factor

6.4.5.2 (3)P

3 should be

used where no

factor specified

- depends on

track

maintenance

standard.

Generally 3 should

be used.

Alternative values

may be determined

for the individual

project.

3 should be used.



35


August

2007


Value

National Annex

Value

Recommended

Value

Derailment of rail

traffic, additional

requirements

6.7.1 (2)P Design

Situations 1 and

2 shall be

considered.

Deck plates and

similar local

elements designed to

support a point load

of 1.4 x 250 kN,

applied anywhere on

the deck plate or

local element. No

dynamic factor

needs to be applied

to this design load

Not considered in

this study

Derailment of rail

traffic, measures for

structural elements

situated above the level

of the rails and

requirements to retain

a derailed train on the

structure

6.7.1 (8)P

Note 1

No

requirements

specified.

Measures to mitigate

the consequences of

a derailment may be

determined for the

individual project.

Not considered in

this study

Assessment of groups

of loads

6.8.2 (2)

Note

Table 6.11 The factors given in

Table 6.11 should be

used.

Where economy is

not adversely

affected, values of

zero or 0,5 may be

increased to 1,0 to

simplify the design

process.

The factors given in

Table 6.11 should

be used.

Fatigue load models,

structural life

6.9 (6) Note 100 years

recommended

The design working

life should generally

be taken

as 120 years.

120 years.

Fatigue load models,

specific traffic

6.9 (7) Note

Special traffic

mix may be

specified

A special traffic mix

may be determined

for the individual

project.

A special traffic

mix may be

determined for the

individual project

noting that the

simple approach to

fatigue may no

longer be

appropriate.

Table 3: Recommended Values in BS EN 1991-2



36


August

2007

Standard loading type

Load Model 71, SW/0

and HSLM

Span BS EN

1991-2:2003

National Annex Recommended

Value

Traction (30% of load on

driving wheels)

all 33.La,b

But <1000kN

up to 3m (L=3m: 99kN) 150 kN 150 kN

from 3 to 5m (L=5m: 165kN) 225 kN 225 kN


from 7

to 25m

(L=25m: 825kN) 24 (L – 7) + 300

kN

24 (L – 7) + 300

kN

over 25m 1000kN max 750 kN 750 kN

Braking (25% of load on

braked wheels)

all 20.La,b

But <6000kN

up to 3m (L=3m: 60kN) 125 kN 125 kN



over 7 m 6000kN max 20 (L – 7) + 250

kN

20 (L – 7) + 250

kN

Table 4: Alternative Values for Traction and Braking BS EN 1991-2



37

All reference to BS EN 1992-2:2005 and National Annex BS EN 1992-2:2005:2007


Value

National Annex

Value

Recommended

Value

Coefficient taking account of long

term effects on the compressive

strength and of unfavourable

effects resulting from the way the

load is applied. αcc

3.1.6 1,00 0,85 for bending

and axial

compression

1,00 for others

0,85 for bending

and axial

compression

1,00 for others

Partial factors for materials for

ultimate limit states and fatigue, γC

and γC,fat

2.4.2.4.(1) 1,50 1,50 1,50


ultimate limit states and fatigue γS

and γS,fat.

2.4.2.4.(1) 1,15 1,15 1,15


serviceability limit states γC 2.4.2.4.(2) 1,00 1,00 1,00


serviceability limit states γS 2.4.2.4.(2) 1,00 1,00 1,00

Partial factor for shrinkage action

γSH

2.4.2.1

1,00 1,00 1,00

Partial factors for prestress,

ultimate limit state γP,fav

2.4.2.2(1)

1,00 0,90 0,90

Partial factor for fatigue loads, γF,fat 2.4.2.3 (1) 1,00 1,00 1,00




38

All reference to BS EN 1993-2:2006 and National Annex BS EN 1993-2:2006 dated 2 May 2007


Value

National Annex

Value

Recommended Value

Partial safety factors 6.1(1)

(BS EN 1993-

1-1)

λM0 = 1,00

λM0 = 1,00 λM0 = 1,00

λM1 = 1,10 λM1 = 1,10 λM1 = 1,10

λM2 = 1,25 λM2 = 1,25 λM2 = 1,25

λM3 = 1,25 λM3 = 1,25 λM3 = 1,25

λM3,ser = 1,10 λM3,ser = 1,10 λM3,ser = 1,10

λM4 = 1,10 λM4 = 1,10 λM4 = 1,10

λM5 = 1,10 λM5 = 1,10 λM5 = 1,10

λM6,ser = 1,00 λM6,ser = 1,00 λM6,ser = 1,00

λM7 = 1,10 λM7 = 1,10 λM7 = 1,10

Partial factors for fatigue

verifications 9.3(1)P γFf = 1,00 γFf = 1,00 γFf = 1,00

Partial factors for fatigue

verifications 9.3(2)P BS EN 1993-

1-9.

γMf varies

between 1,00

and 1,35

depending on

design

assumptions

and inspection

regime

γMf = 1.1 γMf = 1.1

Damage equivalence

factors λ for railway

bridges

9.5.3(2)

λ1 for various

traffic types is

given in table

9.3 and 9.4 in

the Eurocode.

Note 1 –

Recommended

values should be

used.

Note 3 – λ1 should

be specified for

specialised lines.

Recommended values

used but values not

interrogated

Shear factor, ή BS EN

1993-1-1

6.2.6

BS EN 1993-

1-5

1,20

National Choice

allowed but no

National Annex

available.

1,20



39

All reference to BS EN 1993-2:2006 and National Annex BS EN 1993-2:2006 dated 2 May 2007


Value

National Annex

Value

Recommended Value

Determination of design

values of actions on the

bearings and

movements of the

bearings

A.

4.2.1(4)

Values are

included in

Table A.4 in

the Eurocode.

The recommended

values of T0

given in Table

A.4 should be

used, and Tg

should

be taken as 5 °C.

NOTE The

temperature

difference TK is

the maximum

contraction range

or maximum

expansion

range as

appropriate,

according to BS

EN 1991-1-5.

The National Annex

recommendations are

recommended.

Refer to comments in

10.5.


Notes

1. There are other interaction and modification (k) factors that can be specified in the National

Annex but these have not been considered as part of this study.

2. Imperfections and fabrication tolerances have not been considered as part of this study and

may account for some of the differences.



40

All references to BS EN 1994-2:2005 (National Annex not available)


Value

National Annex

Value

Recommended

Value

Partial factor for

design shear

resistance of a

headed stud γV

2.1.4.2(5)P 1,25 National Annex

not available

1,25


Note

1. Other factors are as in BS EN 1992 and BS EN 1993, as described in the other tables.



41

Commentary:

The following summarises the discussions on the recommended values in the preceding tables:

It is recommended that the minimum density of ballast in BS EN 1991-1-1:2002 is increased

from 17kN/m3

to 18kN/m3 as the partial factors for inferior actions is 0,95. The minimum

density is also used when considering bridge dynamic response and Network Rail may wish to

see another value or specify a value in the dynamic response section of BS EN 1991-2:2003.

It was initially recommended that the α factor value is maintained at 1,0 (1,1 specified in

National Annex to BS EN 1991-2:2003) unless specified for a particular project. The impact

of increasing the value on the serviceability limit state design and fatigue assessment of a

structure is not clear where a value other than 1,0 is used because no calculations for this

situation were considered. To maintain the same level of load effects from railway actions at

the ultimate limit state, it was initially suggested that the partial factor is increased from

γQ=1,45 to 1,55. However, a value of α=1,1 will be mandated for new bridges to satisfy the

high speed and conventional rail TSIs and γQ=1,45 is appropriate. It is suggested that

confirmation is sought that the α value used for fatigue assessment has a value of 1,0 except

for special traffic mixes.



42

3 Part 1 - Enhancement of Previous Studies

In 2003, Network Rail and RSSB commissioned Scott Wilson to review the railway loads proposed in

the Eurocodes and National Annexes. The work1 was undertaken over a number of years as the

various Eurocodes standards were published or drafted. The recommendations from the reviews

assisted the decisions on values of factors where national choice was permitted. As part of this RSSB

commission, Mott MacDonald extended and enhanced the work undertaken by Scott Wilson. The first

part of this report describes a parametric study that was undertaken to investigate the transient loads

and effects from railway vehicles. A comparison factor is used to illustrate differences.

3.1 Load Comparison Factor

Throughout Part 1 of this report, the following load comparison factor will be used unless an

alternative factor has been described in the relevant section.

The value of the load or load effect, multiplied by the appropriate partial factor, or product of partial

factors, is calculated in accordance with the British Standards and Eurocodes listed at the start of each

section. The resulting British Standard (BS) value is divided by the equivalent Eurocode (EN) value,

to derive the comparison factor, i.e. BS/EN.

Thus a value equal to unity demonstrates the current load effects calculated, or partial factors in

accordance with, the British Standards, is equivalent to the Eurocodes. A value >1,0 shows the current

British Standards are more efficient, onerous or conservative (higher utilisation) than the Eurocodes

and a value <1,0 shows the Eurocodes to be more efficient, onerous or conservative (higher utilisation)

than the current British Standard.

1 NETWORK RAIL REPORT ―Appraisal of Eurocode for Railway Loading‖ and RSSB report T696 ―Appraisal of

Eurocodes for Railway Loading‖



43

4 Comparison of Design Load Effects

British Standards Eurocodes (incl. National Annex)

BS 5400-2:2006

RC/GC5510

BS EN 1991-1-1:2002

BS EN 1991-2:2003

The Standards referred to in Section 4 are listed above.

4.1 Partial and Combination Factors

The following partial factors and combination factors were considered in the work by Scott Wilson.

The two design situations considered were effectively the British Standards load combination 1

together with the derailment conditions specified in clause 8.5.1 of BS 5400-2:2006. To enable direct

comparison with the work undertaken by Mott MacDonald, the factors were not changed:

4.1.1 Eurocodes

(i) Serviceability Limit State

Action γ (G or Q) α Φ

Ballast

depth

factor

Leading

Action ψ0

Permanent Self weight

(steel) 1,35

Self weight

(concrete) 1,35

Superimposed

Track

1,35

Ballast 1,35 30%

Other 1,35

Transient LM71 1,45 varies varies 1,00 0,80

Walkways 1,50 1,00 0,80

Table 8: Eurocode SLS Partial and Combination Factors used for Investigating α and Φ



44

(ii) Ultimate Limit State

Action γ (G or Q) α Φ Ballast

depth

factor

Leading

Action

ψ0


(steel)

1,00

Self weight

(concrete)

1,00

Superimposed

Track

1,00

Ballast 1,00 30%

Other 1,00


Walkways 1,00 1,00 0,80

Table 9: Eurocode ULS Partial and Combination Factors used for Investigating α and Φ

(iii) Accidental (Derailment)

Action γ (G or Q) α Φ

Ballast

depth

factor

Leading

Action ψ0


(steel) 1,00

Self weight

(concrete)

1,00

Superimposed

Track

1,00

Ballast 1,00 30%

Other 1,00


Walkways 1,00 1,00 0,80

Derailment 1,00 1,00

Table 10: Eurocode ACC Partial and Combination Factors used for Investigating α and

Φ

4.1.2 British Standards

(i) Serviceability Limit State

Action γf3 Φ Combination 1 γfL

Permanent Self weight (steel) 1,00 1,00

Self weight (concrete) 1,00 1,00

Superimposed

Track

1,00 1,00

Ballast 1,00 1,20

Other 1,00 1,00

Transient RU shear

RU bending

1,00 Ф2

Ф3

1,10

Walkways 1,00 1,00



45

Table 11: British Standards SLS Partial and Combination Factors used for Investigating α and Φ

(ii) Ultimate Limit State

Table 12: British Standards ULS Partial and Combination Factors used for Investigating α and Φ

(iii) Derailment

Table 13: British Standards ACC Partial and Combination Factors used for Investigating α and Φ

4.1.3 Deck Types

The previous studies also defined a number of deck types whose assumed properties were provided

and which have been retained for this study:

Very light; All steel direct fastened (e.g. lightweight truss girder bridge)

Light; All steel direct fastened (e.g. all steel Z-type)

Medium All steel ballasted (e.g. all steel Z-type and standard box girder bridges)

Heavy; Steel main girders and concrete floor (e.g. standard Z, D and E-type bridges)

Very heavy; All concrete half through (e.g. flyovers as used on Dutch railways)




Superimposed

Track

1,10 1,20

Ballast 1,10 1,75

Other 1,10 1,20

Transient RU shear

RU bending

1,10 Ф2

Ф3

1,40

Walkways 1,10 1,50




Superimposed

Track

1,10 1,20

Ballast 1,10 1,75

Other 1,10 1,20

Transient RU shear

RU bending

1,10 Ф2

Ф3

1,40

Walkways 1,10 1,50

Derailment 1,10 1,00



46

4.2 Variation of Load Classification Factor, α.

α is a ‗load classification factor‘ for lines carrying rail traffic which is heavier than lighter than normal

rail traffic (α = 1). It is applied to the rail traffic live load effects and is independent of span. For

international lines a value of α not less than 1,1 is recommended (BS EN 1991-2:2003 cl.6.3.2.(3)P))

and this value has also been recommended in the draft National Annex for BS EN 1991-2:2003.

Furthermore, the technical specification for interoperability (TSIs) for new structures on high speed2

and conventional rail3 lines mandates a value of α = 1,1.

This phase of the study has largely validated the previous Scott Wilson work, although small

differences in calculating the ballast weight were noted. The deck types proposed by Scott Wilson

were considered to be reasonable approximations. α is a function of the rail traffic live load on the

bridge and therefore any variation in value has a bigger effect on light decks as the transient rail traffic

load forms the most significant proportion of the total load. The dynamic factor, Φ3, was applied to

bending moments.

In accordance with the commission objectives, the variation of α between 0,9 to 1,2 for the Eurocode

load calculations was considered4. Note that long span heavy and short span light structures are

unlikely to be used and the values have been shaded to reflect this in the summary tables in Appendix

A1 and in an example, Table 14, below. The results were then compared to loads and effects

calculated for the same structures in accordance with British Standards; i.e. spans and nominal weight

of materials remain the same. Selected graphs comparing the ULS bending moments for variation of

with span, are included in this section. All graphs and summary tables are included in Appendix

A1.

Span (m)

Bridge Type 2.0 3.0 5.0 7.0 10.0 15.0 20.0 30.0 40.0 50.0

VL 0.93 0.93 0.92 0.92 0.92 0.93 0.95 0.95 0.95 0.95

L 0.93 0.93 0.92 0.92 0.92 0.93 0.94 0.94 0.94 0.94

M 0.94 0.95 0.94 0.94 0.95 0.93 0.95 0.95 0.95 0.95

H 0.94 0.95 0.94 0.95 0.95 0.94 0.95 0.96 0.96 0.96

VH 0.94 0.95 0.95 0.95 0.96 0.95 0.97 0.97 0.97 0.97

Table 14: Comparison of ULS Bending Moments where α = 1,10

The results of the study summarised in the following graphs indicate that α has the greatest effect on

lighter bridges over short spans.

The comparison between bridges designed to the British Standards and the Eurocodes, indicates a

maximum variation of 0,85 – 1,10 for the ULS bending moments of very light bridges over the ranges

of α considered, compared to a maximum variation of 0,87 – 1,11 for the ULS bending moments of

very heavy bridges.

With α = 1,0 the average ULS comparison factor ≥ 1,0. This implies that the British Standards

provide a slightly more onerous loading.

The following graphs demonstrate this for the ULS bending moments. The load effects are calculated

for both permanent and transient actions (P/T) and U denote ULS. Note that α is only applied to the

live load and the transient load proportion of the total load.

2 High Speed TSI 96/48/EC as amended

3 Conventional Rail TSI 2001/16/EC as amended

4 Note that BS EN 1991-2 requires a specific value of α specified in 6.3.2.(3)P



47

Very Light Bridges Bending Moments

ULS

0.00

5000.00

10000.00

15000.00

20000.00

25000.00

30000.00

35000.00

40000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) B

en

din

g M

om

en

t (k

Nm

)

Alpha Value 0.9

Alpha Value 0.95

Alpha Value 1

Alpha Value 1.05

Alpha Value 1.1

Alpha Value 1.2

British Loading

Figure 1: ULS Moments in Very Light Bridge Main Girder for Variation of α (Alpha)

Medium Bridges Bending Moments

ULS

0.00

5000.00

10000.00

15000.00

20000.00

25000.00

30000.00

35000.00

40000.00

45000.00

50000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) B

en

din

g M

om

en

t (k

Nm

)

Alpha Value 0.9

Alpha Value 0.95

Alpha Value 1

Alpha Value 1.05

Alpha Value 1.1

Alpha Value 1.2

British Loading

Figure 2: ULS Moments in Medium Weight Bridge Main Girder for Variation of α (Alpha)



48

Very Heavy Bridges Bending Moments

ULS

0.00

20000.00

40000.00

60000.00

80000.00

100000.00

120000.00

140000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) B

en

din

g M

om

en

t (k

Nm

)

Alpha Value 0.9

Alpha Value 0.95

Alpha Value 1

Alpha Value 1.05

Alpha Value 1.1

Alpha Value 1.2

British Loading

Figure 3: ULS Moments in Very Heavy Bridge Main Girder for Variation of α (Alpha)

The effects of variation of α on the shear forces demonstrates a greater difference between the British

Standards and the Eurocodes shear forces calculated for shorter span, lighter bridges. The majority of

results indicate that the Eurocodes produce more onerous shear forces than the British Standards. This

is due to the combined effect of α and different dynamic factors, 2 for British Standards and 3 for

Eurocodes, that are applied to shear force effects.

For shorter spans, the dynamic factor is greatest. Therefore the comparison with the ULS shear force

calculations is approximately 0,88 with α set as 1,0. For α = 1,1 the comparison factor reduces to

approximately 0,80. However as spans increase the variation is reduced. A further study of the effects

of the dynamic factor for shear is described in section 4.3.



49

Very Light Bridges

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) S

he

ar

Fo

rce (

kN

)

Alpha Value 0.9

Alpha Value 0.95

Alpha Value 1

Alpha Value 1.05

Alpha Value 1.1

Alpha Value 1.2

British Loading

Figure 4: ULS Shear in Very Light Bridge Main Girder for Variation of α (Alpha)

Medium Bridges

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

4000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) S

he

ar

Fo

rce (

kN

)

Alpha Value 0.9

Alpha Value 0.95

Alpha Value 1

Alpha Value 1.05

Alpha Value 1.1

Alpha Value 1.2

British Loading

Figure 5: ULS Shear in Medium Weight Bridge Main Girder for Variation of α (Alpha)



50

Very Heavy Bridges

0.00

2000.00

4000.00

6000.00

8000.00

10000.00

12000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) S

he

ar

Fo

rce (

kN

)

Alpha Value 0.9

Alpha Value 0.95

Alpha Value 1

Alpha Value 1.05

Alpha Value 1.1

Alpha Value 1.2

British Loading

Figure 6: ULS Shear in Very Heavy Bridge Main Girder for Variation of α (Alpha)

Note that if the traffic mix does not represent real traffic (assumed to be the case where α is greater

than 1,0) BS EN 1991-2:2003 cl. 6.9.(3) states that the simple approach to fatigue cannot be used.

However, it is understood that the allowable stress limits obtained from derivation of the fatigue detail

categories in BS EN 1993-1-9 include sufficient margins to allow the use of the simple approach using

the prescribed fatigue load model (LM71 or SW/0 with no α applied) where the actual traffic is

represented by the standard fatigue spectrum (see BS EN 1991-2:2003, Annex D).

4.3 Variation of Dynamic Load Factor, Ф.

This is a factor for representing the dynamic effects of rail traffic loads. For tracks with standard

maintenance the value of Φ3 is recommended, ranging between a minimum of 1,0 and a maximum of

2,0. The value is calculated using the determinant length, defined in table 6.2 of BS EN 1991-2:2003.

The National Annex to BS EN 1991-2:2003 recommends Φ3 be used .

The British Standards recommend Φ3 be applied to moments and Φ2 applied to shear forces due to live

load effects. The definition of Φ3 is the same in both the British Standards and Eurocodes.



51

Table 15: Range of Factor Φ Considered in Study

The spreadsheets used in the α study (refer to 4.2) were used, with all other factors remaining constant,

including α set at 1,1. Φ is a function of 1/L, therefore a variation in the value has a bigger effect on

shorter decks. The formulae for the calculation of Φ in the Eurocodes and the British Standards are

the same and therefore the study only looked at the affect of altering the Φ factor applied to shear load

effects.

The variation of Φ between Φ2 and Φ3 was considered over the range with intermediate values set at

intervals of one third (refer to Table 15). The influence is shown in the tables and graphs included in

Appendix A2. Note that long span heavy and short span light structures are unlikely to be used and

the values have been shaded.

The results of the study indicate that the variation of the dynamic factor has the greatest effect on the

shorter spans. As the spans increase, the comparison factors tend towards a common value. For the

shorter spans the comparison factor at ULS is around 0,81, tending towards a value of 0,94 for longer

spans. This variation is expected as the value of the dynamic factor has the greatest affect for the

shorter spans.

The following graphs show the comparative shear forces for the range of spans considered at ULS

with all graphs included in Appendix A2. The load effects are calculated for both permanent and

transient actions (P/T) and U denotes ULS. The Eurocodes calculations result in higher shear forces

than British Standards, even when the lower value of the dynamic factor is used. The difference in the

values of the shear forces is therefore attributed to the application of α = 1,1 to the Eurocode actions,

as discussed in the previous section of this report (refer to section 4.2) and the difference in the value

of Φ.

Span (m)

Factor 2,0 3,0 5,0 7,0 10,0 15,0 20,0 30,0 40,0 50,0

Φ2 1,67 1,67 1,53 1,41 1,31 1,21 1,16 1,09 1,06 1,03

Φ2 + 1/3.(Φ3 - Φ2) 1,78 1,78 1,62 1,48 1,36 1,25 1,19 1,11 1,07 1,03

Φ2 + 2/3.(Φ3 - Φ2) 1,89 1,89 1,70 1,54 1,41 1,28 1,21 1,12 1,07 1,04

Φ3 2,00 2,00 1,79 1,61 1,46 1,32 1,24 1,14 1,08 1,04



52

Medium Bridges Shear Forces

ULS

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

4000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) S

hear

Fo

rce (

kN

)

Dynamic Factor 1

Dynamic Factor 2

Dynamic Factor 3

Dynamic Factor 4

British Loading

Figure 7: ULS Shear in Medium Weight Bridge Main Girder for Variation of Φ

Very Heavy Bridges Shear Forces

ULS

0.00

2000.00

4000.00

6000.00

8000.00

10000.00

12000.00

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0

Span (m)

U (

P/T

) S

hear

Fo

rce (

kN

)

Dynamic Factor 1

Dynamic Factor 2

Dynamic Factor 3

Dynamic Factor 4

British Loading

Figure 8: ULS Shear in Very Heavy Bridge Main Girder for Variation of Φ

The increased shear force due to the use of Φ3 combined with α = 1,1 will lead to higher shear forces

calculated in accordance with the Eurocodes compared to the equivalent calculations using the current

British Standards. However the scale of the increase will only result in changes in section sizes or

connection details where shear governs the design.



53

5 Live Load Surcharge on Substructures

Refer also to section Error! Reference source not found., Error! Reference source not found..


BS 5400-2:2006

RC/GC5510

BS EN 1991-2:2003


5.1 Differences in Applied Actions

The current British Standard GC/RC5510 Clause 19.6 stipulates a load of 150kN/m over a 2.5m width

which is usually slightly more onerous then the loading criterion within BS 5400-2:2006 Clause

5.8.2.1 that specifies a blanket 50kN/m2 applied on areas occupied by the track.

Design Standard Nominal Applied Load

(unit width)

γfL γf3 ULS Applied Load

(unit width)

BS 5400-2:2006 50kN/m 1,20 1,10 66,0kN/m

GC/RC5510 60kN/m 1,20 1,10 79,2kN/m

Table 16: British Standards Live Load Surcharge Values and Partial Factors

BS EN 1991-2:2003 cl 6.3.6.4 states that the equivalent characteristic vertical loading due to rail

traffic actions for earthworks under or adjacent to the track may be taken as the appropriate load

model (LM71 in this study) uniformly distributed over a width of 3,00m at a level of 0,70m below the

running rail. Assuming the four 25t axles are distributed over the 6.4m between the 80kN/m UDLs,

this equates to a load of 52.1kN/m2.

Design Standard Nominal Applied Load

(unit width)

α γQ ULS Applied Load

(unit width)

BS EN 1991-2 52.1kN/m 1,10 1,50 86,0kN/m

Table 17: Eurocode Live Load Surcharge Values and Partial Factors

Considering a unit width of retaining structure, the GC/RC 5510 nominal load applied is the greatest.

Comparing with the Eurocode value, the load comparison factor is 1,15. However, the Eurocode

partial load factors are greater than the British Standards, the comparison factor at ULS is 0,92.

The effect of the Eurocode live load surcharge acting at a lower position below the running rail was

considered. This reduces the height of application of the Eurocode load on the retaining structure to

{H - 0.335 / H}. H is the height between the base of the retaining structure and the bottom of the

sleeper, where the surcharge is generally considered to apply in British Standards. Comparing the

resulting shear and moment on a range of heights, the comparison factors vary as shown in Table 18.



54

Comparison with

GC/RC5510

H = 7m H = 5m H = 3m H = 1m

Nominal ULS Nominal ULS Nominal ULS Nominal ULS

Shear 1,21 0.97 1,23 0,99 1,30 1,04 1,73 1,39

Bending 1,27 1,02 1,33 1,06 1,46 1,17 2,60 2,08

Table 18: Comparison of the Live Load Surcharge Effects on Typical Retaining Structures

The difference in nominal loads indicate the scale of difference when considering equilibrium (EQU)

(BS EN 1990:A2 Table A.2.4(A)) whereas the ULS comparison indicates the differences when

designing retaining structure elements (STR) (BS EN 1990:A2 Table A.2.4(B).



55

6 Longitudinal Actions


BS 5400-2:2006

RC/GC5510

BS EN 1991-2:2003


The draft British National Annex recommends the current British Standards approach to the

calculation of longitudinal loads due to traction and braking be used. As the National Annexes will

eventually be withdrawn, and it is possible that the values in the Eurocode are adopted, the

longitudinal forces were calculated in accordance with the Eurocodes and compared with the values in

the current British Standards and National Annex.

A range of spans were considered, between 3m and 350m, and the braking and traction forces for both

characteristic and ultimate limit state calculated and compared.

Longitudinal loads were calculated in accordance with current British Standards: BS 5400-1:1998 and

BS 5400-2:2006 with reference to GC/RC5510.

Longitudinal loads were also calculated in accordance with the Eurocodes BS EN 1990:2002 and BS

EN 1991-2:2003 noting that the National Appendix amends the Eurocode to the equivalent BS 5400-

2:2006 value.

6.1 Traction

A range of spans were considered and the traction forces for both characteristic (nominal) and ultimate

limit state calculated. Table 19 shows the calculated traction forces for the structures considered.

Figure 9 and

Figure 10 show the trends between 3m and 350m.

Note that α shall be applied to longitudinal actions due to trains and is included in the comparison.



56

Structure

Type

Span British Standards Eurocodes (not National Annex)

UL

S C

om

pa

rison

Fa

ctor

Nominal

Value

kN

γfL

(C1)

γf3 ULS

Value

kN

Characteristic

Value

kN

α γQ Leading

Action

ULS

Value

kN

Deck type

1- Z type

15,5m 504 1,4 1,10 776 511 1,10 1,45 1,00 816 0,95

Deck type 2

– E Type

35,0m 750

(maximum

limit)

1,4 1,10 1155 1000

(maximum

limit)

1,10 1,45 1,00 1595 0,72

Deck type 3

– Box

Girder

24,0m 708 1,4 1,10 1090 792 1,10 1,45 1,00 1263 0,86

Deck type 4

- Composite

20,0m 612 1,4 1,10 942 660 1,10 14,5 1,00 1053 0,90

Deck type 5

– Pre-

stressed

Concrete

7m 300 1,4 1,10 462 231 1,10 1,45 1,00 369 1,25

Deck type 6

– Filler

Beam Deck

8m 324 1,4 1,10 499 264 1,10 1,45 1,00 421 1,18

Substructure

type 1 -

7m* 300 1.5 1,10 462 231 1,10 1,45 1,00 369 1,25

Table 19: Comparison between Traction Forces

The current British Standard characteristic (nominal) values (included in the National Annex) are

greater than the Eurocode values for spans less than 14.7m. The maximum characteristic (nominal)

comparison factor is 2,27 for a 3m loaded length. Above 14.7m the Eurocode values are greater and

this can be seen when considering the typical structures studied.

The maximum characteristic traction force based on the current British Standards is 750kN compared

with 1000kN specified in the Eurocode and this gives rise to the minimum characteristic (nominal)

comparison factor of 0,75. Figure 9 shows the characteristic traction forces calculated using the

Eurocode and the current British Standards.



57

Comparison of Characteristic (Nominal) Traction Action

-100

100

300

500

700

900

1100

0 5 10 15 20 25 30 35 40 45 50

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Traction

EN1991-2 Traction

Figure 9: Comparison between Characteristic (Nominal) Traction Forces

The differences in the factored traction values at ULS are marginally less than for the characteristic

traction values. At ULS the maximum comparison factor is 2,19 for a span of 3m and the minimum

comparison factor is 0,72 at the cut off limit. Design to the current British Standards is more onerous

where the span is less than 13m and more onerous for the Eurocode where spans are greater than 13m.

Figure 10 shows the ULS traction forces calculated in accordance with the Eurocode and the current

British Standards.

Comparison of ULS Traction Action

0

200

400

600

800

1000

1200

1400

1600

1800

0 5 10 15 20 25 30 35 40 45 50

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Traction

EN1991-2 Traction

Figure 10: Comparison between ULS Traction Forces



58

When the National Annex is withdrawn, and if the Eurocode values are adopted, the design of

bearings to resist longitudinal forces, the provision of lateral stability for substructures, and the design

of substructures within the allowable horizontal movement limits, will be less onerous for short spans

(approximately <15m) but more onerous for medium spans (approximately 15m to 50m), where

traction is the critical action,. Above approximately 30m using current British Standards and above

50m for the Eurocodes, braking governs the design of substructures.

6.2 Braking

A range of spans were considered and the braking forces for both characteristic (nominal) and ultimate

limit state (ULS) were calculated. Table 20 shows the calculated braking forces for the typical

structures considered. Figure 11 and Figure 12 show the trends between 3m and 350m.

Note that α shall be applied to longitudinal actions due to trains and is included in the comparison.

Structure

Type

Span British Standards Eurocodes (not National Annex)

UL

S C

om

pa

rison

Facto

r

Nominal

Value

kN

γfL

(C1)

γf3 ULS

Value

kN

Characteristic

Value

kN

α γQ Leading

Action

ULS

Value

kN

Deck type

1- Z type

15,5m 420 1,4 1,10 646 310 1,10 1,45 1,00 512 1,26

Deck type 2

– E Type

35,0m 810 1,4 1,10 1247 700 1,10 1,45 1,00 1155 1,08

Deck type 3

– Box

Girder

24,0m 590 1,4 1,10 908 480 1,10 1,45 1,00 766 1,19

Deck type 4

- Composite

20,0m 510 1,4 1,10 785 400 1,10 1,45 1,00 638 1,23

Deck type 5

– Pre-

stressed

Concrete

7m 250 1,4 1,10 385 140 1,10 1,45 1,00 223 1,73

Deck type 6

– Filler

Beam Deck

8m 270 1,4 1,10 416 160 1,10 1,45 1,00 255 1,63

Substructure

type 1 -

7m* 250 1.5 1,10 385 140 1,10 1,45 1,00 223 1,73

* assuming the deck on the substructure is a 7m simply supported span, fixed at one end.

Table 20: Comparison between Braking Forces



59

The current British Standards characteristic (nominal) values (included in the National Annex) are

greater than the Eurocode values. The maximum comparison factor for the characteristic (nominal)

braking forces is 3,11 for a span of 3m and the minimum comparison factor is 1,02 for a span of

300m. The current British Standards characteristic braking force for a span of 295m equates to the

maximum characteristic braking force of 6000kN specified in the Eurocode. No such cut off exists in

the current British Standards. Figure 11 shows the characteristic braking forces calculated to the

Eurocode and the current British Standards.

Comparison of Characteristic (Nominal) Braking Action

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Braking

EN1991-2 Braking

Comparison of Characteristic (Nominal) Braking Action

0

1000

2000

3000

4000

5000

6000

7000

8000

0 50 100 150 200 250 300 350 400

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Braking

EN1991-2 Braking

Figure 11: Comparison between Characteristic (Nominal) Braking Forces

The difference in the ULS values of braking actions are marginally less than the characteristic values.

With α = 1,1 and γQ,sup = 1,45 applied, the overall ULS factor for the Eurocode is 1,595. For the current

British Standards with the relevant factors are γfL = 1,40 and γf3 = 1,1 which gives an overall ULS

factor of 1,54. This means that at ULS, where the loaded length is above 154m, the Eurocode value is

greater than the current British Standards until the Eurocode reaches a cut off limit of 9570kN (at a

loaded length of approximately 305m).

The maximum ULS comparison factor is 3,01 for a span of 3m and the minimum comparison factor is

0,98 for a span of 300m. Figure 12 shows the braking forces calculated for ULS in accordance with

the Eurocode and the current British Standards.



60

Comparison of ULS Braking Action

0

50

100

150

200

250

300

350

400

450

500

0 2 4 6 8 10 12 14 16 18 20

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Braking

EN1991-2 Braking

Comparison of ULS Braking Action

0

2000

4000

6000

8000

10000

12000

0 50 100 150 200 250 300 350 400

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Braking

EN1991-2 Braking

Figure 12: Comparison between ULS Braking Forces

When the National Annex is withdrawn, and if the Eurocode values are adopted, the design of

substructures within the allowable horizontal movement limits, the design of bearings to resist

longitudinal forces, and the provision of lateral stability for substructures, will be less onerous or

remain unchanged, where braking is the critical action. Traction will govern the design of short and

medium spans (to approximately 30m using current British Standards, to approximately 50m using the

Eurocode). Figure 13 provides a comparison of the characteristic braking and traction forces

calculated to the Eurocode and using the current British Standards.

Comparison of Characteristic (Nominal) Braking and

Traction Action

-100

100

300

500

700

900

1100

0 5 10 15 20 25 30 35 40 45 50

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Braking

EN1991-2 Braking

BS5400:2 Traction

EN1991-2 Traction

Comparison of ULS Traction & Braking Action

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60

Loaded length (m)

Fo

rce (

kN

)

BS5400:2 Braking

EN1991-2 Braking

BS5400:2 Traction

EN1991-2 Traction

Figure 13: Comparison between Characteristic (Nominal) & ULS Longitudinal Train Forces



61

7 Accidental Actions

7.1 Derailment Effects


BS 5400-2:2006

GC/RT5110

BS EN 1991-2:2003

The Standards referred to in Section 7.1 are listed above.

The application of derailment effects varies significantly between the Eurocode and the relevant

British Standard GC/RT5110. In the Eurocode, BS EN 1991-2:2003 and its associated draft National

Annex, derailment effects are based upon the application of Load Model 71 in two positions:

Design situation I (referred to here as case 1): Derailment of railway vehicles, with the

derailed vehicles remaining in the track area on the bridge deck with vehicles retained by the

adjacent rail or an upstand wall.

Design Situation II (referred to here as case 2): Derailment of railway vehicles, with the

derailed vehicles balanced on the edge of the bridge and loading the edge of the superstructure

(excluding non-structural elements such as walkways).

These situations are to be considered as accidental loading, with the partial factor used being 1,0. It

should also be noted that the α value, used in the calculation of ‗classified vertical loads‘ due to

railway traffic actions, shall also be applied to derailment actions. Its value is taken as 1,1 as

discussed in this report.

Design Situation I is concerned with the major failure of structural elements, and should be considered

under the STR set of equations from BS EN 1990:2002. Design Situation II is concerned with the

overturning and collapse of the structure, and should be considered under the STR and EQU set of

equations from BS EN 1990:2002.

The British Standards specify three conditions:

Case a. For the serviceability limit state, derailed coaches or light wagons remaining close to

the track shall cause no permanent damage.

Case b. For the ultimate limit state, derailed locomotives or heavy wagons remaining close to

the track shall not cause collapse of any major element, but local damage may be accepted.

Case c. For overturning or instability, a locomotive and one following wagon balanced on the

parapet shall not cause the structure as a whole to overturn, but other damage may be

accepted.

The derailment effects were calculated for a range of spans from 2m to 50m (as previous studies by

Scott Wilson). Comparison factors were not produced due to incompatibility between the different

design situations although Eurocode design situation II is similar to British Standards case b (checking

the ultimate limit state of the structure (STR) and Eurocode design situation II can be compared to

British Standards case c (checking the stability of the structure (EQU).

Figure 14 and Figure 15 show the variation of the moments and shears due to the different derailment

cases for both the Eurocode and for British Standards.

Comparing the Eurocode design situations with the British Standards cases, the Eurocode is more

onerous. The primary reasons for the differences are the loads and the factors applied to them and the

position the load is applied. Refer to table Table 21)



62

Standard Design

Situation

/ Case

Applied Load Applied

Factors

Position of

Applied

Load

Length of

Distribution

EN 1991-2:2003 I LM71 (8No

250kN + 80kN/m)

α x 1,4 Within 1,5x

track gauge

unlimited

EN 1991-2:2003 II LM71 (8No

250kN + 80kN/m)

α x 1,4 Along edge

of structure

20m

BS5400-2:2006 a Pair of 20kN/m

udls + 100kN

γf3=1,10 Within 2m of

the track cL

unlimited

BS5400-2:2006 b No rows of 4No

180kN

γf3=1,10 Anywhere on

structure

4.8m

BS5400-2:2006 c 80kN/m γf3=1,10 Along edge

of structure

20m

Table 21: Derailment Loads

Refer to section 4 for the combination and partial factors used.

Moments Due to Derailment Effects

0

5000

10000

15000

20000

25000

30000

35000

40000

2 3 5 7 10 15 20 30 40 50

Span (m)

Mo

me

nt

(kN

m)

Case 1

Case 2

SLS (a)

ULS (b)

ULS (c)

Figure 14: Design Moments due to Derailment Effects



63

Shears Due to Derailment Effects

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2 3 5 7 10 15 20 30 40 50

Span (m)

Sh

ea

r (k

N) Case 1

Case 2

SLS (a)

ULS (b)

ULS (c)

Figure 15: Design Shears due to Derailment Effects

The results of the study indicate that the derailment loadings for the Eurocode result in more onerous

loadings than those from the current British Standards. This means that elements designed specifically

to sustain derailment loading will require increased capacities and consequently increased element

sizes. This study did not cover local derailment loading and the associated effects on member sizes

due to this. However for the typical bridges used in this study, the designs would be governed by the

Permanent/Transient design situations rather than the derailment cases.



64

7.2 Collision Effects


BS 5400-2:2006

GC/RC5510

BS EN 1991-1-7:2006

The Standards referred to in Section 7.2 are listed above.

Impact from derailed trains with structures spanning across or alongside railway lines is included in

BS EN 1991-1-7:2006. There are two classes of structure that could be subjected to derailment impact

and the class of structure depends on the number of potential injuries to the occupants of the structure

in the event of collapse:

Class A structures are those that span across or near to the operational railway that are either

permanently occupied or serve as a temporary gathering place for people or consist of more

than one storey of the structure.

Class B structures are massive structures that span across or near the operational railway such

as bridges carrying vehicular traffic or single storey buildings that are not permanently

occupied or do not serve as a temporary gathering place for people.

BS EN 1991-1-7:2006 gives specific, static equivalent actions for class A structures adjacent to

railway lines where the line speed does not exceed 120km/h noting that the values may be reduced

where the elements are protected or the line speed is below 50km/h.

The resulting design loading (i.e. no partial factors to be applied to the actions) is summarised in Table

22:

Distance from Rail (d) Force in the Direction

of the Track

Force

Perpendicular to

the Track

Direction

Height above Track for

Point of Application

d<3m Specified by project Specified by project Specified by project

3m<d<5m Fdx = 4000kN Fdy = 1500kN 1,80m

d>5m Fdx = 0kN Fdy = 0kN N/A

Table 22: Eurocode Collision Loading (Class A Structures)

For a bridge spanning across or close to the railway, class B is appropriate and pier impact must be

considered. For class B structures the equivalent static actions must be determined for the individual

project. The draft NA does not provide a design value for impact with class B structures but instead

leaves the design value to be determined for individual projects on the basis of a risk assessment.

Assuming the risk based approach is undertaken in accordance with the informative information in BS

EN 1991-1-7:2006 Annex B, this is likely to be time consuming and expensive and the project sponsor

may decide that the class B structures are to be designed to resist specified loads (for example the class

A actions or the minimum robustness requirements contained within British Standards.

The Eurocode class A actions parallel to the tracks are significantly more onerous than the collision

loading for railway traffic currently recommended for situations where the line speed does not exceed

200km/h in GC/RC5510 Appendix H. The actions perpendicular to the track are more onerous in

accordance with British Standards and tend to be the critical design criteria for the design of piers.



65

It must be noted that:

the Eurocodes consider the hazard zone within 5,0m of the track centreline compared to 4,5m

from the cess rail in the case of the British Standards (note that the UK National Annex

requires the British Standards definition define the hazard zone).

the applicable speed is 120km/h in accordance with the Eurocode compared to 200km/h in the

British Standards.

A ULS partial safety factor γfL or γQ=1,00 should be applied to all impact loading for design to the

Eurocode and when using the GC/RC5510 recommendations. γf3=1,10 should be applied the impact

loading for design to GC/RC5510 to get the design load effect from the stated design force.

The GC/RC5510 loading recommendations are summarised in Table 23:

Distance from Rail (d) Force in Any Direction Height above Ground for Point

of Application

d<4,5m 2000kN or 500kN 1,2m or 3m

d>4,5m F = 0kN N/A

Table 23: GC/RC5510 Collision Loading

Table 24 below compares the shear and moment at the base of a pier, assumed effectively a cantilever

from a base 1,0m below rail level.

Standards Parallel to Tracks Perpendicular to Tracks

Moment (kNm) Shear (kN) Moment (kNm) Shear (kN)

GC/RC5510 4840 2200 4840 2200

BS EN 1991-1-7

(Class A)

11200 4000 4200 1500

Comparison

factor (CF)

0,432 0,550 1,152 1,467

Table 24: Comparison of Design Criteria for a Typical Pier in the Hazard Zone

In the absence of further guidance in the National Annex, or from the UK Railway Industry, and on

the assumption that the design values for class A structures are adopted for class B structures, there are

potentially significant cost implications for the design of class B structures.



66

8 Vertical Deformation and Rotation


BS 5400-1:1998

BS 5400-2:2006

BS 5400-3:2000

BS 5400-4:1990

GC/RC5510

UIC776-3R

BS EN 1990(A1):2002

BS EN 1991-1-1:2002

BS EN 1991-2:2003

BS EN 1992-1-1:2004

BS EN 1993-1-1:2005


The maximum vertical deformation and rotation of the typical railway bridges selected for this study

were calculated to the current British Standards and compared with the Eurocode values. The applied

actions considered were the SLS (Characteristic) transient railway actions (LM71 / RU) and associated

permanent actions.

Table 25 summarises the calculated deflections and compares the values:

Deck

Type

Span British Standards Eurocodes Comparison Factor

Mid span

Deflection

End of

Deck

Rotation

Mid span

Deflection

End of

Deck

Rotation

Mid span

Deflection

End of

Deck

Rotation

1 15m 33,8mm 0,0090rad 32,3mm 0,0086rad 1,046 1,047

2 35m 50,2mm 0,0057rad 49,9mm 0,0057rad 1,006 1,000

3 24m 44,5mm 0,0074rad 43,9mm 0,0073rad 1,014 1,014

4 20m 30.9mm 0.0051rad 34.6mm 0.0049rad 0,89 1.041

5* 7m 6,7mm* 0,0031rad 5,8mm* 0,0026rad 1,15 1,12

Table 25: Comparison of Deflections for the Typical Decks Studied

*Note: deflection in Table 25 has been calculated under characteristic actions, however the

deformation should be considered under the quasi-permanent load case in accordance with BS EN

1992-1-1:2004 Clause 7.1. Deflections and rotations include live load and are total values excluding

any pre-stress. For Deck type 5 (pre-stressed concrete deck) the total deflection should be considered

as summarised in Table 26:

Deck Type 5 British Standards

Mid span Deflection

Eurocodes

Mid span Deflection

Comparison

Factor

Prestress Deflection -3,45mm -3,14mm 1,10

Perm Load Deflection 1,07mm 0,93mm 1,15

Live Load Deflection 5,60mm 4,87mm 1,15

Total Deflection 3,21mm 2,67mm 1,20

Table 26: Summary of Deck Type 5 (Pre-stressed Concrete Beams) Deflections

The differences in the deformations of the steel structures were a maximum of 1,046 for the vertical

deformation and 1.047 for the rotation. The minimum comparison factor was 1,000. The small

differences are mainly attributable to the different partial factors on the actions. There are also

differences in the modulus of elasticity (E) specified in the codes: 205kN/mm2 in current British

Standards compared to 210kN/mm2

in the Eurocodes. For equal load effects, the Eurocode would

therefore give smaller deflections.



67

The differences were greater for the reinforced concrete structure. The comparison was 1,15 for the

vertical deformation and 1,12 for the rotation. This is attributed to the differences in the short term

modulus of elasticity specified in the codes (for fcu = 50MPa, E = 34kN/mm2 in current British

Standard compared with an E 37kN/mm2

in the Eurocodes), the different partial factors on the actions

and how the codes calculate the effective, cracked section properties.

The comparison for the composite concrete and steel structure was 0,89 for the vertical deformation

and 1,041 for the rotation. This is attributed to the differences in the modulus of elasticity specified in

the codes (as above) and the different partial factors on the actions.

Although there are differences, they should not result in any significant changes in the costs of

construction of railway structures due to increase in the size of structural elements.



69

9 Wind Effects


BS 5400-2:2006 BS EN 1991-1-4:2005

BS EN 1990:2002(A1) Annex A2

BS EN 1991-1-1:2002

BS EN 1991-2:2003


The calculation and application of wind actions on typical railway bridges (see Part 2) was studied to

complete the work undertaken by Scott Wilson for Network Rail. Only the wind action on railway

structures and wind coexistent with railway traffic actions has been considered. A full review of BS

EN 1991-1-4:2005 and the draft National Annex to BS EN 1991-1-4:2005 dated 23rd

June 2005, has

not been undertaken.

The wind actions were calculated in accordance with the current British Standard and the Eurocodes

for the typical railway structures and compared. It is noted that the draft National Annex modifies key

clauses of the Eurocode and the study has considered the proposed modifications in the National

Annex, in the calculations for this study. Explanation of the differences between the published

Eurocode and the amendments made in the National Annex, should be available from the BSI

committee responsible for BS EN 1991-1-4:2005 (B525/1). For the purposes of this study, it was

assumed that the structures are located in a rural location near Sheffield, 50km from the sea at an

altitude of 30m with the bridge 10m above the ground and topography factors were not considered.

The approach to the calculation of the wind actions is similar for both the current British Standard and

the Eurocode in that the basic wind velocity is factored to account for environmental conditions and

the probability of occurrence. However, the factors accounting for the environmental conditions are

not directly comparable. The Eurocode combines a number of the individual factors contained in the

current British Standard. For example, the Eurocode roughness factor is a function of the altitude,

terrain and wind direction, all of which are separate factors in the current British Standard.

The Eurocode also includes factors not considered in the current British Standard, including the

application of a seasonal factor and, in calculating the peak velocity pressure, the Eurocode considers

wind turbulence. The draft National Annex simplifies the calculation of the peak velocity pressure

and provides figures and correction factors. The resultant environmental factors can be compared to

the British Standard, BS 5400-2:2006, environmental factors, which is the product of several factors

squared (Sg.Sp.Sa.Sd)2. The resulting value can be considered to be equivalent to the Eurocode

exposure factor Ce. Therefore the dynamic pressure head, q, based on the calculation method in the

British Standard can be expressed as 0,5.ρ.vb2.ce. The comparison factor for the environmental factors

or wind pressures, considering the assumed location and environment for the typical structures, was

1,01.

Furthermore, different terminology is used in the Eurocode, for example, what is referred to as

topography in the current British Standard is referred to as orography in the Eurocode.



70

The principal difference between the Eurocode and the current British Standard is in the calculation of

wind actions on railway bridges with railway vehicles on them. The key factors contributing to this

difference are:

The maps showing the basic wind speed are not the same, with the Eurocode values for the

fundamental basic wind velocity generally less than the basic wind speed to BS 5400-2:2006.

The Eurocode has a maximum wind speed in this situation whereas the current British

Standard does not.

The height of the railway vehicles is also greater in the Eurocode than the current British

Standard.

The calculation of the wind force (drag) coefficients is different.

The ULS combination factors are different and a combination including transient railway

traffic loading as the primary action acting together with wind as a secondary action is

possible.

Some important aspects affecting the limiting values of wind speed on railway bridges coincident with

railway traffic are as follows:

The Eurocode recommends a cut off limiting the fundamental value of the characteristic basic

wind velocity to a value of 25m/s. Depending on the location of the structure and assuming

orography is not significant, this equates to a peak velocity pressure of approximately 980kPa

which is the equivalent pressure due to a maximum characteristic gust wind speed of 40m/s in

the current British Standard.

The limiting fundamental value of the basic wind velocity in the Eurocode is appropriate, as

the maximum gust speed for overturning of trains, clause B10.1 b), of GM/RT2149

'Requirements for Defining and Maintaining the Size of Railway Vehicles', sets a limit of 35

m/s in order to limit pantograph sway when trains are operating at maximum speed and

maximum cant deficiency.

Furthermore GM/RT2142 'Resistance of Railway Vehicles to Roll-Over in Gales', sets limits

on wind speed of 40.8 m/s for typical passenger trains and 31 m/s for typical freight trains.

However, this standard is under review and the values are being revised to 36.5 m/s and 30.5

m/s respectively.

Network Rail Company Standard RT/LS/S/021, Issue 2, October 2004, 'Weather - Managing

the operational risks', sets a limit of wind gust speed of 90 mph (40 m/s), at which train

services should be suspended.

Although, for the design of bridges, there is a case for adopting the lower limits set for train operation

in GM/RT2142, additional conservatism is achieved by adopting a higher value. Therefore, a higher

limit for the maximum characteristic gust wind speed of 40 m/s is recommended for adoption in the

National Annex to BS EN 1991-1-4:2005. Note that for all locations, with the exception of central

and northern Scotland, the fundamental basic wind velocity (specified on the wind action contour map

in the National Annex to BS EN 1991-1-4:2005) is less than the 25m/s limiting value specified in BS

EN 1991-1-4:2005.

Where the fundamental value of the basic wind velocity exceeds the limiting value in the Eurocode,

the limiting value should be used when wind and railway traffic acting together is considered. If the

railway traffic action is the leading action, the combination factor for the maximum wind force with

traffic action is ψ0 = 0,75. The maximum wind force ψ0 FWk that can act simultaneously with railway

traffic is limited to ψ0 FW**. In the latter case, a combination factor with a value ψ0 = 1,00 applies.



71

The height of the railway vehicles in the Eurocode is greater than for the current British Standard.

When calculating the wind area, the depth to be considered, in both the Eurocode and the current

British Standard, is the height of the train plus the depth of the bridge below the rails. The comparison

factor for the wind area is a minimum of 0,93.

The effective depth of the bridge considered, d, also affects the b/d ratio used in calculating the force

(drag) coefficients. The current British Standard and the Eurocode have different relationships and are

not directly comparable. The Eurocode calculates the force coefficient on the total depth of the

structure plus the vehicle height whereas the current British Standard calculates the drag coefficient

based on the vehicle height only. As the two charts used to determine the coefficients are different,

the effect of the difference is difficult to determine without further analysis. However, the force factor

in the Eurocode is generally greater than the drag coefficient calculated using the current British

Standard. The drag factor comparison factors range between 0,80 and 1,00 where there is no live load

and between 0,73 and 1,05 with live load.



72

9.1 Wind - Ultimate Limit State

In accordance with BS EN 1990:2002 the design effect, Ed, is calculated from equation (6.10). The

recommended values of the partial factors, load classification factor, combination factors and dynamic

factors, specified in BS EN 1990:2005(A1) Annex A2, BS EN 1991-1-1:2002 and BS EN 1991-

2:2003, are summarised in Table 27. The wind action partial factors are as recommended in the

Eurocode and not as set out in the draft National Annex.


depth

factor

Leading

Action

ψ0 ψ1

Permanent Self weight (steel) 1,20

Superimposed

Ballast

1,35

30%

Other 1,35

Transient LM71 1,45 1,10 Ф2 1,00 0,80 0,80*

Wind + live

load#5

1,50 1,00 0,75 0,50

Table 27: Eurocode ULS Partial and Combination Factors used for Wind Study

* decks considered are single track or decks where a single track effect governs.

# assumes the fundamental value of the basic wind velocity is less than the limiting value (see above)

In accordance with BS 5400-1:1998 the design load effect, S*, is calculated from the equations in

clauses 2.3.1 and 2.3.2. The values of the partial factors and dynamic factors specified in BS 5400-

2:2006 are summarised in Table 28:

Action γf3 Φ Combination 1 γfL Combination 2 γfL

Permanent Self weight (steel) 1,10 1,05 1,05

Superimposed

Ballast

1,10 1,75 1,75

Other 1,10 1,20 1,20

Transient RU shear

RU bending

1,10 Ф2

Ф3

1,40 1,20

Wind + live load

Wind only

1,10

1,10

1,10

1,40

Table 28: British Standards ULS Partial and Combination Factors used for Wind Study

5 Following the completion of this study, the partial factor for wind load has been confirmed as 1,70 in NA EN

1990(A1):2005..



73

9.1.1 Summary of ULS Wind Combination Results

The results in Table 29 present the comparison between the total wind (horizontal effect, Fhz) and

coexistent railway traffic action (vertical load affect, Fvt) for the deck types considered in the typical

railway structure studies.

Action British Standard Eurocodes

Str

uct

ure

Actions Leading

Action

Co

mb

inati

on

To

tal

Lo

ad

Co

mb

inati

on

fact

or

To

tal

Lo

ad

Co

mp

ari

son

Fa

cto

r

Co

mp

ari

son

Fa

cto

r

Fvt (R

U)

Fh

z (

win

d)

ψ0

Fvt (L

M7

1)

Fh

z (

win

d)

Fvt

Fh

z

Deck 1 Wind only Wind 2 31 50 0,62

Wind &

railway traffic

Wind 2 2281 173 0,80 2205 215 1,03 0,81

Wind &

railway traffic

Railway

traffic

1 2661 0,75 2756 162 0,97


Wind &

railway traffic

Wind 2 4341 254 0,80 4197 431 1,03 0,59

Wind &

railway traffic

Railway

traffic

1 5064 0,75 5246 324 0,97


Wind &

railway traffic

Wind 2 3178 181 0,80 3072 310 1,03 0,58

Wind &

railway traffic

Railway

traffic

1 3708 0,75 3840 232 0,97


Wind &

railway traffic

Wind 2 2756 176 0,80 2664 312 1,03 0,57

Wind &

railway traffic

Railway

traffic

1 3215 0,75 3330 233 0,97


Wind &

railway traffic

Wind 2 1383 53 0,80 1337 85 1,03 0,62

Wind &

railway traffic

Railway

traffic

1 1614 0,75 1672 64 0,97


Wind &

railway traffic

Wind 2 1573 87 0,80 1520 116 1,03 0,75

Wind &

railway traffic

Railway

traffic

1 1836 0,75 1902 87 0,97

Note that the railway actions have α = 1,10 applied, but no dynamic factor.

Table 29: Summary of ULS Wind Combination Results



74

9.2 Wind - Serviceability Limit State

In accordance with BS EN 1990:2002, the design effect, Ed, is calculated from equation (6.14b) (i.e.

for the characteristic combination of actions). The recommended values of the partial factors, load

classification factor, combination factors and dynamic factors, specified in BS EN 1990:2005(A1)

Annex A2, BS EN 1991-1-1:2002 and BS EN 1991-2:2003, are summarised in Table 30. The wind

action partial factors are as recommended in the Eurocode and not as recommended in the draft

National Annex:


depth

factor

Leading

Action

ψ0 ψ1

Permanent Self weight (steel) 1,00

Superimposed

Ballast

1,00

30%

Other 1,00

Transient LM71 1,00 1,10 Ф3 1,00 0,80 0,80*

Wind + live load# 1,00 1,00 0,75 0,50

Table 30: Eurocodes SLS Partial and Combination Factors used for Wind Study

*single track only is considered in the comparison.

# assumes the fundamental value of the basic wind velocity is less than the limiting value (see above)


clauses 2.3.1 and 2.3.2. The values of the partial factors and dynamic factors specified in BS 5400-

2:2006 are summarised in Table 31:

Action γf3 Φ Combination 1

γfL

Combination 2

γfL


Superimposed

Ballast

1,00 1,20 1,20

Other 1,00 1,00 1,00

Transient RU shear

RU bending

1,00 Ф2

Ф3

1,10 1,00

Wind + live load

Wind only

1,00

1,00

1,00

1,00

Table 31: British Standards SLS Partial and Combination Factors used for Wind Study



75

9.2.1 Summary of SLS Wind Combination Results

The results in Table 32 highlight the total wind (horizontal effect, Fhz) and coexistent railway traffic

action (vertical load affect, Fvt) for the deck types considered only.

Action UK Eurocode

Str

uct

ure

Actions Leading

Action

Co

mb

inati

on

To

tal

Lo

ad

Co

mb

inati

on

fact

or

To

tal

Lo

ad

Co

mp

ari

son

Fa

cto

r

Co

mp

ari

son

Fa

cto

r

Fvt (R

U)

Fh

z (

win

d)

ψ0

Fvt (L

M7

1)

Fh

z (

win

d)

Fvt

Fh

z


Wind &

railway traffic

Wind 2 1728 143 0,80 1521 143 1,14 1,00

Wind &

railway traffic

Railway

traffic

1 1901 0,75 1901 108 1,00


Wind &

railway traffic

Wind 2 3288 210 0,80 2894 288 1,14 0,73

Wind &

railway traffic

Railway

traffic

1 3617 0,75 3617 216 1,00


Wind &

railway traffic

Wind 2 2408 150 0,80 2119 207 1,14 0,72

Wind &

railway traffic

Railway

traffic

1 2649 0,75 2649 155 1,00


Wind &

railway traffic

Wind 2 2088 146 0,80 1837 208 1,14 0,70

Wind &

railway traffic

Railway

traffic

1 2296 0,75 2296 156 1,00


Wind &

railway traffic

Wind 2 1048 44 0,80 922 57 1,14 0,77

Wind &

railway traffic

Railway

traffic

1 1153 0,75 1153 43 1,00


Wind &

railway traffic

Wind 2 1192 72 0,80 1049 77 1,14 0,92

Wind &

railway traffic

Railway

traffic

1 1311 0,75 1311 58 1,00

Table 32: Summary of SLS Wind Combination Results



76

9.3 Discussion

For design load combinations involving wind in the current British Standard, load combination 2

considers two load situations: wind only and wind plus traffic.

9.3.1 Wind Only

The ULS partial load factors in the British Standard where wind acts alone are γfL = 1,40 and γf3 = 1,10

giving an equivalent ULS factor = 1,54. The Eurocode partial factor value for wind alone is γfL =

1,506. Therefore the comparison factor (assuming the actions are equal) for the applied ULS factors is

1,03.

The SLS partial factors for this case are all 1,00 ( i.e. the characteristic values). For the typical

structures considered, subject to wind only, the Eurocode is more onerous with comparison factors

ranging between 0,77 and 0,96 at SLS (characteristic) and 0,62 and 0,77 at ULS. The differences are

primarily due to a greater wind force coefficient in the Eurocode.

9.3.2 Wind (Leading) and Railway Traffic

(i) ULS

Where traffic is considered acting with the wind, for the wind component, the ULS partial factors in

the British Standard are γfL = 1,10 and γf3 = 1,10, which is equivalent to a ULS factor of 1,21. For the

railway traffic component the factors are γfL = 1,20 and γf3 = 1,10 which is equivalent to a ULS factor

of 1,32.

The current British Standard only considers the case where wind is the leading action. The equivalent

Eurocode partial factor at ULS considered is γQ = 1,506 for the wind action, not the value of 1,70

recommended in the draft National Annex for BS EN 1990 (A1):2005, Annex A2. Applying the load

classification factor α = 1,1 to the railway traffic component, along with a partial factor γQ = 1,45 and

a combination factor ψ0 = 0.80, results in an equivalent factor of 1,28 at ULS. Assuming the actions

are equal, the comparison factors for the applied ULS actions are 0,81 for the wind and 1,03 for the

railway actions.

For the typical structures considered, the wind applied in accordance with the Eurocodes is generally

greater than the current British Standard with comparison factors between 0,57 and 0,81 at ULS. The

differences are due to, a greater wind force coefficient, partial factor and, wind area, in the Eurocode.

(ii) SLS

The SLS partial factors are 1,00 and the combination factors are the same as for the ULS. For the

typical structures considered, the wind applied in accordance with the Eurocodes is generally greater

than the current British Standard with comparison factors between 0,70 and 1,00 at SLS

(characteristic). The differences are due to, a greater wind force coefficient, partial factor and, wind

area, in the Eurocode.

Where the railway loading is the leading action, the comparison factor for the SLS vertical load is 1,00

and where the wind is the leading action, the comparison factor is 1,14. The difference is attributed to

the load combination factor applied in the Eurocode.


1990(A1):2005..



77

9.3.3 Railway Traffic (Leading) and Wind

The Eurocode allows wind to be combined when the railway traffic is the leading action. In this case

the Eurocode ULS factors are γQ = 1,45 for the railway traffic component and application of the load

classification factor α = 1,1, gives an overall equivalent factor at ULS of 1,60. The coexistent wind

action partial factors are γQ = 1,507 and ψ0 = 0,75 which is equivalent to a ULS factor of 1,13.

The SLS partial factors are equal to 1,00 and the combination factors are the same as for the ULS.

As the load combination involving railway traffic as the leading action and wind as the accompanying

action does not exist in the current British Standard, it is not possible to make an equivalent

comparison. This additional case could lead to an increase in the size of structural elements which are

primarily designed to resist railway traffic actions but which are susceptible to wind actions. The

design of wind susceptible structural elements to the British Standard would normally involve

designing the element to resist the railway traffic actions. The element would then be checked to

establish that the stresses due to wind, combined with the reduced stresses due to railway traffic

actions within combination 2, are within the permissible limits.

For design to the Eurocodes, structural elements such as bearings, transverse bracing, main girders,

stiffeners (end and intermediate U frames) and their connections, may have to be enlarged to carry full

railway traffic as the leading action coexistent with wind as the accompanying action. The change in

the section sizes for the structural elements of continuous bridges or integral (e.g. portal frame)

structures, could be subject to a further increase in stress if thermal effects are also considered. This is

explained in section 10.

It is recommended that the partial factor adopted in the National Annex, γQ, is taken as 1,50 rather than

the recommended value of 1,70 in the draft National Annex, to avoid further conservatism. (Refer to

footnote).


1990(A1):2005.



78

10 Temperature Effects


BS 5400-2:2006 BS EN 1991-1-5:2003

BS EN 1990:2002(A1) Annex A2

BS EN 1991-1-1:2002

BS EN 1991-2:2003


There are two temperature effects to consider:

Global effects (expansion and contraction)

Effects of temperature difference

10.1 Ultimate Limit State Actions

In accordance with BS EN 1990:2002, the design effect, Ed, is calculated from equation (6.10). The

recommended values of the partial factors, load classification factor, combination factors and dynamic

factors specified in BS EN 1990:2002(A1) Annex A2, BS EN 1991-1-1:2002 and BS EN 1991-

2:2003, are summarised in Table 33:


depth

factor

Leading

Action

ψ0 ψ1


(steel)

1,20

Superimposed

Ballast

1,35

30%

Other 1,35

Settlement 1,20

Transient LM71 1,45 1,10 Ф3 1,0 0,80 0,80*

SW/0 1,45 1,10 Ф3 1,0 0,80 0,80*

Temperature

global

1,508

1,0 0,60 0,60

Temperature

difference

1,508 1,0 0,60 0,60

*decks considered are single track or decks where a single track effect governs.

Table 33: Eurocode ULS Partial and Combination Factors used for Temperature Study

8 Following the completion of this study, the partial factor for thermal load has been confirmed as 1,55 in NA EN

1990(A1):2005.



79


clauses 2.3.1 and 2.3.2. The values of the partial factors and dynamic factors for railway traffic live

load specified in BS 5400-2:2006 are summarised in Table 34:

Action γf3 Φ

Combination 1

γfL

Combination 3

γfL


Superimposed

Ballast 1,10 1,75 1,75

Other 1,10 1,20 1,20

Settlement 1,10 1,20 1,20

Transient LM71 shear

LM71 bending 1,10

Ф2

Ф3 1,40 1,20

SW/0 1,10 1,40 1,20

Temperature

Global

1,10 1,30

Temperature

difference 1,10 1,00

Table 34: British Standards ULS Partial and Combination Factors used for Temperature Study

10.2 Serviceability Limit State Actions

In accordance with BS EN 1990:2002, the design effect, Ed, is calculated from (6.14b) (i.e. for the

characteristic combination of actions). The recommended values of the partial factors, load

classification factor, combination factors and dynamic factors, specified in BS EN 1990:2002(A1)

Annex A2, BS EN 1991-1-1:2002 and BS EN 1991-2:2003, are summarised in Table 35:


depth

factor

Leading

Action

ψ0 ψ1


(steel)

1,00

Superimposed

Ballast

1,00

30%

Other 1,00

Settlement 1,00

Transient LM71 1,00 1,10 Ф3 1,00 0,80 0,80*

SW/0 1,00 1,10 Ф3 1,00 0,80 0,80*

Temperature

global

1,00

1,00 0,60 0,60

Temperature

difference

1,00 1,00 0,60 0,60

*decks considered are single track or decks where a single track effect governs.

Table 35: Eurocode SLS Partial and Combination Factors used for Temperature Study


clauses 2.3.1 and 2.3.2. The recommended values of the partial factors and dynamic factors specified

in BS 5400-2:2006, are summarised in Table 36:



80

Action γf3 Φ Combination 1

γfL

Combination 3

γfL


Superimposed

Ballast

1,00 1,20 1,20

Other 1,00 1,00 1,00

Settlement 1,00 1,00 1,00

Transient LM71 shear

LM71 bending

1,00 Ф2

Ф3

1,10 1,00

SW/0 1,00 1,10 1,00

Temperature

global

1,00

1,00

Temperature

difference

1,00 0,80

Table 36: British Standards SLS Partial and Combination Factors used for Temperature Study

10.3 Global Temperature Effects

The movement of the decks was calculated assuming simply supported spans fixed in position at one

end. Structures were assumed to be in a rural location near Sheffield, 50km from the sea at an altitude

of 30m and the bridge 10m above the ground. The temperature assumed when constructing the bridge

is (specified as) T0, = 10˚C. The global temperature was considered as the leading effect with no

coexistent load (i.e. only expansion and contraction was calculated for the typical deck types

considered). A 120 year return period was considered.

The results are summarised in Table 37. Temperature is considered as the leading action.

For the Eurocode calculations of the movement allowance required for bearings and expansion joints,

the temperature range considered is the difference between the specified temperature at time zero , T0,

and the maximum / minimum effective bridge component of temperature, Te, modified by +/- 10˚C.

i.e. Where the installation temperature is specified, the range of uniform contraction, ΔTN,con = T0 –

Te.min + 10 C and the range of uniform expansion, ΔTN,exp = Te.max - T 0 - 10 C.

Note that had the temperature range not been specified, the maximum / minimum effective bridge

component, Te should be modified by +/- 20˚C.

British Standards Eurocodes Comparison Factor

Deck

Sp

an

Contraction

(mm)

Expansion

(mm)

Contraction

(mm)

Expansion

(mm)

Contraction

(mm)

Expansion

(mm)

SLS ULS SLS ULS SLS ULS SLS ULS SLS ULS SLS ULS

1 15m -5,2 -6,9 6,8 9,0 -7,2 -10,8 9,5 14,3 0,72 0,64 0,72 0,63

2 35m -12,2 -16,1 16,0 21,1 -16,8 -25,2 22,3 33,4 0,73 0,64 0,72 0,63

3 24m -8,6 -11,4 11,5 15,2 -11,5 -17,3 15,8 23,8 0,75 0,66 0,73 0,64

4 20m -5,3 -7,0 6,0 7,9 -6,0 -9,0 7,0 10,5 0,88 0,78 0,86 0,75

5 7m -1,7 -2,2 1,9 2,6 -2,0 -3,0 2,3 3,5 0,85 0,73 0,83 0,74

6 8m -1,9 -2,5 2,2 2,9 -2,3 -3,5 2,3 4,0 0,83 0,71 0,85 0,73

Table 37: Summary of Expansion and Contraction with T0 Specified (+/- 10°C)



81

If the expansion and contraction range is to be included on bearing schedules, DT*d, further

modifications are required in accordance with BS EN 1993-2 Annex A.4:

ΔT*d = ΔTK + ΔTg + ΔT0

where ΔTK is the maximum contraction range or maximum expansion range as appropriate (ΔTN,exp

or ΔTN,exp in accordance with BS EN 1991-1-5).

ΔTg = 5 C to allow for the temperature difference in the bridge

ΔT0 = between 0 C and 30 C to take into account the uncertainty of the position of the bearing

at the reference temperature.

If the Eurocode adjustment factor for modified temperature T0 is not applied (i.e. if calculating effects

of resisting the movement due to thermal effects, the differences are summarised in Table 38.

British Standards Eurocodes Comparison Factor

Deck

Sp

an

Contraction

(mm)

Expansion

(mm)

Contraction

(mm)

Expansion

(mm)

Contraction

(mm)

Expansion

(mm)

SLS ULS SLS ULS SLS ULS SLS ULS SLS ULS SLS ULS

1 15m -5,2 -6,9 6,8 9,0 -5,4 -8,1 7,7 11,6 0,96 0,85 0,88 0,78

2 35m -12,2 -16,1 16,0 21,1 -12,6 -18,9 18,1 27,1 0,97 0,85 0,88 0,78

3 24m -8,6 -11,4 11,5 15,2 -8,6 -13,0 13,0 19,4 1,00 0,88 0,88 0,78

4 20m -5,3 -7,10 6,0 7,9 -4,0 -6,0 5,0 7,5 1,33 1,17 1,20 1,05

5 7m -1,7 -2,2 1,9 2,6 -1,3 -2,0 1,6 2,4 1,31 1,10 1,19 1,08

6 8m -1,9 -2,5 2,2 2,9 -1,5 -2,3 1,8 2,8 1,27 1,09 1,22 1,04

Table 38: Summary of Expansion and Contraction with T0, not applied

If a deck is not free to expand or contract then the induced force in the deck will be proportional to the

expansion or contraction figures above.

10.4 Discussion

Values of the coefficient of thermal expansion (CTE) for concrete and composite structures are

different in accordance with British Standards and the Eurocode: CTEBS = 1,2x105 whereas CTEEN =

1,0x105 in the Eurocode. This leads to small differences in the calculated expansion and contraction.

The comparison factor (CTEBS/CTEEN) for thermal expansion coefficients is 1,20 for concrete and

composite structures. There are also differences in the partial safety factors that lead to differences at

the limit states:

The British Standard ULS partial load factors for a global temperature effect alone are γfL = 1,30 and

γf3 = 1,10 giving an equivalent ULS factor = 1,43. The Eurocode value for temperature, γQ = 1,509.

Therefore the comparison factor for the applied ULS factors is 0,95. The SLS factors for this case are

all 1,00 (i.e. the characteristic values).

In accordance with the Eurocode, the temperature range calculated from time zero, T0, is modified by

adding up to a further 20 C to the temperature range. This leads to bigger bearings. For example, if

the installation temperature T0 was specified as 10˚C, then for the 35m long E-type considered, the

SLS movement range calculated in accordance with the Britsish Standards will be 28,2mm compared

to 39,1mm required in the Eurocode (CF=0,72).

9 Following the completion of this study, the partial factor for thermal load has been confirmed as 1,55 in NA EN

1990(A1):2005.



82

Where the Eurocode temperatures were not modified, the resulting movement was similar to the

current British Standard values with the comparison factors ranging from 0,88 to 1,33 at SLS and 0,78

to 1,17 at ULS (i.e. the current British Standards are slightly more conservative in most cases

considered). This was primarily due to the difference in the coefficient of thermal expansion for

concrete and the different partial factors.

It is recommended that the partial factors remain as recommended in the draft National Annex for BS

EN 1990:2005(A1), Annex A2, but that the modification to the temperature range is not made where

the temperature at the time when execution will take place has been assessed with sufficient accuracy.

10.5 Thermal Gradient Effects

A continuous, three span bridge was considered (parametric study) and the effect of the temperature

difference was taken into account. Bending moments and shear forces were calculated at the mid span

of the centre span and at a pier.

10.5.1 Temperature Only

The temperature gradients through the sections, and hence the theoretical locked in stresses, moments

and axial force, are the same in accordance with the current British Standard and the Eurocode.

However, the Eurocode is more conservative as the applied partial factors on the thermal effects are

greater than those in the current British Standard.

(i) ULS

The British Standard partial load factors for the effects of temperature gradients are γfL = 1,00 and γf3 =

1,10 giving an equivalent factor = 1,10. The Eurocode value for the partial factor γQ = 1,5010

.

Therefore the comparison factor for the applied factors is 0,73.

(ii) SLS

The British Standards partial factors for this case are γfL = 0,80 and γf3 = 1,00 giving an equivalent

factor = 0,80. The Eurocode value for the partial factor γQ = 1,00. Therefore the comparison factor

for the applied factors results is 0,80.

10.5.2 Temperature Coexistent with Railway Loading, Temperature Leading Action

(i) ULS


1,10 giving an equivalent factor = 1,10. The Eurocode value for the partial factor γQ = 1,509.


Where the railway traffic actions are coexistent with the temperature effects (temperature is the

leading action) the British Standard partial load factors are γfL = 1,20 and γf3 = 1,10, giving an

equivalent factor = 1,32. For the Eurocode, applying the load classification factor α = 1,10 to the

railway traffic component along with the partial factor γQ = 1,45 and the combination factor ψ0 = 0,80,

results in an equivalent factor of 1,28. Therefore the comparison factor for the applied factors is 1,03.

10

Following the completion of this study, the partial factor for thermal load has been confirmed as 1,55 in NA EN

1990(A1):2005..



83

(ii) SLS


1,00 giving an equivalent factor = 0,80. The Eurocode value for the partial factor γQ = 1,00.


Where the railway traffic actions are coexistent with the temperature effects (temperature is the

leading action) the British Standard partial load factors are γfL = 1,00 and γf3 = 1,00 giving an

equivalent factor = 1,00. For the Eurocode, applying the load classification factor α = 1,10 to the

railway traffic component along with the partial factor γQ = 1,00 and the combination factor ψ0 = 0,80,

results in an equivalent factor of 0,88. Therefore the comparison factor for the applied factors is 1,14.

10.5.3 Temperature Coexistent with Railway Loading, Railway Loading Leading Action

The Eurocode allows temperature effects to be combined when the railway traffic is the leading action,

along with other actions, including wind. The most onerous Eurocode combination at ULS will be

railway traffic as the leading action, wind accompanying (ψ0) and thermal secondary (ψ1). The ULS

partial factors are γQ = 1,45 for the railway traffic component and a load classification factor α = 1,1,

which results in an overall equivalent ULS factor of 1,60. The coexistent wind action partial factors

are γQ = 1,5011

and ψ0 = 0.75 which equates to a ULS factor of 1,13. The partial factors for the

coexistent thermal actions are γQ = 1,5012

and ψ1 = 0.60 which results in an equivalent ULS factor of

0,90.

The SLS partial factors are equal to 1,00 and the combination factors are the same as the ULS

combination factor values; 1,00 for the railway traffic, 0,75 for the wind actions, and 0,6 for the

thermal effects.

As no equivalent combination (railway traffic as the leading action and temperature accompanying)

exists in the current British Standard, no comparison is possible. This combination could lead to

increases in the size of structural elements of continuous bridges or integral (e.g. portal frame)

structures, primarily designed to resist railway traffic actions but that are susceptible to wind and

thermal actions.

10.5.4 Conclusion

Although the effects of temperature gradients rarely govern the design of continuous bridges at ULS,

they often contribute significant components of stress that must be accounted for at SLS. Together

with the increased design stresses from the coexistent railway traffic load, this will lead to changes in

the size of structural elements and their connections, compared to the current British Standard. This

implies that a greater margin of capacity will be provided compared to current practice where SLS

governs the design.

11

Following the completion of this study, the partial factor for wind load has been confirmed as 1,70 in NA EN

1990(A1):2005. 12

Following the completion of this study, the partial factor for thermal load has been confirmed as 1,55 in NA EN

1990(A1):2005..



84

11 Groups of Loads

The Eurocodes for loading include a different approach to that traditionally considered in design using

British Standards. Rather than relying on the designer to combine the primary railway live loads

(vertical forces) with the applicable secondary live loads (traction, braking, centrifugal force and

nosing force) for the element being designed as individual load components, BS EN 1991-2:2003

provides a table with a number of groups of coexistent loads to consider, depending on the number of

loaded tracks. When using the groups of loads instead of combining the loads individually, all of the

groups in the table, which is replicated below, must be considered where relevant (e.g.SW/2 not used

in UK). The partial load factors and combination factors are then applied to the load group as a whole,

using the same factors that would be applied to the individual components. Effectively each load

group may be considered as a single action equivalent to the collective effects of the individual load

components.

Figure 16: BS EN 1991-2 Table 6.11 Groups of Loads

For design of railway bridges in accordance with Table A2.3 of BS EN 1990:2002 + A1:2005 (Annex

A2), combinations may include either:

Load groups (leading action) + other operating actions (leading action) + non-railway traffic

loads (accompanying actions) or

Individual components of rail traffic actions considered as a single (multi-directional) leading

action + non-railway traffic loads (accompanying actions)

Non-railway loads may also be considered as leading actions and combined with groups of loads or

individual components of traffic actions as accompanying actions.



85

In the design of typical superstructures such as those considered in this study, using the groups of

loads rather than determining the critical railway traffic actions individually, would not have resulted

in any difference in the design details or the margin of capacity.

In the design of certain elements to BS EN 1991-2:2003 table 6.11 (Figure 16 above), such as bearings

and substructures, where horizontal forces perpendicular to and parallel with the track govern the

design, the use of groups of loads will result in a lower net force, as one of the applied horizontal

forces may be reduced by 50%, and hence a reduced margin of capacity. The origin of these reduction

factors is unknown. This contradicts BS EN 1991-2:2003 cl 6.8.2(1) NOTE which states that in some

cases it is necessary to consider other appropriate combinations of unfavourable individual traffic

actions.

BS EN 1991-2:2003 table 6.11, is potentially confusing, as the non-critical (favourable) load effects

are specified a value (1,0, 0,5 or zero). The draft UK National Annex acknowledges this point and

states that where economy is not adversely affected the values of zero or 0,5 may be increased to 1,0

to simplify the design process. It will be the decision of the infrastructure owner to decide whether

factors less than unity can be used in design.

BS EN 1991-2:2003 also allows the vertical force component to be reduced by applying a factor of 0,5

if it is a favourable effect. With this factor applied to the vertical actions it may not be logical to

consider the maximum coexistent horizontal forces and this should be taken into account by designers

for the design of individual structural elements.

On balance, it is therefore recommended that the draft UK National Annex includes a requirement

stating that in all situations, the values of zero or 0,5 should be increased to 1,0 to simplify the design

process and to adequate robustness for the design of all structural elements. This is usually the case

when considering the design of individual components to British Standards and hence there would be

no effect on design using the Eurocodes.

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