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This document is the property of Railtrack PLC. It shall not be reproduced in whole or in part without the written permission of the Controller, Railway Group Standards, Railtrack PLC. Published by Safety & Standards Directorate Railtrack PLC Railtrack House DP01 Euston Square London NW1 2EE © Copyright 2000 Railtrack PLC

Recommendations for the Design of Bridges

Synopsis This document gives recommendations for the design and loading for bridges. It supports Railway Group Standards GC/RT5110 and GC/RT5112.

Signatures removed from electronic version

Submitted by Dean Benson Standards Project Manager

Authorised by Brian Alston Controller, Railway Group Standards

Railway Approved Code of Practice GC/RC5510 Issue Two Date August 2000

Document Withdrawn as of February 2009 Uncontrolled When Printed

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Recommendations for the

Design of Bridges

R A I L T R A C K 1

Railtrack Approved Code of PracticeGC/RC5510 Issue Two Date August 2000 Page 1 of 48

Contents Section Description Page

Part A

Issue Record 2 Responsibilities 2 Health and Safety Responsibilities 2 Supply 2

Part B

1 Purpose 3 2 Scope 3 3 Definitions 3 4 Principle 3 5 Duties and Competency 4

Recommendations Relating to GC/RT5110 6 Intended Use and Life 5 7 Structural Adequacy 9 8 Materials and Workmanship 12 9 Adequacy of Structural Gauging, Clearances and Dimensions 13 10 Execution / Decommissioning 17 11 Future Maintenance 17 12 Compatibility with Other Infrastructure 18 13 Operational Safety 20 14 Design Control Procedures 21 15 Limitations on Use 21 16 Identification of Structures 21 17 Structures Owned by Outside Parties 22 18 Records 22

Recommendations Relating to GC/RT5112 19 Railway Traffic Loads and Load Effects 23 20 Walkway Loads 27 21 Road Traffic Loads 28 22 Pedestrian and / or Cycle Traffic Loads 28 23 Other Traffic Loads 29 24 Aerodynamic Effects of Rail Traffic 29 25 Non-Traffic Loads and Load Effects 29 26 Bridges not Owned by Railtrack 30 27 Records 30 28 Lists of Loads and Load Effects 30

Appendices

A Loads and Load Effects Required by GC/RT5112 to be Considered in the Loading Specification for Bridges 31 B Modifications to and clarification of BS 5400 Parts 3, 4 and 5 32 C Existing Substructures Affected by New Construction 33 D Provision for Future Traffic Developments and Selection of Traffic Mix 35 E Modifications to and Clarification of UIC Leaflet 776-3R (1989) 36 F Recommendations for Infill to Open Handrailing for Underline Bridges 37 G Profiles for the Tops of Parapets to Overline Highway Bridges 38 H Collision Loads from Railway Traffic 39 I Further Recommendations on Loading for Underline Bridges 41 J Collision of Road Vehicles with Bridge Superstructures 44 K Design Information that should be supplied by the infrastructure controller 45

References 47



2 R A I L T R A C K

Railtrack Approved Code of Practice GC/RC5510 Issue Two Date August 2000 Page 2 of 48

Part A Issue Record

This document will be updated when necessary by distribution of a complete replacement.

Revisions in the reissued document are marked by a vertical black line in the right hand margin adjacent to the revision.

Issue Date Comments One August 1998 Original Document which supports Railway

Group Standards GC/RT5110 “Design Requirements for Structures” and GC/RT5112 “Loading Requirements for the Design of Bridges”

Two August 2000 Reissued document providing for revision to GC/RT5110

Responsibilities

Railway Group Standards are mandatory on all members of the Railway Group * and apply to all relevant activities that fall into the scope of each individual’s Railway Safety Case. If any of those activities are performed by a contractor, the contractor’s obligation in respect of Railway Group Standards is determined by the terms of the contract between the respective parties. Where a contractor is a duty holder of a Railway Safety Case then Railway Group Standards apply directly to the activities described in the Safety Case.

Railtrack Approved Codes of Practice are non mandatory documents detailing suitable and sufficient means of meeting the mandatory requirements of a Railway Group Standard.

* The Railway Group comprises Railtrack and the duty holders of the Railway Safety Cases accepted by Railtrack.

Health and Safety

Responsibilities In issuing this document, Railtrack PLC makes no warranties, express or implied, that compliance with all or any documents published by the Safety & Standards Directorate is sufficient on its own to ensure safe systems of work or operation. Each user is reminded of its own responsibilities to ensure health and safety at work and its individual duties under health and safety legislation.

Supply

Controlled and uncontrolled copies of this document may be obtained from the Industry Safety Liaison Dept, Safety and Standards Directorate, Railtrack PLC, Railtrack House, DP01, Euston Square, London, NW1 2EE.



Design of Bridges

R A I L T R A C K 3


Part B 1 Purpose

The purpose of this document is to give recommendations for the design of bridges and supports Railway Group Standards GC/RT5110 and GC/RT5112.

2 Scope The overall scope of Railway Group Standards is as specified in Appendix A of GA/RT6001.

Specifically the contents of this document apply to bridges on, over or under Railtrack Controlled Infrastructure.

This document is applicable to permissible and enhanced permissible speeds up to 300km/h unless otherwise noted. See sections 6.3.3; 7.2.1; 9.1.1; 9.1,2; 19.1(a) and (k); 19.8.1; 19.9; Appendix H; Appendix I.2.

Whilst primarily applicable to bridges on, over or under Railtrack controlled infrastructure, the recommendations of this document may be applied also to Railtrack-owned bridges remote from the line, such as side bridges, on Railtrack-owned (but not controlled) infrastructure.

Unless explicitly stated otherwise, the recommendations of this document apply to new bridges and so far as is reasonably practicable to:

• complete superstructure reconstructions of existing bridges; • significant alterations, strengthening and extensions to existing bridges.

This document contains recommendations which are applicable to the duty holder of the following category of Railway Safety Cases:

• Infrastructure Controller.

3 Definitions Bridge (definition as given in GC/RT5112) A structure of one or more spans whose prime purpose is to afford passage over an obstruction or gap. Structures where all parts are buried below the surface at a distance greater than their diameter or span are excluded.

For the purpose of this document, a bridge is deemed to include associated elements such as wing walls, handrailing and fencing.

Design Information in the form of drawings, electronically stored data, diagrams, mathematical expressions, numerical quantities and / or words (including performance, materials and workmanship specifications) which together describe in detail what is to be constructed and, where appropriate, how it is to be constructed; the design process includes all the activities leading to the production of this information (including structural design as appropriate).

Structure Gauge A description of a line inside which fixed infrastructure should not intrude. Description will include rules for curvature, cant, speed, track fixity and requirements for staff excess and emergency evacuation.

4 Principle The principle of this document is to quote, verbatim and boxed, each part of sections 5 to 18 of GC/RT5110 and sections 6 to 8 and the Appendix of GC/RT5112, and to give recommendations which will generally enable the requirements of these documents to be met with respect to bridges.



4 R A I L T R A C K


5 Duties and Competency

5.1 Responsibilities and Duties The responsibilities and duties of all persons responsible for the design of structures shall be clearly defined in writing and understood by these persons.

The responsibilities and duties of design organisations should be made clear in the relevant design brief, scope of works, tender documentation and / or other relevant documents. The infrastructure controller should take reasonable steps to verify that organisations undertaking design have adequate management procedures to ensure that individual designers understand their responsibilities and duties.

Preparation of design briefs (including performance requirements and design constraints) is part of the design process; the infrastructure controller should therefore ensure that those preparing design briefs (whether employees or not) understand the extent and nature of their responsibilities and duties as regards design.

5.2 Assessment of Competence The skill, expertise, training and experience of those employed shall be appropriate to the nature and complexity of the structures being designed. This competency shall be assessed by the person making the appointment.

The CDM Regulations set out requirements for those managing construction / design work with respect to competency.

The infrastructure controller should take reasonable steps to verify that individual designers within design organisations are suitably competent. Assessment of competence should normally involve inspection of the designer’s CV as a minimum, but this may not be necessary if the assessor has direct knowledge of the designer’s capabilities. Such direct knowledge may indeed be a preferable indicator of competence.

Although it may be regarded as a strong pointer, professional qualification should not be taken to be as a necessary criterion of competence, nor in itself a sufficient criterion.



Design of Bridges

R A I L T R A C K 5


Recommendations relating to GC/RT5110 6 Intended Use and Life

6.1 Intended Use The following shall be specified for the design of the structure:

• the traffic (including type and intensity where appropriate), persons and / or equipment that the structure is required to support and / or the level of protection to be provided taking into account reasonably foreseeable future traffic

The traffic, persons and or equipment that the bridge is required to support should generally be specified as the design life (variable traffic) and / or superimposed loading on the bridge. So far as traffic is concerned, the type, size, weight, frequency and speed will generally need to be considered.

The loading for bridges is specified in GC/RT5112. Further recommendations are given in section 19 to 28 of this document. Guidance on the speed of rail traffic and selection of traffic mix to be considered in the design is given in Appendix D of this document.

The level of protection mainly relates to protection against accidental loads and should normally be expressed as the design loading due to collision of vehicles (or waterborne vessels) passing over or under the bridge with elements of the bridge together with any preventative and protective measures (fenders, kerbs, level of redundancy). The design loading is normally expressed in terms of static equivalent design forces but a more complex dynamic analysis may be appropriate in certain cases.

In all cases, the design loading should be stated explicitly in the Approval in Principle (AIP) submission. See section 14 of this document.

The level of protection should also be taken to relate to such matters as provision of barriers and handrailing, electrical bonding etc. Recommendations are given in sections 9.1.2 and 13.4 respectively of this document.

The traffic passing over the bridge and the traffic passing beneath the bridge should be considered.

In establishing the intended use, due consideration should be given in the design of the bridge to the likely or reasonably foreseeable future rail traffic including:

• maximum size of vehicles (and their loads); • maximum linespeed; • maximum axle weight and axle spacing; • future overhead electrification; • associated considerations for persons working on or near the track.

6.2 Intended Life The following shall be specified for the design of the structure:

• the intended life of the structure (where appropriate).

6.2.1 General The intended life of the bridge should be stated explicitly in design documentation and recorded in the AIP submission. It is particularly important to state this when the intended life is short.



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The intended life should be specified as the design life, as follows:

• generally for new bridges and new bridge superstructures: 120 years (as given in BS 5400); in exceptional circumstances a shorter life may be specified but this should be justified in the AIP submission;

• for all other situations (eg, partial superstructure reconstructions, repairs, strengthening, remedial works etc.) The infrastructure controller should specify both the intended life of the new elements of the bridge and the further intended life of the existing elements to be retained.

6.2.2 Extended Life Where the cost of replacing a bridge is likely to be particularly high, consideration should be given to specifying an intended life longer than 120 years. This could apply to large bridges or where the indirect costs of erection, disruption to either road or rail traffic etc. are likely to be disproportionate to the direct costs of the structure. It should also apply where future maintenance will be restricted (eg, bridges constructed by thrusting or jacking).

Where the intended life is longer than 120 years, the effects of fatigue should be treated quantitatively. Consideration, as appropriate, should also be given to the following:

• greater than normal allowance for future increase in amount, weight and / or speed of traffic;

• increased return period values for wind, temperature range, flood levels etc.; • increased sacrificial thickness of steel; • increased partial factors for materials; • enhanced resistance to corrosion of concrete reinforcement (eg, increased

cover, less permeable concrete, stainless steel or epoxy-coated bars); • requirement by Railtrack on the designer to submit a statement of how the

design provides for long life and appropriate maintenance.

6.2.3 Temporary Bridges The intended life for temporary bridges should be considered on a case by case basis but procedures should be in place to ensure that the use does not exceed the specified intended life unless the consequential risks are properly assessed and controlled.

6.3 Actual Life 6.3.1 General The main design influences on the actual life are on fatigue endurance and durability. The actual life can also be affected greatly by the buildability, the maintainability and the standard of worksmanship. In all these the quality of detailing plays an important part. All these aspects should therefore be considered in developing the design.

CIRIA Report 155 gives further recommendations on the buildability of bridges.

6.3.2 Joints and Bearings Joints and bearings often have an adverse effect on the durability of structures. So far as is reasonably practicable, bridges should be designed to reduce or eliminate the occurrence of joints, including movement joints, joints between elements and construction joints in concrete.



Design of Bridges

R A I L T R A C K 7


6.3.3 Corrosion Protection Steel bridges and bridge elements should have a corrosion protection system in accordance with railway industry standards and appropriate to the likely conditions of application and service, except for:

• bridges or bridge elements with a limited intended life; • bridges or bridge elements made of steel with improved atmospheric

corrosion resistance, in which case sacrificial steel thickness should be provided in accordance with Highways Agency standards and guidance.

6.3.4 Waterproofing In order to achieve satisfactory durability, bridge decks should generally be waterproofed except for:

• bridges with a limited intended life; • bridge types for which the application of a waterproofing membrane may not

be practicable, for example, most bridges installed by thrusting or jacking through soil.

In such cases alternative means of ensuring satisfactory durability should be considered.

For underline bridges crossing watercourses, accommodation openings, rural footpaths and the like where the deck consists of a number of separate structural elements (eg, reinforced concrete slabs), consideration may be given to leaving the gaps between the elements unwaterproofed provided that each element is waterproofed on the upper surface and sides.

For all overline bridges where overhead electrification is present, effective means of waterproofing should be provided to prevent water running or dripping through the deck onto the electrical equipment or forming icicles above it. (See section 13.3 of this document.)

Effective waterproofing is particularly important for steel, reinforced concrete and prestressed concrete bridge decks carrying public highways where de-icing salts may be used. The waterproofing systems for such decks should be in accordance with Highways Agency standards.

Waterproofing systems for underline bridge decks should be in accordance with railway industry standards and appropriate to the likely conditions of application and service.

6.3.5 Disposal of Water For new bridges and bridge superstructure reconstructions, adequate provision should be made for the disposal of water from the superstructure.

6.3.6 Ballast Depth Requirements for ballast depths are set out in GC/RT5014. For permissible or enhanced permissible speeds greater than 200km/h, specialist advice should be sought.

For underline bridges carrying ballasted track, the ballast depth should generally be at least 200mm below the underside of the sleepers at the low rail position, regardless of sleeper type. This is in order to:

• avoid damage to the bridge deck waterproofing caused by track tampers etc; • ensure satisfactory longitudinal distribution of wheel loads.



8 R A I L T R A C K


If, in exceptional cases, a lesser ballast depth is unavoidable:

• provision should be made to protect the bridge deck waterproofing • the wheel load distribution proportions given in Appendix I.3 of this document

should not be used without further justification.

7 Structural Adequacy The structure shall be designed with reasonable professional care to provide adequate resistance to the intended applied loads (including its self-weight) and the likely effects of external influences during its intended life assuming appropriate standards of execution and maintenance.

7.1 General In order to meet the requirement for bridges to be designed with reasonable professional care, the infrastructure controller should ensure that:

• preparation of design briefs (including performance requirements and design constraints) is undertaken by competent people

• organisations undertaking bridge design have suitable experience and expertise and adequate management to ensure proper quality

• individuals undertaking bridge design are competent engineers and have suitable experience and expertise

• in certain cases (eg, large or complex bridges or those of novel type of construction or complex partial reconstructions) consideration is given to requiring the design to be effectively controlled by named individuals

• designs are adequately checked by competent engineers • designers are made aware (by means of this document or by other means)

that, although the recommendations of this document are appropriate and sufficient in the great majority of cases, there may be certain exceptional circumstances where this is not so and that designers (including those preparing design briefs) are responsible for taking reasonable steps to identify such circumstances and making appropriate provision.

CIRIA Report 63 gives further guidance on the duties expected of designers and on their liabilities in law. (See particularly 5.4.4 and Appendix 4 of Report 63.)

7.2 Intended Applied Loads Recommendations for the intended applied loads are given in sections 19 to 28 of this document.

7.3 Accidental Events and Vandalism The structure shall also be designed and executed with sufficient robustness so that it will not be damaged by accidental events (for example, train derailment) or vandalism, to an extent disproportionate to the original cause.

7.3.1 Protection of Overline Bridges from Derailed Trains Recommendations for dealing with accidental actions for overline bridges and end impact walls beyond buffer stops are given in Appendix H of this document.

Note: the recommendations are only valid for speeds up to 200km/h.

Priority should be given to reducing the likelihood of occurrence of such events by the provision of protective and / or preventative measures (rather than measures to deal with such events after they have occurred) because of the uncertain nature of any outcome.

Where a bridge is supported by individual columns closer than 4.5m to the running edge of the nearest rail, a degree of continuity should be built into the structure as given in Appendix H of this document.

Further advice and recommendations are given in UIC Leaflet 777-2R (but should be ignored where they conflict with the recommendations of this document).



Design of Bridges

R A I L T R A C K 9


7.3.2 Protection of Underline Bridges from Road Vehicle Strikes 7.3.2.1 New Bridges For new bridges over public roads, the headroom provided should be at least 5.7m where this can be achieved with reasonable economy and otherwise should be as given in HMRI Railway Safety Principles and Guidance Part 2, Section A, Chapter 4.

For new bridges, if in exceptional circumstances it is not reasonably practicable to achieve the headroom as given in the HMRI Railway Safety Principles and Guidance, any lesser headroom should be identified in the AIP submission and justified in terms of the risk to train operations from road vehicles striking the bridge. The following should be taken into account:

• the volume, speed and nature of likely highway traffic • the presence of nearby low-headroom bridges or other structures which

effectively protect the bridge from being struck • the robustness of the type of bridge construction • the commercial consequences of train delays due to bridge strikes.

Where the headroom is less than 5.7m, protection should be provided to the superstructure against the effects of strikes by road vehicles as given in Appendix J of this document.

Where there is a particularly high risk of bridge strikes, consideration should be given to the provision of impact protection beams. Protection beams should be:

• as robust as can be achieved with reasonable economy • mounted clear of the main structure of the bridge so far as can be achieved

with reasonable economy • mounted on supports integral with the main bridge supports (as required by

Highways Agency standards) • where convenient, designed to perform a secondary function associated with

the bridge, eg, carrying a walkway (but not cables or pipes, because of the risk of damage due to impact).

Highways Agency documents may be used as guidance to the design of protection beams.

For bridges over water, suitable protection should be provided to the superstructure and substructure against the effects of hydraulic action, scour and, where relevant, possible impact from flooding debris or waterborne vessels.

7.3.2.2 Bridge Reconstructions For bridge reconstructions over public roads, existing conditions are often such that 5.7m headroom cannot reasonably be provided. In such cases the headroom should be the maximum that can be achieved with reasonable economy (taking into account the risk from bridge strikes at the site), generally as follows in order of preference:

38. at least 5.7m 38. at least 5.3m, with Appendix J provisions 38. at least 5.1m, with Appendix J provisions 38. an improvement on the existing, with Appendix J provisions and

protection beams unless the risk from strikes is small 38. an improvement on the existing, with Appendix J provisions 38. not less than the existing, with Appendix J provisions and protection

beams unless the risk from strikes is small 38. not less than the existing, with Appendix J provisions and robust

construction 38. not less than the existing, with Appendix J provisions 38. not less than the existing.



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Any headroom less than 5.7m should be identified and justified in the AIP submission, taking into account the factors given in section 7.3.2.1 of this document. In addition, the previous history of bridge strike incidents at the site should be considered.

7.3.3 Protection of Underline Bridges from Derailed Trains For underline bridges, robust kerbs should be provided to contain the wheels of derailed vehicles, as given in HMRI Railway Safety Principles and Guidance Part 2, Section A, Chapter 4. The height of such kerbs should be at least 300mm above the top of the adjacent rail (preferably 350mm higher to allow for future track lifting). Kerbs should preferably be set at least 1500mm from the adjacent rail running edge (so that the back of the “offside” wheel of a derailed train will be restrained by the cess rail before the “nearside” wheel strikes the kerb.) However, it is accepted that in many cases it will not be practicable to achieve this with reasonable economy.

Kerbs may be considered as robust if they are designed to resist the horizontal loading given in section 19.1 of this document. For half-through bridges, the main girders may be deemed to act as robust kerbs provided that their height is as given above.

Recommendations for the vertical loading to take account of the possible effects of derailed trains on underline bridge superstructures are given in section 19.1 of this document. Such loading need not be applied to secondary structural elements such as cantilevered walkways. For certain superstructure types (eg, trusses or bowstring arches) the possibility of a derailed train striking an above-rail structural element such as a vertical or diagonal member should be considered. A reasonable degree of robustness and / or redundancy should be provided for such members.

7.3.4 Protection from Vandalism Where bridges are situated in areas known to be subject to vandalism, consideration should be given to measures which minimise the risk of damage to the bridge through vandalism and damage to other parts of the infrastructure or to trains through vandalism by users of the bridge. (See section 9.3.2.2 of this document.)

7.4 Bridges where Loading is the Responsibility of Another Authority Where the traffic loading is the responsibility of another authority, the loading together with any requirements for controlling the loading shall be agreed with that authority.

This will generally only apply to the specification of traffic loads for road bridges. Occasionally, however, other organisations may need to be involved (eg, London Underground Ltd, British Waterways Board, train operating companies). The requirements should be determined in consultation with the relevant authority at an early stage and any decisions recorded.

7.5 Application Standards The loading and resistance requirements shall be based on suitable standards (eg, European or British Standards and Codes of Practice), current best practice or appropriate risk assessment.

Either European or British Standards and Codes of Practice should be used.

Whichever is chosen, a complete set of consistent documents should be used, covering loading, design, execution (construction) and material / workmanship specifications.

Where European Standards are used, ENV versions should be used only in conjunction with the UK National Application Document.



Design of Bridges

R A I L T R A C K 1 1


Other industry standards and advice (eg, those of the Highways Agency) may generally be used for guidance provided they do not conflict with the recommendations given in this document.

7.5.1 Steel, Concrete and Composite Bridges Steel, concrete and steel / concrete composite bridges (and parts of bridges) should be designed in accordance with the relevant parts of BS 5400 with the modifications given in Appendix B of this document. (These modifications should be identified in the AIP submission but do not need to be further justified.)

7.5.2 Timber, Aluminium and Brickwork / Masonry Bridges Timber, aluminium, and brickwork / masonry bridges (and parts of bridges) should be designed in accordance with the relevant parts of BS 5268, BS 8118 and BS 5628 respectively, in each case making due provision for:

• the application of loading expressed in limit state terms to permissible stress design methods

• the effects of repeated application of live loading • the weather exposure conditions to which the bridge will be subjected.

These provisions should be described in the AIP submission.

7.5.3 Bridges of Other Materials Bridges (and parts of bridges) constructed of materials other than as given above should be designed in accordance with recognised national, industry or other standards or, where no such standards exist, in accordance with justifiable methods.

These standards and methods, together with the supporting justification, should be described in the AIP submission and the design subject to an independent (category 3) check.

7.5.4 Foundations and Earth-Retaining Elements New foundations for bridges should be designed generally in accordance with BS 8004.

New earth-retaining elements of bridges should be designed generally in accordance with BS 8002.

7.5.5 Reinforced Soil Elements Reinforced soil abutments, wingwalls and other elements of bridges should be designed in accordance with BS 8006 and in accordance with the manufacturer’s recommendations for proprietary systems. For elements subject to railway loading, the following should:

a) To avoid the possibility of loss of pull-out resistance due to soil vibrations, the top layer of reinforcement should not be less than about 1.0m below the underside of the track ballast (this does not apply if the reinforcement is more than 2m horizontally from the nearest rail).

a) For construction in the vicinity of DC-electrified lines, the possible effects of stray-current corrosion should be limited by suitable measures such as fill material with high resistivity, additional sacrificial thickness of steel reinforcement, or use of non-metallic reinforcement. These measures should be identified in the AIP submission.

a) The differential settlement between the reinforced soil elements and other elements of the bridge should be limited so as not to cause unacceptable irregularities in the longitudinal alignment of the track (for example, at run-on and run-off locations).

a) The differential settlement transverse to the track should be limited so as not to cause unacceptable twist in the track.





7.5.6 Bearings For bridge superstructure reconstructions, provision should be made for deck-end rotation in order to prevent this rotation from being transmitted to the existing abutment tops. Bridge bearings should be designed in accordance with the relevant part of BS 5400, except for:

• bridges up to 15m thermal expansion length, bearings may be designed as fixed at both ends unless in particular cases there are reasons why it is inappropriate to do so

• bridges up to 20m thermal expansion length, bearing sliding surfaces may be plain steel-on-steel unless in particular cases there are reasons why these would be inappropriate (eg, slender piers)

• bearings at halving joints warrant particular consideration. Such joints should be used only in exceptional circumstances and only where adequate access for inspection and maintenance is provided

• the use of bearings to resist uplift forces should be identified in the AIP submission. The design of such bearings should take into account the effects of repeated load cycles.

For superstructure reconstructions, where the ability of existing abutments to withstand horizontal pressures cannot reasonably be demonstrated, restraint (eg, bearing keepstrips) should be provided to allow sufficient movement of the superstructure due to temperature change but so that, should movement of the abutment tops occur in the future, such movement is limited. In such cases the superstructure should be designed to resist any anticipated propping forces. (See also Appendix C of this document.)

See also section 11.2 of this document regarding replacement of components.

7.5.7 Existing Substructures Affected by New Construction Where only the superstructure of an existing bridge is reconstructed, or in other cases where new construction is associated with the total or partial retention of existing substructures, the following should apply:

• the remaining part of an existing substructure need not be deemed unacceptable for continuing service solely because it does not comply with the criteria applicable to new structures

• the soil supporting an existing substructure need not be deemed unacceptably loaded solely because the assessed loading will be higher than the loading considered acceptable for the same soil supporting a new structure.

Further guidance on the treatment of existing substructures affected by new construction is given in Appendix C of this document.

8 Materials and Workmanship

Suitable materials and standards of workmanship shall be specified for the structure, including any processes required for the approval of new materials. Both structural and health and safety aspects shall be considered.

The life of a bridge can be significantly affected by the choice of materials and standard of workmanship. Of particular importance is the choice of steel grade and quality of welding.

The specification for materials and standards of workmanship should be based on current European, national or rail industry standards where appropriate.

In specifying materials and standards of workmanship, the methods of work necessary or likely resulting from the design should be taken into account (eg, the type and quality of welding achievable, the specification for the protective coating, the forms of construction associated with confined spaces such as box girders, the degree of shop / site fabrication).



Design of Bridges



9 Adequacy of Structural Gauging,

Clearances and Dimensions

9.1 General Requirements The location and dimensions of the structure (including any intended equipment that it is designed to support) shall provide, where appropriate:

• for the safe movement of vehicles, persons (including those whose mobility is impaired) and / or equipment;

9.1.1 Clearances to the Railway The clearance requirements for the safe passage of rail vehicles and the structure gauge for heights above the rail level less than or equal to 1100mm are set out in GE/RT8029. GE/RT8029 covers speeds up to 140mph (225km/h).

The requirements for personal safety and access are given in GC/RT5203.

The clearances provided should also take into account operational safety including electrical clearances. (See section 13 of this document.)

The provision of bridge girders in the space between tracks (the “six-foot”) should generally be avoided where this is reasonably practicable because it inhibits future operational flexibility and often makes access for future examination difficult.

The position of the bridge elements relevant to the track that determine the clearances provided for vehicles should be specified by the infrastructure controller.

9.1.2 Walkways and Handrailing to Underline Bridges Underline bridges should be provided on both sides with walkways and continuous handrailing or equivalent pedestrian barriers.

Walkways may be formed at cess ballast level or they may be raised or otherwise separate. GC/RT5203 sets out the requirements for such walkways.

GC/RT5203, issue one, only covers speeds up to 125mph. This is currently being revised to cover speeds greater than 125mph.

Raised or separate walkways should be at least 700mm wide, with a non-slip surface free of tripping hazards. Brush-finished or exposed-aggregate concrete may be deemed to be non-slip. Girder flanges may form part or all of the walkway width unless the presence of doubler plates, bolt heads or other projections form a tripping hazard.

Raised walkways should be provided with ramps or steps down to cess level at each end. Step rises and goings should comply with the recommendations of BS 5395 Part 1 for semi-public stairways. The width of the stairway may be reduced to 500mm provided the width of the walkway at waist height is not reduced below 700mm.

GC/RT5203 sets out the requirements for immediate access to a place of safety where the walkway is raised more than 500mm above the level of the ballast adjacent to the walkway, cess or sleeper.

Where steps are provided on both sides of the track they should generally be staggered to provide intervals not exceeding 20m.

Where the linespeed is greater than 100mph, the interval between steps should be considered on a site specific basis, taking into account the sighting distances, the speed of trains and the number of tracks.





Where use of steps would entail a vertical or near-vertical climb (eg, to the top flange of a girder) suitable grab handles should be provided.

Clearances of steps and grab handles should be checked.

Handrailing should be as follows:

Height: at least 1250mm above the adjacent walkway or cess level.

Loading: as given in section 20 of this document. Form: either solid or of open construction. If the latter, there should be:

• a continuous top rail; • a continuous kerb or kicker plate at least 150mm high; • at least one intermediate rail or other infill as given in Appendix F

of this document.

Where an underline bridge has two or more separate superstructures carrying adjacent tracks with longitudinal gaps between them, the gaps should either be edged with handrailing as above or they should be covered with plates or gratings to protect trackside workers and to prevent ballast from falling through the gaps.

Choice of cover type should take into account any requirements for allowing daylight to penetrate to below the superstructure.

Where a walkway intended for use by the public or by persons other than those authorised to go on or about the line is attached to an underline bridge, the walkway should be separated from the railway by a suitable barrier and should be provided with a suitable parapet on the side remote from the railway.

9.1.3 Lateral Clearances to Highways Lateral clearances to public highways should be determined in consultation with the relevant Highway Authority taking into account the infrastructure controller’s legal obligations.

Lateral clearances to private roads should be determined in consultation with the owner or user of the road taking into account the infrastructure controller’s legal obligations and the provisions within any relevant agreement between the infrastructure controller and other parties.

9.1.4 Vertical Clearances to Highways Recommendations for vertical clearances to public highways are given in section 7.3.2 of this document.

Vertical clearances to private roads should be as large as can be achieved with reasonable economy, determined in consultation with the owner and / or user(s) of the road and taking into account the infrastructure controller’s legal obligations and the provisions within any relevant agreement between the infrastructure controller and other parties.

9.2 The location and dimensions of the structure (including any intended equipment that it is designed to support) shall provide, where appropriate:

• adequate protection and / or deterrence from unauthorised access (eg, trespass or vandalism)

9.2.1 Layout of Fencing etc. The layout of fencing in the vicinity of bridges should be such that the fences, together with the structure of the bridge where appropriate, form a continuous barrier against trespass onto the railway. Where a fence abuts the end of a wingwall to form part of such continuous barrier, the end of the wingwall should



Design of Bridges



be at least as high as the adjacent fence and should be formed such as to deter climbing.

Where appropriate (eg, on pipe bridges and certain footbridges) chevaux-de-frise or other barriers should be provided to deter people from making unauthorised passage along the top or outside of the structure.

Where the layout of fencing is such that members of the public have access to the top of wingwalls or abutments, suitable fences or barriers not less than 1100mm high should be set on the wingwalls / abutments to give reasonable protection against falling.

GC/RT5201 sets out the minimum requirements for lineside security.

Reasonable provision should be made to protect those who may be walking along the cess or working on embankment slopes against falling from wingwalls or abutments.

9.3 The location and dimensions of the structure (including any intended equipment that it is designed to support) shall provide, where appropriate:

• adequate protection to vehicles or persons using or affected by the structure.

9.3.1 Parapets to Overline Road Bridges The containment level of parapets to overline bridges carrying road traffic (including accommodation and occupation bridges) should be in accordance with Department of Transport Standard BD 52/93 (which supersedes the former Standard BE 5). Parapets may be of metallic, reinforced concrete or reinforced brickwork / masonry (sandwich) construction.

Where existing bridge parapets are repaired or rebuilt, an improvement to the level of containment should be made if this can be achieved with reasonable economy, but P6 containment level need not generally be provided.

Parapets to all overline bridges should be as given in HMRI Railway Safety Principles and Guidance Part 2, Section A, Chapter 4. Where the width of the top of the parapet is more than 100mm, a steeple coping should be provided. Guidance on suitable profiles is given in Appendix G of this document.

Where separate copings are used, they should be firmly fixed to prevent dislodgement by vandals or accidental impact.

In respect of equestrian use, generally parapets 1800mm high need be provided only:

• where equestrian use is exceptionally heavy; • where equestrian use is moderate but the bridge is narrow and there is no

verge or footway (eg, a designated bridleway bridge).

Where reasonably practicable, parapets should be constructed 50mm higher than the minimum recommended to allow for future road or footway resurfacing.

9.3.2 Layout etc. for Footbridges 9.3.2.1 Prevention of Injury All accessible parts of footbridges should be free of sharp edges or projections which could be reasonably foreseen to cause injury.

9.3.2.2 Protection of the Railway from Vandalism At locations where vandalism is known to be a problem, consideration should be given to the provision of parapets at least 1800mm high or enclosing screens to footbridges to prevent objects from being thrown onto the railway. Mesh screens





should be such that a 50mm diameter sphere cannot be passed through without distorting the mesh.

9.3.2.3 Width and Internal Headroom For footbridges at stations or giving access to stations, the width should be suitable for the current and anticipated pedestrian flows and should additionally be agreed with the relevant station operator. Where appropriate, requirements for emergency evacuation should be taken into account and agreed with the relevant authorities including the Fire Authority.

For footbridges carrying public footpaths, the width should be in accordance with the reasonable requirements of the relevant highway authority (but need not generally be as wide as given in Highways Agency standards: a clear width of 1400mm between handrails is considered sufficient unless heavy pedestrian flows are likely).

In all cases the clear width between handrails should be at least 1200mm as given in HMRI Railway Safety Principles and Guidance Part 2, Section B, Chapter 5.

For covered footbridges, internal headroom should be as given in BS 5395. At stations, internal headroom should additionally be as given in HMRI Railway Safety Principles and Guidance.

9.3.2.4 Stairways, Steps and Ramps Except as given below, stairways, steps and ramps forming part of the structure of footbridges should be as given in HMRI Railway Safety Principles and Guidance Part 2, Section B, Chapter 5.

Where it is not reasonably practicable to comply with the above (eg, where a change in direction between stair flights cannot be accommodated) this should be stated and justified in the AIP submission.

9.3.2.5 Footbridges not Owned by Railtrack For footbridges which are not owned by Railtrack and which are not at stations nor give access to stations, the above recommendations in respect of width and in respect of stairways, steps and ramps and internal headroom need not apply.

9.3.2.6 Provisions for Safe Movement of Persons (including those who are disabled) at Footbridges Reference should be made to the document “Meeting the needs of disabled passengers” published by the Office of the Rail Regulator.

9. 4 Structures Over Electrified Railways The following requirements apply to parapets of structures that are over railways electrified on the 25kV overhead or conductor rail system and where pedestrians, animals, pedal cycles and vehicles drawn by animals are not excluded by Order.

Parapets shall not be less than 1500mm high (1800mm where the bridge is frequently used by equestrian traffic), shall have an inner face which is smooth and imperforate over its full height without hand or footholds and shall be provided with steeple copings or equivalent. In addition, parapets shall extend at least 3000mm beyond any uninsulated overhead equipment.

Consideration shall be given to providing additional protective measures on footbridges where vandalism is known to be a problem in the area.

Consideration should be given to providing transparent parapets where it is important that people can be seen from outside the bridge (for example, where mugging is likely to occur).

Where parts of bridges (eg, road approach ramps or footbridge stair flights) run essentially parallel to and adjacent to railways electrified on the overhead



Design of Bridges



system, screening or other protection should be provided as necessary to prevent people (and anything they might reasonably be carrying) from coming closer than 2.75m to uninsulated electrical equipment.

10 Execution / Decommissioning

The structure shall be designed so that there is at least one safe and feasible method for its execution and for its subsequent decommissioning.

10.1 Execution (construction, erection) The safe and feasible method for the execution of the structure should take into account:

• the likely disruption to traffic and the economic consequences of such disruption;

• the effect of the execution on existing infrastructure; • the time available for the erection; • the equipment (including back-up equipment) required for the erection

(including in the case of cranes any particular requirements to protect road / rail / pedestrian traffic or infrastructure such as OLE or buried services);

• the adequacy of any temporary works (including temporary use of permanent works in a completed or uncompleted condition);

• the need for any temporary bracing or support to structural elements during the erection process;

• the nuisance which may be caused to nearby residents.

Where bridges are to be erected during closure of road or rail traffic, consideration should be given to a trial erection of bridge prior to the actual erection.

The method of execution envisaged by the designer should be stated in the AIP submission. In appropriate cases a detailed description, drawings etc. should be included.

10.2 Decommissioning Any hazards associated with decommissioning which would not be apparent from inspection of the bridge or from inspection of its likely design / construction records should be stated in the AIP submission.

Particular attention should be paid to bridges:

• which require temporary bracing during erection; • whose stability is affected by adjacent structures (eg, multispan arch

bridges); • which include the use of toxic materials; • where the abutments rely on propping from the superstructure for their

stability.

11 Future Maintenance The structure shall be designed so that future foreseeable maintenance requirements can be carried out safely including, where appropriate:

• examination of the structure • replacement of components, materials (eg, paint) or equipment with a

planned life less than that of the structure.

11.1 Future Examination The requirements for future foreseeable examination and maintenance of a bridge should take into account:

• the disruption to traffic (this should include the traffic using the bridge and the traffic passing beneath the bridge);





• the difficulty and method of gaining access; • the extent to which parts of the bridge become buried after installation.

11.2 Future Replacement of Components Consideration should be given to the requirements for the reapplication of any protective treatments or other components with an intended or likely life less than that of the rest of the structure.

Consideration should also be given to the replacement of the bearings. The method of attaching the bearings to the structure should be carefully considered so that the bearings can be removed without undue difficulty. For metallic bearings, there should preferably be bolted connections top and bottom to enable removal of the bearing with only minimal jacking-up of the superstructure and without the need for breaking out into the substructure. (Provision of a supplementary plate under the bearing bottom plate, with the latter screwed into the former, may be helpful in this respect.)

It is likely that the bridge will need to be jacked up to permit the removal and insertion of replacement bearings; provision may therefore have to be made for additional stiffening to take the high local forces from the jacks and associated eccentric load effects. If such provision is made, the location and safe capacity of jacking points should be recorded and should preferably also be shown physically on the structure.

Where there is no provision for jacks on the abutments or piers, the likely effects of the temporary support structures on restricting traffic and on services adjacent to or beneath the temporary supports should be taken into account.

12 Compatibility with Other Infrastructure

The structure shall be designed so that:

• the structure itself and any equipment it supports does not affect the safe functioning of any adjacent, proposed or existing structure or equipment

• adjacent proposed or existing structures or equipment will not affect the safe functioning of the structure or the equipment it supports.

12.1 Track / Bridge Interaction The design of underline bridges should take into account the effects of the bridge on the track and vice versa. These effects are known as track / bridge interaction and are principally due to thermal expansion / contraction, traction / braking of rail traffic and deformation of the bridge under traffic loads.

Track / bridge interaction is likely to be most significant for bridges with long expansion length carrying CWR track. GC/RT5021 specifies the requirements for assessing the need for and providing adjustment switches.

In the following cases track / bridge interaction effects may be deemed covered by the design loading given in this document:

• bridges carrying ballasted or non-ballasted CWR track with adjustment switches as above;

• single-span simply-supported bridges up to 30m expansion length, carrying ballasted CWR track without adjustment switches;

• two-span simply-supported or continuous bridges with each span up to 30m expansion length, carrying ballasted CWR track without adjustment switches, provided that the fixed point for expansion is at the intermediate support;

• single-span bridges up to 15m expansion length, carrying non-ballasted CWR track without expansion switches;

• two-span simply-supported or continuous bridges with each span up to 15m expansion length, carrying non-ballasted CWR track without adjustment switches, provided that the fixed point for expansion is at the intermediate support;



Design of Bridges



• all bridges carrying jointed track. (However, rail joints should be kept clear of bridges as set out in GC/RT5020.)

In other cases track / bridge interaction effects should be considered and justified for each bridge and agreed at the AIP stage. UIC Leaflet 774-3R may be used for guidance.

12.2 Retention of Ballast Suitable provision should be made to retain the ballast on the bridge, at either end of the bridge, and at the transition between the bridge and the adjacent track formation.

Where run on / run off slabs are provided at the ends of bridges, particular care should be taken to provide for maintaining the depth and integrity of the ballast supported by such slabs.

11.2 Compatibility of Bridge with other Adjacent, Proposed or Existing Structures and Equipment

12.3.1 General The bridge and any equipment it supports should be compatible structurally and in all other respects with other adjacent fixed assets or features of the infrastructure.

In particular consider, where appropriate:

• track and track components (see section 12.3.2) • provision and maintenance of services; • the effect of forces or pressures (including those due to thermal expansion)

transferred to other adjacent features of the infrastructure; • the presence of services adjacent to or carried by the bridge (including the

ability to add new services to overline bridges without damaging the waterproofing);

• power supply and electrification equipment; • train control (signalling) equipment; • telecommunications equipment; • plant; • any other identified feature.

12.3.2 Track and Track Components For track and track components, the infrastructure controller should specify:

• track system over or under the bridge • horizontal and vertical alignment; • cant and cant deficiency; • ballast depth (see section 6.3.6, Appendix E and Appendix I.5 of this

document).

Adequate provision should be made for access, loading of materials and clearances for track maintenance and track renewal.





13 Operational Safety Other influences or requirements which may affect the safety of railway operations or the safety of persons whose duties take them on or near the line shall be considered and taken into account, including:

• the safety of train operations of other railway infrastructure owners that are likely to be affected by the structure

• sighting of train control equipment or other lineside signs • the safety of staff on platforms • provision for staff on or about the track including the provision of positions of

safety • aerodynamic effects from passing trains • potential arcing of electric power equipment • ground water where this has the potential to affect train control or other

safety critical equipment (for example, in tunnels).

13.1 Sighting of Train Control Equipment or other Lineside Signs It is particularly important that the sighting of signals is not obstructed or reduced.

13.2 Provision for Staff on or about the Track Where reasonably practicable the supports of bridges should not reduce existing sighting distances of trains for staff on or about the track.

13.3 Potential Arcing of Electrical Power Equipment The clearance between a bridge and electrical equipment at a different potential should be maximised so far as can be achieved with reasonable economy. Although the arcing distance between such elements in dry conditions for the 25kV overhead electrification system is less than 80mm, the presence of damp conditions and the presence of foreign bodies (eg, birds) increases the risk of arcing at considerably greater distances.

The clearances to electrical equipment should provide adequate tolerances for future maintenance. Normal and minimum clearances are given in GM/TT0101 This will be superseded by GE/RT8025 in due course.

Clearances should also be as given in HMRI Railway Safety Principles and Guidance Part 2, Section C, Chapter 3.

At certain locations, overhead electrification equipment needs to be higher than normal or needs increased clearance to bridges. (Examples include locations close to public road level crossings and some locations where track switches and crossings are present.) In such cases the infrastructure controller should specify the clearance required.

All bridges crossing over overhead electrified railways should be waterproofed to avoid potential damage through flash over.

13.4 Electrical Bonding Bridges and service ducts crossing over or under overhead electrified railways should be effectively electrically bonded, as follows:

) Metal underline and overline bridges should be bonded to the traction return rail or earth wire.

a) The components of metal bridges should be connected by welding or by substantial, clean metal-to-metal bolted or riveted joints.

b) Exposed metal parts of underline and overline bridges (eg, handrails and bearings of concrete bridges) should be connected together and bonded as above.



Design of Bridges



c) Concrete reinforcement (including prestressing anchorages) should be bonded as above if it is accessible or if it is electrically connected to accessible metalwork.

) Concrete, timber and masonry overline bridges should have a bonded metal plate attached to the underside in certain cases.

) Embedded service ducts in bridges should be non-metallic.

Reference should be made to railway industry standards for detailed requirements. The infrastructure controller should specify the relevant standards.

Where dual overhead and third-rail electrification is present, there is a likelihood of high current flow through the earth. At such locations, The infrastructure controller should consider specifying precautions against stray-current corrosion (eg, electrical bonding or electrical isolation of substructure reinforcement cages).

14 Design Control Procedures

The design control procedures for the structure are given in GC/RT5101, Technical Approval Requirements for Changes to the Infrastructure.

GC/RT5101 gives requirements for approval procedures at each of the following four phases of a scheme:

• remit • approval in principle (AIP) • design and checking • execution (construction, erection) and commissioning.

Bridges should be designed to be appropriately economical on a whole life basis.

Other than in very straightforward cases, the AIP submission should include evidence that alternatives to the type of structure proposed have been considered and approximately costed.

15 Limitations on Use Any limits on the use of the structure shall be stated, recorded and controls put in place for the limitations to be observed (for example, notices and / or physical restrictions.

Methods for ensuring that any limits on the use of the bridge are observed could involve restricting the type and speed of traffic or, in the case of bridges carrying pedestrian or road traffic, preventing the use of a the bridge by heavier traffic by means of suitable barriers or raised kerbs or weight restriction plates.

16 Identification of Structures

GC/RT5100 sets out the requirements for the identification of structures.

Bridges should preferably be identified by means of number plates unless the bridge is located in area of high vandalism. In the latter case, identifying the bridge using painted marking should be considered. Consideration should be given to colour-coding such number plates or painted markings to indicate ownership and maintenance responsibilities.

The unique identification and the location should also be recorded.





17 Structures Owned by Outside Parties

Procedures shall be in place to ensure that, so far as is reasonably practicable, the requirements of this document are applied to intended structures that fall within the scope of this this document and that are owned by outside parties.

Legal documentation authorising other organisations to construct bridges over, under or taking support from Railtrack land should include the requirements of GC/RT5110 and GC/RT5112 and so far as is relevant the recommendations of this document.

18 Records Procedures shall be in place for records of the drawings, calculations, risk assessments, limits on use and other relevant information which relates to the fitness for purpose of the structure to be prepared and retained for the life of the structure by the Railway Group member responsible for the safety of the structure. Copies of the records shall be made available to the person or organisation responsible for maintaining the structure as required.

Requirements for the management of Safety Related Records of Elements of the Infrastructure are given in GI/RT7001.

GI/RT7001 gives requirements in respect of the management of records.



Design of Bridges



Recommendations relating to GC/RT5112

19 Railway Traffic Loads and Load Effects

19.1 Normal Railway Traffic Loading Bridges carrying railway traffic of standard gauge shall generally be designed for full RU type loading as specified in BD 37/88 “Loads for Highway Bridges”.

Note: BD 37/88 covers Railway Loading and supersedes BS 5400 Part 2.

Except as otherwise given in this document, all relevant clauses of BD 37/88 should be applied, including Table 1 with the modifications given in Appendix I.5 of this document.

The RU load model should be deemed to include the following associated loads and load effects, all as specified in BD 37/88 except as otherwise given in this document:

( ) Dynamic effects (with the modifications to Tables 16 and 17 of BD 37/88 given in Appendix I.2 of this document) Note: The dynamic factor identified in Appendix I.2 is only valid for speeds up to and including 200km/h.

( ) Dispersal of concentrated loads (with the modifications given in Appendix I.3 of this document).

( ) Concentrated load on deck plates and local elements.

( ) Application of loading to multi-track bridges.

( ) Lurching (deemed in BD 37/88 to be taken into account by the specified dynamic factors).

( ) Nosing (but see Appendix I of this document for longitudinal distribution).

( ) Centrifugal load (but see Appendix D of this document for applicable speed).

( ) Longitudinal loads (traction / braking).

( ) Load combinations and partial factors.

( ) Derailment loads.

( ) Loading for fatigue investigations (based on the intended life of the bridge as given in the AIP submission, not necessarily 120 years as is specified in BD 37/88). The fatigue loading set out in BS 5400 Part 10 is only valid for speeds up to and including 200km/h.

Additionally, a single nominal horizontal point load of 100kN should be applied at any point to a robust kerb (see section 7.3.3 of this document) to allow for the effects of a derailed train.

Appendix I of this document gives further recommendations on the application of railway traffic loads.

The infrastructure controller should generally specify:

• the maximum design speed of rail traffic (for centrifugal force effects and for clearances);

• the total annual design tonnage per track (for fatigue effects);





• the design traffic mix: heavy, medium or light, as given in BS 5400, Part 10 (for fatigue effects),

taking into account reasonably foreseeable future traffic developments (eg, changes in the density, speed or type of traffic).

Guidance on provision for future traffic developments and selection of traffic mix is given in Appendix D of this document.

19.2 Reduced and Enhanced Loading In exceptional cases, where safety and the safety of interworking are not adversely affected, a lighter loading may be permitted which shall be defined by multiplying the RU type loading by a factor. The provision also exists for adopting a heavier loading on restricted sections where this is appropriate.

The factor to be applied to the full RU type loading shall not be less than 0.75. Written approval to the use of a loading other than full RU type loading shall be obtained from Railtrack at the Approval in Principle stage of the project under the procedures identified in Railway Group Standard GC/RT5101 “Technical Approval Requirements for Changes to the Infrastructure”.

The safety of interworking relates to situations where there is a transfer of safety risk from one Railway Group member to another and/or the safety between various parts of the network.

For new bridges and complete superstructure reconstructions, the infrastructure controller should generally specify any cases where the design traffic loading is to be other than full RU.

Reduced loading should be considered only where both the following apply:

• it will result in significant economic benefit • control measures are or will be in place to ensure that any vehicle including

engineer’s trains and emergency vehicles (including their speed) using the bridge will not exceed the reduced design loading.

Where factored RU loading is used, items (c), (g), (h) and (j) listed in section 19.1 of this document should all be calculated using the same factor.

The dynamic effects specified in BD 37/88 comprise an envelope of the effects of different representative types of traffic, taking account of light trains running at high speed and heavier trains running at slower speeds. Hence they are not directly applicable to reduced loading based on actual train types and speeds. In cases of reduced loading, therefore, dynamic effects should be taken into account as follows:

(t) The dynamic effects specified in BD 37/88 (as modified by Appendix I of this document) should be applied to the factored RU loading.

(t) The static load effects of the actual train types should be multiplied by the appropriate dynamic factor (1 + ϕ) obtained from UIC Leaflet 776-1R ((1979 Edition with 1987 amendments) - Commentary on Dynamic factors.

(t) If the dynamic loading derived from factored RU loading (DLRUfac) is less than the dynamic loading derived from actual train types (DLactual), the RU factor should be increased sufficiently so that DLRUfac ≥ DLactual.

In all such cases an appropriate traffic mix for fatigue shall be established taking account of the design life of the structure and the proposed rail traffic and any reasonably foreseeable changes to the rail traffic using the structure.

The standard load spectra specified in BS 5400 Part 10 for use with RU loading are not applicable to reduced loading; hence Table 4 of BS 5400 Part 10 is not



Design of Bridges



applicable. The fatigue effects in such cases should be based on the actual reasonably foreseeable traffic. The traffic mix may be based on the appropriate train types given in Figure 19 of BS 5400 Part 10.

19.3 Additional Loading for Continuous Bridges The RU type loading was developed for simply supported Bridges and covers the special vehicle Type 6 shown in Appendix 101 of UIC Leaflet 776-1R “Loads to be considered in the design of railway Bridges”. In continuous Bridge construction the effects due to vehicle Type 6 may not be covered by the RU Load Model. The effects due to the SW/0 Load Model shown in Figure 1 of this Railway Group Standard shall therefore be considered unless otherwise specified by Railtrack. This Load Model corresponds to vehicle Type 6.

On multi-track Bridges, only one track shall be loaded with the SW/0 Load Model.

The SW/0 Load Model does not have to be considered in any fatigue check.

Whereas RU type loading shall be curtailed as necessary in order to produce the most unfavourable load effect, Load Model SW/0 shall not be curtailed and need not be repeated.

Load Model SW/0 covers certain abnormally heavy vehicles. It consists of two lengths of 133kN/m UDL each 15.0m long, separated by an unloaded length of 5.3m (as shown in Figure 1 of GC/RT5112).

19.4 Loading for Alterations / Partial Reconstructions For altered bridges, where it is proposed to alter the structure of the Bridge, the loading specified shall meet the requirements of the Principles of this Railway Group Standard, and shall be such that the lesser of the following applies:

• the loading capacity of the bridge is not reduced; • the requirements of clauses 6.1.1 and 6.1.2 of this Railway Group Standard

are met.

The principles referred to above are general requirements which it may be assumed are satisfied by following the recommendations of this document.

Sections 6.1.1 and 6.1.2 referred to above are quoted verbatim in sections 19.1, 19.2 and 19.3 of this document.

For alterations to existing bridges (including partial reconstructions such as redecking on existing main girders) the design loading should be specified by the infrastructure controller in accordance with the requirements given in the boxed text above from GC/RT5112. In such cases suitable allowance should be made for the associated loads and load effects listed in section 19.1 of this document.

19.5 Loading for Temporary Bridges Temporary bridges designed to carry rail traffic shall in general be designed in accordance with 6.1.1 and 6.1.2 of this Railway Group Standard. In exceptional cases, where safety and the safety of interworking are not adversely affected, a lesser loading may be permitted. In all such cases, the loading shall take into account the rail traffic that will be permitted to use the temporary bridge, the intended life of the temporary bridge, any site specific hazards and any control measures required to prevent overloading of the temporary bridge.

19.6 Railway Traffic Surcharge Loading for Bridge Substructures For abutments and similar soil-retaining substructure elements, railway traffic surcharge loading for each track may be taken as a uniformly distributed linear load of 150kN/m, uniformly spread over a width of 2.5m and acting at the level of the underside of the sleepers. This may be deemed to take into account dynamic effects.





19.7 Dynamic Effects for Substructures For piers, columns and similar substructure elements (but excluding crossheads and the like), dynamic effects of railway traffic loading need not be considered unless the slenderness ratio L/r of the element exceeds 30 (where L is the element’s effective length and r its radius of gyration).

19.8 Deformations Deformations for Bridges carrying rail traffic shall be in accordance with UIC Leaflet 776-3R “Deformation of Bridges”. In section 8 of Leaflet 776-3R, the values in Table 5 shall apply.

Lesser deformations may need to be specified for appropriate levels of passenger comfort.

19.8.1 General All bridges should be designed so that the deflections under load do not encroach on any required clearances.

Specialist advice should be sought for speeds greater than 200km/h and the requirements agreed at the AIP stage.

19.8.2 Vertical Deformations The recommendations of UIC Leaflet 776-3R should be followed, with the modifications and clarifications given in Appendix E of this document.

It is important that the twist (cant gradient) of the track is considered on skew bridges. Twist effects are likely to be particularly severe at the intermediate support positions of multi-span simply-supported skew bridges.

Where the bridge carries more than one track, identification of the most severe load case should be considered carefully.

Where the track on the bridge is curved, the calculated twist should include the twist due to the loading on the bridge and the twist due to any designed track geometry (eg, in transition curves).

In cases of bridge superstructure reconstructions where it is not reasonably practicable to comply with the twist criteria given in Section 5 of UIC Leaflet 776-3R, this should be identified and justified in the AIP submission.

In all cases the twist (cant gradient) of the track due to the loading on the bridge and to any designed track geometry should not exceed 1 in 400 under the actual existing and foreseeable rail vehicles using the bridge.

For vertical deflections, in place of the values given in section 8 Table 5 of UIC Leaflet 776-3R, Railtrack should consider specifying more onerous criteria as follows:

• on main lines: Table 3 values; • on principal passenger routes and otherwise where high standards of

passenger comfort are important: Table 4 values.

In addition, the natural frequency of the bridge should be limited to the values given in UIC Leaflet 776-3R. These limits are intended to ensure that the dynamic effects are covered by the dynamic factors given in BD 37/88.

In assessing the natural frequency of the bridge, the method identified in UIC Leaflet 776-3R may be used. For half through bridges, the effect of the deck may be included if appropriate (with due allowance for shear lag effects) so that the bridge is considered as a large channel section.

19.8.3 Lateral Deformations Lateral deformations may be neglected for bridges with decks having high in-plane shear stiffness (eg, concrete slabs, shear-connected beams, continuous



Design of Bridges



steel deck plates). For bridges with open or non-continuous decks, lateral deformation effects should be taken into account as follows:

• horizontal deflections should not exceed the maximum values given in section 7 of UIC Leaflet 776-3R

• lateral flexibility ( = L3/EIlateral for a simply-supported bridge span L) should not exceed 3mm/kN

• lateral frequency under permanent loads should not be less than 1.2Hz.

19.8.4 Camber Bridges with span greater than 12m should preferably be cambered to improve their appearance. Camber should generally be equal to the dead load deflection plus half the serviceability live load deflection.

For multi-span bridges and skew bridges with constant-depth main girders, the levels of the bearings should generally be such that all parts of the main girder soffits lie in a continuous circular curve when viewed in elevation square to the girders.

19.9 Deck Acceleration and Resonance The passage of trains over bridges at high speeds can cause excessive deck accelerations, which tend to destabilise ballast due to resonance and impact effects. In addition, the load effects can exceed those predicted by quasi-static methods based upon the dynamic factors given in Appendix I.2 for speeds greater than 200km/h.

A check should be carried out to determine whether a specific dynamic check is required. The method of check and the design acceptance criteria should be agreed at the AIP stage.

Where a dynamic analysis is required it should include:

• a check of the maximum peak deck acceleration • a comparison of the results of the dynamic analysis with the results of the

static analysis multiplied by the dynamic factor Φ (The most unfavourable values of moments, stresses, etc. should be used for the bridge design)

• a check that the additional fatigue loading at high speeds and at resonance is covered by consideration of the stresses derived from the results of the static analysis multiplied by the dynamic factor Φ (The most unfavourable values of moments, stresses, etc. should be used for the bridge design).

The effects are likely to be more severe on lightweight, small span structures and on the cross girders of through or half through bridges. It is recommended that the methods for analysing these effects currently being developed by UIC should be used but specialist advice should be sought.

20 Walkway Loads Walkways to underline bridges should be designed for nominal loading as follows:

• a uniformly distributed load of 4kN/m2 • for local elements, a patch load of 2kN applied to a circle 100mm diameter or

a point load of 1kN, whichever has the more severe effect • where the walkway supports a cable route, an allowance of 1kN/m or the

actual weight of the cables, whichever is greater • horizontal handrail loading of 0.74kN/m or a horizontal force of 0.5kN applied

at any point to the top rail, whichever has the more severe effect.





21 Road Traffic Loads Bridges carrying road traffic shall generally be designed for standard highway loading as specified in BD 37/88.

For all public highway Bridges, the number of units of HB loading and any requirements for abnormal indivisible loads shall be determined in conjunction with the Highway Authority.

For occupation and accommodation Bridges, a lesser load than that specified in BD 37/88 for accommodation Bridges may be permitted as long as the safety and the safety of interworking are not adversely affected and all other legal obligations are met. Any lesser loading shall be suitably justified.

For reconstructions of existing occupation and accommodation bridges, the infrastructure controller’s legal obligations may be taken into account in determining the loading. However, designing for historic load-bearing obligations may not be sufficient.

Reconstructed bridges should be designed to carry the heaviest traffic that may reasonably be expected to use them, or else positive means should be provided to prohibit traffic of excess weight.

For Bridges designed to carry other types of road or vehicular traffic the loading shall be specified by Railtrack.

22 Pedestrian and / or Cycle Traffic Loads

For Bridges supporting footways and / or cycle tracks open to the public, the loading shall generally be designed in accordance with the requirements of BD 37/88.

Further to BD 37/88, for foot / cycle track bridges:

• the uniformly distributed load should be taken as 5kN/m2 regardless of the loaded length or width;

• for local elements, a nominal patch load of 2kN should be applied to a circle 100mm diameter or a point load of 1kN, whichever has the more severe effect.

For other Bridges, the loading to be considered for pedestrian traffic shall generally be in accordance with the requirements for service walkways given in UIC Leaflet 776-1R.

Further to UIC Leaflet 776-1R (1979 Edition with 1987 amendments), the loading for bridges intended to be used only by pedestrian railway staff should be as given for walkways in section 20 of this document.

Where Bridges are designed to carry pedestrian or cycle traffic only, suitable provision shall be made to prevent use of the Bridge by vehicular traffic which could affect safety of train operations.

Physical means should be provided to prevent unsuitable vehicular traffic from using pedestrian / cycle bridges (eg, bollards, chicanes, doors, steps). Reliance should not be placed upon warning notices alone.



Design of Bridges



23 Other Traffic Loads The loading shall be determined in conjunction with the relevant authority and shall meet the requirements of the Principles contained in this Railway Group Standard.

The principles referred to above are general requirements which it may be assumed are satisfied by following the recommendations of this document.

24 Aerodynamic Effects of Rail Traffic

For most underline bridges and overline bridges carrying roads, the aerodynamic effects due to passing rail traffic may be deemed negligible. However, such effects should be considered for:

• footbridges • bridges supporting station canopies or similar structures; • parapets of underline bidges • cladding panels attached to bridges • for other bridges where the line speed of rail traffic is greater than 160km/h

(100mph).

Eurocode ENV 1991-3 (and its UK National Application Document when published) may be used for guidance.

The slipstream effects of passing rail traffic should be considered where appropriate.

25 Non-traffic Loads and Load Effects

25.1 General Except as otherwise given in this document, loads and effects other than traffic loads and their effects should be taken into account for all bridges as given in BD 37/88.

Appendix I of this document gives further recommendations on the application of permanent and superimposed dead loads for underline bridges.

25.2 Loads Due to Flowing / Tidal / Navigable Water. Where bridges cross flowing / tidal / navigable water, the substructures / foundations should preferably be kept clear of such water where this can be achieved with reasonable economy.

Where substructures / foundations are in such water, all likely resulting loads should be allowed for, taking into account the:

• hydraulic loads on substructures • impact from waterborne vessels on substructures • impact from waterborne debris on substructures • hydraulic / impact loads on superstructures (see 25.3 of this document) • loss of support due to scour / softening of subsoil • unbalanced soil loading due to scour.

25.3 Hydraulic / Impact Loads on Superstructure Whether or not substructures / foundations are in such water, all likely resulting loads on the superstructure should be allowed for, taking into account the:

• hydraulic loads (including uplift effects), where water levels could be higher than the underside of the superstructure

• impact from waterborne vessels • impact form waterborne debris.





In all cases the design water levels and flows should be taken as the greatest reasonably foreseeable during the intended life of the bridge, unless reliable procedures are put in place to ensure that the bridge is closed to traffic when hydraulic conditions reach a predetermined level.

26 Bridges not Owned by Railtrack

Where the Bridge is not owned by Railtrack, Railtrack shall use its best endeavours to ensure that the loadings to which the Bridge is designed comply with the requirements of this Railway Group Standard.

Legal documentation authorising other organisations to construct bridges over, under or taking support from Railtrack land should include the requirements of GC/RT5112 and so far as is relevant the recommendations of this document.

Where this is not the case, the details shall be recorded and the relevant authority notified.

Where the safety of train operations or the safety of interworking is likely to be affected the matter shall be brought to the attention of the HMRI.

27 Records Railtrack shall ensure that:

• the loading, together with any risk/reliability analyses used to specify the loading of Bridges, is fully documented and retained in accordance with GC/RT5142 “Management of Infrastructure Records”;

• such information shall be made available to the person or organisation responsible for maintaining the Bridge.

GC/RT5142 has been superseded by GI/RT7001.

28 List of Loads and Load Effects

Appendix A of this document reproduces the list given in the Appendix of GC/RT5112 of loads and load effects that are to be considered in the loading specification for bridges and indicates how these loads and load effects are addressed by this document.



Design of Bridges



APPENDIX A LOADS AND LOAD EFFECTS REQUIRED BY GC/RT5112 TO BE CONSIDERED IN THE LOADING SPECIFICATION FOR BRIDGES The list below reproduces the list given in the Appendix of GC/RT5112. The references in brackets show where each item is addressed in this document. • traffic loads and their effects (eg, road traffic, rail

traffic, pedestrian traffic) including: - dynamic effects; (Sections 19.1, 19.2, 19.9) - effects of repeated loading (fatigue); (Section 19.1) - traction and braking forces; (Section 19.1) - nosing forces (rail traffic only); (Section 19.1) - centrifugal forces; (Sections 19.1, 21) - skidding forces (road traffic only); (Section 21) - deformations (including track twist); (Section 19.8) - aerodynamic effects; (Section 24) - effects of track / bridge interaction; (Section 12.1) - deck acceleration and resonance effects. (Section 19.9) • permanent loads relating to the bridge: - self weight of the bridge; (Section 25, Appendix I.5) - non-structural loads carried by the bridge

(including an adequate allowance for the variability of ballast depth where appropriate);

⎡Section 6.3.6, Section 25⎤ ⎣Appendix E, Appendix I.5⎦

- internal forces (eg, prestressing, creep). (Section 7.5.1) • other site specific loads and load effects,

including those due to the following:

- soil pressure; (Section 7.5.4, Appendix C) - settlement (including effects of mining

subsidence); (Section 7.5.4) *

- water pressures (including those from exceptional flows, storms and flooding);

(Section 25.2, 25.3)

- scour; (Section 25.2) - erection, construction or maintenance activity; (Section 10.1) - environmental influences (eg, wind,

temperature). (Section 25.1)

• accidental loads due to the following: impact from train derailments, both on and

beneath a bridge; (Sections 7.3.1, 7.3.3)

impact from errant road vehicles, both on and beneath a bridge;

(Sections 9.3.1, 7.3.2)

impact from vessels beneath a bridge over a navigable waterway;

(Section 25.2, 25.3)

other accidental loads and load effects, such as those due to soil subsidence, may need to be considered at particular sites.

* specialist advice should be sought regarding effects of mining subsidence





APPENDIX B MODIFICATIONS TO AND CLARIFICATIONS OF BS 5400 PARTS 3, 4 AND 5 PART 3 The draft modifications to BS 5400 Part 3 dated May 1997 (or later) may be used. However, either a single dated set of such modifications should be used complete or they should not be used at all.

Until such time as the new revision of BS 5400 Part 3 is published officially, the intention to use draft modifications should be indicated in the AIP submission.

PART 4 Clause 4.1.1.1 (b) Prestressed concrete beams should be designed as Class 2 members but with no tensile stresses under permanent loads (serviceability limit state).

Clause 4.2.2 In sub-paragraph (a), all live loading should be ignored.

Clause 4.7 The last paragraph should be deleted and replaced by the following:

“For unwelded reinforcing bars the limiting stress ranges for fatigue should be as follows:

(xi) for bridges carrying railways, in accordance with Part 10, where in Table 8:

• m = 9, K2 = 0.75 x 1027, σ0 = 160 N/mm2 for bars < 16mm dia; • m = 9, K2 = 0.07 x 1027, σ0 = 125 N/mm2 for bars > 16mm dia;

(the simplified procedure given in Part 10 Clause 9.2 may be used where the loading is the standard railway bridge loading);

(xi) for bridges carrying highways, in accordance with current practice of the Highways Agency.”

PART 5 BS 5400 Part 5 should be replaced in its entirety by the Department of Transport document dated December 1987 entitled “Design of composite bridges. Use of BS 5400 Part 5: 1979 for Department of Transport structures” (commonly known as the “yellow document”), with the following modifications to that document:

Yellow Document Clause 5.3.2.5 For bridges subject to railway loading, the value of γm should be taken as 2.05, not 1.85 as stated.

Yellow Document Clause 5.3.3.1 Change the ending of the first paragraph to “. . . whichever is the least, except that” and add immediately afterwards the text of sub-clause (b) of BS 5400 Part 5 Clause 5.3.3.1 (“connectors may be placed in groups . . .”).

Yellow Document Clause 5.3.3.6 Delete this Clause and replace it with Clause 5.3.3.6 of BS 5400 Part 5.

Yellow Document Clause 6.3.4 For bridges subject to railway loading, the value of γm should be taken as 1.5, not 1.4 as stated.

Yellow Document Clause 7.5.1 Add after the 3rd paragraph the text of the 3rd paragraph of BS 5400 Part 5 Clause 7.5.1 (“Alternatively, connectors may be placed in groups . . .”).



Design of Bridges



APPENDIX C EXISTING SUBSTRUCTURES AFFECTED BY NEW CONSTRUCTION Where the superstructure of an existing bridge is to be reconstructed on existing abutments, or in other cases where new construction is associated with total or partial retention of existing substructures, the nature and extent of the existing substructures to remain should be identified in the AIP submission and should be subject to the approval of Railtrack. (Signature of the AIP submission may be deemed to be approval.)

The following guidelines may be applied:

(1) IF all the following conditions are satisfied:

(i) an existing substructure is in satisfactory condition and shows no significant signs of distress or undue settlement;

(ii) the effects of dead loading on the existing substructures or subsoil will not be significantly increased as a result of the new construction (having regard to masonry stresses and to maximum and average soil pressures);

(iii) the effects of live loading on the existing substructures or subsoil will not be significantly increased following the new construction (having regard to masonry stresses and to maximum and average soil pressures);

(iv) the stability of the existing substructures against overturning and sliding will not be significantly reduced as a result of or following the new construction;

(v) there are no particular geotechnical considerations which give cause for concern;

THEN the existing substructures may normally be considered adequate for retention without modification and without the need for structural or geotechnical analysis.

(2) IF conditions (i) and (v) above are satisfied, but effects of dead and / or live loading on the existing substructures or their tendency to sliding / overturning will be significantly greater than existing,

THEN the following should apply:

• Appropriate structural and / or geotechnical analysis should be carried out.

• Account should be taken of any more or less favourable distribution of loading as a result of the new construction (For example: (a) a freely-supported span may be replaced by a portal structure which, although heavier, effectively struts the abutment tops, preventing rotation about their bases; (b) a superstructure which bears near the front face of an abutment may be replaced by a new superstructure which bears further back, thus improving the abutment’s stability and reducing the maximum soil pressures beneath it; (c) beam type construction will generally distribute loads more evenly throughout the abutment than a half through type structure; (d) the effects of a half through type structure can be improved by providing cill beams with substantial strength and depth).

• When considering the acceptability of additional soil loading, due distinction should be made between soil types which may fail completely and those whose response is likely to be no more severe than increased settlement. Increased settlement may be acceptable. However, in such cases, the new substructure should be designed to accommodate the effects of any likely increased total or differential settlement.





• Underpinning and / or strengthening should be considered as appropriate.

• Such underpinning does not necessarily have to carry all the foundation loading. It may be sufficient to design underpinning to carry the incremental loading only, or in some other way to share the load between new and old work. (However, such load sharing should not be relied upon unless it can be verified that the underpinning structure / soil system will settle under increased loading in an essentially ductile manner and will be able to withstand any tension which may result from the application and removal of live loading. (Useful information may be found in Burland and Kalra’s paper “Queen Elizabeth II Conference Centre: geotechnical aspects”, Proc. Instn Civ. Engrs, Part 1, 1986, 80, Dec., 1479-1503.)

(3) IF conditions (ii), (iii), (iv) and (v) above are satisfied but the existing substructures are showing significant signs of distress,

THEN the following should apply:

• The cause of distress should be determined (eg, earlier existence of rail joints, high local forces especially at abutment corners, malfunctioning or no bearings, failure of waterproofing / drainage, vegetation, increase in ballast depth, settlement, effects of mining, reduction in passive pressure due to road lowering, trenching or scour).

• Appropriate structural and / or geotechnical analysis should be carried out.

• Distinction should be made between movement / damage which has occurred in the past but has since stabilised and movement / damage which is ongoing. In the case of the former, remedial work may not be required.

• Remedial work should generally be considered as a first choice rather than complete replacement of the existing substructures, allowing where appropriate for sharing of load between new and old work.

(4) An existing bridge superstructure may act as a prop to the abutments (whether designed to or not). Consideration should therefore be given to the stability of existing abutments when the superstructure is removed. Where necessary, temporary props should be provided and / or limitations placed on soil surcharge loading behind the abutment (eg, by restricting the use of construction plant or by reducing the height of fill behind abutments during reconstruction).



Design of Bridges



APPENDIX D

PROVISION FOR FUTURE TRAFFIC DEVELOPMENTS AND SELECTION OF TRAFFIC MIX As a guide, the following provisions are recommended as reasonable unless particular circumstances dictate otherwise:

Speed Where there are known proposals to increase the speed, the design speed for loading purposes (eg, centrifugal force effects) should take this into account.

In assessing any future increase in train speed, the possible introduction of tilting trains should be considered. These have the potential for travelling round curves at higher speeds (enhanced permissible speeds) than conventional trains.

The design speed for loading purposes should be specified by the infrastructure controller. BD 37/88 specifies a design speed equal to vt+10)km/h in the calculation of centrifugal loads (vt is the greatest speed envisaged on the curve in question), but is only valid generally for speeds up to 200km/h

Where the design speed is in excess of 200km/h and there is a risk of increased dynamic effects due to resonance, the design speed should be specified by means of a range of speeds. The range of speeds should take into account overspeeding where this is likely to result in significantly higher dynamic effects due to resonance.

Tonnage In the absence of known proposals regarding traffic developments, annual tonnage for design purposes should be taken as the existing annual tonnage x 1.3.

Where the existing annual tonnage is not known, it may be assumed by determining the Track Category and linespeed at the location in question and reading off the maximum “equivalent tonnage” from the diagram in GC/RT5023 “Categorisation of Track”. Because equivalent tonnage is greater than actual tonnage, the former may be deemed to allow for future growth.

Traffic Mix The traffic mixes (traffic types) for fatigue design purposes are described in BS 5400 Part 10. They may alternatively be approximated as follows:

Light: Essentially multiple-unit traffic, but allows for about 5% by number loco-hauled passenger or parcels trains. No significant freight (other than engineering trains).

Medium: Mainly passenger or parcels traffic (multiple-unit or loco-hauled), but allows for about 25% by number 25-tonne-axle freight trains.

Heavy: Mainly freight traffic.





APPENDIX E MODIFICATIONS TO AND CLARIFICATIONS OF UIC LEAFLET 776-3R (1989) The following modifications of and clarifications to UIC Leaflet 776-3R (1989) should apply:

Section 1 Delete the first paragraph and replace with: “All deformations due to permanent loading should be calculated under all permanent loads; those due to live loads should be calculated under the specified design loading, including dynamic effects, with a partial factor for loads of 1.0.”

Section 3 The fixed load should include an allowance for future increase in ballast depth. This allowance should normally not be less than 100mm; in particular local circumstances a greater allowance may be appropriate.

Section 4 (Comments) For camber, see section 19.8.4 of this document.

Section 7 The applicable speed range (1, 2 or 3) should be appropriate to the design speed for loading as given in the AIP submission.

Fig. 1 The notes should be amended as given in Appendix I.2 of this document.



Design of Bridges



APPENDIX F RECOMMENDATIONS FOR INFILL TO OPEN HANDRAILING FOR UNDERLINE BRIDGES Open handrailing should have, in addition to a continuous top rail and a raised kerb or kicker plate, one of the following:

(a) at least one intermediate rail or wire parallel to the top rail such that the clear distance between any two rails / wires or between a rail / wire and the kerb / kicker plate does not exceed 550mm;

(b) vertical or near-vertical infill bars or wires such that the clear distance between bars / wires does not exceed 150mm;

(c) other arrangements (including ornamental arrangements) of rails or bars or wires or similar elements such that a 600mm x 200mm rectangle with its long sides vertical will not pass through;

(d) mesh infill.

Intermediate or infill elements should be able to withstand without permanent deformation a horizontal loading of 1.0kN/m2 or a horizontal force of 0.5kN applied at any point, whichever has the more severe effect.





APPENDIX G PROFILES FOR THE TOPS OF PARAPETS TO OVERLINE HIGHWAY BRIDGES Parapet profiles are subject to the approval of HM Railway Inspectorate. The following profiles are recommended as likely to be approved:

(a) where the width of the parapet top is greater than 100mm but does not exceed about 250mm (eg, reinforced concrete construction):

One of the profiles given in BS 6779 Part 2;

(b) where the width of the parapet top significantly exceeds 250mm (eg, brick sandwich construction):

• a shallow slope on the highway side, 35 ± 1° to the horizontal; if there is a separate coping, no overhang on this side;

• a steep slope on the railway side, 60 ± 1° to the horizontal, with an overhang if appropriate;

• hence an apex angle 85 ± 2°; there may be an apex chamfer up to 30mm wide;

(c) an equilateral triangle; there may be an apex chamfer up to 30mm wide.

Profile (c) should preferably be used for brick sandwich type parapets up to about 350mm thick but for greater thickness this profile results in very large copings.



Design of Bridges



APPENDIX H Collision Loads from Railway Traffic The following requirements are applicable to permissible line speeds up to 200km/h. The UIC are currently developing recommendations for permissible line speeds up to 300km/h. Specialist advice should be sought when designing structures for line speeds in excess of 200km/h. H.1 General With reference to paragraph 8.6 of BD 37/88 this section gives recommendations for accidental loading on bridge supports near railway lines.

These recommendations apply to the supporting structures for new vehicular bridges and similar structures and to structures carrying hazardous materials (eg, gas) constructed over or alongside railway tracks. They do not apply to lineside railway infrastructure such as overhead line masts or signal gantries. They should be applied to new and reconstructed footbridges where reasonably practicable taking into account the nature of the rail traffic and the track layout adjacent to the bridge. The recommendations take account of:

• the definition of a hazard zone where the risk of impact is greatest; • the need for columns and piers to withstand the effect of light impacts that

might occur from derailed coaches or freight wagons without sustaining irreparable damage;

• the prevention of a progressive collapse of the superstructure in the event of a major accident which results in the loss of a support.

Wherever reasonably practicable, supports carrying bridges over or alongside railway tracks should be placed outside the hazard zone.

H.2 Structures Within the Hazard Zone Where there is no reasonably practicable alternative to placing supports inside the hazard zone they should preferably be monolithic piers rather than individual columns.

The hazard zone should be assumed to extend for a width of 4.5m from the nearest rail. All supports located between railway tracks should be considered to be inside the hazard zone. Where individual columns are used within the hazard zone, the design of the bridge above them should incorporate a degree of continuity such that the removal of any one column will not lead to the collapse of the remainder of the structure under the permanent loads and primary and secondary live loads in accordance with combination 1 of Table 1 of BD 37/88; the ultimate limit state partial factors should be as specified in Table 1 but limited to 1.0 on live loads.

To provide robustness against the effect of light impacts, all piers or columns within the hazard zone should be designed to withstand without collapse a single horizontal design force of 2000kN acting at a height of 1.2m above the adjacent ground level and a single horizontal design force of 500kN acting at a height of 3m. The two forces may act in any direction but need not be considered to act simultaneously. These forces should be combined with the permanent loads and the appropriate primary and secondary live loads as given above.

The connections between columns and their bases should be such that they can resist a horizontal design force of 2000kN at the ultimate limit state without being dislocated. Pin jointed connections should be avoided.

H.3 Buffer Stops and Impact Walls Supports to bridges which could be endangered by vehicles running past buffer stops should be avoided wherever reasonably practicable. Where this is not





reasonably practicable, additional end impact walls should be provided which, together with the buffer stops, protect the supported bridge.

Buffer stops should have as large a braking capacity (energy absorbing capacity) as is reasonably practicable to provide.

When designing such an end impact wall, suitable allowance may be made for the restraint provided by the track where this is securely connected to the wall (eg, by means of a concrete slab to which the rails are fastened directly).

For tracks serving passenger traffic, the end impact walls should be designed for a horizontal design force of 5000kN at a height of 1.0m above the top of the rail where a buffer stop with a minimum braking capacity of 2500kNm is provided.

In shunting and marshalling areas where a buffer stop with a minimum braking capacity of 2500kNm is provided, the end impact walls should be dimensioned for a horizontal design force of 10000kN at a height of 1.00m above the top of the rail.

H.4 Plinths and Platforms Where individual columns are used, a solid plinth should be provided to a height of 915mm +0-25mm above rail level or 1200mm minimum above ground level where lateral clearance permits. The height of the plinth should be constant and the ends of the plinth should be suitably shaped in plan to deflect derailed vehicles away from the column. A solid platform construction should be used to provide similar protection from derailed vehicles for individual columns within station areas.

The column base should be structurally separated form the protecting plinth or platform by means of an air gap or compressible material surround the column base.

H.5 Structures in Embankments Columns and piers located within embankments, or at the bottom of embankments, may require special consideration even if outside the hazard zone because of the possibility of derailed vehicles rolling down the embankment. If it is not reasonably practicable to arrange the design to avoid the situation, appropriate measures should be taken to safeguard such columns and piers. Consideration should be given to:

• the use of guard rails; • a retaining structure to widen the top of the embankment; • the use of massive piers.



Design of Bridges



APPENDIX I FURTHER RECOMMENDATIONS ON LOADING FOR UNDERLINE BRIDGES BD 37/88 should be modified as follows: I.1. Simply Supported Main Girder and Rail Bearers (BD 37/88 Figure 21) In Figure 21 of BD 37/88 the reference to shear force at point X should be corrected as follows:

• The shear force at point X is the end shear for span ‘a’ multiplied by a L

I.2. Dynamic Effects (BD 37/88 Tables 16 and 17) The dynamic effect created in the structure by the movement of vehicles at speed is covered by multiplying the static RU load model by dynamic factors.

The values given in Table 16 of BD 37/88 should be corrected as follows:

For values of (L) from 3.6 to 67m:

dynamic factor for evaluating bending moment

= 2.16 + 0.73;

(L)0.5 - 0.2

dynamic factor for evaluating shear

= 1.44 + 0.82.

(L)0.5 - 0.2

These dynamic factors are applicable to full RU type loading where the deflection of the bridge is within the limits given in UIC leaflet 776-3R (in Fig1 of which the expression for δu for spans between 20 - 100 metres should be corrected to read δu = 0.56L 1.184) and when the permissible or enhanced permissible speed is not greater than 200km/h. Where these conditions are not met, allowance for dynamic effects should be based on the recommendations given in Appendix H of ENV 1991-3.

In Table 17 of BD 37/88 the following definitions for dimension (L) should be added:

Structural Element Dimension L (m) Battle deck type floor with closely spaced cross girders or ribs and without longitudinal ribs:

• cross girders or ribs

• deck plate

• concrete slab decks

twice the cross girder spacing plus 3m

cross girder spacing plus 3m

the lesser of the span of the main girders or twice the main girder spacing





I.3 Distribution of Axle and Wheel Loads When designing members for which the local effects of wheel loads is critical, a allowance should be made for eccentricity of loading inside vehicles by distributing axle loads to the wheels in the proportions

5 : 4 9 9

For the purpose of determining the patch loading under a sleeper, for ballasted track the wheel load may be distributed over three adjacent sleepers in the proportions

1 : 1 : 1 4 2 4

provided that the ballast depth is at least 200mm below the underside of the sleepers at the low rail.

Alternatively, for ballasted or unballasted track the longitudinal distribution of vertical wheel loads along the rail into the bridge deck may be determined by grillage analysis, beam on elastic foundation analysis or other suitable method.

The patch loading at the underside of the sleeper should be taken as follows:

• two separate patches, centred one under each rail; • patch length (parallel to rail) = sleeper width; • patch width (transverse to rail) = 600mm.

Below the underside of the sleeper, each patch load should be taken as distributed through the ballast at an angle of 1 horizontal to 4 vertical.

I.4. Application of Loading On multitrack bridges, the derailment loading set out in BD37/88 should be considered on one track in combination with RU loading on the other tracks as appropriate.

The nominal nosing load set out in BD37/88, may be distributed over three adjacent sleepers in the proportions 1 : 1 : 1 . 4 2 4 Walkways and similar secondary structural elements which are outside the robust kerb (see section 9.1.2 of this document) need not be designed to carry derailment loading. If, however, such an element is designed to carry derailment loading, the design of the bridge as a whole should be such that it will not overturn when the derailment loading for overturning and instability set out in BD37/88 is applied along the outer edge of the element.

Where bridges carry curved track, centrifugal effects should be taken into account in determining the proportion of vertical load carried by each rail. Several factors are involved:

• the amount of track cant; • the different speeds of heavy and light trains; • possible future changes in cant and speeds.

Reasonably conservative assumptions should be made in determining the worst likely effects. Such effects may be significant for types of construction in which individual elements are loaded essentially by one rail (eg, railbearers, narrow unconnected longitudinal beams or girders).

I.5 Permanent Loading for Underline Bridges Design Dead Load (BD 37/88 5.1.2.1) γfL values for dead loads at ULS of 1.1 for steel and 1.2 for concrete should be used in place of the values given in BD 37/88 Table 1.



Design of Bridges



Nominal Superimposed Dead Load (BD 37/88 5.2.1) For calculating the nominal superimposed dead load, the depth of ballast from the underside of sleepers at the lowest rail to the top of the bridge deck should be taken as 300mm unless the bridge carries a greater depth of ballast.

In the latter case, the actual depth of ballast should be used.

Ballast density should be taken as 21kN/m3. (This allows for dirty waterlogged ballast.)

Design Superimposed Dead Load (BD 37/88 5.2.2) For superimposed dead load, γfL should be taken as 1.75 at ULS and 1.2 at SLS for track ballast for a depth measured from top of sleeper to 300mm below the underside of the sleeper; the same values should be taken for slab track.

For additional ballast depth or fill γfL should be taken as 1.20 at ULS and 1.00 at SLS.

For track, γfL should be taken as 1.20 at ULS and 1.00 at SLS based on the heaviest likely future track type. This should generally be assumed to be UIC 60 rail with full-depth concrete sleepers at 600mm spacing unless the construction of the bridge is such that track of this weight could not reasonably be laid.

Removal of Superimposed Dead Load (BD 37/88 4.5.2) Due regard should be taken of the case where either reballasting or resurfacing work is being undertaken and for the temporary case during erection.

Each bridge should be considered individually and a realistic assessment made; particular care is needed when continuous elements are being considered.

For guidance it may be assumed that:

• where live load is present, the superimposed dead load (ballast) can be reduced by up to half over the full length of the bridge; where live load is not present, the superimposed dead load (ballast and track) can be removed partially or completely over the full length or part length of the bridge;

• whether or not live load is present, for a multi-track bridge the superimposed dead load (ballast and track) can be removed partially or completely over the full length or part length of the bridge for one or more tracks.





APPENDIX J

COLLISION OF ROAD VEHICLES WITH BRIDGE SUPERSTRUCTURES

Section 7.3.2 of this document recommends that provision be made in certain cases to enable bridge superstructures to withstand (to some extent) the effects of possible strikes by road vehicles.

These provisions should be as given in BD 60/94 for Highways Agency bridges, except that references to the “Overseeing Organisation” should be taken as referring to Railtrack.



Design of Bridges



APPENDIX K

DESIGN INFORMATION THAT SHOULD BE SUPPLIED BY THE INFRASTRUCTURE CONTROLLER (This Appendix sets out the information that should be supplied by the infrastructure controller as a minimum when preparing a remit for bridge design. Particular bridges may require additional items to be specified)

K.1 New and Reconstructed Bridges 1.1 Loading for underline bridges:

• maximum speed of rail traffic intended to use bridge; • annual tonnage per line; • rail traffic mix; • design load when other than full RU loading • for bridges where the permissible or enhanced permissible speeds and

the maximum speed of the vehicle are greater than 200km/h:

- details of each train configuration (including axle loads and spacing)

- details of the normal operating speed of the vehicle at the bridge (this may be less than the maximum speed of the vehicle but nevertheless may cause greater load effects as a result of resonance).

- the range of speeds to be considered.

1.2 Loading for overline bridges:

• number of HB units; • special types of road or vehicular traffic (only where not otherwise

covered in BD 37/88).

1.3 Deflections:

• permitted vertical and horizontal deflections (see tables in UIC Leaflet776-3R).

1.4 Accidental actions:

• containment level of parapets for overline bridges; • whether impact protection beams are to be provided for underline

bridges; • minimum headroom for underline bridges.

1.5 Intended life of new bridge or new bridge superstructure if other than 120 years.

1.6 Standards for design additional to those referred to in this document.

1.7 Track requirements:

• horizontal and vertical alignment; • cant and cant deficiency; • ballast depth.

1.8 Structural gauging clearances and dimensions including an allowance for future or changed overhead electrification equipment and particular vehicles intended to use the bridge.





1.9 Requirements for compatibility with adjacent infrastructure including any proposed changes including the following where appropriate:

• track components; • signalling equipment; • overhead electrification equipment (including requirements for

bonding); • lineside access; • telecommunication equipment; • plant.

1.10 Any site specific hazards (eg, mineral workings, disused mine shafts, services).

K.2 Altered Bridges 2.1 Generally as identified in section K.1 of this Appendix and:

• load capacity of remaining (unaltered) parts of the bridge; • required load capacity for new / strengthened elements of the bridge; • intended further life of remaining (unaltered) elements of the bridge; • intended life of new elements of the bridge.



Design of Bridges



References Railway Group Standards

GA/RT6001 Railway Group Standards Change Procedures

GC/RT5014 Track Standards Manual: Section 6 – Ballast and Formation

GC/RT5020 Track Standards Manual – Section 3: Rail Joints

GC/RT5022 Rail and Rail Joints (to be issued Autumn 2000)

GC/RT5021 Track System Requirements

GC/RT5023 Categorisation of Track

GC/RT5101 Technical Approval Requirements for Changes to the Infrastructure

GC/RT5110 Design Requirements for Structures

GC/RT5112 Loading Requirements for the Design of Bridges

GC/RC5142 Management of Infrastructure Records

GC/RT5201 Lineside Security

GC/RT5203 Infrastructure Requirements for Personal Safety in Respect of Clearances and Access

GM/TT0101 Clearance Requirements for Electrified Lines and T&RS (to be superceded by GM/RT8025 Electrical Clearance Requirements for Electrified Lines).

GE/RT8029 Management of Clearances and Gauging

GI/RT7001 Management of Safety Related Records of Elements of the Infrastructure

The Catalogue of Railway Group Standards and the Railway Group Standards CD-ROM give the current issue number and status of documents published by the Safety & Standards Directorate.

British Standards BS 6779 Highway Parapets for Bridges and Other Structures

BS 5400 Steel Concrete and Composite Bridges (inc. BD 37/88)

BS 5268 Structural use of Timber

BS 8118 Structural use of Aluminium

BS 5628 Approved Code of Practice for use of Masonry

BS 8006 Approved Code of Practice for Strengthened / Reinforced Soils and their Fills

BS 8002 Approved Code of Practice for Earth Retaining Structures

BS 8004 Approved Code of Practice for Foundations

BS 5395 Stairs, Ladders and Walkways





UIC Leaflets 776-1R Loads to be Considered in Railway Bridge Design

(1979 Edition with 1987 amendments)

774-3R General Principles for Calculating Longitudinal Forces in a Bridge, its Bearings and its Sub-structure. Recommendations for a simple case

776-3R Deformation of Bridges (1989 Edition)

777-2R Structures Built over Railway Lines (Construction Requirements in the Track Zone)

Office of the Rail Regulator Meeting the Needs of Disabled Passengers

Department of Transport Documents Design of Composite Bridges. Use of BS 5400: Part 5: 1979 for Department of Transport Structures (December 1987)

BD 37 / 88 Loads for Highway Bridges

BD 52 / 93 The Design of Highway Bridge Parapets (Supersedes BE 5)

BD 60 / 94 The Design of Highway Bridges for Vehicle Collision Loads

CIRIA Bridges - Design for Improved Buildability (Report 155) Rationalisation of Safety and Serviceability Factors in Structural Codes (Report 63)

HSE (Her Majesty’s Railway Inspectorate) Railway Safety Principles and Guidance

EUROCODE ENV 1991-3 Traffic Loads on Bridges (including UK National application document when published)

Institution of Civil Engineers Burland and Kalra “Queen Elizabeth II Conference Centre: geological aspects”
