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
.
Submitted by
Dean Benson
Standards Project Manager
Authorised by
Brian Alston
Controller, Railway Group Standards
Railway Approved Code of Practice
GC/RC
5510
Issue Two
Date August 2000
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Recommendations for the
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R A I L T R A C K
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Page 1 of 48
Contents
Section
Description
Page
Health and Safety Responsibilities
Recommendations
Relating to
GC/RT5110
Adequacy of Structural Gauging, Clearances and Dimensions
Compatibility with Other Infrastructure
Recommendations
Relating to
GC/RT5112
Railway Traffic Loads and Load Effects
Pedestrian and / or Cycle Traffic Loads
Aerodynamic Effects of Rail Traffic
Non-Traffic Loads and Load Effects
Lists of Loads and Load Effects
Loads and Load Effects Required by
Considered in the Loading Specification for
Modifications to and clarification of BS 5400 Parts 3, 4 and 5
Existing Substructures Affected by New Construction
Provision for Future Traffic Developments and Selection of Traffic Mix
Modifications to and Clarification of UIC Leaflet 776-3R (1989)
Recommendations for Infill to Open Handrailing for Underline
Profiles for the Tops of Parapets to Overline Highway
Collision Loads from Railway Traffic
Further Recommendations on Loading for Underline
Collision of Road Vehicles with
Information that should be supplied by the infrastructure controller
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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.
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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
.
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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.
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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.
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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.
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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).
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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:
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.
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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.
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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).
b) 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.
c) 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).
d) The differential settlement transverse to the track should be limited so as not
to cause unacceptable twist in the track.
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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).
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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.
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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
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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
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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
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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
);
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•
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;
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•
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.
12.3 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.
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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:
a) Metal underline and overline
bridges
should be bonded to the traction return
rail or earth wire.
b) The components of metal
bridges
should be connected by welding or by
substantial, clean metal-to-metal bolted or riveted joints.
c) Exposed metal parts of underline and overline
bridges
(eg, handrails and
bearings of concrete
bridges
) should be connected together and bonded as
above.
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d) Concrete reinforcement (including prestressing anchorages) should be
bonded as above if it is accessible or if it is electrically connected to
accessible metalwork.
e) Concrete, timber and masonry overline
bridges
should have a bonded metal
plate attached to the underside in certain cases.
f) 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.
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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.
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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:
(a) 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.
(b) Dispersal of concentrated loads (with the modifications given in Appendix
I.3 of this document).
(c)
Concentrated load on deck plates and local elements.
(d) Application of loading to multi-track
bridges
.
(e) Lurching (deemed in BD 37/88 to be taken into account by the specified
dynamic factors).
(f)
Nosing (but see Appendix I of this document for longitudinal distribution).
(g) Centrifugal load (but see Appendix D of this document for applicable
speed).
(h) Longitudinal loads (traction / braking).
(i)
Load combinations and partial factors.
(j) Derailment
loads.
(k)
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);
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•
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:
(a) The dynamic effects specified in BD 37/88 (as modified by Appendix I of
this document) should be applied to the factored RU loading.
(b) 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.
(c)
If the dynamic loading derived from factored RU loading (DL
RUfac
) is less
than the dynamic loading derived from actual train types (DL
actual
), the RU
factor should be increased sufficiently so that DL
RUfac
≥
DL
actual
.
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
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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.
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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
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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 ( = L
3
/EI
lateral
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/m
2
•
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.
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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/m
2
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.
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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.
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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.
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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
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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:
(i) for
bridges
carrying railways, in accordance with Part 10, where in Table 8:
•
m = 9, K
2
= 0.75 x 10
27
,
σ
0
= 160 N/mm
2
for bars < 16mm dia;
•
m = 9, K
2
= 0.07 x 10
27
,
σ
0
= 125 N/mm
2
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);
(ii) 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
γ
m
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
γ
m
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 . . .”).
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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.
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•
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).
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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 v
t
+10)km/h in the
calculation of centrifugal loads (v
t
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.
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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.
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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/m
2
or a horizontal force of 0.5kN
applied at any point, whichever has the more severe effect.
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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.
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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
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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.
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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
δ
u
for spans between 20 - 100 metres should be
corrected to read
δ
u
= 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
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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)
γ
fL
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.
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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/m
3
. (This allows for dirty waterlogged
ballast.)
Design
Superimposed Dead Load (BD 37/88 5.2.2)
For superimposed dead load,
γ
fL
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
γ
fL
should be taken as 1.20 at ULS and 1.00 at
SLS.
For track,
γ
fL
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.
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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.
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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
.
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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
.
Uncontrolled When Printed
Recommendations for the
Design of Bridges
R A I L T R A C K
4 7
Railtrack Approved Code of Practice
GC/RC
5510
Issue Two
Date August 2000
Page 47 of 48
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
Uncontrolled When Printed
Recommendations for the
Design of Bridges
4 8
R A I L T R A C K
Railtrack Approved Code of Practice
GC/RC
5510
Issue Two
Date August 2000
Page 48 of 48
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”
Uncontrolled When Printed
Document Outline
- Home
- Main Menu
- Document Menu
- Infrastructure RC Index
- Contents
- Part A
- Part B
- 1 Purpose
- 2 Scope
- 3 Definitions
- 4 Principle
- 5 Duties and Competency
- 6 Intended Use and Life
- 7 Structural Adequacy
- 8 Materials and Workmanship
- 9 Adequacy of Structural Gauging, Clearances and Dimensions
- 10 Execution/Decommissioning
- 11 Future Maintenance
- 12 Compatibility with Other Infrastructure
- 13 Operational Safety
- 14 Design Control Procedures
- 15 Limitations on Use
- 16 Identification of Structures
- 17 Structures Owned by Outside Parties
- 18 Records
- 19 Railway Traffic Loads and Load Effects
- 20 Walkway Loads
- 21 Road Traffic Loads
- 22 Pedestrian and / or Cycle Traffic Loads
- 23 Other Traffic Loads
- 24 Aerodynamic Effects of Rail Traffic
- 25 Non-traffic Loads and Load Effects
- 26 Bridges not Owned by Railtrack
- 27 Records
- 28 List of Loads and Load Effects
- Appendices
- A Loads and Load Effects Required by GC/RT5112 to be Considered in the Loading Specification for Bridges
- B Modifications to BS 5400 Parts 3, 4 and 5
- C Existing Substructures Affected by New Construction
- D Provision for Future Traffic Developments and Selection of Traffic Mix
- E Modifications to and Clarifications of UIC Leaflet 776-3R (1989)
- F Recommendations for Infill to Open Handrailing for Underline Bridges
- G Profiles for the Tops of Parapets to Overline Highway Bridges
- H Collision Loads from Railway Traffic
- I Further Recommendations on Loading for Underline Bridges
- J Collision of Road Vehicles with Bridge Superstructures
- K List of Vehicle Types for which the Recommendations Given in Section 9.1.1 of this Approved Code of Practice are Vali
- References
- Cross References
- GC/RT5014
- GC/RT5021 (2)
- GC/RT5021 (3)
- GC/RT5022
- GC/RT5023
- GC/RT5101
- GC/RT5110
- GC/RT5112
- GC/RT5203
- GI/RT7001
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