Recommendations for the Design of Bridges

Transcription

1 Recommendations for the Design of Bridges Synopsis This Railway Group Approved Code of Practice gives recommendations for the design and loading for bridges. It supports Railway Group Standards GC/RT5112 and GC/RT5110. Signatures removed from electronic version Submitted by Patricia Dingwall Standards Project Manager Authorised by Richard Spoors Controller, Railway Group Standards 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 House, Floor DP01 Railtrack House, Euston Square, London NW1 2EE Copyright 1998 Railtrack PLC

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3 Recommendations for the Design of Bridges Page 1 of 63 Contents - Section Description Page Part A Issue Record 3 Application 3 Health and Safety Responsibilities 3 Supply 3 Part B 1 Purpose 4 2 Scope 4 3 Definitions 4 4 Principle 4 5 Duties and Competency 4 Recommendations Relating to GC/RT Intended Use and Life 6 7 Structural Adequacy 9 8 Materials and Workmanship 13 9 Adequacy of Structural Gauging, Clearances and Dimensions Execution / Decommissioning Future Maintenance Compatibility with other Infrastructure Operational Safety Design Control Procedures Limitations on Use Identification of Structures Structures Adjacent to Railtrack Land Records 23 Recommendations Relating to GC/RT Railway Traffic Loads and Load Effects Walkway Loads Road Traffic Loads Pedestrian and / or Cycle Traffic Loads Other Traffic Loads Aerodynamic Effects of Rail Traffic Non-Traffic Loads and Load Effects Bridges not Owned by Railtrack Records Lists of Loads and Load Effects 31 RAILTRACK 1

4 Page 2 of 63 Withdrawn Document Recommendations for the Design of Bridges Appendices A Loads and Load Effects Required by GC/RT5112 to be 32 Considered in the Loading Specification for Bridges B Modifications to BS 5400 Parts 3, 4 and 5 33 C Existing Substructures Affected by New Construction 35 D Provision for Future Traffic Developments and Selection of Traffic Mix 37 E Modifications to and Clarifications of UIC Leaflet 776-3R (1989) 38 F Recommendations for Infill to Open Handrailing for Underline Bridges 39 G Profiles for the Tops of Parapets to Overline Highway Bridges 40 H Collision Loads from Railway Traffic 41 I Further Recommendations on Loading for Underline Bridges 43 J Collision of Road Vehicles with Bridge Superstructures 47 K List of Vehicle Types for which the Recommendations Given in 48 Section of this Approved Code of Practice are Valid L Design Information that should be supplied by Railtrack 49 Figures A Precast Concrete Beam & Parapet Types 51 B Precast Concrete Beam & Parapet Types 52 C Integral Concrete Deck & Parapet Types 53 D Integral Concrete Deck & Parapet Types 54 E Cantilevered Parapet Types 55 F Cantilevered Parapet Types 56 G Half Through Steel Girder Types 1 57 H Half Through Steel Girder Types 1 58 I Half Through Steel Girder Types 2 59 J Half Through Steel Girder Types 2 60 K Measurement of Lateral Clearance to Underline Bridge 61 Girders for Canted Track L End and Centre Throw 61 References 62 2 RAILTRACK

5 Recommendations for the Design of Bridges Page 3 of 63 Issue Record Part A This Approved Code of Practice will be updated when necessary by distribution of a complete replacement. Amended or additional parts of revised pages will be marked by a vertical black line in the adjacent margin. Issue Date Comments 1 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 Application This Approved Code of Practice is not mandatory, but it gives recommendations on how the requirements of GC/RT5110 and GC/RT5112 can be met. Health and Safety Responsibilities In issuing this Approved Code of Practice, Railtrack PLC makes no warranties, express or implied, that compliance with all or any part of this document 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 Approved Code of Practice may be obtained from The Catalogue Secretary, Safety and Standards Directorate, Railtrack PLC, Railtrack House, DP01, Euston Square, London, NW1 2EE. RAILTRACK 3

6 Page 4 of 63 Withdrawn Document Recommendations for the Design of Bridges 1 Purpose 2 Scope Part B This Approved Code of Practice gives recommendations for the design of Bridges and supports Railway Group Standards GC/RT5110 and GC/RT5112. This Approved Code of Practice applies to Bridges on, over or under Railtrack Controlled Infrastructure. It covers linespeeds of rail vehicles up to and including 200km / h (125mph). Whilst primarily applicable to Bridges on, over or under Railtrack Controlled Infrastructure, the recommendations of this Approved Code of Practice 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 given otherwise, the recommendations of this Approved Code of Practice apply to new Bridges and as far as is reasonably practicable to: complete superstructure reconstructions of existing Bridges; significant alterations, strengthening and extensions to existing Bridges. 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 Approved Code of Practice, a Bridge is deemed to include associated elements such as wing walls, handrailing and fencing. Design Information in the form of drawings, 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). 4 Principle 5 Duties and Competency The principle of this Approved Code of Practice 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 Railway Group Standards to be met with respect to Bridges. 5.1 Responsibilities and duties The appropriate Director within Railtrack shall ensure that the responsibilities and duties of all persons responsible for the design of Structures are clearly defined in writing and understood by these persons. The responsibilities and duties of external design organisations should be made clear in the relevant design brief, scope of works, tender documentation and / or other relevant documents. Railtrack should take reasonable steps to verify that organisations undertaking Bridge Design have adequate management procedures to ensure that individual designers understand their responsibilities and duties. 4 RAILTRACK

7 Recommendations for the Design of Bridges Page 5 of 63 Preparation of design briefs (including performance requirements and design constraints) is part of the design process; Railtrack should therefore ensure that those preparing design briefs (whether Railtrack 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 must be appropriate to the nature and complexity of the Structures being designed. This competency must be assessed by the person making the appointment. Railtrack 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. RAILTRACK 5

8 Page 6 of 63 Withdrawn Document Recommendations for the Design of Bridges 6 Intended Use and Life Recommendations relating to GC/RT Intended use Railtrack shall ensure that the traffic, persons and / or equipment that the Structure is required to support and / or the level of protection to be provided is specified. The traffic, persons and or equipment that the Bridge is required to support should generally be specified as the design live (variable traffic) and / or superimposed loading on the Bridge. As 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 Approved Code of Practice. 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 Approved Code of Practice. 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 Approved Code of Practice. 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 and 13.2 respectively of this Approved Code of Practice. 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 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 Railtrack shall ensure that the intended life of the structure is specified (where appropriate) 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. 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 (e.g. partial superstructure reconstructions, repairs, strengthening, remedial works etc.) Railtrack 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 RAILTRACK

9 Recommendations for the Design of Bridges Page 7 of 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 (e.g. Bridges constructed by thrusting or jacking). Where the intended life is longer than 120 years, the effects of fatigue should be treated quantitatively. Consideration should also be given to the following, as appropriate: 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 (e.g. 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 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 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 Joints and Bearings Joints and bearings often have an adverse effect on the durability of structures. As 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. Where circumstances permit, new Bridges should preferably be designed as monolithic structures (i.e. without articulating bearings) 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 in the following cases: RAILTRACK 7

10 Page 8 of 63 Withdrawn Document Recommendations for the Design of Bridges 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 Waterproofing In order to achieve satisfactory durability, Bridge decks should generally be waterproofed except in the following cases: 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 (e.g. 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 13.1 of this Approved Code of Practice.) 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 Disposal of water For new Bridges and Bridge superstructure reconstructions, adequate provision should be made for the disposal of water from the superstructure Ballast depth 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 applies in addition to any requirements given by track standards and is in order to: avoid damage to the Bridge deck waterproofing caused by track tampers etc.; ensure satisfactory longitudinal distribution of wheel loads. If in exceptional cases a lesser ballast depth is unavoidable: the wheel load distribution proportions given in Appendix I.3 of this Approved Code of Practice should not be used without further justification. provision should be made to protect the Bridge deck waterproofing; 8 RAILTRACK

11 Recommendations for the Design of Bridges Page 9 of 63 7 Structural Adequacy Railtrack shall ensure that the Structure is 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, Railtrack 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 (e.g. 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 Approved Code of Practice or by other means) that, although the recommendations of this Approved Code of Practice 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 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 Approved Code of Practice. 7.3 Accidental events and vandalism The Structure shall also be designed and executed in such a way that it will not be damaged by accidental events or vandalism, to an extent disproportionate to the original cause 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 Approved Code of Practice. 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 Approved Code of Practice. Further advice and recommendations are given in UIC Leaflet 777-2R (but should be ignored where they conflict with the recommendations of this Approved Code of Practice) Protection of underline Bridges from road vehicle strikes 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 RAILTRACK 9

12 Page 10 of 63 Withdrawn Document Recommendations for the Design of Bridges 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 Approved Code of Practice. 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 as 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, e.g. 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 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: 1. at least 5.7m; 2. at least 5.3m, with Appendix J provisions; 3. at least 5.1m, with Appendix J provisions; 4. an improvement on the existing, with Appendix J provisions and protection beams unless the risk from strikes is small; 5. an improvement on the existing, with Appendix J provisions; 6. not less than the existing, with Appendix J provisions and protection beams unless the risk from strikes is small; 7. not less than the existing, with Appendix J provisions and robust construction; 8. not less than the existing, with Appendix J provisions; 9. not less than the existing. Any headroom less than 5.7m should be identified and justified in the AIP submission, taking into account the factors given in Section of this Approved Code of Practice. In addition, the previous history of Bridge strike incidents at the site should be considered. 10 RAILTRACK

13 Recommendations for the Design of Bridges Page 11 of 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 Approved Code of Practice. 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 Approved Code of Practice. Such loading need not be applied to secondary structural elements such as cantilevered walkways. For certain superstructure types (e.g. 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 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 of this Approved Code of Practice.) 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 (e.g. 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 Railtrack shall ensure that the loading and resistance requirements are based on suitable standards (e.g. 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. Other industry standards and advice (e.g. those of the Highways Agency) may generally be used for guidance provided they do not conflict with the recommendations given in this Approved Code of Practice 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 RAILTRACK 11

14 Page 12 of 63 Withdrawn Document Recommendations for the Design of Bridges modifications given in Appendix B of this Approved Code of Practice. (These modifications should be identified in the AIP submission but do not need to be further justified.) 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 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 should be described in the AIP submission Foundations and earth-retaining elements New foundations for Bridges should be designed generally in accordance with BS New earth-retaining elements of Bridges should be designed generally in accordance with BS 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 apply in addition: 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); 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 Bearings New Bridges should preferably be designed as integral structures (without bearings) where circumstances permit this without undue penalty in first cost. For Bridge superstructure reconstructions, provision should be made for deckend 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 as given below: 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. For 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 (e.g. 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. 12 RAILTRACK

15 Recommendations for the Design of Bridges Page 13 of 63 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 (e.g. 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 Approved Code of Practice.) See also Section 11.2 of this Approved Code of Practice regarding replacement of components 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 Approved Code of Practice. 8 Materials and Workmanship Railtrack shall ensure that suitable materials and standards of workmanship are 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 necessarily or likely resulting from the Design should be taken into account (e.g. 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). 9 Adequacy of Structural Gauging, Clearances and Dimensions 9.1 General Requirements Railtrack shall ensure that the location and dimensions of the Structure (including any intended equipment which it is designed to support) provide, where appropriate for the safe movement of vehicles, persons (including those who are disabled) or equipment Clearances to the railway The clearance requirements for the safe passage of rail vehicles are given in GC/RT5204. (This will be superseded in due course by GC/RT5102.) RAILTRACK 13

16 Page 14 of 63 Withdrawn Document Recommendations for the Design of Bridges The clearance 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 Approved Code of Practice.) Underline Bridges should be designed to minimise the encroachment of girders into the platform gauge (the cross-hatched area indicated as available for girders in Appendix D of GC/RT5204). Such encroachment (particularly by girders in the six-foot ) inhibits future operational flexibility, but often it cannot reasonably be avoided where construction depth needs to be minimised. In such cases, the tolerance on the required minimum clearances should be the maximum that can be achieved with reasonable economy, generally as follows in order of preference for lateral dimensions. (These are based on an envelope using a 200m radius curve, with 150mm cant, 125mm cant deficiency with a vehicle speed of 125mph or the maximum speed of the vehicle if less and the vehicles listed in Appendix K of this Approved Code of Practice. They provide for a 50mm clearance between vehicle and Bridge.): mm at a height of 915mm above rail level (a.r.l.) + T + 75mm tolerance; or 775mm at a height of 870mm a.r.l. + T + 75mm tolerance; mm at a height of 915mm a.r.l. + T + 50mm tolerance; or 775mm at a height of 870mm a.r.l. + T + 50mm tolerance; mm at a height of 915mm a.r.l. (for nominally straight track only); or 775mm at a height of 900mm a.r.l mm clear of the swept envelope of all vehicles likely to use the Bridge; 5. < 50mm in exceptional circumstances, but in all cases such clearances should be justified and appropriate control measures provided for maintaining the clearance. Notes: (a) The above clearances are with respect to the running edge of the nearest rail. (b) To allow for the effects of track cant, clearances should be calculated with respect to axes perpendicular and parallel to the plane of the rails. (This is illustrated in Figure K of this Approved Code of Practice.) (c) T is an allowance for end and centre throw of vehicles on circular curves, deemed sufficient to cover all vehicle types listed in Appendix K of this Approved Code of Practice. (Railtrack should specify clearances where they are required to cover vehicle types additional to those listed.) T = / R mm on the inside of the curve T = / R mm on the outside of the curve where R is the radius of the curve in metres. (Example: for a curve of radius 500m, T = 90mm inside, 70mm outside.) (End and centre throw are illustrated in Figure L of this Approved Code of Practice.) (d) For non-circular curves (e.g. transitions, turnouts), T should be calculated on the basis of the smallest radius within a distance of 20m from the location at which the clearance is being considered. Alternatively, in place of T, exact values for throw may be used, based on the actual track geometry and all vehicles likely to use the Bridge. (e) Where R is less than 200m, in place of T, exact values for throw should be used, based on the actual track geometry and all vehicles likely to use the Bridge. (f) Clearances corresponding to 3, 4 and 5 above should be regarded as substandard and identified as such in the AIP submission. (g) Clearances corresponding to 5 above should additionally be agreed by HMRI. (h) The above recommended clearances may not be applicable on routes where tilting trains are proposed. Clearances should be considered further in such cases. 14 RAILTRACK

17 Recommendations for the Design of Bridges Page 15 of 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. 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. Where a walkway is raised more than 500mm above the level of the ballast adjacent to the walkway, cess or sleeper, GC/RT5203 requires immediate access to be provided where reasonably practicable. 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 (e.g. 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 Approved Code of Practice. 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 Approved Code of Practice. 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 Lateral clearances to highways Lateral clearances to public highways should be determined in consultation with the relevant Highway Authority taking into account Railtrack s legal obligations. RAILTRACK 15

18 Page 16 of 63 Withdrawn Document Recommendations for the Design of Bridges Lateral clearances to private roads should be determined in consultation with the owner or user of the road taking into account Railtrack s legal obligations Vertical clearances to highways Recommendations for vertical clearances to public highways are given in Section 7.2 of this Approved Code of Practice. 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 Railtrack s legal obligations. 9.2 Railtrack shall ensure that the location and dimensions of the Structure (including any intended equipment which it is designed to support) provide, where appropriate adequate protection and / or deterrence from unauthorised access 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 be at least as high as the adjacent fence and should be formed such as to deter climbing. Where appropriate (e.g. on pipe Bridges and certain footbridges) chevaux-defrise 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 Railtrack shall ensure that the location and dimensions of the Structure (including any intended equipment which it is designed to support) provide, where appropriate adequate protection to vehicles or persons using or affected by the Structure 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. The criteria given in BD 52/93 for the provision of P6 high containment parapets need not generally be applied retrospectively to existing Bridges. 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 Approved Code of Practice. 16 RAILTRACK

19 Recommendations for the Design of Bridges Page 17 of 63 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 in the following cases: where equestrian use is exceptionally heavy; where equestrian use is moderate but the Bridge is narrow and there is no verge or footway (e.g. 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 Layout etc. for footbridges Prevention of injury All accessible parts of footbridges should be free of sharp edges or projections which could be reasonably foreseen to cause injury 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 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 At stations, internal headroom should additionally be as given in HMRI Railway Safety Principles and Guidance 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 (e.g. where a change in direction between stair flights cannot be accommodated) this should be stated and justified in the AIP submission 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. RAILTRACK 17

20 Page 18 of 63 Withdrawn Document Recommendations for the Design of Bridges 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 July 1994 published by the Office of the Rail Regulator. (This document is currently being updated.) 9. 4 Structures Over Electrified Railways The following requirements apply to parapets of Structures which are over railways electrified on the 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. The 3000mm dimension given above should be measured horizontally. Where parts of Bridges (e.g. road approach ramps or footbridge stair flights) run essentially parallel to and adjacent to railways electrified on the overhead 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 Railtrack shall ensure that the Structure is designed so that there is at least one safe and feasible method for its Execution and for its subsequent decommissioning Execution (construction, erection) The safe and feasible method for the execution of the structure should take into account the following: 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); 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 Decommissioning Any hazards associated with demolition or 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 the following Bridges: 18 RAILTRACK