intro bridge

AN INTRODUCTION TO

CONCRETE BRIDGES

Taiwan High Speed Rail Project

Engineering design at the cutting edge

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excellent vehicle for the industry to

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to enhance the use of concrete.

The Concrete Bridge Development Group has many set objectives includingthe identification and commissioning of future bridge research needs, the promotion of best practice and the provision of a focus for the bridge industry.Not least has been the specific effort to aid and support students and youngengineers.

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The ConcreteBridge Development Group

AN INTRODUCTION

TO CONCRETE

BRIDGES

An Introduction to Concrete Bridges

First published 2006

© Concrete Bridge Development Group

ISBN 1 904482 26 0

Published for and on behalf of the Concrete Bridge Development Group by

The Concrete SocietyRiverside House4 Meadows Business ParkStation ApproachBlackwater, CamberleySurrey GU17 9ABTel: +44 (0)1276 607140 Fax: +44 (0)1276 607141E-mail: [email protected] Website: www.concrete.org.uk

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Printed by Cromwell Press, Trowbridge, UK.


CONTENTS

1. Introduction.............................................................................................................................5

2. Bridge types.............................................................................................................................5

3. Aesthetics.................................................................................................................................. 7

4. Bridge decks.............................................................................................................................7

5. Loading.......................................................................................................................................10

6. Analysis.......................................................................................................................................10

7. Substructures and foundations...................................................................................11

8. Material selection.................................................................................................................14

9. Pre-tensioned and post-tensioned concrete......................................................17

10. Precast concrete in bridge construction................................................................18

11. History of pre-tensioned concrete beams in bridges....................................20

12. Durability and detailing.....................................................................................................21

13. Construction planning.......................................................................................................25

14. Inspection and maintenance.........................................................................................26

15. Health and safety....................................................................................................................27

16. Future trends.............................................................................................................................27

17. Further reading........................................................................................................................28

Acknowledgement

This publication was kindly supported by The Concrete Centre. Please visit them at www.concretecentre.com for further information.


There are several basic bridge types that are usually adopted for the construction of concrete bridges with various combinations of layout used for the superstructure (deck) and substructure (supports and foundations).

2.1 Slab bridgesFor short spans, the simplest form of bridge deck is a concrete slab. Slab bridges can be cast in-situ in either reinforced or prestressed concrete. In longer spans, the self-weight of the slab may be reduced by using polystyrene void formers in the construction. Solid slab bridges may also be constructed from precast prestressed concrete beams – normally inverted T-shaped beams – with in-situ concrete infi ll and topping. This form of construction is economical for spans up to about 18m.

2.2 Beam and slab bridgesBeam and slab bridges are generally constructed of precast prestressed concrete beams with an in-situ concrete slab. In-situ beam and slab construction, known as a ribbed deck, is rarely used now but can be found in older, existing bridges.

Beam and slab bridges are economical for spans from 12m to 36m, but the span may be limited by the length of beam that it is permissible to transport. In the UK this is normally 30m. Beyond this a special order is required from the Department for Transport, which permits lengths up to 40m when the beams are transported to motorway sites via the motorway network. Longer-span box beams can be cast in-situ and post-tensioned.

A series of spans over several piers can be constructed as an ‘integral’ bridge, without movement joints. In this type of bridge, either in-situ concrete or precast concrete beams can be used, with the joints

1. INTRODUCTION

Concrete will be found somewhere in all bridges – in the foundations, abutments, piers, retaining walls and deck. For a bridge deck’s main supporting members, there may be a choice between in-situ or precast concrete, structural steel beams or a combination of the two materials – known as composite construction.

Concrete is versatile. It can be cast to any shape so diffi cult geometrical requirements, such as a bridge with pronounced skew or curvature, can be easily satisfi ed. Concrete bridges can be designed with high span/depth ratios, so shallow decks are possible.

2. BRIDGE TYPES

Figure 1: Slab bridge on A30, Bagshot, Surrey Figure 2: Beam and slab bridge at Oyster Creek, Gambia


9


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between the precast beams fi lled with in-situ concrete. The deck may be supported by elastomeric bearings at the piers, and longitudinal movements are resisted by dowels or anchors. Alternatively the beams may be cast into the pier structure. This arrangement, without any movement joints, has typically been used for bridge structures with overall lengths of up to 100m, although longer lengths are possible. It has become popular because of the problems caused by the penetration of water and de-icing salts through movement joints in other forms of construction.

2.3 Framed bridgesSlabs and abutments are often connected monolithically to form a portal-frame. This type of construction is usually cast in-situ and can be used instead of slab, or beam and slab bridges. As with integral bridges, there are advantages to be gained by avoiding movement joints.

For short spans, a concrete culvert can be used as a simple form of framed bridge. Box-shaped reinforced concrete culverts are suitable for spans of up to 6m and the units can be precast.

2.4 Concrete archesArched solutions are ideally suited to utilise the principal qualities of concrete working in compression as long as height clearance considerations below can be fully satisfi ed. The behaviour of the arch will depend on the rigidity of the foundations and the type of backfi ll used. In-situ concrete poured on formwork is normally used for longer-span monolithic arches, whereas precast concrete is available for short-span two- or three-pinned arches from specialist manufacturers. Arch bridges should be an aesthetically pleasing solution where the site layout and foundation conditions permit.

2.5 Integral bridges and continuous constructionConcern over the durability of bridges constructed using movement joints has encouraged the use of integral bridges, especially for highway structures. These are bridges built without movement joints in the carriageway surface and may also avoid the need for bearings. In the UK all highway bridges less than 60m in overall length and less than 30° skew must be built using integral principles in order to maximise their performance and durability (BA42/96 The Design of Integral Bridges). For this type of construction, behaviour of the deck

will aff ect the substructures and vice versa, so a full appreciation of their interactive behaviour needs to be understood.

Continuity is the structural connection of adjacent spans of a bridge to eliminate joints in the deck between spans. Continuity is usually provided to carry imposed loads more effi ciently and to avoid maintenance problems associated with expansion joints. All spans of a bridge – not only at intermediate supports but also between decks and abutments – are thus connected together longitudinally.

2.6 Long-span bridgesThe use of a fully supported soffi t using formwork for long-span in-situ concrete bridges is expensive, and may also be diffi cult. These bridges are often constructed incrementally using travelling formwork or concrete sections cast on stationary formwork, with the bridge pushed out from the abutments – a system known as ‘incremental launching’. These bridges are frequently post-tensioned.

Segmental bridges are made from precast concrete units, stressed together with strands or bars. The units are normally counter-cast against each other to ensure a good fi t, then glued together in-situ. Spans can be built out from the abutments and from the piers. When building out from a pier, the deck is often cantilevered in both directions so that the sections under construction balance each other. The cross-section is usually cellular or box shaped, with the deck slab cantilevered out transversely on either side.

Bridges with spans of over 250m may be designed as arches, or as suspension or cable-stayed bridges. Arches have been used successfully for spans of up to 400m.

Suspension and cable-stayed bridges may have concrete decks, either of in-situ concrete – constructed using travelling formwork – or precast concrete segments stressed together. In these bridges the primary means of deck support is achieved using suspension cables and hangers.

Figure 3: Arch bridge - Scammonden, M62, Yorkshire

Figure 4: Precast balanced cantilever bridge - A39, Bideford, Devon


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In the great majority of modern bridges a concrete deck slab provides the structural support for the asphalt running surface. The thickness of the concrete slab will vary, depending upon the form of bridge deck that supports it. The deck is defi ned as that part of the superstructure that spans longitudinally between supports.

Bridge appearance is as important as economical and effi cient design. Concrete is a very versatile material that can be moulded and fi nished in a variety of forms to give the desired eff ect. Bridges are often designed to last 100 years or more, so it is essential that they are integrated into the environment in a manner that complements and enhances the surroundings.

Overall appearance can be subjective but general advice is available in documents such as BD41 The Design and Appearance of Bridges published by the Highways Agency, which encourages designers to aim for slender decks in relation to the headroom, balanced span openings and minimising the bulk of the end supports.

Even with standard prestressed bridge beams, there is ample opportunity for the designer to infl uence the appearance of bridges utilising precast concrete components. Individuality can be

expressed in the deck support structure (bankseats, abutments, piers and crossheads), the edge of deck treatment and in the combined overall eff ect of structure with landscape.

Visual eff ects can be created, contrasting deck edges with shadow lines or by varying the ratio of deck-edge cantilever or string-course depth to overall deck thickness. Continuous decks can be designed with shallower elevations that are pleasing to the eye. Special concrete fi nishes and textures are also possible, especially where the public will pass close to the structure.

3. AESTHETICS

4. BRIDGE DECKS

Reinforced concretesolid slab

Voided slab Precast beam and in-situ slab deck

Multi cell box section

Single cell box section

Figure 5: Typical deck sections


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4.1 Deck typesFor short spans a solid reinforced concrete slab, cast in-situ, is the simplest and most cost-eff ective solution. The fl at soffi t of the in-situ reinforced concrete makes the formwork, fi xing of reinforcement and concreting very simple with a corresponding reduction in cost.

As spans increase, there will be a need to increase the reinforcement and introduce some prestressing; the deadweight of the deck itself can be reduced by introducing voids within the slab using polystyrene formers. They are usually of circular section to enable the concrete to fl ow under them to the deck soffi t. It is very important, however, that these void formers are fi rmly held in position to prevent fl otation and that the concrete under the voids is well compacted. Reinforced concrete voided slabs are more economical than the prestressed concrete alternative up to about 25m span. The exact change-over point depends on comparative costs of reinforcement and prestressing at the time of construction.

If the location of the bridge does not suit in-situ slab construction then precast pre-tensioned concrete beams may be used. Inverted T-beams placed side by side and infi lled with concrete provide an alternative to the in-situ reinforced concrete slab.

For longer spans, beams and slab construction is used with a 200–250mm concrete deck slab supported on precast pre-tensioned beams spaced at 1.0–2.0m centres.

Precast beam construction utilises high quality, factory-made components that can be quickly erected on site and is therefore particularly useful when bridging over live roads, railways and waterways where interruptions to traffi c must be minimised. The standard beams currently in use are the M, U, Y and super Y beams which can be used for spans up to 40m. Detailed information may be obtained from the Prestressed Concrete Association (see www.britishprecast.org) or its member companies.

4.2 Construction methods for longer spansThe span-by-span method of construction is used in multi-span viaducts with individual spans of up to 80m. A span plus a cantilever of about one-quarter the next span is fi rst constructed. This is then prestressed and the falsework is moved forward and a full span length is then formed and stressed back to the previous cantilever. In-situ construction is used for smaller spans.

As the spans increase, the cost of falsework also increases. To minimise this, the weight of the concrete to be supported at any one time is reduced by dividing the deck into transverse segments. These segments, which can be in-situ or precast, are normally erected on either side of each pier to form balanced cantilevers and then stressed together. Further segments are then added, extending the cantilever to midspan where a small closure is formed of in-situ construction to make the spans continuous. In precast construction, the segments are match-cast against one another and jointed with epoxy resin before being stressed together.

Straight or curved bridges of single radius and of constant cross-section may be built in short lengths from one end and incrementally launched. Completed sections are pushed off the casting bed, with the whole deck travelling forward and propelling the leading face towards the next support.

Cable-stayed bridges are normally built using a form of precast segmental cantilever construction, successively building out from the support towers.

Figure 6: Medway Bridge - In-situ balanced cantilever bridge

Figure 7: Launched deck, Taiwan High Speed Rail

Figure 8: Segmental construction

Figure 9: Span by span construction - A16, Brebant, Holland


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4.3 Span ranges for concrete bridgesFigure 13 below illustrates the range of spans that may be achieved using various types of concrete construction.

Figure 10: Incremental launch - Ceirog Viaduct, North Wales Figure 11: Incremental launch - Pushing ram, Medway Bridge

Figure 12: Cable-stayed bridge - Dee Crossing, North Wales

IN SITU

CONSTRUCTIONTYPE

DECK TYPE SPAN RANGES / M

PRECAST

RC solid slab

RC voided slab

Prestressed voided slab (Internal bonded )

Incremental launching

Span by span(Supported on launching truss)

Span by span(Supported on scaffolding)

Segmental balanced cantilever

Arches

Inverted T beams cast into slab

M, U and Y beams with deck slab

Segmental balanced cantilever(erected by Crane)

Segmental balanced cantilever(erected by lifting gantry)

Cable stayed bridges bybalanced cantilever

- Definite range - Possible range extension

Figure 13: Span ranges for concrete bridges


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Whether the bridge is carrying a road, railway, waterway or just pedestrians the deck will be subjected to various types of load:

■ Self-weight

■ Environmental, e.g. wind, snow, temperature eff ects

■ Traffi c

■ Accidental loads, e.g. impact

■ Temporary loads, e.g. during construction or maintenance.

Bridges in the UK are generally designed in accordance with British Standard BS 5400, which gives details of the load combinations to be used for various bridge applications. Additional standards are published by the Highways Agency and Network Rail to supplement British Standards. Many of these standards are being upgraded to Eurocodes and in time these will state the basic requirements for bridges in the UK and other European member states. Specifi c requirements will be incorporated into a National Annex.

The analysis of a bridge should be undertaken by a designer who has received suffi cient training and experience. The method of analysis selected should be appropriate to the type of bridge being considered. On many concrete bridges the bending moments and shears resulting from the application of traffi c load on a bridge deck are not necessarily carried by just the portion of bridge deck immediately under the load. When the aff ected area defl ects, the deck bends transversely and twists, thereby spreading load to either side. The assessment of load that is shared in this way and the extent to which it is spread across the deck depends on the bending, torsion and shear stiff ness of the deck in both longitudinal and transverse directions. Computer methods are generally used to analyse the load eff ects. The most versatile of these is the grillage analysis, which treats the deck as a two-dimensional series of beam elements in both the longitudinal and transverse directions. This method can be used for slab, beam and slab-and-voided slab decks where the cross-sectional area of voids does not exceed 60% of the area of the deck.

Box girders are now generally designed as one or two cells without any transverse diaphragms. These are usually quite stiff torsionally but can distort under load giving rise to distortional and warping stresses in the walls and slabs of the box. It is then necessary to use three-dimensional analytical methods such as 3D space frame, folded plate (for decks of uniform cross-section) or a 3D fi nite element method.

5. LOADING

6. ANALYSIS


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A bridge is supported at the ends on abutments and may have intermediate piers. Both abutments and piers are usually constructed from reinforced concrete. The positions of the supports and the lengths of the spans are determined by the topography of the ground and the need to ensure unimpeded traffi c under the bridge.

Piers and abutments carry high loads, and their foundations may require piling. The design and method of construction of the foundation will depend upon the ground and groundwater conditions.

The substructure of a bridge is particularly at risk from damage caused by fl ooding, overfl ows from blocked drains, freezing and thawing weather conditions, and exposure to de-icing salts from sprayed or leaking water. The concrete in the substructure must be capable of resisting all forms of attack. Design for durability is vital.

The design of the substructure and foundation requires an understanding of the interaction between the substructure and the ground on which it is to be built and the structure to be supported. A thorough site investigation should be carried out. However, it may not be possible to obtain precise information about the soil conditions, in which case the designer must make sound judgements based on the data that can be obtained.

The cost of the substructure is often greater than that of the superstructure, and it is important to carry out the bridge design as a whole rather than allow the design of the deck to impose unnecessary restraints on the design of the substructure. Many bridges are designed to be continuous structures that are integral with the abutments: for such bridges the deck and the substructure have to be designed together.

The eff ects of the construction of the bridge on the progress of other parts of the work, such as earth moving, must also be taken into account. The substructure must be designed so that it can be constructed as quickly and easily as possible: the emphasis should be on simplicity and ‘buildability’, which will invariably contribute to economy. At the same time, the substructure must have an attractive appearance which is in keeping with the bridge and its surroundings.

7.1 The siteOn restricted sites the choice of substructure is often controlled by the space available and the plant that can be used. In particular, large-bored piles and raking piles require a considerable amount of space. Overhead power lines can seriously restrict the use of plant. The interaction of construction with existing traffi c is an essential factor in the design of the work. If it is possible to acquire additional land for construction, this may be cheaper than the cost of delay caused by extending the programme.

Groundwater conditions will aff ect the design: for example, it may not be possible to lower the water table due to the eff ect it might have on the stability of neighbouring structures. In this case it will be necessary to construct the foundation under water, and this may require the design to be in mass concrete rather than reinforced concrete.

7. SUBSTRUCTURES AND FOUNDATIONS

Figure 14: Substructures - M20, Maidstone, Kent


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7.2 Site investigationThe purpose of the site investigation is to provide information about the soil profi le and groundwater conditions across the site. The extent of the investigation will depend upon the nature of the site and the type of structure to be built. Trial pits and deep boreholes will provide a general picture of the ground and groundwater conditions. A more detailed study of samples from boreholes and in-situ tests in trial pits will give further information, but it should be borne in mind that the precise position of the foundations may not be known at the time the survey is carried out. All of the information obtained must be carefully examined and interpreted into data to be used for the design.

7.3 FoundationsThe choice of foundation for an abutment or a pier is normally between a spread footing and piling. Where ground conditions permit, the spread footing will provide a simple and economic solution. Excavations for foundations should be left open for as short a time as possible before the concrete is placed in order to limit ground disturbance.

Piling will be needed where the ground conditions are poor and cannot be improved, the bridge is over a river or estuary, the water table is high or site restrictions prevent the construction of a spread footing. It is sometimes possible to improve the ground by consolidating, grouting or applying a surcharge by constructing the embankments well in advance of the bridge structure.

Diff erential settlement of foundations needs to be controlled, and the construction sequence will have an eff ect on settlements. In the early stages of construction, abutments may settle more than piers but piers will settle later when the deck is constructed.

7.4 AbutmentsThe overall appearance of a bridge structure is very much dependent on the abutments and piers.

The structural design of the abutments is closely related to that of the bridge deck, and for an integral bridge the structure must

be designed as a whole. Abutments are usually constructed of reinforced concrete but, in suitable circumstances, mass concrete without reinforcement may provide a simple and durable form of construction.

If the deck is constructed before the main excavation is carried out, contiguous bored piles or diaphragm walling can be used to form an abutment wall. The cost of this type of wall construction is high, but can be off set against savings in the amount of land required, the construction time, the cost of temporary works and by minimising the disruption to traffi c. A facing of in-situ or precast concrete or blockwork will normally be required after excavation. Reinforced earth construction may be suitable where there is an embankment behind the abutment, and here precast concrete facing is often used. Replacement of the ties during the life of the structure is diffi cult so the selection of appropriate ties and fi xings is very important.

Where a bridge is constructed over a cutting it is usually possible to form a bankseat abutment on fi rm undisturbed ground. Alternatively, bankseats may be constructed on piled foundations. However, where bridges over motorways are designed to allow for future widening of the carriageway, the abutment may be taken down to full depth so that it can be exposed at a later date when the widening is carried out.

7.5 WingwallsThe design of wingwalls is determined by the topography of the site and can have a major eff ect on the appearance of the bridge. Wingwalls are often taken back at an angle from the face of the abutment for both economy and appearance.

On integral bridges wingwalls should be aligned parallel with the span direction and this has the benefi t of minimising soil pressures.

In-situ concrete is normally used, but precast concrete retaining wall units are available from precast concrete manufacturers. Concrete crib walling is also used for the construction of wingwalls and its appearance makes it particularly suitable for rural situations. Filling material must be selected carefully to ensure that it does not fl ow out, and the fi ll must be properly drained.

It is important to limit the diff erential settlement between the abutment and the wingwalls. This problem can be overcome by cantilevering wingwalls from the abutment or by supporting the whole structure on one foundation. If movement joints are selected then detailing should either include some form of shear connection or incorporate some means of disguising relative movement.

Figure 15: Boring rig

Figure 16: Skelton Bridge 12A, Cleveland, showing abutments and wingwalls


17

7.6 PiersThe simplest and most economic bridge pier is a vertical member or group of members with a uniform cross-section. Sections can be rectangular, square, circular or elliptical. The shaping of piers can make them aesthetically pleasing but complex shapes will increase the cost unless considerable re-use of forms is possible. Standardisation of shapes and sizes for several bridges in the same contract leads to economy. The durability of concrete in the piers will be helped if the design is simple, the detailing good and the deck overhangs the pier.

Raking piers and abutments may help to reduce the span for high bridges but they do require expensive temporary propping and support structures. This complicates the construction process and considerably increases costs.

7.7 Design considerations for substructuresThe design of the substructure, as for any structure, must ensure stability, structural safety and serviceability.

It is usual to assume that an acceptable amount of movement of an abutment or wingwall will occur, and this is taken into account in the design. Normally the backfi ll is a free-draining material and the wall has a satisfactory drainage system built into the structure: if these conditions are not satisfi ed then higher design pressures

must be used. If fi ll is to be compacted behind the abutment then due allowance must be made for the pressure due to compaction. Traffi c loading and vibration caused by traffi c must also be taken into account. If bankseat abutments are used, their stability against slipping must be checked carefully. The calculated resistance in front of the toe of a wall should be ignored if there is a possibility of excavation in this area for drainage or utilities.

Creep, shrinkage and temperature movements in the bridge superstructure can create forces on the abutments, and these must be determined. Diff erential settlement is a factor to be considered. Piers and, to a lesser extent, abutments are vulnerable to impact loads from vehicles or shipping and must be designed to resist impact or be protected from it. Substructures of bridges over rivers and estuaries are subjected to scour and lateral forces due to water fl ow, unless properly protected.

It is diffi cult to accurately predict bridge settlement by calculation and any predictions should be compared with a study of case histories of structures on similar ground. The design of a bridge to control diff erential settlement may result in the foundations being larger than those required solely for stability.

The durability of the substructure will be improved by proper consideration being given to all aspects of its design and construction. Careful selection of materials and mixes for the concrete, the design and detailing of the structure to prevent damage due to water and de-icing salts, and supervision and control of the quality of the work are all essential for durability.

Figure 17: Piers - Docklands Light Railway, London


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8. MATERIAL SELECTION

8.1 Ready-mixed concreteConcrete has been a major construction material since Roman times and remains so today. Originally, all the ingredients (cement, fi ne and coarse aggregates and water) were mixed on the building site. In the 1930s, however, the idea of mixing at a dedicated off -site plant and delivering to local sites was fi rst originated. It was the birth of an industry that developed rapidly and soon became recognised throughout the world.

Established in the UK since the 1950s, the ready-mixed concrete industry off ers nationwide coverage from approximately 1,200 batching plants. All major suppliers are certifi ed with organisations such as the Quality Scheme for Ready Mixed Concrete (QSRMC), an independent assessment organisation approved by the National Accreditation for Certifi cation Bodies (NACB). This ensures that the customer will receive a consistent, quality product that will meet the specifi cation and be fi t for the purpose intended, providing that it is placed, compacted, cured and protected to the required standards.

8.2 Why use ready-mixed concrete?Concrete is a basic construction material consisting mainly of naturally occurring materials but its production in large volumes to meet rigorous modern specifi cations requires considerable expertise and experience. While it is possible to mix it on site, ready-mixed concrete is now used in all but exceptional circumstances for the following reasons:

■ Design options enhanced

■ Pre-sales advice on mix design and the concreting operation

■ Production and technical support under the control of dedicated and experienced professionals

■ Independent verifi cation provides external assurance that the quality of concrete supplied conforms with that ordered

■ Coordinated and fl exible supply in terms of quantity, rate and back-up facilities, normally via a central despatch offi ce that coordinates all deliveries in a defi ned area

■ Increased site space

■ Availability of up-to-date technology, materials and plant

■ Increased speed of construction.

Figure 18: Typical pour

Figure 20: Typical ready-mixed concrete delivery truckFigure 19: Modern ready-mixed concrete plant


19

8.3 Ready-mixed concrete in bridgesMore than one million cubic metres of ready-mixed concrete are used every year in bridge construction throughout the UK. They are usually high-profi le structures and are very visible in many landscapes.

The aesthetic qualities of a bridge are of environmental signifi cance both in terms of its design and the appearance of the large areas of concrete that are normally visible. Such considerations are very much in the minds of approval bodies and local planning offi ces when bridges are fi rst planned and then designed. The use of concrete off ers many alternatives in shape, form, colour and type of surface fi nish.

The use of ready-mixed concrete guarantees that these high standards can be achieved and that is why it plays such a prominent role. It has been used in all modern bridges including major structures such as Second Severn Crossing, Skye Bridge, the Dee Crossing and the new Medway Bridges on the Channel Tunnel Rail Link and A2/M2 Motorway improvement.

Bridge exposure to all weather conditions and heavy traffi c usage is the ultimate test for concrete performance. The consistent quality of ready-mixed concrete helps to provide the best solution to the variety of demands placed upon it.

Bridges are normally designed for a 120-year lifespan and the durability of the structure and all of its components are therefore

of paramount importance. The high compressive strength, the resistance to fi re and impact, the adaptability to meet various structural and environmental demands by using specialist materials and mix designs, are all typical examples of how concrete can contribute to the longevity of a bridge structure. These same qualities can also be used to good eff ect, when necessary, in the repair and maintenance of a bridge over its lifetime.

8.4 Specifi cation of concrete mixThe fl exibility that it off ers both designer and contractor is an important factor in meeting these demands. A typical mix for use throughout bridge construction (refer to BS 8500) could be C40/50 – a design mix which gives a compressive cylinder strength of 40N/mm2 and a compressive cube strength of 50N/mm2 after 28 days. Nevertheless, diff erent components of the bridge may need individual variations to aid placement, or to meet end-use requirements, while still meeting the specifi ed strength, e.g.:

■ Piles – higher workability is required

■ Deck – the use of an air-entraining agent may be required to increase frost resistance.

All of these mix variations can be easily accommodated by a ready-mixed concrete supplier.

Figure 21: Diagram of main bridge components

Pier

C a b l e stay

PadFoundations

Abutment

Deck

Pile capPiles

Tower (pylon)

Figure 22: Concrete types

Concrete type Uses in bridge construction

HIGH STRENGTH >60N/MM2) Signifi cantly increased span-to-depth ratio allowing thinner beam sections

SELFCOMPACTING To provide increased “fl ow” characteristics to ease placement in areas of dense reinforcement or diffi cult access, e.g. voided deck-slab, whilst producing dense uniform concrete without any need for compaction

LIGHTWEIGHT The use of lighter fl y-ash aggregates for superstructure concrete produces less loading, and therefore smaller foundation are needed

LOW DENSITY E.G. FOAMED, HIGHLY AIRENTRAINED

Free-fl owing concrete for non-structural uses, e.g. backfi ll for abutments and retailing walls

MASS Normally low cement-content for large foundations and bases or backfi ll

PUMPED Designed mix normally with increased fi nes to allow concrete to be placed by a specialist pump


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8.5 GroutsSpecially designed grouts are used within ducts in post-tensioned bridges to protect the steel strand from corrosion. These should comply with The Concrete Society Technical Report 47 (see Further Reading). The use of pre-measured and mixed materials should be the fi rst choice for quality, but this does not exclude combinations of controlled materials on the basis that the quality of the end product is the important factor to ensure adequate protection of prestressing tendons.

8.6 AdmixturesA variety of chemical admixtures can be included in concrete mixes to provide buildability benefi ts and to meet specifi c demands, for example:

■ Air-entraining agent – increased frost resistance

■ Plasticiser – improved fl ow characteristics (easier placement)

■ Accelerator – early high strength (to counter time constraints).

Colouring pigments and special aggregates can be used for aesthetic purposes.

8.7 ReinforcementMost structural concrete is reinforced, normally with steel bars or fabric. It is essential to ensure that such reinforcement is adequately protected by a minimum cover of good quality concrete to counter the varied climatic conditions experienced in the UK.

A new generation of non-ferrous products is becoming available to replace steel with the aim of increasing the durability of concrete structures. Because of their exposure to climate and de-icing salts, bridge design and construction is at the forefront of such technology.

Without adequate protection, steel in bridges may corrode, particularly in countries like the UK where de-icing salts are used during the winter months. Hence, careful consideration must be given to the protection of reinforcement and prestressing tendons. The type of concrete must be correctly selected and the degree of exposure may demand the use of stainless steel reinforcement, especially on parapet edge beams or in the vicinity of deck movement joints. Prestressing tendons may be galvanised in addition to other layers of corrosion protection.

Figure 23: Reinforcement - River Leen Bridge, Nottingham

Figure 24: Non - ferrous reinforcement


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There are two main types of prestressed concrete.

9.1 Pre-tensioned concreteSteel tendons are stressed by jacks anchored to fi xed blocks in the casting yard. Concrete is then placed in moulds or casting beds around these tendons. When the concrete has hardened suffi ciently, the tendons are released. As they try to return to their original length, large compressive forces are applied to the concrete.

This process is nearly always carried out in a factory environment and is the usual way of manufacturing precast prestressed bridge beams.

9.2 Post-tensioned concreteFor this type of construction, normally associated with in-situ concrete, the tensioning forces are applied to the tendons after the concrete is placed and hardened. Ducts are incorporated into the formwork and the concrete is placed around them. After the concrete has hardened, the stressing tendons are threaded through the ducts and are stressed using jacks. A special grout is injected into the ducts around the tendons to provide bond and protection from corrosion. Post-tensioning is mainly carried out on site although it has been used for special precast beams.

Traditionally, post-tensioned bonded tendons have relied on cement grouting for protection. However, inadequate detailing and workmanship in the past have led to corrosion of tendons, the condition of which cannot be monitored. Therefore, in the UK, internal unbonded tendons or external tendons, the condition of which can be monitored at any time, are currently preferred to the bonded type.

Unbonded tendons are normally protected by placing them in ducts, which are subsequently fi lled with grease or wax. Alternatively, external tendons can be left exposed, but protected by galvanising or epoxy coating.

9. PRETENSIONED AND POSTTENSIONED CONCRETE

Stage 1 - Tendons are tensioned and anchored

Stage 2 - Concrete is placed

Stage 3 - Tendons are released and force is transferred to concrete

Prestressing using pre-tensionedtendons

Prestressing using post-tensionedinternal tendons

Stage 1 - Concrete cast with tendons in duct

Stage 2 - Tendons tensioned after concrete has hardened

Stage 3 - Tendons secured at anchorages

Figure 25: Pre-tensioned and post-tensioned concrete


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The use of precast concrete is both widespread and eff ective in modern bridge construction. Many modern bridges are constructed with both in-situ and precast concrete.

10.1 What is precast concrete?Precast concrete is manufactured away from the construction site, in an effi cient factory environment to very high standards and without any concerns about adverse weather. The quality of the concrete can be tightly controlled and the formwork and steel reinforcement or prestressing tendons can be prepared and positioned to extremely high tolerances. After it has been poured, the concrete can be cured eff ectively, again without interference from the weather, to maximise its performance (especially its durability) and appearance. Importantly, it can be stored and delivered to site at precisely the right time in the construction programme.

10.2 Why use precast concrete?

■ Guarantee of high-quality concrete and durability

■ Exceptional standards of dimensional tolerance

■ Excellent surface fi nishes

■ Rapid construction

■ More space on site

■ Avoidance of falsework

10.3 Where can precast concrete be used?Precast concrete can be used in almost all parts of a bridge structure. The use of precast piles is quite common and demand is growing for precast units in abutments but its most widespread use is in the deck support structure, in the form of prestressed beams, and as parapets and string courses.

10.4 Durability of prestressed bridge beamsJoints in decks are a common cause of problems in all types of bridge. A survey of 200 concrete highway bridges commissioned by the Department of Transport highlighted the problems of reinforcement corrosion by water carrying de-icing salts leaking through joints or being splashed onto the reinforced concrete elements of decks and substructures.

The survey showed that the prestressed bridge beams, by comparison, had performed extremely well, for two reasons:

■ Quality of construction (the required cover to reinforcement is more easily achieved in prestressed concrete and so there is less chance of corrosion)

■ Prestressed beams are constructed with high-strength concrete (60–80N/mm2 at 28 days) with low water/cement ratios. The water/cement ratio is generally specifi ed to be less than 0.45, but values below 0.4 are frequently achieved through the use of effi cient plasticisers and water-reducing agents

10.5 Handling and transportation of beamsGreat care must be taken to ensure the prestressed concrete beams are stable during handling, transportation, storage and erection. Transporting long-span beams by road from factory to site is a routine operation although careful planning is essential.

It is advisable to strengthen the longer SY beams and provide a supporting frame to enhance safety and stability during erection and transportation. Manufacturers will generally off er full support and advice.

10. PRECAST CONCRETE IN BRIDGE CONSTRUCTION

Figure 26: Precast beams in position Figure 27: Delivery of a precast beam


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10.6 Deck edges and parapetsThe edges of decks require special beams to provide a vertical or inclined edge face and to support steel or aluminium parapets. These beams are manufactured in precast concrete to match the beams used for the deck, for example UM beams.

Parapets are often manufactured in precast concrete and the high containment situation is a common requirement for railway bridges. The vertical faces can also be given an architectural appearance by using a variety of treatments and surface fi nishes.

10.7 Culverts and archesPrecast concrete culverts and arches can be used to replace underbridges carrying minor roads, services and rivers. They can be installed speedily and economically to provide a durable option.

10.8 Replacement rail bridgesReplacement bridges spanning over or carrying railway lines are ideally suited for the use of precast concrete due to the limited railway possession time available. Site operations can be reduced to a minimum as a trial erection can be carried out off site and the major components marked with guide-lines to facilitate the actual site erection.

Figure 28: Precast box culvert section Figure 29: Precast arch sections


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The fi rst pre-tensioned beams for use in the UK were manufactured in 1940 to meet the demand for emergency bridge construction during the Second World War. In the mid 1950s, at the start of the major road building programme, the precast industry really began to develop, mainly through the work of the Cement and Concrete Association (C&CA) and the Prestressed Concrete Development Group.

A major innovation was the range of prestressed inverted T-beams for 7–15m spans. These were often used with an in-situ concrete infi ll to form a solid, composite deck slab.

In the 1960s, demand for longer-span bridges over two- and three-lane carriageways, spanning 15m–26m and 26m–35m, respectively, led to the introduction of I-beams and box sections. There were technical defi ciencies with these and a clear need was identifi ed for a standard beam for use in the 15m–29m span range. In 1969, following work by the C&CA and the Ministry of Transport, the M-beam was born and it became the fl agship for the next 20 years. M-beams were often used at 1.0m centres in either pseudo box construction or, more simply, in beam-and-slab construction.

Further developments in the mid 1970s, saw the introduction of the U-beam, which was especially suitable for skew decks, the UM beam, used as the edge beam on M-beam decks, and the wide box beam.

These new beams catered for the increasing demand through to the end of the 1980s. Between 1965 and 1982, nearly 7,000 road bridges were built, 6,000 of which were in concrete and more than half of these in prestressed concrete. This refl ected the benefi ts of economy and ease-of-use of standard precast beams.

At the end of the 1980s, however, signs emerged of corrosion of reinforcement in the relatively slender bottom fl anges of some M beams due to ingress of water. The Prestressed Concrete Association (PCA), an association of the leading UK beam manufacturers, addressed this problem and, in 1991, unveiled the Y beam. Not only did it cater for the same span range (15m–29m) but it also proved suitable for use in modern integral, or jointless, bridges. The YE beam soon followed to serve as an edge beam for Y-beam bridge decks.

Development continued with the SY beam catering for the motorway widening programme in the 1990s, which required spans of over 35m in some cases. The TY beam replaced the inverted T beam as it off ered technical advantages such as improved shear capacity and thicker concrete cover to the reinforcement.

11. HISTORY OF PRETENSIONED CONCRETE BEAMS IN BRIDGES

Figure 30: Typical beam sections

MY BEAMS M BEAMS

INVERTED TEE

UM BEAMS

Y BEAMS U BEAMS

YE BEAMS SY BEAMS

DOUBLE TEE BEAMS

Figure 31: Typical deck section


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The speed and cost of construction and the durability of any bridge are greatly aff ected by the attention paid to details. Details that are determined solely by the desire to reduce quantities of materials used, often by small amounts, may result in disproportionately large increases in construction costs and may have an adverse eff ect on durability.

Simplicity and standardisation are the keys to success. One example of a situation where simplicity of construction is preferred is in the use of a wider base on a level formation, to provide stability against sliding, rather than inclining the formation or providing a shear key. The excavation for a shear key or an inclined formation will increase the cost of construction and, in the case of the shear key, may well disturb the ground that is required to resist the sliding action.

Walls must be designed to allow access for concreting: details such as inclines to the faces, curvature on plan and heights that change along the length, will make it more diffi cult to place the concrete and achieve a good fi nish. Attractive concrete surfaces are often diffi cult to form in-situ, and the use of precast facings may provide a better quality fi nish.

Restrictions on sizes of pour and position of construction joints can adversely aff ect the programme for concreting. Such restrictions may be necessary to control movements of the concrete but they should suit the sizes of formwork panel and the construction procedures to be employed.

Bearing shelves at the top of abutments must be detailed with adequate drainage, on the assumption that water will get in. Drainage channels and down pipes must be accessible for cleaning, and many designers locate the drainage channels in front of the bearings for ease of access. Drainage of the backfi ll behind an abutment requires careful attention to detailing of the drainage system. Free-draining granular material is not always available for backfi ll and less permeable materials may have to be used. The eff ects on earth pressures must be taken into account in the design, and the drainage system must be planned to suit.

Good design detailing will make construction easier, enhance durability and also permit easier inspection and maintenance. Typical examples are:

■ Positive drainage of all surface water

■ Provision of chamfers, fi llets, drips in overhangs and chases for tucking in waterproofi ng

■ Use of standard details wherever possible, particularly in precast beams

■ Use for bonded tendons of air-tight, non-metallic ducts; anchorage protection with end caps and provision for grouting anchorage recesses

■ Provision of abutment chambers for inspection

■ Provision for easy access into and along large and long box girders

12.1 Bridge bearingsBearings transfer the loads from an independent deck to its supports. All bridge decks defl ect under load, so the bearings must be able to accommodate the small rotations at the supports. They must also accommodate the horizontal movements of the bridge deck caused by temperature changes, shrinkage and creep, and the shortening caused by prestress. Some bearings allow horizontal movement in one direction only and are restrained in the other, while others allow movement in any direction.

Elastomeric bearings, consisting of layers of steel plate embedded in rubber, can accommodate small horizontal shear movements. PTFE (polytetrafl uoroethylene) bearings can be designed for unlimited free sliding between the low-friction PTFE surface and a steel plate. Pot bearings incorporate rubber discs that permit small rotations, while spherical bearings, moving on a PTFE surface, will permit larger rotations.

Mechanical bearings, such as rockers and rollers, provide either longitudinal fi xity or resistance to lateral forces. Pot bearings, special guide bearings or pin bearings are often used for this purpose.

Bearings need to be inspected regularly and may require maintenance or replacement during the lifetime of the bridge. This can be diffi cult and expensive, so it is important that the structure is designed to make inspection, maintenance and replacement possible.

Where access is diffi cult, the bearing should have the same design life as the rest of the structure.

12. DURABILITY AND DETAILING

Figure 32: Bearings on pier - Mollington Footbridge, M40


26

12.2 Expansion jointsExpansion joints must allow free movement of the bridge, including movements in kerbs, verges and parapets, as well as those in the main deck, but they should not have too serious an eff ect on riding quality.

Leakage at joints leads to reduced durability and disfi guration of the structure below, so joints need to be waterproof or designed to allow for drainage. Joints should also be designed to require minimal maintenance during their lifetime. However, joints may not last the life of the structure, so they should be replaceable.

Small movements at expansion joints can be accommodated by compressible materials such as neoprene or rubber. These joints can be buried and covered by the surfacing, giving an undisturbed riding surface. Buried or ‘run-over’ joints may consist simply of a gap, suffi cient to accommodate the movement, covered by a galvanised

steel plate and a band of rubberised bitumen fl exible binder to replace part of the surfacing. This type of joint is known as an ‘asphaltic plug’.

Larger movements require a fl exible sealing element supported by steel joists or edge beams. Mechanical joints based on interlocking sets of fi nger plates can be used for very large movements. Drainage must be provided for such joints.

Whatever type of expansion joint is used, it is likely to interrupt the surface and give rise to noise. In long structures it is preferable to design for long lengths between joints, rather than incorporate joints at frequent intervals. Longer lengths will result in larger movements at the joints, but will preserve riding quality and reduce maintenance. Integral bridges – constructed with joint-free decks – have been referred to earlier.

Figure 33: Typical section of asphaltic plug joint


27

Figure 34a: Typical section of mechanical joint


28

12.3 Waterproofi ng bridge decksIt is a current UK requirement that bridge decks are waterproofed with an approved system, which may be sheet, board or spray-applied liquid. The deck detailing should allow continuity of waterproofi ng ‘across’ central reservations, verges, service bays and under kerbs. Arrises (external corners) should be chamfered and fi llets should be formed at internal angles. All waterproofi ng systems must be protected using a tinted asphalt layer before the fi nal surface is laid.

Exposed surfaces, such as deck soffi ts, fascias, concrete parapets and parapet plinths may be contaminated with salt water carried by wind or from traffi c spray. Impregnation, when new, with silane or a similar product can give protection for a limited period. However, factory-made precast pre-tensioned beams have an excellent durability record even without any such treatment.

Figure 34b: Typical section of mechanical joint

Figure 35: Spray application of waterproofi ng membrane


29

In the past, mastic asphalt has been used extensively for waterproofi ng bridge decks, but it requires good weather conditions if it is to be laid satisfactorily, so is rarely used now. Preformed bituminous sheeting is less sensitive to laying conditions, but moisture trapped below the sheeting may cause subsequent lifting.

Hot-bonded heavy-duty reinforced sheet membranes, if properly laid, provide a completely watertight layer. These sheets are made in thicknesses of 3–4mm and have good puncture resistance, so it is not necessary to protect the sheet membrane from asphalt laid on top.

Sprayed acrylic and polyurethane waterproofi ng membranes are also used. These bond to the concrete deck surface with little or no risk of blowing or lifting. A tack coat must be applied over the membrane, and a protective asphalt layer is laid before the fi nal surfacing is carried out.

Some bridges have relied upon the use of a dense, high-quality concrete to resist the penetration of water without an applied waterproofi ng layer. It can be advantageous to include silica fume or other very fi ne powdered addition in the concrete.

Communication is the key to success. It is important that the main and/or specialist concrete contractor(s) form a close relationship with the ready-mixed concrete supplier from an early stage. Regular liaison and progress meetings should be held both before and during the concreting programme to ensure a smooth and eff ective operation.

13.1 Concrete specifi cationsA complete understanding of the specifi cation is necessary to establish criteria such as compressive strength, size and type of aggregate, admixtures and workability. The requirements of BS 8500 must be followed. Also, knowledge of the relevant bridge codes, e.g. BS 5400 Part 4 and Highways Agency design standards for bridges such as BD24 and BD57 will be particularly relevant.

BS 8500 requires that the cover to reinforcement be increased by 15mm for cast in-situ reinforced concrete members to give the desired durability for 120 years. Precast prestressed beams also need extra cover but only 5mm.

13.2 Formwork and reinforcementTo ensure that the concrete is poured with the minimum of diffi culty the size, type and position of formwork needs to be assessed together with the density of reinforcing steel (or other materials) and the depth of cover specifi ed. This will ensure easier placement and compaction and will maximise durability.

How the concrete is to be placed into the formwork is a crucial factor to the ready-mixed supplier, for example:

■ Small barrows or skips invariably mean longer discharge times and possible disruption to deliveries

■ A concrete pump may be used for the more inaccessible bridge sections and the larger pours; the mix design will probably need some adjustment to ensure the concrete can be pumped effi ciently

13.3 Size of pour and rate of supplyPlant, transport and labour requirements to meet the demands of the operation need to be established. This will be particularly important on the larger pours that may be required for the construction of a bridge, e.g. mass foundations, bridge deck.

Contingency plans need to be agreed to safeguard continuity of supply in the event of plant or transport failure. This will be especially

13. CONSTRUCTION PLANNING

Figure 36: Concrete pumped into position


30

important when structural elements such as piers constructed as ‘cold’ joints would not be acceptable in such components.

Routes for the ready-mixed trucks to the site and the provision of safe, sound access on site should be cleared with the appropriate authorities and site management.

13.4 Weather conditionsAgreement should be reached with site management on acceptable weather conditions for the placement of concrete and the measures necessary to counter the extreme conditions which may be experienced on a bridge in exposed locations, e.g. wind, ice.

13.5 Testing and curingIt is in everybody’s interests to ensure that qualifi ed personnel are available to carry out the standard testing procedures to British Standards.

Freshly placed concrete must be given adequate protection from rapid surface drying or temperature variations for as long as possible to maximise its performance and appearance. This is an important factor in achieving the high standards of durability required for a bridge.

Figure 37: Ready-mixed concrete being delivered

All bridges should be inspected regularly, to ensure that they are in a satisfactory condition and to locate any potential sources of trouble. Detailed inspections, called Principal Inspections, are normally required every six years with general inspections at more frequent intervals.

Proper attention to waterproofi ng, joint design and detailing, and drainage from the deck, can prevent many of the problems that have caused deterioration of concrete bridges in the past. Adequate cover to reinforcement is vital, so care must be taken during design, specifi cation and construction, to ensure that suffi cient cover is provided.

Other methods are available for improving the corrosion resistance of reinforcement, and the fi nished concrete can be treated with sealing compounds to reduce the penetration of water and de-icing salts.

Bridges are normally designed to require minimal maintenance. However, it will be necessary to carry out routine inspections of drainage channels and down pipes, joints and bearings. Checks on the movement of abutments, piers and walls should be made regularly, and foundations in water courses must be inspected for damage due to scour. Such inspections require access, and this must be anticipated in the design and detailing of the structure. A programme of inspections at regular intervals should be planned and any defects revealed must be attended to without delay.

14. INSPECTION AND MAINTENANCE


31

All bridges should be designed so that they perform safely and can be built in a manner that minimises risk to both the construction team and the public.

Safety factors are built into the design code requirements to cover the variability of loading and material properties for in-service and ultimate conditions.

The Construction Design and Management (CDM) Regulations are a legal obligation for all organisations involved with the construction process: client, designer, contractors and suppliers. A Planning Supervisor needs to be appointed and a Health and Safety fi le provides essential information for each organisation throughout the construction process and during the maintenance life of the structure.

15. HEALTH AND SAFETY

16. FUTURE TRENDS

Today’s requirements for durable, continuous, integral bridges will lead to increased use of precast concrete in bridge structures. The bridge deck is one area that may be exploited by incorporating a new range of prestressed concrete T or even double-T beams in the design. With such decks, in-situ concrete would be required only as a ‘topping’ to stitch the beams together.

The trend towards private Design Build Finance and Operate (DBFO) road contracts with pay-back periods of up to 25 years, underlines the requirements for low-maintenance bridges. An examination of the likely costs over the lifespan of a bridge (whole-life costing) is now considered an essential part of the overall equation. The use of precast concrete elements, with their advantages of quality, speed and effi cient construction, will have a considerable benefi cial impact.


32

AMERICAN CONCRETE INSTITUTE. ACI 343R-88, Analysis and Design of Reinforced Concrete Bridge Structures. ACI, Detroit, 1988, 162 pp.

CIRIA. Report 155, Bridges – Design for Improved Buildability. CIRIA, London, 1996.

CIRIA. RP490: Buildability of Bridges. CIRIA, London, year.

CLARK L.A. Concrete Bridge Design to BS 5400. Construction Press, Longman, London, 1983.

TECHNICAL GUIDES published by Concrete Bridge Development Group. TG1: Integral Bridges (1997), TG2: Guide to Testing and Monitoring The Durability of Concrete Structures (2002), TG3: The Use of Fibre Composites in Concrete Bridges (2000), TG4: The Aesthetics of Concrete Bridges (2001), TG5: Fast Construction of Concrete Bridges (2005), TG6: Guide to the Use of High Strength Concrete in Bridges (2005), TG7: Guide to the Use of Self-Compacting Concrete in Bridges (2005), TG8: Guide to the Use of Lightweight Concrete in Bridges (2006)

Further technical guides in preparation: TG9: Assessment of Concrete Bridges (2) (due 2006), TG10: Design Example of Integral Bridges to EC2 (due 2006)

CONCRETE SOCIETY/CONCRETE BRIDGE DEVELOPMENT GROUP. Durable Post-tensioned Concrete Bridges, Technical Report 47 (Second Edition), The Concrete Society, Camberley, 2002, 69 pp.

The Construction (Design and Management) Regulations, SI 1994/3247, HMSO, London, 1994.

HAMBLY, E.C. Bridge Deck Behaviour, 2nd edn. E. & F. Spon, London, 1991, 313 pp.

HAMBLY, E.C. Bridge Foundations and Substructures. HMSO, London, 1979, 93 pp.

HAMBLY, E.C. & NICHOLSON, B. Prestressed Beam Integral Bridges. Prestressed Concrete Association, Leicester, 1991, 29 pp.

LEE, D.J. & RICHMOND, B. Bridges. Civil Engineer’s Reference Book, Ed. L. S. Blake. Chapter 18. Newnes-Butterworth, London, 1988, 71 pp.

LlEBENBERG, A.C. Bridges. Handbook of Structural Concrete, Eds F. K. Kong et al. Chapter 36. Pitman, London, 1983, 168 pp.

PRESTRESSED CONCRETE ASSOCIATION. Precast Bridge Beams – Product Information Sheets.

PRITCHARD, B. Bridge Design for Economy and Durability. Thomas Telford, London, 1992, 192 pp.

READY-MIXED CONCRETE BUREAU. The Essential Ingredient. British Cement Association, Camberley, 1993–1997.

SOUBRY, MA. CIRIA Report C543. Bridge Detailing Guide. CIRIA, London, 2001.

TOMLINSON, M.J. Foundation Design and Construction. Pitman Publishing Limited, London, 1980, 793 pp.

WELTMAN, A.J. & HEAD, J.M. Site Investigation Manual. CIRIA Special Publication 25. CIRIA, London, 1983, 144 pp.

BRITISH STANDARDS INSTITUTION. BS 6031: 1981. Code of Practice for Earthworks. BSI, London, 1981, 86 pp.

BRITISH STANDARDS INSTITUTION. BS 5400. Steel, Concrete and Composite Bridges. Part 1: General Statement, Part 2: Specifi cation for Loads, Part 4: Code of Practice for Design of Concrete Bridges, Part 5: Code of Practice for Design of Composite Bridges. BSI, London, 1978-1990.

BRITISH STANDARDS INSTITUTION. BS 8500. Concrete – Complementary British Standard to BS EN 206-1, Part 1: Method of Specifying and Guidance for the Specifi er, Part 2: Specifi cation for Constituent Materials and Concrete. BSI, London, 2002.

DEPARTMENT OF TRANSPORT. Manual of Contract Documents for Highway Works.

Volume 1. Specifi cation for Highway Works.

Volume 2. Notes for Guidance on the Specifi cation for Highway Works.

Volume 4. Bills of Quantities for Highway Works. DoT, London.

HIGHWAYS AGENCY. Design Manual for Roads and Bridges.

Volume 1. Highway Structures – Approval Procedures and General Design.

BA 41, The Design and Appearance of Bridges.

BA 42, The Design of Integral Bridges.

BD 24, The Design of Concrete Highway Bridges. Use of BS 5400: Part 4: 1990.

BD 57, Design for Durability.

Many construction activities are potentially dangerous so care is needed at all times. Current legislation requires all persons to consider the eff ects of their actions or lack of action on the health and safety of themselves and others. Advice on safety legislation may be obtained from any of the area offi ces of the Health and Safety Executive.

All advice or information from the Concrete Bridge Development Group is intended for those who will evaluate the signifi cance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted. Readers should note that all publications are subject to revision from time to time and should, therefore, ensure that they are in possession of the latest version.

17. FURTHER READING

intro bridge

Documents

budget bridge design

use of concrete

concrete bridgesfirst

bridge engineering expertise

management of concrete

sectors bridgeowners

group acts

concretebridge industry