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Research ProgrammeEngineering
Design of railway structuresto the structural Eurocodes
Part 1
Copyright© RAIL SAFETY AND STANDARDS BOARD LTD. 2009 ALL RIGHTS RESERVED
This publication may be reproduced free of charge for research, private study or for internal
circulation within an organisation. This is subject to it being reproduced and referenced
accurately and not being used in a misleading context. The material must be acknowledged as
the copyright of Rail Safety and Standards Board and the title of the publication specified
accordingly. For any other use of the material please apply to RSSB's Head of Research and
Development for permission. Any additional queries can be directed to [email protected].
This publication can be accessed via the RSSB website: www.rssb.co.uk.
DisclaimerThis document has been prepared for the titled project or named part thereof and should not be relied
upon or used for any other project without an independent check being carried out as to its suitability and
prior written authority of Mott MacDonald being obtained. Mott MacDonald accepts no responsibility or
liability for the consequence of this document being used for a purpose other than the purposes for which
it was commissioned. Any person using or relying on the document for such other purpose agrees, and
will by such use or reliance be taken to confirm his agreement to indemnify Mott MacDonald for all loss
or damage resulting therefrom. Mott MacDonald accepts no responsibility or liability for this document
to any party other than the person by whom it was commissioned.
To the extent that this report is based on information supplied by other parties, Mott MacDonald accepts
no liability for any loss or damage suffered by the client, whether contractual or tortious, stemming from
any conclusions based on data supplied by parties other than Mott MacDonald and used by Mott Mac-
Donald in preparing this report.
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 —
Part 5: Code of practice for
design of
composite bridges
May 1982
BS 5400-10:1980:1980
Incorporating Amendment No. I
Steel, concrete and
composite bridges -
Part 10: Code of practice for
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
BS EN 1991-1-4:2005 Eurocode 1: Actions on
structures - Part 1-4: General
actions - Wind actions
April 2005
DRAFT National Annex to BS
EN 1991-1-4:2005
UK National Annex to
Eurocode 1 - Part 1-4: General
actions - Wind actions
June 2005
BS EN 1991-1-5:2003 Eurocode 1: Actions on
structures — Part 1-5: General
actions — Thermal actions
March 2004
National Annex to BS EN 1991-
1-5:2003
UK National Annex to
Eurocode 1 — Part 1-5: General
actions — Thermal actions
April 2007
BS EN 1991-1-7:2005 Eurocode 1: Actions on
structures — Part 1-7: General
actions — Accidental
actions
September 2006
DRAFT National Annex to BS
EN 1991-2:2003
UK National Annex to
Eurocode 1: Actions on
Structures – Part2: Traffic
Loads on Bridges
Draft, dated 07/08/03.
National Annex to BS EN 1991-
1-3:2003
UK National Annex to
Eurocode 1: Actions on
structures —
Part 1-3: General actions —
Snow loads
December 2005
DRAFT National Annex to BS
EN 1991-1-4:2005
UK National Annex to
Eurocode 1: Actions on
structures - Part 1-4: General
actions - Wind actions
June 2005
National Annex to BS EN 1991-
1-5:2003
UK National Annex to
Eurocode 1: Actions on
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
National Annex to BS EN 1992-
1-1:2004
UK National Annex to
Eurocode 2: Design of Concrete
Structures Part 1-1: General
Rules and Rules for Buildings
December 2005
BS EN 1992-2:2005 Eurocode 2: Design of Concrete
Structures Part 2: Concrete
Bridges Design and Detailing
Rules
December 2005
6
National Annex to BS EN 1992-
2:2005
UK National Annex to
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
Rules and Rules for Buildings
May 2005
DRAFT National Annex to BS
EN 1993-1-1:2005
UK National Annex to
Eurocode 3: Design of Steel
Structures Part 1-1: General
Rules and Rules for Buildings
Undated Draft.
BS EN 1993-1-5:2006 Eurocode 3: Design of Steel
Structures - Part 1-5: Plated
Structural Elements
October 2006
BS EN 1993-1-8:2005 Eurocode 3: Design of Steel
Structures - Part 1-8: Design of
Joints
May 2005
BS EN 1993-1-9:2005 Eurocode 3: Design of Steel
Structures - Part 1-9: Fatigue
May 2005
DRAFT National Annex to BS
EN 1993-1-9:2005
UK National Annex to
Eurocode 3: Design of Steel
Structures Part 1-9: Fatigue
July 2007
BS EN 1993-2:2006 Eurocode 3: Design of Steel
Structures - Part 2: Steel
Bridges
October 2006
DRAFT National Annex to BS
EN 1993-2:2006
UK National Annex to
Eurocode 3: Design of Steel
Structures Part 2: Steel Bridges
May 2007
BS EN 1994-1-1:2004 Eurocode 4: Design of
composite steel and concrete
structures — Part 1-1: General
rules and rules for buildings
February 2005
BS EN 1994-2:2005 Eurocode 4 — Design of
composite steel and concrete
structures — Part 2: General
rules and rules for bridges
December 2005
National Annex to BS EN 1994-
2:2005
UK National Annex to
Eurocode 4: Design of
composite steel and concrete
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
National Annex to BS EN 1991-
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.
Design of Railway Structures to the
Structural Eurocodes
13
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
Typical bridge designs BS EN 1992-2:2005
National Annex BS EN 1992-
2:2005 dated 31/12/2007
The values in the draft National Annex are recommended.
Typical bridge designs BS EN 1993-2:2006
Draft National Annex BS EN
1993-2:2006 dated 02/05/2007
The values in the draft National Annex are recommended.
Typical bridge designs BS EN 1994-2:2005
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
Draft National Annex BS EN
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
Draft National Annex BS EN
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.
Design of Railway Structures to the
Structural Eurocodes
14
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
Braking BS EN 1991-2:2003
Draft National Annex BS EN
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
Draft National Annex BS EN
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
Draft National Annex BS EN
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).
Design of Railway Structures to the
Structural Eurocodes
15
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
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
Draft National Annex BS EN
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.
Design of Railway Structures to the
Structural Eurocodes
16
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
Wind effects BS EN 1991-2:2003
Draft National Annex BS EN
1991-2:2003 dated 07/08/2003
BS EN 1991-1-4:2005
Draft National Annex BS EN
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
Draft National Annex BS EN
1991-2:2003 dated 07/08/2003
BS EN 1991-1-4:2005
Draft National Annex BS EN
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.
Design of Railway Structures to the
Structural Eurocodes
17
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
Wind coexistent with live load BS EN 1991-2:2003
Draft National Annex BS EN
1991-2:2003 dated 07/08/2003
BS EN 1991-1-4:2005
Draft National Annex BS EN
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
Draft National Annex BS EN
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).
Design of Railway Structures to the
Structural Eurocodes
18
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
Effect of temperature gradient BS EN 1991-2:2003
Draft National Annex BS EN
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
Draft National Annex BS EN
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.
Design of Railway Structures to the
Structural Eurocodes
19
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
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
Draft National Annex BS EN
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
Design of Railway Structures to the
Structural Eurocodes
20
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
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.
Design of Railway Structures to the
Structural Eurocodes
21
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
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.
Changing the proposed partial factor values is not recommended.
Pre-stressed concrete structures BS EN 1992-1-1:2004, BS EN
1992-2:2005, National Annex
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.
Changing the proposed partial factor values is not recommended.
Composite steel and concrete
structures – Filler Decks
BS EN 1994-1-1:2004, BS EN
1994-2:2005, National Annex
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.
Design of Railway Structures to the
Structural Eurocodes
22
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
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
Design of Railway Structures to the
Structural Eurocodes
23
Description of Investigation Relevant Standards (refer to
list of references for dates of
publication)
Summary of Recommended Values, New Studies and Commentary
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.
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
25
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 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
Design of Railway Structures to the
Structural Eurocodes
26
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
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
Not given Not considered in this
study
Limiting values of the
total deck twist for
railway bridges
A2.4.4.2.2(3)P tT is
7,5mm/3m.
Not given Not considered in this
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
A2.4.4.2.3(2) Not given Not given Not considered in this
study
Additional limits of
angular rotations at the
end of decks
A2.4.4.2.3(3) Not given Not given Not considered in this
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
Not given Not considered in this
study
Minimum lateral
frequency for railway
bridges
A2.4.4.2.4(3) The
recommended
value is:
fh0 = 1,2 Hz
Not given Not considered in this
study
Requirements for
passenger comfort for
temporary bridges
A2.4.4.3.2(6) Not given Not given Not considered in this
study
Design of Railway Structures to the
Structural Eurocodes
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
in this study Not considered in
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
in this study Not considered in
this study
Wind forces Fwk 0,75 0,50 0 To be suggested
as part of this
study
0,75 0,50 0
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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)
Actions BS EN 1990:2002 National Annex Recommended
G,sup G,inf G,sup G,inf G,sup G,inf
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
Self weight of other
materials listed in BS EN
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
γP as defined in the
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)
Design of Railway Structures to the
Structural Eurocodes
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)
Actions BS EN 1990:2002 National Annex Recommended
G,sup G,inf G,sup G,inf G,sup G,inf
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
Self weight of other
materials listed in BS EN
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
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
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)
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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
Description Clause Eurocode
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
Design of Railway Structures to the
Structural Eurocodes
34
All references to BS EN 1991-2:2003 and National Annex BS EN 1991-2:2003 dated 3rd
August
2007
Description Clause Eurocode
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.
Design of Railway Structures to the
Structural Eurocodes
35
All references to BS EN 1991-2:2003 and National Annex BS EN 1991-2:2003 dated 3rd
August
2007
Description Clause Eurocode
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
Design of Railway Structures to the
Structural Eurocodes
36
All references to BS EN 1991-2:2003 and National Annex BS EN 1991-2:2003 dated 3rd
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 5 to 7m (L=7m: 231kN) 300 kN 300 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
from 3 to 5m (L=5m: 100kN) 187 kN 187 kN
from 5 to 7m (L=7m: 140kN) 250 kN 250 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
Design of Railway Structures to the
Structural Eurocodes
37
All reference to BS EN 1992-2:2005 and National Annex BS EN 1992-2:2005:2007
Description Clause Eurocode
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
Partial factors for materials for
ultimate limit states and fatigue γS
and γS,fat.
2.4.2.4.(1) 1,15 1,15 1,15
Partial factors for materials for
serviceability limit states γC 2.4.2.4.(2) 1,00 1,00 1,00
Partial factors for materials for
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
Table 5: Recommended Values in BS EN 1992-2
Design of Railway Structures to the
Structural Eurocodes
38
All reference to BS EN 1993-2:2006 and National Annex BS EN 1993-2:2006 dated 2 May 2007
Description Clause Eurocode
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
Design of Railway Structures to the
Structural Eurocodes
39
All reference to BS EN 1993-2:2006 and National Annex BS EN 1993-2:2006 dated 2 May 2007
Description Clause Eurocode
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.
Table 6: Recommended Values in BS EN 1993-2
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.
Design of Railway Structures to the
Structural Eurocodes
40
All references to BS EN 1994-2:2005 (National Annex not available)
Description Clause Eurocode
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
Table 7: Recommended Values in BS EN 1994-2
Note
1. Other factors are as in BS EN 1992 and BS EN 1993, as described in the other tables.
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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‖
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
44
(ii) Ultimate Limit State
Action γ (G or Q) α Φ Ballast
depth
factor
Leading
Action
ψ0
Permanent Self weight
(steel)
1,00
Self weight
(concrete)
1,00
Superimposed
Track
1,00
Ballast 1,00 30%
Other 1,00
Transient LM71 1,00 varies varies 1,00 0,80
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
Permanent Self weight
(steel) 1,00
Self weight
(concrete)
1,00
Superimposed
Track
1,00
Ballast 1,00 30%
Other 1,00
Transient LM71 1,00 varies varies 1,00 0,80
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
Design of Railway Structures to the
Structural Eurocodes
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)
Action γf3 Φ Combination 1 γfL
Permanent Self weight (steel) 1,10 1,10
Self weight (concrete) 1,10 1,20
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
Action γf3 Φ Combination 1 γfL
Permanent Self weight (steel) 1,10 1,10
Self weight (concrete) 1,10 1,20
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
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
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)
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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)
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural 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
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
53
5 Live Load Surcharge on Substructures
Refer also to section Error! Reference source not found., Error! Reference source not found..
British Standards Eurocodes (incl. National Annex)
BS 5400-2:2006
RC/GC5510
BS EN 1991-2:2003
The Standards referred to in Section 5 are listed above.
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.
Design of Railway Structures to the
Structural Eurocodes
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).
Design of Railway Structures to the
Structural Eurocodes
55
6 Longitudinal Actions
British Standards Eurocodes (incl. National Annex)
BS 5400-2:2006
RC/GC5510
BS EN 1991-2:2003
The Standards referred to in Section 6 are listed above.
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.
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
61
7 Accidental Actions
7.1 Derailment Effects
British Standards Eurocodes (incl. National Annex)
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)
Design of Railway Structures to the
Structural Eurocodes
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
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
64
7.2 Collision Effects
British Standards Eurocodes (incl. National Annex)
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.
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
66
8 Vertical Deformation and Rotation
British Standards Eurocodes (incl. National Annex)
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 Standards referred to in Section 8 are listed above.
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.
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
69
9 Wind Effects
British Standards Eurocodes (incl. National Annex)
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 Standards referred to in Section 9 are listed above.
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.
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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.
Action γ (G or Q) α Φ Ballast
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..
Design of Railway Structures to the
Structural Eurocodes
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
Deck 2 Wind only Wind 2 143 185 0,77
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
Deck 3 Wind only Wind 2 62 80 0,77
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
Deck 4 Wind only Wind 2 64 88 0,73
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
Deck 5 Wind only Wind 2 6 8 0,70
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
Deck 6 Wind only Wind 2 17 27 0,64
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
Design of Railway Structures to the
Structural Eurocodes
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:
Action γ (G or Q) α Φ Ballast
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)
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 31:
Action γf3 Φ Combination 1
γfL
Combination 2
γfL
Permanent Self weight (steel) 1,00 1,00 1,00
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
Design of Railway Structures to the
Structural Eurocodes
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
Deck 1 Wind only Wind 2 26 33 0,77
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
Deck 2 Wind only Wind 2 118 123 0,96
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
Deck 3 Wind only Wind 2 51 53 0,96
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
Deck 4 Wind only Wind 2 53 59 0,90
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
Deck 5 Wind only Wind 2 5 6 0,87
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
Deck 6 Wind only Wind 2 14 18 0,79
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
Design of Railway Structures to the
Structural Eurocodes
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.
6 Following the completion of this study, the partial factor for wind load has been confirmed as 1,70 in NA EN
1990(A1):2005..
Design of Railway Structures to the
Structural Eurocodes
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).
7 Following the completion of this study, the partial factor for wind load has been confirmed as 1,70 in NA EN
1990(A1):2005.
Design of Railway Structures to the
Structural Eurocodes
78
10 Temperature Effects
British Standards Eurocodes (incl. National Annex)
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
The Standards referred to in Section 10 are listed above.
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:
Action γ (G or Q) α Φ Ballast
depth
factor
Leading
Action
ψ0 ψ1
Permanent Self weight
(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.
Design of Railway Structures to the
Structural Eurocodes
79
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 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
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
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:
Action γ (G or Q) α Φ Ballast
depth
factor
Leading
Action
ψ0 ψ1
Permanent Self weight
(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
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 recommended values of the partial factors and dynamic factors specified
in BS 5400-2:2006, are summarised in Table 36:
Design of Railway Structures to the
Structural Eurocodes
80
Action γf3 Φ Combination 1
γfL
Combination 3
γfL
Permanent Self weight (steel) 1,00 1,00 1,00
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)
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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
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 = 1,509.
Therefore the comparison factor for the applied factors is 0,73.
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..
Design of Railway Structures to the
Structural Eurocodes
83
(ii) SLS
The British Standard partial load factors for the effects of temperature gradients 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 is 0,80.
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..
Design of Railway Structures to the
Structural Eurocodes
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.
Design of Railway Structures to the
Structural Eurocodes
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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