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7/18/2019 Railway Bridges Today and Tomorrow
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Railway Bridges
Today and Tomorrow
22-23 November 2006
Marriott Hotel City Centre, Bristol
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Railway Bridges - Today and Tomorrow 3
Foreword
I am pleased to welcome you to the third in the series of successful Network Rail sponsored supplier
conferences. This time the subject is "The Maintenance and Renewal of Bridges".
The majority of Network Rail's bridges are over 100 years old and are constructed in a variety of materials,
for example cast iron, wrought iron, steel, reinforced concrete, brick, masonry and timber. Future
construction is likely to use more complex forms of composite construction, in particular fibre reinforced
polymers which are already being used to strengthen bridges.
The age and variety of materials presents interesting challenges to Network Rail in order to maintain its
bridges in a safe and fit for purpose condition, as part of a safe, reliable and efficient railway. I believe that
there are opportunities within the Bridges Renewals and Maintenance Portfolios to achieve significant
savings through promoting best practice, adopting lessons learnt and innovative thinking. In addition,eliminating the need for lengthy line closures to do work is an essential part of tomorrow's railway.
Converting these opportunities into actual savings, whether financial or process time or avoidance of
traffic interruption, forms an essential part of achieving the efficiency targets set by the Office of Rail
Regulation.
Selected key suppliers with experience in the design, construction and maintenance of bridges were
invited to submit technical paper synopses on a range of topics for presentation and debate at the
conference. The topics were very varied and included composite materials, safety, innovation and new
materials, minimum future management and maintenance costs, repair and strengthening versus
renewal, standard designs and details, grade separated junctions and direct track fastenings.
The findings from these papers will support the drive for greater efficiency and the delivery of whole life
cost structures. This document contains the fourteen papers which were selected for formal presentation.
The choice of papers was made jointly by representatives from the Engineering and Major Projects &
Investment functions of Network Rail. I extend my thanks to all of you who took the time and trouble to
submit a synopsis.
You are all key stakeholders and vital links in the supply chain which maintains and renews Network Rail's
bridge assets. I trust that you will continue to work with us to provide a safe, reliable and efficient railway.
Professor Andrew McNaughton
Chief Engineer
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Railway Bridges - Today and Tomorrow4
Contents
Paper Title
One Getting the most out of bridge renewals
Design is more than BS5400....Network Rail
Two Repair and Strengthening versus Renewal
Mott MacDonald
Three Jamestown Viaduct - Innovative Strengthening of an Early Steel Viaduct
Corus Railway Infrastructure Services
Four Innovative Techniques Used in the Life Extension Works of Leven Viaduct
Carillion
Five Development o f Standard Designs and Details for Railway Bridges
Network Rail
Six Delivery of Works - Safely
Alfred McAlpine Project Services
Seven Track/Bridge Interaction and Direct Track Fixing
Cass Hayward & Partners
Eight Soil/structure Interaction and Railway Bridge Structures
Ove Arup
Nine Innovation Now & in the Future
Fairfield-Mabey
Ten Design for Future Minimum Management/Maintenance Costs
Gifford
Eleven Advances in Rail Underbridge Replacements
Hyder Consulting (UK)
Twelve Forth Bridge Safety and Production
Balfour Beatty Civil Engineering
Thirteen Skills Competency in the Painting Industry:
The Industrial Coatings Applicator Training Scheme
Institute of Corrosion
Fourteen Recent Developments in Strengthening Technology and the
Strengthening/Reconstruction Decision
Mouchel Parkman/Tony Gee and Partners JV
Page
7
17
23
31
39
47
61
65
75
81
87
97
103
107
Day One 5
Day Two 73
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Railway Bridges - Today and Tomorrow 5
Day One
22 November 2006
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Railway Bridges - Today and Tomorrow6
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Railway Bridges - Today and Tomorrow 7
Paper One
Getting the most out of bridge renewals
Design is more than BS5400....
Ian Bucknall
NETWORK RAIL
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Abstract
The design and construction of railway bridges is one of
the most rewarding jobs in the rail industry. We follow the
successes of engineers who built and maintained Network
Rail's most populous and longest lasting assets.
Design decisions made by today's engineers dictate
whether Network Rail gets the most out its investment inrenewing bridges in its 40,000+ bridge stock. The
purpose of this paper is to challenge those involved in
design decisions to reconsider some of the broader
aspects of successful design.
We must use the opportunity presented by every renewal
to deliver reductions in the on-going management and
maintenance of the bridge stock. The paper examines
Network Rail's functional requirements that will assist with
ensuring designs deliver these objectives and other key
design requirements that have to be satisfied to ensure
long lasting bridges that will serve the railways for inexcess of 100 years.
The functional requirements for railway bridges cover
normal operations and abnormal situations - both
unplanned and planned. Those familiar with the
requirements for road bridge design will see significant
additional requirements. The site specific constraints we
inherit from the initial construction of the railways,
especially limited construction depth - together with our
need to carry out the renewal with minimum disruption to
rail traffic - frequently dictate practicable structural forms.
The paper concentrates on the renewal of underlinebridges, recognising that many of the issues raised are
equally applicable to the renewal of overline bridges and
footbridges.
Optimising design to deliver Network Rail's requirements
at least initial cost maximises the benefits of Network
Rail's investment. Putting the benefits of the investment
at risk from insignificant reductions in initial cost would not
be a success for the rail industry.
1. Introduction
With 40,000+ bridges Network Rail seeks to maximise the
benefits of every bridge renewal. Typically bridge
renewals are carried out to:
• address shortfalls in bridge capability to carry required
railway loads
• address significant condition issues
when consideration of:
• optimal whole life structure maintenance costs
• the need to minimise the risk of temporary speed
restrictions, and;
• other risks that could potentially lead to delays to train
services or restrictions on operations
indicate replacement is the preferred option.
The design decisions made on individual bridge renewals
contribute to Network Rail's overall business objectives -
to improve the reliability of the railways and reduce the
funding requirements for the on-going management andmaintenance of the infrastructure to affordable levels. To
support these overall business objectives, good design:
• delivers the client's functional requirements
• ensures that the proposed works are capable of
execution with minimal disruption to the client's
operations - and especially the client's customers (in this
case the ultimate users of the railways)
• minimises whole life costs by achieving the appropriate
balance between initial costs and the client's on-goingmanagement and maintenance costs
• realises the benefits of innovative techniques whilst
ensuring the risks associated with such innovation are
acceptable
• ensures that the proposed works will be as successful
as the designs of previous railway engineers, who built
and maintained bridges that have given good service for
approaching 150 years
This paper concentrates on the first and last of the above,
and aligns with Network Rail's policy of leading the
decision making on its infrastructure and acting as an
expert client in directing bridge renewal activity. Issues
such as discharge of CDM responsibilities, sustainability
and minimising the risk of possession overruns etc., are
outside the scope of this paper.
2. Functional requirements for underline
bridges
The functional requirements for underline bridges may be
categorised as:
• requirements for minimising structures management
and maintenance - easy to manage and durable
• requirements for normal operation
• requirements for satisfactory performance during
abnormal operation - both unplanned and planned
situations
2.1 Easy to manage and durable
With 40,000 bridges to maintain it is essential that everyopportunity presented by a bridge renewal for reducing structures
management and maintenance costs is taken. To facilitate this
objective the design should address the following requirements.
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2.1.1 Water management
To maximise the life of the structure it is essential to
consider at the start of the design how water will be
managed.
Positive falls, camber, good detailing practice such as
provision of drips and weather flats, avoidance of debris
traps etc. should all be included in the design.
It should be assumed in the design that waterproofing will
fail in the life of the structure. Positive water management
will maximise the life of the structure whilst the benefits of
repairing the waterproofing are evaluated (the cost/
disruption of gaining access by removing the track to most
rail bridges is high).
2.1.2 Durability requirements
In addition to the requirements in the industry standards
sufficient durability will be achieved by:
• appropriate selection of materials• appropriate workmanship specifications
• protective treatment in accordance with Network Rail's
performance specification
Further details are outside the scope of this paper.
2.1.3 No debris traps
Experience with existing bridges indicates that debris
trapped in elements promotes greater rates of corrosion of
metallic elements / deterioration of protective coatings. To
maximise the life of the structure the structural form and
detailing should minimise potential debris traps.
2.1.4 Structural behaviour easily understood
Unnecessary structural complexity and less common
structural forms greatly increase the management and
maintenance costs of railway bridges. In design the
designer has the luxury of many weeks or months to gain
a full understanding of behaviour. When faced with the
task of evaluating "bridge bash" damage and the need to
restore railway traffic in hours such complex structures
are unacceptable.
Network Rail already owns a significant number of historic
landmark structures that require significant managementresources. Any additional proposals for further landmark
structures will only be supported where there is a
compelling business requirement, and such requirements
will be specified by Network Rail.
2.1.5 Fai lure modes
In the unlikely event of the structure being at risk of a
structural failure the design of the structure should be
designed, such that:
• the critical failure mode is one which gives warning
signs of the impending failure (e.g. fail in bendingbefore direct tension failures)
• consideration should be given to providing alternative
load paths [e.g. shear flats (or other physical means) in
cross girder to main girder connections, so that in the
event of bolt failure the deck does not drop with the
potential resultant effect on track alignment
disproportionate to the structural failure]
Structures should not require any special examination
requirements. Preferably, signs of distress should be
capable of being detected by the normal annual visual
examination process.
2.1.6 No hidden detai ls
All main structural elements should be visible from at last
one side.
If this is not possible advice should be sought from
Network Rail at an early stage in the design and
consideration given to providing alternative load paths
that ensure the structure is still acceptable w.r.t the
ultimate limit state and w.r.t. traffic safety deformation
requirements (e.g. former practices of installing
longitudinally post tensioned beams with anchoragesburied under the tracks, preventing access to critical
components, is no longer acceptable).
2.1.7 Access to structural elements
All elements of the structure should be accessible for
examination and maintenance.
2.1.8 Robustness
It is desirable for elements of the structure to have a
degree of robustness so that they are not damaged by
unforeseen events disproportionate to the cause. For
example:
• main girders in half through bridges designed to span
between abutments without the assistance of tension in
the floor (and the main girder / floor connection
checked for adverse longitudinal shear flows and the
floor designed to resist global tension effects)
• bearing stiffeners on main girders formed from two
plates rather than one are more tolerant of eccentricity
of bearing reaction resulting from substructure
movement
• stiffeners to box girder diaphragms formed from plateswith low outstand ratios that can accommodate
excessive load by yielding instead of buckling (also see
Failure modes above and Resistance to bridge bash
below).
2.1.9 Substructure movements
Replacement bridge decks should be designed to
accommodate differential settlement and on-going
movement of existing abutments etc.. Where
longitudinally free bearings are provided at one end of the
deck, consideration should be given to fitting "long stops"
to free movement to facilitate the deck acting as a strut, toresist excessive abutment movement.
Special considerations apply in areas of mining
subsidence.
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Note: It is generally acceptable to reuse existing
abutments when replacing the superstructure providing
the substructure is subject to a similar pattern of loading.
See GC/RC5110.
2.1.10 Deter pigeons
To minimise future maintenance and inspection costs the
design should incorporate provision to deter pigeons.
2.2 Normal operations
The requirements for normal operations are:
2.2.1 Capability to support load
Rail bridges must have adequate strength to carry railway
traffic and other variable/permanent loads for the
anticipated volume of traffic, in accordance with the
requirements of the relevant standards including BD37 and
BS5400 etc..
The standard design load models - RU in BD37 or LM71 inEN1991-2 (together with the additional load model SW/0
for checking continuous structures) - in conjunction with
the associated dynamic factors cover normal rail traffic
loads. The load models include a margin in comparison
with assessment loading requirements, that permits
flexibility in the timing for strengthening works for
structures that have with time deteriorated and no longer
meet design requirements but still meet assessment
requirements.
For bridges designed for speeds in excess of 125mph - or
for "lightweight metallic decks" for speeds over 100mph -
additional checks are required to ensure that the design
caters for the greater of:
• conventional loading, or
• the load effects determined from a dynamic analysis of
the structure subjected to the new European high speed
load model HSLM in EN1991-2.
Extensive studies of the dynamic behaviour of the modern
standard Network Rail box girder bridge indicate this form
o construction is satisfactory for speeds up to 125mph.
In the future, on lines where the Technical Specifications
for Interoperability apply, the TSI requirements for design
and the minimum standard for infrastructure are the same.
In the UK we will be designing new bridges for an
additional margin of 10% at ULS to ensure that we
continue to benefit from the current flexibility to decide the
timing of strengthening works.
The design should allow for the required number and
position of tracks including allowance for tolerance in their
position. The standard safety factors provide an allowance
for increased ballast loading due to future track lifts.
Finally, our guidance on specifying fatigue loading
requirements provides allowance for future growth in
traffic.
2.2.2 Acceptable deformation
In comparison with road bridges, bridges supporting rail
traffic are subject to more onerous deformation limits to
ensure the safety and comfort of rail traffic and
passengers, and limit the effects of deformation on the
track. Deformation limits are specified in railway industry
standards including UIC leaflets and in the future will be
superseded by the bridge performance criteria specified in
EN1990 Annex A2.
Excessive bridge deformations can endanger traffic by
creating unacceptable changes in vertical and horizontal
track geometry, and excessive rail stresses & vibrations in
bridge structures. Excessive deformations can also affect
the loads imposed on the track/bridge system, and create
conditions which cause passenger discomfort.
Generally, deformations are calculated using nominal
loads. The live load to be taken into account includes
vertical loading enhanced by dynamic factors, centrifugal,
nosing and traction, and braking. For ballasted decks,effects such as creep and settlement of foundations may
be assumed to be addressed by track maintenance.
Midspan vertical deflection of the bridge under dead and
superimposed dead loads is checked to ensure that the
natural frequency of the structure is within the known
limits of validity of the allowances for dynamic load effects
in the dynamic factors used in design.
Track twist under load occurs when, for a cross section
normal to the track at any given position, the deflection of
the structure under one rail is different from that of the
other rail. Excessive track twist can cause a derailment.
Track twist should be considered for all locations from off
the bridge (no twist) through the transition region onto the
bridge, across the bridge, and through the transition
region off the bridge. Twist is checked along the
centreline of each track over a gauge length of 3m parallel
to the tracks taking into account the worst possible
combination of tracks loaded and position of rail loading.
Track twist should always be checked on skew bridges. It
can also occur to a lesser extent on bridges subject to
eccentric live load, e.g. double track bridges with onetrack loaded.
When comparing track twist with the values permitted in
UIC Leaflet 776-3R the total track twist should be
considered. The total track twist includes any intended
track design twist resulting from the intended rate of
change of cant that may be present in a transition curve in
the track.
Twist effects are likely to be particularly severe for highly
skewed bridges where track twist limitations frequently
govern the overall design of the bridge. Track twist inregions of skewed intermediate supports in a series of
simply supported spans can be particularly critical.
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Unrestrained uplift at any bearing is not permitted to avoid
the resultant vertical displacement of the track and to
avoid premature failure of the bearing. Uplift should be
checked for bearings at the acute corners of skewed
bridges and at the ends of continuous structures.
Uplift at the end of a deck occurs where the deck beneath
the track extends (away from the span) beyond the
bearings. The vertical downward deflection within thespan is matched by a corresponding upward deflection of
the deck beyond the bearing.
Uplift is limited to avoid destabilising the ballast and limit
uplift forces on track components and ensure acceptable
additional stresses in the rails. Current thinking is that the
limits in UIC 776-3R are not adequate. To maintain
acceptable track quality, recent European research
indicates that the uplift should not exceed about 2mm and
this limit (also in EN1991-2) is likely to be included in a
future Network Rail standard on the design of bridges.
Vertical deflection at midspan under rail loading is
checked to ensure acceptable vertical track radii, that the
structure is not significantly different in performance to
existing rail bridges, and to ensure acceptable levels of
vertical acceleration inside coaches corresponding to
satisfactory passenger comfort.
To simplify bridge design and avoid the need for
train/bridge dynamic interaction, analyses permitted
span/deflection ratios as a function of structural
configuration, span length, speed and passenger comfort
are currently given in GC/RC5510 and UIC Leaflet 776-
3R. These requirements are likely to be superseded by
the advice in EN1990 Annex A2.
In addition, with the maximum adverse rail loading pattern
the maximum vertical deflection should also not exceed
L/600 (EN1990 Annex A2).
For requirements relating to the twist effects of vertical
deformation - which can dictate design - see the above
section on Track twist.
Longitudinal load effects generated in the track by vertical
deflection of the deck etc. Vertical deflection in the spancause a rotation about a transverse axis at the end of the
deck and, depending upon the height of the upper surface
of the deck above, the bearing a corresponding
longitudinal displacement. Together with longitudinal
displacement of the substructure, traction and braking
loads and temperature contraction and expansion these
actions develop additional stresses in the rails and
additional forces on the bearings.
This combined response of the bridge to variable actions
is called track/bridge interaction and can dictate the
design of longer span bridges, multiple spans or continuous bridges. Where track/bridge interaction
checks are required to be carried out by GC/RC5510,
EN1991-2 6.5.4 should be assumed to supersede the
advice in UIC Leaflet 774-3R (also see below).
Rotation of the ends of the deck about a transverse axis
under rail loading: Checks are made on the rotation of the
end of the deck or between the ends of adjacent deck to
limit uplift forces on track components and ensure
acceptable additional stresses in the rails, and limit
angular discontinuities in rail expansion devices and at
switches.
EN1991-2 specifies the relevant requirements. Wheretrack/bridge interaction effects are required to be taken
into account the associated checks on limiting additional
rail stresses may be critical.
For decks with non ballasted track the effect of rotation of
the end of the deck and any uplift at the end of the deck
should be taken into account when determining the load
effects on the rail fastenings, and compared with the
relevant limit state (including fatigue) performance
characteristics of the rail supports and fastening system.
Longitudinal displacement of the end of the deck: Wheretrack/bridge interaction effects are to be taken into
account then the limits in EN1991-2 section 6.5.4 on
longitudinal (and vertical) displacement of the ends of a
deck should be satisfied.
Lateral deformation of the deck under variable loads should
not exceed the maximum values given in UIC Leaflet 776-3R
to ensure acceptable track geometry and passenger comfort.
The limits are defined in terms of the maximum permitted
change in track radius and the maximum change of angle at
the end of a deck. The maximum change of angle is about a
vertical axis and should be assumed to apply to both ends of
a deck and to the maximum total change of angle between
adjacent decks.
To avoid the occurrence of resonance between the lateral
motion of vehicles on their suspension and the bridge:
• the lateral flexibility of the bridge should not exceed the
limit in GC/RC5510 clause 19.8.4
• the lateral frequency under permanent loads should not be
less than the limit in GC/RC5510 clause 19.8.4
The above limits are not likely to be critical for short to mediumspan bridges with solid decks and high in-plane shear stiffness.
Vertical acceleration of the deck: For bridges designed for
speeds in excess of 125mph or for "lightweight metallic decks"
for speeds over 100mph, additional checks are required to
ensure that the bridge deck will not be subject to excessive
dynamic effects including resonance. In such cases,
additional vibrations limits relating to the magnitude of deck
acceleration are required to guard against the risk of ballast
instability. The design of these bridges is outside the scope of
this paper and further advice should be sought from Network
Rail (as indicated above, studies of the dynamic behaviour of the modern standard Network Rail box girder bridge indicate
this form of construction is satisfactory for speeds up to
125mph).
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Effect of deformation on clearances and drainage: When
checking clearances and designing drainage, allowance
should be made for deflection of the structure, e.g. the
relative deflection between the track supported by a
bridge and an adjacent platform carried on a structure
independent of the bridge can govern the design of a
bridge for medium to long spans.
2.2.3 Structure Gauge requirementsIn the design of many railway bridges the space permitted
by the structure gauge for fixed infrastructure is utilised to
its maximum extent.
The shape of the structure gauge, along with the available
construction depth and any width constraints arising from
reusing existing abutments and restrictions on
construction methodology determines the potentially
feasible structural forms at a site.
Depending on bridge span and deck width, half through
forms of bridge construction use the depth from soffit totop of main girders:
• up to top of rail level for the narrowest decks
(shallowest floor structural depth)
• up to platform level for medium spans with the resultant
longer transverse spanning floor members requiring
slightly greater construction depth
• where the above height provides insufficient depth for
adequate main girders, the width (and hence depth) of
the floor is increased to enable the main girders to be
placed outside the "structure gauge"
Details of structure gauge requirements are contained in
the relevant railway standards.
2.2.4 Safe working environment
The design of the bridge should minimise risk to people on
or about the bridge - whether they are:
• staff working on the structure
• other infrastructure maintenance staff, or
• unauthorised persons
Care should be taken to meet statutory requirements for
safe working areas at height with the design providing
adequate handrailing etc.. Kickers should be provided to
walkways and also detailed to minimise the risk of items
on the walkway falling onto persons below the structure.
Similarly narrow gaps between elements at track level
should be infilled to minimise the risk of ballast falling on
persons below. Minimum bolt sizes and plate thicknesses
should be selected to ensure these elements meet the
requirements taking into account the likely section loss in
the life of the structure.
The relevant standard should be consulted for the
requirements relating to the provision of walkways and/or
continuous positions of safety across the structure.
Handrailing on the tops of abutments between adjacent
decks should be provided with mesh infill to retain debris
caught by the passing slipstream of trains. Generally, new
brick walls should not be provided in these locations to
minimise the risk of brickwork hitting persons below in the
unlikely event of the wall being hit by a derailed train.
2.2.5 Accommodate requirements of other
discipl ines including operational requirementsThe structural form and detailing of the bridge should be
designed to ensure a satisfactory interface with other
railway disciplines including:
• accommodating the track curvature, cant and position
• accommodating future track slues and lifts (in addition
to the design accommodating generous tolerances in
the as constructed position of the deck
• accommodating common and site specific track
configurations and component details
• ensuring no adverse effect on signal sighting
(especially ground signals)
• ensuring no adverse effect on sight lines for train
dispatch staff
• minimising the risk of trespass and vandalism at the
site
• accommodating specific infrastructure specified by
Network Rail such as signals, point machines, location
cases for signalling equipment etc.
• including provision for cable routes for signalling
telecommunication, electrical control and electrical
power cables across the bridge
• accommodating track drainage requirements
It is recommended that the design of the "corners" of the
bridge be undertaken at an early stage as it can affect the
final size and configuration of the superstructure. Care is
needed to ensure that requirements relating to the site
constraints relating to structure gauge, bearing positions,ballast wall arrangements, size of existing abutment tops,
adjacent infrastructure, access to bearings, walkways on
and off the bridge, cable route requirements, ballast
retention etc. are met.
2.2.6 Aesthet ics
The appearance of the bridge should reflect the importance
Network Rail places on its investment in infrastructure.
Generally the structure should be sympathetic to its
surroundings. A number of the essential requirements for
the safety of the structure tend to dictate structural forms
and member sizes which tend to give railway bridges adistinctive appearance. Honesty in structural form should be
respected and care taken with structural details, to provide a
visual demonstration of Network Rail's commitment to
maintaining and enhancing the nation's railways.
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Any planning applications or consultation with planning
authorities should always be through Network Rail to
ensure the project enjoys Network Rail's planning rights.
Additional requirements apply to the renewal of listed
structures or structures in conservation areas and in such
cases advice should be sought from Network Rail on the
particular requirements for the project.
2.3 Abnormal si tuat ions (unplanned)
In addition to performing satisfactorily under normal
operations bridges are expected to meet their required
functions/not suffer damage disproportionate to the cause
of the accidental situation.
2.3.1 Resistance to "bridge bash"
Coincident with the renewal of an underline bridge the
opportunity should be taken to ensure that the resultant
structure can continue to carry rail traffic in the event of a
"bridge bash" at the site.
In addition to the requirements in Network Rail's
standards, the designer should also consider the following
strategies:
Avoid
is it reasonably practical to provide an increase in
headroom to 5.7m to make bridge strikes unlikely?
Protect
provision of a protection beam (these should not
carry critical functions such as signalling cables)
Mitigate
restrain the bridge from moving sideways / restrain
uplift
add mass to the structure
provide a flat soffit or ensure floor can adequately
carry loads at ULS if one member removed
Robustness
provide stocky flanges
stiffen web
provide additional main girder flange thickness to
compensate for damage / facilitate repair options
(e.g. dressing of gouges in steel)
Design
deck for industry accidental loads
2.3.2 Resistance to derailment
For the much less likely and more extreme situation
relating to the derailment on a bridge the bridge isexpected to withstand the accidental scenario of a
displaced train without collapsing or overturn (En1991-2
and BD37). For such scenarios local damage is tolerated.
Good bridge design also considers the following
strategies:
Protect
the end of main structural girders
intermediate stiffeners by placing them on the outer
side of main girders (if provided to a centre girder the
bridge should be adequate without the stiffeners onone side of the girder)
robustness in main girders
provide internal robust kerbs to protect discrete
elements such as truss members above track level
Mitigate
robust kerbs are provided to retain the train on the
bridge
accommodate the standard rail loading in adisplaced position corresponding to the retained train
the bridge should not overturn and "make the
derailment worse"
single bearing stiffeners should be avoided in the
vicinity of the tracks so in the event of one being
crippled "all capacity is not lost"
Design
for industry loads
Bridge decks are also designed to resist a point load of
250kN to ensure they have adequate robustness and to
cater for jacking forces generated by rerailing equipment.
The above requirements generally preclude open mesh
infill to grillage floors
2.3.3 Other unforeseen accidental scenarios
Other unforeseen accidental scenarios are mitigated by
general robustness.
For particular issues such as ship impact the relevant
industry standards should be met.
2.4 Abnormal s ituat ions (p lanned)
2.4.1 Track maintenance and renewal
Sufficient ballast depth, typically 200mm, should be
provided to minimise the risk of tamper tynes damaging
waterproofing/the deck (generally a greater ballast depth
will be required to satisfy track construction standards).
Decks with more than one track should be designed to
allow for any adverse effects from the removal of track
and ballast on one deck.
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Designers should consult Network Rail on the
requirements for accommodating track renewal plant on
decks on single track lines (e.g. for accommodating single
line track relaying gantries).
Checks should be carried out to ensure new decks can
accommodate the loading from the latest generation of
railway cranes (e.g. KIROW cranes).
2.4.2 Allowance for excessive dynamic wheel / rail
forces on unballasted decks
Unballasted decks without longitudinal timbers should be
designed for a ULS design load of 600kN point force (with
no additional increment required for dynamic effects) at a
single/along any one rail support to allow for the dynamic
forces generated by out of round wheels / wheel flats
(generally mitigated by the mass of conventional track
components).
2.4.3 Replacement of bridge parts
Provision should be made for the replacement of partswith a design life less than that of the structure. In
particular provision should be made for jacking the
structure to replace discrete bearings.
2.5 Instal lat ion / demol it ion
Typical constraints that influence feasible structural forms
and details include:
• the need to execute bridge renewals with minimal
disruption to users of the railway (dictates the design of
nearly all railway bridges)
• availability of railway possessions to undertake the
installation of the replacement deck
• health and safety considerations dictating acceptable
construction techniques
• the presence of overhead line equipment and
temporary arrangements such as cable bridges for
maintaining railway services throughout the works
• site access and limited site space constraints (e.g.
inner city sites generally require the majority of works tobe carried out off site and site works limited to primarily
installation of whole decks or in-situ installation of
prefabricated units)
• the proximity of adjacent structures and property
owned by Network Rail's neighbours
• generous allowances for construction tolerances,
particularly where component tolerances are cumulative
In addition the risk of possession overruns that disrupt rail
services must be avoided.
Recent advances in bridge construction techniques
utilising the latest generation of high capacity cranes and
transporter systems enable the maximum amount of
works to be competed in advance of the main possession
to install the replacement deck. This tends to reduce
possession overrun risks and enables the structure to
benefit from higher standards of workmanship.
Further discussion of these issues is outside the scope of
this paper and other papers at the conference will expand
on these issues.
3. Conclusions
Network Rail seeks support from all those who influence
the design of bridge renewals to rise to the challenge of
maximising the benefits from our increasing investment in
infrastructure.
The decisions made during design have a major influence
on the suitability of the structure to meet the needs of the
railway’s customers and stakeholders. If we are to
perpetuate the success of the engineers that built and
maintained the railway before us we must ensure that allwork on our bridge stock satisfies the necessary
functional requirements.
This paper supports Network Rail's policy of leading such
works as an expert client in partnership with our suppliers
and identifies the key requirements expected of bridges:
• easy to manage structures with minimal maintenance
costs, no hidden details and the robustness to deliver
reliable rail services under normal and abnormal
conditions
• to carry the required loadings with acceptable
deformation
• with structural forms that satisfy structure gauge and
site specific geometric constraints
•bridge that can be safely constructed and maintained
with minimal disruption to the railway’s customers.
With bridges having an expected life of well over 100
years, it is essential for designers to address the key
business demand for ease of management and reduced
maintenance costs in support of the company's drive toensure railways are more affordable. Designers need to
rise to the challenge of ensuring that the many 100s of
"ordinary" bridges that we replace deliver the performance
and reliability expected of today's railway, and that they
can be built and maintained with minimal adverse impact
on railway customers.
Network Rail places significant demands upon its bridge
stock, and by ensuring that the design of replacement
bridges meets both normal and abnormal operational
needs with margins for growth in traffic, they should serve
us well into the future - thus making the most of theopportunities that arise from bridge renewals.
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4. References
Network Rail Company Standard NR/SP/CIV/020 "Design
of Bridges & Culverts" (Draft)
SCI, "The Design of Steel Railway Bridges", SCI, Ascot
I Bucknall, "Atlantic Road Bridge Brixton", Structural Steel
Design Awards, BCSA, London, 1991
I Bucknall, "New Eurocode requirements for the design of
high speed railway bridges", IABSE Conference, Antwerp
2003,
Various unpublished Eurocode Project Team documents
supporting the development of railway loading and rail
bridge performance requirements in EN1991-2 and
EN1990 Annex A2.
ERRI Committee D214/RP9 Rail bridges for speeds >
200km/h. Final report, Part A Synthesis of the results of D214 Research, ERRI, Utrecht, 1999
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17Railway Bridges - Today and Tomorrow
Paper Two
Repair and Strengthening versus Renewal
Matthew Kynoch
MOTT MacDONALD
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Introduction
To determine the investment for an existing metallic bridge
asset, a logical process must be adopted with significant
business / strategic and technical milestone appraisals in
order to provide a cost effective means of safeguarding
the integrity of the operational railway.
The majority of metallic rail bridges were constructedbefore 1914 and many have already exceeded the
notional design life of 120 years as stipulated by modern
design standards.
The bridge stock has to be appropriately managed as they
all require regular inspections, assessments and routine
maintenance to verify their performance and structural
integrity. However, in general terms the bridge stock, as a
whole, has performed well exhibiting common conditional
and strength problems despite increased traffic loadings
and intensities. It is therefore inevitable that some will
require repair and strengthening or even completesuperstructure renewal.
This paper will aim to identify potential efficiencies by:
• Identifying the key evaluation criteria for comparing
life cycle costing between strengthening and renewal
schemes, including design and implementation best
practices which may influence the decision as to
whether to strengthen or renew
• Addressing theoretical shortfalls in a generic manner
by the identification of common problems and commonsolutions be that through changes to standards or
generic strengthening/repair details
When considering repair and strengthen versus renewal
of a particular bridge, the following key structure related
issues are of importance to the bridge owner:
• Safety of the structure and those that may be affected
by the structure
• Condition of the structure
• Load capacity of the structure in terms of strength and
fatigue/residual life
• Robustness/structural redundancy and resistance
against impact
• Provision of adequate clearances (gauge) between the
structure and the traffic on and beneath the bridge
Bridge Assessment
Before embarking on repair, strengthening or renewal it is
important to maximise both the assessment and condition
appraisal to determine the structure's safe load capacity
and life expectancy. To achieve this to the full, the
assessment codes must be challenged and all available
analyses/assessment techniques exhausted with
sufficient site inspections, intrusive investigations
undertaken to make an informed view on the residual life
of the structure.
Other factors that may be considered are increased
material strengths and operational restraints such as
speed and/or load restrictions. There are other appraisal
techniques available to validate assessment, such as Non
Destructive Testing, structure monitoring and load testing.
If the final assessment identifies a residual shortfall in
capacity, then increased capacity may be achieved in a
number of ways, for example by: 'Strengthening' including
modifying the infrastructure whole structure actions
(adding additional load distributing members); changing
local load paths (by the provision of additional primary /secondary members), or by local strengthening of
individual elements/components or by Renewal.
Feasibility studies are commissioned for structures where
there are obvious advantages and disadvantages for
repair/strengthening and renewal. The information
contained in these reports will form the basis of the
decision whether to repair and strengthen or renew.
Common Problems
Theoretical assessment failures generally fall into
common categories and considering that there are very
few known bridge failures various studies are on going to
challenge the code to see what conservatism, if any,
exists between theoretical shortfalls and actual behaviour.
Common strength problems with theoretical failures are
as follows:
• Centre main girder web shear
• Flexure governed by lateral torsional buckling /
effective length/'U' frame action
• Rivet capacity (shear/bearing)
• Bearing stiffeners
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Common condition related problems:
• Corrosion to trackside faces of webs/stiffeners located
just above ballast/deck plate level (splash zone)
• Deterioration of girder ends/bearing plates where water
runs off the ends of the deck
• Corrosion of metalwork through poor management of water through trough floors and deck plates
• Corrosion of supporting members directly beneath
wheel timbers
Repair and Strengthening
Traditional strengthening techniques involve the
installation of piecemeal steel plates connected byfasteners / welds so that they act integral with existing
structural components to resist a proportion of the live
load effect, noting that it is usually assumed that
permanent load effects are locked into the existing
structure unless otherwise alleviated during the
strengthening works.
One of the common problems following the assessment is
the theoretical shortfall in centre main girder end shear. It
is known that the assessment code has been updated and
is currently being further examined to see if any changes
can be made to enhance capacities to reduce potentialtheoretical failures. A 'top hat' generic repair solution has
been widely used to overcome this problem but has it
limitations as the top hat has to fit outside the existing
lower sector structure gauge clearances but nonetheless
is a very effective solution to improve structure capacity at
a relatively low cost.
Over recent years there has been a gradual introduction
in the use of Fibre Reinforced Polymers (FRP) or steel
plates bonded to the substrate to strengthen existingNetwork Rail structures. FRP have good fatigue and
corrosive resistance and are quick to install, non evasive
and benefits can be realised where welding or bolting is
not permitted, for example, when strengthening of cast
iron.
In knowing the common problems with metallic structures
through a maturing assessment programme, better
grouping and generic repairs can be formulated - a
generic top hat solution being a good example.
Renewal
The available construction depth, lateral clearances and
track positions will to a large extent dictate the deck
replacement option. The majority of existing structures
and subsequent deck replacements tend to be of a half
through type nature with a relatively shallow floor, limiting
the choice of replacement. Direct fastened track forms,
such as 'Edilon' where construction depth is restricted,
have been used but are not generally preferred due to the
maintenance management issues associated with them,
i.e lack of flexibility for track adjustment/tamping
operations.
Standard Design Details have been produced for a
number of bridge types, the principles of which are widely
used and referred to when considering deck
replacements.
Evaluation Criteria
When evaluating repair and strengthening versus
renewal, there are a number of key factors that need to be
considered on a bridge specific basis in order to arrive at
not only the most cost effective solution but the correct
solution for the particular asset in question.
The Four key evaluating criteria are as follows:
• Residual/Design Life
• Availability of funds
• Disruption (possessions/road/river closures)
• Site specific constraints (access/railway infrastructure
/third parties)
Residual/Design Life
The debate on design life will remain as to what lifeexpectancy can be reasonably realised through repair and
strengthening of a 120 year old asset, but provided that
the structure is not showing signs of distress or fatigue
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Paper 2 Repair and Strengthening versus Renewal
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Figure 2 - Typical Girder Web corrosion
Figure 3 - Typical Top Hat Solut ion
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damage, it is reasonable to suggest, through regular
future maintenance - post strengthening - that the
structure can sustain another 120 years in service.
However, most repair and strengthening schemes tend to
have a design life in the region of 30 to 50 years
associated with them.
It is also essential to recognise when a bridge is 'life
expired' or the risk of latent defects is unmanageable anda replacement solution is more appropriate than repair or
strengthening. To make the decision whether to
strengthen or renew, it will also be necessary to take into
account the economic benefits the existing structure
brings to the Network, and the structure's
environment/aesthetics as well as its value to the
community.
Availabi li ty of funds
Key determining factors can be evaluated when
comparing the merits for and against repair andstrengthening versus renewal for a single span or small
spanning multiple span structures. However for large
structures renewal is likely to be prohibitive, due to its vast
size, location/difficult access, environment and terrain it
spans over, and often repair and strengthening is the only
option considered.
For instance, there are very few examples of large remote
structures spanning over water that have been replaced
and those that have are usually as a result of concernsraised by sudden changes in perceived capacity or other
strategic reasons.
These structures require major advance planning/funding
and for the purposes of this paper and the criteria for
evaluating repair and strengthening versus renewal, only
single span or small multiple span structures will be
appraised.
There is an obvious funding difference between repair and
strengthening schemes versus complete superstructure
renewal schemes. Depending on size and complexity, theexpenditure for a typical replacement scheme is likely to
be in the region of £500k to £1M, whereas repair and
strengthening schemes the initial outlay is nearer £150k to
£500k. This combined with future maintenance and other
costs to determine projected whole life costs has to be a
major contributory factor when considering which route to
take.
The status of the bridge is a key factor in firstly prioritising
work on the network whereby primary routes are often
looked upon differently to other routes. For example a
structure on a mainline which has cost benefits instrengthening over reconstructed may be renewed for the
very fact that it has an undesirable track form (wheel
timbers) and can easily be replaced with a concrete (low
maintenance) deck.
Where a marginal cost advantage is to be gained through
repair and strengthening as opposed to renewal, or
whereby the strengthening is of a complex nature, or if
significant hidden parts exist which could warrant
subsequent repair, it may be prudent to reconstruct.
Where track lifting or road lowering is considered
necessary to achieve the desired construction depth, thiscan often angle back in the favour of repair and
strengthening, but nonetheless be considered during the
feasibility stage.
Advantage can be taken of carrying out more than one
repair and strengthening/replacement scheme on the
same line within the same possession, effectively
combining possession related incurred costs (tamping
machine/Permanent way resource etc.) and also
efficiencies can be realised in combining compound
facilities, resources. However, careful consideration
should be given to combining too many schemes at the
same time as the specialist expertise and competency
required in this field is limited.
The extent of the scope of repair and strengthening can
often result in a structure being reconstructed due to the
amount of disruption or rail possessions a repair and
strengthening scheme would require.
Disruption (possessions/road/river c losures)
The implementation cost is not necessarily directly linked
to the requirement to minimise disruption but the need for
possessions/road/river closures is likely to dictate theconstruction programme and the resource required to
complete the works in order to meet that programme.
In general terms repair and strengthening schemes are
considered to be less disruptive to rail/road/river
commuters whereby the work is typically carried out in
rules of route or shorter abnormal possessions. Compare
that to replacement schemes where 52 hours weekend
possessions are generally taken to remove the existing
and install the new bridge deck.
However, the public (non-rail users) may perceivestrengthening to be more disruptive as the programme
tends to be prolonged to suit preparatory work, piecemeal
erection and rail possessions and often underline bridges
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Figure 4 - Hamble Viaduct Strengthening
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will require partial/full road closures for a period of weeks
to enable refurbishment/painting works to the soffit to be
undertaken. However, the public's appreciation of the
effort taken to avoid the need for disrupting trains often
goes unrewarded.
Noise generated by the works is not often looked upon as
a criteria for determining whether the structure is renewed
or strengthened but could have an influence on how thework is to be undertaken. Bridge sites located within built
up areas where significant rivet removal is required
usually receives its fair share of complaints as it is more
often confined to night times when trains are not running ,
and dependant upon the scope of rivet removal, can take
several weeks to remove. Often mitigation measures are
put in place to dampen the sound but from the public's
perception can be seen as disruptive or an inconvenience.
Whereas a bridge reconstruction is relatively intrusive at
the time but the duration over which it occurs is relatively
short and usually well publicised in advance.
The number and duration of trackside possessions for
repair and strengthening schemes can sometimes be
dictated by the need for trackside painting works, many of
which contain original lead pigment. Depending upon the
complexity of the structure and the ease in which
protection boarding/screening can be erected - to protect
not only the trains but against contamination of the
adjacent surroundings - the erection and dismantle time
can absorb a large number of possessions.
If there is insufficient space available to effectively screen
the operational railway from painting activities (such as
centre girders), significant possessions are required to
allow for encapsulation, blasting and reapplication of
protective treatment. As a compromise mechanical
cleaning and single coat paint systems are often adopted
to reduce the number of possessions and complexity of
the encapsulation system.
In some instances it may be more beneficial to remove the
painting from the strengthening contract and combine a
number of painting schemes on the same line to minimisethe overall disruption.
Design remits regularly state that strengthening options
are to minimise the need for possessions. In practice this
can be minimised but not altogether eliminated as in most
instances some form of trackside access is usually
required. As a result, design and detailing is becoming
more complex as special emphasis is being placed on
designing out the need for possessions through
innovative methods, such as the need for staged rivet
removal and erection of plates whilst trains run
unrestricted.
Therefore, the residual strength of individual
components/alternative load paths needs to be fully
understood when removing riveted connections, and
when introducing strengthening plates, special attention
to staged tightening of new connections will be necessary
to prevent initiating locked in stresses.
In terms of risk of possession overrun, it is subjective
either way as to whether strengthening or renewal
presents a greater risk, and throughout the design
process, factors that influence the risk are either designed
out or reduced to an acceptable and manageable level.
Strengthening is often piecemeal and can be curtailed at
relatively short notice provided that appropriate mitigation
measures are in place and the original strength of the
structure/component is restored prior to handing back the
possession. Alternatively, a complex strengthening
scheme may require substantial removal of existing
components that necessitate the need for the complete
reinstatement or some form of temporary works to be in
place prior to handing back.
Conversely, with a deck replacement, by the introduction
of designed 'fit up' tolerances and complete trial erection,
the risk of overrunning the possession should be
significantly reduced. However, there are always the
'unknowns or unforeseen' that could potentially put a deck
replacement at risk from overrunning, such as crane
failure, weather, services etc..
Site constraints
Deck replacements require an appraisal of the existing
substructures and their foundations to determine the
acceptability of the change in load effects. Qualitative
appraisals are undertaken to evaluate the condition of thesubstructures to substantiate 'steady state' conditions
which are generally supported by numerical calculations,
to justify that peak bearing stresses have not significantly
changed.
Abutment repairs may be necessary as a result of this
appraisal, in addition to checking temporary load
conditions to identify what mitigation measures (propping,
anchors, temporary lowering of fill) are required to prevent
the abutments from overturning/sliding.
It is more often the case that repair and strengtheningschemes require some form of access scaffold to be
erected to facilitate the work. When spanning over water
courses, it is often the desire to support the scaffold
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Paper 2 Repair and Strengthening versus Renewal
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Figure 5 - Rockingham St. Cross Girder 'Bottom Hat' Strengthening
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platform from the structure rather than support within the
water course. This by itself may be prohibitive due to the
fact that more load is being added to an already sub
standard structure and the 'Project Team' must take a
view to see if the increase in load significantly affects the
operational railway. This may necessitate the need for phasing of the works or imposing temporary speed or load
restrictions for the duration of the works.
A common advantage that repair and strengthening has
over renewal is that significant lead in times for plate
ordering or shop fabrication is not normally required, due
to its piecemeal nature. Where the scope of works is not
fully understood and repairs of a generic nature are
programmed, solutions can be fabricated relatively quickly
adopting 'off the shelf' plates and sections in order that
they can be erected in time to meet possession/road/river
closure constraints.
A large number of existing bridges have restricted
clearance and no refuges signs attached to them. Deck
replacements introduce the opportunity to improve the
safety of line side access and track geometry/gauging.
Other factors that may or may not affect the choice and
need to be considered are:
• Stakeholders/Third Party Interfaces
• Planning/Listed Building Restrictions
• Statutory Undertakers services and the requirement
for protection/diverting around the works
• Overhead Electrification and whether it can be left in
place during either strengthening, or more likely during
removal of existing and installation of new bridge decks
• DC Third Rail and access required to strengthen
girders positioned within the 'six foot'
• S&T, Power Cables and the requirement for
protection/diverting around the works
• Environmental conditions, watercourses, SSSI,
Protected species, bats etc.
• Requirement to improve headroom or the need for
collision protection beams to prevent mechanical
damage to exposed vulnerable elements
• Requirement to remove undesirable features, such as
wheel timbers, cast iron supports etc.
• Requirement for reapplying waterproofing to the deck
The very fact that structures where remote or difficult
access exists are often in poor state of repair and are up
for implementation due to the complexity in undertaking
previous routine maintenance tells its own story. Where
works are programmed to these structures, the solutions
adopted should either be very low maintenance or have
provision to access the structure for inspection and to
allow routine maintenance in the future to prevent
subsequent deterioration.
Conclusion
There is no straightforward answer on the decision
whether to repair and strengthen or renewal a bridge
asset.
Subject to funds and possession availability, structures
will generally fall into three categories:
• Bridges that are weak and obviously life expired are
replaced
• Bridges that are generally of sound condition and can
be repaired and strengthened at reasonable cost
• Bridges that are marginal:
Generally weak and uncertainties with condition but
can be repaired and strengthened at a cost. The site
however incorporates significant other key
determining factors that detract from reconstructing,
such as: access, impact on rail infrastructure and
third parties, track form, location etc.
The feasibility and evaluation process provides us with
useful information to enable an informed decision to be
made as to whether a structure should be repaired andstrengthened or renewed. However, marginal decisions
may be formulated on a qualitative basis or engineering
judgement or some other unique overriding factor.
Cost Efficiencies could be made by advancing code
knowledge and/or by advancing the present work on
generic repair details to capture generic strengthening
details, both traditional and novel, to reduce the scope or
number of strengthening and renewal schemes. It is also
worth noting that Network Rail currently have an ongoing
commission to identify the need for and development of
further Standard Design Details for replacementunderbridges.
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Railway Bridges - Today and Tomorrow 23
Paper Three
Jamestown Viaduct - Innovative
Strengthening of an Early Steel Viaduct
Robert Dale and Andrew Hanson
CORUS RAILWAY INFRASTRUCTURE
SERVICES
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Background
Jamestown Viaduct was constructed between 1887 and
1890 as part of the Forth Bridge Railway. It is believed to
have been designed and constructed by the engineers
responsible for the world-famous Forth Rail Bridge,
located a short distance to the South.
Jamestown Viaduct is situated between NorthQueensferry and Inverkeithing stations. The line over the
viaduct forms an important link for long-distance traffic
from Edinburgh to Dundee and Aberdeen, and for
commuter traffic from Fife into Edinburgh. The line is also
used by a significant amount of freight traffic, principally
coal being transported to Longannet Power Station.
The viaduct comprises six spans. The four main spans
have early steel superstructures of 33.4 metres span and
approximately 70 degree skew supported by masonry
piers and abutments. A single masonry arch span pierces
each abutment. Each span of the steel superstructures
comprises two simply supported main truss girders with
cross girders supported on the top chords in turn
supporting railbearers. Asteel deckplate fixed to the top of
the cross girders and railbearers supports ballasted track.
The cross girders, railbearers and deck plates are
believed to have been replaced in the early twentieth
century.
The Rosyth Dockyard branch line railway passes beneath
Span 2 and Span 4 crosses the B981 public road. The
bridge soffit is approx. 16m above the rail level of the dock
branch line railway and 12.8m above road level. The other
spans cross open ground.
Because of its height and location, Jamestown Viaduct is
a significant landscape feature and was given 'Category
B' listed building status by Historic Scotland in 2004.
Structural Capacity
Network Rail Scotland has responsibility for ownership
and maintenance of the structure. A structural assessment
carried out by Babtie Group in 2000 on behalf of Network
Rail had found that the main trusses, including both top
and bottom chords, were overstressed.
This assessment was undertaken in accordance with the
then current Railtrack Code of Practice RT/CE/C/015
which used 'permissible stress' criteria. With the advent of
the new 'limit state' Network Rail Assessment Code
(RT/CE/C/025 - Issue 2), Atkins Rail were commissionedto carry out further assessment work. Their report was
issued in October 2004. The findings of this assessment
were broadly similar to those of the earlier assessment in
terms of deficiencies in capacity of the metallic spans.
A brief summary of the dynamic capacities of the various
elements of the bridge are shown below:
Top Booms RA1
Bottom Booms RA1
Ties RA0
Struts RA10Cross Girders RA7 (Shear)
The masonry piers, abutments and arch spans were also
assessed and considered to be adequate.
The report also noted that the paint system had broken
down, allowing moisture to penetrate through to the
steelwork, causing severe corrosion in places.
Strategy for Strengthening
An eight day blockade had previously been arranged for
repair and repainting works to be carried out on the Forth
Rail Bridge during late July 2005. Network Rail recognised
an opportunity to take advantage of this blockade to also
carry out works to Jamestown Viaduct, and instructed
their Civils Framework Contractor, Mowlem, to develop
proposals for a strengthening scheme with this in mind.
Network Rail and Mowlem jointly organised a value
management workshop at which a number of
strengthening and reconstruction options were
considered, with the aim of increasing the capacity to
RA10 at a linespeed of 40mph. Following further
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Paper 3Jamestown Viaduct - Innovative Strengthening of an Early Steel Viaduct
Railway Bridges - Today and Tomorrow
Figure 1 - Aerial Photograph of viaduct.
Figure 2 - West Main Truss Girder Top Boom, showing poor
condition of paint system and resultant corrosion
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discussion, three main options were identified:
• Strengthening of existing superstructure by adding
new steelwork to existing members
• Install new spine truss/beam between existing truss
girders
• Post-tensioning of existing main truss girders
In order to investigate the potential sub-options for the 3
options identified at the value management workshop, it
was agreed that the framework delivery team would ask
shortlisted civil/structural engineering consultants to
tender for the design services element of the Jamestown
project. The tender was prepared in such a way as to
encourage innovative proposals.
Seven completed tenders were received from the
shortlisted consultants and these were appraised and
scored based on a number of factors, including:
• Buildability
• Cost
• Risk
• Programme duration
• Railway possession usage
• Railway temporary speed restriction requirements
• Effects of work on remaining structure
Because of the viaduct's listed building status,
preservation of the existing structural form was also a
significant objective.
Two options were identified and proposed by Corus as
part of their submission:
• Strengthening by the addition of a new central truss
girder beneath each of the spans to support the cross
girders at their mid point and to relieve the existing
truss girders by pre-loading
• Removal of the track and ballast and replacement
with an in-situ reinforced concrete slab designed to act
compositely with the existing steel truss girders and
incorporating a direct fastening track system
Strengthening of the existing steel members was
considered, but a practical solution was not considered
possible because of the amount of additional
plates/sections that would have had to be added to the
existing sections, and in the case of the top chord of the
truss in particular, the obstructions formed by the
connections to other members at the truss nodes.
Complete reconstruction was considered but rejected on
the grounds of the much higher cost and short timescales
available for implementation using the 8 day blockade.
A second value management workshop was held and it
was agreed that the option to be taken forward should be:
"Installation of new composite deck and plating
repairs/strengthening works to the existing structure"
Network Rail then produced a report on the second value
management workshop which was then adopted as the
Project Brief and included within the Project Definition
Document.
The composite solution proved attractive in that itsignificantly reduced the extent of strengthening work
required to the existing steelwork and preserved the
overall appearance of the original structure. It also met all
of the project requirements in terms of buildability, cost,
risk, programme, possession usage and temporary speed
restriction requirements.
By employing value management and value engineering
to agree the scheme selection, the project team identified
the best value option which met the aspirations of the
project, thus ensuring efficient investment to allow
continued unrestricted operation of the railway over theviaduct.
Scheme Development
Composite structural action between the reinforced
concrete slab and the existing structure was designed to
be achieved by welding 8,600 shear studs to the existing
deck plates and by the addition of steel diaphragm panels
between the deck plate and main truss girder top chord in
order to transmit shear between the deck plates and top
chord of the main truss girders. The rows of shear studs
were aligned parallel to the existing railbearers above the
main trusses and to the existing cross girders.
The condition of the existing deck plates would not be
revealed in its entirety until the track, ballast and existing
waterproofing were removed early in the blockade. During
the early stages of scheme development site
investigations were carried out, including trial pits on thebridge deck, which showed the deck plates to be in
relatively good condition at the locations exposed. Further
random non-destructive testing of the deck plates showed
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Figure 3 - Shear Studs welded to deckplate above main
girder top flanges and cross-girders
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the thickness of the plates
to be acceptable. To
prove the feasibility of
welding the shear studs to
the deck plate, trials were
carried out during the site
investigations by welding
a small number of shear
studs to the areas of deckplate exposed in the trial
pits and testing the
connection of the studs to
the deck plate. These
trials were wholly
successful and proved
the strength of the
connections would be
adequate.
It was considered that there was still a risk of previously
undetected corrosion and other defects to the deckplatebeing revealed once the deck was exposed in its entirety,
and a supply of steel repair panels was fabricated
complete with studs already welded to them to cater for
this eventuality.
Overloading of the deck plate by construction plant and
equipment during the blockade was also identified as a
risk and detailed calculations carried out to determine the
allowable level of loading on the deck. Restrictions on the
size and position of plant on the deck were also enforced
to ensure the deckplate was not damaged.
Testing of the original
metal used in the
construction of the
viaduct was also
undertaken to assess the
problems likely to be
encountered in welding to
the original steelwork.
The installation of the
concrete slab and
diaphragm panels
eliminated the need tostrengthen the top chords
of the main truss girders
by plating and also
significantly reduced the
extent of strengthening required to the other members.
A departure from the design code was also agreed to
allow the shear capacity of the cross girders to be
enhanced by the addition of the concrete deck slab, thus
eliminating the need for further steelwork strengthening.
The main truss endposts, bottom chords and the diagonalties within the first three bays at each end of each girder
were all found to be overstressed. The existing ties
comprised pairs of steel plates and strengthening was
achieved by the addition of new steel H-section struts
dimensioned to fit between
the existing ties. Welded and
bolted gusset plates
connected these members to
the existing truss bottom
chord and vertical members.
This strengthening also
partially relieved the load on
the truss end posts whichwere strengthened by the
addition of steel plates
welded to the external faces.
The bottom chords were also
found to be overstressed and
strengthening comprised the
addition of lower flange plates
welded to the existing
members to convert the open
section to a "U" shape. Careful detailing was required to
ensure that the trough created would drain and not allow
water and debris to pond, thus accelerating corrosion.
The skew ends of each span are supported by trimmer
trusses, the top chords of which support the trimmed
cross girders. The trimmer trusses frame into the end
posts of the main truss girders. These trimmer trusses
required strengthening to support the new deck slab, and
this was achieved by the addition of steel plates and
sections welded to the existing members. Several
members also required replacement due to extensive
corrosion of the original steelwork.
Many of the existing plan and
vertical bracing members
were overstressed and rather
than strengthening the
existing members, new
replacement sections were
designed, including the
temporary works required to
facilitate installation.
Many of the existing bracings
and associated gusset plates
were heavily corroded and
repair details were developedfor various scenarios
anticipated from the available
inspection and assessment
records. Detailed inspections
were carried out by Corus once access scaffolding was in
place and the extent of condition-led repairs agreed with
Mowlem and Network Rail. These inspections also
allowed detailed templating to be undertaken so that steel
sections could be fabricated off-site in "shop" conditions.
The design model was used to investigate the stability of
the structure at all stages, which was particularly critical toprioritise the sequence of works and agree loading
restrictions, etc. at the various stages of the work.
The existing steel lattice girder parapets were retained to
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Paper 3Jamestown Viaduct - Innovative Strengthening of an Early Steel Viaduct
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Figure 4 - Installation of new diaphragm plates in the apertures
between the top boom of the main truss girders and the deckplate
Figure 5 - Installation of new struts in the end panels of the
main truss girders
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preserve the appearance
of the viaduct, but had to
be raised by the addition
of a tubular rail supported
300mm above the top of
the existing parapet. A
new steel ballast plate
was designed to retain
the increased depth of ballast and prevent
spillage through the open
latticework. This also
removed the lateral
loading from the ballast
onto the existing lattice
parapet. Steel mesh
panels were also installed
to prevent ballast from falling onto the public road beneath
the viaduct.
The original deck drainage system comprised a series of steel pipes on a grid pattern hanging vertically from the
deck between the main trusses. A number of these pipes
were severely corroded or missing. Construction of the
deck slab required removal of the existing pipes and the
whole system was replaced with outlets located at the
ends of each span which discharge the drainage water
clear of the steelwork superstructure.
Permanent Way
The initial composite deck concept developed by Corus
included direct fastening track, with the rails supported in
special baseplates fixed to the new reinforced concrete
deck slab. This matched the construction depth of the
original structure and only
marginally increased the
dead loading. The track
over the viaduct is curved
and quite heavily canted.
The practicality of
achieving the required
track tolerances during
the main blockade was
discussed in detail withthe client and considered
to be a significant risk
considering the short time
available for construction
of the deck slab. Concern
was also expressed
regarding the transition
zone at each end of the viaduct, where the deck slab
interfaces with the much more flexible conventionally
ballasted track. Track maintenance is generally difficult in
the transition zones, particularly where the alignment is
curved and lateral forces cause the ballasted track tomove, creating a kink in the alignment of the track at the
deck end.
From a maintenance
perspective, Network Rail
preferred to retain ballasted
track over the viaduct and
Corus were asked to
investigate the feasibility of
lifting the proposed rail levels
to accommodate this. A lift of
approximately 400mm wasfound to be required across
the bridge in order to maintain
adequate ballast depth
beneath the sleepers to
permit mechanical
maintenance. Further
modelling of the structure was
carried out and demonstrated
that the additional weight of the ballasted track could be
accommodated by the design. Steel sleepers were
employed to minimise both the combined weight of the
track and ballast and the ballast depth.
A new permanent way alignment was designed by Corus
to accommodate the required track lift over the viaduct.
This was complicated by the existing 1 in 70 gradient and
the curved horizontal alignment. To run out the lifts in
compliance with permanent way design standards meant
that the length of track affected extended well beyond the
extremities of the viaduct itself and onto the approach
embankments.
The approaches to the viaduct are on major
embankments, and geotechnical investigations and
stability checks were carried out by Corus to ensure that
the proposed track lifts would not adversely affect the
embankments. Immediately
beyond the ends of the
viaduct, precast concrete
retention units were designed
to support the raised ballast
levels in the cesses. Checks
were also carried out to verify
the stability of the spandrel
walls of the masonry arch
spans.
A colour light signal is located
just off the North end of the
viaduct on the Northbound
(Down) line. Checks were
required to confirm the extent
of alterations required to the
positioning of the signal head
to ensure that the track lift did not adversely affect the
sighting of the signal by drivers of approaching trains. The
final design involved raising the height of the signal head
by means of a spacer and refocusing the signal head.
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Paper 3 Jamestown Viaduct - Innovative Strengthening of an Early Steel Viaduct
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Figure 6- The original proposal for the superstructure strengthening,
showing the direct fastening track system on the concrete slab deck
Figure 7 - The revised proposal for the superstructure strengthening,
showing the ballasted track, new ballast plates and raised parapets
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Implementation
The design and implementation programmes overlapped
because of the tight timescales and the need to carry out
inspections and surveys. Mowlem commenced work on site
during April 2005. Scaffolding was erected to all four of the
main steel spans to provide access for surveys and
inspections and the critical steelwork strengthening works.
Corus engineers carried out surveys to verify dimensions
and identify the scope of the repair works required to each
span. Lanarkshire Welding were employed by Mowlem as
the steelwork subcontractor and they were highly pro-active
in value engineering and buildability studies with the client
and designer.
The steelwork repairs and strengthening were categorized
into work which had to be carried out before, during and
after the main blockade. The new struts were required to
cater for the additional weight of the concrete slab and
ballasted track, and together with the diaphragm panels,
had to be installed before the blockade.
Site access was complicated by the need to negotiate with
neighbouring land owners for access and positioning of site
compounds. Further restrictions were placed on the project
team by the presence of a designated site of Special
Scientific Interest (SSSI) on the South abutment andapproach embankments. Spans 3 to 6 are adjacent to a
new Park & Ride site, including a multi-storey car park
which was completed in May 2005. Site compounds were
constructed to the North West and the South East of the
bridge; the latter also providing vehicular access to track
level for the work to be carried out during the blockade.
Railway power, signalling and telecommunication cables
were present across the bridge and were carried in a
troughing route attached to the Eastern parapet. Various
cabinets containing relays and switching equipment are
located in the cesses at each end of the viaduct. All thecables were investigated to determine whether any were
redundant and the others were slewed clear of the works at
deck level during the main blockade and reinstated upon
completion.
During the main possession, Network Rail also identified
the opportunity to upgrade the signalling system in the area
as part of a separate project. Close co-operation between
the two project teams allowed this additional investment to
go ahead and to share some costs between the two
projects, thus providing financial efficiencies to both teams.
The concrete mix design for the construction of the deck
slab was critical. It had to combine a rapid gain of strength
whilst retaining a suitable "working time" to allow placement
and also be suitable for pumping. Corus provided a
specification, including the strength requirements at each
critical stage of the works and Mowlem investigated the
various options, finally selecting a micro-silica mix designed
by Tarmac Topmix. The concrete was placed by pumping
from ground level (using the largest concrete pump in the
UK). Trials were carried out in advance of the blockade to
prove the practicality of pumping to the required height
without affecting the properties of the concrete.
The steel reinforcement for the deck slabs was
prefabricated in panels in advance of the blockade,
designed to allow final adjustment if required when
positioned on the deck. The existing movement joints in the
steel deck plates at the ends of each span were retained
and incorporated into the new concrete decks.
During the main blockade (23rd July to 1st August 2005)
approximately 20,000 man hours were worked. This
included:
• Removal of existing track, ballast and deckwaterproofing
• Cleaning of existing deck
• Welding of shear studs to deck
• Fixing 120 tonnes of reinforcing steel and formwork
• Placing 600m3 of concrete
• Installing ballast retention units to all 4 corners of the
viaduct
• Installation of new waterproofing new drainage systems
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Figure 8 - Placing of the concrete was achieved using alorry-mounted pump at road level
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Railway Bridges - Today and Tomorrow
• Installing new ballasted track over the viaduct
• Lifting and re-aligning track on the approaches
The work was carried out using two shifts of 12 hours
each to achieve 24 hour working throughout the blockade.
Corus provided continuous design support on site during
the blockade to ensure that any technical issues could be
dealt with quickly and efficiently.
Work continued on site after the blockade to complete the
outstanding steelwork strengthening/repairs and
repainting of the whole structure. As the viaduct has close
engineering links with the Forth Rail Bridge, Network Rail
agreed with the local authority planners to paint the
viaduct in "Forth Bridge Red" to match its bigger brother.
This also sits well with the local authority's aspirations to
have the whole area designated as a "World Heritage
Site".
Conclusion
The project to strengthen Jamestown Viaduct has been
successful because of the integrated approach by the project
team. The design concept was unusual and is thought to be
the first project to achieve railway bridge strengthening using
a composite reinforced concrete slab on a truss bridge. All the
relevant parties involved in the strengthening work worked
closely together to ensure that the project achieved Network
Rail's aspirations and construction issues were given a high
priority during development of the design to ensure that the
final solution could be implemented efficiently. This was
achieved through formal and informal value engineering
involving all of the relevant parties.
Design work commenced in January 2005 to a very
challenging programme dictated by the availability of the
8 day blockade in late July 2005. This required all parties
to co-operate to ensure that the necessary approvals
were obtained efficiently at each of the design stage
gateways. A detailed design risk assessment was also
prepared in order to ensure all design risks were both
transparent and managed.
The overall cost of the scheme was £5.3 million. The
project has successfully met all the objectives previously
set:
• Cost effectiveness
• Preservation of the original structural form
• Minimisation of disruption to railway operations
• Achievement of the short design and construction
programme
• Capacity of the bridge increased to RA10 at 40mph
linespeed.
The project has been nominated for numerous awards
including the 2006 British Construction Industry Awards
and the National Railway Heritage Awards, and has been
shortlisted for the 2006 'Prime Minister's Better Public
Building Award'.
29
Figure 9 - Upon completion of the strengthening works, the viaduct was painted in 'Forth Bridge Red' to emphasise its links with the Forth Rail Bridge
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30 Railway Bridges - Today and Tomorrow
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31Railway Bridges - Today and Tomorrow
Paper Four
Innovative Techniques Used in the Life
Extension Works of Leven Viaduct
Jon Tree
CARILLION
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1.0 Introduction
Leven Viaduct is a 460m long, twin track, 49 span structure
traversing the Leven estuary at the point it merges with
Morecambe Bay. Constructed in 1857, the viaduct’s original
composition was wrought and cast iron. Decks consisted of
2½' deep, simply supported girders and piers were
constructed from multiple 10½" diameter circular columns.
The original structure was designed with slender sectionsto minimise the imposed loads from wind and tides.
As a result of the ongoing corrosion incurred from the
marine environment, the viaduct has been subjected to a
number of refurbishment and strengthening works prior to
the project described in this paper. These have included the
conversion of all forty-eight piers from cast iron columns to
concrete and brick leaf piers, the replacement of span 37
over the shipping channel, the installation of sheet piles to
protect permanent channels between piers and a number
of smaller routine maintenance items.
In July 2005, Carillion Rail were appointed to replace the
entire superstructure to the viaduct. This was required due
to loss of section from corrosion and change in design
codes. Also included in the contract were brickwork repairs
to all 48 piers and the construction of reinforced concrete
robust kerbs and anchor slabs at either end of the structure.
At a cost of £10.5m, the work was successfully completed
within a 16 week blockade between March and July 2006.
The purpose of this paper is to record some of the technical
challenges faced and innovative techniques developed
during the planning and construction process.
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Paper 4Innovative Techniques Used in the Life Extension Works of Leven Viaduct
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Figure 2 - Aerial view of Leven Viaduct
Figure 1 - Works i n progress
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2.0 History
Developed as part of a conceptual scheme initiated by
George Stephenson to create a railway around
Morecombe Bay, the Leven Viaduct was constructed by
contractors W & J Galloway for the cost of £18,604.
Initially constructed as a single track, the viaduct was
designed specifically to assist widening at a later date to
accommodate dual tracks.
Site investigation prior to construction failed to establish
the presence of bedrock beneath the estuary bed and it
became apparent that the structure would have to be
founded on sands that were 'readily driven away by the
wind when dry'. Various foundations were considered but
the final design was one of 10½" hollow, circular columns
with 2½' discs at the base.
Piles were installed from rigs mounted to moored
pontoons. The method of installing the piles was very
innovative for the time and the subject of much interest.
Once positioned, water was pumped through a hose in
the middle of the pile to an orifice in the centre of the 2½'
discs at the base. This jet served to displace the sands
beneath the pile which, when combined with an applied
alternating rotatory motion, allowed two piles to be driven
to a depth of 6½m at the ebb of a single tide.
The girders for the deck were floated intoposition on pontoons and installed with a
travelling crane. At approximately twice
the length of other spans, span 37 was
constructed in the form of a manually
operated drawbridge to allow the passage
of shipping vessels in the channel beneath
(this was eventually replaced for a fixed
deck around 1904 to comply with new
standards). Rock armour in the form of
rubble-stones were tipped around the
base of the piers to protect against tidal
scour.
In the early part of the twentieth century, considerable
difficulty was experienced in the maintenance of the
viaduct due to constant breakages in the columns around
low water level. Whilst the cast iron performed well both
below and above sea level, accelerated oxidation was
experienced in tidal zones subjected to constant wetting
and drying action.
In 1915, steel caissons were sunk around the six columnsthat made up each of the forty-nine piers and filled with
concrete. With the tops of these caissons at approximate
low water level, the remaining column encapsulation
could be constructed from a 5 course thick brick shell and
also filled with concrete.
With the columns encapsulated, timber trestles were
floated out on high tides and erected either side of
individual piers. These were wedged under the soffit of the
girders to carry the dead weight of the deck and railway
traffic. The tops of the columns were then cut away and
the columns filled with grout. Bedstones and new bearings
were installed before lowering the
decks girders and removing thetrestles.
This project took five years of single
line working to complete.
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Paper 4 Innovative Techniques Used in the Life Extension Works of Leven Viaduct
Railway Bridges - Today and Tomorrow
Figure 3 - Archive photo of or iginal viaduct, showing John
Galloway in the centre
Figure 4 - Original pier design
Figure 5 - Archive drawing, showing the conversion of piers
from cast iron columns to bri ck and concrete leaf piers
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3.1 Access Design and Instal lat ion
Due to the confined, linear nature of the site, access was
identified as one of the key activities in the safe delivery of
the 2006 refurbishment. The following items were
recognised at the planning stage as requiring their own
access:
• Soffit access for new deck installation• Pier repairs
• Edge protection during demolition
• Mobile cages for bearing installation
• Cantilevered walkway to maintain a walking route the
length of the viaduct
The first access required was that for replacing the
existing walkways. 'Up and over' pier end scaffolds were
hung from both bullnose ends of each pier. These
provided a platform 900mm beneath the top of the
bedstones to assist when burning out the existing
bearings, drilling and grouting new bearings and installingnew walkways.
In order to undertake the brickwork repairs, access was
required to the full height of the piers (approximately 6m).
The tidal range at the viaduct varied from nominal, ankle
deep water at low tide to 2m from the deck soffit on spring
high tides. A system was required that would both
withstand the tides and allow access to different levels on
the pier depending on the water level at any given point.
A horseshoe pontoon arrangement was considered that
would fix around the piers and rise and fall with the tides.This was rejected however due to the time restraints it
imposed on the work. Pier repairs would not be feasible
as the tide came in because materials would wash away.
Access to the top section of the pier would be then
restricted to the two hours taken for the tide to go out. The
25 hour cycle of the tides would have also constantly
disrupted shift times.
Remaining soffit access for replacing the main decks was
designed as a boarded walkway spanning from the north
pier end scaffold to the south (1200mm beneath top of
bedstone). Originally designed to be fixed to the pier end
scaffolds, it was observed that by hanging these on chain
blocks they could serve as both soffit access and a
platform on which to execute pier repairs (similar to those
used for window cleaning). In practice these platforms
could be lowered or raised the full height of the pier in less
than ten minutes, although care had to be taken to
observe tide times and keep the platforms in the elevated
position when not in use.
At its peak, the construction program required four
walkways and two decks to be removed a day, resulting in
up to 60m of exposed edge at any given point. Edge
protection was designed as a cantilevered walkway,
drilled and fixed into the existing long timbers by 'hop-up'
brackets.
In areas where decks and walkways were being removed,
barrier tape was erected to demarcate the zone and
custodians positioned to prevent unauthorised access.
Personnel inside the 'exposed edge' zone were instructedby the custodian on the safe walking route and all
personnel adjacent to an edge wore harnesses clipped
onto safety lines.
Once a deck was removed, access was required to
prepare the bedstone and install the new bearings. Mobile
cages were constructed that could be lifted and moved by
road railer as required.
3.2 The Use of Gantries to Replace Decks
To facilitate the replacement of Leven Viaduct'ssuperstructure, each of the 48 spans was considered as four
members: north walkway, north deck, south deck and south
walkway.
Various means were considered for cutting out the original
structure, including oxyacetylene, oxypropane and plasma
cutting. Thermic lances were eventually chosen as the
preferred method due to their speed, resistance to the
elements and ability to reach difficult spots. Existing
walkways were removed and new installed by tandem lifting
from the adjacent line with road railers.
Tandem lifting was also considered for removing the existingdecks. This was rejected however as whilst 12T rail mounted
Plasser cranes had the capacity, the existing deck girders
would not take the applied point loads from the crane's axles.
The final deck installation scheme adopted was two track
mounted gantries. Calculation proved the proposed walkway
section capable of bearing the applied load from a gantry
whilst lifting the heaviest deck unit. A track system was then
designed with a 120mm square box section compatible with
the gantry supplier's leg skates and with a fixing detail to the
new walkways.
Gantry rail sections were then fabricated in 5m lengths with
male/female connections at each end. By 'hay making' these
from the back to the front of the gantry, the gantry could be
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Figure 6 - Deck soffit access, including 'up and over' pier
end scaffolds and mobile, unit beam platforms
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moved the length of the viaduct. Both gantries had motorised
lifting equipment and were moved laterally along the viaduct
by duel operated tirfirs.
Once sufficient new walkways had been installed, a 50T
mobile crane was erected on the west abutment (Ulverston).To avoid in-depth investigation into the capacity of the
existing abutment, a temporary works scheme was
developed that would limit the bearing pressure applied by
the 50T crane to those experienced from the existing rolling
stock in use. Two number 9m long, 1m wide, 400mm deep
reinforced concrete slabs were fabricated and installed in the
up and down line cess for the crane outriggers. With the
crane erected on the abutment and two spans of gantry track
in place on the walkways, the first gantry was constructed on
span 49 (the first span at the west end of the viaduct). This
took 6 days due to strong winds, however in fairer weather it
may have been completed in 3 days.
The first gantry then proceeded east, removing upline decks
and placing them on roadrail trailers on the down line for
removal to Ulverston Station. The second gantry was then
constructed on span 49. This followed the first gantry,
installing new upline decks once the new bearings were
installed.
Once both gantries had reached the east (Cark) end of the
viaduct, they swapped roles and returned to the Ulverston
abutment removing and replacing the down line as they
went. The return journey was found to be significantly faster
(up to five decks installed in a day) as the gantries were not
impeded by scaffold erection (this was all erected in the
upline phase) and the six foot had been removed, reducing
the amount of burning.
3.3 The Use of Direct Fastening Vipa
Baseplates
Before the project, the track was fixed to the deck by means
of long timbers running parallel and fixed to the rail with
traditional baseplates. However, with the maintenance costs
for these timbers escalating due to the limited availability of timber of the required quality, Network Rail were keen to trial
an alternative system.
The system proposed by Network Rail and eventually
realised by Carillion was one of Pandrol VIPA-SP Rail
Fastening Plates bolted to 70mm thick steel stools at 600mm
centres.
The benefits of this system included:
• Reduction in vibration transferred into the deck and piers
due to the internal dampener within the VIPA baseplate
• Reduction in re-radiated noise (use of these baseplates
on a similar structure in Norway was found to reduce
noise levels by 14 dB(A))
• Low vertical stiffness (20 kN/mm) resulting in greater
distribution of axial point loads from rolling stock, therefore
reducing the required capacity from the deck members
• Improved installation tolerances (+/- 1mm in line and
level achievable)
• High electrical resistance which reduces the chance of
circuit problems
• Quick and easy to replace without the need to cut the
rail
From the outset, Network Rail were keen to adopt a 'top
down' procedure for positioning the vipa plates. The use of
40m long slave rails was considered at the planning stage as
a method of aligning the baseplates on the stalls. This was
rejected however due to the requirement for additional road
rail resource (all be it part time) to move these rails about.
To simulate the slave rails, two jigs were designed and
fabricated that fitted snugly into the vipa baseplates at the
correct gauge. The first jig consisted of two cradles shaped
to receive pipe lasers, one cradle along the centre line of
each rail. The second jig contained brackets to receive
perspex laser targets, also positioned along the centre lines
of the rails. By setting out the start and end of any length of
vipa baseplates by traditional methods (total station and
dumpy level), the laser jig could be set to the centre lines of both rails and the target jig used to line and level all the
intermediate baseplates. The use of lasers instead of slave
rails also reduced manual handling risks to the workforce.
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3.4 Plant and Mater ial
Logistics
Prior to Carillion's tender, the
Life Extension Works were
originally anticipated to be
executed over two 16 weeks
blockades a year apart.
However, by developing the
high level methodology
described in 3.2, Carillion were
able to produce a programme
condensing the project into one
blockade.
To reassure Network Rail that
the proposed methodology was
achievable, detailed hourly
programmes were prepared for
repetitive activities such as
deck installation. These werethen subjected to QRA
(Quantitive Risk Assessment)
analysis to investigate the
impact of certain activities (such as scaffold erection, deck
burning etc) taking longer than anticipated or being
delayed. Whilst the program had very limited float, the
QRA analysis produced sufficiently positive results to gain
the clients confidence.
In brief, the methodology consisted of removing existing
walkways and transporting them to Cark station. Here the
scrap would be unloaded by crane ready for collectionand the RRV loaded with a new walkway to return to the
viaduct. Once back, the new walkway was installed, the
RRV loaded with another scrap walkway and the process
repeated. Walkway replacement proceeded on both the
up and the down line simultaneously at a rate of two each
side a day. With all walkway traffic travelling east to Cark,
new and old decks were free to be transported out of
Ulverston in the west.
In order to achieve the required output of four walkways
and two decks replaced in a day (actually exceeded in the
later phases of the contract), 'dispatch and receive' zones
were implemented between the viaduct and Cark and
Ulverston Stations. These were clearly demarcated and
each zone exclusively controlled by a machine controller
who would authorise and record all plant movements in
that zone. Pedestrian access was strictly forbidden in
these zones and only one machine allowed in at any
point.
With all road rail plant either occupied with deck or
walkway installation (or trapped between the two), it was
apparent at planning that any material or plant deliveries
during the day would disrupt production. For this reason,
a dedicated resource of 2 RRVS and 4 men wereallocated as a 'load out' gang, operating between 6pm
and 9pm after each shift. Their duties included moving
tools and equipment to where they were required for the
following day, delivering consumables (gas, water, fuel
etc), moving gantry track, tidying up and removing surplus
materials. The production achieved in the day shift was
found to be directly proportional to the success of the
previous nights 'load out'.
At 5pm after every shift, the senior members of the project
team (including Project Manager, Senior Engineer, Senior
Supervisor and Client) would meet to review the daysprogress and agree the work for the following day. A 'Daily
Coordination Sheet' (described in more detail in 4.0) was
then prepared for the following day and issued to the
Engineering Supervisor for briefing and further distribution
to COSSs and machine controllers.
3.5 The Refurbishment of Span 37
Site investigation and analysis into the existing span 37
prior to tender had identified that the existing deck was of
sufficient capacity and condition to warrant refurbishment
rather than replacement. The decision was taken by
Network Rail that this was the preferred option and
Carillion proceeded on their instruction.
The greatest challenge faced with this operation was the
removal of the existing lead paint without pollution to the
estuary. Over and under scaffold similar to that used on
the other spans for soffit access (but without the chain
blocks) was erected the full length of the span.
The scaffolding was then fully encapsulated in a material
called EnviroWrap. This recyclable fabric, similar in
appearance to viscuine (except white), could be heat
sealed together in panels around the outside of thescaffolding. Further heat was then applied to the entire
membrane, causing it to contract and become taught, like
the surface of a drum. Whilst more expensive than
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traditional monoflex sheeting, this system gave a more
thorough, robust encapsulation from which very little dust
escaped.
With the existing steel blasted (with care taken not to overload
the soffit scaffold with blast debris), the span was inspected to
reveal that little repair was required other than a small amount
of work to the stiffeners on the main girders. With this
complete, new deck plates were bolted to the existing crossbeams, new pandrol rail support stalls fixed and new
walkways hung from the outside girders. The original steel
received an XM92 paint specification.
Had span 37 been remote to the rest of the project, the works
could have been executed significantly faster. However, due
to its location, access had to be maintained for the movement
of deck sections to and from the gantries. To facilitate this, one
track had to be live for the majority of the operation, essentially
making the refurbishment two separate tasks (up and down
line) rather than one.
In its final state, the downline walkway was required to carry
three 11Kv United Utility cables in a trough beneath the durbar
walkway plates (diverted from the existing galvanised UU
trough that was to be removed within the scope of works).
Unfortunately, the contract programme required the cables to
be diverted before the installation of the new walkway.
Due to their size and relative stiffness, the cables had to
installed within 75mm of their final position before United
Utilities would divert the power and allow Carillion to
commence removing the original galvanised duct route from
beneath the new south walkway legs. A temporary works
scheme was adapted that hung the cables in a suspended
trough 75mm above their final place of resting within the new
walkway, thereby allowing the diversion to take place. The
new walkway was then installed about the UU cables before
removing all temporary works and lowering the cables into
position in a one hour outage. Great care and rigorous site
briefings were then undertaken to protect the live cables in the
south walkway for what remained of the contract.
3.6 Deck Art icu lat ion and the Use of
Anchor Slabs
Whilst archive drawings existed for the original structure, the
horizontal load transfer from deck to deck was unclear. Each
span consisted of simply supported girders housed in
channelled iron bearing pads. Spans appeared to be bolted
together at their main girder webs in groups of five. However,
whatever movement may have originally been
accommodated, it had long disappeared as the bearings
rusted over and became composite with the main girders.
In order to imitate the existing articulation and minimise the
transfer of horizontal live loads into the existing piers, the
decks were designed to transfer loads from one deck to
another by means of communal bearing plates betweenspans. Each bearing plate consisted of two pot bearings, one
fixed, the other with +/-4mm longitudinal clearance to
accommodate thermal expansion/ contraction of the 9m
spans. Any movement beyond this 4mm (caused by trains
braking, accelerating or thermal effects on the decks/rail)
would then be transferred into the next span and so on down
the viaduct.
Upon reaching the ends of the viaduct, means for containing
this horizontal force were required to avoid failure of the
existing abutments. New reinforced concrete sill beams were
designed and constructed to receive the four end span's
bearings. These sill beams were then stitched to reinforcedrobust kerbs (installed for train containment at the approach to
the viaduct) as well as mass concrete anchor slabs. The mass
of these anchor slabs (580T at Ulverston, 320Tat Cark) were
sufficient to absorb any applied horizontal load that had not
dissipated into the rest of the structure.
Whilst the new spans were designed to transfer horizontal
load along the length of the viaduct, the refurbished span 37
was not and subsequently represented a weak link in the
chain. In order to efficiently transfer horizontal loads from span
36 to span 38, two trusses (upline and downline) were
designed to prop the bearing plates either side of span 37,thereby bypassing the existing girders.
Each truss consisted of two number, 20m long, 300mm deep
I section beams. These were braced horizontally at 1.5m
centres by diagonal angle irons. The trusses (similar in shape
to unit beams, except larger) were floated into position
underneath span 37 on pontoons on a spring high tide. RMD
strongbacks were set across the top flanges of the main
girders above the track and tirfirs slung from these, with their
wires extending through purpose drilled 30mm holes in the
new deck plates. By attaching eight tirfirs to each truss, the
trusses could be manually tirfed from the pontoons to their
final position under the soffit of each line. Once in position, the
pontoons were retrieved to Barrow Docks and the trusses
welded and bolted into position.
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4.0 Health, Safety and Environmental
Management
Due to the nature of the project, the Leven Viaduct Life
Extension Works potentially included all the most serious
and frequent hazards faced by the construction industry.
These were not limited to, but included:
• Working at height (when the tide was out)
• Working over fast flowing tidal waters (with the tide in)
• Working in close proximity to road rail plant
movements
• Hot works, including welding and burning
• Repetitive manual handling
• Confined lifting operations
• Exposure to the elements
• Work in extremely environmentally sensitive areas
Each of the above hazards were identified at the planning
stage with robust, practical systems designed to mitigate
the risk. On site these risks were managed by ensuring all
personnel received an explicit induction explaining the site
rules, after which they were tested to confirm their
understanding. All operatives also received regular
briefings throughout the project.
Carillion also operate a system of BAT (Behavioural Action Teams) and SAG (Safety Action Group) meetings.
This is an effective method of involving everyone in the
management of Health, Safety and the Environment on
site.
BAT groups consisted of appointed artisans who would
meet once a fortnight to discuss and record what they
considered the most pressing HS&E concerns for the site
at that time. Representatives from the BAT team would
then attend fortnightly SAG meetings, at which their
concerns would be tabled and also any other items raised
by the SAG team. The members of the SAG team
generally consisted of approximately one third artisans
and two thirds management, with subcontractors also
instructed to attend. The SAG meetings provided an
excellent means of opening lines on HS&E
communication from apprentice artisan up to Regional
Director.
After close collaboration with Network Rail, the Method
Statement/Operating Plan procedures were modified to
suit the unique nature of the site. Method statements were
written for all site activities and briefed to the workforce on
a weekly basis as standard, however the site used daily
workplan sheets to authorise operations instead of weeklyoperation plans.
The daily work plan sheets (shown in 3.4) consisted of a
single A3 sheet on which a schematic of the site showed
all plant movements for the day, a more detailed diagram
of the viaduct showed the location of various gangs (e.g.
burners) as well as approved walking routes, names and
phone numbers of all key personnel, the tide times and
the day’s weather forecast.
Before accessing the site, all personnel received a COSSbriefing from daily work plan by the Site Access Controller,
with whom they signed on. They were then permitted to
access and work on the structure under the supervision of
'territory custodians'. These were COSSs identified by
green hard hats, positioned approximately every 100m
along the viaduct. They protected operatives within zones
rather than individual gangs and were not required to give
additional briefings or collect signatures, as this had been
done by the Site Access Controller.
The use of daily coordination sheets and territory
custodians proved to be a very effective means of controlling safety on a heavily populated, linear site. In the
sixteen weeks of the project, with over 10,000 man days
of construction, there was not a single serious incident.
5.0 Conclusion
The Life Extension Works to Leven Viaduct provided an
opportunity to develop many innovative techniques in the
execution of the works. As to be expected, some of the
methods employed were more successful than others but
the lessons learnt on this contract shall be invaluable to
similar projects in the future.
Without doubt, a significant contribution towards the
success of the scheme was the relationship between the
client and principle contractor. By maintaining an open,
honest dialogue the project team were able to discuss and
resolve problems rapidly and often to mutual advantage.
Carillion's decision to involve subcontractors and client in
SAG and BAT meetings also generated a culture in which
everyone had equal responsibilities for health and safety
in the work place.
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39Railway Bridges - Today and Tomorrow
Paper Five
Development of Standard Designs and
Details for Railway Bridges
Jason Johnston
NETWORK RAIL
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Abstract
The development and use of Standard Designs and
Details (SDD) is one of the steps taken by Network Rail to
improve network safety, asset reliability, and increase
efficiency. The focus of this paper is on the development
of SDD for footbridge and underbridge replacement
schemes.
The footbridge SDD is currently at the Approval in
Principle stage (GRIP Stage 4). The paper discusses the
rationale behind selection of the structural form. The
limitations of application in terms of span and clearances
are described along with details of the access options
provided.
The development of underline bridge SDD is currently in
the early design development stage (GRIP Stage 3). This
paper is being published part way through a Feasibility
Study aimed at determining the requirements for
underbridge SDD. Formal peer review arrangements arein place to help guide the study and ensure robustness of
the conclusions. Whilst this contracting strategy is
unconventional it is considered necessary as this work is
expected to have far reaching consequences for future
underbridge renewals.
The functional requirements of underbridges and an
understanding of a 'typical underbridge renewals profile',
based on recently completed schemes and schemes in
the Business Plan, is being used to guide the
development of SDD. The paper describes how Value
Engineering principles are to be used to shortlist bridgeforms and determine the optimum level of standardisation.
Keywords: Efficiency, Footbridge, Function, Safety,
Standard Design and Detail, Underbridge, Value
Engineering.
Introduction
The development and use of Standard Designs and
Details (SDD) is one of the steps taken by Network Rail to
improve network safety, asset reliability, and increase
efficiency. The main focus of this paper is on the
development of SDD for footbridge and underbridge
replacement schemes.
It is helpful to first look at the background to the efficiency
drive and the structured approach taken by Network Rail
to develop the library of SDD. Further supporting
information is provided on areas of design responsibility
around application of SDD on projects along with
discussion on the benefits of using SDD and the control
measures needed.
Background to Efficiency Drive
Network Rail has been set challenging efficiency targets
by the Office of Rail Regulation (ORR). Unit costs are
required to be driven down by 30% by the end of the
current five year control period in March 2009 whilst
simultaneously improving network reliability and safety.
Major Projects & Investment (MP&I) Civils are working
closely with the Director of Civil Engineering to meet this
challenge. The resulting Civils Efficiency Strategy sets
out the overall approach to achieve these target savings.
The strategy identifies twenty-seven initiatives broadly
under four main themes:
• Design and the development process
• Contracting and procurement
• Resource utilisation and productivity
• Culture
Two initiatives under the 'Design and the development
process' theme relate to the development and use of
SDD.
Phased Development
The SDD are being developed in accordance with theGuide to Railway Investment Projects (GRIP) process and
procedures. A four phase approach has initially been
adopted with selected existing, territorially based SDD
developed first. The first issue of SDD (Ref. 1) in June
2006 focused on brick and masonry repairs and has been
issued both internally within Network Rail and externally to
our supply chain in CD-ROM format. The CD-ROM
contains the standard drawings, generic technical
approval Forms A and B, and technical user manuals.
The second issue of SDD (Ref. 2) in August 2006 includes
earthwork related SDD. Phases three and four covering
SDD for footbridges and underline bridges are planned for issue in 2007. It is intended that future issues will be
through a web based system.
Design Responsibi lity
Design responsibility for the application of SDD on
projects ultimately depends on the terms and conditions of
contract. The terms relating to design responsibility in the
suite of Network Rail standard forms of contract are
unchanged following the introduction of SDD. In the case
of a construct only contract (with design completed under
a separate professional services contract) Network Rail
accept responsibility for the design and appropriate
application of SDD. For design and construct contracts
the Contractor accepts design responsibility and for
appropriate application of SDD.
Benefits & Controls Needed
The benefits of using SDD include:
• Reducing design development timescales and costs
• Adopting good practice in the design and detailing of
Civil Engineering works
• Minimising contractor and sub-contractor costs
associated with uncertainties in detailing requirements
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• Reducing the volume and costs of Maintenance works
through the adoption of good practice
• Streamlining the Technical Approval process for
commonly used designs and details
The development of a library of SDD also requires
controls to be put in place to ensure appropriate
application, continued use, and that they are kept relevantand up to date.
In order to ensure the appropriate application work
instructions (Ref. 3) have been issued to define the
Technical Approval process for using SDD in Civil
Engineering works. The work instructions supplement
Network Rail's requirements for technical approval as
defined in NR/SP/CIV/003 (Ref. 4). The work instructions
define both 'simple' and 'complex' applications of SDD.
Simple applications are where a generic Form A and a
project specific Form B are required for the application of
SDD. In practical terms for bridge renewal schemes the'complex' category will more than likely apply whereby
project specific Form A and B are required.
Where demanded by the complexity of the SDD, a
Technical User Manual (TUM) will be developed to help
ensure appropriate use of SDD, particularly where there
are a number of standard elements which together
comprise a solution. Footbridges and underbridges with
Medium or High level of standardisation are expected to
have a TUM.
Appropriate application is further strengthened with each
set of SDD drawings containing an outline Designer Risk
Assessment. The assessment considers the generic
hazards during design, construction and operation stages
and provides suggested mitigation measures. The risk
assessment is required to be developed by the scheme
Designer for any specific application of SDD on a project.
In terms of ensuring that SDD are used the Work
Instruction defines responsibilities of both the Client
(Asset Engineer) and the project Sponsor (Renewals
Engineer) to identify potential opportunities and for the
particular requirements to be agreed in the project remit.
The process of obtaining financial authority for projectswill be used to challenge investment papers - the
presumption being that SDD should be used unless it can
be demonstrated that use of non-standard design and
details is more appropriate. Existing business reporting
systems and the Cost Analysis Framework (CAF) will be
used to capture the use and associated benefits of SDD.
Feedback on the suitability of SDD is actively encouraged.
Feedback using the 'User Feedback Form' on the CD
(Ref. 1 & 2) will be periodically reviewed to ensure that the
SDD remain appropriate and reflect the needs of the
Asset Engineers and the delivery teams. At appropriatestages the SDD library will be modified and extended.
Development of Footbridge SDD
The approach to standardising design and details is centred on
using current best practice which aims to strike the optimum
balance between function, cost and safety. The development
process began with a workshop to identify best practice across
a range of civil engineering works including 'non-station'
footbridge renewals. The workshop attendees comprised
Network Rail engineers from national and territory teams,consultants, framework contractors, as well as representatives
from the steelwork fabricator industry. The structural form
selected for the footbridge SDD is commonly referred to as the
'London Midland' type (Fig. 2). This is a proven solution with at
least 40 recently constructed as part of West Coast and Cross
Country Route Modernisation schemes.
The footbridge SDD is currently at the Approval in
Principle stage (GRIP Stage 4) and applies only for 'non-
station' renewals. The design covers a main span range
of up to around 25m (nominally spanning four tracks), with
both stair and ramp access options (Fig. 3). The main
span has two geometrical arrangements with and without
in-span stairs thereby providing an option compliant with
the Disabled and Discrimination Act (Ref. 5). In terms of
vertical clearances the supports (either single column or
two or four leg trestle) are detailed to enable use on lines
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Figure 1 - Example of the footbridge structural form adopted for SDD
Figure 2 - Typical section through footbridge main span
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with or without overhead electrification. The access
spans have two structural forms with a shorter spanning
'stringer beam' and a longer spanning 'truss'. The SDD
access options enable project teams to optimise the
number of supports based on site constraints. Options
are available for full or partial enclosure of the main and
access spans. The requirement to use such protective
measures will be determined by project level risk
assessment.
The footbridge SDD initiative has recently been extended
to enable application to non-mainline stations. Additional
features will include cable conduits, lighting provision, and
lift shaft accommodation.
Development of Underbridge SDD
The development of underline bridge SDD is currently in
the early design development stage (GRIP Stage 3). This
paper is being published part way through a Feasibility
Study aimed at determining the requirements of
underbridge SDD. The following sections provide an
insight to the approach being taken including the
establishment of 'functional' requirements of underbridges
and use of the Business Plan to guide the study (Fig. 4).
The overall contracting strategy for the Feasibility Study is
fairly unconventional but is well suited to this project which
is expected to have far reaching consequences for underbridge renewals. Network Rail is working with Cass
Hayward and Partners LLP on the main study and has
also formally engaged a number of other leading
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Figure 3 - Typical arrangement of SDD footbridge showing stair
and ramp access optionsFigure 4 - Process diagram showing principle activities in
Underbridge SDD Feasibil ity Study
Main Span
Superstructure
Main Span
AccessStairs
Access
Ramps
PLANScale 1:200
ELEVATIONScale 1:200
ELEVATION ON MAIN PLANScale 1:200
Main Span
SuperstructureMain Span Support
Superstructure
Stair/Ramp Support
Stairs &Columns Stairs &Columns25000 Column C/CRS
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consultants to review deliverables and provide guidance
during the study.
The formal peer review workshops are proving to be an
excellent opportunity to draw on the wealth of experience
of other leading consultants in this field. The peer
reviewers comprise senior bridge engineers from within
Network Rail, Atkins, Hyder Consulting, Mott MacDonald,
Scott Wilson Railways, and Tony Gee & Partners. Thefirst of three 'Peer Review Workshops' was held in
October, with the last two planned in November and
December. The later workshops will be further supported
by leading fabricators from both the steelwork and pre-
cast concrete industries as well as representatives from
our framework contractors.
Establishing Functional Requirements of
Underbridges
The first objective of the feasibility study was to establish
the functional requirements of underbridges. Thisinvolved consultation with key stakeholders along with a
review of the draft Network Rail standard on the design of
bridges (Ref. 6). The functional requirements are
summarised in Table 1 against various categories
including normal operations, abnormal situations, and
also installation and demolition.
It is recognised that against each functional requirement
there are a number of related (parallel) issues that require
consideration. These have been identified as part of the
study but for reasons of brevity have not been included in
this paper. The functional requirement and associated
parallel issues, along with a set of agreed desirable andundesirable features will be used to assess bridge form
options for potential development as SDD.
Examples of Desirable Features:
• Sacrificial elements at steel/concrete or
ballast/structure interface
• Simple robust steelwork details
• Early warning of distress
• Good run on/run off details
• Open stiffeners to steel deck plates
• No intermediate web stiffeners on track face
• Multiple bearing stiffener legs and protection to ends
of main girders
• Simple anti-uplift/displacement restraints
• Simple bearing arrangements
Examples of Undesirable Features:
• Hidden details
• Complex detailing leading to unnecessarily high
construction cost
• Box girders with difficult access
• Bird nest crevices
• Noisy rattling (loose) plates
• Expansion joints (short spans)
• Site welding
• Heavily stiffened thin steel plates
• Fatigue stress raising details
• Open deck floors
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Category
Normal Operations
Abnormal Situations
(Unplanned)
Abnormal Situations(Planned)
Installation/
Demolition
Functional Requirements
Capability to support load
Acceptable deformation
Satisfy durability requirements
Satisfy structure gauge requirements,
and construction depth/headroomconstraints
Facilitate safe working environment
Accommodate interdisciplinary
requirements
Satisfy operational requirementsEasy to manage
Sympathetic aesthetics
Bridge bash resistant
Capability to support derailment load
Accommodate substructure movement
Capability to support on-track plant
loads
Able to easily replace parts(maintenance or emergency)
Ease of construction (and eventual
demolition)
Table 1 - Summary of Underbridge Functional Requirements
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Underbridge Characteristics in Future Plans
The Network Rail Business Plan (Ref. 7) is used to guidethe development of SDD for underbridges. The definition
and certainty of the plan has been greatly enhanced over
recent years due to considerable early investment in the
development phase of projects. The Business Plan
identifies 72 underbridge replacement schemes up to
March 2009. The breakdown of these between territories
and also the typical minimum and maximum span is
provided in Table 2 and Figure 5. The key characteristics
of these structures such as span, skew, available
construction depth, and installation constraints do not
form part of the Business Plan and had to be separately
sourced from the territory engineering teams.
Supplementary information from 64 recently completed
schemes is also used to improve the robustness of this
development tool (Table 2 and Figure 5). The details of
schemes recently completed are based on data held
within the CAF. Together, the details of the schemes in
the Business Plan and those recently completed will be
used to establish a typical national underbridge renewals
profile. This profile will capture not only typical span
frequency, but construction depth (top of rail to deck soffit)
constraints and installation constraints, i.e. proportion
installed as one unit or multiple elements assembled in-situ. These three key factors are being used to guide the
development of SDD.
Interestingly, 25% of schemes involve spans less than
5.0m, 60% less than 10.0m, 80% less than 15.0m, and
90% less than 20.0m. The three peaks in the span versus
frequency plot centre on 3.5m, 7.0m and 12.5m. These
approximately coincide with square spans over
accommodation access or single lane road without and
with pedestrian access, and a two lane road with
pedestrian access.
Based on the data collected almost all the structures
spanning over a road have sub-optimum headroom (less
than 5.7m) and are therefore potentially at risk of being
struck by road vehicles. This is consistent with the fact
that there are over 2000 annual bridge strikes incidents on
the network each year. This statistic, combined with the
often limited opportunities to adjust track levels, is
consistent with available construction depth being a key
consideration when replacing underbridges.
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Territory
LNE
LNW
Scotland
Southern
Western
15
22
8
11
8
1.8
3.5
3.6
1.9
3.1
48.0
23.1
41.5
24.7
13.2
34
5
7
19
7
2.4
7.8
2.5
2.0
3.1
35.0
19.1
10.7
26.0
13.7
4
1
2
8
1
No. Min. (m) Max.(m) No. Min. (m) Max.(m)
U/B Spans Recently
Completed (from 2002/03)
U/B Spans in Current
Business Plan (to March-09)
Entries with
incomplete
span data
Table 2 - Summary of spans of recently completed and future underbridge replacement schemes
(from 2002/03 to 2008/09)
Figure 5 - Spans of recently completed and future underbridge replacement schemes (from 2002/03 to 2008/09)
Span (m)
F r e q u e n c y
( N o .
S p a n s )
T w oL an eR o a d
( wi t h p e d e s t r i an
a c c
e s s )
T w o
L an eR o a d
( wi t
h o u t
p e d
e s t r i an a c c e s s )
A c c
om o d a t i on /
S i n gl eL an d R o a d
( wi t h o u t
p e d
e s t r i an a c c e s s )
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Based on national feedback from the territory engineering
teams the installation methodology for recently completed
schemes (and that expected for future schemes) consists
of around 60% installed as one unit either using a crane
or transporter, with the remaining 40% involving assembly
of multiple elements in situ.
Further validation of the Business Plan data and 'typical
national underbridge renewals profile' will be undertakenby comparing the output from Network Rail's concurrent
Route Availability (RA) project. The first phase of that
project will be completed at end of December and any
relevant findings fed into this project.
Assessment of Potent ial Solut ion Types
The feasibility study will consider the degree to which
existing SDD, commonly used designs and details, and
other potential solutions (for example reinforced and/or
pre-stressed concrete) meet the requirements for
function, as well as economy and safety.
The recommendations on which options should be
developed as SDD, along with the optimum level of
standardisation will be established using qualitative 'Value
Engineering' techniques.
Preferred Solution Types
The value that each solution (X) represents will be
determined using the ratio of its function over cost as
shown in Equation 1. It is expected that the value each
solution represents will vary with span. Therefore theassessment is expected to be based on specific span
ranges (S) e.g. 1.8m< S5 ≤5m, 5< S10 ≤10m, 10< S15
≤15m, 15< S20 ≤20m, and 20< S30 ≤30m.
The level of functionality achieved for each solution (within
the applicable span range) will be based on the
summation of scores against the weighted functional
requirements, parallel issues and level of
desirable/undesirable features. The cost element for each
solution type will be based on whole life considerations
but normalised against the lowest cost solution. It should
be noted that these value assessments will not only
consider existing bridge forms but also modifications to
such forms as necessary to reduce the number of
'undesirable' features.
The solutions to be short listed for SDD will be based on
those representing best value. The aim is to ensure that
adequate and overlapping SDD coverage is provided for
the typical national underbridge renewals profile.
Ensuring that the SDD options overlap in terms of span
range, construction depth and buildability options
provides Asset Engineers and delivery teams with a
limited range of options to meet typically encountered site
constraints.
Optimum Level of Standardisation
Against the short list of best value options each will be
further assessed to determine the optimum level of
standardisation. The Value of Standardisation (Y) will be
determined for three potential levels: Low, Medium or
High. The value that each level of standardisation
represents will be determined using Equation 2.
The Low level of standardisation is expected to comprise
examples of best practice standard details only, whilst at
the other extreme the High level will involve the full design
of all principal elements similar to the existing 'box girder'
SDD (Ref. 8). The Medium level will involve partial design
of principal elements similar to existing 'Z' Type SDD (Ref.
9). Other factors to be taken into account include the
Frequency of SDD usage which will be determined using
the Business Plan data as a guide, and Savings expected
to accrue from each application. The Cost factor relates
to the capital investment needed to develop Option X SDD
with Y level of standardisation.
Conclusions
The development and use of SDD is one of the steps taken
by Network Rail to improve network safety, asset reliability,
and increase efficiency. The focus of this paper is on the
development of SDD for footbridge and underbridge
replacement schemes.
The footbridge SDD is currently at the Approval in Principle
stage (GRIP Stage 4). The paper discusses the rational
behind selection of the structural form. The limitations of
application in terms of span and clearances are described
along with details of the access options provided.
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Paper 5 Development of Standard Designs and Details for Railway Bridges
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Equation 1
Value (X)s =Function (X)s
Cost (X)s( )
Equation 2
Value (Y) =Frequency x Saving (Y)
Cost (Y)( )
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The development of underline bridge SDD is currently in the
early design development stage (GRIP Stage 3). This paper
is being published part way through a Feasibility Study aimed
at determining the requirements for underbridge SDD.
Formal peer review arrangements are in place to help guide
the study and ensure robustness of the conclusions. Whilst
this contracting strategy is unconventional it is considered
necessary as this work is expected to have far reaching
consequences for future underbridge renewals.
The functional requirements of underbridges and an
understanding of a 'typical underbridge renewals profile',
based on recently completed schemes and schemes in the
Business Plan, is being used to guide the development of
SDD. The paper describes how Value Engineering principles
are to be used to shortlist bridge forms and determine the
optimum level of standardisation.
References
1. Network Rail CD-ROM of Civil Engineering Standard
Designs and Details, NR/CIV/SD/CD/1 (Issue 1) June 2006
2. Network Rail CD-ROM of Civil Engineering Standard
Designs and Details, NR/CIV/SD/CD/2 (Issue 2) August
2006
3. Network Rail Company Standard NR/WI/CIV/151
'Technical Approval of Standard Designs and Details for Civil
Engineering works, (Issue 1) April 2006
4. Network Rail Company Standard NR/SP/CIV/003
'Technical Approval of design, construction and maintenance
of Civil Engineering infrastructure' (Issue 2) April 2004
5. The Disability Discrimination Act 2005
6. Network Rail Company Standard NR/SP/CIV/020 "Design
of Bridges & Culverts" (Draft)
7. Network Rail Business Plan 2006/07 (August Period 5)
8. Railtrack PLC, Standard Half Through Underbridges,
Steel Box Girders and Transverse Ribbed Floors, 1996
Revision of Design
9. Railtrack PLC, Standard Half Through Underbridges Z-
TYPE Girders & Composite Deck, 1996 Revision of Design
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Figure 6 - Span Range and Structure Depth of Various Bridge Forms (based on Peer Review 1 Information Pack by Cass
Hayward & Partners LLP) N.B. Thickness of bars is indicative of relative structure depth (top of deck to soffit)
Span (m)
Extent of
European use
Construction Depthincreases with span
Construction Depth varies withspan and form
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47Railway Bridges - Today and Tomorrow
Paper Six
Delivery of Works - Safely
Ray Ekins
ALFRED McALPINE PROJECT SERVICES
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Across the Network Rail (NWR) Western territory from
London, west to Penzance and North West to Pwllheli on
the Cambrian Coast, are extensive sections of track that
are prone to damage and or speed restrictions. These are
often a result of failing sea defences, falling rocks from
escarpments or faces within deep cuttings, unstable
embankments & cuttings, poor drainage, and lastly,
timber, steel, cast iron, concrete, stone or brick bridges
and associated structures being at their safe working limitand approaching the end of their working life.
In the last 4 years under the Western Territory Framework
Agreement (WTFA) until recently known as "GWESPA"
(Great Western Earth Works & Structures Partnering
Arrangement), Alfred McAlpine Project Services (AMPS)
has worked at over 400 locations across this territory,
putting 3 million man hours into many varied schemes.
Currently a team of NWR and AMPS staff (10 & 50 people
respectively) are based in Stonehouse, with a further 104
directly employed on site and various subcontractors.
Civil Engineering challenges include working adjacent to
the railway, tidal estuaries, sea front locations, rivers,
inaccessible locations, geological issues, environmental,
ecological, weather, structural etc. As a result of these
challenges there are resulting complex safety &
environmental issues which need to be incorporated into
the project.
The purpose of this paper is to explain how we deliver
these works safely and in an environmentally friendly
manner whilst meeting NWR's other requirements, i.e. on
time and to budget, all factors being paramount to the
continued success of the project.
Safety is simply an integral part of the operation. Very few
issues are just "safety" or "environmental"; this approach
has been the key of successful project delivery which
currently enjoys nearly 600 days without a serious
accident and an AFR of 0.0.
• The project encourages joint and collaborative working
with NWR, sub-contractors, statutory bodies etc. and
ensuring a safe and healthy work force and public
• Whilst AMPS recognise NWR's needs and difficultieswe have to ensure the process from the advice of work
packages through to the issue of project Health & Safety
files satisfies legislation, the NWR and AMPS
requirements by ensuring adequate Planning,
Organisation, Control & Monitoring is given
• We also have to satisfy our ISO9001, 14001 &
OHSAS18001 accreditations and maintaining our RSC,
CAC and Linkup certifications
• We use an integrated AMPS & NWR system
Broadly, the process is as follows:
• Initially NWR develops a Works Package of Civil
Engineering remediation needs. This may be because of
long term Temporary Speed Restrictions as a result of
Track Quality Problems or gradual slope failure or small
rock falls (where the failing face was covered in
vegetation) and thus not visible, has alerted NWR to
potentially severe problems. This was the case at
Winterbourne and most recently at Chipping Sodbury
cuttings where urgent resolutions of the problems were
required. The timing of the works can also be dictated to
by the availability or not of railway Possessions. A "Form A" is produced by AMPS to agree in principal the concept
of work and envisaged methodology, and is accepted by
NWR. Project delivery can commence up to two years or
more before any physical works start
• The issue of the Work Package starts the process and
AMPS are responsible for collating from the NWR
archives and other sources information on the site,
existing structures and services
• In liaison with our Designers the remit is reviewed. The
design has to ensure that unacceptable risks are notintroduced to the railway whilst ensuring efficiencies can
be made. Design Risk Assessments are produced and
submitted with a "Form B" for detailed design to AMPS,
together with Commercial, Safety & Environmental Risk
Assessments and target costs. If significant changes are
made to the design a "Form B Addendum" is issued
• The procurement process is initiated for our Sub-
Contractors and material suppliers which meet the
relevant Linkup, CHAS (Contractors Health and Safety
Assessment Scheme) & AMPS requirements and
depending on the nature of the works will give specialist
advice and occasionally prepare detailed method
statements and risk assessments
• Running parallel to the above is the Health & Safety
Plan (known as Project Management Plans [PMP] within
AMPS). This is developed including detailed planning of
the operation; further possession planning is undertaken
by AMPS. Method statements and Risk Assessments
are written by Alfred McAlpine and the contractor and
reviewed by NWR. Staff are also identified and any
resultant training needs are resolved. "Form C" for
Temporary Works are also produced unless these are
complex in nature and if so are done at the Design stage
• With everything prepared, men, materials, facilities and
plant etc. are mobilised for the start of the works. As
many as 25 sites may be running at one time
• On Completion of the works or possession (may or may
not be in stages) a "Form E" is issued, during this time
the Health Safety File is being developed for handing
over to NWR
• With the site clear, the works move into the
maintenance stage
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The following gives examples of Planning, Organisation,
Control, Monitoring & Review undertaken across the
project supplemented with additional safety improvements- AMPS Business Management System and the Safety
Observation Stations.
Planning
Incorporates: Possession Planning, Design, Ground
investigation, Environmental, appropriate approval forms,
target price, construction stages and commissioning.
With a supporting team of 5 persons under the Senior
Planner, Primavera P3 Planning software is used to
control the planning of approximately 70 sites per year,
with a value ranging between £100k to £8.0m. Planningcan commence up to 2 years before construction stages.
Some work packages have such delaying problems as
awaiting DTI approvals due to environmental constraints.
Typical problems include:
• Temporary works have to be kept to a minimum and
where they are required, these works are incorporated
into the program at the earliest possible stage to ensure
they are not rushed and are produced in a safe and
timely manner
• Sub contractors are identified and communicated withfrom the earliest possible time in the program lifecycle.
Making them aware of our safety culture and policies
ensures that a good safety record is maintained on site
• Completing the design of schemes as early as possible
allows engineers the necessary timescales to produce
Health and Safety plans and method statements within a
safe and timely manner
Organisation
With all NWR and AMPS staff centrally based within a two
storey building located in the heart of the geographicalarea covered by the project and working along side each
other, an excellent inter-working between all parties has
been achieved, thus ideas can easily be floated, issues
resolved and delays in communicating between one office
and another have been reduced. Within easy walking
distance are some of the Designers again who can
provide an excellent interface to the project. Nearby are
the heavy stores facilities provide for a ready supply
whether for emergency or routine works a variety of
instantly available materials.
With a multifaceted workforce of whom several are SafetyCritical (COSS, ES, IWA & Machine Controller) they are
also trained to CPCS for Plant, CSCS for safety, Lifting
Operations, Confined Spaces etc.. They and the sub-
contract staff are supervised by General Foremen then
Sub-Agents followed by Agents (many of whom are
approved by NWR as CREs), supported by the Works
Manager who reports directly to the Project Manager.
We have made a conscious decision to employ as many
of our staff and workforce as possible. We have 75
directly employed staff and 4 sub-contract commercial
staff.
Our workforce is set at 10% above the minimum planned
requirement (allowing for sickness and training). The
shortfall is made up as labour only sub-contractors who
are generally hand picked from three main companies.
Our direct workforce is 68 strong at present.
Over the last 41/2 years we have built up a good safety
culture within the organisation. The provision of good
training, equipment and PPE has shown a reciprocal
commitment by the workforce. Having a direct labour
force is cost effective, as multi-skilled our men can
operate dumpers, then rollers etc.. The initial trainingcosts are out weighed by resource effectiveness as most
operations are not manual.
Controlling
The Project Quality System complies with BS EN ISO
9001 2000 and applies to all work undertaken by the
AMPS, our consultants, sub-contractors and suppliers.
The Construction Team has the primary responsibility to
deliver and verify quality by planning, controlling and
checking their work. See Appendix 1.
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Figure 1 - Chipping Sodbury cutting
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Monitoring
All activities are monitored using various methods;
examples noted below include Health & Safety, Quality
and Measurement of our Performance.
• To ensure the project is compliant to many safety
standards we are subject to constant monitoring by
ourselves, NWR and other organisations. These includeyearly NWR project management audits & Contractor
Assurance Case audits, supported by site inspections by
their staff. In addition to these we are subject to BSI and
other body's audits as part of our accreditation
processes. We also monitor ourselves with Directors,
Safety Advisors and Site Management undertaking site
audits. The Railway Safety Case is independently
audited yearly and the supporting documents internally
audited yearly also. AMPS also audit the management
systems. Lastly we audit our safety critical suppliers of
plant and people and assess all other supply companies.
The principal aim is two fold: one, to identify failings
against the relevant standard and, two, to identify good
practice which can be utilised across the company.
• Monitoring of the works is also undertaken through the
development and implementation of Quality Control
Plans. These identify key stages of the works which are
subject to inspection and test processes
• Another form of monitoring is the Key Performance
Indicator (KPIs), these consider:
Contractor Accident Rate
Result of NWR Safety Engineer's Site Inspections
On-site Quality
Train Minute Delays
Progress
Efficiencies
Review
As each work package draws to a close, progressively
AMPS and NWR review all areas as part of a continual
improvement process, such as:
• Accident and Incident review has formed a key part to
their reduction. Since commencement of the project all
incidents & accidents whether near miss, minor or major
have been reviewed at site, at Stonehouse and at
respective headquarters and forms part of our safety
culture. The review process includes site teams, Rail
Operations Group meetings, NWR / AMPS ProgressMeetings, AMPS QUENSH (Quality, Environmental,
Safety and Health) & Directors Meetings. Serious
incidents which are, or potentially are RIDDORS are
subject to an ARC - Accident Review Circle - this is a
joint meeting between the injured, witnesses, Site
Supervision & management, Principal QUENSH Advisor
and Director and if the injured party is a sub-contractor,
his Director is invited.
• Statistical analysis is undertaken by headquarters and
locally providing useful drivers to identify problems and
then target these with adequate H&S resources toresolve them as shown on the diagram in Appendix 2.
Examples of this include the Glove Policy and Eye
Policy. The former was a forerunner to Network Rail’s.
• The review of Health & Safety audits previously
mentioned is again critical to improving long-term safety.
Since January 2004 all site inspections with any
resulting corrective actions have been logged; these
total 1386 including recommendations. All corrective
actions are graded and reviewed with the Health &
Safety Advisors and site teams, at the joint Network
Rail/AMPS progress meetings, Rail Operations Groupand others. One outcome has been the steady decrease
in findings whether by AMPS or Network Rail staff based
on man hours worked.
You will notice within Appendix 3 that problem areas have
included access, the Construction Phase Health & Safety
Plan, house keeping, plant and waste.
• An Achilles heel to safe working practices is attitudes
and perception by all persons. To assist the Project
Manager, a questionnaire is issued to all site staff
annually to seek their view whether they strongly agree
or disagree to the safety questions posed. This was the
initial Behavioural Safety Initiative at GWESPA, coupled
with Safety Committee meetings; they provide a valuable
communication tool to all parties to ensure the workforce
voice is heard and therefore safety improved. Within
Appendix 4, is the questionnaire containing 30 questions
with the results for this year. This questionnaire was
developed by the SQE team to give the workforce a
chance to comment and provide management with
feedback on H&S issues. This year's results are being
currently analysed by the Project Manager to identify
target areas for improvement. An initial review indicates
though there is increased safety awareness Q30, we stillhave a long way to go as Q8, 16 & 25 would indicate.
• Lessons Learnt is an ongoing process, during the
weekly site meeting an outcome of a particular issue, for
example, coping with unexpected changes in Ground
Conditions which has resulted in Design changes and
work content is reviewed for its success or failure.
• During the life of the project Safety Workshops have
been held at a nearby hotel where all grades of
employee have been able to freely discuss problems
and assist in recommending improvements, receivesafety and environmental presentations.
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Safety Improvements
AMPS has introduced or supported many safety
initiatives, e.g. company wide Drugs & Alcohol Policies,
Behavioural training, Worker involvement - MAD (Make a
Difference), 365, 1 day safety presentations held off site
including, Safety Net Videos, railway emergency drills,
work force medicals, Passport System for induction which
cuts costs on inductions particularly on Possessions, etc.. All have contributed to making the workplace safer.
Further examples new in 2006 are the supporting
processes - AMPS Business Management System and
the Safety Observation Stations.
1. AMPS Bus iness Management System
AMPS manage project delivery with the aid of an
integrated business management system introduced in
spring 2006 to bring together all the different disciplines
within one controlling system and are an underpinning
management tool. This combined approach replaces theformer SHEMS system which as the title suggests only
considered Safety, Health & Environment.
Figure 2 shows the integrated Business Management
System, which consists of nine manuals.
Project Management Plan
A key component is the Project Management Plan for
projects - this defines how we will manage a project. All
the information required to complete the project in line
with Railway Safety & Standards Board Standards, NWR
Company Standards, AMPS company standards, project
requirements and legislation.
Figure 3 shows the Project Management Plan, which
consist of four sections.
• Section C - Defines common arrangements and
requirements for QUENSH
• Section S - Specific requirements for Health & Safety
• Section Q - Specific requirements for Quality
• Section E - Specific requirements for Environmental
• Project File - QUENSH Records
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Figure 2 - Integrated Business Management Syst em Figure 3 - Project Management Plan sections
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Rail
This Rail Procedures Manual contains Procedures to aid
AMPS to work on NWR's infrastructure in a safe and
compliant manner, in recognition of requirements
contained within the Contractors Assurance Case,
Railway Safety Case and Linkup. These procedures are
supported by Rail Standard forms, Guidance forms,
Training, Risk Assessments and Work Instructions.
The Rail Procedures Manual also interfaces between
RSSB & NWR standards and AMPS Business
Management System. It comprises the following sections:
• Rail Procedures
• Appendix A - Rail Standard forms
• Appendix B - Rail Guidance notes
• Appendix C - Rail Training
• Appendix D - Rail Risk Assessments
• Appendix E - Rail Work Instructions
2. Safety Observati on Station
These are A1 size boards (see Appendix 7) with loose
cards for safety improvements and near misses to be
reported. They are to be used on all sites from early
October and they should:
• Encourage reporting of near misses and safety
improvement suggestions by all persons on site
• Provide simplified near miss reporting
• Record safety improvement suggestions from
employees
• Give a format for giving feedback
• One system across all projects
Any suggestions that will improve QUENSH management
are to be raised, for example:
• Method of working
• PPE
• New materials
Interpretations
• An unplanned event that did not result in injury, illness,
damage, environmental impact or product loss - but had
the potential to do so
• The difference between a near miss and an
incident/accident can be a fraction of a second or a few
millimetres that may not be there the next time
• Near misses are warnings of accidents in the making
Reporting
By reporting these warnings and looking for their causes,
we can help prevent incidents/accidents. Typical items
include:
• Behaviour - ignoring site rules/procedures
• PPE - damaged or not used
• Slips, Trips & Falls - untidy work area• Poor Supervision - uncontrolled plant movements
• Lifting & carrying - kerbs lifted by hand
• Environmental Issues - dust & noise from plant
• Danger to the Public - uneven temporary footpaths
• Traffic Management - signs/cones blown over
• Access & Egress - obstructed walkway
• Excavation - no supports
• Plant & Equipment - speeding, poorly maintained
• Work at Height - no edge protection
• Hazardous Substances - unmarked/open container
• Services - mechanical excavation too close
See also Appendices 5 & 6.
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Appendix 1 - Quali ty Control Arrangements
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Appendix 2 - Breakdown of Accidents and Incident on WFTA
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Appendix 3 - Health, Safety and Environmental Audit Findings
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Appendix 4 - Health and Safety survey
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Appendix 5 - Lessons Learnt
Appendix 6 - Near Miss Report ing
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Appendix 7 - Safety Observation Board
A near miss is where it all starts so
Share It and Stop It!
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Appendix 8 - Typical schemes
Chepstow rock face
River Yeo br idge
Patchway cutting
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60 Railway Bridges - Today and Tomorrow
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Railway Bridges - Today and Tomorrow 61
Paper Seven
Track/Bridge Interaction and Direct Track
Fixing
Alan Monnickendam
CASS HAYWARD
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62 Railway Bridges - Today and Tomorrow
Introduction
The presence of a bridge within a length of continuously
welded rail results in the rail being subjected to the
following effects:
• Additional stresses due to structural deformation as a
train crosses the bridge
• Additional stresses due to the thermal movement of the
deck
In addition, under traction and braking longitudinal loads
are shared between the rail and the bridge deck.
The mutual influences of bridge and rail structural
behaviour are known as Track/Bridge Interaction (TBI).
This paper describes analyses used to investigate these
phenomena with reference to recent experience of
bridges with direct track fixing systems.
The need for TBI
Hitherto rail stresses due to these effects were generally
regarded in design as being within acceptable limits by
satisfying the structural deformation criteria specified in
UIC 776-3R (Deformation of Bridges). However, where
headroom requirements demand particularly slender
structures these limits often cannot be achieved. Also, the
more widespread use of direct track fastening systems
often results in deck configurations which are out with the
limits of applicability of the rules contained in thisdocument.
Where such a situation arises a more rigorous approach
is required which often results in a specific interaction
analysis being performed. This involves modelling the
structure, the rails and their connection to the bridge deck
and a length of normally supported track off both ends of
the structure. These calculations are generally
undertaken using the guidelines given in UIC 774-3R
(Track/Bridge Interaction - Recommendations for
Calculations), which also specifies the limits which have to
be achieved for the various criteria, including rail stresses,
rail movements relative to the deck and deck movements
relative to adjacent decks or embankments.
It should be noted that this document also provides a set
of simplified rules which, if satisfied, will obviate the need
for a more complex analysis. Some of these have also
been embodied in Appendix G of EN1991-2 (Actions on
Structures - Part 2: Traffic Loads on Bridges).
Direct Track Fixing Systems
The most common types of modern direct track fixingsystems are usually referred to as the embedded rail
system and the discrete baseplate system.
The embedded rail system involves setting the rail in a
preformed trough within the structure and surrounding it
with a pourable resilient compound which cures over time
to provide continuous vertical and horizontal support to
the rail. The main advantage of this system is the degree
of flexibility it allows to achieve the correct vertical and
horizontal alignment of the rail over the bridge. It appears
to be more suited to short span bridges due to concerns
over the time and expense involved in removing andreinstating longer sections of resilient material and track in
the event of a rail breakage in the future.
Discrete baseplate systems rely on a fabricated baseplate
to provide support to the rail at appropriate intervals
depending on the track category, and generally utilise a
bolted connection to attach the rail to the structure.
Whilst offering support more consistent with conventional
ballasted track, this system is much less flexible in terms
of both vertical and horizontal alignment and requires
significantly greater attention to construction tolerances
than the embedded rail system.
Bridges incorporating both systems have been
constructed in the UK within the last year.
The Behaviour of the Track
In undertaking a track/bridge interaction analysis it is
necessary to model the horizontal connection of the rail to
the structure as well as the appropriate vertical support
stiffness. For discrete baseplate systems the horizontal
connection behaves in a non-linear manner and depends
on the type of fixing adopted. Essentially the resistance
of the track to longitudinal displacement increases rapidly
at low levels of displacement and remains constant once
it has attained a certain value (Fig. 1).
Paper 7Track/Bridge Interaction and Direct Track Fixing
Figure 1 - Relationship between resistance of the track to mov ement and longitudinal displacement
Resistance of
the track k
Longitudinal displacement of the rail u
Scatter range
of curves
Theoreticalrelationship
(bilinear)
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63Railway Bridges - Today and Tomorrow
In the analysis this is represented by a bi-linear relationship. This form of relationship is also appropriate
for the modelling of the sections of ballasted track off the
structure. Figure 2 shows how the relationship for
ballasted track varies for different conditions of loading
and ballast. A linear relationship is adopted for embedded
rail systems.
Suggested values of resistance for direct track fixings are
given in the UIC document or values obtained by testing
of specific units may be available from the manufacturer.
Modelling
In view of the bi-linear nature of the longitudinal
connection stiffness a track/bridge interaction analysis
requires the adoption of non-linear analysis methods.
In addition to acceleration/braking and thermal actions,
the model must be capable of accurately representing the
rotation of the deck ends under vertical live loading and
the associated horizontal movement due to the vertical
offset of the bearing from the neutral axis of the deck.
The analysis will provide information on rail stresses,
longitudinal bearing reactions, displacements of the railrelative to the structure and forces on fixings.
Case Studies
Recent bridge designs utilising direct track fixing have
raised a variety of issues in relation to track/bridge
interaction.
Wellington Road (NEC1/24) and Ladgate
Lane(MBW1/11)
Wellington Road U/B (Newcastle) and Ladgate Lane U/B(Middlesborough) were originally conceived as similar
structures for deck reconstruction, but the former was
eventually constructed to a different design. Both are
short span bridges, 9.0m and 9.8m respectively, withheadroom constraints requiring minimum construction
depth. The solution proposed involved the adoption of a
precast concrete filler beam deck with preformed troughs
to accommodate an embedded rail system. The main
difference between the two structures was that Ladgate
Lane was skewed at approximately 23 degrees to the
road below compared with the square span at Wellington
Road.
As the Wellington Road structure satisfied the
deformation criterion of UIC 776-3R no further
consideration of rail stresses was required. The skew at
Ladgate Lane was accommodated by continuing the
embedded rail for a short distance off the bridge to provide
a square transition back to ballasted track. Although
Ladgate Lane was of very similar proportions, the fact that
the direct track fixing continued off the structure meant
that it was outside the limits of applicability of UIC 776-3R.
This document states that rail stresses should be
determined by direct calculation for structures of this form.
A track/bridge interaction analysis was undertaken for this
structure which predicted that additional rail stresses
would be within the acceptable limit of 72N/mm2.
The new structure was installed during a possession atChristmas 2005 (below).
Paper 7 Track/Bridge Interaction and Direct Track Fixing
Figure 2 - Resistance/Displacement relationships for ballasted track
Figure 3 - Ladgate Lane following reconstruction
Resistance (k)
of the track
(kN/m)
Resistance of the rail in sleeper (loaded
track) (frozen ballast track without
ballast)
Resistance of sleeper in ballast only
(loaded track)
Resistance rail in sleeper (unloaded
track) (frozen ballast or track without
ballast)
Resistance of sleeper in ballast
(unloaded track)
Displacement (mm)
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64 Railway Bridges - Today and Tomorrow
Selby Canal (TCW1/21)
Selby Canal Bridge is a 36m single span structure
carrying the Doncaster to Selby line over Selby Canal
approximately 1 mile to the south of Selby town centre.
The existing bridge, which carries twin tracks on
longitudinal wheel timbers is scheduled for reconstruction
in 2007. Two schemes have been developed for thisstructure, one utilising the embedded rail system, and the
second using the Pandrol Vipa discrete baseplate system.
Ultimately it is the latter that has been selected for
implementation. Due to the length of the structure and the
fact that the directly fixed track continued off the bridge to
accommodate the large skew (55 degrees) track/bridge
interaction analyses were undertaken for both options.
One of the objectives was to ascertain whether it would be
possible to replace the existing jointed track with CWR.
Analysis of both schemes showed that if CWR were
installed without an expansion switch at one end of thebridge then the rails would be overstressed under a
combination of vertical and longitudinal live loading and
extreme thermal effects.
Leven Viaduct (CBC1/34)
Leven Viaduct, which was reconstructed earlier in 2006, is
a 49 span, 460m long structure which carries the
Cumbrian Coast Line over the Leven estuary to the east
of Ulverston. The original structure was completed in
1857 and comprised a series of simply supported riveted
girder decks, with span lengths typically of the order of
8.5m to 9.5m. The structure was originally supported on
cast iron trestle piers but these were subsequently
encased in brick faced mass concrete. The permanent
way over the structure comprised jointed rails on
longitudinal timbers. As part of the Form B design
process outline schemes were prepared based on both
reinstatement of the longitudinal timbers and the adoption
of CWR on Pandrol Vipa baseplates. In order to
determine whether the latter was viable a track/bridge
interaction analysis was undertaken.
Due to the overall length of the complete structure and the
fact that every connection point between the rail and thestructure had to be modelled this proved to be a
demanding task. Modelling was further complicated by
the need to take account of pier flexibility and the bearing
articulation which permitted a small amount of movement
between the deck and substructure. This introduced a
further degree of non-linearity to the modelling process.
In addition to determining rail stresses the process was
required to determine the distribution of longitudinal forces
between the intermediate piers, abutment bearings and
rail under braking and traction.
As certain assumptions had to be made regarding pier and abutment stiffness and the degree of bearing fixity at
span 37 (which was the only element of the original
structure to be retained), sensitivity analyses had to be
undertaken to ensure that the most onerous effects were
identified for the critical locations. This requirement,
combined with the large number of load cases that had to
be considered resulted in approximately 150 separate
analyses having to be undertaken. These analyses
demonstrated that CWR could be adopted across the
bridge.
Final Remarks
• Direct track fixing systems offer a more sustainable and
maintainable track support system than longitudinal
timbers
• Track/Bridge interaction analysis is a time consuming
process. Clearer, deemed to satisfy rules need to be
developed to ensure simple, short span structures with
direct fixing can be adopted without recourse to expensive
analysis
• On complex structures, sufficient sensitivity analysis
needs to be undertaken to ensure that critical conditions
have been identified for all elements
Paper 7Track/Bridge Interaction and Direct Track Fixing
Figure 4 - Pandrol Vipa Baseplates fixed to support stools
Figure 5 - Completed track on the up line deck
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65Railway Bridges - Today and Tomorrow
Paper Eight
Soil/structure Interaction and Railway
Bridge Structures
N.J. O'Riordan and O.J. Riches
OVE ARUP
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Appropriate analysis of the railway bridge structures can
achieve significant economies in both rail upgrade and
new-build situations. For example, coupled analyses of
existing bridges and their foundations under the various
load cases for upgraded lines can provide reliable
predictions of performance in service that minimise the
need for new or strengthened foundations. Similarly,
recent advances in the understanding of the soil/structure
behaviour of integral bridge abutments enableeconomies to be made in the construction of new,
bearing-free bridges. Examples of soil-structure
interaction analyses in these situations are provided and
the associated requirements of ground investigations and
analytical techniques are described.
1.0 Introduction
The process of design and analysis of railway bridge
structures and their foundations is often simplified into
the derivation of a system of forces for a defined series of
load cases. Foundation design is reduced to theprovision of reactions to that system of forces, and a
check is made to ensure that an adequate reserve of
safety exists for those reactions, generally using limit-
equilibrium methods. The design is complete. However,
such simplification can lead to uneconomic foundations,
inappropriate structural or ground treatment and, in the
case of integral bridges, unbuildable bridge abutments.
The arrival of new design codes such as Eurocode 7 will
enable closer examination of the serviceability limit state,
to ensure that design is carried out with due recognition
of common bridge design situations which are essentially
displacement, rather than force, controlled.
2.0 Upgrades of existing masonry
bridges
Current trends in increasing line speed result in new
loading conditions for old bridges. These bridges were
constructed either pre-code, or have sustained a range of
modifications which make assessment difficult today. For
multi-span masonry or hybrid bridges, the way in which
these new loads find their way into the foundation system
can be obscure. For example braking loads are applied
through the rail and sleepers onto the bridge deck, but to
what extent is that load transferred longitudinally into the
comparatively stiff abutment system: can each pier be
considered to act in isolation?
Figure 1 shows the deformed mesh, plotted to anexaggerated scale, from a finite element (PLAXIS)
analysis of a triple span bridge. Bearing replacement was
to be carried out at 3 of the supports; however it was
unclear whether replacement was necessary at the wider
of the two piers. Simple analyses, whereby the forces
were apportioned according to pier footing stiffness, had
shown that the foundation could become overstressed
under the new loadings. As a result, underpinning of the
footing at the widest pier was considered.
At the wider pier, a number of support conditions were
considered, the most extreme being that the deck/pier connection could fail in tension, thereby transferring
braking forces onto adjacent supports through the
bearings. The analysis explicitly included material
properties for ballast, deck, masonry and bearings, as
well as the founding soils. The soils were carefully
investigated and were found to be locally stiffer under the
footings, as a result of long term loading over the lifetime
of the structure. The analyses included this variation in
soil stiffness.
As a result, it was found that the adjacent supports were
sufficiently stiff to keep displacements of the rail, deck
and footings to within acceptable values, without the
need for treatment of ground or deck connection at the
wider pier location.
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Paper 8Soil/structure interaction and railway bridge structur es
Railway Bridges - Today and Tomorrow
Figure 1 - Finite element analysis of 3 span bridge under combined train breaking and acceleration on adjacent tracks
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3.0 Dynamic analysis of bridge structures
The analysis described above was carried out using
quasi-static loads, with no allowance for the generally
beneficial effects of inertia and damping. Sometimesrecourse to full dynamic analysis of bridges under train
loading can also result in substantial savings.
O'Riordan et al (2003) and Montens et al (2003)
presented the results of dynamic analyses of piled slab in
which the performance of piles under vertical cyclic load
testing was combined with service loadings from Eurostar
and heavy freight trains for the design of the Channel
Tunnel Rail Link over an 11km length of high speed line
across the West Thames marshes. Pile stiffnesses were
derived from vertical and horizontal cyclic load tests on
individual prototype piles. Theeffect on pile response to the
rotational stiffness at the pile/slab connections was also
examined in the pile load testing. Figure 2 shows a typical
slab arrangement in cross-section and Figure 3 shows the
output from an LS DYNA 3D finite element analysis. Thetrain suspension system and rolling axles were fully
modelled, as were the piles. Straightforward application of
design standard UIC 719-R would have resulted in a
cyclic characteristic force of 560 kN/pile. Results from
dynamic analysis showed a maximum of 340 kN/pile
under passing trains, concentrated in those piles at the
ends of each 60 to 120m length of slab.
In this case, soil-structure interaction analysis enabled the
pile and slab design to be optimised, providing a more
economical solution than the straightforward application
of the design standard.
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Paper 8 Soil/structure interaction and railway bridge structures
Railway Bridges - Today and Tomorrow
Figure 2 - Illustrative cross-section of piled slab supporting ballasted track, after Montens et al, 2003
Figure 3 - Time history ou tput from dynamic analysis,
single heavy freight train at 95 km/hr
CROSS SECTION
60m slab - 4 pile groups - HFT 98kmh
A x i a l f o r c e
i n
p i l e
( k N )
Time (s)
Axial force - beam 402251 - Pile 1 Flow 13
Oasys T/HISVersion 8.2
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4.0 Soil-structure interaction for integral
bridges wi th embedded abutments
In order to avoid the costs of maintenance and repair to
movement joints in bridge decks, there is increasing use
of integral bridges for road and rail (Hambly,1997). In the
UK, the Highways Agency position is that all bridge decks
up to 60m in length and with skews not exceeding 30
degrees are generally required to be continuous. Figure 4
illustrates such a bridge. Resistance to longitudinal
thermal and braking forces is in consequence provided
directly by the soil at the abutments and at any
intermediate support. The way in which the soil at the
abutments resists these repetitive, transient forces has
been the subject of theoretical and laboratory-scale
studies in the UK, for example Springman et al (1996),
England et al (2000), Xu et al (2003) and Cosgrove and
Lehane (2001). All studies show that soil resistance
increases with numbers of cycles of repetitive movement
of the abutment. The soil resistance is controlled by the
magnitude of the movement and/or rotation which arise
from the imposition of deck forces on the abutment. Some
full-size abutments have been instrumented with
inclinometers, thermistors and pressure cells and theassociated measurements have been reported by Darley
et al (1998) and Barker and Carder (2001, 2006).
Current design guidance follows two separate
approaches:
i) the application of specified distribution of lateral soil
pressures which varies with type of abutment (HA,
2003), referred to as the 'K* method', and which
resembles a limit-equilibrium design method, or;
ii) soil-structure interaction analysis using constitutivesoil models of varying complexity
The K* method is implicitly limited to situations where
abutments retain normally consolidated soil, and is widely
regarded as over-conservative, especially for embedded
abutments (see for example Muir-Wood, 2001). The
second approach can be applied to any situation,
provided that the stress history and stiffness of the soil at
the abutment is properly modelled. We find that, where
measurements exist, the soil pressures can be
adequately described using a single monotonic push
arising from the thermal expansion of the bridge deck.
This considerably simplifies soil structure interaction
analysis, but nevertheless provides the opportunity for
economic design. Figure 5 shows apparatus developed
by England et al (2000), and Figure 6 shows the results of
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Paper 8Soil/structure interaction and railway bridge structur es
Railway Bridges - Today and Tomorrow
Figure 4 - Construction of an integral highway bridge with embedded wall abutments
Figure 5 - Apparatus for measurement of soil pressures
acting on a rigid retaining wall sub jected to repetitive
cyclic loading,(after England et al, 2000)
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simulations using the retaining wall programme FREW
(Pappin et al, 1986).
The horizontal soil stiffnesses implied by the best-fit
curves in Figure 6 are about 4 or 5 times higher than
would be expected for soil undergoing a single application
of load. The total (i.e. double-) amplitude of movement in
the test reproduced in Figure 6 is 0.25%, equivalent to a
thermal cyclic movement of 125mm for a 5m high
abutment that is free to rotate at the base.
Integral Bridge Analysis
The analysis of integral bridges is complicated by the high
degree of redundancy of these structures, the associated
induced load effects (e.g. temperature loading, creep and
shrinkage) and the global response of the whole bridge tolocally applied loads. As the soil response to bridge
movements is essentially non-linear, care needs to be taken
to establish the critical (extreme) soil responses and to
conservatively combine these with the appropriate load
effects. A single 3-dimensional grillage model, representing
the entire bridge and foundation is required, to analyse,
combine and envelope the large number of different loads
applied to the bridge.
The analysis procedure shown in Figure 7 allows critical soil
responses to be identified in FREW, by applying the
constrained forces and moments derived from a grillagemodel of the deck (the connection to the abutment is
modelled as encastre) directly to a FREW model where the
axial and rotational stiffness of the deck have been
modelled. This soil response can then be simply converted
to a soil pressure (for the more highly loaded soil zones) and
soil spring values (where the soil response is well within the
elastic range) to be applied to a GSA model. The analysis
results for the combined load effects in the grillage model
correlate closely to those achieved in the FREW model.
In addition the time dependent effect of repeated soil loading
can also be modelled in FREW as described above and
demonstrated in Figure 6, and thus the soil response tothermal expansion after repeated loading cycles can be
identified.
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Paper 8 Soil/structure interaction and railway bridge structures
Railway Bridges - Today and Tomorrow
Figure 6 - Results of FREW analyses of Test SW25 of England
et al (2000), geometry upscaled 10 times. Measured values
are shown dashed. Solid lines are pressures obtained using
the quoted horizontal Young's modulus values.
Figure 7 - Analysis Procedure for Soil/Structure Interaction of Integral Bridges
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Comparison of Limit Equilibrium and Soil/Structure
Interaction Analysis Methods
The following exercise was carried out for the Highways
Agency, to demonstrate the effectiveness of simple soil
structure interaction methods and to allow a direct
comparison to be made between limit equilibrium
methods and soil structure interaction methods for integral
bridge analysis. This is part of on going research to
support the development of a new design standard for
integral bridges.
The effect of different soil loading approaches was
investigated on a 35m span integral portal bridge withembedded abutments (see Figure 8). The design of this
form of structure, which provides a low maintenance
structure that allows the deck to be quickly erected in
short road closures/railway possessions is documented
elsewhere (Riches et al, 2005).
Limit Equilibrium Approach
Earth pressure distribution was calculated in accordance
with standard limit equilibrium theory (i.e. ka and ko to BS
8002) with vehicle surcharges applied as a constant
pressure behind the abutment.
These loads were applied directly to the three dimensional
grillage model in accordance with proposed rules to be
included in a new Bridge Design code on integral bridge
designs, whereby a pressures are applied over a defined
zone as indicated in Figure 9. Below this point the soil
response was obtained by applying elastic soil springs.
In accordance with BD 37/01, 4 critical soil responses
were identified:
Group 1 min ko
Group 1 max ko + vehicle surchargeGroup 3 min ka
Group 3 max k*
Soil Structure Interaction
The soil pressures and elastic soil spring values were
obtained from a FREW analysis by applying deck
restrained forces and moments (obtained from a 2D
grillage model of the deck with encastre ends) from the
following load cases to identify the soil response:
Group 1 min Dead load hogging moment
Group 1 max Maximum deck hogging moment +
vehicle surcharge applied to soil
Group 3 min Thermal contraction + dead load only
hogging moment.
Group 3 max Thermal expansion + maximum deck
hogging moment (soil properties modified to model long
term soil response)
In order to model the long term soil response in FREW soil
stiffnesses were obtained using 'small strain' soil
stiffnesses, for example those values published by Seed
70 Railway Bridges - Today and Tomorrow
Figure 8 - Bridge geometry and structural form
Figure 9 - Soil pressure distribution using the limit equilibrium
approach
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and Idriss (1970) applicable to a shear strain level of 10-
6. Other formulations are available, for example in Lehane
et al (1996), and these lead to similar, very high, values of
horizontal soil stiffness for the repetitive load effect under
thermal cycling of the bridge deck.
For both approaches, the loads were applied to a grillage
model and factored, combined and enveloped to generate
an ULS envelope of load effects. A comparison of the two
approaches was then carried out, and a summary of our
findings is presented in Table 1 below.
This exercise demonstrates the limitations of the simpleapplications of limit-state theory soil pressures to such
structures. Simple limit state theory cannot accurately
define the distribution of soil pressures which are
generated as a direct response to abutment movement
caused by deck loading. The use of a soil/structure
approach to identifying critical soil pressures should lead
to significant cost savings in abutment reinforcement and
piling costs and promote the design of new and innovative
bridge forms.
The new bridge design code, currently being
commissioned by the Highways Agency, is likely to
promote the use of soil structure analysis techniques. This
will also encourage the design of such structures for
railway under-bridges, leading to new, cost effective and
low maintenance bridge forms.
Conclusions
Several uses of soil-structure interaction analyses are
presented. All have enabled more economic design
solutions to be selected, based on careful consideration of
bridge and soil displacements, and their relationship to
both the serviceability and ultimate limit states. In
particular, the use of soil-structure interaction analyses
will enable the design of integral (bearing-free) bridges tobe optimised, resulting in cost-effective solutions.
Acknowledgements
The authors acknowledge the support of their colleagues
in Arup, and those clients, which include Network Rail,
Highways Agency, and Union Rail (Northern) Ltd., who
have given us the real project challenges to enable
appropriate solutions to be developed and built.
71Railway Bridges - Today and Tomorrow
Figure 10 - Soil pressure distribution using soil structure
interaction
% Decrease in Load Effect
Negligible
Negligible
Negligible
30%
20%
Deck Sagging Moment
Deck Hogging Moment
Deck Axial Load
Abutment Moment (tension
on front face)
Pile Moments
Table 1: Reduction in global load effects on an integralbridge achieved by using soil/structu re interaction analysiscompared to limit equili brium soil l oads.
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References
1. Barker KJ and Carder DR (2001, 2006). The long term
monitoring of stresses behind three integral bridge
abutments Technical Paper 10. Concrete Bridge
Development Group.
2. Cosgrove EF, Lehane BM and Ng CWW (2001) Sand
tested under cyclic triaxial conditions with constant radialstress.Proc.Int Conf, Soil Mechanics and Geotechnical
Engineering Vol 1 pp63 to 68.
3. Darley P, Carder DR,and Alderman GH (1994)
Seasonal thermal effects on the shallow abutment of an
integral bridge in Glasgow TRL Reprt 178 Transport
Research Laboratory UK.
4. England GL, Tsang NCM and Bush DI, Integral Bridges
- A fundamental approach to the time - temperature
loading problem, Thomas Telford Limited, 2000.
5. HA (2003)Design Manual for Roads and Bridges,
Volume 1, Section 3, Part 12, BA 42/96 The design of
integral bridges, Highway Agency
6. Hambly E (1991) Bridge deck behaviour. 2nd edition.
EN Spon.
7. Lehane B, Keogh DL and O'Brien EJ Soil-structure
interaction analysis for integral bridges, in Advances in
Computational Methods for Simulation (ed. BHV
Topping).Civil-Comp Press, Edinburgh pp201-10. 1996
8. Montens S, J-J Leullier, K Benadda and S Jenkins
(2003) Design of piled slabs for the Channel Tunnel Rail
link. Proc. Symp Structures for High Speed Railway
Transportation IABSE Antwerp
9. Muir-Wood D and Nash D (2000) Earth pressures on
an integral bridge abutment: A numerical case study Soils
and Foundations vol. 40, no6, pp. 23-28
10. O'Brien EJ and Keogh DL Bridge Deck Analysis. E
&FN Spon. 1999
11. O'Riordan N. Ross A, Allwright R and Le Kouby A.(2003) Long term settlement of piles under repetitive
loading from trains. Proc. Symp. Structures for high
speed railway transportation. IABSE Antwerp.
12. Pappin JW, Simpson B, Felton PJ and Raison C,
Numerical analysis of flexible retaining walls, Symposium
on computer applications in geotechnical engineering,
The Midland Geotechnical Society, April 1986.
13. Riches O.J., Carstairs N.A., Jones A.E.K (2005), A
simplified integral composite bridge connection ICE
Proceedings, Bridge Engineering 158 Issue BE2.Seed HB and Idriss IM, Soil moduli and damping factors
for dynamic response analysis, EERC Report No.70-10,
Berkeley CA, 1970.
14. Springman SM, Norrish ARM and Ng CWW, Cyclic
loading of sand behind integral bridge abutments, TRL
Report 146, Transport Research Laboratory, 1996.
15. Xu M, Bloodworth AG, Lee MMK (2003) Numerical
analysis of the embedded abutments of integral bridges. Proc.
Symp. Structures for high speed railway transportation. IABSE Antwerp
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73Railway Bridges - Today and Tomorrow
Day Two
23 November 2006
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74 Railway Bridges - Today and Tomorrow
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75Railway Bridges - Today and Tomorrow
Paper Nine
Innovation Now & In The Future
Alex Cole
FAIRFIELD-MABEY
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76 Railway Bridges - Today and Tomorrow
Network Rail has set a challenge to the industry. It has
identified that it needs to produce significant efficiency savings
that will translate into cost savings year on year. Contractors
and specialist suppliers need to work together to innovate and
deliver these cost savings. Successful teams would be
rewarded with repeat business and the opportunity to
continue innovating. So how can Network Rail make this
happen; how are other clients approaching this problem; what
are the benefits of success; and what are the present barriersthat exist to ensuring that the industry lives up to this
challenge? This paper attempts to answer some of these
questions from a specialist bridge steelwork contractor's
viewpoint.
As one of the UK's leading bridge steelwork contractors,
Fairfield-Mabey is involved in the fabrication, erection and
protective treatment of around 50 bridges annually. As a
result, we have significant specialist experience of the issues
relating to steel plate procurement, plated steelwork
fabrication, different bridge steelwork erection techniques
(e.g. using heavy cranage, incremental launching or self propelled motorised trailers), and bridge steelwork protective
treatment.
In addition to its specialist experience, the company has
arguably the most automated fabrication facilities in the world
dedicated to bridge steelwork fabrication. These operate 24/7
for 50 weeks of the year and use some of the most advanced
fabrication techniques available to the industry including:
• A fully integrated CADCAM system avoiding the need for
fabrication drawings on the shop floor and significantly
reducing the effects of human error
• Computer Numerically Controlled plate profiling, drilling
and marking machines
• Automated plate edge grinding and girder assembly
machines
• Abrand new state of the art robotic welding facility
The combination of significant specialist bridge steelwork
experience and highly automated fabrication facilities is
unique to the company and, as a result, many project
teams like to involve us in developing their designs to help
minimise costs and risks associated with their bridge
steelwork. Many understand that advice is time specific
and that this will change as new technology is introducedto the marketplace, modifying the balance between
different cost components (e.g. if steel material prices
rise). In an attempt to control this process, we collate its
specialist knowledge in a Value Engineering Database,
which we put at the disposal of the teams on the projects
we are involved in.
We are involved in the Value Management process on
many projects for many end users including the Highways
Agency, County Councils, private developers and
Network Rail.
Each end user currently adopts a different approach to the
procurement of their project and some adopt different
approaches on different projects. Before we look at the
most common approaches and what innovation results, it
is worth considering the different stages of a design and
the points at which cost savings can be made.
The design process typically involves a conceptual design
stage followed by a detailed design phase. At the conceptdefinition stage, stakeholder requirements are analysed
along with client preferences and the concept of the
structure is determined. In the case of bridge steelwork,
this involves choices of materials - concrete, steel, timber
etc. - and structural configuration - through plate girder,
through box girder, ladder beam, multi girder, bowstring
arch, through truss, cable stayed, etc. It is at this stage
that critical cost related decisions are made and it is at this
stage that specialist input can have the most impact.
Savings of 25% to 35% of structure cost have
successfully been realised on recent projects by involving
us at this concept definition stage. If specialist input is notprovided at concept definition stage, it is not too late to
change structural form later, but the implications in terms
of redesign costs and consequential affect on programme
often make such changes very difficult.
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Figure 1 - Robot Welding at Chepstow
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77Railway Bridges - Today and Tomorrow
It is important for specialists to give honest advice. For a
steelwork contractor, this means that, if it is clear that a
concrete solution is the best solution for a particular
problem, we need to say so. In addition, it is important for
the project team to listen to all of the advice given by the
different specialists, analyse each of the different possible
solutions, and choose the best solution for the project, not
an individual member of the team.
Having chosen a concept, the team can then proceed to
detailed design. For projects involving a steelwork
contractor like ourselves, this includes defining steelwork
details that suit automated fabrication including robotic
welding, that have the right balance of material and
workmanship costs, that suit the chosen erection method,
and that give the client a quality whole life solution in the
quickest possible time and at the lowest possible price.
If the right details are used, cost savings of 5% to 10% can
be delivered by involving a specialist steelwork contractor
during the detailed design development stages. Again, it isimportant to ensure that the input is provided at the right
time, to avoid any rework and wasted cost and effort from
a design point of view.
The above clearly demonstrates that it is best to involve specialist
suppliers as early as possible in the design development process,and preferably right at the start, before any design work has been
done - effectively when the team is looking at a 'blank sheet of
paper'. In practise, many end users adopt procurement
techniques that entail the involvement of specialists much later.
The most common and most traditional form of
procurement is the 'construct only' competitive tender.
In this, the end user commissions a conceptual and
detailed design from a consultant. The consultant may
or may not involve specialists in this work, but the latter are often reluctant to get involved as it is usually more
beneficial to wait until the tender period and then take
advantage of one's specialist knowledge to help win the
work. Having picked a contractor, the end user then
expects 'value engineering' initiatives to deliver
savings. These initiatives can work, but their success is
often restricted by programme and savings are often
outweighed by the time, cost and risk associated with
the redesign. For bridge steelwork, this process is
unlikely to involve changing the structural design
concept and therefore the most it will deliver in terms of
savings is 5% to 10% of structure cost, assuming of course that the value of the savings are the full value
and the specialist does not ask for a share. We do not
have a problem with this form of procurement. In fact,
with a market share approaching 75%, Fairfield-Mabey
likes such projects as they are often a good source of
additional profits. The company looks for a share of the
savings it generates, making this form of procurement
a theoretical 'win-win' situation for all involved. The
traditional 'construct only' competitive tender does not,
however, produce the largest possible savings for end
users such as Network Rail as many of the possible
savings do not materialise because of the associated
implications on programme and additional design work,and because they are only getting a share of the
savings from the small number of changes that are
adopted.
The next logical step in procurement route is 'Design
and Build'. Here, the end user invites tenders on a
Design and Build basis. Contractors then employ a
designer to produce as much design as they need to
provide accuracy of price. At this stage, however, the
contractor's spend is at risk and he wants to spend as
little money as possible before he is awarded the
project. Some team up with specialists such asFairfield-Mabey to help with this process, and the result
can be a low cost design concept. Many do not,
however, and again the design ends up very similar to
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Figure 3 - Erection of Leven Viaduct
Figure 4 - Leven Viaduct
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78 Railway Bridges - Today and Tomorrow
that which is produced via the 'construct only' competitive
tender process, but lacking in detail. Then, a big risk
comes into play, the 'design growth' risk. How much will
the design that the specialist has priced change by before
he builds the bridge? This risk is very difficult to price, and
many contractors have lost money as a result of getting it
wrong. The inevitable result is that risk allowances grow
and any savings generated by getting specialists involved
go to mitigating the effects of post award design growth,or increasing the contractor's and specialist's possible
gain. Again, we are more than happy to get involved in
such projects and have successfully made money on
many of them. They do not always, however, provide the
best result for the end user like Network Rail. This is
because any savings that are generated by getting
specialists involved during the tender process are usually
counteracted by the risk allowance for future design
growth, whilst any savings generated post award only
serve to increase the contractor's and specialist's return
from the project.
The most modern form of procurement technique has
commonly become known as 'Early Contractor
Involvement' (ECI). In this, the contractor is employed
under a professional services agreement to work up a
design and associated target price. In the event that the
target price goes over budget, the end user can choose
not to proceed or, in exceptional circumstances, to put the
project out to competitive tender. Contractors can getspecialists involved at the right stage - the concept
definition stage. The largest project savings can thus be
made and, because the contractor and specialists are
involved in developing the design, construction method is
taken into account, and programmes become more
realistic. Price competitiveness is demonstrated via an
'open-book' arrangement and by benchmarking against
other competitively tendered projects. If the process
works well, the end user gets all of the benefit from the
involvement of the contractor and his team of specialists.
The contractor and specialists get a fair return and it is a
true 'win-win' situation for all.
With repeated use of the ECI procurement route involving
the same project teams, continuous improvement can be
bought to the fore, with team members taking what has
been learnt from project to project and improving on it
each time. As each project is completed, trust develops
and traditional contractual relationships are broken down
to the benefit of future projects.
We are involved in a large number of ECI schemes for many clients. We have seen many successes, and some
failures. The most important ingredient to this form of
procurement route is trust between the parties. It is often
when this breaks down that the process fails to deliver
Best Value to the client. It is without a doubt the most
difficult procurement route to administer and get right, but
when it works, it can deliver significant savings to the end
user.
The main benefit to specialists from such a form of
procurement is long-term visibility of workload and the
assurance that the work will be carried out in a nonadversarial partnering environment.
Certainty of future workload would enable specialists to
plan better for the future, to continue to invest in new
technology, and to continue to deliver better value to their
customers.
End users such as Network Rail can benefit significantly
from the ECI procurement route. This would be one way
of generating the efficiency and cost savings it is looking
to achieve. Its ECI project teams could then be involved in
driving the industry forward, reviewing and updating
specifications and developing new standard designs for
its infrastructure. This would not involve simply tweaking
existing designs. To get real savings, design codes and
other criteria need to be challenged and developed for the
good of all.
The most important ingredient to making the ECI process
work is trust between the parties. Without this, it is
doomed to failure. Our industry is full of people who do not
trust each other.
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Figure 6 - Gelderd Road Bridges, Leeds R & R
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79Railway Bridges - Today and Tomorrow
When a specialist steelwork contractor suggests that a
project team should design a bridge to suit its automated
facilities, or involve him early in the design process, he
gets mixed responses. Some, who have not worked in this
way before, assume that all the specialist is trying to do is
gain an advantage over his competitors. They suggest
that he will take advantage of the situation by inflating his
prices and making exorbitant returns. Others, who have
seen the benefits on past projects, would often like for it to
happen, but are constrained by policies that dictate that all
contracts should be competitively tendered.
Clearly, the responsibility rests with the specialist to
convince project teams that he can help deliver better
value through early involvement and that he can be
trusted not to take advantage of the situation. It is also
clear, however, that a team approach and a willingness to
adopt a modern approach to procurement such as ECI,
would enable specialists help deliver the cost and
efficiency savings that Network Rail is looking to achieve.
Figure 8 - Erection of River Tame Bridges, TV4
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81Railway Bridges - Today and Tomorrow
Paper Ten
Design for Minimum Future Management
/Maintenance Costs
Tim Holmes and Dr. Paul Jackson
GIFFORD
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Introduction
One of the most prevalent complaints of civil engineers
over the last twenty to thirty years has been the apparent
lack of foresight in considering the future needs of road
and rail transport on the development of new
infrastructure, and the lack of consideration when
refurbishing the existing network of future operational
service requirements.
The authors have been involved in many projects where
the 'Brief' is solely concerned with solving the present
situation with no recourse to considering whether the
preferred option will facilitate further expansion. A very
pointed example in the late 1970s was a new motorway
contract which was originally designed as three lane and
then for cost reasons re-designed as two lane with no
accommodation for future widening. Widening is now
taking place with major issues concerning land take,
bridge replacement/widening and all the other associated
issues of disruption, service undertaker diversions andeffects on other adjoining infrastructure. All of these had
been major problems the first time around.
Even now, on major upgrading schemes, there appears to
be still no apparent consideration to potential future
modification needs and, even worse, no actions are taken
with respect to potential future management issues
associated with the continued re-use of the modified
infrastructure. There appears to be a view that 'Design'
and 'Future Management' of the Infrastructure are totally
distinct areas. Indeed, until quite recently, the
organisational set up within many private engineeringpractices and public engineering departments reflected
this view.
For a Bridge, 'Future Management' embraces a number of
major issues reflecting its continued 'Functionality', i.e.
how can it continue to meet the 'Operational' requirements
of the road or rail network. It is considered that these key
issues include future steady state maintenance, renewal
and upgrade of components, future modification or
demolition and replacement and ability to remain 'fit for
purpose' when subject to events such as fire, impact and
flood. 'Functionality' should also include provision for
inspection and repair, renewal and supply of futureservices, re-gauging and even protection from graffiti and
pigeon roosting.
Maintenance is a key issue and in the last twenty years
great strides have been made in the understanding of the
various modes of degradation of structures and in the
development of robust specifications for various bridge
components. However, there is still a lack of
consideration of 'maintenance' in Design, particularly with
respect of adopting 'Best practice' solutions and providing
the necessary access for undertaking maintenance and
the future replacement of components or indeed givingthought to 'over-design' in certain critical areas.
It is the Authors' considered opinion that there is need in
'Design' for an 'Operational Limit State' that reflects the
'Future Management' needs of the structure.
In giving consideration to this additional 'Limit State', it is
recognised that 'Cost' must still be a major issue in the
development of any proposed scheme. To date, 'Future
Management' Issues have to a large degree been ignored
given the discount rate mechanism used in any 'WholeLife Costing' comparison that has been undertaken. Also,
there has been a lack of political will for spending now to
facilitate the future 'Operational Needs' of structures.
This paper gives some thoughts on the content of an
'Operational Limit State' and also on the methods that
should be adopted in determining the appropriate way
forward for a particular Rail bridge scheme. This can be
termed 'Design for Minimum Management/Maintenance
Costs'.
Aspects of Funct ional ity
This 'Functionality' can be separated under a number of
different headings:
• Maintenance
• Modification/Replacement
• Rail Operations
• Exceptional Events
• Secondary Components
• Third Party Issues
a) Maintenance
This should embrace:
i. The use of standard detailing promoting Best Practice
- this is already well underway within Network Rail for
steel footbridges and this is to be extended to rail
underbridges. This is a great step forward that promotes
both buildability (another key issue of design) and also
'state of the art' structural steelwork detailing that gives
proper emphasis to future maintenance by the provision
of suitable components, connections and a robust
protection specification.
ii. Designing out of Maintenance Issues - consideration
must be given to the elimination of potential critical areas
for corrosion or where access is difficult.
As an example, Integral bridges are favoured by the
Highways Agency as they eliminate joints and bearings.
Consideration should be given to their use but they can
also have their disadvantages. For instance, their
design can be complex and their use for upgrading
existing structures may necessitate modifications to the
substructures. They also preclude the future jacking of
the structure which could be a major problem if, for instance, re-gauging could be a potential functional
requirement for the bridge.
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'Over-design' of critical components should be
considered; this is often a very cost effective way of
introducing further life into the structure. This is very
common practice on marine structures for very good
reason and could easily be adopted for bridges.
iii. Form and Material Type - more emphasis should be
given on the choice of form and material type to minimise
future maintenance issues. It is recognised that the formand material type are dictated to a large degree by
issues of geometry, loading criteria, ground conditions,
etc but it is felt that more consideration should be given
to evaluating the maintenance issues that could arise
from each potential solution. The ongoing debate of the
use of GRP versus concrete and steel solutions should
be evaluated.
iv. Specific Maintenance Issues - it is important to
recognise that for particular structures, their functionality
is directly related to their condition. This can be, for
example, maintaining the protection works for potentialscour to river and marine works. It is also an extremely
important matter for structures such as underpasses for
pedestrians where their safe use is related to issues of
drainage, vandalism, graffiti, lighting, etc.. These should
be critical elements of the 'Design', especially as
'maintenance' will probably be a regular occurrence.
The effects of pigeon roosting can both be an
environmental issue and also lead to potential
maintenance problems for the structure. Again, the
Design must reflect this.
v. Access - Future access for inspection and
maintenance needs to be an integrated part of the
Design and must give due consideration to rail
operational matters. Where the cost of conventional
external access is high, either in terms of direct or
disruption cost, further thought should be given to
designing it out. For instance, the Highways Agency
uses Inspection Galleries for access to bearing
shelves/end of beams/drainage.
From an inspection perspective, it is important that a
General Inspection can report visually on all key
components. It is considered that reliance on the
Principal Inspection, possibly with difficult access issues,is inappropriate for monitoring ongoing maintenance
issues.
b) Modification/Replacement
It is considered that much more emphasis needs to be
taken during the development of options to potential
modifications that may need to be undertaken to maintain
the functionality of the structure during its potential 120
years life. It is recognised that many of the replacement
structures over the next five to ten years will be in areas
of the network where there will be major logistical issues.For these especially, consideration of future modification
could be considered to be a key requisite of the design.
Modification may not take place but to design simple
practical methods does not need to be a costly matter.
For instance, for potential widening of a structure, the
Design could explore the over-design of particular
components, facility for the removal of the edge members
and the introduction of couplers buried in the structure.
There is a general need to think much more in Design
about the use of 'modular systems' for easy erection and
removal.
More thought also needs to be given to substructures interms of potential upgrade/modification. Presently, major
issues are being experienced on the upgrade of quite
recent substructures on road and rail schemes where all
the information is not available covering issues such as
backfill properties, pile capacities, chemical testing
results, etc.. Even where the information is available,
there is a lack of reserve capacity for
upgrading/modification without major recourse to further
site investigation and strengthening. On the older stock of
structures, every bridge deck reconstruction raises issues
of abutment stabilisation during the works and of potential
dead or live load increases. For new structures or major upgrades, it would not be expensive to provide a reserve
of capacity to cater for a potential future modification of
the structure. This could include allowing for temporary
stability during any deck re-construction.
c) Rail Operations
For a rail structure, it is imperative that its future
functionality addresses the needs of the 21st Century
railway and beyond! To this end there are key issues
associated with matters such as:
• Potential Upgrading for Gauging clearances, in particular
headroom
• Track re-alignment
• Power/signal implications, e.g. fixings for OHLE masts
• Provision of Access/Safe walking routes, etc.
• Communication cables, drainage, etc.
Obviously, Technical Approval does include the short term
inter-disciplinary issues but more strategic thinking shouldbe undertaken. For instance, future implications of re-
gauging for freight could necessitate lowering of the tracks
or raising the structure on an overbridge. Potential for
jacking the structure or deepening the foundations could
be appropriate.
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d) Exceptional Events
Bridge strikes are a major issue with rail underbridges,
especially as headroom cannot readily be increased.
Even with impact design, there is still a major risk of
damage to the edge girders and of movement of the
structure. Independent barriers have been used on some
bridges which, although preventing damage to the bridge,
can cause safety issues with the itinerant vehicle andother road users. The use of crash cushions or other
forms of sacrificial component that act like a crumple zone
to dissipate the energy from the impact, should be
considered as a possible way forward.
Design for functionality should also consider the
implications of vandalism, fire, flood and the like.
e) Secondary Components
Although robust Specificat ions exist for all bridge
components, such as joints, bearings, and waterproofing,it is imperative that the Design includes the choice of
appropriate proprietary products. These should meet the
structural needs of the bridge and be able to be
maintained in a suitable manner to meet their predicted
service life.
The Design must also recognise that Secondary
Components will need to be replaced from time to time.
Therefore they should be easily replaceable without
compromising the structural performance of the structure
and without progressive dismantling of adjacent elements.
The Design also needs to assess the need for temporary
works and access required for replacement including
implications for traffic closures.
For bearing replacement, it is essential that provision is
made for jacking, such as the incorporation of additional
stiffeners and jacking plates, so that this can be carried
out with least disruption.
f) Third Party Issues
In assessing the continued functionality of a structure, it is
important to consider the future 'Operational' needs of
Third Parties affected by the bridge. For a rail bridge, thiscan obviously include a Highway Authority, Statutory
Undertakers, Local Developers, etc. A number of issues
can arise which the Design should attempt to address.
These include:
• For an overbridge, Statutory Undertakers apparatus
can have a major effect on the form of construction and
on providing suitable access for their maintenance and
possible replacement. They can have significant
implications for the water tightness of the structure. It is
therefore essential to realise the need to develop
appropriate details around the services including, wherenecessary, allowance for relative movement between the
services and the structure, and which at the same time
protects the structure from ingress of water
The Design must also consider the effects on the
structure of future maintenance and replacement of the
services and also the replacement of secondary
components associated with the services. For
underbridges, access to services beneath the structure
may have implications on stability of the structure and
this should be considered during the Design.
• Provision of additional ducting for future additional
services should be considered during the Design.
Experience has shown this to be a sensible approach to
avoid potential modifications to the bridge at a later date
• The Design must also reflect the maintenance needs
for the Highway Authority associated with areas such as
lighting, drainage, highway improvements and the like
The Way Forward
The above has discussed what should be considered indesign beyond the immediate issues of strength and
serviceability. It remains to consider how this might be
encouraged within existing Contractual Arrangements.
This can be particularly difficult when Contracts are let on
a Design and Build basis. The idea is that tenderers
should compete to achieve the minimum price within a set
of defined criteria. It is therefore desirable to include all
the issues considered above within the criteria.
Ideally, many of these issues would be considered
quantitatively as an additional limit state which might be
called the "operational limit state".
There is a gradual move towards such quantitative design
and the concept of a limit state of durability has been
raised. In principle the life could be calculated and
checked against the required design life just as other
limits are checked.
In practice many of the issues considered cannot be
analysed in this way, or perhaps cannot yet be analysed
in this way. Durability itself has not reached this point
although modern design codes such as EN 1992 are
moving in that direction.
Another alternative is to incorporate what is required in
the Specification or other documents. The Highways
Agency has moved a long way in this direction with
numerous documents defining what is required. One of
the most significant is Design for Durability, the document
which promoted the move to integral bridges.
Specifications also define such components as
waterproofing.
A disadvantage of this approach is that it is prescriptive
and could stifle innovation. There is a move towards
performance specifications but it is difficult to measuremany aspects of performance. For example, use of epoxy
coated or stainless steel reinforcement, which are not
normally used in standard UK specifications, may give as
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good a durability performance with other aspects of
current specifications relaxed, e.g. cover, concrete quality
or the requirement for waterproofing. However, this is not
easy to prove.
Some of the issues effectively have to be considered by
the client side, and cannot be incorporated in a Design
and Build Contract. A design and build contractor cannot,
for example, decide what provision for future increases incapacity are needed. It may, however, still be useful to
quantify such issues.
One potentially useful approach is a 'Risk Evaluation'
Register which can act as an audit trail for determining
which issues as detailed above should be included for in
the Design of a particular structure. It is recognised that
cost will always be a major factor in some of the decision
making BUT it is considered that many matters are key to
the future functionality of the structure and must be
reviewed in detail.
In addition to more obvious "risks" such as of accidents,
probabilities of major increases in services requirements
or traffic increases could be considered. The potential
cost saving by providing for these in advance could then
be evaluated. Although the estimated probabilities are
unlikely to be accurate, they will give some indication of
whether such provision is viable.
Closing Remarks
Many of the issues raised here are no doubt being taken
into account. However, there is much scope for improving
the consideration of long term management of structures
in design, and the ways in which these might be
encouraged have been proposed.
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87Railway Bridges - Today and Tomorrow
Paper Eleven
Advances in Rail Underbridge
Replacements
Andrew Dugdale
HYDER CONSULTING (UK)
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88 Railway Bridges - Today and Tomorrow
Abstract
U-Decks, or 'Bathtubs', are a recent introduction to the UK
rail infrastructure, the benefits being in simplified
fabrication, improved appearance and reduced
construction depth. The 13m span structure in Darlington
was replaced during the weekend of 27-30 August 2004
using two identical U-Decks. The paper reviews the
construction 4 bridge deck replacements (including oneU-deck) and comments upon the constraints leading 4
very different solutions
The paper describes the benefits of the U-deck deck,
reviews the main structural aspects and compares the
design with more traditional U-frame steel rail underbridge
solutions. The paper reviews construction depths for
several types of deck including ballasted and fixed tracks.
The U-deck is constructed by welding the girder webs
directly to the single deck plate. The deck is in filled with
concrete and provides a fully tanked bridge deck for waterproofing. The composite action of the concrete infill
enabled the construction depth to be minimised to
220mm, compared to 250mm for a standard battle deck.
This saving in construction depth facilitated the provision
of ballasted track, whilst maintaining the existing
headroom and avoiding the need for a track lift.
The off-site fabrication of the steelwork and in situ
concrete enabled the decks to be craned into position
during a single weekend possession. A review of
construction techniques (Crane v Heavy duty transporter)
is also included, together with discussions on buildability.
Keywords: Rail Bridge, U-Deck, Steel, Construction
Depth.
1.0 Introduction
In 2004 the British Government introduced a White Paper
entitled 'The Future of Rail' [4] which updates the 10 year
plan presented by the SRA as a vision of the rail network
in 2010. The original vision for increasing the nation's rail
passenger capacity by 50% has now been moderated to
35%. Since publishing the initial plan it has been
identified that much of the UK rail network is running closeto capacity, with capacity of main lines often dictated by
discreet bottlenecks. Moreover, the desire to increase
freight traffic by 20% is at odds with running an efficient
high speed passenger service on the same tracks.
Throughout the current London North Eastern (LNE) territory,
secondary routes have been identified for upgrading to
primary freight routes, thereby opening up the East Coast
Main Line (ECML) for an increased volume of high speed
passenger trains. These secondary routes contained many
of Britain's 40,000 railway bridges and tunnels [17] which
require ongoing inspection and maintenance, the majority of
which span local roads and are in the span range of 10 to
20m.
Many of these structures date back to the original
construction of the railways, in times when road traffic was far
less than today and headroom restrictions were considered
acceptable. As a result, the current rail network includes a
significant proportion of rail underbridges with a clearance
less than 5.3m as currently required by the Highways Agency
document TD27/96 [8]. In recent years the number of bridge
strikes reported to Network Rail has shown a steady increase.
Between April 2003 and March 2004 there were 1870 bridge
strikes at railway bridges over a road reported to Network Rail
[13]. The demands on bridges on the modern rail network are:
• Increased line speed
• Increased capacity to Route Availability (RA)10
• Design Life of 120 years
• Headroom clearance to be maintained or improved
Since 2000 Hyder Consulting have been working with May
Gurney Rail under their Structures Partnership with Network
Rail to assess the feasibility for strengthening and
replacement of bridge decks. This paper reviews four recent
replacements with particular emphasis on the modern U-
Deck design. The structures reviewed are:
• Neasham Road (DSN1/2): Twin U-deck installed by
crane. The steel deck with composite concrete floor was
chosen in conjunction with the desire for ballasted track for
its minimal construction depth
• Ridley Hall (NEC2/96): Reinforced concrete slab
incorporating Edilon direct fixing installed by HDT
• Forge Road (NEC1/20): Twin girder with transverse
battle deck installed by HDT. Twin ballasted track was
provided with shallow depth concrete sleepers
• Sand Lane (ABE1/7): Twin 'Z' girder half through type
with steel battle deck type floor units installed by crane.
Ballasted track was provided on steel sleepers with a
tracklift of 125mm
Paper 11 Advances in Rail Under bridge Rep lacements
Figure 1 - Neasham Road Underbridge (Cantilever footway and concrete deck in fill omitted)
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Railway Bridges - Today and Tomorrow
2.0 Design Constraints
2.1 Possession availability
A distinctive feature of bridge replacements in the modern
railway environment is the requirement to be installed and
commissioned within possessions; typically the rails and
ballast are removed, the deck replaced and the track re-
opened within a 54 hour period. Often these possessionstake place on bank holidays and their very nature
necessitates 24 hour working. This high pressure
environment creates risks of its own which must be
managed by the Contractor. The designer role, reinforced
by the Construction (Design and Management)
Regulations [9], is to ensure that all risks are 'designed
out' as far as reasonably practicable. This is best
achieved through early consultation with the Contractor
during the feasibility stage.
Throughout the design and construction process May
Gurney and Hyder convened regular workshops involving
the designer and construction teams. It was found
advantageous to include hold points on the design until
reviews were complete to ensure that previous lessons
were incorporated and time-consuming site operations
were avoided during the possession period.
Understanding the risks to the programme during the
possession period were key to delivering successful
designs, ensuring installation and track hand-back within
the permitted timescale. Often off-site fabrication wasrequired, with bridge deck components erected close to
the bridge site; this acted both as a trial erection and
allowed components, too large to be transported by road,
to be erected. Wherever possible possession activities
were reduced to an absolute minimum, with consideration
for adverse weather conditions taken into account.
2.2 Geotechnical Considerations and Exist ing
Abutments
During the early stages of the feasibility design it was vital
that the designer undertook an adequate site investigationto determine ground conditions and the condition of the
existing abutments. Significant savings in both time and
money were achieved by retaining the existing abutments.
Appendix C of GC/RC5510[12] gives guidance on the
assessment of existing abutments for re-use.
Ground conditions were established through the use of
trial holes and dynamic probes, while the condition of the
abutments was obtained through structural inspections
and coring to determine thickness and depth of the
foundations. Where record drawings were available they
were verified by coring, otherwise typically up to 10 coresin each abutment were required.
Where existing abutments were retained, the construction
depth and requirement for access to bearings for
inspection and replacement usually meant that the cill
beam level needed to be reduced. It was found that this
was best achieved by removing the existing beams or
stonework to a reduced level, providing a level bed of in-
situ concrete (usually lean mix) and providing new
reinforced concrete cill beam units; braking forces can be
resisted by doweling into the retained abutment if
required. The size and number of the units will begoverned by installation techniques and weight limitations.
2.3 Environmental Issues
Environmental issues are increasingly important and need
to be reviewed at the feasibility stage. An environmental
checklist was prepared in accordance with
RT/LS/P/007[14] to satisfy the client's requirements and
included in the Environmental Management Plan. Liaison
with the Local Authorities, Environment, English Nature
and local groups highlighted the presence of protected
flora, fauna or wildlife, in particular bats often use the
existing bridge soffits as roosts. Trees in the vicinity of the
bridge were considered for Tree Preservation Orders as
this could impact on the use of cranes or the Heavy Duty
Transporter (HDT) on approaches to the bridge location
from the temporary erection area.
2.4 Land Availabili ty
During the feasibility stage (GRIP Stage 3) land ownership
in the adjacent areas of the bridge was determined; this
was achieved inexpensively through searches of HM
Land Registry. This is vital if items are to be lifted over
private land, or if a site compound and temporary erectionarea are required. The lack of a suitable area for
temporary erection during the week preceding the
possession meant that Neasham Road Underbridge could
not practically be installed using the HDT method.
Consideration was also given to working space and site
access during the possession. Construction of temporary
steps on the approach embankments made access
between road and rail level easier. Without immediate
access to the site, the designer should take into account
walking distance between abutments and transfer of
materials and equipment during the abutment preparationstages of construction.
Advances in Rail Underbridge Replacements
Figure 2 - Neasham Road
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90 Railway Bridges - Today and Tomorrow
Paper 11 Advances in Rail Under bridge Rep lacements
2.5 Installation Techniques
Several techniques are available for the installation of
bridges, the two most common techniques for
Underbridge replacement are the use of cranes and the
HDT. The advantages of each method are listed in Table
5, however, at an early stage in the feasibility design, the
choice of installation technique can have a significant
impact on the choice of structure.
For the crane option it was important that a suitable
working area was available in the immediate vicinity of the
bridge site. The emphasis of the design is for light
components which can quickly be lifted into position. This
method is well suited to bridge decks accommodating a
single track as lifting radii become restricted with heavier
decks for multiple tracks.
For the HDT it was vital that a suitable temporary erection
area was available close to the bridge (within one mile)
and that the road was suitable in terms of strength andwidth to accommodate the Transporter with the bridge
attached. The HDT facilitates attachment of the cill beams
to the deck or decks thereby reducing the number of
possession activities. This method is well suited to wide
structures supporting multiple decks where access and
temporary erection areas are available.
2.6 Construct ion Depth
Finally, construction depth must be considered by the
designer. For railway bridges subjected to RU loading in
accordance with BS5400 part 2 [1], it is usual for fatigue
to govern the design in spans up to around 20m. Thus theuse of 355 grade steel offers no advantage over that of
275 steel. For semi-through bridges the construction
depth, i.e. the distance between the top of the rail and the
deck soffit, can be considered as being made up of three
elements:
• Track Depth - the distance from the top of the rail to
underside of sleeper
• Ballast Depth
• Structure Depth
Deck construction depths can be optimised in a number of
ways before consideration is given to the deck
construction. It is, therefore, of significance that the
designer determines the need for ballasted track and rails
to be used by liaison with the Permanent Way Engineer.
Furthermore, consideration should be given to the use of
tracklifts and their effect on the vertical alignment of the
track.
The use of ballasted track is preferred by Network Rail as
it optimises flexibility for future track works, however, this
is not always compatible with the existing headroom.
Many older bridges made use of waybeams to limit
construction depths, the challenge to the modern
engineer is to provide a solution of minimal construction
thickness, which maintains headroom, and improved train
ride quality.
Ballasted Track
Several options are available to the designer to limit
construction depth where ballasted track is required.
Table 1 presents the various options showing how track
and ballast depth can be minimised. The designer should
also be aware that reductions in ballast thickness may
have an adverse structural affect due to reductions in
wheel load distribution, in such circumstances
considerations shall be given to load dispersal and
protection to the waterproofing during the design.
Table 1 - Ballasted Track
Sleeper Type
Depth
Waterproofing
4mm membrane,
13mm protectivematting, 3mm
tolerance
Ballast
In accordance with
GC/RT5014 and
RT/CE/S/102
Sleeper
In accordance with
RT/CE/S/049 and
RT/CE/S/029
Baseplate/pad
BS 113A rail
Total Construction
Depth
Concrete
(F 10)
20
250
204
10
159
653
Shallow
concrete
(EF 29)
20
250
165
10
159
633
Timber
20
250
130
44
159
603
Steel
20
200
100
10
159
489
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91Railway Bridges - Today and Tomorrow
Direct Fastening Track
Where the installation of a ballasted track is not possible
other options are available to the designer. For the Ridley
Hall (NEC2/96) bridge, four options were considered as
detailed in Table 4. For differing spans the construction
depth of the deck may vary, however, the table gives an
indication of the savings in construction depth offered bythe Edilon system and other direct fixings to reinforced
concrete decks.
Structure Depth
Various standard forms of bridge deck have been
developed and adapted for use on Britain's Railways
since the 1950's. The Steel Construction Institute (SCI)
gives details, examples and descriptions of the various
forms of standardised bridges (A-Type to E-Type) in their
Design Guide for Steel Railway Bridges.[5]
The forms of construction adopted by Hyder are
presented in Table 3, together with typical construction
depths. These include an adaptation of the Z-Type which
was adapted from the A-Type; the girder bottom flange is
offset from the centreline of the web to provide access
between the six-foot girder for inspection andmaintenance. For the proposes of this paper, only the U-
Deck is considered in detail
Table 3 - Construction Depths for Direct Fastening TrackEdilon direct fixing to
concrete filler beam
deck
300
N/A
Incl.
N/A
187 (Edilon)
487
Longitudinal timbers
on steel battle deck
300
25
250
10
159
744
Pandrol 'Vipa' type
clip direct fixing to
concrete filler beam
deck
300
25
45
0
159
529
Pandrol 'Vanguard'
type clip direct fixing
to concrete filler
beam deck
300
25
20
0
159
504
Fixing Type
Depth
Deck
Waterproofing
4mm membrane, 13mm protective matting ,
8mm tolerance
Fixing system
Pad
BS 113A rail
Total Construction Depth
Figure 3 - Ridley Hall prior to installation of Edilon system
Paper 11 Advances in Rail Underbridge Replacements
Steel sleeper
300
200
150
Concrete/ hardwood
sleeper
300
250
200
Category of Track
In accordance with
GC/RT5014
1
2
3, 4, 5, 6
Table 2 - Construction Depths for Ballasted Track*
*GC/RC5510 recommends a minimum of 200mm to allow for
tamping and distribution of wheel loads
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92 Railway Bridges - Today and Tomorrow
Paper 11 Advances in Rail Under bridge Rep lacements
Structure
Depth
(mm)
220
-
377
250
Construction
Depth
(mm)
824
487
981
744
Cross Section DrawingBridge
DSN1/2
Neasham
Road
NEC2/96
Ridley Hall
NEC1/20
Forge
Road
ABE1/7
Sand
Lane
Girders
4 U-Deck
-
2 Semi-
Through
4 Z-type
No of
Tracks
2x1
2
2
2x1
Deck
Construction
Composite
Reinforced
Concrete
slab
Battle
deck
Battle
deck
Table 4 - Bridge Deck Types and Construction Depths
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93Railway Bridges - Today and Tomorrow
3.0 The U-Deck Solution
The U-Deck solution was chosen for Neasham Road for
its low construction depth and suitability for installation by
crane with minimal possession activities. U-Decks have
been successfully installed in several locations throughout
the UK including the East and West Coast main lines [16].
The Neasham Road solution has a span of 13.095m and
a skew angle of 25 degrees. The benefits of thisconstruction are simplified fabrication and erection,
improved appearance and reduced construction depth.
The U-Deck design
does away with the
traditional discreet
U-frames and
utilises a
c o n t i n u o u s
constraint to the
bottom flange from
the composite deck.The U-frame action
was then
considered to act at
unit centres as
detailed in Clause 9.6.4.2.2 of BS5400 Part 3 [2]. This
approach meant that web stiffeners were not required on
the outside face of the girders and the often limiting
fatigue Class F [3] weld between the web stiffener and
underside of the top flange was omitted, permitting a
higher value fatigue Class D. The steel/concrete
composite floor design made use of a single floor plate,
which was integral with the main girders, reducing
construction depth to 220mm, compared to 250mm for astandard battle deck. This saving in construction depth
facilitated the provision of ballasted track, whilst
maintaining the existing headroom and avoiding the need
for a track lift. The solution is ideally suited for short spans.
Steelwork
The U-Deck was fabricated by welding the girder webs
directly to the single deck plate. Transverse stiffeners and
shear studs were then welded to the top side of the deck
plate before the deck was in-filled with concrete to provide
a fully tanked bridge deck ready for waterproofing. The
width between inner faces of the girder webs was chosento allow adequate clearance between the sleeper ends
and the waterproofing protection boards for ballast,
typically this dimension should not be less than 100mm or
2.5 times the ballast size, however, in practice it is often
the structure clearance gauge which governs the overall
distance between the top flanges of the cess girders or
robust kerb.
Robust Kerb
The robust kerb requirements of GC/RC5510 [12] were
accommodated by increasing the depth of the cess girder
such that the top flange was a minimum of 300mm above
track level. The top flange was then at the same level as
the cess walkway which was supported on brackets
cantilevering from the side of the cess girder. The
increased girder depth required the deck to be sufficiently
wide such that the cess girder does not infringe the
structure gauge.
Inner Girder
The top flange level of the inner girders was lowered
below the structure gauge so that the inner girder top
flanges were accommodated outside the lower sector
structure gauge as defined in Appendix 1 of GC/RT5212[11]. Designers should note that this area has been the
subject of a Network Rail derogation [10] to reinstate the
area previously defined as available for bridge girders in
Appendix B of
the now
w i t h d r a w n
G E / R T 8 0 2 9
[15]. The
height of the
cess girder top
flange is
t h e r e f o r e
limited to
110mm above
rail level.
3.1 Analys is and Design
Robustness
The flush soffit plate of the U-deck makes it less
susceptible to local distortion and buckling and the small
outstand of the flange beyond the main girder web greatly
reduces the likelihood of a flange peeling type failure.
Typically the outstand was limited to 50mm which was
further reduced by a large fillet weld to leave as small anactual outstand as possible without reducing the fatigue
classification of the deck plate to class G.
Collision Impact Protection
In low headroom situations the deck is required to sustainthe collision effects specified in BD37/01 [6]. In the case
of Neasham Road an independent impact collision beam
was provided beneath the safe cess walkway. Having
Paper 11 Advances in Rail Underbridge Replacements
Figure 4 - Neasham Road bridge prior to casti ng the concrete deck
Figure 5 -Neasham Road bridge U-Deck l ifted by 1000 tonne crane
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94 Railway Bridges - Today and Tomorrow
independent bridge decks and collision beams increased
the likelihood of the railway remaining operational in the
event of a collision. The alternative to providing the
independent protection beam would mean the bridge
bearings would need to be designed to accommodate the
500kN horizontal and vertical (uplift) forces associated
with collision. In this case the impact collision beam was
anchored into the cill beam to resist applied horizontal and
vertical (uplift) loads in accordance with BD60/94 [7].
Addi tional ULS requirement
U-deck cross members were assumed to transmit all deck
loads into the main girder web by shear via the deck
stiffener/web welded connection. In view of the fact that
this critical connection cannot be inspected once the deck
slab has been completed, it was considered desirable to
have alternative load paths available to ensure that
premature failure does not lead to excessive deformation
of the structure. To this end it is also assumed that the
deck plate must be capable of carrying the loads into the
main girder web without reliance on the rib/main girder web connection. This additional ULS requirement was
considered in the design of the web/flange (deck plate)
fillet welds.
4.0 Crane v Heavy-Duty Transpor ter
Buildability is a major factor in the choice of any bridge
deck replacement. The availability of land both
immediately adjacent to and local to the bridge site can
dictate the method of installation which in turn can
influence the form of the structure. Furthermore, with
possession availability at many sites limited to Christmasand Easter blockades, consideration needs to be made
for weather conditions and the possibility of high winds
which may hamper attempts to lift structures by crane.
The crane method
requires land to be
available in the
immediate vicinity
of the bridge site to
allow the crane
and, importantly, its
outriggers to be
p o s i t i o n e d ;c o n s i d e r a t i o n
should also be
given to the
delivery to site of
the new structure,
typically on
articulated wagons.
This method may
limit the width of the structure, which ideally should be
prefabricated outside of any possessions. In the case of
Neasham Road underbridge the 1000 tonne crane was
used for lifting the new structures and cill beams in turn. Adequate width was avai lable within the highway
boundary while no suitable working area was available for
the erection of the bridge on temporary trestles.
The Heavy Duty Transporter (HDT) method requires an
adequate area in close proximity to the bridge site to
facilitate fabrication of the deck prior to the possession.
Usually this area will be within 500 metres of the bridge
site to limit the time taken for the HDT to traverse between
the temporary and permanent sites. This method of
installation will typically include attaching the cill beams to
the deck, loading the deck with ballast and the addition of
any ancillary ballast retention units. This operation willrequire crane lifts to erect the components of the bridge,
which can be susceptible to high winds, therefore,
consideration needs to be given to erection in the
temporary location in the days or weeks prior to the
planned possession. The strengths and weaknesses of
the crane and HDT method of installation are compared in
Table 5.
The Heavy Duty Transporter method was successfully
utilised at Ridley Hall (ELR: NEC2/96). This choice was
influenced by the limited working space immediately
adjacent to the bridge which would have made the craneoption impractical; limiting the lifting capacity to 14 tonne
would have required the deck to be constructed in several
sections with in situ stitches. In this instance the deck was
attached to the cill beams in the week leading up to the
possession, then driven into position during the
possession. The use of the HDT facilitated the use of a
monolithic reinforced concrete deck without the need for
stitch joints, thereby reducing the number of possession
activities.
The ability to undertake a single lift of the deck and cill
beams offered significant time savings to the Contractor
during limited possession periods. In this instance the
deck units are attached to the cill beams and the entire
structure lifted in one operation. Where track access is
remote or limited, ballast can be stacked on the deck prior
to installation to
reduce the need to
transport materials
over long distances.
The crane method
was successfully
utilised for Neasham
Road (DSN1/2).Here the choice was
influenced by land
availability; the road
was sufficiently wide
to accommodate the
1,000 tonne crane,
combined with the
shortage of suitable
working areas to erect the bridge for use by the HDT. In
this instance the deck was chosen such that each unit
could be easily transported as a single unit. The U-deck
was fabricated, concrete deck cast and waterproofingapplied off site. The units were then driven to site during
the possession weekend; the sizes of the units were such
that no additional site fabrication was necessary. Careful
Paper 11 Advances in Rail Under bridge Rep lacements
Figure 6 - Forge Road bridge deck and cil l beams installed by HDT
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95Railway Bridges - Today and Tomorrow
planning of the sequence of delivery of the deck units and
cill beams was required due to the limited road width and
restrictions on site access.
Accuracy of installation was a consideration taken intoaccount by the designer. Clearance to the railway
structure gauge is critical and often reduced to a minimum
to tie into existing abutments and embankments.
However, consideration needs to be given to the method
of installation and time available to achieve accuracies
with care taken to ensure they are specified too onerous.
The accuracy of the HDT installation is governed by the
lowering of the support over the axles, as the deck is
lowered into position; there is an associated transverse
movement which results from the cam effect of the
lowering mechanism. As all four corners of the deck are
landed simultaneously there is little opportunity to man-handle the structure into its final position. A time
consuming system of trial and error will pursue if a high
degree of accuracy has been specified by the designer.
Contrast this with the crane method where the operator
can take the weight of the element, allowing minute
adjustments to be made to the final landing position of the
deck.
5.0 Conclusions
It is essential that the contractor and designer work
closely together to produce a solution which is practical to
build within the constraints of a railway possession.
Attention to details and tolerance at an early stage,
combined with ensuring they are achievable in a timely
and cost effective manner, will ensure the success of the
scheme.
Headroom and construction depths are often found to be
at odds with the preference for ballasted track. There are
numerous options available to the designer to reduce
construction depth and early liaison with Network Rail will
ensure a suitable compromise is achieved. Where
headroom of 5.3m can not be achieved, the preference is
to provide independent collision protection beams,allowing replacement without affecting the safe operation
of the railway.
The use of the U-Deck is a cost effective and practical
solution for spans up to around 20m and offers significant
advantages in terms of durability and flexibility of
installation methods over other solutions. Furthermore,
the structure depth of 220mm offers a saving of 30mm
over the traditional steel battle deck.
The designer should pay attention to the deck ends and
interaction between the different structural elements. Thedesigner should make use of three dimension computer
models to verify their design to avoid clashes of pre-
fabricated elements.
Finally, the successful implementation of the project will
be achieved if careful planning is implemented at all
stages of the design process by the design and
construction team.
Paper 11 Advances in Rail Underbridge Replacements
Table 5 - Crane v Heavy-Duty Transporter
Crane
Landing tolerance easily
achieved of +/- 5mm.
Availability for use for generalsite lifting of ancillary
components and materials.
Lower cost of equipment hire.
Heavy Duty Transpor ter
Minimal risk of lost lift due to high
winds.
Single lift for deck, cill beam,transition slabs, ballast etc.
minimises possession activities.
High lifting capacity. Weight Limit
of 27 Tonne per axle (Typically 6
or 8 axle units are used).
Crane
Increased risk to lift as a result of
strong winds.
Large working area requiredadjacent to final location for
crane outriggers.
Multiple lifts for cill beams, deck,
walkways etc.
Heavy Duty Transporter
Increased cost per contract lift.
Working area required in closeproximity to final location for
erection of bridge components.
Tolerance easily achieved of +/-
25mm.
Strengths Weaknesses
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96 Railway Bridges - Today and Tomorrow
Acknowledgments
The author would like to thank May Gurney Rail and
Network Rail (LNE territory) for their permission to publish
this paper. The views expressed are those of the author
and not Network Rail or May Gurney Rail.
References
1. BS5400 part 2 (1978) Steel concrete and composite
bridges, Specification for Loads. BSI.
2. BS5400 Part 3 (2000) Steel concrete and composite
bridges, Code of Practise for design of steel bridges. BSI.
3. BS5400 part 10 (1980) Steel concrete and compositebridges, Code of practice for Fatigue. BSI.
4. Department for Transport (2004) The Future of Rail -
Making it Happen. HMSO.
5. D.C. Iles (2004), Design Guide for Steel Railway
Bridges, P138. Steel Construction Institute.
6. Highways Agency (2001) BD37/01 Loads for Highway
Bridges, Design manual for Roads and Bridges. HMSO.
7. Highways Agency (1994) BD60/94 The Design of Highway Bridges for Vehicle Collision Loads, Design
manual for Roads and Bridges. HMSO.
8. Highways Agency (1996), TD27/96, Cross Sections
and Headrooms, Design manual for Roads and Bridges.
HMSO.
9. HSE (1994) The Construction (Design and
Management) Regulations. HMSO.
10. Network Rail (2204)Deviation Certificate Number
04/050/NC.
11. Network Rail (2003) GC/RT5212, Requirements for
Defining and Maintaining Clearances, Issue 1. Railway
Safety.
12. Network Rail (2000) GC/RT5510 Recommendations
for the Design of Bridges, Issue 2. Safety and Standards
Directorate.
13. Network Rail (2004) NR/CE/GPG/003 Prevention of
Bridge Strikes, A Good Practise Guide for Transport
Managers, Issue 1. Safety and Standards Directorate.
14. Network Rail (2004) RT/LS/P/007, Project
management and the Environment, Issue 2. Network
Rail.
15. Railtrack plc (2000) GE/RT8029 Management of
Clearance and Gauging Issue 1. Safety and Standards
Directorate.
16. Sadler & Wilkins (2003), Short Span Railway
Underbridges: Developments, NSC Vol 11 No 6. Steel
Construction Institute.
17. www.networkrail.co.uk/companyinformation/index.htm
Paper 11 Advances in Rail Under bridge Rep lacements
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97Railway Bridges - Today and Tomorrow
Paper Twelve
Forth Bridge
Safety and Production
Malcolm Hyatt
BALFOUR BEATTY CIVIL ENGINEERING
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98 Railway Bridges - Today and Tomorrow
1. Introduction
The Forth Bridge is one of the wonders of the world. The
refurbishment of the Bridge is essential to ensure that it
both remains operational and is there for generations to
come.
Safety is everyone's number one priority but sometimes
achieving what is required is not so easy. On the bridge,the team has to date maintained an excellent safety
record while achieving production.
The aim of this paper is to try to demonstrate that is
possible to continually minimise safety risk and maintain
or increase production efficiencies.
We will talk about some of the safety measures that are in
place to combat the hazardous working environment that
exist on the bridge, and the efficiencies that the project
continues to gain.
2. About the Forth Bridge
The 2.5 km. (1.5 mile) Forth Railway Bridge, the world's
first major steel bridge, with its gigantic girder spans of
521 m. (1710 ft.) ranks as one of the great feats of
civilization. It was begun in 1883 and formally completed
on 4 March 1890 when HRH Edward Prince of Wales
tapped into place a 'golden' rivet.
The bridge was constructed by Tancred-Arrol, and
designed by civil engineers Sir John Fowler and Benjamin
Baker. The design was finally developed after the TayBridge disaster.
The balanced cantilever principle was adopted. The main
crossing comprises tubular struts and lattice-girder ties in
three double-cantilevers (named Queensferry (Southern)
- Inchgarvie (Middle) and Fife (Northern)), each
connected by 105 m. (345 ft.) 'suspended' girder spans
resting on the cantilever ends and secured by man-sized
pins. The outside double-cantilever shoreward ends carry
weights of about 1000 tonnes to counter-balance half the
weight of the suspended span and live load.
Each of the 110 m. (361 ft.) high double-cantilevers is
supported on well-founded granite faced piers. The
bridge's construction involved the employment of 4,000
men at times, the use of 54,000 tonnes of steel and
driving 6,500,000 rivets. Its total cost was £3,200,000.
During operations, rescue boats were stationed under
each cantilever saving at least 8 lives, but still at least 57
men lost their lives, and it is alleged that over 400 were
injured. The fact that a temporary hospital was set up in
the grounds of a local hostilely gives an indication of the
level of accidents and injuries.
Today, our aim is for zero accidents or incidents and with
changes in law, vast improvements in plant, materials
there is no reason why this should not be a realistic goal.
3. The Present Contract
Network Rail (NR) carried out a structural and
maintenance assessment of the structure, which resulted
in 2001, Balfour Beatty being awarded Civil Engineering a
Co-Operative Non-Binding Agreement Contract to
refurbish approximately 220,000m2 of the 450,000m2 of
bridge members, which is to run until 31st. March 2009.
Within this agreement Network Rail instruct work by the
issue of an annual Work Bank Instruction (WBI) which
details Members to be refurbished.
In Year 1, it was the intention to refurbish a number of
selected bridge members to learn about the constraints of
working efficiently on the structure, so that information
could be gained to allow movement to agreement of
annual target costs with pain/gain mechanisms.
Sub-contractors that are working with BBCEL to carry out
the works are as follows:
South
Coatings Pyeroy
Access provision SBG
Steel repairs RBG
North
Coatings, Access provision and Steel repairs are all
carried out by Palmers
BBCEL are the Principle Contractor, providing all welfare
facilities, delivering all materials to the workface, ad allprogramming co-ordination functions.
4. The Contract Requirement
The basic requirement is to remove the existing lead
based paint and provide in its place a glass flake epoxy
coating system which is designed to a 20 year life.
However, it is hoped that with a well managed
preventative maintenance programme that the system will
last a lot longer.
A brief listing of the sequence of activities is:
• Programme of works developed and agreed
• Preparation of Risk assessments and method
statements
• Access scaffolding designed and agreed
• Materials taken out to the bridge by barge or rail
• Access erected in accordance with design
• Encapsulation erected
• Steel repairs assessed by NR
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99Railway Bridges - Today and Tomorrow
• Steel Repairs carried out
• Blasting and Painting
• Encapsulation dismantled
• Access dismantled
The co-ordination of the above activities requires accurateand detailed planning with input from all parties to ensure
that safe systems of work are developed with a view to
achieving or bettering the required outputs.
5. Safety - General
BBCEL operate under a Contractors Assurance Case
related to Link-Up registration as well a being accredited
to ISO 9001,14001 etc.
All of our processes are controlled by a document called
the Project Management Plan, which describes themeasures and documents required to carry out the Works.
Examples of documents that are controlled are:
• Risk assessments
• Method Statements
• Works Procedures
• Programme
• Environment Controls
The Forth Bridge Refurbishment Project has not had a
reportable accident since commencing in April 2002.
That's over 1.7million man-hours without a reportable
accident.
We believe this has been achieved by proactive safety
management by main contractor and sub-contractor
management, and the positive attitude of the workforce.
We consider that involvement of the Workforce is
essential to maintaining the level of safety that is required.
All are aware that on a Project of this nature, that
complacency may well be one of the biggest dangers. To
this end it is important to keep reinforcing the safety
message. This is done mainly through the following:
• Safety Inductions given as a minimum at the start of
each Year
• Safety Representatives participate in safety meetings
and safety inspections
• Work Face Risk assessments carried out by the
Workforce. These are checksheets that the gang will go
through each morning or at change of location or
activity, to assess the local risk to themselves or to
others
• Briefing sessions for new themes or topics
• Weekly safety inspects which involve the workforce
• Regular toolbox talks covering a range of subjects
• Implementation of a Behavioural Based Take C.A.R.E.
It is worth spending some time on "Take C.A.R.E."
C Conscious A Actions
R Reduce
E Errors
Conscious Actions Reduce Errors
Whilst we have this safety record we still have a small
amount minor accidents, and incidents.
The "Unsafe Act" can be described as the the route cause
of all accidents. In the majority of cases the "Unsafe Act "
results in no consequences, or sometimes it might resultin a near miss or property damage. However, under
different condition the same unsafe act might result in
minor or even major injury.
So the aim of this scheme is to attempt to reduce the
occurances of the Unsafe Act.
The idea is to engage the workforce in a programme of
observations of their group's activities, assessing the
outputs of these observations against a set of agreed
criteria, and agreeing actions to improve on the
observations.
We view this as a long term process and are looking
forward to long term reduction in the small quantity of
unsafe acts and consequently minor accidents and
incidents.
6. Programme
The traditional belief that when painting the Forth Bridge,
you just start at one end, work towards the other, and
when you get there you start again is just not true.
In fact, the programme or sequence of work is developed jointly between Network Rail and BBCEL for the
implementation works, and are based on Network Rail
Requirements, safety criteria and budget.
These are:
• Member criticality - Network Rail identify through
detailed inspected and structural assessment, the
bridge members that are in most need of refurbishment
• Global Loadings" - the restrictions caused by the
strength of the bridge on the weight of scaffold atvarious locations and the effect of the wind due to the
encapsulation
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100 Railway Bridges - Today and Tomorrow
• Safety - Exclusion Zones. During access erection an
exclusion zone is set in areas below to ensure no other
operations are carried out at the same time
• Safety - Manual Handling. As much as possible
access activities are programme to ensure that manual
handling is minimised. An example of this would be to
programme an access dismantle sequential with an
adjacent access erect
• Budget
7. Access Provision
The highest point of the bridge is approximately 306ft
above mean water level, and the lowest is a matter of a
few feet, and as such all access work on the bridge is
deemed to be work at height.
All activities on the Bridge rely on the provision of access
scaffolding to enable the work to be carried out safely andthe provision of adequate environmental controls.
The access scaffolding is provided by sub-contractors
SGB and Palmers, who employ up to 30 scaffolders each
on the Project. They each employ scaffolders at various
levels up to and including IRATA 3 grades for abseiling.
Believe it or not the need for abseiling techniques is
limited as in most cases the scaffolding for a particular
member can be safely commenced with more traditional
techniques such as double lanyards, running lines or
retrievable inertia reels.
We employ a safety boat to monitor all activities that
require personnel to be protected from a fall, i.e. leading
edge activities. The safety boat is an essential part of the
safe system of work for the access provision and as such
is linked by radio to all access squads and Bridge Control.
A substantial amount of scaffold is erected above the track
which provides its own challenges. The safe system of
work that has been developed is as follows:
• All personnel that are working above the track on
scaffolding or encapsulation activities are subject to
medical surveillance
• With each squad working above the track is a COSS
and lookouts as appropriate. These safety critical
personnel work as normal on the track and control the
activities above.
• The COSS will ensure that all personnel are briefed
and will test the Safe System of Work
• The lookout will upon sight of a train, signal in the
prescribed way
• Upon receiving the signal the personnel will stop work
securing all materials
• When the train has past the COSS will give the go
ahead to recommence works
As the system of unassisted lookout is the lowest of the
Safety Hierarchy, we have endeavoured throughout the
period of the Project to move up the hierarchy and have
carried out several trials with ATWS.
Initially, in situ trials were carried with "Track 02", but
unfortunately, due to various reasons at that we couldn't
utilise this system, but we have not given up and are at
present, with Network Rail managers are evaluating the
"Minimel" system, which we hope will prove successful.
Apart from the obvious personnel safety issues, there is a
secondary reason why we are considering the use of this
system. Approximately 200 trains use the bridge through
the working day, and we have recorded that up to 30% of
the working hours can be lost due to stoppages to allowtrains to pass.
The lookouts give warnings on first sight of a train, which
on this bridge is generally far greater than the minimum
sighting distances in accordance with the Rule Book. The
ATWS system would be set so that the warning would be
given at a distance in accordance with the Rule Book but
less than that given by the lookouts. We anticipate that a
saving of between 5 and 10% could be achieved on
scaffolding costs if this was implemented in the future.
A simple but effective efficiency, was changing from ladder
access to staircase access. At the south end of the
project, access to the work areas is gained via a 500m
trek along walkway in the approach spans. BBCEL,
inherited a system where changes in height in access
walkways were accomplished by the use of ladders. One
of these ladders was positioned at the Southern Jubilee
tower and was approximately being 8m in height.
Consequently, during the walk out to the work areas
approximately 50 men would have queue to climb the
ladder in the morning and again when they left the bridge
at night. This equated to inefficiency off about 300man
minutes a day times. The change from ladder to staircase
has eradicated this problem ensuring that personnel get tothe work areas quicker which means more time spent at
the workface.
In general all ladders on the main walkways have now
been replaced by staircases. However, due to the nature
of the access scaffolding design based on all of the
constraints outlined above, it is not always possible to
provide access staircase actually at the workplace,
therefore, ladders are provided.
To keep manual handling of materials and tools to a
minimum a series of mini hoists, gin wheels are utilisedbased on the circumstances.
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101Railway Bridges - Today and Tomorrow
Through constant review of the processes or methods for
each activity, which includes ways in which we can
improve efficiency while maintaining the safety attitude
the scaffolding activities are on the whole becoming more
efficient.
Some examples of this are two adjacent identical vertical
columns. The first one that was scaffolded in 2002/2003
took 3392 man-hours while the adjacent column in 2004took 2223 man-hours, an efficiency of 34%. Another
example is the access erection of the suspended spans.
The Northern Span took 8039 man-hours in 2003, while
the Southern Span took 6776 man-hours, an improvement
of approximately 16%.
The removal of the existing old paint system in
preparation for the new system requires that the steelwork
blast cleaning to bare metal with a profile of SA 2½. Steel
that is corroded or has lost section sufficient to make
redundant or near redundant is repaired or replaced.
Obviously, the removal of the paint system using the tried
and tested method of dry grit blasting, is potential both
hazardous to the operatives and the public, and could be
extremely hazardous to the Environment.
The access scaffolding that is erected to provide a stable
platform to allow these operations to be carried is
designed to be encapsulated using a heat applied "Shrink
Wrap" polyethylene material.
BBCEL introduced this method at an early stage, and
immediately proved itself more efficient than previously
used cladding material for the follow reasons:
• Comes in rolls that are easier to transport and handle
• Can be cut and sealed around incoming members and
scaffold tubes etc., thus ensuring that no grit escaped
and minimised the amount of rain water that enters an
area. This was previously extremely difficult to achieve.
• Better environmental protection
• Is more resilient than traditional methods of cladding
• Is safer to erect and dismantle
• Manufactured to European Standards
• Traceable fire resistance
8. Coatings
The system of encapsulation described above protects the
environment from the effects of the paint removal process as
well as the personal not involved in the actual operation.
The removal of the original lead paint system is carried out in
accordance with current legislation including but not limited
to:
• Network Rail Company Standard
• The Control of Lead at Work Regulations
The existing lead paint is removed from the bridge by the
process of dry grit. Dry grit removal is used as it obtains the
best steel profile and is easier to contain.
Before grit blasting can proceed the following precautions arein place:
• An appropriate Risk Assessment has been carried out
• All persons who may come into contact with lead working
must be subject to a monitoring of blood level concentration
which is carried out by a Medical Practitioner or body
approved by the H.S.E. There is a statutory trigger level of
70 milligrams of lead per 100 millilitres of blood, at which
point the HSE must be notified. On the bridge we have
never had personal whose lead/blood levels reach this point
as we generally take action when or if, through themonitoring process the there is a rise from the norm, the
person is talked to ensure that all of the precautions that
should be in place are being utilised.
• Some control measures are:
1. Blood monitoring
2. Use of full face masks are air fed
3. Full protective clothing
4. Personal hygiene - washing prior to eating or
drinking
5. Provision of suitable facilities for changing out of
lead contaminated clothing which are isolated from
clean areas and canteens
6. Shower facilities
The recovery of the spent grit is by vacuum suction which
drastically reduces the amount of manual handling required.
We currently have two such systems set up, one at
Queenferry and another at Fife. In year 4 these systemsremoved well over 1000 tonnes of spent grit. Whilst
expensive to set up year on year these systems reduce
overall costs (mainly labour) by up to 40%.
Despite these constraints the project has continued to show
efficiency improvements year on year, through continual
review of methods etc..
Examples of production efficiencies while maintaining safety
culture are as follows:
• The first one is the suspended spans. The northern spanwas coated in 7882 man-hours in 2004, while the
southern span took 6772 man-hours, an efficiency of
about 14%
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• The second is the comparison between the east and
west bottom booms at Queensferry. In 2003, it took 5386
man-hours to west booms, while in 2004, 4516 man-hours
were used. An efficiency of 16%
9. The Project Overall
The safety challenges for this project are immense, with
working from height, working over water, adverse weather conditions, over and around trains, with lead based paints
etc. The need to work extremely safely is paramount and
to improve efficiencies.
The safety record speaks for itself, although as explained
earlier, we are conscious that complacency could be our
worst enemy. And have therefore put in place measures to
counter this and continue to strive for our goal - ZERO
ACCIDENTS.
We have also talked about continuing to achieve
production efficiencies and have given a few examples.
Year 2 (2002/2003) has been used as the efficiency
benchmark for future performance, as year 1 was a year
of setting up and learning.
The overall project efficiency has continued to be
achieved since and in Year 4 and the overall project cost
of producing one square metre of painted bridge member
was 80% of that of Year 2, i.e. a reduction of 20%.
Moving forward it is expected that by the end of Year 6 a
further 10% efficiency would be achieved.
10. Conclusion
Hopefully, this Project can be taken as an example of one
where Safety the No. 1 priority, and through constantly
reviewing methods, process production efficiencies are
still being achieved.
Certainly for a long term Project such as this it is possible
to maintain an excellent safety record and produce
production efficiencies.
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Railway Bridges - Today and Tomorrow
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103Railway Bridges - Today and Tomorrow
Paper Thirteen
Skills Competency in the Painting
Industry: The Industrial Coatings
Applicator Training Scheme
Dr. Stuart Lyon
INSTITUTE OF CORROSION
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104 Railway Bridges - Today and Tomorrow
Summary
This paper describes the background, structure and
operation of the Industrial Coatings Applicator Training
Scheme (ICATS). The benefits that will accrue to clients in
reduced lifetime cost of asset ownership, and to
contractors in employing a qualified and certificated
workforce, are highlighted.
Background
The costs of corrosion to the UK economy were first
analysed by a DTI committee chaired by Dr. T.P Hoar of
Cambridge University and set up in 1969 by the then
Minister for Technology (Tony Benn). The main
conclusions of the Hoar Report , published in 1971, were:
(a) that the costs of corrosion were approximately 3-4% of
GNP per annum, (b) that about one-quarter of these costs
could be saved by the application of then currently known
technologies and (c) that better training and dissemination
in the industry was essential in order to contain costs. Asa direct consequence of the Hoar report, the Corrosion
and Protection Centre came into being at UMIST (now
The University of Manchester) to provide postgraduate
education, academic research and consultancy into the
corrosion protection industry. Soon afterwards, the two
main professional interest groups in the UK merged their
activities to form a learned professional society, now
known as The Institute of Corrosion.
Similar surveys undertaken in the USA and Japan shortly
after the publication of the Hoar report arrived at very
similar conclusions. More recently, an updated surveywas commissioned in the UK. Although more limited in
scope this estimated that the economic cost was still of
the order of 2-3% of GNP per year. It is rather difficult to
conceive the scope of such losses however an effective
(albeit naive) way is to consider an annual loss of 3% of
GNP as equivalent to the entire infrastructure of the
country disintegrating (due to corrosion processes) in
between 30-40 years. Or, on a more personal note, that
corrosion costs around £600 per capita per year;
equivalent to around 1-2p in the pound for each tax-payer.
Coating Inspection
Since its formation, the Institute of Corrosion (ICorr) has
been pre-eminent in the promotion of training and
certification in the protective coatings industry. Schemes
for the training of supervisors and foremen were
developed in 1975, with the support of the Construction
Industry Training Board (CITB); however, these were not
initially successful. Later, in 1978, a scheme for painting
inspector certification was set up at Bircham Newton and
further developed in collaboration with the US society
NACE. Unfortunately, this scheme was withdrawn from
the UK in 1987.
Starting again in the late 1990's, ICorr developed an
entirely new scheme for coating inspectors that was
compliant with EN 45013 "General criteria for certification
bodies operating certification of personnel". This is
currently delivered on behalf of ICorr by Argyll and Ruane
Ltd at their training centre in Sheffield. These courses,
which now include Coatings Inspection (paint, metallic,
pipeline and fire-proof) and Cathodic Protection, are
highly successful. Currently there are well over 2000
persons certificated at Levels 1, 2 and 3. ICorr inspectors
work in all sectors, and at all levels, of the protective
coatings industry and the ICorr qualification is recognisedas a benchmark standard worldwide.
Unfortunately, coating inspection does not, by itself,
guarantee a satisfactory job. Inspectors, will generally
focus on key aspects of the coating application process
while ensuring compliance with specifications. On the
other hand, poorly trained coating operatives (e.g.
blasters, painters and sprayers) are likely to try to make
their job as easy as possible and subvert in some way the
inspection process.
Coating Failures
Surveys, carried out by ICorr and others, have shown that
in the period 1982 to 1992 over 80% of coating failures
were due to poor surface preparation or application. More
recently, in the period 1992 to 2002, such failures have
been compounded by the introduction of new coatings
formulations that are much less tolerant of traditional
surface preparation methods and require novel methods
of application.
Figure 1 illustrates a comprehensive coating failure on
bridge steelwork several years after maintenance; indeed
it looks as though no work had been done at all. This poor
result is due to a lack of understanding, by the contractor
and operatives, of the surface preparation requirements of
modern coating systems. Rust-through and blistering isclearly evident.
Paper 13Skills Competency in the Painting Industry
Figure 1 - Poor surface preparation
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105Railway Bridges - Today and Tomorrow
Figure 2 shows adhesion failure caused by solvent
retention (premature over-coating), also as a result of
poor contractor/operator understanding. These failures
are both premature, unsightly and require urgent
remediation and neither was prevented by coating
inspection.
Competencies
Currently, the only way to demonstrate competence as a
painter or coating applicator is via the relevant NVQ at
Level 2. However, it is only very recently, after extensive
collaboration between ICorr and CITB, that this has been
extended to include competencies relevant to industrial
coatings application. Holders of current NVQs are most
likely to be assessed for commercial decorating, which is
not at all the same as effectively painting structural
steelwork. Also, although NVQs may demonstratecompetency, they do not include training nor are they a
certification scheme.
In May 2002 The Institute of Corrosion promoted a
conference in York to review current training in the
industry. Over 50 delegates attended representing major
interests including clients, contractors and coatings
manufacturers. The outcome of was the formation of an
industry-wide task group with the remit to develop a new
training and certification route for artisan painters and
coatings operatives in the industry. Membership of the
task group comprised stakeholders from all industry
sectors including: Network Rail, Highways Agency (HA),CITB, Corus, National Grid/Transco, British Coatings
Federation (BCF), British Constructional Steel Association
(BCSA), and the Association of Consulting Engineers
(ACE). The outcome of this task group was the Industrial
Coatings Applicator Training Scheme (ICATS), which is
currently being rolled out across the UK.
Sector Schemes
National Sector Scheme (NSS) specifications are
designed to provide a quality management system for
Highway Works, compliant with ISO 9001:2000. They arealso consistent with the HA requirement for evidence (by
certification) of a trained and competent workforce. Thus,
simultaneously with the introduction of ICATS, NSS
Committee 19: "Corrosion Protection of Transportation
Infrastructure Assets", was constituted, with the Institute
of Corrosion prominently represented. NSS 19 has now
produced the final draft for Scheme 19A: "Corrosion
Protection of Ferrous Materials by Industrial Coatings".
Great care has been taken, in drafting, to ensure that it is
essentially sector neutral. Thus, it is hoped that it may
also be used in other sectors. The NSS Scheme 19Adocument is due to be published as a draft for comment
before the end of 2006. After a short consultation period,
it shall then become mandatory for all new highways
works from mid 2007, thus enforcing a trained workforce.
Outside the transportation industry, National Grid/Transco
have, in recent Invitations to Tender for painting works,
also recognised the advantages offered by the use of a
trained and competent workforce by the ICATS route.
ICATS Training and Certi fication
The scheme is a comprehensive structured training
programme for the training, certification and registration of
industrial surface preparation and coating operatives.
ICATS was produced in response to demands from
specifying/procurement authorities for evidence of
practical training and competency in industrial surface
preparation and protective coating application that
complements other industrial skills sector schemes.
ICATS is owned by ICorr and managed by its trading
subsidiary Correx Ltd., as Certificating Body, on behalf of
ICorr. The scheme is operated in accordance with the
relevant ICorr requirements document and controlled by
an Advisory Committee of stakeholder representatives
that reports to ICorr and Correx Ltd. The current scheme
provider is Argyll and Ruane Ltd., who also deliver the
ICorr Coating Inspector Training and Certification
Schemes.
ICATS delivers practical training in the workplace that is
not offered by any other training scheme. It incorporates
up-to-date practices and the use of modern high-
performance coating materials. ICATS exceeds the
evidence for training requirements of the existing NVQ
Level 2 for Decorative, Finishing and Industrial PaintingOperations.
Operation of ICATS
The scheme has a mandatory Basic Unit: "Industrial
Coatings Applicator" that comprises 6 modules:
• Health and Safety
• Site Access
• Plant and Equipment
• Surface Preparation
• Types of Paint and Application• Quality Control
Paper 13 Skill s Competency in the Painting Industry
Figure 2 - Coating adhesion failure
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106 Railway Bridges - Today and Tomorrow
The following optional Specialist Units may be taken after
the Basic Unit:
• Abrasive Blast Cleaning Operator
• Paint Sprayer
• Thermal (Metal) Sprayer
• Water Jetting Operator
Certification is awarded to candidates who havesuccessfully completed each individual Unit.
Companies wishing to have a workforce certificated under
ICATS must first register with Correx Ltd. Upon
acceptance, registered companies may then nominate
experienced individuals from their company to attend an
ICATS "Train the Trainer" course. Subject to meeting the
acceptance criteria, these individuals then attend a 2 day
course at the Scheme Provider's premises.
After successful completion of the course, certification as
an ICATS Trainer is awarded by Correx Ltd. Certificated
trainers are then qualified to train and assess operatives
in the workplace for individual certification as Industrial
Coating Applicator. Operative training need not be
undertaken by a company's own trainers but may also be
undertaken by registered trainers at another site as a
service, for example to smaller contractors.
Once certified, Trainers and Operatives are issued with a
certification card and are then qualified to work for any
company registered into the scheme. The scheme card is
valid for 3 years and re-certification is required after this
period.
Workplace trainers and the training of operatives is
subject to periodic audit at the company premises. The
audit process includes confirmation that procedures are
being correctly followed as well as observation of training
sessions to ensure that the learning outcomes are being
effectively imparted.
Delivery of ICATS
Operative training is delivered in the workplace of a
registered company by a registered ICATS Trainer.
Qualification for the Basic Unit should take approximately
40 hours, but is not required to be continuous and may be
taken at any convenient times. The training materials
comprise a high quality multi-media application available
on CD-ROM or via the Internet, backed up by printedspiral-bound books.
Benefits of ICATS
To the client the benefit of a properly trained, skilled and
certificated workforce is obvious as it will reduce the
incidence of premature coating failure, enhance coating
lifetime and reduce overall lifetime costs. As indicated
above the HA intend to make ICATS mandatory sometime
during 2007 for contractors who wish to tender for
highways painting works and most local authorities will
follow this lead. Other major clients, including from theconstruction, infrastructure and offshore sectors have also
indicated that they will adopt and promote the scheme
Registered contracting companies will thus benefit as they
will have documentation of a competent workforce and will
therefore be eligible to tender for contracts where ICATS
is mandatory. It will also provide a competitive edge when
applying for registration on approved contractor lists.
Paper 13Skills Competency in the Painting Industry
Figure 3 - ICATS training materials
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107Railway Bridges - Today and Tomorrow
Paper Fourteen
Recent Developments in Strengthening
Technology and the Strengthening
/Reconstruction Decision
Lee Canning, Neil Farmer, Dr. Sam Luke and
Ian Smith
MOUCHEL PARKMAN/TONY GEE ANDPARTNERS JV
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108 Railway Bridges - Today and Tomorrow
Introduction
The use of fibre reinforced polymer (FRP) composite
materials for strengthening metallic, concrete and timber
structures has developed significantly in the past 15
years. This strengthening technology is now generally
well accepted with the construction industry and a number
of design guidance documents are available for the use of
engineers.
However, the design methods and both technical and
practical limitations are relatively new to design
engineers, and specialist designers are required to ensure
an economic and practical design which is critical for a
successful installation of the FRP strengthening scheme.
Mouchel Parkman and Tony Gee and Partners have been
expert advisors and designers, acting in a joint venture
(the 'JV'), to Network Rail from 2001 for FRP
strengthening schemes on Network Rail infrastructure.
This commission came about after a report by Mouchel
Parkman on the benefits to be gained by Network Railusing FRP strengthening in 2000. Under this
arrangement, the design of every FRP strengthening
scheme on Network Rail infrastructure must be designed
by one of the JV partners and checked by the other at
Category 3 level.
Since the beginning of this commission, the JV has
undertaken the feasibility, design, check and site
supervision of FRP strengthening to 13 structures,
including overbridges, footbridges, an aqueduct, and an
underbridge, strengthening both cast iron and concrete
bridges. A further 8 structures are currently at feasibility or design stage. The technique is not a panacea, however,
and 5 structures which initially appeared suitable were
eventually rejected for FRP strengthening after detailed
consideration. The total capital cost of each scheme has
varied from £10,000 to over £2m, and provided total
cumulative cost savings of over £5m compared to other
strengthening or reconstruction options.
The JV has also developed generic specifications for FRP
strengthening to metallic and concrete substrates,
undertaken road shows to disseminate the work done on
FRP strengthening to Network Rail engineers and to
obtain feedback, and advised on the content for CETANs.The knowledge developed during this period has also
been useful in providing information to be used in recent
design guidance documents.
The JV arrangement has enabled the problems
encountered, solutions and lessons learned to be collated
and reviewed in a relatively short timeframe, and to be
used in updating design methods, specifications and
CETANs.
A short descript ion of current FRP strengthening
technology is provided, and two particular FRPstrengthening schemes presented below, with discussion
focussing on technical and practical issues, cost savings,
risk mitigation measures and management of residual
risk, and lessons learned. In addition, from the experience
gained in the JV, conclusions are drawn on what
situations are favourable for FRP strengthening as
opposed to other strengthening methods or
reconstruction, and where this would not be the case.
FRP Strengthening Technology
Structural FRP strengthening methods developed initiallyin the military and marine industries, and have only been
transferred to the civil engineering industry since the
1980's. Initial applications comprised flexural
strengthening of reinforced concrete slabs and beams
and confinement strengthening of reinforced concrete
columns. Extensive research has been undertaken, and is
still ongoing, to further develop applications and design
methods for a variety of structural members and substrate
materials. The current status of the technology enables
flexural, shear, torsional and confinement strengthening of
reinforced concrete, steel, wrought iron, cast iron and
timber members, with varying levels of design guidanceand maturity. The application methods are also wide
ranging, including in situ wet lay-up optionally
incorporating vacuum infusion and 'pre-preg' materials,
bonded pultruded or pre-formed plates, strips or bars, and
mechanically fixed plates. The FRP may be installed
unstressed, or prestressed by direct action or by structural
jacking or load modification. The materials used include
carbon, aramid and glass fibres. However, by far the most
common application in the UK is flexural strengthening of
reinforced concrete slabs and beams with carbon FRP
(CFRP) pultruded plates. There has also been significant
confinement strengthening of reinforced concretecolumns to improve impact, axial, flexural and shear
strength. The design guidance for both these methods is
also the most developed.
Strengthening of metallic structural members is still
relatively novel and nearly always comprises flexural
strengthening by bonding FRP composite material to the
soffit of a beam, although design guidance is available for
shear and other types of strengthening.
Preliminary theoretical and experimental work has been
undertaken on FRP strengthening of masonry arches, but
requires further development to enable safe and efficientdesign guidance. In particular, the difficulty in actually
assessing the real behaviour, strength and failure modes
of an arch is a barrier to developing useful design
guidance for strengthening methods.
All the FRP strengthening methods currently used on
Network Rail infrastructure have comprised flexural
strengthening of cast iron girders or reinforced concrete
slabs or beams, although feasibility work has also been
undertaken on shear strengthening. This is probably due
to the fact that the majority of assessment failures on
Network Rail infrastructure are under flexure.
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109Railway Bridges - Today and Tomorrow
FRP Strengthening Case Studies
Maunders Road Overbridge, Stoke-on-Trent
The bridge is located in the
Milton area of Stoke-on-
Trent, Staffordshire (Figure
1). The structure was built in
the mid-1800's and carriesan unclassified road over a
cutting on the now disused
Stoke to Caldon Quarry
railway line. The effective
span of the bridge is 7.84 m
with a carriageway width of
5.0 m and a 1.1m wide
footway on one side of the
carriageway. The bridge
comprises of 6 primary cast
iron girders, the middle
girders being spaced atapproximately 1.43m
centres and the edge
girders at 1.23m. These
girders support transverse
spanning brick jack arches
which in turn support road
base and asphalt
pavement.
A structural assessment in
the late 1990s identified that
the main girders had a
capacity that would only
allow them to support 7.5
tonnes vehicles and the
edge girders only 3 tonnes
vehicles. One edge girder,
that which did not support a
footway, had been propped
by the addition of a steel
capping beam over a brick
wall. The prop was intended
to offer support to the cast-
iron edge beam, however,
the steel beam was badlycorroded with a perforated
web and was assessed as
providing no support to the
bridge girder.
The road was unclassified
and within a residential
area, however it was the
only route to a small
industrial area that included a steelwork galvanising factory.
The bridge was regularly trafficked by 40 tonnes heavy
goods vehicles (HGVs), -though the road layout was suchthat such vehicles could cross the bridge only slowly, and
normally only when oncoming traffic stopped to allow the
HGVs to negotiate
bends immediately beside the bridge. The highway
authority required the bridge to be strengthened to carry
40 and 44 tonne vehicles and 30 units of abnomal HB type
loading.
Several options, including
replacement of the bridge,
were examined. However,
the costs of diverting thepublic utilities that were
supported by the bridge
were substantial. The
cheapest option was to jack
up the bridge girders at mid-
span, thereby relieving the
dead and superimposed
dead loads, then bond
CFRP laminates either side
of the temporary prop before
the latter was de-stressed
(Figures 2 and 3). Thereby,the strengthened composite
section acts efficiently in
resisting both dead and live
loads.
Hammersmith Road
Bridge
Hammersmith Road and
Kensington High Street
(A315) in West London is
one of the major
thoroughfares from the
London Borough of
Hammersmith and Fulham
to the Royal Borough of
Kensington and Chelsea and
on into Central London
(Figure 4). The route runs
approximately parallel to the
A4 and is a necessary link
for local businesses and bus
services. Approximately
perpendicular to the A315,
along the borough boundary,is Network Rail's West
London Line and a branch of
London Underground's
District Line. The District
Line branch has the specific
purpose of serving the two
busy exhibition halls on
either side of Hammersmith
Road: Earls Court and
Olympia, while the West London Line (WLL) connects
Falcon Junction (near Clapham Junction) and Willesden
West London Junction. At the intersection of the A315and the two railway lines there is a road over rail crossing.
This structure is known as Hammersmith Road Bridge.
This is a three span bridge crossing the single track
District Line in its western most span, the two track WLL
Paper 14 Recent Developments in Strengthening Technology and the Strengthening/Reconstruction Decision
Figure 1 - Maunders Road overbridge
Figure 2 - Jacking out dead load on Maunders Road overbridge
Figure 3 - CFRP strengthening on jacked structure
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110 Railway Bridges - Today and Tomorrow
in the centre span and a disused siding within the eastern
span. The LU District Line is fourth rail electrified and the
Network Rail WLL is third rail electrified with a crossover
within the structure.
The two siding spans have a span of 5.25m with the
central span being 10m. The carriageway of the bridge
has a width of up to 14.8m
with footpaths of 4.5m oneither side. Each span is
made up of 11 simply
supported longitudinal hog
back symmetrical cast iron
beams spaced
approximately 1.8m apart
and two outer simply
supported asymmetric cast
iron beams. Between the
beams there are
transversely spanning
shallow masonry jackarches in all but two bays of
each span. The other bays
are formed by cast iron
deck plates
accommodating large
service pipes. Trial holes
during the assessment
stage found a large
number of services,
ranging from small traffic
power cables, through
banks of communications
fibre optics to large
diameter (c. 21") high
pressure water and gas
mains. The deck plates
have cast-in perpendicular
and diagonal downstand
stiffening ribs and therefore
do not present a flat soffit.
Previous assessment of
the structure had shown
the internal girders to have
7.5T ALL capacity, but the
external girders were at fullcapacity under dead load
alone, and the deck plates
could only withstand 3T
ALL.
A number of options were
considered at the feasibility
stage, including reducing
the spans, dead load
reduction by foamed or
lightweight concrete and
thinner surfacing, post-tensioning of the girders,
reconstruction, and
unstressed CFRP plate
bonding to the girders and
deck plates. The recommended option was CFRP
strengthening with some dead load reduction, based on
minimal disruption to the highway network, railway
network, and statutory services, and the lowest cost
estimate of approximately £1.5m excluding possession-
related costs such as possession management, provision
of safety related personnel etc.. Reconstruction in this
instance was simply not
feasible due to the existenceof numerous services,
possession availability and
the important nature of the
highway thoroughfare.
Currently, the span over the
disused siding has been
strengthened during daytime
hours, and the span over the
London Underground
District Line has been
strengthened during a 52 hr possession at Christmas
and New Year 2004/5 for the
girders and part of the deck
plates, and a 52 hr
possession in July 2005 to
complete strengthening of
the deck plates (Figures 5
and 6). In addition, topside
works have been undertaken
including reinstatement with
lightweight concrete,
waterproofing and re-
surfacing. Strengthening of
the main span is pending the
availability of a suitable
possession on the Network
Rail WLL, possibly in
2007/8. The current cost of
the scheme is £2.5m
including all possession-
related costs.
Maintenance inspections to
the strengthened spans
have shown no deteriorationto the CFRP strengthening.
Paper 14Recent Developments in Strengthening Technology and the Strengthening/Reconstruction Decision
Figure 4 - Hammersmith Road overbridge (A315)
Figure 5 - Strengthening of girders using CFRP plates
Figure 6 - Strengthening of deck plates using CFRPcruciforms and plates
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Railway Bridges - Today and Tomorrow 111
Paper 14 Recent Developments in Strengthening Technology and the Strengthening/Reconstruction Decision
Figure 7 - Procedure for implementation of FRP composite strengthening technology onto Network Rail infrastructure
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112 Railway Bridges - Today and Tomorrow
Discussion of FRP Strengthening Issues
The case studies described previously show the various
stages in the complete design process (from initial advice
to installation and finally in-service maintenance). These
stages are defined more rigorously in Figure 7. From the
experience gained from all the FRP strengthening
schemes on Network Rail infrastructure, and also other
infrastructure, a number of factors are clearly favourablefor the feasibility of a FRP strengthening scheme. These
include:
i) Presence of services. Where a large number of
services are present, any strengthening options
requiring invasive works near services, or reconstruction
options, become less feasible due to the risk of damage
to the services and cost of diversion.
ii) Requirement for continuous trafficking. FRP
strengthening can typically be undertaken under single
lane running, occasionally with short road closures (nomore than 1 day). Other strengthening methods, and
reconstruction, often require full road closures of the
order of weeks.
iii) Cast iron substrate. Bolting and drilling into cast iron
is generally not recommended, which leaves bonding
and clamping as acceptable fixing methods.
Furthermore, the assessment of cast iron is essentially
based on linear elastic principles; the higher the modulus
of a bonded strengthening material, the greater its
strengthening effect. This means that UHM CFRP
composite materials are very effective.
iv) Assessed capacity. There is a limit to a structure
being strengthened with FRP materials, which varies
with the type of substrate and assessment or design
philosophy. However, where the assessed capacity is
greater than 3 to 7.5T ALL, unstressed FRP
strengthening is usually technically feasible and cost
effective. Where the assessed capacity is less than this,
some form of dead load mobilisation is usually required
(e.g. prestressing, jacking or large-scale reinstatement
of fill with lightweight material).
v) Possession length. FRP strengthening can typicallybe undertaken within rule-of-the-route overnight
possessions, and therefore has a lesser requirement for
long possessions (although in some cases it may still be
more efficient to undertake the FRP strengthening in a
long possession).
vi) Interested parties. Where a large number of parties
have a serious interest in a scheme, less intrusive
strengthening methods tend to be more conducive to
achieving overall approval. FRP strengthening has
minimal visual impact to a structure, and usually the
structure is not in a temporarily weakened state duringFRP strengthening, as may occur for other strengthening
methods.
As well as being cost effective, FRP strengthening methods
usually minimise disruption to both the railway and highway
network (for overbridges). This has an effect on the successful
development of any strengthening scheme, due to the need
for liaison and acceptable solutions for both Network Rail and
the local authority. In many cases, where a solution has
otherwise been difficult to find that is acceptable to all
concerned parties, FRP strengthening has been the only
viable solution.
FRP New-Build Technology
In the past 25 years, and particularly in the last decade,
advances have been made in the use of FRP composites for
new and replacement structures, and structural components
in general. Approximately 150 footbridges, and 100 vehicular
bridges, constructed using FRP composites, have now been
installed worldwide. FRP composites have also been used
in offshore and industrial applications for walkways and
parapets, in aerospace and marine applications for
secondary and primary structural components.
Recent significant uses of FRP composites for new-build
include Halgavor footbridge over the A30, West Mill vehicular
bridge in Oxfordshire, and Mount Pleasant Occupation
bridge over the M6 in Lancashire (Figure 8), and various
station footbridges (Figure 9).
Paper 14Recent Developments in Strengthening Technology and the Strengthening/Reconstruction Decision
Figure 8 - Mount Pleasant FRP bridge during load testing
Figure 9 - Kosino station footbridge, Russia
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Consultants are currently reporting to Network Rail on the
implications of FRP composites for structural components
and new-build on the railway infrastructure, including
footbridges, overbridges, underbridges, platforms and
platform canopies, and other structures. The main
benefits to be gained in using FRP composites for new-
build are:
i) Greater durability and minimal maintenance. This alsohas a follow-on impact as it reduces costly and disruptive
maintenance works on the railway.
ii) Simple and quick installation due to the pre-fabricated
and lightweight nature of FRP composite structures.
iii) For overbridges, minimal road closures are required
due to the ability to have all bridge furniture, including
surfacing and parapets, pre-installed on the structure
which can then be craned in.
Currently, the business case for FRP compositefootbridges is favourable on capital cost, and becomes
very competitive when whole life costs are included. The
case for vehicular bridges is less clear, although likely to
improve in the near future; the benefits of using an FRP
composite structure would need to be considered on a
project-specific basis, being particularly favourable where
disruption to the railway and highway are critical.
Currently, an all-FRP composite sidebridge is under
design in LNE territory (Form A stage) to replace a
wrought iron girder/jack-arch structure over a canal.
Additionally, there is great scope for the use of FRP
decking systems for re-decking of masonry arches and
girder/jack-arch type structures, where a pre-surfaced
FRP composite deck acts to reduce dead load in addition
to strengthening.
The use of FRP composites for building-type components
(e.g. platforms, platform canopies etc.) generally has a
longer track record than for bridges, and there appear to
be no barriers to these applications; indeed, a number of
secondary or non-structural FRP components are already
being used on the railway infrastructure, such as
stairways and parapets to signal boxes, walkways and
handrails retro-fitted to existing bridges and stair treadreplacements.
Summary
The approach taken by Network Rail in using FRP
strengthening methods on their infrastructure has
provided a number of benefits:
i) Cost savings over other strengthening
methods/reconstruction.
ii) Minimal disruption to the railway and highway
network.
iii) Control of risk by only allowing FRP strengthening
where there is sufficient knowledge and design
guidance, designed and checked by experts, and
critically reviewed after each installation. This enables
best practice to be quickly developed for the benefit of
Network Rail (and other infrastructure owners).
The total cost saving achieved currently to Network Rail,
accrued due to the use of FRP strengthening over other strengthening/reconstruction methods to 13 structures, is
approximately £5m. The cost saving for any particular
structure has ranged from marginal (for concrete
structures where steel plate bonding may also be feasible,
albeit with practical and durability issues) to over £1m
(where the bridge has numerous services and
reconstruction is the only other option).
The use of FRP composites for new-build, reconstruction,
on the railway infrastructure is likely to provide cost
benefits, as well as less disruption to both the railway and
highway, benefiting Network Rail, local authorities and the
public alike.
Acknowledgements
The views expressed in the paper are those of the authors
and not necessarily those of Network Rail, Mouchel
Parkman or Tony Gee and Partners.
Paper 14 Recent Developments in Strengthening Technology and the Strengthening/Reconstruction Decision
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Notes
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115Railway Bridges - Today and Tomorrow
The material used in this publication is Revive Silk, manufactured by a
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and biodegradeable, and meets the National Association of Paper Merchants (NAPM) recycling standards.
Revive Silk is made from a minimum of 75% post-consumer waste, the
remaining 25% being mill broke virgin fibres. The virgin fibre is totally
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