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CIRIAC543
Bridge detailing guide
Michael Soubry BSc(Eng) ACGI MICE MIStructE CEng
London, 2001
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;e'.!• •_ "arin. knowledge. buildin. be" , ...ct/ce
6 Storey's Gate, Westminster, London SW1 P 3AUTELEPHONE 020 7222 8891 FAX 020 72221708EMAIL [emailprotected] www.ciria.org.uk
Bridge detailing guide
Soubry,MA
Construction Industry Research and Information Association
Publication C543 © CIRIA2001 ISBN 086017543 X
ii
Keywords
Bridges - detailing, design, construction, durability, maintenance, inspection, concretesuperstructures, steel superstructures, subways, culverts, support structures, bearings,joints, fixings, retaining walls, integral construction
Reader interest Classification
Bridge-owners and AVAILABILITY Unrestricted
operators; detailers,CONTENTS Recommendations based on best
designers and specifiers;current practice
constructors and specialistsuppliers STATUS Committee-guided
USER Bridge design engineers,technicians and constructors
Published by CIRIA, 6 Storey's Gate, Westminster, London SW1P 3AU.
All rights reserved. No part of this publication may be reproduced or transmitted inany form or by any means including photocopying and recording without the writtenpermission of the copyright holder application for which should be addressed to thepublisher. Such written permission must also be obtained before any part of this
publication is stored in a retrieval system of any nature.
This publication is designed to provide accurate and authoritative information in regardto the subject matter covered. It is sold and/or distributed with the understanding thatneither the author(s) nor the publisher is thereby engaged in rendering a specific legal orany other professional service. While every effort has been made to ensure the accuracyand completeness of the publication, no warranty or fitness is provided or implied, andthe author(s) and publisher shall have neither liability nor responsibility to any person or
entity with respect to any loss or damage arising from its use.
CIRIAC543
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Summary
This guide was commissioned by the Quality Services Civil Engineering Division of theHighways Agency (HA) and has been prepared for those active in the bridge engineeringindustry. The need for a bridge detailing guide was identified by an earlier HA/CIRIAresearch project on bridge buildability. In particular, guidance is provided for engineersand technicians engaged in the preparation and development ofdetails for highway andaccommodation bridges, subways, culverts and retaining walls. Thus the guideconcentrates on the detailing issues that follow conceptual and analytical design. Thescope is further limited to spans up to 60 m and, in the case of steelwork details, to steelgirder/concrete slab composite construction.
Details selected for the guide represent basic principles that have proved to be reliable ineveryday use in terms ofdurability and ease ofconstruction, inspection, maintenanceand repair. Explanatory notes emphasising the principles and issues involved areprovided. However, the guide is intended as a live document and will be revised andextended as a result of feedback by the industry. A formal feedback procedure isincluded.
The guide is based on research in the UK and internationally, and the selected detailshave been subject to wide review by practitioners within the industry. In cases wherethere were differences of opinion the preferred details represent a majority view.
iii
iv
Health and safety
Construction activities, particularly on bridge construction sites, havesignificant health and safety implications. These can be the result of theactivities themselves, or can arise from the nature of the materials andchemicals used in construction. The report does not endeavour to givecomprehensive coverage of the health and safety issues relevant to the subjectit covers, although its importance is emphasised by particular sections dealingwith health and safety. Readers should consult other specific publishedguidance relating to health and safety in construction.
Government reorganisation
Recent Government reorganisation has meant that the responsibilities of the Departmentof the Environment, Transport and the Regions (DETR) have been moved variously tothe Department ofTrade and Industry (DTI), the Department for the Environment, Foodand Rural Affairs (DEFRA), and the Department for Transport, Local Government andthe Regions (DTLR). In particular, the DTLR now has responsibility for the HighwaysAgency. References made to the DETR in this publication should be read in this context.
For clarification, readers should contact the Department of Trade and Industry.
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Acknowledgements
The project leading to this guide was commissioned by the Quality Services CivilEngineering Division of the Highway Agency, and was carried out under contract toCIRIA by Hyder Consulting Limited.
Research team (Hyder Consulting Limited)
MrMA Soubrywith valuable contributions, assistance and research from many other members of staff,both in the UK and overseas and, in particular, by Mr J B Harris.
Steering group
The guide was prepared with guidance from a steering group and two technicalcommittees, which included the following:
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CIRIAC543
Mr R A McClelland (chairman)
Mr J M Barr
Mr C V Castledine (Steel T C chairman)
Mr S Chakrabarti
Mr M Chubb (Concrete T C chairman)
Mr G Cole
Mr T J Collins
Mr J Darby
MrD C C Davis
MrIMGibb
MrD Gordon
Mr R Johnstone
Mr A E Norfolk
MrD Pheby
MrMNRanft
MrD Thomas
Mr G E Webster
Mr P F Whatling
MrKR Wilson
MrR Wrigley
Dr B W Staynes (research manager)
Alfred McAlpine Civil Engineering
High Point Rendel
Butterley Engineering Ltd
Highways Agency
W S Atkins & Partners
Surrey County Council
The Welsh Office
Mouchel Consulting Ltd
Mott MacDonald Ltd
Peter Brett Associates
John Laing Construction Pic
The Scottish Office, National Roads
Directorate
Kent County Council
Pell Frischmann Consultants Ltd
Balfour Beatty Civil Engineering Ltd
Health & Safety Executive
Owen Williams Consulting Engineers
Kvaemer Technology Ltd
The Maunsell Group
Gifford & Partners
CIRIA
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Consultation
In addition to those in the foregoing lists, the following consultants and organisationsprovided important contributions and/or advice:
Acer Engineers and Consultants Inc (USA)
Amec Civil Engineering Ltd
Babtie Group
British Steel
Carl Bro Group
Concrete Bridge Development Group
Mr R Craig (WS Atkins Transportation Engineering)
DOE Northern Ireland Roads Service
Durham County Council
Mr J E Evans (Flint and Neil Partnership)
Fairfield Mabey Ltd
W A Fairhurst & Partners
Freeman Fox International (Dubai)
Grace Construction Products Ltd
Hyder Consulting (Australia) Pty Ltd
Hyder Consulting (Thailand) Limited
Mr D C lIes (Steel Construction Institute)
Ove Amp & Partners
Priority Metals and Fasteners Ltd
PSC Freyssinet Ltd
Mr J Robb (Mott MacDonald Ltd)
Schlaich Bergermann and Partner (Germany)
Sir William Ha1crow & Partners Ltd
Tarmac Construction Ltd
Thorburn Colquhoun Ltd
Tony Gee & Partners
Universal Sealants (UK) Ltd
Warwickshire CC
Watson Steel Ltd
Mr P J Williams (the British Constructional Steelwork Association Ltd).
Due to the wide coverage of the contents of this document many others, not listed, wereinvolved and their contributions are, nevertheless, greatly appreciated.
Note
CIRIA and the author gratefully acknowledge the support of the funding organisationsand the technical help and advice provided by the members of the steering group.Contributions do not imply that individual funders necessarily endorse all viewsexpressed in published outputs.
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Contents
List of figures and tables xi
1 INTRODUCTION 1.1
1.1 Objectives 1.21.2 Scope 1.21.3 Methodology 1.31.4 Associated documents 1.31.5 How to use this guide 1.4
3 CONCRETE SUPERSTRUCTURES 3.1
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2 PRINCIPLES BEHIND GOOD DETAILING.......•...•.•.•.•....•.•.•......•........•.•.•.• 2.1
2.1 Aesthetics 2.12.2 Health and safety 2.2
2.2.1 General 2.22.2.2 CDM 2.22.2.3 Construction operations .2.22.2.4 Access - general 2.32.2.5 Internal access 2.32.2.6 Lighting and walkways 2.42.2.7 Seepage of water 2.42.2.8 Security 2.4
2.3 Buildability 2.42.3.1 General 2.42.3.2 Concrete 2.52.3.3 Steel 2.6
2.4 Durability 2.72.4.1 Concrete 2.72.4.2 Steel 2.8
2.5 Maintainability 2.92.5.1 General 2.92.5.2 Inspection 2.92.5.3 Maintenance activity 2.9
3.1 General. 3.13.1.1 Preamble 3.13.1.2 Chamfer 3.33.1.3 Drip inducer (or drip) 3.43.1.4 Waterproofing 3.63.1.5 Surface water drainage 3.93.1.6 Subsurface drainage 3.143.1.7 Verges and troughs 3.173.1.8 Parapet beams (edge beams) 3.233.1.9 Movement joints 3.28
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3.2 Slab bridges 3.363.2.1 Preamble 3.363.2.2 Reinforcement detailing 3.363.2.3 Edge cantilevers 3.413.2.4 Voided slabs 3.43
3.3 Beam and slab bridges 3.463.3.1 Preamble 3.463.3.2 Diaphragms 3.47
3.4 Box girder bridges 3.513.4.1 Preamble 3.513.4.2 Post-tensioning 3.523.4.3 Ventilation and access 3.563.4.4 Box - drainage 3.57
3.5 Subways and Culverts 3.583.5.1 Preamble 3.583.5.2 Reinforcement. 3.583.5.3 Waterproofing and drainage 3.603.5.4 Joints 3.633.5.5 Lighting 3.67
4 STEEL SUPERSTRUCTURES..........................•....•.•.•.•................................... 4.1
4.1 General 4.14.1.1 Preamble 4.14.1.2 Bolted connections 4.54.1.3 Welded connections 4.54.1.4 Fatigue 4.84.1.5 Doubler plates 4.8
4.2 Steel/concrete interfaces 4.104.2.1 Shear connectors 4.104.2.2 Permanent formwork 4.154.2.3 Precast concrete permanent formwork 4.154.2.4 Glass-reinforced-plastic (GRP) permanent formwork 4.17
4.3 Stiffeners 4.224.3.1 Preamble 4.224.3.2 Intermediate web stiffeners .4.224.3.3 Bearing stiffeners 4.254.3.4 Cope holes 4.29
4.4 Splices 4.314.5 Bracing 4.34
4.5.1 Requirements for bracing 4.344.5.2 Cross-bracing 4.384.5.3 Other types of bracing 4.434.5.4 Skew 4.44
4.6 Plate girder cross-heads 4.454.7 Variable-depth girders 4.504.8 Weathering steel. 4.574.9 Services 4.60
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5 FIXINGS FOR BRIDGE FURNITURE 5.1
5.1 General. 5.15.2 Anchorages 5.25.3 Bedding of base plate 5.75.4 Bolts, nuts and studs for fixings 5.95.5 Parapets 5.11
5.5.1 Preamble 5.115.5.2 Metal parapets 5.125.5.3 Concrete parapets 5.135.5.4 Other forms ofparapet... 5.16
5.6 Safety fences 5.175.7 Lighting columns 5.195.8 Services 5.23
6 SUPPORT STRUCTURES 6.1
6.1 General 6.16.2 End supports 6.2
6.2.1 Preamble 6.26.2.2 Abutments 6.26.2.3 Wing walls and slopes 6.9
6.3 Intermediate supports 6.116.4 Bearing plinths and downstands 6.126.5 Access to bearing shelves 6.176.6 Drainage of bearing shelves 6.21
7 RETAINING WALLS 7.1
7.1 General 7.17.2 Cantilever walls 7.2
7.2.1 Preamble 7.27.2.2 Reinforced concrete wall stems 7.37.2.3 Drainage of RC cantilever walls 7.9
7.3 Embedded cantilever walls 7.117.4 Gravity walls 7.167.5 Reinforced soil walls 7.21
8 INTEGRAL BRIDGES 8.1
8.1 General 8.18.2 Concrete superstructures 8.3
8.2.1 Preamble 8.38.2.2 Construction sequence 8.38.2.3 Continuity of deck at intermediate supports 8.4
8.3 Steel superstructures 8.128.3.1 Preamble 8.128.3.2 Construction sequence 8.128.3.3 Continuity of deck at intermediate supports 8.12
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8.4 End supports 8.138.4.1 Preamble 8.138.4.2 Frame abutment 8.138.4.3 Embedded wall abutments 8.218.4.4 Piled abutments 8.218.4.5 End screens 8.248.4.6 Bank pad abutments 8.258.4.7 Reinforced soil. 8.26
8.5 Run-on (approach) slabs 8.278.5.1 Preamble 8.278.5.2 Forms of construction 8.278.5.3 Connections between slab and abutment 8.33
8.6 Other forms of integral bridge 8.388.6.1 Arches 8.388.6.2 Boxes 8.38
References Rl
Appendix A Procedure for feedback R5
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Figures and tables
FIGURES
NB The list above does not include the details, which are listed at the start of thechapter in which they appear.
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Figure 1.1
Figure 3.1
Figure 3.2
Figure 3.3
Figure 3.4
Figure 3.5
Figure 3.6
Figure 4.1
Figure 4.2
Figure 4.3
Figure 4.4
Figure 4.5
Figure 4.6
Figure 4.7
Figure 4.8
Figure 4.9
Figure 4.10
Figure 7.1
Figure 7.2
Figure 7.3
Figure 7.4
Figure 8.1
Figure 8.2
Figure 8.3
Figure 8.4
Figure 8.5
Figure 8.6
Figure 8.7
TABLES
Table 4.1
Table 5.1
Location of details in the guide 1.4
Concrete slab bridge superstructure - cross-sections 3.37
Construction of circular voided decks 3.44
Construction of polygonal voided decks 3.44
Concrete beam and slab bridge superstructure 3.46
Concrete box girder bridge superstructure (single-cell type) 3.51
Subway/underpass structure 3.59
Steel/concrete composite beam and slab bridge superstructure, typicalfour-plate girder shown 4.3
Steel/concrete composite bridge superstructure (diagrammatic) .4.4
Welds - diagram showing dimensioning .4.7
Types of intermediate bracing for composite I-girder bridges 4.36
Types ofbracing at supports for composite I-girder bridges 4.37
Steel/concrete composite bridge superstructure. Typical four-girdertwo-bearing integral cross-head utilising flat flange splice plates ........ 4.46
Steel/concrete composite bridge superstructure. Typical four-girdertwo-bearing integral cross-head utilising bent-flange splice plates 4.47
Variable-depth steel girder bridge 4.51
Discontinuous longitudinal stiffeners 4.56
Sloped longitudinal stiffeners 4.56
Embedded cantilever wall - features 7.11
Gravity walls - concrete shapes 7.16
Gravity walls - gabions 7.20
Reinforced soil walls - basic types 7.21
Integral bridge abutments - accommodation of deck movements 8.14
Integral bridge end support types - Sheet 1 8.15
Integral bridge end support types - Sheet 2 8.16
Integral bridge - example of rigid (frame) type 8.17
Integral bridge abutments - examples of pile flexure type 8.22
Run-on slabs - construction forms 8.30
Masonry arch (integral) bridge 8.38
Dimensional constraints on shear studs (Detail 4.2.1-1) .4.12
Summary of parapet group designations 5.11
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1
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Introduction
As has happened in many other countries, the UK highways bridge stock has exhibiteddurability problems in recent years, While there are several causes of deterioration,many of the problems are attributed to poor detailing and a lack of appreciation ofbuildability by designers (I, 2). CIRIA Report 155 (3), published in 1996, addresses bridge
buildability issues,
This guide has been prepared for use by active members of the bridge engineeringprofession. The target readership comprises consultants, contractors, bridge owners andtheir maintaining agents, It will be of direct use to trainee engineers (includinggraduates), technicians and incorporated engineers involved in detailing highway bridgedesigns. It should also be of value to chartered engineers as they develop designs, and tosite staff, as it provides advice on the function and relative merits of various details.
The design process develops from feasibility and conceptual design through to detaileddesign. The details in this guide are intended for use in the detailing stage that follows.While designers will be aware of and may anticipate use of details in this guide, ingeneral, advice on design is specifically excluded. Some design issues, such as accessduring and after construction and CDM requirements, are directly relevant to thedetailing stage, however, and are identified in Chapter 2.
Although there are many sources of advice on good detailing, rarely is such advicecollected together. Organisations engaged in bridge design and/or construction usuallyhave their own preferences. Most available professional information comes as adviceincidental to treatises on particular projects or subjects.
As modem mass production methods are increasingly applied in the constructionindustry, details will tend to be repeated within projects and from project to project. It istherefore important to identify best practice and eliminate deficiencies.
When selecting details for this guide, emphasis has been placed on those representingbasic principles that have proved to be reliable in everyday use in terms of durabilityand ease of construction, inspection, maintenance, repair and demolition. Only details
that can be clearly defined have been included, together with supportive text explainingthe rationale and dealing with durability and buildability issues. The principlesformulated should enable sound special case details to be developed. The details havebeen prepared in a way that allows them to be readily adopted by designers, but carewill still be needed to ensure that the details, and developments from them, are correctlyinterpreted and applied.
The details are also supplied on the CD-ROM provided with this book. The softwareused is AutoCAD R14.
1.1
1.1
1.2
1.2
OBJECTIVES
1. Provide examples ofbridge details that represent current good practice, enhancedby explanatory notes and advice to emphasise the principles and issues involved ineach. The guide contains a set of details that:
• are technically sound
• are inherently durable
• satisfy requirements for ease of construction
• result in low maintenance costs
• have a good appearance.
2. Recommend details through which a degree of standardisation is encouraged. Thisshould enable the design, detailing and construction of bridge structures to becomemore efficient, and lead to both short- and long-term benefits for bridge owners andfor those charged with their maintenance.
3. Provide a sound basis upon which alternative approaches may be developed byidentifying the function of the details in the guide and relevant prompts and pitfalls.There is no intention to inhibit the development of alternative approaches.
4. Encourage feedback, through which details in the guide can be improved in the lightofconstructive comment and be supplemented by additional details (see Section 1.6).
SCOPE
The details are intended for use in the following highways structures:
• highway bridges
• accommodation bridges
• subways and culverts
• retaining walls.
A significant proportion ofbridge work in the UK includes renovation. While the bookconcentrates on details for new structures, they may also be considered for strengtheningor renovating existing structures.
The scope of the guide has been limited in four ways.
1. It concentrates entirely on details and detailing issues to be implemented after theconceptual and analytical design process has been completed.
2. It provides details for spans up to 60 m, although most of the details are based onthe span lengths of the majority ofbridges, ie up to 20 m.
3. Steelwork details are limited to steel girder/concrete slab composite bridges, themost common form of steel highway bridge constructed in the UK.
4. Details for foundations are not included.
This guide has been prepared primarily for application to UK highway bridges, but willbe useful for other applications.
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1.3
1.4
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METHODOLOGY
The work included a desk study to review:
• the research contractor's in-house information
• details and advice made available by industry sources
• feedback on health and safety issues
• feedback on durability from bridge management programmes
• relevant overseas practice.
The bodies approached for details were chosen as representing sources with highconcentrations of state-of-the-art bridge engineering. They included various industryinstitutions, bridge maintaining authorities and county councils. Approaches were alsomade internationally.
A CIRIA steering group and specialist technical panels provided advice and guidance onthe content and development of the project.
ASSOCIATED DOCUMENTS
CIRlA Report 155, Bridges - design for improved buildability (3), should be read in
association with this Bridge detailing guide, as it addresses problems of buildability andsets down guidelines for improvements in this area.
Other important publications include:
• The Institution of Structural Engineers' manual on reinforced concrete detailing (4)
• The Steel Detailer 's Manual, by Hayward and Weare (5)
• SCI-P-185 Steel Bridge Group: Guidance notes on Best Practice in Steel BridgeConstruction (6)
• SCI-P-163 Integral Steel Bridges - Design Guidance (7).
Advice on durability issues can be obtained from:
• DMRB Standard BD 57/95 (I)
• DMRB Advice Note BA 57/95 (8)
• DMRB Advice Note BA 42/96 (9)
• DMRB Standard BD 47/99 (10).
Relevant CIRlA publications include:
• Report 146 Design and construction ofjoints in concrete structures (II)
• Report 166 CDM Regulations - work sector guidance for designers (12)
• Report 174 New paint systems for the protection ofconstruction steelwork (13)
• C558 Permanentformwork in construction (14)
• C559 Improvingfreeze-thaw resisting concrete in the UK(15)
• C568 SpecifYing, detailing and achieving cover to reinforcement (16).
1.3
1.5 HOW TO USE THIS GUIDE
Figure 1.1 shows the principal parts of a typical highway structure and indicates thechapter containing relevant details.
Chapters are divided into sections covering particular bridge types or structural fonns.Many details are common to some or all the structure types. These are found at thebeginning of the chapters concerned. Cross-reference back to these details is madewhere appropriate.
In Chapters 3 and 4 the general fonns of the particular bridge types are illustrated. Thedetails available in the guide are identified by reference numbers on these illustrations.
The numbers of the details relate to their location in the guide. The first three digitsindicate the section number in which the detail is found. The fourth digit is a sequencenumber of the details within the section.
Furniture fixing(chapter 5)
Concrete or steel
4)
Note
Figure 1.1
1.4
••
Bearing plinths(chapter 6)
Support structure(chapter 6)
Typical cross-section of bridge and pier
Retaining walls (Chapter 7)
Integral bridges (Chapter 8)
Location of details in the guide
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Principles behind good detailing
The sections below introduce the principles behind the details in this guide. The primaryrequirements of the structural design are strength, safety, durability and buildability ofthe principal members. It is, however, the competence of details that determine whetherthe performance as a whole is satisfactory.
Bridges that satisfy requirements for safety (Section 2.2) and buildability (Section 2.3),and have details that are durable and easy to maintain (Sections 2.4 and 2.5), are likelyto be economical to construct and maintain.
AESTHETICS
Most bridges have a pleasant appearance when newly built, but after some years theydevelop their real character. Rainwater channelled by intricate features begins to stainthe surfaces. Such features become less prominent relative to these natural markings. Itfollows that bridges should be kept as simple as possible. Rainwater flows should be
anticipated and details incorporated to suit. For example, grooves and similar features inthe exposed surfaces can channel water and create beneficial shadow patterns if carefullylocated, although the influence of the prevailing wind makes prediction very difficult.
Structural details should be rationalised and, so far as possible, made common toprovide visual cohesion throughout a bridge, and with the other bridges in the sameproject. Details should not be over-complicated or dominate the overall structure.
Construction joints should be located to ensure that they do not detract from the bridge'sappearance. They are often defined with a groove or recessed feature, which avoids theconcrete surface from showing a ragged joint and allows two different concrete pours toshow slightly different colours without unpleasant effect.
Movement joints often concentrate moisture flow, usually accompanied by leaks. Deckjoints and other discontinuities should be kept to a minimum, and so located as tominimise any deleterious effect. Integral bridges are now being specified for appropriatenew works. The minimal joints they incorporate are expected to improve appearance.
Disguising poor details is rarely satisfactory. Fair-faced high-quality concrete provides along-lasting satisfactory appearance. The designer should seek to use the structure'snatural facets to best advantage rather than impose additional features or components. Iffeatures are added that result in congested reinforcement, poor-quality concrete orcracking, these attempts to improve appearance will be negated. Unless required forspecial aesthetic reasons, cladding, which requires extra maintenance, should be avoided.
A durable bridge should sustain its good appearance if the design takes into account:
• good detailing of drainage
• shapes that control staining
• a minimum of crevices or discontinuities for the build-up of dirt
• ease of inspection and maintenance.
The Design Manualfor Roads and Bridges (17) provides further guidance on this topic.
2.1
2.2
2.2.1
2.2.2
2.2.3
2.2
HEALTH AND SAFETY
General
Construction activities, particularly on site, have significant health and safetyimplications. These can arise from the nature of the processes, materials and chemicalsused in construction. This section does not endeavour to give comprehensive coverageof the health and safety legislation, but it raises relevant detailing issues and, inparticular, those related to access during construction, operation and maintenance.
The choice ofa particular form of construction should be made with an appreciation ofthe construction process and the need for maintenance. Where maintenance will becarried out in high-risk areas, such as adjacent to high-speed traffic, the requirement for
such activity should be minimised.
When working close to high-speed traffic, there should be a safety zone for protection ofthe workforce in addition to the necessary working space. For motorways, this safetyzone is a minimum of 1.2 m wide, so for bridge structures with narrow verges the nearside lane will need to be closed when maintenance activity takes place within the verge.
Other published guidance on health and safety issues in construction should beconsulted as necessary. Further information can be obtained from CIRIA Report 166,CDMRegulations - work sector guidance for designers (12), which has sections on
bridge construction and bridge maintenance.
COM
The Construction (Design and Management) Regulations 1994 (CDM) (18) require a
health and safety plan and a health and safety file to be properly prepared. Designersneed to consider hazards and risks that will arise at the following stages:
• construction
• operation (use)
• inspection and maintenance
• modification (eg widening) or demolition.
The regulations require hazards to be eliminated, or reduced so far as is reasonablypractical, with residual risks identified so that they can be managed by the relevantorganisation (eg main contractor).
Hazards and risks that may occur during inspection and maintenance should be includedand/or referenced in the maintenance manual for a bridge or suite ofbridges (Section 2.5).
Bridge details should conform to the above requirements. The general issues related toaccess are equally applicable to the construction, inspection and maintenance stages.
Construction operations
Hazardous situations can be created where insufficient space is available to undertakethe work safely, eg where rectangular voids with restricted headroom have been detailedin a deck and the soffit formwork has to be stripped out through a narrow gap. In suchcases, the use of permanent formwork or void formers should be considered.
Badly detailed and congested reinforcement can also create construction difficulties.
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2.2.4
2.2.5
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Where ground conditions are unsuitable to support necessary falsework, consideration
should be given to supporting the falsework off the permanent works foundations.
Permanent formwork offers the advantage of protecting the areas beneath the bridgedeck against falling items, and avoids the need to send operatives below the deck toremove temporary works. CIRIA C558, Permanent formwork in construction (141,provides detailed advice on its use.
Access - general
Design/detailing considerations regarding general access to bridges may be affected by:
• nature of the crossing (road, railway, river etc)
• adjacent landscaping (steep embankment slopes, large trees etc)
• location of buried services
• height of parapets and pilasters
• verge or pavement widths and surfacing
• street furniture including lighting columns.
It is no longer normal practice to provide access manholes in road surfaces, chiefly forsafety reasons. Closing traffic lanes on busy highways creates risks for both drivers andoperatives. Traffic congestion resulting from lane closures creates additional risks.
Access into box girders should be arranged from the abutments or, where the boxes arediscontinuous, through the soffit. Care must be taken to provide safe access to locationsin the soffit. Size of openings, ease of entry and rescue requirements including anchorpoints also need to be considered. Heavy skews may create particular difficulties, andspecial measures are needed for arch, cable-stayed and suspension bridges.
Internal access
The size of openings at entry and between the cells of a structure should be decided aspart of the designer's consideration of hazards and risks. Any minimum required bystatute or other applicable authority should be taken into account. Based on Section 30of the Factories Act 1961 (now withdrawn) it is recommended that absolute minima of460 mm x 410 mm or, if circular, 460 mm diameter, should be provided unless there areother adequate means of egress. Access size should allow necessary equipment (egventilation or stressing equipment and/or a loaded stretcher) to be handled safely. Thespacing of the access points influences this assessment. Platforms should be provided ataccess and egress points along with appropriate lifting points.
Designers should avoid details that present hazards or create access problems. Boxgirder structures present particular difficulties, as internal inspection is required. Underthe Confined Spaces Regulations 1997 (19l, the interior of a box girder must be recognised
as a confined space. Associated requirements include:
• trained personnel
• risk assessments
• emergency procedures
• controlled entry
• approved methods of working
• air monitoring.
2.3
2.2.6
2.2.7
2.2.8
2.3
2.3.1
2.4
The designer/detailer should therefore consider:
• the means and ease of access
• spacing of manholes
• spacing of ventilation openings
• frequency of inspections
• methods of internal protection
• frequency of subsequent maintenance.
Lighting and walkways
The frequency of inspections and maintenance visits makes installation of permanentlighting essential in large box girder bridges. They improve both safety and efficiency,thereby justifying the investment. The infrequency of visits to the interiors of smallbridges makes a permanent lighting installation unnecessary, although the provision ofintrinsically safe power-points protected from misuse is appropriate. Incorporation of
permanent walkways and materials-handling routes can be considered, but these in turn
need to be maintained and require handrails if there is likely to be a fall greater than 2 m(eg tops of piers).
Seepage of water
Water may enter structures through faulty weatherproof seals, leaking road drainagepipes or condensation. As part of their risk assessment, designers should minimise thehazards of slipping on wet surfaces and of infection from the build-up of fungi in boxgirders by making allowance for water to be dispersed.
Water ingress into smaller hollow sections should be considered even when no entry isenvisaged. Problems from deadweight effects and bursting due to ice formation havebeen known to occur.
Security
Improved access to all parts of bridges makes security more difficult. The security risksat each location of a new bridge should be assessed and appropriate measures taken.Secure doors to the access routes may be necessary in some locations and surveillancesystems may need to be installed for full security. Public access to girders over roadsand railways etc should be prevented. For example, permanent access ladders shouldstop out of reach from the ground, or locked fold-down ladders should be provided.
BUILDABILITY
General
Reference should be made to CIRIA Report 155, Bridges - designfor improvedbuildability (3).
Designers need to recognise the significance of labour and plant costs. Minimising thematerial in each element does not necessarily result in overall economy. Within a projectthe geometry ofdetails should be rationalised and dimensional standardisation sought tomaximise the reuse of items such as formwork.
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2.3.2
CIRIAC543
Designers need to consider the erection process, and any requirement for temporary
stability measures should be included within the information provided to the contractor.
The contractor may be responsible for the design of temporary bracing and will beresponsible for the erection process, but he must be made aware of any features withinthe permanent works design that may affect stability during the construction phase.
Lifting operations must be considered and lifting points provided in any element wherenormal slinging techniques would be unsafe or inappropriate.
The need to modify elements during construction on site should be avoided. It istherefore important to be realistic about tolerances and clearances appropriate to theconstruction industry. In particular, allowance needs to be made for potential errors inalignment and/or position of previously constructed components.
Most bridge structures need joints. Examples include:
• construction joints in concrete
• site assembly joints in steel
• movement joints to permit flexural and temperature movements etc.
Joints should be kept to a minimum. Integral bridges (Chapter 8) reduce the need forjoints, hence the trend to this type of bridge.
The designer/detailer should allow for necessary clearances. In addition to health and
safety requirements (Section 2.2), all construction operations need space for accessand/or the use of construction equipment. Simple examples include clearance for thebody and movement of hydraulic jacks to tension pre-stressing tendons, and the spaceneeded for swaged couplers and their equipment. When preparing details, due allowanceshould be made for construction clearances and for future inspection and maintenance.
Simplicity is desirable. Complex details, although sometimes unavoidable, can createdifficulties and attract extra cost. Standard details should, in general, be simple details.
National and international standards and specifications list many materials and grades ofconstruction materials and products. Not all material grades are readily available andthere will be regional variations. It is prudent for those planning construction to
investigate the sourcing and availability of materials.
Concrete
The principle of maximising the repetition ofdetails is particularly applicable to formedconcrete shapes. In addition, the designer should consider the difficulties that can occurwhen striking formwork, the use ofpermanent formwork (see Section 2.2), the potential
for the use of travelling formwork and the ease of concrete compaction.
The use of travelling formwork is possible if the lines and angles of the structural shape
are generally uniform. For example, in the case ofconstant-depth box girders, designersshould consider keeping the internal cross-section uniform throughout the length of thestructure. Changes ofcross-section may minimise the material quantities but result inextra formwork costs.
Compaction is easier in shapes that allow direct placing of the concrete. Re-entrantcomers, nibs and unnecessary fillets should be avoided, as the formwork is difficult toconstruct and may be difficult to concrete.
2.5
2.3.3
2.6
Where a "fair face" finish avoiding shutter joints is specified, options are limited. This isillustrated in Figure 7.3 ofCIRIA Report 155 (3). Unless it is an essential part of thedesign, an expensive finish such as F3 (see Clause 1708.4 (i) of Specification forHighway Works (46)), which does not pennit conventional shutter ties, should be avoided.
The correct choice of construction joint locations should be planned, and a practicalconstruction sequence determined during the design process. The location ofconstruction joints is part of this process and, where possible, early discussion with thecontractor can be valuable. Despite the widespread use of "kickerless" construction inbuilding works, the use of "kickers" cast with the previous pour is still recommended forbridges to allow positive location and sealing of shutters for interconnecting elements.Further infonnation maybe obtained from CIRIA Report 146, Design and constructionofjoints in concrete structures (11).
Satisfactory reinforcement detailing is a critical part of achieving buildable and durablestructures. Simplicity of arrangement should be sought. Bars should be lapped orcurtailed at locations appropriate to the envisaged construction joints. Congestion can bereduced by reversing alternate bars and/or staggering laps. Also, a careful choice ofreinforcing bar shape (for example, see Detail 7.2.2-2) can help avoid the risk ofinadequately fixed reinforcement becoming displaced during concreting.
Reinforcement protruding from one pour should not have a critical cover dimension on asubsequent pour. Tolerances need to allow for the total of cutting, bending and shuttertolerances. The size of reinforcement bends may also be significant. In such cases, largescale details, taking into account cutting and bending tolerances, may be needed toensure fit. CIRIA publication C568, Specifying, detailing and achieving cover toreinforcement (16), provides additional guidance.
Steel
The designer needs to take into account the relevant phases of steel construction. Thesemay include fabrication of the transportable elements, site assembly and erection.Different techniques and processes may apply to each.
Some modem fabrication methods are highly automated. The designer should be awareof fabricators' equipment, plant and welding techniques. The most economic productionand the most consistent quality will usually be achieved when automated factoryfabrication accounts for a high proportion of the work.
Whether for works fabrication, site assembly, automated processes or handwork, theprinciple of maximising the repetition ofdetails also applies to steelwork. It is importantto avoid specifying oversize welds (see Section 4.1.3) and to provide access fortightening HSFG bolts (see Section 4.4).
Designers should try to avoid the use ofbutt welds unless they are essential for strengthor fatigue perfonnance. The work, including special edge preparation where required, ismore labour-intensive than for fillet welds, and testing requirements are more expensiveand demanding.
An erection procedure should be established at the planning stage and allowed for in thedesign. Items affecting site erection include access constraints, lifting limitations,stability of elements in the temporary condition, and the detailed relationship betweensteel and precast concrete elements.
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2.4
2.4.1
CIRIAC543
The detailing of site joints will significantly affect the success ofa project. Site-boltedconnections are generally preferred by steelwork erectors because they can be made
quickly and are not so weather-constrained. The choice between using bolted or welded
connections on site is project-specific depending on, for example, aestheticconsiderations and the number of connections to be made. The theoretical location ofshear studs can be onerous. Consideration should be given to avoiding provision ofshear studs on splice plates.
Some of the details requiring particular care in composite steel/concrete bridgeconstruction relate to permanent formwork (BA 36/90 (20). These details are usually
repetitious and the benefits of any improvements are multiplied many times. CIRIAPublication C558, Perrnanentformwork in construction (14), provides detailed advice.
DURABILITY
Concrete
Exposure to the cumulative effect of humidity, runoff, rain, spray, freeze-thaw, de-icingsalts and atmospheric contaminants causes deterioration of bridge structures. Penetrationof de-icing salt (a chloride) is the main cause of rapid corrosion of steel reinforcement. Itis therefore essential to provide resistance to penetration of de-icing salts. CIRIA C559,IrnprovingJreeze-thaw resisting concrete in the UK (15), provides guidance.
Durable bridge structures usually have simple details that allow speedy natural sheddingof rainwater and spray. Bridge decks should have uninterrupted top surfaces because itis almost impossible to ensure the water-tightness of discontinuities. In this context:
• manholes and prestressed anchorages in the upper surface of decks should beavoided
• movement joints should be kept to a minimum because they are particularlysusceptible to penetration by water
• reinforcement should be designed to control crack widths.
Generally, there should be more than one line of defence against the penetration ofmoisture. Although in dryer climates waterproofing is not always necessary, in the UKthe practice is for the top of structural bridge decks, ie beneath the surfacing, to bewaterproofed with an impermeable membrane. Specific bridge details related towaterproofing are included in Section 3.1.4. A system of approval for the membranesthemselves has been established (see BD 47/99 (10).
Vertical surfaces in contact with soil are also generally waterproofed (Chapter 7). Otherconcrete faces are capable of shedding water naturally and so are left exposed to theelements. Where these surfaces are subject to spray from passing traffic, it is normalpractice to reduce the permeability of the concrete surface by applying a silane treatmentto protect against contamination by de-icing salt. The remaining exposed concrete needsto be adequately resistant to water penetration.
Weaknesses in waterproofing membranes or treatments may lead to deterioration ofreinforced concrete. Detailing should be such that failures of a waterproofing systembecome evident during routine maintenance inspection. For example, the discharge ofsub-surface drainage to a visible open channel should be considered.
2.7
2.4.2
2.8
Only very dense concrete has long-term durability. While the quality of the concrete mixis significant, the prime cause of reduced concrete density is inadequate compaction.Poor reinforcement detailing and formwork shapes that impede the flow of concrete andrestrict access to vibrators make it more difficult to compact concrete fully under siteconditions. The use of concrete details that facilitate compaction, coupled with welldesigned concrete mixes, is essential. Awkward ledges and comers where water cancollect, which in winter probably contains salt in solution, should be avoided.
A principal cause ofpoor durability of reinforced concrete is inadequate concrete coverto reinforcement. Adequate cover thickness must be specified to suit the conditions, butinadequate cover can still occur during positioning of the reinforcement. While lack ofattention to good workmanship is one of the causes, related problems commonly occur.For example, the constrained leg of a bar (eg the middle run of aU-bar running betweentwo faces of a wall) should have adequate tolerance and not be the run-out dimension.Unless due allowance is made for the presence ofdrip grooves and similar re-entrantdetails, cover may be reduced below the minimum required. Detailed advice is providedin CIRIA C568, SpecifYing, detailing and achieving cover to reinforcement (16).
Further information can be obtained from the HAlCSS/TRL publication Watermanagement for durable bridges (21).
Steel
As with concrete bridges, it is important to avoid accumulation of water on or within thebridge structure. Details that avoid water entrapment should be selected. The adoption ofsuch details should not have a significant effect on steel bridge economics.
The failure of any imperfect welds can also lead to durability problems, eg breakdownof protective coatings. Full attention should therefore be paid to the detailing and qualitycontrol of all connections, ie not only main structural joints but also the attachment ofsubsidiary members such as bracing, access platforms and handrails.
Weathering steel
Weathering steels achieve their resistance to corrosion by their capacity to develop aprotective patina through oxidation. Other steels rely upon protective coatings to achievesatisfactory durability. Some aspects of detailing particular to the use of weathering steelcan be found in Section 4.8.
Protective coatings
When protective coatings are used it is essential that the steelwork details enablepainting or spraying ofall exposed surfaces to be readily achieved, as corrosion willstart where there is incomplete coverage. It should be noted that too thick a layer ofpaint under HSFG bolts may result in a loss of tension.
Protective coating technology is under continual development. In recent years, theemphasis has been on improving ease and speed of application, environmentalfriendliness and toxicological characteristics. CIRIA Report 174, New paint systems forthe protection ofconstruction steelwork (13), gives guidance on the selection, applicationand specification of coatings for use in the general fabrications industry. It also takesinto account statutory regulations, including: Environmental Protection Act (1990) (22),
the Construction (Design and Management) Regulations 1994 (CDM) (18) and Control ofSubstances Hazards to Health Regulations (COSHH) (23).
CIRIAC543
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2.5
2.5.1
2.5.2
2.5.3
CIRIAC543
Fatigue
Fatigue cracks cause durability problems in parts of steel bridge structures directly
affected by cyclic traffic loading, ie steel decks or top flanges of composite steel!concrete superstructures. Designers should ensure that stress concentrations areminimised. For example, notches should be avoided. This is particularly important intension members.
BS 5400: Part lO (24) sets out classifications for welds of different types. While detailedanalysis can be used to evaluate fatigue performance, the most effective way to achievedurability is to select details with a non-critical fatigue life.
MAINTAINABILITY
General
Two issues have prompted major bridge owners to assess the health of their assets:
• accelerated deterioration resulting from the increased use of de-icing salt becamemore and more evident
• the unification of European traffic loading, which led to the UK road bridge stockhaving to be formally certified as being capable of carrying higher loads than thosefor which they were originally designed.
Also, as the demands on the network increase, computerised bridge managementsystems including comprehensive databases of bridge stock have been, and are being,developed. These aid engineers in deciding where best to invest maintenance funding.
Inspection
The process of maintenance involves a programme of inspections. The design engineershould make adequate provision for access. Although sometimes compromises have tobe made, the aim should always be for all parts of a structure to be accessible and visiblefor direct inspection.
The chosen means of access should affect the use of the bridge as little as possible, ie
the need to reduce the road capacity while inspection or routine maintenance is beingcarried out should be avoided.
Additional space should be provided within abutments (see Detail 6.5.0-2) etc, to enablethe bearings and the ends of superstructure members under movement joints to beinspected. Early consideration during design/detailing stages usually enables simplesolutions to be)ncorporated. Allowance should be made for access for equipment.Permanent provision of some equipment may be appropriate on major structures.
Section 2.2 (Health and safety) provides further advice on this subject.
Maintenance activity
A bridge should last for its design life (120 years) provided that due attention is paid tothe maintenance of the less durable parts. Unfortunately, the life of some manufacturedcomponents such as bearings and movement joints cannot be given a life rating of morethan about 20 years. The trend, therefore, is to use integral bridges that avoid bearings
2.9
2.10
and joints. Where the use of bearings and joints is unavoidable, ease of replacement isan important consideration.
Designers should endeavour to avoid all short-life components and make all otheraspects of bridge structures as free from maintenance as possible. Simple examplesinclude the natural shedding ofdirt and debris (by avoiding nooks and crannies) and theuse of self-draining slopes (eg 1 in 20). Accumulations of dirt tend to hold water thatmay contain de-icing salt.
Design/detailing issues should include provision of information relating to replacementof manufactured components, taking into account:
• health and safety requirements (Section 2.2)
• the effect on the structure and waterproofing when joints are cut out for replacement
• the load to be taken while a bearing is removed for replacement
• the jacking-point positions, and sufficient room for jacks with the capacity required
• lifting synchronisation
• the ability ofjacked members to carry the temporarily redistributed loads.
Restrictions on lane loading should be minimised. Early consideration at the design!detailing stage will usually allow simple solutions to be incorporated.
The designer will prepare a maintenance manual for a structure or suite of structurestaking into account matters arising during construction. This will identify particular
characteristics of the structure, and the recommended inspection and maintenanceprogramme. Replaceable items and the planned sequence for the construction will belisted, and advice on access provided.
Health and safety risks will be identified in the health and safety file, which shouldinclude appropriate cross-referencing to the maintenance manual to avoid duplication.Sometimes the two documents are amalgamated. The maintenance manual and thehealth and safety file need to be easy to use, store and update.
CIRIAC543
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3
3.1
3.1.1
Concrete superstructures
GENERAL
Preamble
In addition to this General section, this chapter is divided as follows:
• slab bridges
• beam and slab bridges- box girder bridges•• subways and culverts.
-
This first section includes details that are considered to be applicable to most concretesuperstructures. Reference should be made to the relevant sections for the individualbridge types. Appropriate cross-references are made to other parts of the guide.
The details to be found in this chapter are as follows:
-
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CIRIAC543
3.1.2-13.1.3-13.1.4-13.1.4-23.1.4-33.1.5-13.1.5-23.1.5-33.1.6-13.1.6-23.1.6-33.1.7-13.1.7-23.1.7-33.1.7-43.1.7-53.1.8-13.1.8-23.1.8-33.1.9-13.1.9-23.1.9-33.1.9-43.1.9-53.1.9-63.2.2-13.2.2-23.2.2-33.2.3-13.2.4-13.3.2-13.3.2-2
Chamfer 3.3Drip inducer (water-shedding) 3.4Waterproofing tuck 3.7Waterproofing fillet 3.8Waterproofing - chamfer 3.9Surface water drainage - kerb channel... 3.10Surface water drainage - positive system (kerb inlet) 3.11Surface water drainage - through-deck connection 3.12Subsurface drainage - dispersal through kerb inlets 3.14Subsurface drainage - through-deck outlet 3.15Subsurface drainage - soffit outlet detaiL 3.16Verge - waterproofing and falls 3.18Verge 3.19Verge service trough - in situ concrete 3.21Verge service trough - precast concrete V-beams 3.22Verge service trough - precast concrete Y-beams 3.22Parapet beam - typical features 3.24Parapet beam - reinforcement.. 3.26Parapet beam - discontinuity joint.. 3.27Movement joint (contraction) - range 0 mm to +3 mm 3.29Movement joint - range 0 mm to 10 mm total.. 3.30Movement joint - range 10 mm to 20 mm total 3.30Movement joint - range 20 mm to 40 mm total 3.31Movement joint - range >40 mm 3.32Movement joint - parapet beam cover plate 3.34Transverse reinforcement - arrangement 3.39Transverse reinforcement - voided slabs 3.40Transverse reinforcement - narrow decks 3.40Cantilever reinforcement 3.42Void drainage 3.45Diaphragms - ending at side face 3.48Diaphragms at abutment - soffit 3.49
3.1
3.3.2-33.4.2-13.4.2-23.4.2-33.4.3-13.4.4-13.5.3-13.5.3-23.5.3-33.5.3-43.5.4-13.5.4-23.5.4-33.5.4-4
3.5.4-53.5.5-1
Diaphragms at skew abutment 3.50Post-tensioning (external) - deviator block arrangement.. 3.53Post-tensioning (external) - deviator ducting 3.54Post-tensioning (external) - anchorage blister 3.55Ventilation - box superstructure 3.56Drainage through deviators 3.57Subways - typical cross-section 3.60Subways - waterproofing 3.61Subways - waterproofing at end 3.61Subways - cut-off drains 3.62Subways - joints 3.63Subways - construction joint 3.64Subways - movement joint 3.65Culverts - joints, in situ construction 3.66Culverts - joints, precast construction 3.66Subways -lighting 3.68
3.2
The text discusses the principles behind the choice of detail, but each detail is to be readand used in conjunction with its own notes. Some of the details in this section will applyalso to steel/concrete composite construction (see Chapter 4).
CIRIAC543
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3.1.2
Detail 3.1.2-1
Chamfer
A chamfer is a feature whereby an external comer in concrete is formed using angles ofless than 90°, generally 45°.
Sharp comers (90° or tighter) are difficult to form to a clean edge in concrete becausethe aggregate cannot get into the comer. A weak laitance finish is left, which is easilydamaged, often upon removal of shutters. To avoid this untidy edge and so enhance theappearance of the finished structure and improve durability, it is generally accepted thatcomers should be chamfered.
Chamfer
.,
.. "."
Lf)
N
PREFERRED.-.
---.
---
AVOID
REMARKS
•
•
•
•
•
•
Size and shape as shown.
Square or sharper corners in formed concrete.
Circular or more complex decorative details should be avoided, as they tend to have thesame inherent weakness as square corners.
The 25 x 25 chamfer is the easiest to form from standard timber and so is the mosteconomical.
Larger chamfers may be more suitable on heavy civil engineering pours where largeraggregate (eg 37.5 mm nominal) is used. In these cases, larger-radius corners on thereinforcement might be required.
Chamfers are normally detailed by use of a general note. This would appear on ageneral notes drawing or be repeated on all the concrete detail drawings.
A set of standard details prepared for a specific project should include a scale illustrationof the standard chamfer.
-.
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CIRIAC543
• The standard chamfer would not normally be shown on drawings to scales of 1:20 orsmaller but should be shown on larger-scale drawings.
• Larger chamfers are required on external corners that are to be covered by awaterproofing membrane (see Detail 3.1.4-3).
3.3
3.1.3 Drip inducer (or drip)
A drip inducer is a recess or groove within, or a protrusion below, an underside surface.Its purpose is to interrupt the flow of any water along that surface and cause it to dripoff, a watershed.
Water running down or blown against the side face of the parapet beam of a bridge willthen run or be blown along the soffit of that beam and any adjacent cantilever and downthe side face of the deck itself, causing unsightly staining and reducing durability. Bypreventing most of the water from following this path, the presence ofa drip in theunderside of the parapet beam helps avoid this defacement.
Detail 3.1.3-1 Drip inducer (water-shedding)
. ", ~.' '," ...... ........ .. ~. ~ ."
,<
2.5
'.", .rd"
. ~" ....:,.', .
30
, .,
15 15
.'
(A) (8)
•.'
'.. .. ,.~ .
"",",,' ... ," • ;t
. ~ :...'
a
, '..
'.'~.
'. ;.."~' .
....... .
(C)
3.4 CIRIAC543
-- PREFERRED. Option A tapered recess. While both A and B have been used extensively, Option A is
the more recent and is considered to be the most effective.
• Option C is also favoured where a downstand beam is required to mask irregularities inthe deck pour and achieve a good alignment to the parapet beam. In this case, thedownstand itself forms the drip.-
AVOID •
- •
REMARKS •-•-•-•-•-
--
•
Right-angled recesses.
Any reduction in cover to reinforcement in the vicinity of the drip.
A right angle offers the most effective drip, but the edges are tapered slightly to alloweasy removal of the timber former. The lead drip edge could be a right angle.
The dimensions shown in Detail A are considered to be the minimum to achieve thedesired effect. A wider, deeper recess detail will achieve some improvement but notbeyond 75 x 25 mm.
The need to provide a recessed drip in conjunction with Detail C should be considered ifthe width of the downstand increases beyond 200 mm.
Because of the continuity of the drip groove and its location in a very vulnerable area,open to the elements, it is important that cover to the reinforcement in the vicinity of thedrip does not reduce below that required by the specification.
Consideration should be given to where the drips of water will land, so that the problemis not transferred to another critical point, eg the top of the bottom flange of an adjacentmain girder.
Another way of forming a drip is to use a flat aluminium or plastic strip glued or riveted tothe concrete edge face and projecting 20-25 mm below the soffit. This is more likely tobe suitable where aesthetic considerations are not important and the main aim is toprotect the concrete soffit and deck face, such as within abutment galleries.
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CIRIAC543
• Dimension D, downstand of Option C, value to be 50 mm minimum for drip inducement,but may be greater for other purposes, eg see Detail 3.1.8-1 for use with edge beams.
3.5
3.1.4
3.6
Waterproofing
A waterproofing layer is a continuous impenneable layer designed to protect the bridgedeck against the deleterious effects of surface water, especially waterborne de-icing salts.
Asphalt surfacing is not waterproof and rainwater will pass through it. At times and incertain places the rainwater will contain high concentrations of chlorides arising fromwinter salting operations. Waterproofing of bridge decks in the UK is therefore essentialto safeguard their long-tenn integrity.
The approval, manufacture and use of waterproofing systems on highway bridges in theUK is governed by BD 47/99 (10), which stipulates bond perfonnance for the adherence
of the waterproofing system to the deck. This is to allow for the effects of vehiclebraking and also to contain the effects of any failure that might occur by preventing theflow of water underneath the layer. The achievement of this is heavily dependent on theskill and application of the workforce. -
BD 47 (10) also requires all systems to have a protective layer of 20 mm of sand asphaltof a different colour, generally red, to the other surfacing materials. This is intended asan aid during highway resurfacing operations when machinery is used to plane off theworn surface. The distinctive colour of the protective layer allows it to be identifiedwhen the thickness of the road surfacing varies from that expected and the depth ofplaning can be adjusted to suit so as to avoid damaging the waterproofing.
The efficiency of the materials themselves is usually without question. Failure of awaterproofing system usually occurs at its joints and its ends. The extent of the effect ofa failure depends upon the bond. The success of a system therefore relies heavily uponthe skills of the applicator, but good detailing can also contribute greatly to that success.Features instrumental in securing the effectiveness of a waterproofing system are tucks,fillets and chamfers - see Details 3.1.4-1 to 3.1.4-3.
Integrity testing during application is an important activity.
The choice of system is highly dependent on the finished condition of the deck. Themanufacturer should be involved in the deck preparation process.
A protective layer must be provided from coping to coping. The footway/verge area isjust as vulnerable to damage as the carriageway area because of the activities necessaryin relation to services.
CIRIAC543
A tuck is a recess in the concrete in which to seal (tuck) the end of a waterproofing layerto guard against the ingress of water underneath or behind it.
---------
Detail 3.1.4-1
Waterproofing tuck
Waterproofing tuck
3111LJ
(A) (8)
-PREFERRED. Option A, because it allows easy removal of the former and offers a gentle angle around
which to return the waterproofing layer, thereby avoiding damage.
------------
AVOID
REMARKS
CIRIAC543
•
•
•
Option B.
The right-angle top edge is preferred to enhance the drip effect. Aesthetics are notimportant here.
Irrespective of the waterproofing system, tucks should always be detailed and providedto facilitate maximum choice, both in the original construction and in the future formaintenance work.
3.7
Detail 3.1.4-2
Waterproofing fIllet
A fillet ensures that the angle of a re-entrant corner is reduced generally to a change indirection of 45° at any single point.
There is a danger when laying waterproofing material into a sharp corner that a void willbe left behind it, which may allow the layer to be punctured during subsequentoverlaying operations. The risk may be minimised by reducing the degree of angle bymeans of a fillet.
Waterproofing fillet
...Waterproofing
Mortar fillet
(A)
75min.
Formed concrete
(8)
PREFERRED.
•
Either of these options is acceptable, although Option 8 will generally be used ifstructural design requires the thicker section.
Option A is easy to form.
AVOID
REMARKS
3.8
•
•
•
•
•
•
Timber fillets are subject to decay in the long term and should be avoided.
80th options require some care to secure a good finish for the waterproofing.
Option 8 is likely to be reinforced across the splay.
Fillets should be used whichever waterproofing system is planned.
Care is needed to dress the waterproofing layer properly around the fillet.
Proprietary pre-formed bitumen fillets can also be used so long as they are compatiblewith the waterproofing system.
CIRIAC543
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Detail 3.1.4-3
Waterproofing external corners
External comers will need to be chamfered if waterproofed to avoid thinning (stretching)or splitting the material on sharper comers.
Waterproofing - chamfer
'A' x 'A' chamfer
<1
<J
-REMARKS • Dimension A: size of external corner chamfer where the waterproofing membrane is
applied; value to be 50 mm minimum
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3.1.5
CIRIAC543
• On abutment back walls dimension A is often 100 mm. Using this larger size is expectedto affect the reinforcement of the corner, requiring a larger bend radius on the bar.
Surface water drainage
Rainwater falling onto a bridge deck affects the structure in three ways.
1. As surface water on the top of the paved carriageway, footway and verge.
2. As subsurface water in the matrix of the permeable highway construction.
3. As leakage through any points of weakness in the waterproofing system and
expansion joints.
To protect the structure from the adverse effects of this water and the contaminants itcarries it must be collected and removed from the bridge quickly and simply.
Surface water
The crossfalls and longitudinal alignment of the highway on the bridge should bedesigned to allow surface water to run off the deck and into gullies beyond the bridge, thusavoiding the need for a positive drainage system on the bridge deck. See Detail 3.1.5-1.
If the bridge is too long or the alignment unsuitable for this to occur, then the system forcollecting and transporting the water must be as simple as possible. See Detail 3.1.5-2.
3.9
Detail 3.1.5-1 Surface water drainage - kerb channel
Fall n1fJ__Ch_a_n_n_el_~--=_~=F=a=lI==PREFERRED. This detail is preferred for its simplicity. Water runs from footway and carriageway and
then off the decks to the drainage system beyond.
REMARKS
3.10
•
•
••
•
•
This will be the normal detail where the bridge span is less than the spacing betweengullies for the road carried. It will also be the detail where the longitudinal and crossfallson the bridge are deemed adequate to keep the build-up of water in the channel to anacceptable level.
The adjacent highway drainage system should be designed to provide a gully immediatelyuphill of the bridge to minimise the volume of surface water runoff onto the deck.
Ponding on the deck must be avoided.
Seals between the kerb and carriageway surfacing were often detailed in the past but,with the greater effectiveness of waterproofing systems, are now considered to beunnecessary.
Avoid low spots (sag profiles) on bridge decks if at all possible.
See Detail 3.1.7-2 in Section 3.1.7 for additional information.
CIRIAC543
-
l \~(A) ~_)~!:;;;<1:;;·~~l~_===-;;;;
Bock exit pipe / .-to carrier angled S t'in direction of flow ec Ion
---
Detail 3.1.5-2 Surface water drainage - positive system (kerb inlet)
- Fall
-Section
PREFERRED. Placing the main carrier drain away from the kerb-edge, Option A, is preferred if spaceand cover permit.
Limitations in fall can lead to surface water remaining in the units and associatedpipework, which, if any leaks were present, could allow water to find its way through anyweakness in the waterproofing system into the concrete.
Piping diagram
Typical kerb unit
~)----:)~-lDI-~)--)~))
Piping diagram
)
•REMARKS
--
--
-
--
-
• Units can be used contiguously or separated.
- • A version of the unit exists that will collect subsurface water too (see Detail 3.1.6-1).
• This detail keeps all the drainage system above the waterproofing layer.
-----
•
•
•
•
Both options work well with regular maintenance. They are prone to blockage, and outletpipes should offer a larger cross-section than the individual inlet holes to the gullies.Access points for cleaning the main carrier drain should be located off the bridge deckwherever possible.
The units must be set on a thin mortar bed and with backing.
Adequate cover must be provided to the carrier drain to avoid damage from vehiclesmounting the footway.
The protective layer to the waterproofing system will run under these units.
--
CIRIAC543 3.11
Detail 3.1.5-3
Gullies and carrier drain
If the amount of water to be collected is such that kerb inlets are not adequate, eithergullies or a more positive carrier from the kerb inlet system will be needed.
Surface water drainage - through-deck connection
. ~ :." ~ . ",
Void to be formedin fine concrete
Top of pipe -----------..level with top ofwaterproofingprotection layer
Double spigot 150 dia.-~------Hductile iron pipewith integrally cast orrwelded puddle flangecast into deck slob
II
ICentreline of --~--carrier drain~ I
Heavy duty, hinged lid,surface entry box
Pipe spigot to protrudesufficiently for full pipejointing
Pipe bend radius
3.12
A i B
!- --- IL.,...J,
I
UII ,, I
~I I
I II ,, I
~I I
i I,, I
/~---~~/
,/ et.)/ Outlet
through. I deck/,
I,II
h
CIRIAC543
-- PREFERRED •
•-•-•-
AVOID •-•
- REMARKS ••-•-•-•
- •
- •
----------
CIRIAC543
The drainage system to be above the waterproofing.
If it is not possible for the drainage system to be above the waterproofing, breaksthrough the waterproofing must be limited to accommodate the adequate minimumnumber of outlets and the edges of the waterproofing system sealed around them.
Any pipe runs through the deck should be short, straight and as near vertical aspossible.
Longitudinal carrier drains that cannot be located above the waterproofing should bebelow the soffit of the deck.
Longitudinal pipe runs cast into the deck.
Bends in down pipes through the deck.
There must be no joints in pipes running through the deck.
Waterproofing must be dressed around the outlet pipe in a way that prevents subsurfacewater leakage between the pipe and the deck concrete.
For deep deck slabs (more than 700 mm) use spigot and socket pipe with the socket atthe top.
Dimension A, defining location of corner drain: value to be appropriate for pipeconnections and bends.
Dimension B, distance of outlet from kerb line: value to suit maintainable connections.
Dimension F, length of pipe top from puddle flange: value to ensure flange is near centreof deck slab.
Drains must permit rodding to clear obstructions.
3.13
3.1.6
Detail 3.1.6-1
Subsurface drainage
This is water within the matrix of the carriageway, footway and verge constructionmaterials. Asphaltic surfacing is not waterproof, so surface water will permeate into andthrough the pores. The degree to which this occurs depends on the speed of surfacewater runoff and the material specification.
This may not be a problem if there is a longitudinal fall in the horizontal alignment overthe bridge and the joint at the low end is of the "buried" type (see Details 3.1.9-1, 3.1.9-2and 3.1.9-4), which will allow the water in the matrix to flow over the joint and away.
Where any other type ofjoint forms a barrier or the falls are insufficient to facilitateeffective dispersal, then water will be trapped inside. If not dispersed, this may freeze incold weather and cause damage to the surfacing. Also the pumping action caused by thepassage of wheels over the surface of a saturated matrix can result in very highsubsurface pressures, which also damage the surfacing and will exploit any weaknesswithin the waterproofing system.
Subsurface drainage is essential, therefore, and should be provided at all low areas andcritical locations, ie kerb inlets (Detail 3.1.6-1) and through-deck outlets (Detail 3.1.6-2).
Care needs to be taken to locate the discharge pipes clear of structural members below.See also Section 4.8, Weathering steel.
Subsurface drainage - dispersal through kerb inlets
Other details asDetail 3.1.5-2
Typical kerb unit
REMARKS
3.14
• This unit has inlet pores below surface level that drain the water from within the blacktopmaterial. In this case, the outlet pipe will be located lower in the unit to avoid trapping thewater.
CIRlAC543
-Subsurface drainage - through-deck outlet
Typical subsurface drainage unit
,..; .", ...
. ~ ..
Outlets positioned at1.0 m centres acrossdeck
Location of outlets at abutments
Extend outletwith flexibletube if oufallneeds to becontrolled
Waterproofingdressed intoUPVC funnelhead
3.1.6-3
ISand asphalt protectionomitted over anarea 200 x 200
-- -,-1._
Detail 3.1.6-2
Water permeable anti-contamination300 x 300 membrane to be placedover funnel cover. Membrane tobe suitable for use with thetemperatures of road surfacing
Decksoffit
Permeable coverto funnel
Water entrythrough coveror side slots rin unit _ L
50 mm 1.0. pipe or '.flexible tubing todischarge to positivedrainage or drip ifacceptable toground -------.,:-
-
-
-
-
-
-
-
--
REMARKS •- •
- •
- •
•-•-
-
Outlets sited at all low points.
Special attention is needed to accommodate outlets through the reinforcement and toavoid loss of cover at the external surface.
The build-up of subsurface water can be alleviated by the use of buried joints at the lowend of the deck that allow water to flow over them.
Downpipes must permit drilling or rodding to clear obstructions.
Some expansion joints have slotted drains that run the length of the joint and dischargethrough the expansion gap. This may offer additional capacity but should not replace thethrough-deck outlet.
All drainage discharge pipes should be led to drain channels, or channels located to suitpipes. to avoid water running over the surface of the concrete and potentially creating aslippery surface.
-----
CIRIAC543 3.15
Detail 3.1.6-3
PREFERRED.
Subsurface drainage - soffit outlet detail
~50 di'UPVC pipe0N
DECK .30.1>. ~
~~...
I. 100
Min. 40 mm I.D. pipescrewed to outer pipe withflexible sealant after
(A) (8)deck cast and soffitshutter removed
50 dia. UPVC
DECKpipe
L ...
oN
o-(C)
Outlet Option A.
REMARKS
3.16
•
•
Outlet Option C involves cutting holes in soffit formwork and thus increases costs.
Outlet Option A is the simplest to form, but it is important that the threaded or clippedconnection is sealed. Proprietary products exist for these.
CIRIAC543
----
3.1.7 Verges and troughs
This section deals with the area between the parapet beam and kerb. A trough forservices cables and pipes is often required here.
Verges
The width of the verge is determined by:
In new works it will generally be a minimum of 600 mm wide, but it may be narrower onexisting structures.
---
•••
the need for a footway
curvature of the carriageway on a straight bridge or its angle to it
the need to provide a visibility splay due to alignment or an adjacent junction.
--------------
CIRIAC543
The area is vulnerable to the ingress of surface water through permeation. This couldresult in full saturation occurring, depending upon the nature of the fill used and theexistence or absence of an outlet. This permeation occurs through the surface of theverge or footway and, at the low side of the deck, from water in the road channel.Permeation also occurs in the matrix of the surfacing seeping through the joints in thekerbs and any cracks or interstices in the backing or bedding concrete.
The verge is often used for the location of services. Activities associated with servicesincrease the possibility of damage being caused to the deck and the waterproofingmembrane. This, and the other issues mentioned above, should be considered whendetailing a verge or trough.
3.17
Detail 3.1.7-1 Verge - waterproofing and falls
CarriagewayVerge orfootway
in 40 minimum-r------_I Designed highway cross-fall / camber
Parapetbeam
.•..
in 20 minimu-~ -.. .
Concrete bridge deck
-..•..
(A)
--
Concrete bridge deck
-..•..
(8)
-.. \L---------,
Concrete bridge deck
(C)
PREFERRED. Option A or B.
AVOID • Backfall on the surface towards the parapet beam must be avoided.
REMARKS • The surface over a verge or trough will normally be paved and laid to a crossfall tominimise the possibility of permeation through the surface. The water will then drain offto the road channel and thence into whatever drainage system there is.
• The waterproofing, together with its protecting layer, must be carried across the full widthof the deck, including verges and troughs. The protecting layer should preferably be ofthe same type as within the carriageway, but it does not have to be. However, it must becontinuous from parapet beam to parapet beam including under the kerb and its bedding.
3.18 CIRIAC543
-- Detail 3.1.7-2 Verge
----
For parapet beam
see detail 3.1.8-1Verge surfacing(optional)
Fall-3.1.2-1
3.1.4-1
3.1.4-2
Service ducts optional,see chapter 5
Precast concrete kerbwith backing ofconcrete class st 1
Road surfacing
20 mm red sand asphaltwaterproofing protectionlayer
Waterproofing (assumed20 mm maximumthickness)
BRIDGE DECK
Where verge is on the low side of bridge,dral~age. pipe to be provided at low pointto aid dlspersol of woter from free drainingbackfill
-PREFERRED • Detail as shown, because it offers the most structurally economic section for the
parapet/deck beam.
• Precast concrete kerb should be chosen to suit the requirements of the authority for typeof highway carried, ie:
(a) for motorways, full batter, 45° splay
(b) for roads other than motorways, either:(i) as for motorways(ii) half batter.
• Fall on verge to be towards carriageway. Value to be:
(a) preferably, at least 3.0 per cent
(b) not less than 2.5 per cent.
-----
-----
REMARKS
CIRIAC543
•••
•
•
•
•
Infill matrix to be structural concrete to avoid area becoming saturated.
If services are to be accommodated, place continuous ducts within the infill concrete.
If access to the location of services is required through the verge surface (for activitieswhere drawing or withdrawing cables through existing ducts is not possible) measures toease the excavation should be taken. An infill of either foamed concrete or a freedraining material such as a granular fill or a weak no fines concrete, both with positivedrainage outlets, can be used.
Dimension A to provide positive upstand value to be not less than 50 mm but not greaterthan 100 mm. Allowance will need to be made for width and crossfall variations tomaintain minimum height.
If any space remains in the verge area after utilities ducts have been provided, additionalempty ducts should be laid down at the time of construction. This will avoid the damagethat is likely to arise if ducts are added later.
Dimension B to suit requirements of the authority for the highway carried.
For further issues to be considered when accommodating services see Section 5.8.
3.19
3.20
Troughs
Sometimes a larger utility main than can be fitted into the verge space needs to beaccommodated. This can be done in several ways; see Section 5.8. One solution is toprovide a service trough, generally in the footway/verge area of the deck. It isunsatisfactory to position a service trough in the carriageway because disruptive trafficmanagement may be necessary when work is required.
A typical example is given in Detail 3.1.7-3. Other options when using precast concretebeams are illustrated in Details 3.1.7-4 and 3.1.7-5. Reference should also be made toSection 4.9 and Detail 5.8.0-1.
A design and detailing difficulty with troughs is the need to ensure that the arrangementis sufficiently strong to transfer forces from parapet impact into the main body of thesuperstructure.
CIRIAC543
Verge service trough - in situ concrete
----------
Detail 3.1.7-3
Plinth for precastslobs over servicesif required showndotted
3.1.8-1
3.1.4-1
Protection layerwith waterproofingunder
oIf)
N
3.1.6-2
Fall---
Footway surfacing
'----I- Additional tuck
'---+- 3.1.4-3
"'----_+_ Granular material toclause ·s·
3.1.4-2
• The fill material must be free-draining with positive outlets.
• Reference S is to refer to the relevant project specification clause for granular fill material.
--------------
AVOID
REMARKS
CIRIAC543
•
•
•
•
•
•
Service trough at edge of deck
Service troughs to be avoided if at all possible.
A trough must be waterproofed throughout and provided with a good protective layer,especially to the invert, eg 50 mm-thick fine concrete.
Consideration should also be given to protecting the waterproofing on the side walls ofthe trough, possibly with an additional layer of membrane.
An additional tuck to the deck side of the trough should be provided to seal the maindeck waterproofing and so limit seepage in the event of any damage occurring.
An option to limit the ingress of water and so reduce the likelihood of saturation is toprovide precast concrete overslabs, as shown in Detail 5.8.0-1 (Section 5.8), and towaterproof over the top.
Reinforcement to the service trough to be detailed to permit the service trough andparapet beam to be cast separately to the main deck. Special care is needed in detailingto control restraint cracking.
3.21
Detail 3.1.7-4 Verge service trough - precast concrete U-beams
Pipe -------\---l-_-..J
Saddle unit
50 diameter drainageducts through diaphragmin each beam to dischargeinto channel on abutment shelf
REMARKS •
•
•
The detail using U-beams will require the deck slab to continue over the top of the troughbut with discrete access being provided within. Deck and hatch covers must bewaterproofed over. Covers could be inset into deck slab.
No water or gas mains must be allowed in U-beam troughs due to the inaccessibility andthe danger of escaping gas or liquid filling the gap.
There must be provision for longitudinal drainage and outlet.
Detail 3.1.7-5 Verge service trough - precast concrete V-beams
~ Service bay
3.1.4-1
..... . 4
,-
.4,
50 diameterdrainage ducts
REMARKS
3.22
• Free-draining infill must be provided for use with this detail.
CIRIAC543
-------------
-----
--
3.1.8
CIRIAC543
Parapet beams (edge beams)
The beams along the edge of a bridge have several important functions. In particular,and since they are usually in full daylight compared with other bridge elements, theyprovide the architectural feature that plays one of the most important parts in definingthe bridge's character. They also form the surface upon which the parapets are mounted.The beam can either be cast in situ or made in precast units.
In situ parapet beams are normally cast after completion of the deck to achieve a bettervertical alignment. While in situ parapet beams can be designed as continuous membersto provide stiffening to the deck edges, they more often incorporate discontinuities alongtheir length at regular intervals. The form a discontinuity can take is shown in Detail3.1.8-3. The designer will choose whether or not to include discontinuities and, if so, atwhat spacing. The choice will relate to the control of cracking, the effective location ofthe neutral axis of the various members making up the superstructure and the reductionof design loading effects attracted to the edge beams.
Parapet beams, due to their location, are exposed to significant attack from chemicals,abrasion and impact effects. Careful attention must be given to protecting andprolonging the durability of parapet beams by accurate reinforcement detailing and useof air-entrained concrete as well as silane impregnation
3.23
Detail 3.1.8-1 Parapet beam - typical features
3.1.2-1
Fall ..
Top ofverge
Waterproofing
3.1.4-2
Permittedconstructionjoint
To suit 1 in 20fall. 15 min.
50min.100mox.
3.1.2-1
Other data as for option (A)
To suit 1 in 20fall, 15 min.
50min.
100mox.
3.1.3-1C
Permittedconstruction joint
in 20
Width
ll),....
.J::
0..Qlo
(A) Downstand (8) For use withcomposite decks
Width
To suit 1 in 20 fall.15 min.
50min.100mox.
..•..
Fall -in 20
:5CI.Qlo
3.1.2-1
(C) Flush soffit
3.24 CIRIAC543
• Option A is preferred because placing of reinforcement may be easier.
---
PREFERRED. Face of parapet beam is cast in one pour.
-REMARKS • The depth of the parapet edge beam should be constant along the deck. It may differ
from one side of the bridge to the other depending on crossfall, however.
-• The width of the parapet edge beam is determined by parapet post fixings and the
position of the reinforcement. A width of 500 mm is regularly adopted.
• Where a parapet edge beam carries a lighting column in addition to a parapet system,local widening on the outside of the beam may be necessary (see Detail 5.7.0-4).
• 1 in 20 minimum crossfall to parapet beam is required to ensure surface water falls intothe deck rather than down the face of the parapet beam, which would cause staining.
-----------------
CIRIAC543
•
•
•
•
•
75 mm downstand allows for fluctuations in alignment of main deck to achieve goodalignment to the parapet beam.
Dimension A, width of downstand in Option A, needs to be chosen with care in relationto requirements for reinforcement (see Detail 3.1.8.2) and concrete cover. A value of200 mm is suggested. See also Section 3.1.3 concerning the downstand.
Dimension C, thickness of parapet beam at end of cantilever on Option C, needs to bechosen with similar considerations, but excluding downstand, as for Dimension A.
If the main deck is to be left for any length of time before the parapet beam is cast,exposed steel should be grout-washed and a temporary stick-on drip applied to theexposed vertical face to avoid staining of the soffit.
Option B is more likely to be used on steel/concrete composite decks where fluctuationsin level are greater.
3.25
Detail 3.1.8-2 Parapet beam - reinforcement
Pa rapet fixing cradleSee detail 5.2.0-1
(A) First optionfor Detail 3.1.8-1A
~ --..Top of verge
~~r------n-~Top of verge
(8) Second optionfor Detail 3.1.8-1A
(C) For Detail 3.1.8-18
PREFERRED • Reinforcement Option A is preferred because it is easier to construct. There is norequirement for reinforcement bars to pass through the vertical stop-end at the edge ofthe deck slab.
REMARKS
3.26
•
••
•
•
Illustration of reinforcement is diagrammatic. The size and strength of the reinforcementneeds to be designed to suit the particular circ*mstances.
Cover must be maintained at drip grooves and tucks.
The bob (right-angled bend) in the downstand is provided to ensure that longitudinalbars do not fall to the bottom of the shutter during concreting.
Option C provides greater flexibility for adjustment of level, which may be needed insteel/concrete composite decks but has the disadvantage of bars projecting through endconstruction joint of deck cantilever.
Care must be taken in detailing the reinforcement to accommodate the anchorage cradlefor the parapet.
CIRIAC543
Section B-B
Parapet beam - discontinuity joint
-----------.--
Detail 3.1.8-3
2 part polyurethanesealant. Plan shapeto manufacturersinstructions
Joints locatedmidway betweenparapet posts
'F8
•II
<
,.II
~
>
~ I d
IIIII
Sectional plan A-A
'F8
• Reinforcement must not pass through the discontinuity joint.
• Joints are best located mid-way between parapet posts for aesthetic reasons.--
REMARKS • If discontinuities are required for any reason, sealing prevents unsightly stains/leaching.
•
-------
CIRIAC543
If the parapet edge beam is cast continuously then the width of the joint is determined bythe thickness of a board or separator able to support wet concrete. If lengths of beamsare cast in alternate lengths then building paper would be a suitable separator.
• When determining sealant gap width refer to CIRIA Special Publication 80 (25).
3.27
3.1.9
3.28
Movement joints
Almost all bridge superstructures contain joints of some kind. Construction joints inconcrete permit initial shrinkage. Except where a bridge is particularly designed as anintegral bridge (see Chapter 8), joints will also be required to permit expansion andcontraction movements caused by temperature fluctuations. The amount of movementwill depend upon the length of continuous deck able to move from a fixed point. Evenfixed ends of the bridge must allow for some flexural movements. Various joint seals tosuit different amounts of movement are shown in Details 3.1.9-1 to 3.1.9-5.
When the longitudinal deck movements become significant it may be necessary to coverthe gaps with sliding plates, particularly where pedestrian access is involved. Detail3.1.9-6 is an example of the use of such plates.
There are three basic functional requirements for movement joints.
1. Accommodate movement of the bridge.
2. Protect the edges of the surfacing.
3. Protect against the ingress or entrapment of water.
These requirements are needed for the following reasons.
1. The movements of a bridge cause varying gaps to form between the abutmentand the deck and these can get quite large. An expansion joint should afford asmooth transition for the safe passage of vehicles, cyclists and pedestrians ontoand off the bridge deck. Open joints collect debris and prevent movement jointsfunctioning and are no longer acceptable, so seals are required that facilitate themovement.
2. Ifunsupported, the exposed edges of the surfacing would soon break away underthe action of the traffic, causing potholes to form and presenting a danger to thepublic. Expansion joints must provide that support.
3. Failure to seal the expansion gap against the ingress of surface water opens theinaccessible but exposed faces of deck and abutment to attack from waterbornedeicing salts, thereby threatening reinforcement and stressing anchorages andcables in this area. If water is trapped in the surfacing behind the expansion joint,the pumping action of the wheels of passing vehicles can cause the material tobreak up.
Additional functional requirements are that the joint must, in operation:
• withstand traffic loads and accommodate movements. In so doing, it must not giverise to unacceptable stresses in the joint or in other parts of the structure
• have good riding quality and not cause inconvenience to any class of road user
• not present a skidding hazard
• not generate excessive noise or vibration under traffic
• be able to be easily inspected and maintained. Any parts liable to wear should beeasily replaceable
• form a continuous waterprooflayer with the deck waterproofing system.
The current UK Highways Agency standard for expansion joints is BD 33/94 (26) and itsaccompanying Advice Note is BA 26/94 (27). These lay down qualitative and quantitativerequirements for proprietary expansion joints both in manufacture and installation.
CIRIAC543
----------
It is not the purpose of this guide to proceed through the design/specification process,but it may be useful to highlight the importance of the following practical requirements:
• determining the effective bridge temperature at time of installation to get the correctgap width within the range required
• distributing the total movement between the number of expansion joints on thestructure (although the current preference is to use continuous construction with aminimal number ofjoints)
• having due regard to the different users of the bridge, eg use of cover plates forpedestrians
• preparing notes of any special maintenance requirements for inclusion in themaintenance manual.
The generic descriptions of the different types ofjoints are:
• buried
• asphaltic plug
• nosings
• elastomeric/reinforced elastomeric
• elastomeric elements in metal runners
• cantilever, comb or tooth.
-Integral bridges (see Chapter 8) are designed to accommodate movement withoutexpansion joints, but they still require joint seals at the extreme ends.
--
Detail 3.1.9-1 Movement joint (contraction) - range 0 mm to +3 mm
Waterproofing membranecontinuous across joint
Red sand asphaltprotective layer
Use only at construction joints or cracks.
f----Additional layer of waterproofingmembrane laid over debonding tapeand adhered to bridge deck oneither side
;J :'(1.-·L:d':' tope 'o;d m, ,entoen"of bridge deck joint or crack
Construction jointor crack
This joint should be used to maintain integrity of waterproofing at any construction jointwhere slight movement is anticipated.
This detail has little capacity for repetitious movements and should not be used for jointsat, for example, the fixed end of bridges.
30x10sealed
•
•
•REMARKS
AVOID
-
-
-
-
-
--
--
CIRIAC543 3.29
Detail 3.1.9-2 Movement joint- range 0 mm to 10 mm total
Red sand asphaltprotection layer
Surfacing
150
Butyl rubbermembrane bondedto deck concrete
Closed cellpolyethylenefoam
30x10 sowcut crackinducer sealed withhot poured rubberbitumen
Waterproofingmembrane
Buried joint
Detail 3.1.9-3 Movement joint- range 10 mm to 20 mm total
Surfacing
12 thick expandedpolyethylene closedcell foam bonded toends of plate
375 butyl rubbermembrane bonded todeck concrete
350x 16mm galvanizedmild steel plate
Surfacing
R.d 'ood "Ph'~~7 30,10 '0'0,1 0'0",inducers sited aboveCom ,Imp of I .dg" of pial., ,,,,,dwaterproofing 175 175 with rubber bitumenmembrane laid r---Jloose Waterproofing
600 butyl rubbermembrane bonded todeck concrete -----'
Flexible rubber compound/bitumen seal/filler ---~
Expanded polyethyleneclosed cell foam --------~
3.30 CIRIAC543
.-
.-
-Detail 3.1.9-4 Movement joint - range 20 mm to 40 mm total
A·~··.·:"D.fC;: .. •· Drain tube dischargingto abutment shelf
Caulk25 minimum overlapof waterproofing membranewith binder matrix
Asphaltic plug type(A)
Plug
25
~50 ~50Binder/stone matrix
50 ~ 50Aluminium or I ~ Deck surfacing
steel plat,....e__-.,;::,....,..;:... FALL Red sand asphalt
Waterproofing
Locating pin.-
-
--
.-
Asphaltic plug type of joint, Option A, is generally proving to be the preferred type.
------
Deck surfacing (minimum 100 thick)
Red sand asphalt
.......
PREFERRED.
20x25 deeprubber bitumen sealant
40mm thick Asphalticplug joint over 3 mmthick steel cover platewith locating pins.
Waterproofing system on deckturned down over ballast wall
"'------"''-:'::~~~~-Joint caulked and sealed.
Woterproof membranecontinued over deck joint
Buried asphaltic plug type(B)
--
REMARKS •
•
The designer should refer to SA 26/94 (27) and, in particular, to Table 1 of SD 33/94 (26),
for further information on joint type options and associated movements.
At the low end of a bridge a buried joint (Details 3.1.9-2 to 3.1.9-4) should be usedwhenever possible to avoid entrapment of water.
- • For sizes of the joint materials, refer to the manufacturer's details. The sizes shown onthe details are typical.
---.-
-CIRIAC543 3.31
Detail 3.1.9-5 Movement joint - range> 40 mm
WaterproofingSpecial attention to interactionbetween deck reinforcementand fixing loops to ensure goodfit. especially on skew bridges.
Tuck to seal against ingress ofwater behind joint
...
"
Red sand asphaltwaterproofing protectivelayer
'.,.
Typical proprietary movement joint cast into deck
Epoxy mortartransition strip
1. of
Ibolt
I
1. of fixing bolt
IRoad surfacing
(wearing ~c~o~u:.:rs~e~)L_--l'=!C-=::i===:!==r~7J==~==*==:L_---II_c~.. I(
Bedding mortar /- ~ " ~5iJ;~~;;;~5 mm min. thick
I
ILevel of top of wolfand of top of upstandto suit application ofbedding mortar thicknessafter scabbling preparation
Secondary collection ofseepage water takento positive drainage
Abutment I I Bridge deck---- ---=--ballast wall
* - Cross carriageway sub-surfacedrainage channel (slotted pipe) positionedat low point (preferably clear of movementjoint construction) and connected topositive drainage outlet (such as detail 3.1.6-2)and water jetting flushing point
Typical proprietary movement joint bolted to deck
3.32 CIRIAC543
• Lengths are joined at site by welding or vulcanising to the desired profile.
-----
REMARKS •
•
•
Where a joint has to permit longitudinal movements in excess of 40 mm, proprietaryunits will be required.
Proprietary joints are usually assembled at the factory ready for use and delivered tosite, pre-set for a specified gap dimension, in lengths up to 12 m for casting in or boltingto the structure.
Normally, any neoprene elements in the joint are provided as a single continuous strip,but this can be cut and vulcanised to suit shapes of joints or intersections.
• Where joints are cast into a structure it is important to allow for connecting the joint tothe deck reinforcement in the manner described in the manufacturer's instructions.
--
--
---
----
-CIRIAC543
• Where joints are to be bolted to the structure it is important to consult manufacturer'sinstructions and details when detailing the concrete outlines at the joint. Bolts shouldcome within the deck reinforcement.
3.33
Detail 3.1.9-6 Movement joint - parapet beam cover plate
DETAIL A
~---5 gapbetweenplate andconcrete overthis lengthon deck sideof joint
2 no.polyurethanesliding pads50 dia.fastened todeck
Deckside
2 no.cast insockets
Abutmentside
Face ofparapet
Section C-C
150
.4 :....• ABUTMENT
.J. ." ..
'------, .
Detail AShowing 5 mm gapon deck side ofjoint
3 thk.stainlesssteel coverplate boltedto concretean abutmentside
2 no. 'f'fixings forM16 dia. Bbolts:- resinanchors orcast insockets
Section B-B
lE-o
'f'B
3.34
Section D-D Typical plan on parapet beam cover plate
CIRIAC543
• Ensure fixing holes are clear of parapet rails and post fixings.
• An allowance of 5 mm should be made for transverse deck movements.
• As an alternative sliding surface to the polyurethane pads shown, neoprene pads or askim of epoxy mortar would be suitable.
-----
REMARKS •
•
This detail need only be considered for joint gaps in excess of 75 mm.
An alternative arrangement to bending the stainless-steel plate round the angles of thechamfer is to fabricate them round the 90° corner without a chamfer.
• The designer may wish to extend the deck movement joint into the parapet edge beam,in which case a parapet beam cover plate detail would not be required.
• The recess to take the plate is optional. The plate can be fitted without a recess.
-
--------
--
CIRIAC543
• Reinforcement cover must always be considered and maintained.
3.35
3.2
3.2.1
3.2.2
3.36
SLAB BRIDGES
Preamble
For the shortest spans, simple reinforced construction is the usual choice. It is costeffective since the flat, level soffit results in uncomplicated falsework, formwork andreinforcement. As the span length increases, the slab has to be thicker to carry the load.This extra weight of the slab itself then becomes a problem, which can be solved in oneof three ways. The first is to add tendons and pre-stress the in situ solid slab; the secondis to reduce the dead weight of the slab by incorporating "voids", often polystyreneblocks; thirdly, precast pre-stressed inverted tee beams can be used with in situ concreteinfill (see Figure 3.1). The precast beams are efficient up to about 16 m span. Voidedslab bridges can be used successfully up to about 25 m span and are generally moreeconomical than pre-stressed in situ concrete slabs.
Figure 3.1 shows, diagrammatically, cross-sections of typical slab bridges in the variousforms of construction, ie the solid slab, inverted tee beam with in situ concrete infill andvoided slab
Reinforcement detailing
When reinforcement is finally positioned within the confines of a shutter it will bebecause the designer has considered factors other than those pertaining just to thereinforcement itself These will include specification, reinforcement type and scheduling,wastage, storage on site, laps, protection and the placing and vibrating of concretearound it. The following text expands on these issues, although fuller guidance should besought from other industry publications.
Specification
This will normally be to a British Standard or a Eurocode or both, and is usuallydetermined before the contract award.
Type and scheduling
The designer will determine the type - either high-yield or mild steel. Thereafterreference should be made to Clause 5.8.3.2 ofBS5400 : Part 4: 1990 (28) for instructionon scheduling
CIRIAC543
-----
...---- Surfacing including waterproofing
In situ concrete slab
3.1.8-1
Typical solid slab form
----
Beams are shown with a levelsoffit but could be arranged tosuit carriageway camber. Surfacingcould then be a constant thickness
r----Surfacing including waterproofing
In situ concrete infill
Precast prestressedinverted Tee-beams
--
Typical concrete composite form
.............
r----Surfacing including waterproofing
In situ concrete slab
':·.'0 0 0.0 0 0 D D D D D D:---
-CIRCULAR VOIDED
Typical voided slab forms
RECTANGULAR VOIDED
- Figure 3.1 Concrete slab bridge superstructures - cross-sections
--
-CIRIAC543 3.37
3.38
Wastage - supplier
The reinforcement supplier will usually charge its clients for the total steel tonnage usedto manufacture the required shape. This tonnage will include those offcuts that remainafter cutting and cannot be further used. Prior to cutting and bending, reinforcement isinitially provided to the supplier in 12 m straight lengths. The designer should thereforeconsider either detailing bars as 12 m lengths wherever possible, to minimise handlingtime, or restricting cut lengths, for whatever final shape, to 2.4, 3, 4 or 6 m. Detailing thereinforcement can then be based on these lengths albeit with a slightly higher frequencyof lapping as a result. This practice will also make for easier recognition of the correctbar from a stack on site. Overall, this should lead to cost/time benefits for the client.
Laps/lapping
Lapping should, first, be avoided at positions of maximum stress and, second, staggeredas shown on Detail 3.2.2-1, so that no two laps are adjacent to each other.
Placing and vibrating concrete around reinforcement
Clause 5.8 ofBS 5400: Part 4: 1990 (28) gives guidance on matters affecting design
details, particularly with respect to concrete cover to reinforcement. It is important forthe designer to consider further whether the aggregates can pass between layers ofreinforcement either vertically or horizontally and whether sufficient space is availablefor vibration and consolidation of the concrete. Space should be left for the normal75 mm-diameter poker vibrator used on site, although a 50 mm version can be obtained.
Protection
The ingress of chloride ions from winter salting is the main cause of corrosion ofembedded reinforcement in the UK so protective measures must be carefully consideredat the design stage. Such measures may include corrosion-inhibiting concrete admixtures,increased concrete cover and a concrete surface sealant or impregnant such as silane.Alternatively, reinforcement can be coated with fusion-bonded epoxy, but the use of suchreinforcement is not covered by standards and its use in the UK has not been frequent.
It is also important to provide measures for control of early age cracking in concreteresulting from thermal restraints, plastic settlement, plastic shrinkage and loss ofmoisture. Such measures should include the provision ofadequate distribution steel, andgood detailing and mix design. Where practical, the use of precast concrete made infactory conditions should be considered to reduce the effect of the above difficulties.Good details and specifications allied to effective site supervision will further assist
preventative measures.
The complexity and size of the structural elements influence the amount ofconcretecover to reinforcement and placing tolerance. Therefore, it is important when schedulingreinforcement to ensure that the specified cover can be achieved. Particular care isneeded at grooves, tucks etc. Detailing of reinforcement also needs to take care of allstages of reinforcement fixing, particularly the need for subsequent layers to be passedbetween layers already placed and achieve the required cover at all points. Furtherrequirements and advice are to be found in DMRB BD 57 (I) and BA 57 (8).
CIRIAC543
AI V
Top reinforcement
1- --------------------- ------
-----------------------1- -----Bottom reinforcement
I t
: h iV
----------------
Detail 3.2.2-1
Note Detail 3.1.8-2for reinforcementarrangement.
When dealing with voided construction, two approaches to casting the deck are possible.With circular voided construction it is usual to cast the whole deck depth in oneoperation, and the polystyrene void formers must be secured against flotation as shown
in Figure 3.2 in Section 3.2.4. With polygonal voided construction the bottom slab mustbe constructed first and then the void formers fixed in position as shown in Figure 3.3.Construction of the deck then continues with the webs, followed by the top slab.
Transverse reinforcement - arrangement
sets of bars reversed
Cross-section
Sets of bars alternately reversed
- REMARKS •
Plan
Reverse alternate reinforcement in top and bottom of bridge decks has four advantages.
.-
--
(1 )
(2)
(3)
(4)
Bars are easily adjusted to take out tolerances in the width of deck shuttering,ensuring that the required concrete cover to reinforcement at the bridge deckfascia can be provided.
Laps are staggered as an inherent part of the method.
The number of different bar marks is minimised.
Reinforcement congestion is minimised, thus facilitating placing and compactionof the concrete.
--
CIRIAC543
• Last reinforcement to be placed are the top transverse bars (supported by U-bars frombottom).
3.39
Detail 3.2.2-2 Transverse reinforcement - voided slabs
Alternate setsof bars reversedto stagger laps
, ....-,I \, I.... _/
'------'--- Bars in bottom mat of reinforcement to beof the same diameter and have same concretecover across whole slab to avoid adverseeffects on fixing of void formers
REMARKS •
•
Voids need to be secured against buoyancy (see Section 3.2.4).
Reinforcement shown is indicative only; reinforcement other than main transversereinforcement has been omitted for clarity.
Detail 3.2.2-3 Transverse reinforcement - narrow decks
Side cover tobe increasedto suit bendingtolerance
Alternate sets of barsreversed to stagger laps
8000 Maximum
Note required on drawingto advise site staff ofcover variations
Laps not advisablein bottom reinforcement
REMARKS
3.40
•
•
Reinforcement shown is indicative only, with reinforcement other than main transversereinforcement omitted for clarity.
To minimise cover variations bar scheduling should ensure that leg of reinforcementacross the bottom is not a run-out dimension.
CIRIAC543
------------------
------
3.2.3
CIRIAC543
Edge cantilevers
When cantilevers are adopted as an edge ofdeck detail their arrangement is usuallydictated by other features of the bridge such as kerb lines, optimum spacing for thesupporting members, need for service troughs, appearance (shadow cast), etc.
There is a movement in the industry that favours standardising the overall cantileverlength, ie the structural width and cantilever length should be matched so that astandardised cantilever length is achieved. A value of 1400 mm is put forward forcurrent consideration and feedback (see Detail 3.2.3-1). This relates to the standardshutter board width (1219 mm or 4 ft), assuming a 200 mm-wide edge beam. Thisreasoning may not hold when the cantilever soffit is significantly sloped. Otherinfluences on length of cantilever, W, are considered to be the relationship with depth,D, of the main superstructure. For aesthetic reasons W should be greater than D,preferably l.5D. (See also Detail 4.8.0-1.)
A parapet beam (sometimes referred to as the string course or edge beam), will usuallybe required. Reference should be made to Details 3.1.8-1 and 3.1.8-2 for the principlesto follow.
3.41
Detail 3.2.3-1 Cantilever reinforcement
Parapet cradleanchorage
Design main deckreinforcement(where at samelevel as deck top
(A) For steeply inclined cantilever
Laps
Optional
Deck design~
";nfo,cement \\~
Permittedconstruction-----joint
(8) For horizontal cantilever
3.1.8-2
Parapet cradleanchorage
3.1.8-2
REMARKS
3.42
• Laps in reinforcement are to be provided if cantilevers are to be shuttered after the maindeck pour.
CIRIAC543
----------------------
3.2.4
CIRIAC543
Voided slabs
Construction
A reference is made to the placing of the bottom layer of reinforcement in circularvoided slabs in Section 3.2.2. Advice on the installation of void formers in bridge deckscan be found in BA 36/90 (20).
Principal features in the construction process that influence the reinforcement detailingof voided slabs are:
• sequence of placing the void formers and fixing the reinforcement
• buoyancy of the void formers in wet concrete
• shape of void formers
• sequence of casting the concrete.
Because void formers are invariably subject to buoyant forces that exceed the weight ofthe mat of reinforcement it is necessary to tie the voids down positively, to the decksoffit formwork. Circular voids will be tied down with fixings through the deckformwork, see Figure 3.2. The choice of soffit formwork finish must therefore allow forthe tie anchors. On polygonal voided slabs the bottom layer should be cast first in orderto assist placing and compacting of the concrete and to provide an anchorage for thevoid former during the subsequent pours (see Figure 3.3). It is usual for the bottom layerof concrete to be curtailed before the edge face is reached so that the construction jointdoes not affect the fascia concrete (see Figure 3.3). Reinforcement should be detailedwith this in mind.
For the polygonal voids the bottom mat of reinforcement is placed on the soffit shutterfirst together with starter bars for the "webs". Once the top mat of reinforcement is inposition it is impossible to place the void formers. Detailing of the reinforcement musttake account of this sequence, and starter bars and laps must be placed accordingly.
Drainage
It is inevitable that any leakage through the waterproofing will find its way into the voidsand an appropriate drainage route should be provided (Detail 3.2.4-1). The outlet detailfollows the recommendation ofBA 36/90 (20). Alternative outlets can be adopted from
Detail 3.1.6-3, however.
3.43
Plastic protectionstrip to void formershown hatched
The cradle must beadequately tied to thereinforcement to resisttransverse forcesduring concreting
Straps or wiressecured throughsoffit formwork
••
••
••
•
••••
Spacer block should belocated directly undercradle adjacent to strap
Figure 3.2 Construction of circular voided decks
Straps or wiressecured to anchorcast into bottomslob
Void former
1st Pour
Protection toformer shownhatched
Anchor
·4
Feoture to mosk]construction (coulddoub~ os drip ~duce0
Figure 3.3 Construction ofpolygonal voided decks
3.44 CIRIAC543
--------
Detail 3.2.4-1 Void drainage
A
Rectangular orcircular void former
\ AUPvc downpipespositioned at lowerend of void.
Elevation on endof void in deck
Section A-Athrough void
(circular void shown)
Enlarged view of downpipe
,." .-
If)N
3.1.6-3
. . ,
, •• , '." 'I I';, ,'. "I'
40 dia --=---- I IUPVC pipe '" '
, ' •• " ".1 I, .'.,
-
--
-
-
• If the voids do not have a significant fall it is recommended that outlet pipes are used atboth ends of the same void.
----
REMARKS •
•
Outlet pipes are normally positioned at the low ends of voids where a significantlongitudinal fall is present. In the case of circular voids, one outlet pipe is sufficient, whilein the case of rectangular or polygonal voids two pipes at the same end may benecessary.
The detail shown where the outlet pipe leaves the deck slab is as shown in SA 36/90 (20).
Other alternatives at the exit point are shown on Detail 3.1.6-3.
-----
CIRIAC543 3.45
3.3
3.3.1
Figure 3.4
3.46
BEAM AND SLAB BRIDGES
Preamble
Beam and slab bridges are probably the commonest form of concrete bridge with spansof up to 40 m in the UK today. This is largely due to the introduction of standard precastpre-stressed concrete beams specifically for use in highway bridge construction.Reference should be made to Precast Concrete Association publications for details ofavailable cross-sections.
They have the virtue of simplicity, economy, wide availability of the standard sections,and speed of erection. The precast beams are placed on the supporting piers orabutments, usually on rubber bearings. An in situ reinforced concrete deck slab is thencast on permanent shuttering that spans between the beams.
The precast beams can be joined together at the supports to form continuous beams,which are structurally more efficient but may entail higher costs. However, this approachdoes allow the number of bearings to be reduced, thereby affording scope for improvingaccess. Further information about continuous construction can be found in Chapter 8.
Some of the different cross-sections can be mixed on the same deck so that the bridgeedge appearance and/or function is different from the interior. This is normal practice.
Figure 3.4 shows, diagrammatically, a typical concrete beam and slab bridge.
Cross-section
Concrete beam and slab bridge superstructure
CIRIAC543
-.
-.
-.
-.
-.
--.
-.
-.
--.
-.
---.
----.
---.
3.3.2
CIRIAC543
Diaphragms
Diaphragms are members constructed transversely to the main superstructure membersthat provide stiffening to the overall action of the superstructure thereby increasing itsload-sharing characteristics. They are constructed over the full depth or part depth of themain beams. Diaphragms mainly occur at support positions where they can also bedesigned to transmit jacking loads for bearing replacement. They can reduce the numberofbearings needed and so provide better access.
In some cases, diaphragms act as little more than trimmers, stiffening what wouldotherwise be an unsupported edge of the deck slab, but can still be part of a bearingreplacement scheme.
The depth and thickness adopted for diaphragms is a matter for careful considerationbecause the derivation of appropriate details will influence this significantly. Variousdetails follow for one particular type of bridge, but the principles illustrated can beextended to other types.
In this section, diaphragms only at end supports (abutments) are shown. For diaphragmsat intermediate supports see Chapter 8, where their continuity is considered inconnection with integral bridges.
3.47
Detail 3.3.2-1 Diaphragms - ending at side face
04,---- ---....~.. .4 : II
Precastconcretebeams
,."-. 'j. '.
Underside ofdiaphragm
..(A)
End ofdiaphragm oroptionol UBeam edge
.·4r------------......
~' ",4 .. fl'
Underside ofdiaphragm
...."
REMARKS • Either of the two positions shown is an acceptable position for the end of a diaphragm ifsuch a diaphragm is deemed necessary by design.
3.48 CIRIAC543
-.
Diaphragms at abutment - soffit
Precastconcretebeam
k ;- . -.,--. t=--IIr-( ( ) )
J
150 -
i-I rI II II III
'-- Precastconcretebeam
Detail 3.3.2-2-.
-.
--
--.
(A) (B)
...----.
,-- Z'I r - " r - ~==:::::::jI 1
4 F=-+-
[: I ~======I=_=lprecast-lG concretebeam
(C)
PREFERRED •-.
----
REMARKS •
•
•
Options A or B are preferred, although all are acceptable.
While the structural dimensions of the diaphragm result from design, the principle offinishing the underside of the in situ concrete level with underside of the beam as shownin Option A has the added advantage of being able to accommodate any arrangementfor lateral movement restraint. Thus Option A is more suitable at the fixed end of abridge deck and, by the same token, Option B is suitable only at the free end.
Option A applies only where the beam bottom flanges do not meet. Where they meet,the diaphragm depth will be shallower and will often be level with the top of the bottomflange, as shown in Option B.
Option B shows the limited need for soffit formwork if beams are contiguous.
-• Options A and B allow the slotted holes in the beams to be used for transverse
reinforcement.
-• When the beams are pre-tensioned Options A and B cover and protect the ends of all
the strands.
-• Option C is difficult to form.
---
CIRIAC543 3.49
Detail 3.3.2-3 Diaphragms at skew abutment
In situ concretediaphragm
Precast beams
Plan on squared ends ofbeams showing diaphragm
(A)
Plan on angled ends ofbeams showing diaphragm
(8)
PREFERRED. Squared ends with appropriate clearances detailed are preferred.
REMARKS
3.50
• Width of diaphragm needs to be increased to make allowance for skew dimension ofbeams.
CIRIAC543
--------
3.4
3.4.1
BOX GIRDER BRIDGES
Preamble
For a span range of 45 m to 250 m, prestressed concrete box girders are an effective andeconomic choice of bridge construction. The main spans are hollow and the shape of thebox may vary from span to span and along the bridge, ie deeper in cross-section at theabutments and piers and shallower at midspan. Techniques for construction will varyaccording to the actual design and situation of the bridge.
Figure 3.5 shows, diagrammatically, a cross-section of a typical concrete box bridge.The superstructure cross-sections can have vertical or sloping webs (for example, seeDetail3.4.4-l or Detail3.4.3-l) and multiple cells. While concrete box girders are oftenpost-tensioned (using either an internal or external pre-stressing system) they are alsosuccessful in reinforced concrete.
-------
"... ~
..... ~ .
~..
Cross-section showingvertical walls
... .
..~
..
-------
Figure 3.5
CIRIAC543
Concrete box girder bridge superstructure (single-cell type)
3.51
3.4.2
3.52
Post-tensioning
Post-tensioning the concrete in a box girder bridge is chosen from two fundamentalmethods. Either "external" cables are used (cables inside the box, usually, but clear of,running alongside, the main concrete sections), or "internal" cables (cables that arethreaded through ducts that have been cast into the main concrete sections, thensurrounded with grout making them effectively monolithic with the concrete section).The method pursued will follow consideration at the design stage of issues such as costs,ease of inspection, maintenance and cable replacement. It is clear from an inspection,maintenance and replacement standpoint, that external cables are an advantage. Otheraspects, however, may lead the designer towards adopting internally grouted cables. Theinternal cable method has proved popular in the past but concerns have arisen about thelong-term overall structure durability. The designer is advised to seek further guidancefrom specific publications such as the Concrete Society Technical Report No. 47,Durable Bonded Post-Tensioned Concrete Bridges (29), and BD 58 and BA 58, The
Design ofConcrete Highway Bridges and Structures with External and UnbondedPrestressing (DMRB 1.3.9 and 1.3.10).
The principal components of the external pre-stressing system are the anchorages and thedeviators. The anchorages are where the large pre-stressing forces for the tendons arelocked off and transferred into the structure. The deviators are the devices to change theslopes of the tendons and convert the longitudinal forces in the tendons into the verticalforces that support the bridge.
Exposed anchorages are usually securely protected behind a removable cap. If the bridgeneeds to be rehabilitated, the caps can be removed and the tendon ends bared for detensioning if sufficient length of cable has been left uncut.
In whatever system, if replacement of pre-stressing cables is intended, considerationmust be given to the design of the gallery/back wall configuration and the allowance forsufficient strand to remain beyond the anchorage for de-stressing.
CIRIAC543
---
Detail 3.4.2-1 Post-tensioning (external) - deviator block arrangement
Other tendons will bepassing throughun-deviated but arenot shown
l . J...... r
• • • •
.. . .. .j
....J L(A)-
---
-
3.4.4 1
l . . J/" "
-I
L r'\ --l.. : . ~ '.' •. '--0-(
~ -3.4.2-2---
(8)
PREFERRED.-- REMARKS •
"Vertical" deviators, Option A, are preferred as causing less obstruction to access anddrainage and offering deviator capability at both top and bottom.
Option B is suitable where bottom tendons are used at the centre of the box.
• Option B obstructs access and drainage.
• The possibilities for standardisation of the form of deviators within a project, along withthe need for anchorage blisters (see 3.4.2-3), need to be considered by the designerand detailer.
-----
CIRIAC543 3.53
Detail 3.4.2-2 Post-tensioning (external) - deviator dueting
Tendon4 .
. ' •• \ Deviator black
(A) Bellmouth or trumpet end
...
: <l .
'\Deviator
Deviator
Flexible materialinsert around duct
Tendon
block
(B) Flexible material insert around duct
. '"4
6. ".45 -
. "\Lotar
Deviator
Tendon
block
PREFERRED.
(C) Oversized duct bent to smaller radius thanrequired by exact geometry
A ducted bellmouth, Option A, is preferred. The difficulties in forming the bellmouth areoutweighed by the avoidance of other problems.
AVOID
REMARKS
3.54
•
•
•
Cable imparting local forces on to the concrete at the entry or exit of the deviator.
Deviator duct can be formed from plastic or steel tubing or removable formwork.
Option C is only acceptable when the designed tendon radius is greater than theminimum permitted radius for the particular tendon type. The deviator radius used mustnot be less than the permitted minimum.
CIRIAC543
-
I 1
t---I-- c.....----- •
<> 1\ / <
~~ T';:'o" 0"9"In elevation
Stressing duct settingout data to be givenon prestressing profile
Idrawings IA
V
-------
Detail 3.4.2-3
'L'
Post-tensioning (external) - anchorage blister
Space for passageof other tendons
Tendon anchorageorientated parallelto slab soffit
-Tendon anchorage Section A-A
rrII
I IIII
I 1/ I
Tendon angle l II JInPlan~1LL i - n
I
I I I II I II I I I II I II II I I I
I I II I II I I
_U
Stressingduet settingout data tobe given onprestressingprofiledrawings
Section through box showinglocation of top anchorages
------ Plan on B-B
-REMARKS •
•
Dimension L, length of anchorage blister, value to be designed for shear strengthconnection with box.
Dimensions Yand H, setting out point for anchorage, value to suit pre-stressing jackclearances and tendon profile.
--
--
CIRIAC543 3.55
3.4.3
Detail 3.4.3-1
Ventilation and access
Where inspection and maintenance is required to take place inside a box girder theworking space must be treated as a confined space. As such, it is subject to the ConfinedSpaces Regulations 1997 and, in particular, the Approved Code of Practice, Regulationsand Guidance (19) issued by the Health and Safety Commission (HSC).
Aside from these issues, it is good practice to provide ventilation to what would otherwisebe a closed box; Detail 3.4.3-1 shows one such measure. Another method is to keep theends of the boxes open, in which case other forms of ventilation may not be necessary.
If remedial works need to be carried out inside a box, forced ventilation would mostlikely be required regardless of whatever permanent vents are present.
Ventilation - box superstructure
See detail ofventilation tube
tt of box
Section through segment
200mm dia. UPVCwith Bird Cover
As close to topas possible, avoidingexternal tendonpositions
REMARKS
3.56
•
•
••
Detail of ventilation tube
Size and spacing of ventilation ducts are dependent upon box volume and whether anyother means of ventilation are present.
Extra ventilation ducts are only as required by design. Access manholes may double asventilation points.
Locate vents so that they are not obstructed by external tendons at high level.
Ventilation ducts often serve other purposes during construction.
CIRIAC543
-.
---.
---.
--.
-.
--.
---
3.4.4
Detail 3.4.4-1
Box - drainage
Although in theory the application of waterproofing to the top surface of box structures
will keep the interior dry, industry experience indicates that some seepage will stilloccur. Therefore the design should ensure that seepage water cannot collect inside a box.Unless a truly sealed environment is required for the box interior, drainage outletsshould be incorporated through the box soffit. The drainage path must be continuous andtrapped water, eg behind deviators, avoided. Outlets should be positioned clear oftendons and other interior items.
Drainage through deviators
Drainage hole throughdeviator see below
Section through segment
-REMARKS •
•
Drainage holes through deviators should be positioned on the low side of the bottomslab, but they may be required on both sides if the bottom slab is level.
Where the positioning of the post-tensioning ducts necessarily encroaches on the mostsuitable position for the drainage hole, the hole may be re-sited as close to the optimumposition as possible.
• The hole shape and dimensions are considered to be the most efficient, but each aspectmay be varied to suit individual conditions.
-.
-
-CIRIAC543
•
•
Water collected inside the box at the lowest positions in each span can be dischargedthrough outlet pipes as shown on Detail 3.1.6-3.
Where pre-stressing anchorage blisters occur at low level and holes cannot be permittedto pass through, then the floor of the box should have falls to re-direct the water.
3.57
3.5
3.5.1
3.5.2
3.58
SUBWAYS AND CULVERTS
Preamble
Figure 3.6 shows a longitudinal section and end elevation on a typical rectangularsubway or underpass.
The internal dimensions of the structure are determined by the intended usage and canaccommodate pedestrians, equestrians, cyclists and vehicles either singly or in anycombination. Refer to the DMRB (17) for guidance on these dimensions.
The box sections can be formed using in situ concrete or precast concrete, the latterbeing manufactured in a range of sizes to suit most applications mentioned above andalso for culverts. Where precast concrete is selected, consideration must be given to theweight of the units and how they will be manoeuvered on site.
For details ofprecast subways and culverts reference should be made to the proprietarysuppliers.
The majority of the remainder of this section concerns in situ concrete construction.
Reinforcement
Subways and culverts are often constructed in situ in three stages, ie the base, the wallsand the top slab. Starter bars are needed at the construction joints, which are at the boxcomers, and bars must project sufficiently to develop the required bond strength.
Sometimes the height of wall and span of top slab are such that the ends of one set oflaps encroach very near to the start of the next. Also, if conventional starter bars areadopted for the top slab, the bars will need to cantilever out from the inside face of thewall across the top of the box. This cantilevering ofbars obstructs the movement ofshutters during wall construction and, in extreme cases, the bars will need to beseparately supported. In these cases, the designer should ensure where possible that"standard" lap lengths are replaced by designed lap lengths.
Several studies have been made into the relative strengths of different reinforcementarrangements including those reported by the Cement and Concrete Association (30).
Some arrangements avoid any cantilevering of bars across the box. If the design cantolerate the reduction in efficiency of this type of reinforcing, their use can greatlysimplify the construction.
CIRIAC543
----.-
-
Typical longitudinal section
-Carriageway level Pedestrian safety
handrailing
-.-
--.-
---.-
------
Figure 3.6
CIRIAC543
Half cross-section/half portal elevation
Subway/underpass structure
3.59
3.5.3
Detail 3.5.3-1
Waterproofing and drainage
To avoid unsightly penetration of damp into subways a waterproofing system must beapplied to the outside of the structure. Waterproofing the roof is essential to remove thegreatest risk of penetration. A good drainage system behind the walls will relieve waterpressures and reduce the risk of penetration through the walls and, depending upon thefinishes chosen, it may not be necessary to apply a full tanking system to the walls.
Detail 3.5.3-1 shows a typical subway cross-section. Details 3.5.3-2 and 3.5.3-3 show anarrangement of waterproofing on the cross-section and behind the headwall.
Detail 3.5.3-4 shows the collection of surface water at the subway portal. Where thedischarge is too low for the normal highway drainage system, pumping will be needed.This requires careful detailing of the collection chamber and security measures to allowease of maintenance, pump replacement and resistance to vandalism.
Subways - typical cross-section
3.1.4-3
Concrete class C15P150mm nominal thicknesslaid to falls (see REMARKS)
Protection layerto waterproofing
CW level
Carriageway constructionand fill
225 min. thicknesspermeable drainagelayer
150 dia. porous pipecan be encased inno fines concretedischarging throughweep holes in end(or wing) wall
Concrete classST1 bedding
7.2.3-2
Waterproofing tounderside ofcarriageway surfacing
REMARKS
3.60
••
Base extended to increase bearing area can act as a foundation to permeable backing.
Surfacing shown is appropriate for accommodation (access) traffic. Where other wearingsurfaces are required. appropriate detail must be provided.
CIRIAC543
--
For section A-A at headwallsee detail 3.5.3-3
--------
Detail 3.5.3-2 Subways - waterproofing
Protection layerto waterproofing
Pro rietarwa erproo mgsystem
Walls aintedtypically withtwo coats ofbituminouspaint
Carriageway level
Constructionjoint
4
4.
Carriageway constructionand intermediate fill
3.1.4-3
Subways - waterproofing at end
Waterproofing turnedup and tucked intoheadwall
Waterproofing tounderside ofcarriageway surfacing
wrap aver side edgeconstruction joint
Typical cross-section
Wearing surface
.<l
Detail 3.5.3-3
-
-
-
-
-
---
-
-Section A-A at end of subway
------
CIRIAC543 3.61
Detail 3.5.3-4 Subways - cut-off drains
..,:,•.......
(A)
Outside Inside
Pce'ocmed eonecete,\channel and grating
Fall...~~~~
.'1 '//, //, /" //~ U'
£ILJ L1 <J• <:::l L1
·11 '. .• <;J. 40 .- ". " . .,
r ,. .', . . " . .... ',", :'.. ." .".. . "... ~.. .>
Outside Inside
Slab locally thickened anddished to form drain
. .' ..."
'. . .- ',: '. .. ".".' '::" ,: :'.,~ '",<:.. ~.; ",","-""".'-'':-'
(8)
PREFERRED. Option A
REMARKS • Option B is cheapest to form but is not recommended for pedestrians, cyclists orequestrians.
• Water collected in cut-off drains must be discharged into a main highway drainagesystem. Direct discharge may not always be possible due to difference in levels, in whichcase this would need to be through pumps.
• Grating must be robust and fixed down.
• Outlet pipe must be of bigger diameter than holes in inlet grating. Generally, a minimumdiameter of 150 mm is recommended; experience has shown that smaller pipes areeasily blocked.
3.62 CIRIAC543
-----
3.5.4
Detail 3.5.4-1
Joints
Where possible, subways and culverts should be designed to be constructed withoutjoints. Where joints cannot be eliminated the principles in Detail 3.5.4-1 should be
followed.
Subways - joints
--------
~--,----,---,--- Construction joint, Cj,See detail 3.5.4-2
r---r-- Movement joint,See detail 3.5.4-3
J-----,~------
IIIIIIII
Movement joint,See detail 3.5.4-
Construction jaint, Cj,_-L.--'-_L--JSee detoil 3.5.4-2
Elevation on wall
Cj
Cj''':.~.'
Part section
---------
REMARKS
CIRIAC543
•
•
Designer should establish the spacing of joints, both construction and movement, to suitreinforcement of wall and necessary resistance to cracking. Detail shows typical solutiononly for identification of details.
For discussion of position of construction joint in wall above base slab (kicker height)refer to Section 7.2.
3.63
Detail 3.5.4-2 Subways - construction joint
Roof construction joint
Wall construction joint
240 wide externalwaterstop
Waterproofing system(see detail 3.5.3-2)
. "
... ".. .Inside face
20 x 20 off whitepolysulphide sealant
240 wide externalwaterstop
20 x 20 off whitepolysulphide sealant
Base construction joint
REMARKS • Groove for sealant is cast into the first side of joint poured. Joint former is left in duringcasting concrete of subsequent pour.
3.64 CIRIAC543
--------
Detail 3.5.4-3 Subways - movement joint
Waterproofing system (see detail 3.5.3-2)Cover strip laid loose over waterproofing membrane
Bridge deck flashing adhered to slab withmembrane over centre box of flashing cut through.
10 wide x 20 deep saw cutfilled with hot poured bitumen
polysulphide sealant
20 closed cellpolyethylenejoint filler
20 x 20 off whitepolysulphide sealant
Roof movement joint
240 wide externalwaterstop
."
.".' r;.....,..~"c-"-- 20 closed cellpolyethylenejoint filler
Bridge deck flashing adhered to slabwith membrane over centre boxof flashing cut through.
10 wide x 20 deep saw cutfilled with hot poured bitumen
Cover strip laid looseover waterproofing membrane
or fill (see detail 3.5.3-1)
Waterproofing system (see detail 3.5.3-2)
'.
20 closed cellpolyethylenejoint filler
J
Inside face
20 x 20 off whitepolysulphide sealant
240 wide externalwaterstop
Waterproofing system(see detail 3.5.3-2)
---
-
--
-
-
- Wall movement joint Base movement joint
- REMARKS • Roof movement joint: detail of top shown is appropriate where vertical clearances arecritical and road surfacing needs to be laid directly on to the subway roof.
-• Where vertical clearances are sufficient to allow a protection layer to be applied over
roof waterproofing (see Detail 3.5.3-2), carriageway construction need not be saw-cutand sealed.
---
•
•
Base movement joint: detail of top shown is appropriate for accommodation access(minimal) traffic. Where other wearing surfaces are required, appropriate detail must beprovided.
Proprietary products used at joints are to be selected and applied in accordance with themanufacturers' requirements.
CIRIAC543 3.65
Detail 3.5.4-4 Culverts - joints, in situ construction
Preformed jointfiller
Outer face""'l
~.... .d.~~..
'e.q .. . .......<>. <t -...:.
~.. <>
4·. .... 4. <t...d t7.
<t
110 90 k
Rubber bitumen]rsealant I 1/
(A)
joint filler
Rubber bitumenq d..
sealant
4.4 . II.. 4-
25 dia. stainless<t <t
Debondingsleeve
steel dowels~~Inner face
600 mm longat 300 crs.
(8)
REMARKS • Special precautions should be taken during construction of Option 8 to ensure goodalignment of dowels.
Detail 3.5.4-5 Culverts - joints, precast construction
Closed cell polythenejoint sealant
Polyurethane jointsealant
Compressiblesealant strip
75Inner face
REMARKS • Joint sealant on either or both faces is optional •
3.66CIRIAC543
-.---------------------
3.5.5
CIRIAC543
Lighting
The need for the lighting of a subway will depend upon its usage and the policy of theowning authority. Civil engineering provisions for lighting should be established indiscussion with the lighting and electrical engineers at an early stage of the design toallow incorporation of the necessary details.
Provisions will depend upon the nature and number of the lighting fittings required. Thechoice of fittings will be determined by the location of the subway and the need forresistance to potential vandalism.
Detail 3.5.5-1 shows one such installation for cross-connection. Actual requirements willbe decided to suit local requirements.
3.67
Subways - lighting
Cornice lighting units can eitherbe continuous or be set intoin situ cornice with duct for coble1
Detail 3.5.5-1
Junction box
Transverse cables shoulda.nly be used in exceptional ~circ*mstances / I
o[{)I<)
4
Cable draw pit
Elevation on inside wall of subway
25 dia. galvanisedconduit terminatingin recessed boxbehind lightingcornice
400 x 300 x 75 dp.internal recessedlighting boxes withvandal proof door
Cornice lighting units
50 dia. duct 450min. radius bend
----:~-""~I-----400 x 400 x 400L.-;......:..-'- -'--'----__--' coble draw pits
Section
AVOID • Ducting within walls and base should be avoided where possible.
REMARKS • If cast in ducting is needed, duct sizes and bends radii must be sufficiently large to alloweasy drawing of electric cables.
• Locations of junction boxes and draw pits to be decided in discussion with servicesengineers.
• Corrosion-resistant fittings should be specified.
• All units in pedestrian subways should be cornice-mounted and vandal-resistant.
3.68 CIRIAC543
---
4 Steel superstructures
--
4.1
4.1.1
GENERAL
Preamble
Each detail is to be read and used in conjunction with its own notes, but the textdiscusses the background to the choice of details.
Figure 4.2 shows a beam and slab superstructure in diagrammatic form. It provides a keyto some of the details to be found in this chapter, which are as follows:
For bridges with spans up to about 25 m, universal beams are feasible; however, abovethis span fabricated plate girders are normally used. The details in this chapter primarilyrelate to plate girders, but many apply also to universal beam solutions.
This chapter illustrates details for the most frequently used form of steel bridge, the steelgirder and concrete slab composite bridge (see Figure 4.1). This is the commonest usageof steel in highway bridges in the UK. Its benefits are the simplicity and speed of erectionof the main support members (steel). This is followed by casting of the concrete deckwithin formwork supported by the main members.
Welds - web to flange 4.7Doubler plate 4.9Shear connectors - studs 4.11Steel/concrete interface - top flange with in situ deck 4.13Steel/concrete interface - at in situ concrete downstand 4.14Permanent formwork - precast concrete planks 4.16Permanent formwork - GRP - arrangement of reinforcement 4.17Permanent formwork - GRP - panel arrangement.. 4.18Permanent formwork - GRP - bearing on to flange 4.19Permanent formwork - GRP - pre-camber 4.20Permanent formwork - GRP - typical data tabulation 4.21Intermediate stiffener 4.23Layout of intermediate web stiffeners 4.24Bearing stiffener - intermediate support, single leg 4.26Bearing stiffener - intermediate support, twin leg 4.27Bearing stiffener - end support 4.28Welds - cope hole 4.30Splice 4.32Splice - plate 4.33Cross-bracing - elevation 4.39Cross-bracing - connection 4.40Cross-bracing - intersection 4.42Plate girder cross-head 4.48Cross-head to main girder connection 4.49Typical stiffener/bottom flange connections at bends in flange 4.49Steel girder make-up 4.52Variable-depth girder - bent flange at pier 4.54Weathering steel- edge cantilever 4.58Weathering steel- runoff strip 4.59
4.1.3-14.1.5-14.2.1-14.2.1-24.2.1-34.2.3-14.2.4-14.2.4-24.2.4-34.2.4-44.2.4-54.3.2-14.3.2-24.3.3-14.3.3-24.3.3-34.3.4-14.4.0-14.4.0-24.5.2-14.5.2-24.5.2-34.6.0-14.6.0-24.6.0-34.7.0-14.7.0-24.8.0-14.8.0-2
--
--
---
-
-
-
--
-
-
-
-
-
CIRIAC543 4.1
4.2
The principal arrangements of beam and slab bridge superstructures are those where themain girders are supported:
• directly on the columns and abutments, leaf piers or by column cross-heads; or
• by a transverse spanning pier diaphragm beam that acts integrally as a cross-head andis itself supported by the substructure.
The latter arrangement is further discussed in Section 4.6.
When detailing steelwork, account should be taken of the maximum sizes of unit that canbe transported to the site. The positions of site joints may depend upon this. Each sitewill have its own access problems and must be studied individually. The overall heightlimit (including vehicle bogies and bed) is generally 4.5 m with the permissions forspecial loads typically allowing up to 5.0 m. However, the vehicular transportregulations limit ordinary loads to 18.3 m in length. Overall widths are generally limitedto 2.9 m where possible, but the abnormal load width limit is 4.3 m. Curvature will, ofcourse, increase encroachment on these limits for the same cross-section. The standardlimits can be exceeded when special transport arrangements are made and referenceshould be made to SBG Guidance Note 7.06 (6) and CIRIA Report 155 (3).
Available steel plate sizes vary from manufacturer to manufacturer and reference needsto be made to them. Usually flange and web plates are cut from plate, available inthicknesses 10, 12 and 15 to 75 mm in 5 mm increments, up to a maximum length of18.3 m. Other thicknesses can be provided if ordered in sufficient quantity. Longitudinalcamber in a plate girder is achieved by cutting the web to suit.
Two principal forms of connection are in use in bridge construction, namely:
• bolts
• welds.
Welding provides the more versatile connection and it results in a tidy finish. As ageneral rule, shop welding is cheaper than bolting and, therefore, unless bolts arerequired for a particular reason, workshop connections should normally be specified aswelds. Reference should be made to SBG Guidance Note 1.09 (6) for a comparison of
bolted and welded site connections.
The usage of bolts is outlined in Section 4.1.2. Welds are dealt with generally in Section4.1.3, which includes a particular detail of a web to flange weld, typical for bridge I-beams.
Other forms of construction, such as orthotropic decks, are outside the scope of thisguide and readers should obtain specialist advice about these.
CIRIAC543
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
();u»()
~w
The provIsion of sporeducts for future servicesinstallation is recommended Verge infill
concrete
4.2.1-2
Fabricated steelplate girders(or rolled sections)
-------- ---
4.2.1-1
2.5% fall
Permanent formwork(if used)
In situ R.C. deck
2.5% fall
4.2.3-1---
kerbI"'". ". ,.
Cross-section
Figure 4.1 Steel/concrete composite beam and slab bridge superstructure, typical four-plate girder shown
.j:>,
w
Concrete deck and surfacing
Elevation showing a main girder span (diagrammatic)
\I
I<t.
Pier
Splice
Pier diaphragms
Stiffeners usually fixed vertically(not square to flange) for aestheticreasons
, \ Web stiffeners
4.3.2-14.4.0-1
Steel girder
4.3.3-1 or 4.3.3-2
I
\I
\
<t.Pier
~
~
<tMain girder
Permanent formwork4.2.3-1
For alternative formsof bracing see section4.4 and figures 5.4
<tMain girder
4.2.1-2
Link bracing(see text)
4.1.3-1
Half cross-section showing typical cross-bracing
()
55»()
~c..>
Figure 4.2Steel/concrete composite bridge superstructure (diagrammatic)
----
---------
4.1.2
4.1.3
Bolted connections
High-strength friction-grip (HSFG) bolts make the connection by pressing together thetwo surfaces to be joined sufficiently tightly to transmit the design force in frictionbetween the surfaces in contact (faying surfaces). This ensures no slippage occurs up tothe designed serviceability capacity and, as a result, the stiffness of the joint is morepredictable than that of one using black bolts. HSFG bolts can be tightened withcontrolled applied torque or using the "part tum" method. To ensure full design frictionis achieved, detailing must be compatible with the design assumption for slip factor, egthe surfaces are coated with aluminium spray, zinc primer, or are bare (grit-blasted) etc.Full paint systems are never used on faying surfaces. Reference should also be made toSBG Guidance Note 2.06 (6).
Use of fitted bolts (into close-tolerance holes) is also permitted, but they are rarely used.They are not recommended because of the high cost of the accurate drilling required andbecause of the risk of thread damage.
"Black" bolts (bolts that are not pre-loaded in normal clearance holes) are permitted onlyfor joining or attaching non-structural elements of items. It is a requirement ofBS 5400 (31)
that black bolts are not used in permanent main structural connections of highway andrailway bridges. Where members are included for temporary purposes only, such astemporary wind bracing or stiffening for transportation, black bolts are normallysatisfactory. They are tightened using simple conventional methods without torquecontrol and are cheaper. Where black bolts are used in permanent (non-structural)connections consideration should be given to providing lock nuts or similar to preventthe bolts working loose.
Welded connections
Welding is a skilled process utilising trained and tested operatives working to anapproved or certified welding procedure. To be performed successfully, the workingconditions need to be of a minimum standard. Under factory (workshop) conditions theenvironment should be suitable for both automated and manual welding.
The working environment must be considered and, where found to be unsatisfactory,must be controlled if welding is proposed.
Welding of site joints is usually avoided unless appropriate precautions can be taken.Site welding is appropriate:
• when there are particularly demanding requirements with respect to visualappearance; or
----
• when set-up costs including testing and time-related costs can be spread over asignificant number ofjoints.
----
CIRIAC543
There are two main types of weld, fillet and butt. Fillet welds are typically used in Igirder web/flange joints and for attachment of stiffeners and gusset plates and/or whenjoints can be made by lapping the members. Butt welds may be full or partialpenetration. Full-penetration welds are typically used in shop splices in webs or flanges(including at changes in plate thickness).
Fillet welds are detailed according to the design strength required but are usuallystandardised so that not too many different weld sizes are specified. The 6 mm filletweld is recognised as the industry minimum for bridges. This size and 8 mm can usuallybe completed with one pass using any welding process, while 10 mm and 12 mm are
4.5
4.6
possible with automatic equipment. Larger sizes are proportionately more expensive,often needing more than one pass of the welding equipment and additional preparationper pass. The designer will design for strength according to the throat thickness of theweld, but the size of the fillet weld on drawings in the UK has traditionally been given asthe leg length (which has a nominal value...j2 times the throat size). In other Europeancountries the convention is not firmly established and either throat or leg length can be inuse. The trend is towards using the throat thickness to specify fillet weld size (see Detail4.1.3-1 and BS EN 22553 (32), the current UK standard which covers both methods).
Certain processes, such as submerged are, are often used for web/flange welds in plategirders and achieve significant penetration (and thus a larger effective throat) with agiven leg length.
Where butt welds are specified it should be made clear (in most cases) that they arerequired to be full-penetration welds. Where the design strength of the weld is requiredto be equivalent to the full strength of the parent metal this should additionally bespecified as a full-strength butt weld. Note that a "full-strength" weld can be madewithout full penetration but with external reinforcement.
Partial-penetration butt welds should generally be avoided.
Whichever weld type is chosen the access available for welding should be considered bythe designer, to ensure that welds can be properly made and inspected.
Care should be taken to design the correct size of weld for its function. Distortionincreases as weld sizes increase. Oversize welds should therefore be avoided.
Detailing principles are illustrated on a web to flange weld, Detail 4.1.3-1 , which is to beread in conjunction with Figure 4.3.
CIRIAC543
Welds - web to flange
------
Detail 4.1.3-1
flange
(A)
s'W'a'p'
s'W'a'p'
flange
(8)
z'f'
z'f'
PREFERRED.
----------
--
AVOID
REMARKS
•
•
•
•
•
Option A shows a requirement for deep-penetration fillet weld. This results in a connectionthat, under workshop conditions, is cost-effective. Option B shows a standard fillet weld(which requires a greater weld metal deposit to achieve the same strength). (NOTE: Notall fabricators have equipment capable of achieving deep-penetration welds).
Welds specified as full-penetration butt welds should be avoided because they requirethe additional work of back-gouging and testing.
Welds specified as partial-penetration butt welds should be avoided because of extrapreparation costs. Imperfections are difficult to eliminate and much testing is required toensure the required strength is achieved and that the root shape is not sub-standard.
Detailing should permit automatic fabrication to be used wherever possible, bestachieved by early pre-design discussion with contractors.
The size of weld should be kept as small as is adequate for the design, becauseshrinkage effects and cross-bending of the flanges will increase as the weld sizeincreases. 6 mm fillet welds are commonly used.
Symbols specified in accordance with BS EN 22553 (32) require dimensions W, P and/or F:
• W, specified design throat thickness of the deep-penetration fillet weld, is to be statedusing the "s" before the value
• P, the apparent (surface) size of the deep-penetration fillet weld, is to be stated afterthe throat thickness using the "a" before the value. The difference between Wand Pis the depth of penetration
• F, the designed fillet weld leg length, is to be stated using "z" before the value.
flange
Web
- Deep-penetration fillet Fillet
--
Figure 4.3
CIRIAC543
Welds - diagram showing dimensioning
4.7
4.1.4
4.1.5
4.8
Fatigue
Elements of steel bridge superstructures are subjected to cyclic stress fluctuationsprincipally arising from the repeated passage of vehicles. Where the range of these stresscycles is high or where there are a great number of reversals of even a small range thereis a potential for fatigue damage. Most elements have a reasonable resistance to fatigue.However, the basic live load stress in an element can be magnified by the presence ofgeometric stress concentrations and particular weld details can cause further, local, stressconcentration. The choice of welded connection detail is a specialist activity.
BS 5400 : Part 10 (24) classifies shape, weld and attachment details broadly in accordance
with the nature of their local effects on stress and, hence, their susceptibility to fatiguedamage. The level of stress concentration is usually taken into account in the detail class,but sometimes has to be calculated, and is a major consideration in the detailing ofrailway bridges.
Typical constraints resulting from requirements to avoid fatigue damage can be seen inDetails 4.3.2-1 and 4.8.0-2.
Doubler plates
Limitations in construction depth occasionally dictate that thick flanges and webs areappropriate. If plate thicknesses required exceed those available or practicable therequired section strength can be achieved by welding or bolting on additional plates(doubler plates) to increase the flange cross-sectional areas.
While doubler plates are sometimes used over the full length of the girder they aregenerally required to increase the strength only over portions of a girder and can becurtailed outside these portions. As the need for the additional plating ceases, doublerplates are often tapered in width (and sometimes in thickness although this is anexpensive process) to reduce stress concentrations and transfer the forces moreefficiently. The taper also provides a doubler plate detail with acceptable fatigueendurance (reduction oflength of the end transverse weld permitting higher designstresses at the connection).
Care needs to be taken to ensure that the thickness of a doubler plate is not reducedbelow that at which problems of local buckling could arise. The bit ratios for the platesattached by side welds need to be checked.
CIRIAC543
~l ;:-1+L--fl---'-----------------.....-------'+T
Section A-A
------
Detail 4.1.5-1 Doubler plate
--
z'F'-/f- A
-
Plan
Flange doubler plate end
/fA
• Dimension td, doubler plate thickness, should not be more than flange plate thickness, tr.----
REMARKS •
•
•
•
Doubler plates are most commonly used for railway bridges to provide a minimumconstruction depth.
Dimension R, radius at end to reduce stress concentrations. Recommended value of Rnot less than Wd/4.
Dimension Wd, width of doubler plate, should generally be less than parent girder flangewidth, WI, by at least 2 x 50 mm or 2 x tl, whichever is greater.
Dimension L is taper length designed to reduce stress concentrations. Rate of taper isusually 1 in 4 each side.
------- CIRIAC543
• Dimension F is the designed fillet weld leg length.
4.9
4.2
4.2.1
4.10
STEEUCONCRETEINTERFACES
Shear connectors
For a steel/concrete girder to act compositely the steel and concrete must be connectedtogether in a way that allows full transmission across the interface of the horizontal shearstresses. The most frequently used form of this connection is by using shear studs and thedetails herein refer only to these. Studs have the benefit of the results of extensive testingand successful use in service, which have led to the established requirements for their use.
Edge distance of shear stud to edge of flange is required by BS 5400 to be a minimum of25 mm and should preferably be larger; 50 mm is suggested (Dimension G on Detail4.2.1-1). This larger dimension is compatible with the usually specified "return" of theshop coats of protective coating. The final choice of edge distance must also takeaccount of the width of seating required for any permanent formwork (see Section 4.2.3).
Detail 4.2.1-1 (and Details 4.2.1-2 and 4.2.1-3, which also refer) are suitable for rolledbeams, fabricated plate girders or box girders.
CIRIAC543
Shear connectors - studs
--------
Detail 4.2.1-1
I
'" I
'c'
I
I
'c'
I
II'D'_ f----
1I I
I
Longitudinal section
• Dimension A, centres of studs across line of girder, value to suit requirements forresistance to separation.
--------------
REMARKS
CIRIAC543
•
•
•
•
•
•
•
Cross-section
Dimensions are to suit the requirements listed in Table 4.1 and the additional conditionsbelow.
Dimensional constraints in Table 4.1 are derived to satisfy the requirements of BS 5400but are enhanced br the recommendations of good practice within the industry andEurocode 4 Part 2 ( 3).
Dimension D, shear stud diameter, should be chosen with due regard to the availablesupply.
Dimension E, giving position of bottom mat of transverse steel reinforcement aboveflange, value to comply with requirements for durability as the reinforcement extends intoadjacent exposed concrete soffit.
Dimension L, overall height of shear connector, value to suit requirements of dimensionsC and F.
Reinforcement shown is illustrative only but is typical of normal requirements of an insitu deck slab.
Where permanent formwork is used (see Detail 4.2.3-1 ) other constraints apply to thedimensions.
4.11
Table 4.1
4.12
Dimensional constraints on shear studs (Detail 4.2.1-1)
Dimension Not oreater than Not less than Additional constraintsRelative Definitive Relative Definitive
(mm) (mm)
'A' Centres of studs 40t 600 2.5'D' " " except in haunches with sidesacross line of girder >300 to plane of steel flange
where not less than 4 'D' isrequired
'8' Centres of studs 4'L' 600 5'D'
alonq line of qirder 3h
25t'C' Centres of 4 'J' 600
transverse reinforcement(across shear plane)
'D' Shear stud diameter 2 t" " except where the flange issubjected to tensile stresswhere 1.5 t is required
'E' giving position of bottom 50" a-5mm 25 " except where permanentmat of transverse steel formwork is used or there is areinforcement above haunch not exceeding 50 mm:flange when 'E' =< 80 mm.
'F' giving position of 40" " except in regions of saggingunderside of head of longitudinal moment where theshear stud above top of underside of head to be not lesstransverse steel than 40mm into thereinforcement compression zone
'G' Clear distance from 9t 100 25 " "50 preferred,shear stud to edge of " except where permanentflange formwork is used when
adequate clearance to ends ofprecast planks is required
'H' Diameter of head of stud 1.5'D'
'L' Overall height (length) of h - r"" h - 25mm" 100" ""absolute maximum to bestud preferred not greater than h - 25 mm
"lesser of
Keyt Thickness of flange plateh Thickness of concrete deck above flange
Nominal cover to reinforcement
a Aggregate sizevalues in italics will reduce when fy exceeds 235 /lVmrn2
reduction factor =·-j(235'fy)where fy =nominal yield strength of the steel in /lVsq mrn
CIRIAC543
---
Detail 4.2.1-2 Steel/concrete interface - top flange with in situ deck
Location tor measurement ot
---
design thickness of Deck Slob
Crossfall .. ~.". . . " ... ". . . .". t - r;J r;J
.<
". ./
I
/ II
(A)
-----
Top Flangeof Steel Girder
Actual thickness of concrete Deck slab willvary across the span between girders and theaverage will then be slightly greater than designthickness.
Location for measurement ofdesign thickness of Deck Slab
Crossfarr
---- PREFERRED.
t
Top Flangeof Steel Girder
Option A because easier to construct.
(B)
------
AVOID
REMARKS
CIRIAC543
•
•
•
Where Dimension G needs to be less than 50 mm (because of the requiredarrangement of shear studs) Option B should not be used (because of compromise toconcrete cover).
Dimension G, clear distance from stud to edge of vertical concrete, value to suit:
(a) minimum distance (see Detail 4.2.1-1)
(b) minimum recommended concrete cover.
Consideration must be given to the possible need for bottom transverse bars to be bentto accommodate changes in thickness of Option A and avoid excessive cover to thesoffit reinforcement. In practice, this is rarely a problem.
4.13
Detail 4.2.1-3 Steel/concrete interface - at in situ concrete downstand
Crossfall
. ,.
(A)
Crossfall
(B)
AVOID • Need for downstand results from effect of crossfall or camber on wide bridges or boxgirders or other design constraints. Avoid use of a downstand where possible.
• Where Dimension G needs to be less than 50 mm (because of the requiredarrangement of shear studs) Option B should not be used (because of compromise toconcrete cover).
REMARKS • Width at top of downstand not to come within 45° line from base of edge shear stud(BS 5400)
• Where slopes are used and crossfall causes one slope to be critical, keep the otherslope the same.
• Dimension G, clear distance from stud to edge of vertical concrete, value to suit:
4.14
(a)
(b)
minimum distance (see Detail 4.2.1-2, Shear connectors - studs)
minimum recommended concrete cover to suit environmental conditions at thedeck soffit.
CIRIAC543
--------
------,-------
4.2.2
4.2.3
CIRIAC543
Permanent formwork
For decks cast in situ, support has to be provided for the wet concrete. The provision andremoval of conventional plywood or steel formwork, along with its temporary supports,can be an expensive operation for bridges. Formwork that is left in place for the life ofthe structure can offer substantial cost savings. Permanent formwork must be durableand guaranteed to have the same life expectancy as that of the structure itself. Concrete(reinforced) planks are commonly used and glass-fibre-reinforced plastic also satisfiesdurability requirements. Reference should be made to DMRB Advice Note BA 36/90 (20).
Where permanent formwork is used (Details 4.2.3-1 and 4.2.4-2) the tolerance on thelength of formwork planks or panels is critical. In the temporary state, the length should:
• provide adequate bearing on the girder flange, allowing for tolerances
• have sufficient seating length to allow for accidental lateral displacement(displacement transverse to the main bridge girders).
Since the lateral spacing between the steel girders interrelates with these requirementsthe placing of the girders is equally critical. To control the lateral alignment of thegirders it may be necessary to detail spacer bracing in locations where it would nototherwise be required for structural reasons (see Section 4.5).
The seating length for the permanent formwork should be minimised (see Details 4.2.3-1and 4.2.4-4), to maximise the extent of in situ concrete surrounding the shear studs ontop of the steel girder. There is thus a need to consider the risk of accidental dislodgement.As soon as each permanent formwork element is landed it should be adequately securedto the main girders, or to adjacent elements that have themselves been well secured.
Precast concrete permanent formwork
The designed position of all reinforcement in precast concrete plank formwork (Detail4.2.3-1) is critical especially where the plank meets the girder flange. The reinforcementis constrained in all directions to:
• provide correct effective depth for strength
• comply with specified concrete cover requirements for durability
• provide space between bars and the permanent formwork in accordance with designcode ofpractice requirements to avoid impeding concrete placing
• avoid interference with the positions of shear studs
• be compatible with all top flange steelwork details such as cover plates etc.
The resulting arrangement of the reinforcement that runs parallel to the formwork planksneeds to be consistent with the width of the planks.
Some concrete planks in common use for permanent formwork rely upon a welded trussof reinforcing bar for their strength to span in the temporary condition. The bottom ofthis truss is cast into the surface of the concrete (Detail 4.2.3-1). The manufacturerdesigns the truss to suit the plank span, main deck slab thickness and concrete placingloads. Should the bridge designer require any of the reinforcement within the permanentformwork plank to be participating in the permanent works design strength it isrecommended that the detailer calls up such reinforcement and adds the instruction "donot tack weld" or "permanent works reinforcement not welded to lattice".
Control of the manufactured dimensions of the planks and of the detailing are critical tothe success of the use ofprecast concrete plank permanent formwork.
4.15
Detail 4.2.3-1 Permanent formwork - precast concrete planks
Precast concretepermanent formworkunit
40 cover to reinforcementto be provided at all locations.
Where gap <6,gun applied approvedsealant (ref. 'S')6mm deep approx.
Reinforcement tobe placed onspacer blocks overprecast units.
Where gap >6,pre-formed sealantplug 15x15pressed into joint(ref. 'U')
Where gap >6,approved sealantover and aroundpre-formed sealantplug joint (ref. 'S')
Shear studs andpermanent formworkto be set out toavoid clashes withslab reinforcement.
Shear stud
Precast concretepermanent formwork
Precast concrete form workunits bedded on girder flangewith self adhesive polyethylenefoam and/or approved sealant.Paint system to be appliedto top and edge of girderflange before positioning andbedding of precast concrete units.
Detail at end of permanentformwork plank
Section A-A through plank
REMARKS • Refs S, T, and U are to refer to the relevant project specification clause numbers.
• Dimension 0, clearance between main slab reinforcement and precast plank, value tobe aggregate size + 5 mm.
•
•
For critical dimensions of shear studs, see Detail 4.2.1-1.
Refer to Table 13 of BS 5400 : Part 4 (28) and BD 57/95 (1) for concrete cover toreinforcement.
4.16 CIRIAC543
-.
-.
--.
-
4.2.4 Glass-reinforced-plastic (GRP) permanent formwork
GRP fonnwork is generally thinner than precast concrete planks, so the positioning ofreinforcement in the fonned concrete slab is less critical. Transverse reinforcement maybe spread more evenly along the length of the girders, care being required only to ensureadequate clearance between bars and the fonnwork ribs to avoid obstructing the flow ofconcrete during placing (see Detail 4.2.4-1). The GRP itself provides a durableprotective layer to the underside of the deck slab and the provision of concrete cover tothe soffit of the slab is then not as critical to durability.
The inherent flexibility of the thinner GRP fonnwork dictates that particular allowancemust be made for its deflection under the load of the wet concrete. Either:
GRP fonnwork (in its conventional fonn) does not contribute to the final strength of thereinforced concrete deck slab. It must, however, be of a fonn that attaches to the soffit ofthe fonned concrete deck sufficiently securely to ensure it will not become detachedduring the whole life of the bridge.
-.
--.
--
•
•
the fonnwork must be manufactured with an accurate pre-camber that will avoid apennanent downward bulge (increase of thickness) in the soffit of the deck slabbetween the girders (see Detail 4.2.4-4); or
an allowance would need to be made for the extra weight of the increase in averagethickness of the concrete.
-. Detail 4.2.4-1 Permanent formwork - GRP - arrangement of reinforcement
'c' min. cover
Note: Bars B1 to be placed locally tomaintain 'C' cover to formwork-.
L...Q)- >0u
0-.
--. Section through permanent formwork
showing relationship to reinforcement
-.REMARKS • Dimension C, clearance between main slab reinforcement and GRP panel, value to be
aggregate size + 5 mm.
-.
-.
-.
-.
-.
-CIRIAC543 4.17
Detail 4.2.4-2 Permanent formwork - GRP - panel arrangement
All JOints a e be tope on teeface prior to costing the deck slob
I--- - - - - - - --
I"'s' ..,
<>Girder top flange -l <>
~1
c0a.
--- f---:0~u
c? j~ w \ >Girder top flange
r-- - - - -L
- - --.. r to d he oncr te
Plan on permanent formwork units
REMARKS • Dimension S, nominal width of a panel, to be slightly larger than the manufactureddimension of the individual panels, which allows a manufacturing and placing tolerance.
• Dimension P, position of end ribs, is from manufacturer's data.
• Panel details may vary from those illustrated, depending upon the manufacturer.
• For sample of tabulated data, see Detail 4.2.4-5.
• For typical value of Dimension G, overlap of permanent formwork on to beams, seeDetail 4.2.4-3.
4.18 CIRIAC543
25 min.
---
Detail 4.2.4-3 Permanent formwork - GRP - bearing on to flange
----------
Girder top flangeType 'B' sealant appliedafter concrete has cured
Expandite strip 8M 100butyl mastic stripor similar approved
Paint system (if weatheringsteel not used)
• Dimension T, thickness of GRP, value to be from manufacturer's data.
• Dimension K, extent of outer-edge of butyl mastic strip, to be approximately 2 mm lessthan G.
---------
REMARKS •
Section at edge of top flange
Dimension G, overlap of permanent formwork onto beams. Value depends uponformwork design and span and as otherwise dictated by interference of structuralfeatures, such as the presence of girder splice plates. Typical minimum value is 40 mm.
CIRIAC543 4.19
Detail 4.2.4-4 Permanent formwork - GRP - pre-camber
A
All reinforcement to bespoced at high point
Permanent formwork panelspre-cambered to counterdead lood deflection. Forvalues see TABLE(refer to detail 4.2.4-5)
o
------t------I. 'C' .1
REMARKS
4.20
•
Section through deck beams
For Dimensions A, C and D, refer to Detail 4.2.4-5.
CIRIAC543
----------------
Detail 4.2.4-5 Permanent formwork - GRP - typical data tabulation
TABLE OF PRE-CAMBER VALUES (SAMPLE)
LOCATION GIRDER ACTUAL MODEL TYPE PRE-CAMBER
REF (eg SPACING CIC CLEAR SPAN (manufacturer's (mm)
STRUCTURE (mm) (mm) reference)
No)
SN A C E D
TABLE OF GRP FORMWORK DATA (SAMPLE)
MODEL TYPE OVERALL CENTRES OF No OF RIBSI MAXIMUM
(manufacturer's HEIGHT (h) RIBS (t) PANEL CLEAR SPAN
reference) (mm) (mm) (mm)
E H R (from J
manufacturers'
data)
----
REMARKS •
•
Tabulation of parameters and dimensions of formwork panels may be necessary forcorrect manufacture of the GRP panels.
Notation SN is to be appropriate identifier code for panel location.
--• Dimension A, girder spacing: keep identical as far as possible to help maintain Dimension
C as constant.
• Dimension C, clear spans between girders and thickness of concrete deck slab. Keepidentical as far as possible to avoid small changes in the panel dimensions.
• See Detail 4.2.4-4 for illustration of dimensions
• Dimension H, overall height of panel, from manufacturer's data.
-------------------
CIRIAC543
•
•
•
•
Non-standard details of permanent GRP formwork panels (ie different from the particularmanufacturer's norm (E)) may need to be agreed with the manufacturer and developedfor particular situations. In such cases, the non-standard dimensions and parametersshould be clearly identified on the drawings.
Dimension D, required pre-camber, value to suit stiffness of particular formwork modeltype and actual span.
Dimension R, centres of ribs of permanent formwork, from manufacturer's data, but may,with agreement of manufacturer, be non-standard to suit required reinforcement pattern.
Dimension J, maximum clear span, is the limiting clear span dictated by design of GRPformwork for the particular thickness of concrete slab.
4.21
4.3
4.3.1
4.3.2
4.22
STIFFENERS
Preamble
The principal function of a stiffener is to prevent web buckling by reducing the size ofthe unstiffened panel dimensions. Web stiffeners are usually required on only one side ofa web (see Detail 4.3.2-1). Stiffeners can also transfer forces from bearings or pointloads up and down through the body of the girder, or as part of a bracing system as fulllength members or shorter members (gussets) connecting with flanges.
The thickness of stiffener plates should be equal to a plate thickness already usedelsewhere on the bridge, because small amounts of plate of different thicknesses areuneconomic. The thicknesses chosen should preferably be from plate in general stock(see Section 4.1.1).
Stiffeners may need extension beyond the widths derived from strength design to allowthe connection ofbracing members (see Detai14.5.2-1) etc. Provided that the strength ofthe extended stiffener is adequate with reduced notional yield strengths their extensionneed not comply with the nominal limits.
Intermediate web stiffeners
Transverse (vertical) stiffeners
The intermediate stiffener in DetaiI4.3.2-1A is attached to the top flange and stabilises/stiffens the connection between top flange and web. This provides resistance totransverse flexure arising from local loading of the deck slab. Potential fatigue problemscan arise in the flange/web weld if there is transverse participating bracing, and this mayneed to be taken into account. Local transverse plane frame analyses can indicate theorder of magnitude of the stresses.
The unattached ends of stiffeners are shown shaped (a slope of 1:2 is suggested as beingthe compromise most preferred in the industry). This allows for making the weld and foraccess for application and maintenance of the protective coating over the main girderflange to web weld and to the end of the stiffener itself.
Sizes of stiffeners are governed by the outstand limits, which are related to the thicknessof the stiffener plate (refer to BS 5400: Part 3 (31), which specifies a maximum width-tothickness ratio of 10: I for S355 steel unless other design criteria are satisfied).
To improve long-term durability, ease of maintenance and aesthetics, intermediatestiffeners on edge girders of steeVconcrete composite bridges should be located on theinside face of the web, thus reducing their exposure to weather. A typical layout ofintermediate stiffeners is shown in Detail 4.3.2-2.
CIRIAC543
-----
Detail 4.3.2-1 Intermediate stiffener
~2""'J 1
-----
'w' x 'r'Intermediatestiffener
(A)
Cope hole(see 4.3.4-1) 'w' x 'T'
Intermediatestiffener
(8)
-PREFERRED • Option A, with the stiffener attached to the top flange, is preferred for construction with a
composite concrete deck to reduce potential fatigue problems at the junction of flange toweb due to flexure of the deck slab.
- REMARKS • Dimension 09, gap between stiffener and flange, typically 25 mm to 35 mm, to:
(a) be sufficient to allow welding rod manipulation for sealing weld across endsof stiffener
(b) but not exceed maximum of five times thickness of the girder web
(c) preferably not exceed 50 mm.
•-•-•
•- •
•-----
CIRIAC543
Dimension 010, setback of stiffener where it joins flange, typically 20 mm to 25 mm, tobe sufficient to ensure that edge of flange outstands at least 10 mm from toe of stiffenerweld (fatigue constraint).
If intermediate bracing is connected to an intermediate stiffener, the stiffener should bewelded to both top and bottom flanges.
Fabricators may wish to extend intermediate stiffeners to a flange to simplify assembly.In such cases consideration must be given to durability and fatigue.
Dimension F is the designed fillet weld leg length.
Dimension W is the designed width of stiffener.
Dimension T is the designed thickness of stiffener.
4.23
Detail 4.3.2-2 Layout of intermediate web stiffeners
Ii: bridge
I
REMARKS
4.24
• The positioning of stiffeners should take account of the need to attach cross-bracing andsupporting services. There are benefits for aesthetics, maintenance and durability ifstiffeners are not placed on the outside face of the bridge.
Longitudinal (horizontal) stiffeners
Horizontal or longitudinal stiffeners are rarely required other than for long-span bridges.For deep girders, they are sometimes necessary to reduce the web panel height to preventbuckling.
The detailer needs to give consideration to the intersection of the vertical and horizontalstiffeners. Where the design permits, horizontal stiffeners are best detailed indiscontinuous lengths with unattached ends (see Figure 4.9). However, the design mayrequire horizontal stiffeners to be continuous, being achieved by:
• welding to vertical stiffeners
• fitting and welding to vertical stiffeners, or
• passing through slots in vertical stiffeners.
For further information refer to Section 4.7.
CIRIAC543
-------
--------------
4.3.3
CIRIAC543
Bearing stiffeners
Bearing stiffeners are required at supports and where applied loads or supportingreactions are concentrated at particular locations along the length of a girder. Adequateconnection to the main girder web allows bearing stiffeners to be designed to act asstruts compositely with a portion of the web. Connection to the flanges allows a bearingstiffener to transmit load through the flange to the point of application of a load above,or to a bearing below. The bearing connection to the flanges may either be through aweld fully designed for the purpose (often a butt weld if the loads are high) or,preferably, by preparing the ends of the stiffener to fit the surface of the flanges (withprovision of a fatigue-resistant fillet weld).
Bearing stiffeners should use plates symmetrical on both sides of the main girder web.Unsymmetrical bearing stiffeners are contrary to the requirements of Standards and mayonly be used where the design has accounted for the eccentric stresses that result.
Bearing stiffeners can use a single leg (see Detail 4.3.3-1) or, if temperature and othermovements and/or high loading dictates, utilise multiple legs. Details 4.3.3-2 and 4.3.3-3show typical twin leg stiffeners for use at either intermediate support points or at endsupports respectively. Reference should also be made to SBG Guidance Note 2.04 (6).
Bearing stiffeners should be detailed so as to be in a vertical plane under dead loadconditions.
4.25
Detail 4.3.3-1 Bearing stiffener - intermediate support, single leg
z'F'
'Ol'x'T' stiffener
'010'
II
Cope hole(see 4P152)
z'F'
Fittedend
Cope hole(see 4.3.4-1)
REMARKS • Dimensions 01 and T, stiffener outstand and thickness, to be sufficient to carry axialload and spread it sufficiently to the bearing.
• Dimension D10, setback of stiffener where it joins flange, typically 20 mm to 25 mm, to besufficient to ensure that edge of flange outstands at least 10 mm from toe of stiffener weld.
• Dimension F is the designed fillet weld leg length.
4.26 CIRIAC543
Bearing stiffener - intermediate support, twin leg
------
Detail 4.3.3-2
A
ctbearing
Stiffener vertical notperpendicular tobottom flange
A
Fillet weld
ctbearing
----
Elevation of girder showingmulti-leg stiffener
Stiffeners fittedto bottom flangeand fillet welded
"-------f-----~T---- ----r ....
,r_.J...:_-:_-_ -_-_-_-_1.J,
___J ~ _
Section through girdershowing stiffeners
Dimension 01, stiffener outstand, to be adequate to carry axial load and spread itsufficiently to the bearing.
Dimension 02, half spacing of load-bearing stiffeners, to be:
(a) appropriate for effective load transfer to bearing;
(b) sufficient to allow space for welding rod manipulation (01 < 2 x 02 is suggestedas allowing adequate welds but SBG Guidance Note 2.04 (6) recommends
2designers allow 01 < 13 '02').
(c) not greater than 25 x thickness of web to comply with BS 5400 : Part 3 (31),
clause 9.14.2.2, requirements for pairs of bearing stiffeners acting together.
--
---------
REMARKS •
•
<tbearing
II
II
:01I
I'02' I '02'
Sectional plan A-A
- - ctgirder
-CIRIAC543 4.27
Detail 4.3.3-3 Bearing stiffener - end support
Concrete deck slab(show studs omittedfor clarity)-----------,
'w' x 'T' bearing stiffener(one each side of web).
Holes required in webfor reinforcement ofconcrete diaphragm--_____
shear studs@ 's' clc
~ of bearing
For elevation
--on End Frameshowing bracingsee Figure 4.5
V'C'X'D' bearing plate'E' thk. tapered to suit
~===================::::;;=======±=======~ rood gradient along'-- --+ ...J main girder
z'G'
REMARKS
4.28
•
•
•
•
•
•
•
Dimension A, overrun of bottom flange. Typically 20-25 mm to provide clearance foradequate flange to web weld return (the extension of the weld continuously around thecorner).
Dimension B, location or centres of shear studs, sufficient to allow appropriate clearancefrom edge of steelwork to stiffener for surrounding concrete.
Dimensions C x D are defined width and length of bearing plate to suit size of bearing.
Dimension E, thickness of bearing plate, to be sufficient to permit tapering as well asretain adequate depth for any tapped holes for bearing fixings, and for capability tospread the load.
Dimension G to be the size of fillet weld to secure bearing plate.
Dimensions Wand T, stiffener outstand and thickness, to be sufficient to carry axial loadand spread it sufficiently to the bearings.
The detail shown is suitable for use with a concrete end trimmer. The channel is notalways needed but some form of bracing can be expected to be required for theconstruction condition. Effective bracing can also be provided without the use ofconcrete.
CIRIAC543
Cope holes
In the past, a larger snipe, as shown in DetaiI4.3.1-C, has been used. This has thefollowing disadvantages:
When three plates to be welded are brought together at right angles, eg web, flange andstiffener, the third plate needs to be trimmed to avoid the weld connecting the first twoplates. There are two preferred solutions for this.
1. To shape the stiffener to suit the web/flange weld and to subsequently weld over toseal the comer completely, DetaiI4.3.4-1A. This is particularly applicable whereautomated stiffener welding equipment is used.
2. To use a quadrant cope hole, DetaiI4.3.4-lB. This should have a radius as large aspracticable to allow the sealing welds and corrosion protection to be completedwithin the cope hole.
-----------------------
4.3.4
CIRIAC543
•••
difficulty of welding through the snipe to seal the stiffener at the 45° comer
difficulty of applying the protective coating into the hole through the comer
potential fatigue due to high stress concentrations at the comers of the triangularhole
4.29
Flange
Detail 4.3.4-1 Welds - cope hole
~~
"'-Small snipe to suitweb to flange weld size
(A)
Web
(8)
'c' rodius cope hole
Stiffener
PREFERRED •
(C)
A small snipe (450 chamfer) which is welded over, Option A, or a properly formedquadrant cope hole, Option S, are preferred.
AVOID
REMARKS
4.30
•
•
•
A large snipe (45 0 chamfer), Option C, should be avoided because of the difficulty ofsatisfactorily welding and protecting in the corners.
Dimension C, radius of cope hole, value to be as large as practicable but constantthroughout project.
Typical recommended value for C, 50 mm, or a minimum of 40 mm.
CIRIAC543
----------------------
4.4
CIRIAC543
SPLICES
Bolted splices are often required to connect steelwork sections together on site. Splicesare nonnally positioned near the point of contraflexure. Bolts may need to be arranged tominimise section loss resulting from the holes in tension splices.
On a typical I-beam there are two flange splices and a web splice. Each splice requiresthe plates of the two lengths of beam to be connected together using splice plates. Wherethe thickness of flanges or web of the two lengths are different, pack plates are requiredon the thinner of the two plates to make their surfaces flush at the splice.
Web splice plates should extend over as much of the web depth as practicable. Very longplates can be split into two or three sections for ease of handling but this adds to thedifficulty of sealing. In positioning the bottom and top rows of bolts in a vertical spliceplate, care must be taken that they do not clash with the flange bolts to the extent that atightening tool cannot be fitted on either the web or the flange bolts. (Refer to Haywardand Weare (5) for definitive advice on torque wrench clearances.) Account may be taken
of the principle that bolts in flanges will nonnally be inserted with the head underneathand that, in webs of outer girders, bolt heads will be on the outside. Tightening tools(torque wrenches) will nonnally require clearance for tightening the nut, which willtherefore be on top or inside.
Generally a single outer splice plate and two inner splice plates are used on flanges. Thesingle plate could be thinner than the two inner plates so that its cross-sectional areamatches them, but it is preferable for the inner and outer plates to be of the samethickness for simplicity of fabrication and of thicknesses available from general stock(see Section 4.1.1). However, the fonn of the plates will sometimes be varied to suit therequirements for construction, for example to provide an unobstructed path for launchingrollers. Where the cross-sections of inner and outer plates are not detailed to match, thedesigner should take account of any moment developed due to the eccentricity betweenthe centroid of the splice plates and the centroid of the flange.
The gap between spliced girders typically needs to be 5-10 mm, with the largerclearances used for larger girders.
Splice plates should nonnally be rectangular and of constant thickness. Except wherestress and maximum bolt-spacing limitations dictate, there is generally no advantagein tapering the end edges of splice plates. (This is unlike the ends of flange doublerplates - see Section 4.1.5 - which provide increased cross-sectional areas over finitelengths of girder).
Nuts and washers and/or bolt heads on top flange splice plates restrict the spaceavailable for shear connectors. A general recommendation is that studs, at reducednumbers per row but still complying with allowable maximum spacing and probably ofshorter length, should be fixed to the flange splice plate to provide some continuity ofshear connection across the splice location (see Detail 4.4.0-1).
Flange splice plates should be set back from the edge of the parent flange by 5 mm orlO mm. This allows for tolerances and can also improve its appearance. Wherepennanent fonnwork is seated on the flange, the flange splice plates will need to befurther reduced in width to give space for seating the fonnwork to avoid specialfonnwork details being needed.
4.31
Detail 4.4.0-1 Splice
4.4.0-2 1No.pl. 'w'x'T'x"L'
o
Studs relocated toavoid fouling splice
o 0 0 o
L..:.-~rt-----":"'--' 0 0 0 0 0
Plan on top flangePockingto suit
r-Cl@c
, I
-'-1-'--l- -:- I -:- -:--:- -:- 1-:- -:-
-:- -:- :-:--:- -:-1-:--l- -:-1-:-
-:- +:-:- -:--:- -:- J-l- -:-
2No.pl. 'W'x'T'x"L'
Elevation
Packingto suit
-',,-,-
-:--:-
ooto
1No pi 'W'x'T'x"L'
~I/
r 7t I
~r=-:--:- -:- -:--:--1-:--:--:--:-+1 }gL
» ++-:--:--:- U+-:--:--:--:- T <>
~fgF _1__'__1__1__1_ D ~I__I_ -1-_1__1_ -i-:- -:- -:- -:- -:- !-:- -:- -:- -:- -:-JI
'os' n@'D7' 06 n@'D7' 'os'~ ~
ooIf)
Plan on bottom flange
4.32 CIRIAC543
-
000I- - -1---
I---1---
n@'07' '06' n@'D7'
CXJa
Closer spacing of studs to maintain shear stud
density across splice location if required
Shear studs should be avoided an splice plates
as far as possible subject to maximum stud
spacing (see detail 4.2.1-1)
Plan on top flange plate
CXJa
.~
Splice - plate
Values of 07 and 08 are recommended to be slightly larger than nominal minimumvalue to allow for tolerances on position.
Dimensions 01, 02, 03 and 04 indicate varying flange thicknesses. Splice positions willgenerally be chosen to be appropriate for changes of flange section.
Dimensions OS, distance between centre-line of bolt and centre of flange. Value to beadequate to allow clearance for installation and tightening of bolts.
Dimensions 08, edge distance from centre of bolt. Value to satisfy requirements forminimum distance between edge of hole and edge of plate.
Dimension n @ 07 indicates a designed number of uniform bolt spaces. Value of 07 tosatisfy minimum and maximum bolt-spacing limits.
•
•
•
•
•
Any studs on splice to
be positioned to allow
tightening clearonce
to bolts
Detail 4.4.0-2
REMARKS
-
- 0
- -0=
-0
-
-
-
-
--
-
-
-
--
-• Dimensions W, T and L to be designed width, thickness and length of particular splice
plates.
• Dimensions 09, location of web splice plate, value to be appropriate for clearance forinstallation and tightening of bolts.-
-• Refer to Hayward and Weare (5) for advice on torque wrench tightening clearances.
---
CIRIAC543 4.33
4.5
4.5.1
4.34
BRACING
Requirements for bracing
Bracing is required to perform one or more of the functions listed below.
Design requirements
• to provide torsional restraint to the girders at supports
• to transfer horizontal loads to positions of lateral restraint
• to restrain flanges where they are in compression
• to ensure, where appropriate, adequate load distribution between girders when inservice.
Temporary condition requirements
• to ensure the stability of newly landed girders until they are satisfactorilyinterconnected with the rest of the structure
• to provide stability to the main girder system until the deck is in place and at fullstrength, ie during the period of concreting and curing of the of the deck slab incomposite construction
• to share wind loading between individual girders or groups ofgirders until allelements are connected by the finished deck
• to assist and control the lateral alignment of the girders, for example, to ensure thespacing between girders is sufficiently accurate for the placing of prefabricatedtransverse members (eg permanent formwork (see Detail4.2.3-l))
• to assist maintenance of correct pre-cambering and/or pre-deflection of the girdersduring placing of the deck
• to be braced in pairs to facilitate erection.
Any bracing installed specifically, and only, for benefits during the temporary conditioncould be removed after the bridge structure is complete. However, to remove the bracingrequires workers to go back beneath the bridge deck. In many cases, the risk of accidentwould be increased during the removal operation. A risk assessment must be carried outto balance the disadvantages against the advantages of removing the bracing, which are:
• recovery of steel for reuse or scrap value (though the scrap value will be very low)
• elimination of future maintenance ofbracing members
• improvement of aesthetics by reducing the clutter on the underside of the bridge
• cost of bracing being reduced as it would be reduced in size and it does not need tobe corrosion-protected.
While, in some situations, the removal of bracing also removes potential obstacles toaccessing permanent structural elements, consideration should be given to the value ofthe bracing, if appropriately detailed, to assist the safety of inspection and maintenanceaccess.
CIRIAC543
----------------------
CIRIAC543
Bracing for the construction condition that is left in pennanently will be subject to
fluctuating stresses, which may cause fatigue problems, and is the most common reasonfor it being removed. Ifbracing is to be removed, HSFG bolts need not be used for thetemporary fixing, although it may be economic to use a connection system consistentwith the main works.
Reference should also be made to DMRB BA 53/94 (35) and SBG Guidance Note 1.03 (6).
Types of bracing
Figure 4.4 shows, for comparison, possible bracing types that are successfully used inbridges following nonnal good practice. Some suggested limitations on the type ofbracing in relation to bridge girder depth are shown. However, the principal constrainton the effectiveness of triangulated bracing is the height-to-width ratio of the resultingframe, which should preferably not be shallower than I in 5.
Figure 4.5 shows two types of frame bracing at the ends ofa span. This bracing is oftenused in conjunction with a concrete trimmer beam or diaphragm and made compositewith it using shear connectors.
The use of open steel section, eg angle and/or channel, for bracing members is preferredbecause of the simplicity of their connection, lapping and bolting (see Detail 4.5.2-1).
For detailing of cross-bracing see Section 4.5.2. The usage of other types of bracing isoutlined in Section 4.5.3.
4.35
"""wm
."
..... ~
"oEooN
Paired lateral bracing
~Wi~.~ ".!of·"
." ~ ~
c'Eooo
Link brace optional to allow sharingof horizontal load or assist in maintainingbeam spacing in temporary condition
K-bracing
Top bracing member required fortemporary conditions only and maybe detailed to be removed
Cross-bracing()
::0»()01
"""WFigure 4.4 Types of intermediate bracing for composite '-girder bridges
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
()
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~w
A
~!.~
-------
Abutment trimmer
00000000000000000000000
+111+1'"+
Elevation on end frame
+~
A
B
~ ----=
B
Section A-A
For Section B-Bsee detail 4.3.3-3
.j>.
W--J
Figure 4.5 Types of bracing at supports for composite I-girder bridges
4.5.2
4.38
Cross-bracing
Cross-bracing (Figures 4.2 and 4.4 and Detail 4.5.2-1) is commonly and successfullyused. This bracing may be required for a combination of the reasons listed in Section4.5.1. The alternatives of the horizontal members at either top or bottom are shown inthe illustrations.
In the most common range of bridge sizes, cross-bracing (properly triangulated) willgenerally be used for pairs of girders to provide stability during all phases ofconstruction. It should be noted that:
• unless the bracing members and their connections have particular bending capacity,at least one horizontal member (to complete the triangulation) is always needed
• unless horizontal bracing members are provided both top and bottom, diagonalbracing members must be designed in compression where the disturbing forces arereversible.
Theoretically, placing the horizontal member at the top provides a bracing system betterable to stabilise the compression flange under the action of sagging moments at mid-span(and placing it at the bottom is better for regions of hogging moment near supports).However, for practical reasons the horizontal will normally be placed either at the top orthe bottom throughout.
Within spans, girders are normally braced in pairs to restrain them against buckling.Where there is an odd number of girders, link bracing to top and/or bottom flanges isprovided to tie in the unbraced girder. Full bracing across the bridge width is generallyavoided as this can attract unwanted transverse distribution loads. At piers andabutments, bracing (cross and double link, or link at bottom) is usually provided acrossthe full width so as to efficiently transmit lateral loads to the bearing which provideslateral restraint.
Wind loading during construction can be shared between all girders by the addition ofsimple lacing members (horizontals) connected between the cross-braced pairs (seeFigure 4.2). The designer, in consultation with those responsible for the constructionsequence, will specify (horizontal) link bracing if required during construction to resistwind or other disturbing forces. The value of link bracing can also be important as girderspacers where pre-prepared deck units or permanent formwork span between the edgesof flanges of the main girders and have limited bearing (landing) width.
The presence of horizontal members close to the soffit of the deck has the disadvantageof restricting slab construction and is more difficult to remove. Where not needed at thetop, the preference is for horizontals to be at the bottom of the X (see Figure 4.4).
The designer will decide the required location and sizes of bracing members to suit theparticular requirements of permanent and temporary states of the bridge. The usage ofthe bracing, ie either temporary or permanent, should be indicated on the drawings. Anyrequirement to remove temporary bracing should also be specified.
CIRIAC543
) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
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Detail 4.5.2-1 Cross-bracing - elevation
'J' 'J' 'J'
'E'x't'Intermediatestiffener
'E'x't' -l~'1~
Intermediate Istiffener
p
4P134 'E'x't'Intermediatestiffener
REMARKS •
Elevation of typical cross-bracing (with horizontals at top)
Dimension J, centres of girders, generally equal.
"""wco
• Dimension D, between intersection of member centroids, value used for design.
• Dimension C, value to allow sufficient clearance to avoid interference with concrete deck slab construction.
• Dimensions A, Band M to be designed identifying dimensions and weight per metre length of cross-bracing members.
• Dimensions E and t, stiffener outstand and thickness, to be sufficient to accommodate cross-bracing bolts and holes withsufficient edge clearance.
Detail 4.5.2-2 Cross-bracing - connection
'07'
'01' 'n02
Lines of centro; sto meet
'DlO'
4.40
Elevation
CIRIAC543
- •
•
-- •
•-•-
----
--------------
REMARKS
CIRIAC543
•
•
•
•
Bracing to be positioned so that lines of centroids of bracing elements meet at commonpoint with main element centroid line and as close as practicable to intersection of flangewith web. Designer needs to check allowance for eccentricity and compare withtolerances in BS 5400 : Part 6 (36).
Angle bracing members should, preferably, have their horizontal leg at the top to reduceaccumulation of material on the ledge. However, where bracing members are necessaryclose to the underside of a slab there are maintenance advantages in keeping thehorizontal leg low, ie away from the slab.
Dimension 01, value to suit minimum edge and end dimension limits.
Dimension nD2 (where n = no of bolt spaces), value to suit minimum and maximumfastener pitch. Note: critical dimensions where bolts are staggered (as in this detail) aremeasured directly between closest bolts at an angle. Orthogonal dimensions for thedetail are to be derived from this.
Dimension 03, value to suit minimum space for bolt head and for washer, makingallowance to clear root radius of angle.
Dimension 07, clearance between end of bracing member and web. Value to suitavoidance of stiffener to web weld plus tolerance to include for possible oversize weldand large enough to allow maintenance of the protective coating (minimum 15 mm).
Dimension 08, nominal clearance between ends of bracing members. When they are onthe same side of the stiffener sufficient clearance is required to allow maintenance ofprotective coating. Value recommended to be a minimum of 15 mm.
Dimension 010, typically 20 mm to 25 mm, to be sufficient to ensure that edge of flangeoutstands at least 10 mm from toe of stiffener weld.
Where edge, end and spacing dimensions are involved the use of a value 5 mm to10 mm greater than the absolute minimum value is recommended where possible.
4.41
Detail 4.5.2-3
PREFERRED.
Cross-bracing - intersection
'05' Packing Plate
Packing Plate
A single securing bolt is preferred as being the simplest positive solution.
REMARKS • The use of a minimum of two bolts, and of an oversize packing plate, are held in somequarters of the industry as being the norm. Smallness of bracing members sometimesrenders the two-bolt solution impractical.
• The disadvantages of a single bolt compared with a two-bolt solution are consideredinconsequential.
• Should the members be required to provide compression resistance (see 4.5.2) theirconnection at the intersection can be taken into account by the designer in reducing themember's effective length.
• Often cross-bracing is not joined at all at their intersection. The packing plate andsecuring bolt can be omitted where bracing is not subject to loads requiring aconnection, ie other than those arising from their function as bracing. However, thisleaves a poor detail for maintenance and is not recommended.
• Dimension 04 value to suit:
(a) minimum edge and end dimension limits
(b) space for bolt head, making allowance to clear root radius.
4.42
• Thickness 05 value to match thickness of web stiffener plates to which cross-bracing isattached
CIRIAC543
----------------_.
------
4.5.3
CIRIAC543
Other types of bracing
Lateral (channel) bracing
Generally used on smaller, compact bridge structures, the lateral channel bracing (seeFigure 4.4) may be used with universal beams or, perhaps, small plate girders to providestability during the erection of pairs of girders. Extra bracing would be expected at theabutments to provide torsional restraint and the illustration (Figure 4.5) shows this withshear connections ready for composite action with a transverse concrete downstand edgestiffening.
K-bracing
The same general principles as for cross-bracing (see Section 4.5.2) apply to K-bracingexcept that two horizontal members are needed unless the back of the K (bottom memberin Figure 4.4) has sufficient bending capacity.
For ease of construction, the connecting plate at the intersection of the diagonals will bewelded to the horizontal before erection.
Z-bracing
The same general principles as for cross-bracing apply to Z-bracing (see Figure 4.5 foran example at an abutment trimmer), but the arrangement needs to ensure that bothflanges of each girder are given restraint.
4.43
4.5.4 Skew
Apart from the normal implications of rearranging details to enable elements ofa bridgeto fit a skew there is a particular phenomenon with end deflections which needs to betaken into account in the detailing of braced plate girder skew bridges.
The deflection during construction of heavily skewed spans causes a significant twistabout the longitudinal axes of the girders at the end supports (37). The weight of wetconcrete causes vertical deflection of a girder and this is normally allowed for by precambering it. At the end supports of skewed bridges there is a corresponding rotation ofeach girder about its transverse axis (passing through its centre-line of bearing). This endrotation is normal to the plane of the end diaphragm and bracings near the end, which,because they are weak in torsion but stiff in their planes, will force a lateral rotation ofthe adjacent girders about their longitudinal axis. The rotation will always occur unlessforcibly restrained. With stress also arising in the members, this may result in the girdersbeing out of vertical by an unacceptable amount, dependent on the stiffness and depth ofthe girders, if the skew significantly exceeds 20°. The girders must then be twisted outof-vertical before concreting to allow for this.
However, the transverse bracing between girders at the end supports usually has to befitted before concreting (for stability and strength under lateral loads) and, therefore,before this rotation takes place. Where the bracing is a triangulated system, that bracingcan only be rotated about an axis in its plane, ie parallel to the abutment. The fabricationdetails should ideally be dimensioned so that the bracing is unstressed in the final deadloaded state. The bracing members so dimensioned to twist the girders initially cantherefore be expected to be temporarily under stress as they are fitted between girdersbefore concreting. This will require measures to distort the elements to fit them and thisshould be anticipated to avoid site modifications being made to rectify an apparentmisfit. As the weight of concrete is added the ends will rotate and the girders will
become vertical.
The same argument applies when un-triangulated bracing is used (eg the lateral andabutment trimmer bracing, and the central bay of the abutment trimmer shown in Figure4.5). However, being more flexible in the plane of the abutment than ifit weretriangulated, it will accept misalignment mostly with less distress. The estimated amountof twist expected should be included in the design information.
Attention should be drawn to this effect of skew in the contract documents forconstruction so that the pre-set can be calculated carefully. An I-section has a lowtorsional stiffness, so the pre-set twist is usually not too difficult to achieve.
Bridges with a skew exceeding 30° need specialist advice. Particular attention must be
given to:
4.44
•
••
ensuring bearings are appropriate for the control and direction of movements
expected
reinforcing deck concrete to resist the unusual stresses arising
tying down acute-angled comers to resist uplift.
CIRIAC543
------
--.
-.-
.-
.-
-.-
.-
-.-
.-
-.
-
4.6
CIRIAC543
PLATE GIRDER CROSS-HEADS
The use of plate girder cross-heads integral with the construction depth of the mainlongitudinal girders allows the number of support columns to be reduced. Wherenecessary it can, with an increased number of longitudinal girders, allow a reduction ofthe superstructure construction depth. This avoids the penalty of increasing the numberof supports or introducing unsightly cross-heads across the tops of the columns.
The connection details of an integral cross-head to the main girders need carefulattention, particularly the influence of longitudinal and transverse falls. There are variousways of dealing with the falls. Figures 4.6 and 4.7 show the industry's typical solutions.
With both these solutions, the main girders run through the support points with theirflanges horizontal in the transverse direction. The adjacent girder is at a higher or lowerlevel depending upon the direction of the crossfall.
In Figure 4.6 all splices and splice plates are kept parallel with the main girder flanges.The cross-head girder bottom flanges are extended level from the bearings of theadjacent lower main girder flange. Detail 4.6.0-1 shows this solution.
In Figure 4.7 the diaphragm element is fabricated with flanges that run straight betweenthe splices at the edges of the main girder. This necessitates a kink at the splice point andthe splice plates need to be bent to suit. The arrangement keeps the diaphragm girderelements simple, it reduces the number of bends in the flange plates and the resultingkinks are also the least angle compared with other arrangements. However, bearingplates will be tapered in two directions when there is an overall fall in the structure.
In Figure 4.6, stiffeners are shown at the flange kink to resist the vertical load that occursdue to the vertical change in direction of the flange. Such a force also occurs at the kinksin the arrangement shown in Figure 4.7, although the force is less because the angle ofkink is reduced. However, because the kink occurs at a splice, a stiffener cannot beprovided. The force has to be resisted by the flange cantilevering from the web. This isusually possible because the vertical load occurs within the splice where the stress in theflange is reduced where the cover plates are carrying the load.
Other options are that the top flanges of the main girders could be inclined and theflanges of the diaphragm follow through straight. The actual method chosen finally coulddepend on the preferences of the fabricator.
To deal with longitudinal falls it is usual to use the diaphragms vertical, with flangesangled to follow the longitudinal fall of the main girders. Using flanges at right anglestogether with tapered packer plates is possible but unusual. The usual method avoidsmachining of tapered packer plates and simplifies the site connection and is preferred,even though it is rather difficult to fabricate .
4.45
.f>,
~OJ
<tMAIN
GIRDER
<tMAIN
GIRDER
I
<tMAIN
GIRDER
I
<tMAIN
GIRDER
I-r--G
II
J 1
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I
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r
m rn rn wrn I
mII
IIII II
IIII
IIII II I
IIII 1\ II II
II II I II...lI...JL 1\
..JL N ~ ...JL
I
I-V \ j~ \ I
'\ \ ,II I \(j; 4.3.3-2
Stiffeners
Half cross-section showing elevation of cross-head (diagrammatic)
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Figure 4.6 Steel/concrete composite bridge superstructure. Typical four-girder, two-bearing integral cross-head utilisingflat-flange splice plates
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ctBRIDGE
\It
\
ctMAIN
GIRDER
ctMAIN
Stiffeners
Half cross-section showing elevation of cross-head (diagrammatic)
Steeveoncrete composite bridTle structure. Typical four.glrder, two-bearing integral cross-head utilising bent-flange
splice platesFigure 4.7
~
~~
Detail 4.6.0-1 Plate girder cross-head
'w' x 'T' 'w' x '1' 'w' x 'T'
Plan on top flange
All starterp. lates to b,W' x 'T'
5T2 5T25T2 5T2,...---.... 5n+ r-+- -+- -+- r-+- r=J=i I I I I~ I fl!fl.
I Ifl!fl. ~ I ~1
I I I II I I I~ Lc ± I I-
4- ± +5B '-,~ 5B2 5B2 5B1<t 4P742
BEARING ~
ElevationBEARING
4P743
5T1
4P743
'T2' thk web 'T1' thk web
'w' x '1'
'B'
'T2' thk web
Plan on bottom flange
REMARKS • Dimensions A, B, C, D and E to specify correct location of stiffeners measured relative tocentrelines of main girders.
• Notation ST1, ST2, SW1, SW2, SB1 and SB2 identify different types of splice detail tobe designed and drawn to suit. For typical examples, see 4.6.0-2 and 4.4.0-1 (Section 4.4).
•
•
Dimensions W x T to be designed width and thickness of flange and web starter plates.
Dimensions T1 and T2 to be designed thickness of web plates.
4.48 CIRIAC543
-Detail 4.6.0-2
Detail 4.6.0-3
Crassheadgirder
Flange splice platesthis side omittedfor clarity
--f---f--- Web splicePlate
Main girdertop flange5T2
S82
Main girderbottom flange
IIIIIIIIIIIIII
starter ---==f--+--I"I-~~Plates II
IIIIIIIIII
SW2
For general splice guidance refer to Section 4.4
Typical stiffener/bottom flange connections at bends in flange
Dimensions shown are typical and for illustration only. Actual dimensions to be chosento suit project design. Bolts are omitted for clarity.
The welded cruciform joint resulting from the connection between the starter plates andthe main girder web needs consideration of the risk of pulling the through-plate apart.The development of this detail is a specialist activity related to the specification of thesteel and welding procedure. For more information refer to SBG Guidance Note 3.02 (6).
Cross-head to main girder connection
•
•
•
REMARKS
-
-
-
--
-
-
-
-
-
-
-
--
- 'R' radius tobottom flange
- z 'F"z F'
z 'F'z 'F'
-- 'R' radius to
bottam flonge
- REMARKS • Stiffeners or gussets are required at all significant changes of flange direction.
• Dimension F is the designed fillet weld leg length.
--
• Dimension R, radius of bend in flange plate. Value to be sufficiently large to ensure thatthe plate properties are not affected. Value to suit fabricator, but typically 10 timesthickness of flange plate or 150 mm minimum.
-- CIRIAC543 4.49
4.7 VARIABLE-DEPTH GIRDERS
Variable-depth (haunched) girders are an economic option in large continuous bridges,due to high moment and shear capacity requirements at the piers *. Haunched profiles
provide reduced construction depth over the central portion of spans, where maximumclearances are usually required. The curved soffits of variable-depth girders also present
a more pleasing appearance for larger-span bridges.
A part-elevation/section of a typical steel bridge with variable-depth girders is shown inFigure 4.8. As with parallel-flanged girder bridges, the stiffeners at piers are provided on
both sides of the web, but intermediate stiffeners are necessary only on one side. For
aesthetic reasons these are located on the inner face, at the same time improvingdurability by presenting the uncluttered surface to weathering. A typical layout ofintermediate web stiffeners is shown in Detail 4.3.2-2.
While the analysis of girders with non-parallel flanges can be more complex, in most
cases variable-depth girder details are the same as those used for parallel-flange girders.The details included in Section 4.3 (Stiffeners) and Section 4.5 (Bracing) are applicable.
It is usually possible to obtain steel plate of sufficient width for the webs of variable
depth girders direct from the rolling mills. The web plates need to be cut accurately to
the required profile before attachment of the bottom flange. The curvature of the bottomflange is achieved by drawing (forcing) the flange plate to follow the profile of the web
plate closely during the fabrication process. It is only necessary to pre-bend flange platesat abrupt changes of angle, for example adjacent to the bearings. Bends in a bottomflange plate at a pier with typical stiffeners are shown in Detail 4.7.0-2. Such changes of
angle can also be achieved by full-strength butt welding of straight pieces ofplate.
Theoretically, increasing the effective depth of girders enables the flange platedimensions and web thicknesses to remain constant. In practice, however, designers
often increase the thickness of flange and web plates as the load effects concentrate
towards the piers, thus keeping the plate thicknesses generally in proportion to theoverall section. The thicker webs and flanges are easily introduced at the normal splice
points required (see Detail 4.4.0-1 ).
Buckling of the web plate is dependent upon the depth and thickness of the plate, and thelength of the web panels between stiffeners. Web buckling can be avoided by one or
more of the following:
• thickening the web plate
• reducing the spacing of the intermediate transverse (vertical) stiffeners
• introducing longitudinal (horizontal) stiffeners.
It is generally more economical to keep the web panels between stiffeners approximately
square.
4.50
* The term "haunched" is sometimes reserved/or girders with an abrupt change in the slopeo/the soffit.
CIRIAC543
)) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )
<i: bridge
\
<i: pier
\
[=f=]Half elevation
~ bearing
-- - -
rf=....
--- - - - -- - - - - -
-
-- - - - -- - -- - - - - -- - - - - - -
4P701
- -~
11 - - - - - LL =r ~.= ~L~_I I
()
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i of bridge
el pier55-head
Verge Hard Carriageway Hard,Verge rRoCo "ob oc
~~strip striP!
permanent formwark
~
~ 1 ~ 1 I
~
v--~
- .... - /'
I Jl I I ~ I
I m m RCP;"
l- - - ~ - T_1- - - - - - - _1-
1-L - - ~
~----T-----------I-----'
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i:n.....
At midspan
Figure 4.8 Variable-depth steel girder bridge
At intermediate pier
Staggered sectional view
~
c.nN
Detail 4.7.0-1 Steel girder make-up
~ ABUTMENT BEARING ~ PIER ~ BRIDGE
'E'I'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A' 'A,I'A' 'A' 'A' 'N 'A' 'A' 'A' 'A' I
r-- h SF
I r I
S TB IS I P8 IS I PB IS PB IS IS IS IS PB IS PB IS TB lSiJ~ 1 ~l ~~ ,~i !
-
I;l.~f -,--- ,
IENOTES TEMPORARY.c ~ROSS BRACING 4.3.2-1
;("- ,!. 0 b.}:;o N~ENOTES PERMANENT
0-.....4.5.2-1 !X= :i \1\
0-...... 0 . 0 . 0ROSS BRACING
ENOTES POSITIONF GIRDER SPLICE
ENOTES POSITION 's'
-r~ Lr '5'F INTERMEDIATE WEB - I-- - J------C--T1FFENERS
TOP FLANGE 'w' x 'T' 'w' x 'r 'w' x 'T' 'W' x 'T' 'w' x 'T'
WEB 'T' 'T' 'T' 'T' 'T'
BonOM FLANGE 'w' x 'T' 'w' x 'T' 'w' x 'T' 'W' x 'T' 'W' x 'T'
SHEAR STUDS 'N'@'8'crs 'N'@'B'crs 'N'@'B'crs 'N'@'B'crs
LEQ.ENDTB- D
CP8- D
CSP- D
oIS - D
oS
()
;Uj;()
rt,VJ Half-elevation of steelwork and girder make-up
Detail 4.7.0-1
-------
REMARKS •
•
•
•
•
Steel girder make-up (continued)
Dimension A, centres of intermediate stiffeners. Value to be designed to suit resistanceto web buckling and positions of bracing. Locations to be clearly indicated in relation toprimary setting-out points (centres of bearings).
Dimension S, longitudinal centres of shear connectors. Value to suit design for numberof connectors per unit length, and detailing constraints (see Table 4.1).
Dimension C, giving location of changes in flange or web plate thicknesses, to be clearlyindicated in relation to overall dimensions of girder.
Dimensions D and H, minimum and maximum overall depths of girder. Value to suitdesign and to define extent of variable depth.
Dimension E, end of girder. Value to be sufficient for end support bearings, bearingstiffeners and any end bracing required.
-• Number of shear connectors across flange, N, to be compatible with designed number of
connectors per unit length, and detailing constraints (see Detail 4.2.1-1).
• Dimension R, radius of girder soffit, is a method of defining the shape of the variabledepth required in relation to the minimum and maximum dimensions of depth.
--------------
CIRIAC543
•
•
Dimension S, giving location of splices, to be chosen to suit transportation size andweight and any changes in plate thicknesses.
Dimensions Wand T, designed widths and thicknesses of plates, respectively, inflanges and webs.
4.53
Detail 4.7.0-2 Variable-depth girder - bent flange at pier
<tPlate girdercrosshead
A AV V
+ + + + + +
+ + + + + +--= ---+ + + + + ++ + + + + +
<> <>
~'T'I
stiffener
Plan on bottom flange
Av
IIIIIIIIIIIII
<> II < >-III
'R' radius to 1/bottom flange- II I-- 'R' radius to
1/ bottom flange
t\-II
z'F' t\-z'F' III-t:::- 1/ z'F' V II z'F' V
~ -==1--:----- j ::...------:- , I I -
-0Co 'Cfl Cll::> c._ Cll-0::::0·-L(j)
0 0to>o u"'-0(f)_
'A' 'A'
4.54
Elevation on J-J
CIRIAC543
-- REMARKS •
•-•- •
-•-•
-•
- •
-
------------
Stiffeners or gussets are required at all changes of flange direction.
Dimension R, radius of bend in flange plate. Value to be large enough to ensure thatthe plate properties are not affected. Value to suit fabricator, but typically ten timesthickness of flange plate, or 150 mm minimum.
Further information on plate bending is available in SBG Guidance Note 5.02 (6).
Dimension A, spacing of stiffeners and start of radius to be sufficient to allow abuttingcross-head plates or bearing plates (where applicable) meet a flat level plate overtheir full width. Bends need to be square to line of girder, so additional allowanceneeds to be made for skew of abutting plates where applicable.
Dimension F is the designed fillet weld leg length.
Dimension W, width of stiffener. Value to allow setback from edge of flange, typically20 mm to 25 mm, to be sufficient to ensure that flange outstands at least 10 mm fromthe toe of stiffener weld.
Dimension T, thickness of stiffener, value to satisfy minimum design and detailingrequirements relative to W.
For cross-head to main girder connection, see Detail 4.6.0-2.
- CIRIAC543 4.55
Figure 4.9
If longitudinal stiffeners are used the following detailing issues need to be considered.
I. If they are used to improve the flow of stress towards the bearing position they needto be continuous, and will act as part of the girder cross section. Continuity isnormally achieved by slotting the intermediate stiffeners and allowing longitudinalstiffeners to pass through. Alternatively, the continuity can be achieved by closefitting and welding on either side of intermediate stiffeners.
2. If they are designed solely for web stiffening, it is important that they do nottransmit longitudinal forces. In this case they should be made discontinuous atintermediate stiffeners. A gap can be left at both ends, see Figure 4.9, or they canbe welded to the face of the intermediate stiffener at one end (to ensure satisfactorylocation) with a paintable gap left at the other end.
Longitudinal stiffeners can collect debris and increase maintenance requirements.Shedding of moisture and debris can be improved by:
• sloping the stiffener away from the web (see Figure 4.10)
• providing a slot for drainage at the lower end of inclined stiffeners.
If longitudinal stiffeners are being considered the benefits need to be evaluated againstthe increases in fabrication costs and aesthetic and maintenance shortcomings.
I I=:J~(~~J~
, I
I I
Discontinuous longitudinal stiffeners
Longitudinal stiffenersloped away from webat 10% slope--
Figure 4.10
4.56
Sloped longitudinal stiffeners
CIRIAC543
----------------------
4.8
CIRIAC543
WEATHERING STEEL
In certain environments "weathering steel" can be used successfully for bridgeconstruction without any protective coatings. This steel relies upon the natural formationof a protective impervious patina during the first few years of weathering. In more severeenvironments, weathering steel still provides greater resistance to corrosion than doregular grades of steel, but it is unable to form an even protective patina. This leads tothe developing colour being uneven, which may be unacceptable in certain situations.Weathering steel should therefore not be used without protective coatings in thefollowing situations:
• in marine environments
• where subject to de-icing spray, ie chlorides
• in continuously wet or damp conditions
• when buried
• in corrosive industrial environments.
In general, the detailing requirements for structures in weathering steel are the same asfor the regular grades. However, careful must be taken to avoid creating any areas onwhich water will collect. Also, a certain amount of rust stain runoff needs to beanticipated as the steel "weathers" and oxides of iron are formed. To preserve a uniformappearance of the steel, the bridge should be detailed to maintain an even exposure as faras possible. Detail 4.8.0-1 illustrates a method of maintaining the even exposure of acomposite plate girder bridge. The cantilever is extended sufficiently to avoid rainregularly being blown onto the bottom half of the girders, which would occur if thecantilevers were much shorter.
Methods of avoiding concentrated runoffs are not so simple to identify. Prevailingconditions are likely to be different for each bridge. Detail 4.8.0-1 goes some way toachieving what is required by reducing the amount of runoff itself.
Where rainwater does reach the girders, water will tend to collect on the bottom flangesin sheltered comers, which may lead to localised corrosion of the bottom flange. Theproblem can be exacerbated by the slight upward distortion of the flanges that may occurduring welding, thus concentrating the collection of water alongside the root. It is veryimportant that stiffeners are not allowed to impede the free runoff of water from theflange. Details, such as good-sized drainage slots, should be provided to ensure thatwater can drain away freely. To avoid these problems, girders should be arranged tohave a camber and/or fall so that water is less likely to collect or pool.
The collecting water will follow the slope and generally shed itself at the end, either atan abutment or pier. Suitably positioned drip plates or runoff strips (Detail 4.8.0-2) canbe successful in keeping the water clear of concrete or other stainable surfaces.
Coating of localised areas of a weathering steel structure, or even the abutments andpiers, can be carried out if it is difficult to ensure that the local environment will remainsatisfactory throughout the life of the bridge.
4.57
As indicated above, some corrosion is inevitable in the formation of the patina andprediction of the extent of further corrosion is difficult. To allow for this corrosion,additional thickness needs to be provided on all exposed faces. The designer shouldadopt a (standard) plate thickness and use a reduced thickness for strength calculationsto suit the allowance. The DMRB allowances (38) are:
• faces in mild environments:
• faces in severe environments:
I mID per face
2 mID per face.
Detail 4.8.0-1
It should be noted, however, that localised corrosive effects, such as from leakage ofchloride contaminated water through an expansion joint, can cause serious deterioration.Care must be taken in such details.
Reference should also be made to SBG Guidance Note 1.07 (6).
Weathering steel- edge cantilever
I
~8
I.<1
4~ ~<1 <1~Di.<l<l.
4 '.1\ . <I'
r--~. " <1 . .W·."l! 4 .<I<I 4 .II.
==-L· <1 j 4 .'<<I
....A.J <I<I
4.. .' <I
W
AVOID
REMARKS
4.58
•
•
Road drainage must not penetrate the slab (ie simple discharge pipes must not be
used).
Make W, width of cantilever, > D, depth of girder. However, cantilevers exceeding 1.5 mare more difficult to build.
CIRIAC543
-------
Detail 4.8.0-2 Weathering stee/- runoff strip
Exterior face
z8z8
Bottom flange
Sectional view A-A
z8
Plan on bottom flange of girder
-----
-
z8
'D' x 'T' run off strip('5') welded all roundexcept as shown.
VJ<:)zQ2L5ro
~ l'0I-
~
A
0::Wo0::<31.Lo....J....J
li
l 'A
•----
REMARKS On unpainted weathering steel bridges, runoff strips can be used on exterior flange legsof outer beams to avoid:
(a) collection of rainwater at bearing stiffeners and subsequent corrosion
(b) staining of abutments by oxides during weathering process.
• Dimension A, distance from support. Value to be sufficient that rainwater runoff fallsclear of surfaces (such as concrete abutments) that could suffer staining. Allowance forwind-borne action should be made.
• Dimensions D and T, cross-section of runoff strip to be selected to suit size of girder,anticipated runoff, and one dimension to match plate thickness elsewhere on bridge.
• S is specification for grade of runoff strip steel to match that of main girder steel.
• Dimension N for no welds required only where BS 5400 (24) class G welding detail is notsatisfactory for fatigue, otherwise weld all round for better durability. Value of N to extendtypically 25 mm from edge of flange (fatigue constraint).
---
CIRIAC543
• For weld detailing nomenclature, see Detail 4.1.3-1.
4.59
4.9
4.60
SERVICES
Many bridges are required to carry services in addition to the primary transportationloads. Provision needs to be made for services at an early stage in the design process. Itis usually necessary to decide upon the particular arrangement to suit the type and size ofservice to be carried.
It is the general and recommended practice for services on steel bridges to be carried inducts cast into non-structural concrete forming the raised verges and footways at theedges, or the central reserves, of the bridge. The size and number of services to becarried and/or the configuration of the bridge structure may dictate the arrangement.Where space is available, the opportunity should be taken to include some spare serviceducts. Reference should be made to Section 5.8 of this book.
Where services are too large to fit within the non-structural concrete, consideration mustbe given to alternative locations. The space between the girders of steeVconcretecomposite bridges is usually available. Suspension brackets using simple proprietaryhangers from the underside of the concrete deck for the support of the ducts or pipeworkare recommended. Maintenance of services beneath bridge decks needs greater planningand preparation. Elaborate permanent arrangements should be avoided if the services canbe reached by modem mobile access equipment.
Utility authorities often seek large service troughs cast into bridge structures, accessiblefrom the top of the bridge deck. However, such troughs may adversely affect thetransverse structural stiffness characteristics of the bridge deck.
Reference should also be made to Section 3.1.7 on verges and troughs.
CIRIAC543
------
--
5
5.1
Fixings for bridge furniture
GENERAL
This chapter deals with fixing to the bridge structure of various components, manynon-structural. These components are known as bridge furniture and include:
• parapets
• safety fences
• lighting columns
• signs
• noise barriers
• services
• movement joints.
The bridge designer has several concerns when seeking to secure these components tothe structure, which are, principally:-
--
•
••
that the bending moments and shear forces from the component are imparted to thestructure in the manner expected
that the fixing is not itself damaged by the failure of the component
that the fixings on the deck do not interrupt the continuous waterproof membraneprotecting it.
---
The proprietary nature of bridge furniture means that there may be several competingsystems available for use with different fixing arrangements (the choice is generallymade by the contractor and agreed by the design engineer). This may require thedesigner to show a designated outline on the drawing where the fixing will beaccommodated. Details will have to be finalised when the selection is made.
Further information on fixings may be found in CIRIA Technical Note 137 (39).
The details to be found in this chapter are as follows:
----
--
CIRIAC543
5.2.0-15.2.0-25.2.0-35.2.0-45.3.0-15.3.0-25.4.0-15.4.0-25.5.3-15.5.3-25.5.3-3
5.5.3-45.6.0-15.6.0-25.7.0-15.7.0-25.7.0-3
Anchorage - cast-in cradle system 5.3Anchorage - individual socket and bolL 5.4Anchorage - resin-grouted stud 5.5Anchorage - expanding socket bolt 5.6Bedding of base plate 5.7Levelling ofparapet beam for large furniture 5.8Fixings - bolts, nuts and washers 5.9Base plate fixings 5.10Concrete parapet - in situ 5.13Concrete parapet - precast 5.14Precast concrete parapet - seating 5.15Precast concrete parapet - temporary stabilisation 5.16Safety fence fixing - on bridge deck plinth 5.17Safety fence fixing - over waterproofing 5.18Lighting column position - at edge of bridge 5.19Lighting column positions - in median 5.20Lighting column and draw pit - in median 5.21
5.1
5.7.0-45.8.0-15.8.0-25.8.0-35.8.0-45.8.0-55.8.0-6
Lighting column and draw pit - at deck edge 5.22Services siting -location 5.24Services ducting at movement joint - range 0 mm to 10 mm total 5.25Services ducting at movement joint - range 10 mm to 20 mm total 5.26Services ducting at movement joint - range 20 mm to 40 mm total 5.27Services ducting at movement joint - range 40 mm to 50 mm total 5.28Services - movement joint 5.29
5.2
5.2
ANCHORAGES
The anchorage is that part of the fixing embedded within the structure. Anchorages canbe formed in several ways. The most satisfactory are:
• cast-in cradle system (comprising four interconnected sockets cast into theconcrete)
• individual sockets and bolts (cast-in or resin-grouted sockets as required).
Other methods that may be required in special circ*mstances are:
• resin-grouted stud anchorages
• expanding socket bolts (not recommended for new construction)
• through bolting (exceptionally, provided that it is cement-grouted).
It is important to check what is acceptable to the client for the use intended. HAPAS(Roads and Bridges), the Highways Authorities Product Approval Scheme administeredby the British Board of Agrement, lists approved anchorage types for bridge parapets.The approvals are reviewed from time to time with the benefit of continuing experienceand feedback. Details 5.2.0-1 to 5.2.0-3 show typical examples of each type.
The choice of anchorage will depend upon the circ*mstances including number,location, what is being fixed and where, and whether it is new works or maintenance.Anchorages for certain uses are tightly specified, such as with parapets, but in othersituations the designer has more freedom of choice. The following notes and the remarksconnected with each detail should assist in making that choice.
In new works, anchorages on decks should be located in individual or continuous plinthsraised above verge level and with a tuck in which to seal the waterproofing.
End anchorages for parapets should be at least 150 mm clear of end ofparapet beam orexpansion joints therein. The details should ensure that anchorages for parapet posts arewell clear, longitudinally, of anchorages for lighting columns.
Anchorages should be independent of the furniture. The type of fixing where thefurniture post is recessed into pre-formed holes in the concrete, once a popular fixing,should not be used. Experience has shown that it is impossible to keep them sealed and
to maintain protection to the hidden portion.
For further information regarding the use of anchorages, see Section 5.4.
CIRIAC543
-------
----
Detail 5.2.0-1 Anchorage - cast-in cradle system
Threaded socket
Typical proprietary cradle anchorage
• Cradle offers good mechanical connection to reinforcement.
• Easy to place and align.
-----
REMARKS •
•
•
•
See also Detail 5.4.0-2 in Section 5.4.
Cradle fixing is more stable than individual cast-in sockets during concrete pour.
Easy to remove and replace bolts after damage to the component (eg after accidentalimpact on a parapet.
An early decision is needed because of different bolt spacings for different componentsand cradle must be placed in position at the optimum time.
• Upstand size is affected.
• Needs careful detailing of surrounding reinforcement.
------
----
CIRIAC543
• Used for fixing steel and aluminium bridge parapets, lighting columns, safety fences etc.
5.3
Detail 5.2.0-2 Anchorage - individual socket and bolt
Replaceable top bolthexagonal head set screw.stainless steel --~
eplaceable top bolthexagonal head set screw,stainless steel
Washer stainless steel
Threaded socket.stainless steel---.....
Pourable resin
Washer stainless steel
Cast-in socket(typical proprietary type)
Resin-grouted socket(typical proprietary type)
REMARKS
5.4
••
•
•
••
Choice of cast-in or resin-grouted fixing (for remarks on resin grout see Detail 5.2.0-3.
Choice of preformed or drilled hole.
Sockets can be set at different levels if no projection is wanted (but care is needed withthreaded connection).
Easy to remove and replace bolts after damage to the component (eg after accidentalimpact on a parapet).
May be used to replace damaged stud fixings if required.
Cast-in socket alignments are difficult to match at one location. A template should beused to hold them in position during casting. (Preformed holes may offer some flexibility.)
CIRIAC543
----
--
Detail 5.2.0-3 Anchorage - resin-grouted stud
Hexagonal head nut,stainless steel
Washer,stainless steel
Threaded stud,stainless steel
Pourable resin
- REMARKS • Easy addition to existing structure.
--
• If being used in new works reinforcement needs to be fixed to suit.
• Possible loss of reinforcement section when drilling.
• Smooth face to hole if coring used. Rotary percussive drilling preferred but coringnecessary if reinforcement hit. Roughen edges of hole.
• Needs care with alignment to achieve accuracy.
• Should not be used for new construction.
• It is critical to get adequate length of resin-bonded anchorage.
• Exposed projecting thread needs to be corrosion-resistant or protected.--------
---
CIRIAC543
•
•
Materials come under COSHH regulations.
Projecting thread is easily damaged. Replacement difficult. Generally needs overcoring- more damage to reinforcement. Replacement with resin-grouted socket to avoid futureproblems is recommended.
5.5
Detail 5.2.0-4 Anchorage - expanding socket bolt
Threaded studstainless steel
REMARKS
5.6
••
•
••
•
•
•
•
Should not be used for new construction.
Easy installation suitable for non-critical locations such as hand rail or lamp bracket.
Ease of installation is especially useful on horizontal or upwards fixings.
Not suitable to resist impacts.
Concrete cover is critical to resist expansion forces.
Can loosen under vibration.
Critical to get adequate length of embedment.
Prone to corrosion.
Inferior fatigue and dynamic performance.
CIRIAC543
--------
5.3
Detail 5.3.0-1
BEDDING OF BASE PLATE
The bedding is the layer of mortar between the base plate and the concrete surface.There is unlikely ever to be a smooth fit between these manufactured and formed orfloated surfaces. The bedding is necessary to fill the gap and has three main purposes:
• ensuring an even spread of applied load to the concrete
• protecting the section of fixing bolts and/or studs between the underside of the baseplate and the concrete
• making up to level any slope of the structure surface to allow for componentsfabricated square to their base plate.
An added advantage is that it provides a small additional height to the base plate of thefurniture to keep it clear of surface moisture.
Bedding of base plate
-----
vJZZZZZ)7J
(A)
PREFERRED •
•
(B)
Option A (or B).
10 mm to 30 mm thick.
(C)
• No bed.
• Cementitious bedding material.
• Bed less than 10 mm thick (impractical, especially if two-pack material used).
---
AVOID •
•
Detail C - end chamfers break off and fall onto whatever is below.
Bed thickness greater than 30 mm (creates curing and stability problems).
REMARKS • Shims to assist in levelling of base plate should be:- a) non-metallic
b) located at three points for best controllability of adjustment
- c) compressible to allow adjustment and avoid point loads.
• Fixings should be given a final tightening after the bedding has cured.
- • Bedding may be a f10wable mix or rammed dry pack.
• Variation in thickness may have to be greater than 10-30 mm where bigger base platesare used as on lighting columns. To avoid this some or all of the slope in the parapetbeam may be taken out within the parent concrete by provision of a recess, plinth orcombination of both.
- • Any slots in the base plate that remain exposed after the bolt/nut and washer are inplace should be sealed to protect the fixing and anchorage area.
-CIRIAC543 5.7
Detail 5.3.0-2 Levelling ofparapet beam for large furniture
Recess (base plate andbedding omitted forclarity)
Base plate
Bedding
Elevation Section A-A
'A'
+ +
l'A
Bedding
Baseplate
+ +
Plan
CD l'A
REMARKS
5.8
• Bedding to be sufficiently thick that underside of base plate is above adjacent surface ofparapet beam.
CIRIAC543
----
5.4 BOLTS, NUTS AND STUDS FOR FIXINGS
Generally nuts, bolts, studs and washers for fixing bridge furniture will be of stainlesssteel. In any event, they, and any connecting sockets, will be of the same or similar metalto avoid galvanic action.
-Nuts, bolts, studs and washers must be protected from touching any part of the base platethey are fixing if there is any danger of galvanic action occurring (see Detail 5.4.0-1).
-Lock nuts may be necessary if vibration or flexing of the component is likely to be aproblem. This can be particularly so with lighting columns.
-Anti-theft nuts should also be considered (one per post fixing) especially in conjunction
with aluminium parapets.
-The minimum length of threaded connection needs to be determined. The actual locationof a socket or fixing may necessitate a change in length ofbolt during construction.
----
Fixings should be given a final tightening after the bedding has cured. Specifying atorque force may be useful, but inaccuracies may result from the overcoming offrictional resistance of existing old fixing sockets.
Any slots in the base plate that remain exposed after the bolt/nut and washer are in placeshould be sealed to protect the fixing and anchorage area.
Before being tightened, nuts and bolts should be lubricated with high-creep-resistant,anti-seize grease.
Il:I>'~-- Socket
Fixings - bolts, nuts and washers
Isolating top-hat washerV-Washernylon 66 ---------'" to BS4320
" stainless steel
Base plate
Bedding
Hexagonal headset screwstainless steel
Detail 5.4.0-1
-
-
--
-
--
REMARKS • The fixing system may be insulated from the base plate of the bridge furniture to avoidgalvanic corrosion by inclusion of an isolating top-hat washer.
----
CIRIAC543 5.9
Detail 5.4.0-2 Base plate fixings
Traffic face
10mm to 30mm max.grout
3.1.4-1
I
I I,--
I IJl~""'., ~., .-'e-··~ ,._ ';"~.
I I ·ol·I~ I~" " .
--t I IReinforcement
Stainless steel anchorage unit for parapets
REMARKS • The principle of the cradle system (Detail 5.2.0-1) is used to secure lighting columns,safety fences, acoustic barriers, signs and parapets.
• Bridge furniture elements can be of aluminium or galvanised steel, so the problem ofgalvanic corrosion should be considered at an early stage.
• The designer must ensure that clear details are given on the drawings showing howdissimilar metals are to be isolated to prevent corrosion from the effects of electrolyticaction.
• It is preferable to specify stainless-steel holding-down sockets and bolts.
• Site staff must be made aware of the minimum length of threaded connection necessaryto provide the requisite fixing.
• All bolts in the system must be checked to ensure they are in place and correctlytightened.
• Refer also to notes dealing with fixing anchorages in general, Section 5.2.
5.10 CIRIAC543
-.
-.
-.
--.
--.
--.
-----.
--.
---.
-.
--.
5.5
5.5.1
CIRIAC543
PARAPETS
Preamble
A parapet is a restraint system generally located on the edge of the bridge to protectpedestrians and errant vehicles.
At the time of carrying out the design of a bridge deck, it is likely that most of the factorsrelated to the chosen parapet system will have been established, eg the class ofcontainment required, height and structural form. The designers should be aware of twodocuments that will assist in understanding how the factors were developed.
1. British Standard BS 6779, Highway parapets for bridges and other structures (40).
2. DMRB Standard BD 52/93, The Design ofHighway Bridge Parapets (41).
In the UK, parapets are known by their DMRB group designation, summarised as Table 5.1.
Table 5.1 Summary ofparapet group designations
Group Application Typical location Level of containment
PI Vehicle Motorway Nonnal
P2 Vehicle/pedestrian All-purpose road Nonnal
P4 Pedestrian etc Footpath and bridleway Low
P5 Vehicle Railway overbridge Nonnal
P6 Vehicle/pedestrian High-risk High
Three structural forms are currently used on UK motorways and trunk roads: galvanisedmild steel, aluminium and concrete. Section 5.4 discusses other forms of parapet.
The two publications mentioned above identify how each type behaves at impact andhow different structural forms can be used on the same structure.
Preserving the integrity of the parapet system is a major issue for the bridge owner ormaintenance authority, so a method covering the future inspection, maintenance, repairor replacement of any damaged components that make up the system must be determinedduring the design stage.
Provision for thermal movement of the bridge parapet needs to be considered at an earlystage of the design and detailing.
All parapet systems, except pedestrian parapet (P4), require special end treatment toprotect the road user against impact or impalement. This will normally take the form ofsplayed ends to unprotected metal rails and safety fencing on approach and egress.
5.11
5.5.2 Metal parapets
Metal parapets systems normally used in the UK are constructed from either galvanisedmild steel or aluminium.
Systems using either material are supplied in component form for assembly in their finalposition on the deck. Each should, preferably, be secured to the deck using the cast-incradle anchorage system and bedding (see Sections 5.2 and 5.3).
Because of the many fastenings involved in a metallic system, the matter of galvaniccorrosion, caused by the electrolytic action of dissimilar metals touching, must beconsidered early in the design and detailing stage.
Other concerns that the designer and detailer must consider with metallic parapets arelisted below.
Galvanised mild steel
• One ofthe most serious problems associated with galvanised steel parapet systems isthe entrapment of water inside a RHS (rectangular hollow section). This may resultfrom the drain holes or galvanising breather holes at the base of the section havingbecome clogged. Apart from corrosion, the winter period freeze/thaw cycle of thetrapped water can cause swelling or distortion of the RHS resulting in possiblesplitting and loss of strength. This matter should be raised when the order is placedwith a manufacturer.
• The paint protection system needs a particular specification appropriate to newgalvanised surfaces.
Aluminium
• The lightness of the metal and the ease with which it can be cut makes theft ofaluminium sections or components a real danger. One way of combating the theft isto camouflage the aluminium with paint. Fewer coats are needed than for steelbecause it is not for protection
• the long-term effects of oxidation of the metal can affect the mode of failure,particularly if hidden from the effects of regular washing by rain
• there is a limited number of aluminium fabrication specialists and this may affect thecompetitiveness of the material in local areas.
5.12 CIRIA C543
------------
5.5.3
Detail 5.5.3-1
Concrete parapets
Concrete parapets are mostly used where a high degree of vehicular containment isrequired, ie road over railway or road over valleys, and are therefore likely to be a P5 orP6 designation. They can be formed in situ as part of the bridge deck or can be precastand attached to the deck by bolting or stitching. The principles applicable to parapetbeams (see Section 3.1.8) also apply.
Concrete parapets need to be able to provide the required vehicle containment withoutdoubling as a main structural member for the bridge (BD 52/93 (41)). To avoid the cross
section of in situ concrete parapets attracting longitudinal stress and affecting the stressdistribution through the main structure, vertical joints through the parapet are oftenintroduced, usually at centres not exceeding 4.5 m. These joints are normally designed totransmit shear between panels, thereby providing continuous shear resistance along thewhole length of the parapet. Where joints are not provided, the bridge design needs totake account of the parapet's interaction with the main bridge cross-section, includingthe effects of differential shrinkage.
Precast concrete parapet units can be heavy and unwieldy items and will require amethod of lifting and manoeuvring to be determined during the design stage. There willalso be a need to provide a stable temporary support during the final adjustments to thevertical and horizontal alignments. Some typical fixing details are illustrated in CIRIAReport 155 (3), Chapter 5, Figure 5.3. Ifa precast anchored system is the chosen formthen care must be taken to provide accessibility to the permanent fixings for inspectionand maintenance.
Concrete parapet - in situ
------------
REMARKS
CIRIAC543
•
•
A parapet or safety fencing is required on the approaches to the ends of a concreteparapet.
Where metal parapets are used on the approach, the type of parapet must be confirmedduring the design and detailing stage, or provision must be made to accommodate thevarious parapet options.
5.13
Detail 5.5.3-2 Concrete parapet - precast
3.1.4-1
Precast
Seating seedetail 5.5.3-3 -------;----,
(iI II I1 I
I II 1I II II II II II I
II/[
3.1.4-=.,3~=..-__- /1/ I
~<:::=-o:::=::::..~~~~~-\=-~---;7f - ---j
// I II / I I
~*~~ ---....---L- --1--1F ----~- 1-71-----1-------- 1 I
_~_ _ ~ II II IL~3.1.4-2
REMARKS • Using an in situ concrete stitch (forming a lapped link between continuity reinforcement)avoids the problems of corrosion and maintenance of other forms of connection.
• Where adjustable anchor bolts are not provided the levelling and alignment of theprecast units, relying solely upon bedding to level, needs greater attention.
• Lifting eyes need to be designed and detailed to suit the erection method.
• Lifting eyes in the precast units should be retained and protected against damage andcorrosion for future use when replacement of a parapet unit is needed.
5.14 CIRIAC543
---
Detail 5.5.3-3 Precast concrete parapet - seating
----
Rubber seating strips10mm thick, bedded tocorrect line and levelon 5mm thick cementg ra ut ------, r-+-+-Precast
concrete
Stainless steel plates200X 1OOx5 positionedeither side of parapetjoint ond bedded tocorrect line and levelon epoxy mortar ------, r-+-+-Precast
concrete
-(A) (8)
- Precast concrete
Bolts in cast in socketsto level precast unit base
Compression seal ta controlbedding grout leakage
(C)
Continuous bedding groutpoured after precast unitspositioned to line and levelon levelling screws
r/("=-=-=-=-l,II I I I"-------
f---~..L.- - - - -1--'==tF=:=:==~fPI'il
___~ Deck slab L_
--
-
--
-PREFERRED.-
----
REMARKS •
•
•
•
Simplicity of rubber seating strips, Option A, which provides better tolerance of seatingirregularities, is preferred.
Upper surface of seating plates must be in line and parallel with the longitudinal,as-designed, finished surface of the concrete deck.
Re-adjustment of alignment of precast units may be necessary to produce a straight lineand smooth level changes.
Where pressure grouting of the underside of the precast units is required, edges of gapwill need to be grout-sealed.
For temporary stabilisation, see Detail 5.5.3-4.
--
CIRIA C543 5.15
Detail 5.5.3-4
PREFERRED.
Precast concrete parapet - temporary stabilisation
Precast concrete
70
Pocket for temporary stabilityfilled with shrinkage compensatedhigh strength flowable repairconcrete
rf -=- -=- -=--=-lI ('-L ~ IJ----------+-- 60 dia. plastic
~__"- -J- Ii---=:d:~!:::::======" sleeve in precastL unit
___ ~ Deck slab
'0' dia. x 's' long.H.Y. reinforcement barthreaded to receive 'W'x'W'xl0thick m.s. washer plateand nut
Resin fixing of bar in'H' dia. holes 'L' deep
Stability provided by anchor studs into the deck slab (typical detail shown) is preferred.
REMARKS
5.5.4
5.16
•
•
•
•
Precast concrete parapet units are unstable, or close to unstable, when placed. Meansmust be provided to ensure they are stable during construction.
Stability can be provided by counterweighting, anchoring to the deck slab or use ofhorizontal/inclined ties.
Dimensions D, H S, Land P, diameters of stud and of hole, length of stud and of holeand projection of stud. Values to be chosen to be compatible with designed temporaryforces, thickness of deck and centres of anchorage.
Dimensions of plastic sleeve, washer and pocket for nut are typical and may need to bechanged to suit actual project requirements.
Other forms of parapet
There are situations where a non-standard form of parapet may prove acceptable.However, this has to be agreed with the Technical Approval Authority. Such a situationmight be in an environmentally sensitive area and/or in a location where resistance toimpact is not critical. The following forms of construction could then be pursued further:
• masonry or brickwork
• reinforced brickwork
• brick-faced reinforced concrete wall
• timber
• tubular hand railing.
Where vehicle access is possible it is likely that a safety fence, barrier or kerb would alsobe installed to give the necessary degree ofprotection to both pedestrians and parapet.
The list of non-standard parapet options mentioned above is not meant to be exhaustive;others may be devised to suit particular situations. Their fixing to the bridge deck canbest be established at the time of design once the parapet form is known.
CIRIAC543
Safety fences on bridge works are normally found in three locations:
SAFETY FENCES
-----
5.6
••
•
in the central reserve separating the carriageways
leading on to and away from the deck parapet system to avoid end-on impact andaid redirection of errant vehicles
in a position to deflect vehicles away from piers and abutments.
Safety fence fixing - on bridge deck plinth
The designer should refer to DMRB documents TD 19/85, Safety Fences andBarriers (42), and TD 32/93, Wire Rope Safety Fences (43), for details of the sections
used for the fences and posts.-,---
----
Detail 5.6.0-1
Typical proprietarycradle anchorage
Standard ·Z· section post shownfor open box beam safetyfence
1OOx65x 7 angle weldedto post as baseplate
Waterproof membraneand protection
Section A-A
v
-;>
-- PREFERRED.
v
Plan
Cradle anchorages for new works.
-• Plinth as base for fixing to avoid holes in waterproofing. This also assists in providing
adequate depth for anchorages if in a thin slab.
REMARKS • Mortar bedding optional assuming stainless-steel bolt used.
-CIRIAC543
• Size of plinth may be affected by anchorage type.
• Continuous plinth allows easier adjustment to location of fixings.
5.17
Detail 5.6.0-2 Safety fence fixing - over waterproofing
Typical proprietarycradle anchorage
---
Standard 'z' section post shownfor open box beam safetyfence
100x65x7 angle weldedto post as baseplate
3.1.4-33.1.4-2
Waterproof membraneand protection
A
Section A-A
"II"II
Plan
A'f
REMARKS
5.18
•
•
Anchorage cradle to be positioned so that the top of socket is at top of surfacing.
Waterproofing membrane to be dressed carefully around the sockets.
CIRIAC543
---.-
-
-.
--.
-.
5.7
Detail 5.7.0-1
LIGHTING COLUMNS
Every effort should be made at the design stage to avoid the need to have lightingcolumns on a bridge. If this is not possible then they must be located behind a protectivebarrier. This may require the safety fence post spacing to be locally reduced.
Lighting column position - at edge of bridge
of lighting column
Lighting column behindmetal parapet on corbel
-.
--
REMARKS ••
•
Protective barrier may be a safety fence, vertical concrete barrier (VCB) or parapet.
Whichever system is used there must be the full design clearance between the barrierand the lighting column to allow for the anticipated deflection under impact.
With the lighting column on the edge of the structure behind the parapet this willnormally require the parapet beams to be corbelled, locally, to receive the lightingcolumn, see Detail 5.7.0-4.
- • Any corbelling required should be of a size that assists access for maintenance.
• Avoid having the metal parapet post and the lighting column in the same transverseposition.
-.
---.
-----
CIRIAC543
•
•
Ensure the lighting column is aligned such that its maintenance door can be opened,and in a direction appropriate for maintenance access.
Ensure the lighting column maintenance door has a safety chain attached to stop itfalling and creating a hazard below.
5.19
Detail 5.7.0-2 Lighting column positions - in median
of lighting columnDetails ofreinforcement andfixings omittedfor clarity
.'.. " '."
~ of lighting column
:.; ... ~ .. ,:'. . .. .... ;..
~~••:"". ....:.'-'.". ·~··.•:·c..··~ : :::: ,.,.•• .;,. • '." •••• ... ._~ -.' '. of ... ". • ..
Lighting column fixedto parapet beam usingapproved cradle typeonchoroge. see detail5.4.0-2 ----"\
Lighting column behind safetyfence in median
Lighting column above verticalconcrete barrier
(A) (8)
REMARKS • Where column is above a VCB or on a high foundation above the main impact zone,ensure it is set back sufficiently to avoid residual impact (from vehicle superstructures).
5.20 CIRIAC543
--Lighting column and draw pit - in median
I I I
I I II I I
.. I I.. ,
A
Lighting column base
uPVC pipe radiusbend to suit diometer ofpipe, space available andcoble requirements ---,
I
uPVC ducts to BS 4660
Detail 5.7.0-3
-
--
-
--
-
--
-
--Drawpit at lighting column on bridge deck upstand
------
Cf. LIGHTINGCOLUMN
For anchoragesee details 5.2.0-1and 5.4.0-2
Removable lockable(anti-vandal) cover
• Duct bend must be a radius bend. Check that the radius is suitable for the cable.
------
REMARKS •
•
•
Section A-A
A wide slab is shown. Where a discrete plinth is used, do not skimp on the plan size ofplinth - the bigger the better.
Duct should project above top of slab or plinth to avoid getting grout into it.
Designer should draw large-scale details to demonstrate path of ductthrough reinforcement and cover to reinforcement.
-----
CIRIAC543 5.21
Detail 5.7.0-4 Lighting column and draw pit - at deck edge
90mm i/d upvc duct, withradius bends for lightingcolumn supply.
-4--':"---':":'_'/ '_' _ --:- ~<:1-.- '_~ PI,-====*"
Section D-D
ooo
LiQhting column fixed to parapet beamusmg approved cradle type anchorage.see detail 5.2.0-1----------------t-h
50mm i/d upvc ductfor lighting cable. ~
'C' x '0' cable junctionbox. all duct/junctionbox connections to besealed with approved sealant.
50mm old upvc ductfor lighting cable.------,.
Cable junction box with'A' x 'B' galvanisedmild steel lockable cover setan 50mm x 20mm rebates.
---~I- --<t, parapet post
------f-°o<0------1-
<0 °
- --<t, parapet post
/fo
Detail of lighting column corbel
REMARKS • Dimensions A and B give overall size of draw pit cover.
• Dimensions C and D give internal size of draw pit/junction box.
• Avoid positioning parapet post next to lighting column. See Detail 5.7.0-1 for otherpositioning requirements.
• Corbel and deck cantilever need to be designed and detailed to resist ultimate failureload of column to ensure structure is not damaged if a large vehicle strikes the column.
• Waterproofing to be dressed around duct where it enters the plinth.
5.22 CIRIAC543
5.8
CIRIA C543
SERVICES
It is important for the designer to identify at an early stage those services, if any, that willneed to be carried by the bridge and how they are to be accommodated. These can be:
• in the verge
• in a scrvice bay/trough
• cast into the deck or in a void in the deck
• attached externally to the bridge generally between the beams in a composite deck.
Services carricd on bridge decks must always be accessible for inspection or
maintenancc. However, statutory undertakers and other service providers invariablyrequest their apparatus be hidden from view as a precaution against vandalism.
Where more than one service is to be carried in a service trough or duct, then positionsrelative to each other must be discussed and agreed by the providers concerned, thebiggest concern being the close proximity of a gas or water pipe and electric cable. Apartfrom these, most other services can sit safely in the same trench, although working spacearound each service is usually mandatory.
Where services cross a movement joint the designer needs to consider the necessaryaccommodation of a similar movement within the service itself or its duct. Alternatively,the service could pass beneath the expansion joint off the deck where the movement canbe accommodated. Provision for road network communication cables sited in verges ormedians should be anticipated by the designer on all bridge decks carrying major roads.
In conclusion:
• attempts should be made to persuade the utility authorities to install their servicesbelow the ground. The presence of services in the deck seriously interferes withfuture maintenance of waterproofing and increases costs
• services should, where required to cross the bridge, preferably be located in thedeck or externally (generally only acceptable between beams).
Gas mains should not be cast in. Water mains should only be cast in if the pipe is carriedin a continuous duct throughout the bridge. Therefore:
• neither gas nor water should be placed in voided concrete slabs
• if pressure mains are located in a trough or verge and need a bolted fixing thisshould only be allowed if plinths can be formed at cach fixing into which thewaterproofing can be dressed.
Utilities have a right to be in the highway and a bridge is part of the highway. There arefive main problem areas arising from services in bridges:
• they inhibit/prevent acccss for maintenance and inspection
• they give problems at movement joints
• ducts carry water and any sumps should be located at the uphill end ofthc bridgedeck to avoid the need for water to drain through the ducts on the bridge
• service bays, being often granular-filled and unprotected, fill up with water unlesswell drained
• damage is caused when services are worked upon.
The designer needs to cover all these issues.
5.23
Detail 5.8.0-1 Services siting -location
Surfacing to footway
Services3.1.7-2 Infill material
Services sited in verges
Precast slab
Infill material
Surfacing to footwcy
.~.
..~
Drainage outletta bearing shelf
3.1.6-3
Mortar filletsee detail 3.1.4-2
31.4-3
d I
REMARKS
5.24
•
Services sited in service trough
Refer to Sections 3.1.7 and 4.9 for various treatments at verge.
CIRIA C<;113
Detail 5.8.0-2 Services ducting at movement joint - range 0 mm to 10 mmtotal
CIRIA C543
, "
BALlAST, WAL}.- •
:
I
r JOint with compression sealin duct or droinage pipe
...'.
• QECK/'OIAPHRAGM... .
I
I
I
I
5.25
Detail 5.8.0-3 Services dueting at movement joint- range 10 mm to 20 mmtotal
Joint shownhatched
Joint cover (see 3.1.9-6)not shown for clarity
Services must passunder or through anyexpansion joint present
A
Typical edge detail at expansion joint
Concrete vergenfill
with 2 layers0' tope both
Joint in verge& c/w over
int width -1 this width (500)Sealedof 'Dens
V ends.
7, .'.
'> Ir -<j' J
.. ' c.~ .
/ . -/ - ~. .~
. -.e Ii\
in/
i
Plastic plocollar to suit pipelubricated with greose
100 outside of
jo
Concrete verginfill
Section A-A
REMARKS • This detail is appropriate to small-diameter services, eg telecom and electric. See alsonotes on Details 3.1.9-2 to 3.1.9-4.
• This detail is limited to a movement of 20 mm total.
5.26 CIRIA C543
Detail 5.8.0-4 Services ducting at movement joint - range 20 mm to 40 mmtotal
Duct/drainage
expansion cnit
Protective sleeve
Cold poured sealat ends
Special prefabricated ~M====t~~~~~~t:j==tJ:j===Iunit capped off untilduct sold or used.
.• 0 .' ".
": Waterproofing
ABUTMENT BRID,I.;E DEC~ •
Duct or drainage pipeMovement joint unit at position in verge
r Protective sleeveabutment side of joint.
." "
'0' ringneopreneseals
".
Service ductsin footway
20mm wide expandedpolyethylene and15mm deep rubberbitumen seal
Temporary pipecapping
End ofwing wall
ABUTMEN, •., <l .4
ElRIDGE DECK.,
Duct movement jointOuter duct in abutment only
CIRIA C543 5.27
Detail 5.8.0-5 Services ducting at movement joint - range 40 mm to 50 mmtotal
wing wall
'0' ringneopreneseals~-
Temporary pipecopping
Service ductsin footway
ABUTME~T •
." '.
-?rotective sleeve debondedbridge deck side of joint. Sleevelength 1000mm equal aboutjoint centre line,
20mm wide expanded polyethylene and15mm deep rubber bitumen seal
ElRIDGE DECK
Duct or drainage pipe
Ducts beneath footway
Duct/drainage expansion unit---1----------------
Protective sleeve
Cold poured seaat ends
.' '.
- Expansion unit toduct connector
100Vl UPVCduct
Expansion unit withwatertight seals
5,28
Ducts in verge
CIRIA C543
Detail 5.8.0-6 Services - movement joint
Manhole
No finesconcrete
Expansion
Pipe sleeved throughwall and sealed -------'
Granular filterdrainage material -----J
Off deck
Service in trough
PREFERRED • Expansion unit for service to be off the bridge superstructure and behind the abutment ina purpose-made chamber.
AVOID
REMARKS
CIRIAC543
•
•
•
•
It is preferable to avoid incorporation of major services within bridge superstructure.
Both bridge owner and utility owner will have input into choice of detail. The utilityowner's interest is mainly in the movement and the bridge owner's in the effective sealing.
Where services are carried on the superstructure, care must be taken to establish whichservices can co-exist in the same access chambers.
Sleeves and holes are to be of sufficient size such that they do not obstruct the passageof the pipe flange.
5.29
6
6.1
Support structures
GENERAL
This chapter deals with elements that support the bridge superstructure and is divided into:
• end supports
• intermediate supports
• bearing plinths and downstands
• access to bearing shelves
• drainage of bearing shelves.
Most of the details that follow are considered to be applicable to bridgeworks in both
concrete and structural steelwork. Readers should refer to the relevant sections for the
individual bridge types. Appropriate cross-references arc made to other parts of the guide.
The details to be found in this chapter are as follows:
CIRIAC543
6.2.2-1
6.2.2-2
6.2.2-3
6.2.2-4
6.2.2-5
6.2.2-6
6.2.3-1
6.2.3-2
6.2.3-3
6.4.0-1
6.4.0-2
6.4.0-3
6.4.0-4
6.5.0-1
6.5.0-2
6.5.0-3
6.5.0-4
6.6.0-1
6.6.0-2
6.6.0-3
6.6.0-4
6.6.0-5
6.6.0-6
6.6.0-7
Abutment - bank seat 6.3
Abutment - cantilever wall 6.4
Abutment - skeletal/spill-through 6.5
Abutment beam/spill-through pier - relative dimensions 6.6
Abutment - diaphragm wal!... 6.7
Abutment - drainage at embedded cantilever wall 6.8
Paving to slopes beneath superstructure 6.9
Abutment - wing wall 6.10
Abutment - wing wall internal angles 6.10
Bearing plinth at abutment - dimensions 6.13
Bearing and plinth 6.14
Bearing plinth reinforcement 6.15
Bearing plinth at discrete column 6.16
Maintenance platform - dimensions 6.18
Abutment gallery - dimensions 6.19
Access positions 6.20
Abutment access from front 6.20
Bearing shelf - drainage 6.21
Bearing shelf drainage - channels 6.22
Gallery - subsurface drainage collection and piping 6.22
Gallery drainage exit route - side exit 6.22
Gallery drainage exit route - level bridge soffit 6.23
Gallery drainage exit route - bridge soffit on crossfall.. 6.23
Drainage exit route - discharge recess 6.23
6.1
6.2
6.2.1
6.2.2
6.2
END SUPPORTS
Preamble
Structural details for end supports need to provide for interaction between soil andstructure. The strength of the design can be based upon the strength of the surroundingsoil with the structure designed to move with it (flexible or sliding design). Otherwisethe structure needs to be designed to resist all the forces, including those from theretained soil (rigid design). Many aspects of end supports are similar to those ofretaining walls and this section should be read in conjunction with Chapter 7.
Important aspects of detailing for the various structural forms of end support (commonlycalled "abutment" on conventional bridges) are noted with the details that follow.Abutment galleries for access are dealt with in Section 6.5.
Further discussion of end supports where they are used for integral bridges is to be foundin Chapter R.
"Run-on", or "approach", slabs are sometimes considered necessary where settlement ofthe backfilling behind the abutment wall is anticipated or is a potential risk. Details ofrun on slabs may be found in Section R.5.
Abutments
The details available for this section show a bank seat, a cantilever (full-height) wall, askeletal and an embedded wall abutment. Embedded walls can be of diaphragm walling(such as shown in Detail 6.2.2-5) and also of contiguous or secant piling for lighterbridging. Steel sheet piling or strengthened or reinforced soil may also used in abutmentconstruction, but these are most effective in conjunction with a small bank seat.
Some details in Chapter 7 show capping beams for steel sheet piling walls. Thesuitability of sheet piling for the particular environment needs careful considerationbefore they are adopted. Reference should also be made to the Steel ConstructionInstitute publications.
Basic types of reinforced soil wall are illustrated in Section 7.5. The bank seats that theywould support should be limited to those that incorporate bearings. The constantmovement ofthe bank seats of integral bridges can cause problems for reinforced soi I.
The detailing of all end supports needs to take account of tolerance and seasonalvariations in the bridge superstructure length.
CIRIA C543
Detail 6.2.2-1 Abutment - bank seat
70mm nominL joint
Upstand formovement joint
Parapetbeam
Maintenance platformsee detail 6.5.0-1
Screen wolj
////
--F:::;;z==:E=::s;;:==r=P~-"-- - ~;.L --- -
730
Wingwoll
~--+---+--Abutment gallery,5.4.0-1 see also detail 6.5.0-2
Blinding
Access floor aroundend of bearing she~
(see detail 5.5.0-4)
REMARKS • Front and back faces of abutment should be kept parallel to ease reinforcementdetailing, and reduce formwork and construction costs,
• The dimensions at the top show a typical way of achieving the required gallery sizeshown in Detail 6,5,0-2.
CIRIA C543 6.3
Detail 6.2.2-2 Abutment - cantilever wall
<t Bearing
.5.0-2Deck outlin
// I
\l/~:~""m,,,,". ooW".oI to rear of abutment
IIIIII
6.4.0-1
7.2.2-4
-y---Blinding
7.2.2-3
REMARKS • On smaller abutments the general preference is for the back wall of the abutment behindthe gallery to follow straight down to the top of the foundation slab (see alternativeoutline shown).
• Where abutment gallery projects out from back of abutment wall below, placing of backfilling and drainage layers can be improved by providing a splay beneath the abutmentgallery projection (see alternative outline shown).
• Depending upon the bridge and embankment construction sequence, the abutmentgallery can be constructed using the fill and blinding as the soffit shutter.
• Water from bearing shelf to be piped to primary drainage system.
6.4 CIRIA C543
Detail 6.2.2-3 Abutment - skeletal/spill-through
I I I Finished groundlevel
Superstructure
Edge beam coping---,
6.6.0-1
Superstructure not shown
--I T--------iI I II I I II I i I I II I I II
-_: jL-------ltL- l
================J
Front elevation Elevation on end
~rT
6.2.3~f'\ III
~ I---~ ~----------;=: ---h
I I I I I
'm' Ir-c-- Ib1=
-<
Plan
REMARKS • The purpose of this type of abutment is to reduce the horizontal longitudinal forces fromthe soil on the abutment or to provide an economical transfer to the foundation level oflarge anchorage forces.
• The pier cross-section (for rigid design) is often rectangular with a sloping front face toprovide increased width of pier at the base necessary for appropriate increased designstrength and stability. The pier cross-section can also be circular (usually for flexibledesign).
• Where top and bottom are connected by a sloping face, the slope is best kept steeperthan 1:6 to reduce formwork uplift problems during casting.
CIRIA C543 6.5
Detail 6.2.2-4
Abutment beam
Abutment beam/spill-through pier - relative dimensions
Abutment beam
100 setback
(A)
100100 setback
Rectangular pier withsloping front face
Pier shape may becircular or rectangularor could be isolated piles.
(B)
100
REMARKS
6.6
• Incorporate set-back dimensions (minimum 100 mm) to avoid clashing of reinforcement.
CIRIA C543
Detail 6.2.2-5 Abutment - diaphragm wall
rt Bearing
~~-
T-Sectiondiaphragm wall
:V Concrete
IIII
r--
wall
-- - - -I- - - --R.C strut
v v
REMARKS
CIRIA C543
•
•
•
A T-section diaphragm wall is shown. The detailing principles apply equally to plaindiaphragm wall, contiguous piled or secant piled abutments.
The capping or abutment beam should only be cast after compaction of backfill iscompleted.
Exposed surfaces can be faced with sprayed concrete or screened with a separatesystem.
6.7
Detail 6.2.2-6 Abutment - drainage at embedded cantilever wall
Bridge superstructure
Access to gallerythrough manholein footpath adjacentSee Detail 6.5.0-3 ---f'......-f-h
Abutment gallerydrainage tomanhole athigh levelsee detail 6.6.0-1
Na fines concreteon front facebetween piles aspermeable layer
75
Pile cut offlevel
{
ContiguousPiling or
secant -------~\ordiaphragmwalling
Selected facintied back to wallform
Access hatch formaintenance ofdrainage collection
100mm dia ----t---H-It
drainage pipewith mesh cover
Crash wall tiedto diaphragm wall
Verge Carriageway
Gully grating withshutter connector
Drainage
REMARKS
6.8
•
•
Selected facing cauld be built off a beam at ground level. Facing would need to beprotected by safety fence in verge (see example in Detail 7.3.0-1A).
Reference should also be made to Sections 7.2 and 7.3, particularly with respect towater collection and discharge.
CIRIA C543
6.2.3
Detail 6.2.3-1
Wing walls and slopes
Where abutments are not ful1-height vertical walls the embankment or cutting will slope
up towards the bearing shelf. It is not possible for vegetation to grow satisfactorily on
slopes that do not have the benefit of sun and rainfall. The surfaces will need to be paved(see Detail 6.2.3-1 ).
Walls extending alongside the abutment (wing walls) will retain the soil supporting theapproach road and form the transition between structure and natural ground. Settlementof these slopes is common and it is important that the walls penetrate sufficiently deeply
below nominal finished ground level to avoid their being undermined (see Detail 6.2.3-2).
Paving to slopes beneath superstructure
~ Typically 50 thk. precast
Abutment---1O-+-~='i-'7~,-,=e.....,-J carcrete paving slabs
face - ISlabs or open blockwork
Vergeconstruction
20 thk. sand carpet
150 thk. sub-base
Reinforced concretesupport beam
REMARKS
CIRIAC543
•
••
•
For dimensions of maintenance platform, see Detail 6.5.0-1.
Where solid slabs are used the sub-base should be a lean-mix concrete.
The edges of both the maintenance ledge and the embankment slabs should be finishedwith a side edging. Such edging can take the form of precast concrete blocks with achannel formed in the top face to guide discharged abutment shelf drainage towards andinto the main highway drainage system.
On slopes adjacent to the bridge the designer may wish to promote the use of a slabtype that can be soiled and seeded, thus allowing grass to grow. In this case the subbase should be complementary to this course and allow adequate drainage to occur.
6.9
Detail 6.2.3-2 Abutment - wing wall
1m to 2m
500 min.cover
Soffit linewall fixeddesign
Fillet seedetail 6.2.3-3
Elevation on wing wall
.....-+-+-- Masking walloptional
or wall
REMARKS • Adjacent to the end of the wing wall, earthworks tend to settle and get rounded off. Thewing wall should therefore extend at least 1 or 2 metres beyond the theoretical top of theslope, as shown, to ensure end of wing wall is well into the ground on approach.
Detail 6.2.3-3 Abutment - wing wall internal angles
ooill
600
Fillet not needed toenable backfilling tobe completed. but maybe needed structurally
\
Less than 90 0
Sectional plans
Greater than 1200
REMARKS
6.10
•
•
Fillets are incorporated to prevent design reinforcement being bent through an angle ofgreater than 90 0
.
A fillet allows compaction against the vertical face.
CIRIA C543
6.3
CIRIA C543
INTERMEDIATE SUPPORTS
Intennediate support is the tenn applied to all piers positioned between the end supports
(abutments) that define the spans. They comprisc one or more vertical load-carryingmembers. Such members may take the fonn of columns (plan dimension ratio less than4: I) or walls (plan dimension ratio greater than 4: I) with plan shapes either circular.
rectangular or other faceted dcsign to create a pleasing aesthetic effect. Construction canbe in steel or concrete or a combination of both.
Support can be provided to the superstructure either:
• through proprietary bearings. or
• by connecting support and superstructure monolithically.
Bearings permit the thennal and f1exural movements to take place with a designed
degree of restraint. If the connection is monolithic the support must be designed and
detailed in a way that suits the articulation of the bridge integrating the rigidity or
flexibility of the other supports. They then need to be sufficiently strong to support thesuperstructure but be sufficiently flexible to pennit movements.
If bearings are to be used at intennediate support positions then a method of replacingthem must be established and recorded in the structure maintenance manual or health andsafety file (see Sections 2.2.2 and 2.5.3). When replacement is required the recorded
method is available to the maintenance contractor. If the contractor wishes to devise amethod of their own. they will need to supply proof to the bridge owner that the structure
will not be detrimentally affected. Areas adjacent to the actual bearing on top ofthe columnor pier can be designated as jacking areas and would need to be suitably reinforced to
allow this to occur. Other ways of providing jacking areas are to incorporate corbels on
the sides of the columns or piers or. alternatively. for the jacks to be supported ontemporary trestling erected on existing foundations.
Cross-heads. connecting across the tops of the supports. are needed where the positionsofthe superstructure elements cannot match those of the supports. Cross-heads can be
supported on bearings (an integral cross-head) or can, be part of the support itself andcarry the bearings. Built in cross-heads (without bearings) are also very efficient - forexample. see Detail 8.2.3-3 in Section 11.2.
6.11
6.4
6.12
BEARING PLINTHS AND DOWNSTANDS
Bridge design can involve large forces, both vertical and horizontal, being transferredbetween superstructure and substructure. Structural bearings provide the necessary load
transfer while permitting the designed movements unless the superstructure is "built in"to the substmcture.
The decision to incorporate bearings into the bridge articulation must, however, takeaccount of the fact that bearings generally have a shorter life than the structure and that
at some stage they may need replacing.
As discussed in Section 6.3, a method by which the superstructure can be supported
during bearing resetting or replacement must be established so that intended areas of
support during jacking can be adequately reinforced.
To assist in determining the condition of a bearing, noting its defects and then dealing
with them, adequate room for inspection and maintenance must be provided all around.
Headroom between soffit and the bearing shelf should be commensurate with installingand replacing the bearing, taking into account bolt lengths and direction of access formaintenance and inspection and for clearing drainage channels. To facilitate access,
there must be minimum headroom of 300 mrn between the superstructure soffit and the
abutment shelf or the top of column. The clearance requirement will vary as the width ofshelf varies (sec Detail 6.4.0-1). Smaller headroom is sometimes acceptable where front
and rear access is available, for example where discrete beams are used.
Other factors that can affect the headroom are the depth of the chosen bearing and the
positioning of jacks for future bearing replacement. Bearing plinths and deck
downstands arc ways of securing this adequate headroom. They also, together, facilitatethe mid-height positioning of the bearing, which is beneficial for visual examination.
Downstands are difficult and expensive to form and are rarely necessary solely for
seating the upper bearing plate. However, downstands do offer easier inspection of thebearings and reduce the required height of bearing plinth. Where downstands are
present, the same design considerations as for the lower plinth will apply. For columns
there are also aesthetic reasons that lead to plan dimensions of the soffit downstandpreferably mirroring those of the column.
Pockets for dowels or holding-down bolts are, generally, only required in the lower
plinth, as top plate fixings are cast in position with the deck or connected to a girder.
The way the bearing is orientated with respect to the plinth and downstand, as well as thedimensions of the top and bottom plates (if present) of the bearing, will influence theplan dimensions of the plinth/downstand.
CIRIA C543
Detail 6.4.0-1 Bearing plinth at abutment - dimensions
Centroid of plinth and bearing
Bearing down stands andplinths to be 'P'larger than bearing
Dimension depends onbearing selected
cE
N00'0
Back face ofabutment shelf
'y'
Table A
Dim 'y' Dim ·z'< 450 300
450 - 750 450> 750 700
---
Dimensions designedto allow access formaintenance ofbearings and drainagewhere access isfrom one side only
REMARKS
CIRIA C543
•
•
•
•
•
•
•
•
Dimension Z is crucial because it is needed to allow access around the whole of thebearing.
Where access is available from only one side, Dimension Z is particularly crucial to allowaccess to the bearing shelf drainage channel.
Relative dimensions for Y and Z given in the table allow access for arm, head andshoulders and whole person respectively, such dimensions being determined from theoverall width of the bearing shelf.
The dimensions need to satisfy requirements for allowing removal and replacement ofthe bearings with the minimal amount of vertical displacement from jacking and theprovision of jacking points.
Where access is available from both sides by virtue of a maintenance platform and anabutment gallery, the dimensions need to be considered in relation to the overall accessprovision and some reductions may be appropriate.
The required height can be provided by a supporting plinth, a downstand or acombination of both.
Refer also to Section 6.5 for relationship to other aspects of maintenance access.
Dimension P, defining size of plinth and downstand, value to suit particular bearings buttypically a minimum of 100 mm to 200 mm larger than bearing. See also Detail 6.4.0-3.
6.13
Detail 6.4.0-2 Bearing and plinth
Pockets for dowels or holding downbolts are only required in lower plinthas top plate fixings are cost in positionwith deck or connected to girder
~ ; ...- -.' ." . ~. ' ..
Tapered packs requiredfor levelling must beremoved and groutingcompleted as soon as
Bearing POSSible
r
!base Plate>
~-'"------'I... ' ·····r "]
Levelling screed orbedding mortarnominal 25mmthick (pourable)
Top of abutmentshelf, column orpier
Tapered packs
-------,-
Bearing baseplate
\ iii
~shim
High density plasticshim left in place
Length1-
Holes forlocation bo Its
cE
oo
Shape andpositions ofpockets to suitproposed bea ringand tolerances
Outline of lowerbearing plate
Dimensions to allow__f--C-I--_plinth reinforcementto enclose bearingfixings
Typical detail for in situ concrete or steel beam superstructures
REMARKS • Pockets could be rectangular on plan or alternatively be one large pocket.
• Pockets for dowels must be located inside reinforcement.
• Compressive zone within plinth to be contained by reinforcement.
• Must be sufficient clearance to remove bearing fixing bolts with minimal jacking.
6.14 CIRIA C543
Detail 6.4.0-3 Bearing plinth reinforcement
95Cover to reinforcement
,I'to comply with BO 57/
[.¥
C---' Lc~ -~
Links
ent
cketsbearing
ts locatedinside reinforcem
'--
7J' 0 0
B/0 0...
bars .// t--po
/ for
/ bol-U bors
u-
Plan on plinth Section B-B
If reinforcement is mildsteel the assemblycould be welded
BearingTypically baseplate60'r--~C==:::::':''---Bedding
}I i
/ ~corner bar must_L4~ _ lie outside of
45' line
Sectional plan C-C
REMARKS • Bursting stresses should be contained by suitable reinforcement.
• Reinforcement for horizontal loads and dowel actions of bolts and short fixing socketsmust be considered.
• Load distribution at 45 degrees must be contained within the plinth reinforcement.
CIRIA C543 6.15
Detail 6.4.0-4 Bearing plinth at discrete column
Deck downstand diMensionsmay be geared towardsbearing size
aa
Column
Bridge dec k soffitany slope in soffittoken out in downstandor bearing taper plate
Could besplayed
25mm nominal thicknessof bedding mortar tospecification clouse
Reinforcement to resistbursting forces isnecessary in the topof the column
REMARKS
6.16
•
•
Elevation
At the design stage, level X should be specified by assuming the suitable bearing withthe greatest depth. On site the depth of the deck downstand may be varied to fit thebearing actually used.
Bearings that are bolted to the column/deck should be so arranged that the bolts can beremoved and the bearing slid out of the gap with minimal jacking.
CIRIA C543
6.5 ACCESS TO BEARING SHELVES
The access requirements at abutments and bearing shelves relate to the need to:
• gain access around the whole of the bearing for ongoing inspection and maintenance
• clear out and maintain the drainage channel and outlet on the bearing shelf
• avoid the difficulties arising from the vulnerability of the faces of the deck end andback wall of the abutment to the corrosive effects of water and water-borne de-icing
salts filtering through the expansion joints and service ducts.
Access to the abutment and end support bearings can be achieved in various ways.
l. From a platform in front of the abutment (see Detail 6.5.0-1).
2. From a gallery located between the end of the deck and the back wall of theabutment (see Detail 6.5.0-2).
3. From ground level by means of a ladder or hydraulic platform.
4. A combination of I and 2, or 2 and 3.
The choice will generally be made on the basis of:
• the form of construction, eg whether the bridge has side spans with slopingrevetments and, if so, the length of the spans and steepness of the revetments
• whether the bridge lies on a routine winter gritting route and is therefore likely tosuffer the frequent application of de-icing salts with their deleterious effects.
SO 57/95 II) and SA 57/95 (KJ express a preference for access galleries. This provision
will allow space for inspection and maintenance of bearings, expansion joints, ballast
wall and deck ends in this highly vulnerable area. It is also expected to allow for theaccommodation and safe operation of any future form of deck jacking.
Smaller bridges with shallow superstructure depth (say less than 1000 mm) could have
their costs significantly increased by the inclusion of access galleries, however. An early
decision whether or not to include an access gallery is essential.
Important detailing issues include:
• Confined Space Regulations 1997
• emergency escape
• traffic management
• security
• drainage
• ease of access including any relevant safety equipment
• provision of lifting points where it is possible that equipment may need to be raised.
CIRIAC543 6.17
Detail 6.5.0-1 Maintenance platform - dimensions
Bridge deck
For abutment gallerysee detail 6.5.0-2
See detailno. 6.4.0-1
Bridge superstructure beams(where applicable)
1.5m to 1.8mclear headroomto deck soffit
Abutment I.) .5m minimum.. I
PREFERRED •
Section through maintenance platform
If the bridge has side spans and the revetment can be built to get to the requisite levelfor a platform, then a platform should be provided.
REMARKS
6.18
•
•
•
•
•
•
The height clearance should not exceed the dimensions given or this will necessitate aspecial ladder or platform for the inspector to see the bearings.
On construction using discrete beams the headroom clearance required is to the deckslab soffit, not the undersides of the beams, provided there is sufficient clearancebetween the beams.
The minimum width of platform of 1.5 m is to minimise the risk of people stepping backand falling down the slope.
Access to the maintenance platform should be from steps down from the road above orup from the road below.
If access to the platform is up a paved slope without steps then the slope and the pavedfinish must be suitable for use by maintenance staff.
See also Detail 6.2.3-1.
CIRIA C543
Detail 6.5.0-2 Abutment gallery - dimensions
AbutmentDeck
I
=flhiS depth to be keptto a minimum and Must
~l-.;;::-______ not be vertically aboveeither face of dec k orbock wall
For dimersion 'Z·see table ondetail 6.40-1
N
cEoo<D...L- _
2.5%
Looo](800 min.)
co 'Eo00 0~ 0
<D
_JOutlet through sidemasking wall topositive outfall
PREFERRED •
•
If the road carried by the bridge is on a regular winter gritting route it is essential that anabutment gallery is provided.
If there is no maintenance platform provided in front of the abutment. or if access to themaintenance platform is difficult or disruptive to provide, an abutment gallery should beprovided.
REMARKS
CIRIA C543
•
•
•
•
•
•
•
•
•
•
The primary purpose of the abutment gallery is to allow access for inspection andmaintenance to as large an area as possible of the end face of the superstructure andthe abutment back wall above the bearing shelf level.
The sloping soffits at the top of the gallery are crucial to ensure that the depth of thesurfaces that are only apart by the thickness of the expansion gap is an absoluteminimum.
The minimum depth of the gallery floor below the bearing shelf is to facilitate work on thebearings from the gallery.
Where the overall height of bridge superstructure is large. the relationship betweengallery overall height and bearing shelf height needs to be considered in relation to theoverall access provision.
800 mm is the minimum suitable width for working and should be provided over thewhole height of the gallery.
For choice of access provision, see Detail 6.5.0-3.
For Detail 6.4.0-1, bearing plinth at abutment, see Section 6.4.
Refer to Detail 6.5.0-1 for maintenance platform in front of abutment.
For drainage refer to Section 6.6.
For collection of sub-surface drainage refer to Detail 6.6.0-3
6.19
Detail 6.5.0-3 Access positions
Lockable access togallery through sidemaskirlg wall fromembankment slope
I--I DECK
L
Access to inside ofbox through trapdoorin soffit per span
Open access to galleryfrom maintenance ledge
REMARKS • When the choice of access is made, due consideration must be given to matters ofsecurity.
• Size of access to be decided following assessment of equipment that may need to becarried in.
Detail 6.5.0-4 Abutment access from front
Maintenance platform
I
Framed, demountable, stainless Isteel mesh security panels I
i(:: BridgeOutline ofbridge superstructure
Hinged, framed,locakable. stainlesssteel mesh panelscovering access toabutmerlt gallery
Finished ground level
Elevation on abutment
REMARKS • In detailing, care must be taken that hinged doors do not foul the various adjacentangled surfaces.
• Due allowance must be made for screens and doors to be compatible with the relativemovements between abutment and superstructure.
6.20 CIRIA C543
6.6
Detail 6.6.0-1
DRAINAGE OF BEARING SHELVES
A most important aspect of bridge detailing and maintenance is the management of water
that inevitably reaches the bearing shelf. Access must be provided to allow blockages to
be cleared and effective drainage to be maintained (see Section 6.5). Details 6.6.0-1 and
6.6.0-2 give guidance on the form of the drainage.
Bearing shelf - drainage
Fall--- Fall
Towards front
(A)
'-.. j.": .... ,
Towards back
(8)
PREFERRED • Both options are appropriate for particular circ*mstances.
REMARKS
CIRIA C543
•
•
Where an access gallery is present, the preferred position of the drainage channel is atthe back of the abutment shelf, which prevents salt-contaminated drainage waterrunning over the front face of the shelf.
Where an access gallery is not present, cleaning and maintenance is more easilytackled from the front and hence the drainage channel is best positioned at the front.However, where adequate clearance is provided between bearings, putting the drainagechannel at the front is optional.
6.21
Detail 6.6.0-2 Bearing shelf drainage - channels
Semi-circular
(A)
Splayed
(8)
PREFERRED •
•
•
Semi-circular drain channel, Option A is preferred.
Semi-circular shape is normally compatible with circular drainage pipes.
The shape former could be either plastic or salt-glazed wear and should also be left inplace as protection to the concrete.
REMARKS • Both shapes are easy to form, strip and clean.
Detail 6.6.0-3 Gallery - subsurface drainage collection and piping
Positivecollectionprovided
'-----+_ Outlet frombridge decksubsurfacedrainage
REMARKS • Gutter needs to be detailed to ensure that bearings are protected and the gutter iscapable of being cleared and maintained.
Detail 6.6.0-4 Gallery drainage exit route - side exit
6.22
flj:' '.": ..:'
,~ "; '~ .~
Rodding eye andpiped connectionto highway drainagevia precast concrete,channelled edging
"." ' .. ,' ..
p.e, channellededging
CIRIA C543
Detail 6.6.0-5 Gallery drainage exit route - level bridge soffit
mt-:'...;.'"'-'-'':-.""":...:'',",--,--_LEV,--E--,~~,D_,E-,-,;~,-K...;.",-,-,SO_.F,-F_IT_-,-_.~.. ,-.'_',-,-.i~~100mm dia, pvcpipes cast intoobutment anddischorging throughfront of abutment
ABUTMENT
Fall-Feature recessto containstaining. Seedetail 6,6,0- 7
Elevation on abutment
Detail 6.6.0-6 Gallery drainage exit route - bridge soffit on crossfall
ABUTMENT
Detail an facecould includea feature recessdischarging intaa channel or beconnected directly
to main drainage~JL ------------_.L.--
Elevation on abutment
Detail 6.6.0-7 Drainage exit route - discharge recess
10 deep
Pipes fromabutment shelfdrainage channel~
l ~ -\
Top ofmaintenanceledge withchannel..... '
Recess to containstaining frompipe
150
oIf)
oon-A-
Elevation on recess Section through recess
CIRIA C543 6.23
7
7.1
Retaining walls
GENERAL
This chaptcr deals with the types of retaining wall that can be expected to be used onhighway schemes. Some types may not be suitable for use on trunk roads or motorways.
Retaining walls can be broadly divided into the following forms of construction:
• cantilever
• embedded cantilever
• gravity
• reinforced soil.
The details to be found in this chapter are as follows:
7.2.1-1
7.2.2-1
7.2.2-2
7.2.2-37.2.2-4
7.2.2-57.2.2-6
7.2.2-77.2.2-8
7.2.3-17.2.3-2
7.3.0-1
7.3.0-27.3.0-3
7.3.0-47.4.0-1
7.4.0-27.5.0-17.5.0-2
Cantilever wall- cross-sectional shapes 7.2
RC cantilever wall- stem shapes 7.3
RC cantilever wall - with typical reinforcement.. 7.4
RC cantilever wall- stem base joint position 7.5RC cantilever wall- stem reinforcement 7.6
RC cantilever wall- coping 7.7RC cantilever wall- coping reinforcement.. 7.7
RC cantilever wall stem - movement joint 7.8RC cantilever wall stem - shear key 7.8
Weep hole 7.9RC cantilever wall - drainage measures 7.10
Embedded cantilever wall - drainage 7.13Steel sheet pile wall - capping 7.14
Steel sheet pile wall - capping at revetment 7.15
Steel sheet pile wall - revetment capping reinforcement 7.15Gravity wall- treatment at top 7.17
Gravity wall - coping provision for parapet 7.18
Reinforced soil wall- base 7.22Reinforced soil wall- coping 7.23
CIRIA C543
Construction of a retaining wall often interferes with the natural drainage of the soilstrata. There is always potential for water to build up immediately behind the wall in the
interstices of the soil backfill.
Even with an impervious clay behind the walL rainwater runoff has the potential tosaturate the back of the wall to its full height. Consideration needs to be given to the
effects of the trapped water, therefore, and an efficient dispersal system is usuallyincorporated into the construction.
7.1
7.2
7.2.1
Detail 7.2.1-1
CANTILEVER WALLS
Preamble
The fonn of construction covered in this section is where the vertical wall stem
cantilevers from, and is monolithic with, a spread foundation. The wall is free-standing
and its stability results mainly from the self weight of the structure and any pennanentsoil loading. "Inverted T-shape" and "L-shape" are popular ways of referring to the
cross-section of these walls; see examples in Detail 7.2.2-1.
Usually the material used for construction is reinforced concrete, allowing the wall to be
either cast in situ or precast.
The wall can have a concrete finish or be clad with another material such as brick ormasonry. Concrete finishes can be as-cast plain, patterned, coloured or specially treated;
the designer should refer to the Concrete Society report on concrete finishes.
Cantilever wall - cross-sectional shapes
(A) (8)
_ Orig~a-'-- g.J.:
(C)
REMARKS:
7.2
••
•
•
•
Dow nstand keyto improve slidingresistance if required ---L -----1
The choice of shape of wall will be dependent upon design considerations.
Option A is more suitable for supporting the sides of an excavation.
Options B or C are preferred for retaining embankments.
Provision of a downstand key is not preferred because the excavation for the downstandwill expose the surrounding soil to potential deterioration from the effects of weather,which would result in reduced resistance to movement.
Possible downstand key for Option A is shown positioned directly beneath the wall stemto simplify reinforcement detailing and reduce the risk of undermining the excavatedslope during construction.
CIRIA C543
7.2.2
Detail 7.2.2-1
Reinforced concrete wall stems
The stem of a cantilever wall is a highly visible structure. It should therefore have
acceptable appearance as well as provide the primary structural strength and be durable.The chosen shape should minimise construction difficulties.
High walls need their greatest strength at their base where, generally, greater thickness is
provided. A stepped thickness wall has not been shown herc in favour of the tapered wall
stem for high walls.
RC cantilever wall - stem shapes
J
I
(A)
I I
(8)
I
REMARKS:
CIRIA C543
•
•
•
•
•
•
Constant wall thickness, Option A, allows easier formwork details and the reinforcementcan be fixed and checked more simply.
Option A is best suited for walls up to about 5 m in height where an illusion of toppling ofvertical faces is not perceived.
Sloping-front face, Option B, is better suited for walls more than 5 m high to counter theillusion of toppling if vertical. It also uses material more effectively and economically,with the gradually increasing strength towards the base matching the increasing bendingmoment and shear force.
Sloping formwork for Option B can create geometrical (plane) problems if height varies.It is expensive to construct, particularly if the wall is curved on plan, as this requiresformwork panels with a conical face.
RC cantilever walls are suitable for high, multi-lift, walls but require care at horizontalconstruction joints, where feature recesses should be considered.
Counterforts or buttresses may be required where the wall height exceeds 10m.
7.3
Detail 7.2.2-2 RC cantilever wall - with typical reinforcement
7.2.2--5 and ~
7.2.2-6
U-bars shape codeinto coping
Minimum lap
7.2.2-3 -
U-bars shope code 38help to stiffen topof cage
-- Wall reinforcement supportedon kicker on both sides
Tension 10
Shope code 55 givesvertical dimensionolaccuracy to cage duringconcrete pouring
Possible lorgeradius bend
AVOID
REMARKS
7.4
•
•
Fixing reinforcement into a concrete pour where it is "cover critical" in the next pourshould be avoided.
In the UK it is usual for vertical and top horizontal surfaces of reinforced concrete belowground level to be given a waterproofing treatment. This treatment, to improve theresistance of minor cracking to the penetration of moisture, conventionally comprisestwo coats of bitumen paint. Where conditions are particularly aggressive or aestheticstandards are particularly high (ie needing to positively prevent penetration of moisturethrough the wall) a sheet or sprayed membrane could be required. For the extent ofwaterproofing treatment, see Detail 7.2.3-2.
CIRIAC543
Detail 7.2.2-3 RC cantilever wall - stem base joint position
Consjoint
II
PV
0 c
Stem0 c
c
~!truction
p c
---__l
~
0 0 0
< >- <>
Base
(A)
Consjoint
II
toV
c
0 c
t
Stemp'7
0 c
truction p (
-- -
0 0
o l><: <>
Base
II
(B)
PREFERRED • A kicker, Option A, is preferred but it must be properly supervised on site to ensure thatkicker position, and the concrete grade in it, are correct and that concrete compactionis satisfactory.
AVOID
REMARKS:
CIRIA C543
•
•
•
•
•
•
Kickerless construction, Option B, can lead to shutter alignment difficulties and groutloss and should be avoided.
Kicker should be cast integral with base slab.
Dimension K, height of kicker. Value to be between 50 mm and 150 mm, dependingupon size of wall, shutter details and site preferences.
The detailer need only be concerned with the height of the kicker in order to plan thedimensions of the starter bars and reinforcement in the next lift of concrete. It is thechoice of the contractor whether to follow these proposals.
Care must be taken to ensure that starter bars have the correct cover to any featuresthat may be present and also allow for any enclosing links that may occur in later stageconstruction.
If bars in stem are constrained in length at the top by a concrete surface the lower endsof the bars should be detailed allowing for a tolerance on the constructed level of thekicker.
7.5
Detail 7.2.2-4 RC cantilever wall - stem reinforcement
Front face
p (
p (
\ b ,
Stem
0 (
0 (
V
Vertical section
(A)
Front face
f\
(V
(
( (
\ ( (
stem
( (
( c
C C
V
Vertical section
(B)
PREFERRED • Placing the vertical bars in the outside layer (Option A) allows concrete to flow morefreely at the face of wall during placing.
REMARKS
7.6
•
•
Placing the horizontal bars in both front-facing layers (Option B) is slightly easier to fix.
Where shrinkage stresses in the longitudinal direction along the wall are critical,placement of horizontal reinforcing bars on outside layer (Option B) can reduce crackwidths in the visible and exposed face.
CIRIA C543
Detail 7.2.2-5 RC cantilever wall - coping
3.1.2-1
3.1.3-1
Constructionjoint
Stem
3.1.2-1
3.1.3-1
Constructio nFallr-r-__"':-=-_-I-_...:..::joint
Stem
(A) (8)
PREFERRED • Option A is simple to reinforce.
• Both options overcome the problem of the underside of the coping not coinciding withtop of construction joint.
REMARKS • Option B is used only when wall coping dimensions must reflect those of the deck stringcourse or parapet beam.
• Recommended fall across top of coping is 5 per cent.
• Dimension A, vertical overlap of coping, is decided by consideration of concrete cover tocoping reinforcement, but should be greater than 10 mm to avoid grout loss.
Detail 7.2.2-6 RC cantilever wall- coping reinforcement
I c
FO'=\,(0
er
I rh
,,<,,-',.<0.'$.,."
~'/Y//,Yk/".
t -0
p 0
0 0
p 0
l
~
Min covat dripgroove
Cradle anchorage for guard railmay need to be consideredwhen arrranging re·nfor ement
Wall reinforcement
Fall
Cradle anchorage for guard railma' need to be consideredwhe arrronging reinforcement
Min coverat dripgroove
(A) (8)
CIRIAC543 7.7
Detail 7.2.2-7 RC cantilever wall stem - movement joint
~ 20x20 20x20Polysulphide sealant Polysulphide sealant
Front face Front face
• • • • • • • • • • • • [• • •
· • • • • • • • • • • • • • •Rear face L Formed or
Rear face
cut groove to Compressive fillerinduce line of cracking
Free contraction joint
Sectional plan
Free expansion joint
Sectional plan
REMARKS • Refer to CIRIA Report 146, Design and construction of joints in concrete structures (11),
for further details of joints in walls.
• Joints in walls should be minimised so far as possible. Spacing of joints should becompatible with designed reinforcement for crack resistance.
Detail 7.2.2-8 RC cantilever wall stem - shear key
rstop
Plastic debonding sleeve orequivalent approved methodenclosing 25mm dia. stainlesssteel dowels, 600 long at
I '\ 300Front face
crs. 7• • • • 1(· . I • •
• • • • Il. • • •Rear face
./~ Approved wate~
Polysulph'de sealant
Polysul ph ide sea lont
Front face
• •II •
• •
• • II. • •Rear face
Approved waterstop
(A) Joggle type
Sectional plan
(8) Dowelled type
Sectional plan
PREFERRED • Option A, concrete shear key, is preferred.
REMARKS • Care with the alignment of dowel bars, Option B, during concreting of joint is important toavoid "lock-up".
• Any dowel bars should be stainless steel. Normal steel is subject to corrosion and istherefore not acceptable and the serviceable life of galvanised steel dowels is unproven.
7.8 CIRIA C543
7.2.3 Drainage of RC cantilever walls
Walls often interrupt a natural flow of water in the soil and arc subject to a build-up of
water pressure behind. Small walls may rely upon weep holes (see Detail 7.2.3-1) to
relieve the pressure. but primary walls on highway schemes should be provided with a
drained permeable layer along the entire rear face (see Detail 7.2.3-2).
Detail 7.2.3-1 Weep hole
GL.
.3 Recess8 featuren optional
150 dia.perforated pipeconnected toweephole pi pe
Concretebedding
Recessfeetureoptional
100 dia .UPVC pipe
150 dia.perforated pipeconnected todrainage outfall
Concretebedding
100 dia.UPVC pipe
ooo
(A) (8)
PREFERRED • A small, upwards, slope of the weep pipe towards the outside face of the wall (Option A)minimises slow weeping and is easier to rod.
• Where positive drainage of the wall backfill is provided, the drain pipe should be lowerthan the weep holes (Option A). Weep holes are then maintained to provide relief ofexceptional conditions only and not carry the bulk of the drained water.
AVOID • Use of weep holes adjacent to footways and hard verges where drained water fromweep holes may become hazardous, particularly in freezing conditions, should beavoided. This particularly applies to Option B.
REMARKS • Where possible, the back of wall drainage should be serviceable without relying on weepholes.
• Option B tends to weep at all times even when carrier pipe is not blocked.
• Weep holes are used, typically, at 3 m centres.
• In urban situations the provision of covers over the weep pipes to prevent deliberateblockage should be considered.
• Wall staining can be contained within a recess feature similar to that shown on Detail6.6.0-7.
• Consideration should be given to the use of vermin covers.
CIRIA C543 7.9
Detail 7.2.3-2 RC cantilever wall- drainage measures
Guardrailrequired
~ Free draining material_____________ I DMRB compliant
Dra inage layer to act aspositive drainage path toperforated pipe and toprotect waterproofing
~I 150 dia. approved
~ perforated pipe laidN to fall, 1:100 min
...-1+----------'--- Mass concrete beddingto pipe
~-l'--------------+---c~Waterproofing(see detail 7.2.2-2)
Waterproofing
7.2.3-1
All buried concretesurfaces are to bewaterproofed inaccordance with'S'
REMARKS • Reference can be made to OMRB Standard BO 30/87, Backfilled Retaining Walls andBridge Abutments (44).
• A 500 mm-wide flat strip of fill alongside the top of the wall at the foot of the slope avoidstendency to overfill and can act for drainage collection.
• Weep holes are not intended to flow continuously. They should be provided only as awall drainage failure indicator.
• A drainage channel in front of the wall can be provided to collect discharge from theweep holes.
• Large volumes of water should be dealt with separately and piped to a main drainagesystem.
• Ref S is to refer to the relevant specifications for waterproofing of buried concretesurfaces.
• Perforated pipe may have positive outfall and so could operate with or without weepholes. The perforated pipe should be provided with an independent rodding point,particularly where there is no weep hole.
• The effects of soil compaction adjacent to any drainage measures should be considered.
7.10 CIRIA C543
7.3 EMBEDDED CANTILEVER WALLS
The walls covered in this section are those that are formed in place either by boring,
deep trench excavation or driving. DMRB Specification BD 42/94, Design a/Embedded
Retaining Walls and Bridge Abutments (4", should be used for reference.
Embedded wall construction can therefore take one of the following fonns:
• contiguous bored piling
• secant piling
• diaphragm walling
• steel sheet piling.
Their features, typified by a bored contiguous pile wall, are shown in Figure 7.1.
Cappingbeam
300 wideconcrete plugbetweenpiles
Fixing
Waterproofing
Precast concretepanel fascio
o co .-('oJ E
- Coppingbeam
Fasciasecuredback topiles
/
Fascia access hatchfor inspectionof cavity atlow level
Figure 7.1
CIRIA C543
Precast concrete fascia
Typical sections
Embedded cantilever wall- features
Masonry fascia
7.11
7.12
Reference should be made to specialist literature for information on how each
construction form is completed. Each of these forms is mentioned in Chapter 6 as being
suitable for use as bridge abutments as well as retaining walls.
Restraints at high level, or struts just below finished ground level, can be included in the
design ofthe contiguous, secant and sheet piling to assist their resistance to lateral forces.
In most cases, the wall face revealed after excavation requires some form of finish to be
applied. Installation tolerances, potential vehicle impact and surface roughness should be
considered when designing the finish. Final finishes should then comply with the project'sprotective coating specification - see DMRB Specification for Highway Works 1461,
Clause 1700. Unless the wall facing is designed for vehicle impact, safety fencing should
be provided to protect thc wall.
The usc of secant (overlapping) piling, diaphragm walling and sheet piling are all
effective in limiting the ingress of water into the excavation, but some provision should
be made for seepage. Where discrete piles are used, more positive measures are
necessary, see Detail 7.3.0-1.
Steel sheet piling is particularly effective in situations where ground disturbance and soil
removal must be kept to a minimum and also where watercourses form part of a bridge
works scheme. Alternative forms of capping for sheet pile walls are shown in Detail
7.3.0-2. For a revetment supported at the top ofa sheet pile wall, an example capping is
shown in Details 7.3.0-3 and 7.3.0-4.
CIRIA C543
Detail 7.3.0-1 Embedded cantilever waif - drainage
~7»Z?722/22\Facing fixed back Angle supportsto angle supports fixed to piles
1200 dia.Contiguousbored pile
1500 UPVCslotted pipe
Reinforced con_cr_e_te__~~fac',ng panels-
FRL
Shotcrete200mm thk.in front of pipepipe
(A)
R.C bored pile Retained cloy
..1... ... .. ... .. +... . .. ... ............
Geotextile~":':':':
75mm 0 perforated .....d•._---
UPVC pipe wrapped •with geotextile
Outlet tovertical drainbetween piles
Geotextilemembrane
750 UPVC perforatedpipes wrapped ingeotextile
Facing panel
In fill concrete
Mesh reinforcement
12000 contiguousbored pile wall
Mesh fixedto pileswith
-+-----+------Iboi~_:;".L---_t:r----_r_galvon isedheavyduty M10expandinganchorbolt and
A252 reinforcement meshsupported on concreteties x 200mm long at1000mm c/c vertically,fixed to piles with suito blefixing
(B)
REMARKS • Option A proVides protection to the vertical clay soil surface between piles. Theperforated pipe is needed to prevent the build-up of water pressure, which otherwisewould tend to burst off the shotcrete providing the protection.
• Option B provides facing in front of the piles in granular soil. The perforated pipeprovides drainage of the retained soil.
• The ability of such wall face drainage to reduce loading on the wall is a sUbject forspecialist design.
• The geotextile retains fine soil particles from entering and blocking the porous pipe.
• Ensure the drainage authority permits groundwater to discharge into its system. If not, amore substantial wall without drainage may present a more economical solution.
• Drainage downpipes should be inspectable and maintainable.
CIRIA C543 7.13
Detail 7.3.0-2 Steel sheet pile wall - capping
Angled reinforcementoptional
(A)
Sheet piling
RC capping
Steel channelcapping
(B)
.....+--11---- Steel filler
Fillet weld
t---- Sheet piling
Steel capping
(C)
Sheet piling
PREFERRED • Reinforced concrete capping, Option A, is preferred because it allows better loaddistribution and can cope with poor tolerances on sheet piles.
REMARKS
7.14
•
•
Steel channel capping, Option S, is more suited for urban use where it can be painted.
Timber capping, Option C, is used mainly in a waterway environment.
CIRIA C543
Detail 7.3.0-3 Steel sheet pile wall- capping at revetment
Construction joint Blinding
Revetment blocks,typical proprietaryblock shown(voids can befilled with topsoil)
REMARKS •
Sheet piling
Consideration should be given to the inclusion of a granular bedding layer to therevetment blocks above the geotextile,
Detail 7.3.0-4 Steel sheet pile wall- revetment capping reinforcement
a
REMARKS:
CIRIA C543
•
'0' dia. holes to be formedin sheet piling for lower legof bar
Dimension D, diameter of hole for reinforcement, to be 25 per cent larger than nominalsize of reinforcement.
7.15
7.4
Figure 7.2
7.16
GRAVITY WALLS
A gravity wall relies on its self-weight to counteract any overturning or sliding effectsresulting from pressure from the retained material.
In this category, walls are formed in unreinforced (mass) concrete, brickwork, timber,precast concrete unit crib walling or stone-filled wire gabions.
The Design Manual/or Roads and Bridges, Volume 2, Section 1 (substructures) (17\
should bc referenced in the design of gravity walls.
Mass concrete
CIRIA Report ISS, Bridges - design/en' improved buildabilitv (11, seeks to develop
unreinforced clements for the construction of abutments and wing walls. Gravity walls,particularly those constructed in mass concrete, fulfil this aim. Gravity walls can only beused where sufficient ground space in the finished state is available. Cost savings resultfrom not having to supply, fix and protect reinforcement embedded in the concrete.Counter to this is the cost of the additional concrete required. The principal drawbacksarc the propensity for surface cracking and imperfections of a mass concrete waiL which,together with its sheer bulk, compromise its appearance. The use of fibre reinforcementin the concrete mix to control cracking of concrete and improve durability should beconsidered as should the use oflow-heat cement (see CIRIA Report 135 (~71).
Examples of shapes of mass concrete retaining walls are shown in Figure 7.2.
Weephole
Examples of mass concrete retaining walls
Gravity walls - concrete shapes
CIRIA C543
Detail 7.4.0-1
An estimate of the construction capability should be made at the time of the design. The
location and number of construction joints in the mass concrete wall will be dictated by;
• the chosen maximum volume of concrete in anyone pour
• the sizes of formwork panels
• the need to limit thermal cracking.
Suggested treatment of the foot of an embankment slopes at the top ofa gravity wall is
shown in Detail 7.4.0-1. Mass concrete gravity walls are not normally reinforced except
sometimes at their tops in the support of parapet fixings, etc.
Gravity wall - treatment at top
in 40 fall..
500 wide flat area
(8)
Massconcrete
1 in 40
Precast concrete drainagechannel laid to fallsdischarging to catch pitsand then to maindrainage
REMARKS
CIRIA C543
•
•
•
Guard rails may be required on top of the wall.
Settlement behind wall could affect the precast drainage channel (Option B), which istherefore more suitable in areas of cut.
Front face of wall could suffer discoloration if drainage measures are inadequate.
7.17
Detail 7.4.0-2
Mass concrete walls can be faced to improve their appearance, a durable facing beingmasonry, suitably fixed.
A permeable layer is usually provided against the rear face of the walls. The measures
will be similar to those in Detail 7.2.3-2. If provided with a positive discharge route, the
potential steady water pressure on the rear face of the wall will be lessened. This could
allow the size of the wall to be reduced. It also lowers the chances ofleakage throughcracks and construction joints in the wall, which could deface the front surface or
damage any finishes.
Gravity wall - coping provision for parapet
Cast in cradleanchorage
Shims to levelprecast unit leftin place then jointsealant opplied
Fro r1 t fa ce -------0-1
Mass car1cretewall
Drainage layerbehind wall
leVelling Jscreed
Precast coping
REMARKS
7.18
•
••
•
Design of the precast slab and foundation must include the required design forces on,and from, the parapet.
Shear and bending stresses must be checked at level of lower construction joint.
Keys can be incorporated in construction joints to resist shear effects if necessary.
Precast slab and foundation must be statically stable with required factors of safety,ie they should not rely upon a moment connection with mass concrete wall.
CIRIA C543
CIRIAC543
Crib walls
An alternative fonn of gravity wall is the crib wall, in which interlocking components are
built up into a framework. The resulting open framework allows the fill material to beexposed on the feature face and thus be planted or seeded ofTering landscaping potential.
They also allow the retained material to be free-draining, so clearance to the highway
needs to be sufficient to allow for the inevitable spillage of soil. Refer to DMRBBD 68/97 (4Xj and BA 68/97 i4'!I. Crib walls arc usual1y proprietary structures and, as
such, the details should be sought from the manufacturer.
Gabions
Another solution to stabilising and strengthening soil slopes, as well as combating
problems of soil erosion, is the gabion wall. The gabions, or cages, are formed from wire
mesh, wired together in their empty state, then filled with stones of larger gauge than the
mesh to create the finished product. The life and durability of the cages must be
considered, and the wire and wire mesh wil1 nonnally have been galvanised or coated
with PVC. The suitability of this form of construction is influenced by factors mainly
connected with the stone filling. Availability, quantity and transportation costs of the
stone should be researched at an early stage in the design process.
Examples of shapes of gab ion wal1s are shown in Figure 7.3.
Some locations are not suitable for gabions, for example, alongside paved footways.Unauthorised persons, particularly children, can easily climb the stepped front faces ofgabion walls and can remove the stone material. There are also restrictions on their usealongside motorway or trunk road carriageways. However, gabions have a proven trackrecord over many decades and, where suitable for the purpose, are cost-effective.
Frictional anchor elements can be attached to gabions to give increased stability whererequired. Gabions can also be built level.
7.19
Figure 7.3
7.20
/
stone filled w',remesh boxes
11'i1"ie-tv~~
Gravity wails - gabiOnS
CIRIAC543
7.5 REINFORCED SOIL WALLS
The reinforced soil system consists, basically, of proprietary reinforcing or anchor
elements, made of galvanised steel or polymer, laid in a suitable fill material. Linked to
the elements are proprietary modular facing panels (normally of precast concrete). The
wall is built by repetition of a simple sequence of operations at successive levels;
installing facing panels, placing and compacting fill, laying reinforcing elements and
placing and compacting further fill, repeating the sequence until the desired height is
reached. The finished wall is able to resist lateral pressure by friction along the
reinforcing elements, which ensure the soil mass acts as a block as a gravity wall.
Examples of preferred types of reinforced soil walls, using discrete and full height
interlocking panel systems, are illustrated in Figure 7.4.
./
./~././ Embankment./ /./ fill
Precastconcretecoping
Reinforcing elements,spacing depends ondesign of wall, loadsetc
Modularinterlocking panels
Full-heightinterlocking panels
Figure 7.4 Reinforced soil walls - basic types
Walls of variable height and formed to curved profiles, can be easily constructed.
A series of walls can be provided where terracing and landscaping is desired. The as
struck surface of the panels of the types of wall shown provides a satisfactory finish.
Details should be compatible with the design guidance of BS 8006 ()O). The types of wall
shown in Figure 7.4 can comply with this standard. The desih'11 of reinforced soil schemes
is a specialist activity.
The position of the junction of flexible elements and inflexible/stiff clements (at
connection with foundations, see Detail 7.5.0-1, or copings, see Detail 7.5.0-2) must be
considered at an early stage in the design.
The design life and durability of the entire structure should be carefully considered,
especially when the integrity of a bridge superstructure may depend on the tensile
capacity of certain members or parts of the members.
Abutments constructed using reinforced soil techniques may need stricter and morelimiting conditions to be specified.
CIRIA C543 7.21
Detail 7.5.0-1 Reinforced soil wall - base
Compacted fill
Q1--- Perforated pipe 150 dia.
lGICC~_
, . "1 Soil reinforcement
I-om;,o,,-,"=-~(A)
Concrete upstandto foundation(optional)
L:_~J-----Concrete stripfoundation
Soil reinforcement
~
---- Drainage layer
Illl.,.••.1U;·:.><" '~I
"'<:, '.,
'>;y~j:yj:! • ....•.... j/,,/..//,/J. ,~... : Perforated pipe 150 dia.
Foundation V I
b,om~1 --
(8)
Facing ponel
PREFERRED • Non-channelled concrete strip base, Option A, is preferred, being easier to form on site.
REMARKS • Perforated pipes must discharge to an approved drainage system and must be roddable.
7.22 CIRIA C543
Detail 7.5.0-2 Reinforced soil wall - coping
Side entrygully
Massconcrete
Precast maskingunit
In situ connection
-'.
Highway parapetsystem
In situ parapet support slab
Tolerance anpanel height
75mm blinding concrete
Safety guard railfor maintenance
100mm dia. perforated pipe setin 100mm thickness surroundof suitable filter materialto drain front ofslope
Precast reinforcedconcrete stringcourse units
Soil reinforcementif required
REMARKS • Service ducts should not be cast into copings.
• Design of the coping system with support slab must include the required design forceson, and from, the parapet.
• The coping system with support slab must be statically stable with required factors ofsafety, ie it should not rely upon a moment connection with top of wall panels.
CIRIA C543 7.23
8
8.1
CIRIA C543
Integral bridges
GENERAL
Integral structures are becoming a preferred fonn of construction for spans up to 60 m
because they eliminate some of the major causes of deterioration that have become
evident in the UK bridge stock in rcccnt ycars. The deterioration is particularly related to
the effects of movement joints in the deck, which are prone to leakage. Movement joints
and bearings are an additional initial cost to the structure, so reducing or eliminating
them can bring significant savings.
For the purposes of this book, an integral bridge is defined as a bridge with "abutments
connected directly to the bridge deck, and without movement joints between spans or
between end spans and abutments". This requires the superstructure of a multi-span
bridge to be fully continuous across the intennediate supports that mayor may not be
built in to the deck. Methods of fonning such continuity are discussed in this chapter.
Continuous, jointless construction, but with bearings and a monolithic screen wall at the
abutments (often knO\\m as "semi-integral"), is also included here.
It is recommended that the designer refer to the following documents from which the
above definition is taken:
• The Design ManualF)r Roads and Bridges (DMRB) Advice Note BA 42/96 (91
• The Design olfntegral Bridges (')1
• Advice Note BA 57/95 (XI and Standard BD 57/95 III, both entitled Design/i)r
Durahilitv.
Up to now, experience with integral bridge works in the UK has been fairly limited and
standard practices are not yet established. This chapter therefore reflects experience
gained in other countries combined with current thinking in the UK.
Integral bridges can comprise both steel and concrete elements, so reference should be
made to the relevant chapters for other details for the individual bridge types, support
structures etc. This chapter deals primarily with details connected with integral bridge
construction that have not been covered elsewhere in this guide. Appropriate cross
references arc made to other parts of the book.
8.1
The details to be found in this chapter are as follows:
8.2
8.2.3-18.2.3-2
8.2.3-3
8.2.3-4
8.2.3-58.2.3-6
8.2.3-7
8.4.2-18.4.2-2
8.4.2-3
8.4.2-48.4.4-1
8.4.4-28.4.5-18.4.6-1
8.4.6-28.5.2-1
8.5.2-2
8.5.2-38.5.3-1
8.5.3-28.5.3-3
Precast beam continuity (Type 1) - wide in situ integral cross-head 8.5Precast beam continuity (Type 2) - narrow in situ integral cross-head 8.6
Precast beam continuity (Type 3) - integral cross-head cast in
two stages 8.7Precast beam continuity (Type 4) - continuous separated slab 8.8Precast beam continuity (Type 5) - tied deck slab 8.9
Diaphragms at piers 8.10
Joint for tied deck slab continuity (Type 5) 8.11
Frame abutment. 8.17Frame abutment, beam and slab - continuity concrete flush with wall 8.18
Frame abutment, beam and slab - continuity concrete wider than wall .. 8.19Frame abutment. beam and slab - beam bearing shelL 8.20Piled abutment - integral bank seat with run-on slab 8.22
Piled abutment - integral bank seaL 8.23End screen - embedded (sheet pile) wall, semi-integral 8.24
Bank pad abutment - sliding typc 8.25Slip membrane - chamfer at edge 8.26
Run-on slab - interface with carriageway 8.28
Run-on slab - buried type 8.31Run-on slab - fill backing to abutment 8.32
Run-on slab - connection types 8.34Run-on slab connection - anchor bars near bottom 8.36
Run-on slab connection - anchor bars near top 8.37
CIRIA C543
8.2
8.2.1
8.2.2
CIRIAC543
CONCRETE SUPERSTRUCTURES
Preamble
The concrete superstructure of an integral bridge could take one of a number of forms. If
the maximum length of such a structure were limited to. say. 60 m then the form of
construction would be chosen from:
• solid slab
• voided slab
• precast pre-tensioned beams
• box girder.
For spans up to 15 m, solid slab construction is the most logical selection for economy
and buildability, although precast beams may be appropriate for particular sites.
Monolithic integral construction avoids claboratc bearing arrangements. Therefore, the
threshold of competitiveness of precast beams should be reached at shorter span lengths
compared with jointed construction.
For spans up to 30 m, precast prestressed concrete beams are the preferred form of
construction. Voided slabs, either reinforced or prestressed, have been used in the past
but. for reasons of buildability. this form of construction is now less used.
For bridges up to 60 m total length, spans in excess ono m are not often required
except, for example. to avoid constructing an overbridge pier in the median between two
carriageways. Precast pre-stressed concrete beams are successfully used for spans up to
40 m. Post-tensioned box girders can be used for spans up to 60 m and beyond.
Reference should be made to Chapter 3. as many of the details shown there arc common
to the superstructures of concrete integral bridges.
Construction sequence
It is important that bridge details permit the construction sequence of an integral bridge
to be compatible with the assumptions made during the design. The drawings should
clearly state the design assumptions. The likely sequence of construction will be:
• construct substructure up to deck soffit level
• place precast beams (where used) on supports (often on small, thin. rubber pads)
• cast deck slab
• cast superstructure and deck continuity at intermediate supports when present
• cast in situ stitches between deck and abutment
• backfill behind abutment.
This sequence will minimise the amount of movement at the abutment due to shrinkage
of the concrete.
For short spans. the whole deck, including the monolithic connection with the abutments.
can often be cast at the same time.
The construction drawings must also specify the sequence of backfilling behind the
abutments where difference in fill levels or fill stages may affect the design assumptions.
8.3
8.2.3
8.4
Continuity of deck at intermediate supports
The principles of bridge superstructure continuity over intermediate supports are not
unique to intcgral bridging. Any continuous construction can adopt the same details
included in this chapter. They should be used in conjunction with othcr appropriatc
dctails found in Chapter 3.
There are different methods of achieving continuity of decks at intermediate supports
when using precast concrete beams. Five solutions that have been used satisfactorily in
the UK are shown in Details 8.2.3-1 to 8.2.3-5. The "Type" numbers refer to those used
in SA 57/95 IX) Details 8.2.3-1 to 8.2.3-3 show in situ integral cross-heads, which may
be designed to develop full continuity moments. Details 8.2.3-4 and 8.2.3-5 provide
continuity through the deck slabs only (partial continuity). Detail 8.2.3-6 shows further
options for the diaphragms at piers.
A form of continuity preferred by many designers and maintenance engineers is the fully
built-in pier. The dimensions of the pier, its slenderness, the ability to accommodate
movement due to shrinkage, temperature and braking loads, and its appearance, are all
important issues. If the span arrangement is symmetrical then the central pier of a two- or
four-span bridge can become the "null point" for movement, so consideration should
always be given to "building-in" this pier. A built-in pier is efficient for resistance to
impact, an additional asset for piers in the vicinity of the carriageway.
The designer must recognise the potential congestion of reinforcement and contlict
between bars within these continuity details. It is advisable for reinforcement to be
drawn at a large scale so that the relative positions of all the bars can be understood.
The arrangements requiring pairs of permanent bearings, namely Details 8.2.3-2
(optionally) and 8.2.3-4 to 8.2.3-6 have the disadvantage that, when jacking is required
to replace bearings, space is not readily available for positioning jacks.
Details 8.2.3-5 to 8.2.3-6 have the disadvantage ofa narrow gap between the two
diaphragms, which is inaccessible should maintenance of those faces be required.
Details 8.2.3-2 (optionally) and 8.2.3-3 to 8.2.3-6 have the advantage of not needing
temporary support during construction.
When two separate diaphragms are used, continuity is provided only in the deck slab at
the top. The flexure of the superstructure (rotation at the ends of the beams) then results
in relative longitudinal movement at bearing level. The design and detailing must take
account of this longitudinal movement at the bearings as well as vertical shear generated
in the connecting top slab.
Other disadvantages and features of the various types of precast beam continuity are set
out in the notes with each detail.
CIRIA C543
Detail 8.2.3-1 Precast beam continuity (Type 1) - wide in situ integral crosshead
AlPrecast bridge beam
Top of beam continuityreinforcement
Crosshead soffit maybe flush with beamsoffit ------fJ
Bottom continuityreinforcement ----t'
Beam embedment 'E'
In situ crosshead
Precast bridge beam
Tap slab/crossheadcontinuity reinforcement
Transverse reinforcementor prestressing throughbeam web holes
Temporary trestlesupported onpier foundation
LSectional view
A-A
PREFERRED • Where full continuity is required, continuity Type 1 is preferred because of the avoidanceof difficulties with lapping reinforcement and its ability to accommodate bridge curvature,both horizontal and vertical.
REMARKS
CIRIA C543
•
•
•
•
•
Beams are erected on temporary supports generally off pier foundations.
Permanent bearings are in single line.
Continuity reinforcement is provided in the slab and at the top and the bottom of bridgebeams. The lapping of reinforcement is normally not difficult.
Only one set of jacks is required at each pier for raising deck for bearing replacement.
Beam embedment length, E, value typically about 1 m.
8.5
Detail 8.2.3-2 Precast beam continuity (Type 2) - narrow in situ integralcross-head
Precast bridge beam
Sectional viewA-A
Bottom continuityreinforcementanchored aroundtransverse baron centreline of piers
Possible temporarycorbels
Top slab/crossheadcontinuity reinforcement
Precast bridge beam
In situ crosshead
Beam embedment
Transversereinforcementthrough beamwebs
Temporary bearings---.L--A--=~~V(or permanent pairs)
Permanent bearings(if others removed)
AjREMARKS • Temporary supports are not required if the permanent bearing shelf is of sufficient width
and continuous.
• Permanent bearings may be in single or twin line.
• Permanent bearings can sometimes be combined with temporary bearings as a widesingle permanent elastomeric bearing.
• If outer pairs of bearings remain in place, design and detailing consideration must begiven to potential relief of load on bearings when spans are alternately loaded.
• Continuity reinforcement is provided in the slab and at and the bottom of bridge beams.The lapping of reinforcement is difficult.
• Only one set of jacks is required at each pier for raising deck for bearing replacement.
• Beam embedment length, E, value typically about 1 m.
8.6 CIRIA C543
Detail 8.2.3-3 Precast beam continuity (Type 3) - integral cross-head cast intwo stages
Beam embedment 'E'
r--
Mortar bed orpad bearing --------'
In situ crossheodfirst stage -------'
Crosshead monolithicwith pier ar on bearingwith temporary fixity J Iduring construction A--7I
Crasshead
length
~f
~-- Top slab/crossheadcantin uity reinforcement
Transverse reinforcementthrough hales in web
Top of beam continuityreinforcement
Bottom continuityreinforcement
In situ crossheadsecond stage
Sectional viewA-A
REMARKS
CIRIA C543
••
•
•
•
•
•
Beams are supported on first stage of cross-head during erection.
Resulting cross-head is monolithic with pier.
Cross-head soffit is normally lower than beam soffit.
Temporary bearing pads are encased in surrounding concrete of Stage 2 cross-headconstruction.
Reinforcement is similar to Type 2 (see Detail 8.2.3-2) depending on the cross-section ofthe Stage 1 cross-head.
No bearing maintenance is required.
Beam embedment length, E, value typically about 1 m.
8.7
Detail 8.2.3-4 Precast beam continuity (Type 4) - continuous separatedslab
Transverse reinforcement jthrough beam webs
A
Separated deck
slab length 'c'Slab reinforcementcontinuous across jointbetween beoms
Precast beam
Com pressible fillerbetween beam andslab
~L
Sectional viewA-A
REMARKS
8.8
•
•
•
•
•
•
•
•
Temporary supports are not required.
Separate bearings and end diaphragms are provided for each span.
Deck slab is separated from support beams for a short length to provide rotationalflexibility and this deck slab length is designed to flex.
There is no continuity reinforcement between ends of beams and there is no momentcontinuity between the superstructures of the spans.
Not recommended where air contamination may cause deterioration to inaccessiblefaces.
Arrangements for jacking up the deck to facilitate replacement of bearings need to beconsidered by the designer and the provisions made described in the maintenancemanual.
Separated deck slab length, C, value typically about 1.5 m.
Designer needs to be satisfied that bearings and continuity top slab can resist the effectsinduced by relative horizontal and vertical displacements (see Section 8.2.3).
CIRIA C543
Detail 8.2.3-5 Precast beam continuity (Type 5) - tied deck slab
8.2.3-7
Anchor bar
Sectional viewA-A
Precast beam
Polystyrenesleeve
F
Transversereinforcementthrough beomwebs ~_.--J
•REMARKS Temporary supports are not required.
• Separate bearings and end diaphragms are provided for each span.
• The tie reinforcement at mid-depth of the slab is debonded for a short length either sideof the joint to permit deck rotation. There is no moment continuity between thesuperstructures of the spans.
• Not recommended where air contamination may cause deterioration to inaccessiblefaces.
• For joints for deck continuity see Detail 8.2.3-7.
• Designer needs to be satisfied that bearings and continuity top slab can resist the effectsinduced by relative horizontal and vertical displacements (see Section 8.2.3).
CIRIA C543 8.9
Detail 8.2.3-6 Diaphragms at piers
Suriacil'\gWaterproofing
In situ concrete
;-8.2..3-7
slob 25 clio. HY ga(vanisedbors, 2400 long.
f~~~~~~t~~~~~~:;~~:;;;:~in~contjnuoustop slab
In situ concretedioptuogm ------'
100 nominal gapbetween precastbeams
Surfacing
Waterproofing
In situ concreteslab
fn situ concretediaphram
100 nominal gapbetween precastbeams -----"
(A)
8earing~
Bearing
8.2.3-725 dia. HY galvanisedbars, 2400 long.in continuouS top slab
EoIII~
tiloUGl'-a..
Low compressionjoint filler 20 thick
Pier
(8)
PREFERRED •
REMARKS •
Option A, although both options are acceptable.
While the structural dimensions of the diaphragm result from design, the principle offinishing the underside of the in situ concrete level with the underside of the beam asshown in Option A has the added advantage of being able to accommodate any
arrangement for lateral movement restraint.
Option A also allows the slotted holes in the beams to be used for transverse
reinforcement.
separate bearings and end diaphragms are provided for each span.
•
•
Designer needs to be satisfied that bearings and continuity top slab can resist the effectsinduced by relative horizontal and vertical displacements (see Section 8.2.3).
Option A covers and protects the ends of the prestressing strands.
Option A does not need soffit formwork if beams are contiguouS.•
•
•
CtRIA C543
8.10
Detail 8.2.3-7 Joint for tied deck slab continuity (Type 5)
For waterproofingover crack seedetail 31.9~ 1
Crock inducer, :ZOx:ZOclosed cell polyethylene
Surfacing
Preformed joint filler, 20 thick
'D' dia. bars, galvanised HY orstainless steel, centrally placedin connection concrete in polystyrenesleeve 50 dia. x 600 long andprotective wrapping
REMARKS
CIRIA C543
•
•
•
•
•
•
Deck slab between spans is separated using compressible joint fillers, but deckwaterproofing and deck surfacing are continuous and an extra membrane is providedover the joint for double protection.
Length of continuity bars to be at least sufficient to develop full anchorage bond into theadjacent spans from the ends of the debonded length.
Thickness of concrete between joint filler and crack inducer, through which continuitybars are centrally placed, is typically 140-180 mm.
Consideration may be given to the efficiency of the protective wrapping to be used and,if guaranteed, the substitution of conventional (HY) reinforcing bar instead of galvanisedor stainless steel.
Waterproofing across the joint subject to slight cracking and movement will requirespecial strengthening (see Detail 3.1.9-1).
Diameter of reinforcement, D, value to be established by designer, typically 25 mm.
8.11
8.3
8.3.1
8.3.2
8.3.3
8.12
STEEL SUPERSTRUCTURES
Preamble
The most appropriate deck type for integral steel bridges is steel/concrete compositeconstruction. This form of construction is successful and economical where spans exceed30 In. Whether standard rolled steel sections, fabricated plate girders or box girders areadopted, the principles are the same.
Reference should be made to Chapter 4 of this book, as many of the details illustratedthere are common to the superstructures of steel/concrete composite integral bridges.
Construction sequence
The designer and detailer should define the construction sequence at the preliminarydesign stage and, as with concrete construction, all details and reinforcement should beselected with this sequence in mind. The drawings should clearly state the designassumptions and any limiting differences in fill levels.
It is preferable for all single and multi-span integral bridges to be designed and detailedto the following construction sequence:
• construct substructure up to deck soffit level
• place stecl beams on temporary supports on piers and abutments
• cast deck slab
• form continuity of superstructure and deck over any intermediate supports
• cast in situ stitches between deck and abutment
• backfill behind abutment.
The different ways of making a composite deck continuous are discussed in Section8.3.3 and the sequence of casting the concrete deck slab may be governed by this.
The details at the abutments may differ from those of concrete integral bridges. The useof an end screen may be more appropriate for steel/concrete composite construction, buta cast in situ concrete stitch is also common. The different types of deck/abutment layout
are described in Section 8.4.
Continuity of deck at intermediate supports
Methods of achieving continuity of steel/concrete composite decks at intermediatesupports usually involve the provision of full-depth continuity, although partialcontinuity has been used outside the UK. The fonner makes both the steel beams andconcrete deck fully continuous; the latter makes only the deck slab continuous.
The simplicity of partial continuity can be attractive to the designer, particularly withregard to the ease and economy of construction. Its disadvantages are that it requiresbearings beneath the end of each beam and a wide pier to support them. The continuousslab is likely to require some maintenance during the 120-year design life.
Although full continuity may incur greater construction costs, the continuous beamrequires only one permanent bearing on which to be supported and piers can be slimmerand more flexible. This flexibility can be part of the bridge articulation using pinnedbcarings. Less maintenancc is a feature of this form of continuity and of integral bridgeconstruction philosophy as a whole.
CIRIA C543
8.4
8.4.1
8.4.2
CIRIA C543
END SUPPORTS
Preamble
The principal difference between integral bridges and conventional bridges is in the
design of the end supports. In a conventional bridge, thermal movement, structural
t1exure, shrinkage etc are accommodated by a designed and clearly delineated movement
joint. In an integral bridge, reliance is placed upon compliance of the soil behind the
abutment with imposed movements of the bridge structure. Any required provision for
movement in the carriageway is then placed outside the structure length where it will
cause less deterioration to the structure.
Figure 8.1 shows three principal methods by which an integral bridge can accommodate
movements of the bridge superstructure.
Figures 8.2 and 8.3 show different forms of end support following the recommendations
from a study tour to North America by a task group from the Concrete Bridge('\1)
Development Group· .
The main types of end support can be further described and categorised as:
• frame
• embedded wall
• pile
• end screen
• bank pad
• reinforced soil.
These are discussed in the following scctions of the guide.
Frame abutment
The first illustration in Figure 8.2 shows the normal arrangement with a full-height
vertical abutment facc. The end support is constructcd integrally with the deck and acts
as a retaining wall for the approaches to the bridge. A sloping face is sometimes
considered, but this is more difficult to build. The movements due to thermal effects and
earth pressure are accommodated by t1exure of the wall stems and slight movement of
the soil backing to the wall.
The frame abutment in its most common form for underbridges and shorter-span
structures is a portal frame structure. While apparently the simplest arrangement, the
significant bending moments at the comers of the frame can cause difficulties with
detailing and congestion of reinforcement. The difficulties increase where precast beams
or steel beams arc used. A typical example, showing a precast concrete beam
superstructure, is shown in Figure 8.4 followed by appropriate details.
8.13
Superstructurecast monolithicwith bank seat Movement .. I f---
7]--
8.5.3-1
Run-on slaboptional
"," ;"'. ,;'::..::~Movement by. ' ' sliding and rotation
Movement by sliding - Type A
Movement .. If--
Superstructurecast monolithicwith bank seat
8.5.3-1
8.4.4- 2
Run-on slaboptional
Movement by pile flexure - Type B
Movement--"It-Highway construction
Diaphragm orend screen
Figure 8.1
8.14
Rigid abutment and slidingbearings - Type C
Integral bridge abutments - accommodation of deck movements
CIRIA C543
Full-height frame abutments are suitable forshort single-span bridges. The horizontalmovements will only be small, so the earthpressures should not be very high.
Frame abutment
Embedded wall abutments are also suitable forshort single-span integral bridges.
Embedded wall abutment
A piled abutment with reinforced soil abutmentwall and wing walls is a form of construction thatshould have a wide application
Figure 8.2
CIRIAC543
Piled abutment with reinforced soil wall
Integral bridge end support types - Sheet 1
8.15
Semi-integral construction with bearings on topof a rigid retaining wall is a design method thatcan be used for full-height abutments forbridges of any length. Jacking of the deck canresult in soil movement under the abutmentsoffit. This can obstruct the deck from returningto its original level
End screen (semi-integral)
Shallow abutments on spread footings are only
~l\l\N\N\ considered to be suitable for situations where
_ the foundation is very stiff and there can be nosettlement problems. A granular fill layer shouldbe placed below the footing to allow sliding.
Bank pad abutment
Piled bank seats are recommended forwidespread use. The piles prevent settlementwhile allowing horizontal movement androtation.
Piled bank seat
Bank seats can be designed as semi-integralabutments. The footing is not required to movehorizontally and piled or spread footings can beused.
Figure 8.3
8.16
Piled bank seat with end screen (semi-integral)
Integral bridge end support types - Sheet 2
CIRIA C543
Continuity joint formedby casting beam endsinto walls - 8.4.2-2or 8.4.2-3 --~
Drainagelayer .. ~
- Superstructure shown as precastbeams but details are relevantto other forms of construction
75 mm UPVCweep pipes
Figure 8.4 Integral bridge - example of rigid (frame) type
Detail 8.4.2-1 Frame abutment
'p' beams'S' long
construction
,2-3\-~""-
1 ~ (;--WallV
LJ L Precast V joint:ill I prestressed 'P'I beamsam
J with 'D' thick r.C. deck slab LIs I--
'w' t-;erge Carriageway Footway 'w'
fall 2.5%- -~r I I
Continuity form
by costing be
ends into wal
8.4.2-2 OR 8.4
REMARKS • Dimension D, thickness of deck slab to satisfy strength design of deck.
• Dimension B, length of precast beams, measured in line of beam to suit any skewrequired.
• Carriageway, footpath and verge dimensions should be given for measurements squareto walls.
• Dimension W, thickness of wall, value to satisfy strength and flexibility design of frame.
• Dimension F, thickness of base slab, value to satisfy strength design of foundation.
• Level L, founding level, to satisfy strata depth and carriageway and footway coverrequirement.
• Type of precast beam, P, to be chosen to suit design of bridge.
• Base of walls could be formed as pins, but are more complicated to construct.
CIRIAC543 8.17
Detail 8.4.2-2 Frame abutment, beam and slab - continuity concrete flushwith wall
8.4.2-4
rA
Construction joint
Waterproofing membranewith sand asphalt protection
Surfacing
.•• 'J''G'I
J.1.4-
Waterproofingmembrane
Sectional view A-A
PREFERRED • Continuity concrete flush with wall face is preferred but additional wall thickness may berequired. The additional frame moments resulting from the additional stiffness needs tobe accounted for in the design.
REMARKS • Dimension W, thickness of wall. Value to be compatible with continuity thickness and tosatisfy strength and flexibility design of frame.
• Dimension J, semi-width of top of wall for temporary support of beams, value typically400 mm, but needs to be larger where the beams are skew to the abutment.
• Dimension H, height of extension of top of wall for temporary support, value to besufficient for lapping of reinforcement to ensure necessary continuity.
• Dimension G, thickness of continuity concrete in wall, value to be sufficient for lapping ofreinforcement to ensure necessary continuity.
• Dimension E, length of embedment of beams. Value to provide sufficient strength ofcontinuity and may extend to incorporate transverse reinforcement through holes inbeams.
• Waterproofing to extend below construction joint on outside of wall.
• Type of precast beam, P, to be chosen to suit design of bridge.
8.18 CIRIA C543
Detail 8.4.2-3 Frame abutment, beam and slab - continuity concrete widerthan wall
Surfacing
31.4-Waterproofing membranewith sand aspholt protection
8.4.2-4
'J'
'-"--'<--.....O-P---- Constructionjoint
'G'
I. 'w' ~I
I----~=-=--~ JI 'E' I
~I- PrecastL -+--------1 pr;stressed
P beam
-,----'j----t-
:r:
Waterproofingmembrane -----lJ
(A) (8)
PREFERRED • Option A, rectangular bottom corner of continuity concrete. This option is preferredbecause of reduction in complexity of reinforcement.
REMARKS • Dimension W, thickness of wall. Value to satisfy strength and flexibility design of frame.
• Bottom corner of continuity concrete wider than wall could be splayed at 45°, Option B,rather than rectangular, thus improving compaction activity but increasing complexity ofreinforcement.
• All other remarks, dimensions and details as for Detail 8.4.2-2.
• For sectional view see Detail 8.4.2-2.
CIRIA C543 8.19
Detail 8.4.2-4 Frame abutment, beam and slab - beam bearing shelf
jr-L -.:,
....:"--------~ ~::-~-
25x25 chamfer
,---+--- Precast concnbeam
Il~
~-----+--- 'A'x'B'x'T' thkbearing pads
/-------IIIII!
L__
Construction joint --t----,
(A)Beoring shelf inclined tomatch longitudinal slopeof precast beam
25x25 chamfer
Construction joint --J----__
/-------~
! / 1I -iI
Precast concretebeam
Mortar bed10 thick minimum
(B)Bearing shelf inclined tomatch longitudinal slopeof precast beam
PREFERRED • Option A, using bearing pad, is preferred.
REMARKS • Positioning and levelling of bearing pads in Option A can be carried out in advance ofplacing precast beams.
• Mortar bed in Option B needs to be prepared at the time of placing beams with attentionpaid to quality control of mortar mix.
8.20 CIRIA C543
8.4.3
8.4.4
CIRIA C543
Embedded wall abutments
The second illustration in Figure R.2 shows the basic principle of an embedded wall
abutment. The end support is formed by a diaphragm wall (or a contiguous. secant orsheet pile wall), which has its toe embedded in ground below the lower ground surface
and the top made integral with the deck.
The form of construction selected for the wall will depend on several factors such as:
• particular site constraints
• total length of deck
• existing. and future. ground conditions
• desirable finish to face of wall.
Concrete walls are more suitable when the movements are relatively small. Greater
movements can be accommodated more readily by steel sheet pile walls. and high
modulus sections (universal beam sections welded to sheet pile sections) are particularlyappropriate for this application. The walls flex under the influence of the movement andare restrained against rotation by their length of embedment.
Piled abutments
Where there is no requirement for the bridge clearance to come close to the abutment
face. the ground may slope up towards the top of the abutment. The commonest andsimplest form of integral bridge abutment for this situation uses a single row of piles but
with various abutment arrangements. An example. piled bank seat. is shown in Figure8.3 and in more detail in Figure 8.5.
Concrete or steel piles can be used. but the designer must carefully consider the forces
and movements induced. not only from the deck. but from soil/structure interaction.Details RAA-l and RAA-2 illustrate the use of steel piles (forms of piling such as steel Hor tubular. precast concrete driven or bored cast in situ concrete are equally acceptable)
with a concrete capping beam cast monolithically with the piles and the deck.
Piles can also be used successfully for semi-integral construction (where the
superstructure is not built-in to the abutment). see the last illustration in Figure R.3. piled
bank seat with end screen. and Detail RA.5-1.
8.21
l"
J"" : L
In situ R.C. ]"-J.. -t= + J- - -wingwall I I
I IIn situ R.C. I Iabutment I I I
~I I II II I
Steel H piles or~ Ibored cast in situ I Iconcrete piles
II I I---lr--
.- In situ R.C.integral abutment
Run on slaboptional
I I I
J1l1
I II I
-T1-r-I I
Steel H piles or I Ibored cast in situ I Iconcrete pjleS~ I
I I I
---Hi---I II I I
LIJ
Joint
Uncompactedfill withrun -on slab
Longitudinal section withrun-on slab
Elevation showing wing wall
Figure 8.5 Integral bridge abutments - examples ofpile flexure type
8.22 CIRIA C543
Detail 8.4.4-1 Piled abutment - integral bank seat with run-on slab
8.5 ..3-1
In situ r.c.integral abutment
Highwayconstruction
Asphaltic plugjaint
R.c.
50 blinding-'----~
concrete
Uncompacted freedraining granular fillwell graded, grain size5mm to 50mm
Bridgesuperstructure
Piles
r
Ground line
Detail 8.4.4-2 Piled abutment - integral bank seat
Asphaltic plug joint
r======rt:!1::!r '[!:,1Uf~I)
lIIIt
p=====r=t=~=l
Road construction
Deck beam r--l~ p~ rI:=j r=;J
G9 f=;J
G=I ~~. 6~ bJ
Construction joint
Concrete cross headbeam/endscreen wall
Select granularfill
'---+----+-----'--------
Steel tubularor 'H' pile
CIRIA C543 8.23
8.4.5 End screens
An end screen is a wall constructed at the end of a bridge deck that extends below thesoffit of the deck and is located beyond the end support of the deck. They use bearings
and this form of construction is sometimes called "semi-integral". Nevertheless, it stillsatisfies the main objectives of BD 57/95 (I) by having no movement joints in the deck.
The first and last illustrations in Figure 8.3 are examples of this type. An embedded wall(sheet pile) abutment with end screen is shown in Detail 8.4.5-1. The end screen acts toretain the material supporting the approaches, and only transfers longitudinal loads.
The designer has to give careful consideration to the detail at the bottom of the end
screen and may wish to limit the amount of movement. Maintenance engineers will also
need regular access in the normal way to inspect the bearings and for their potential
replacement.
Detail 8.4.5-1 End screen - embedded (sheet-pile) wall, semi-integral
Surfacing Asphaltic plug joint
Deck beam
Road construction
Reinforced concreteend screen wall
/lV·~.l-- Drainage layer
Drain
Sheet pHe orHigh Modulus Pile
Holding downbolts set ingrouted pockets
rr~-'--n
Studs for load . ~I Ir·transfer ~I . Ir
I .. IrIi={I I~
G=JIII=<J~11b:J Reinforced concrete
II I~-'-+---capping beam[;=:;!1 I .
I II
r~~~;==~~j~ii;~[j~[~waterprOOfingSlidingbearing
Clearance (sufficient to providefor movement, e.g. thermal).
8.24 CIRIA C543
8.4.6
Detail 8.4.6-1
Bank pad abutments
An integral bridge bank pad abutment is an end support constructed monolithically withthe deck, which acts both as a shallow foundation for the end span, and as a shallowretaining wall for adjoining pavement and embankment. The second illustration inFigure 8.3 indicates the type.
The bank pad form of construction is probably the most buildable end support and soshould be used wherever possible. It can be used where the foundation material is firmenough to prevent significant settlement problems. Some settlement can beaccommodated in the design of the deck and a bank pad on a well-compactedembankment construction is feasible. Ifthere is doubt about predicted settlement, or ifground conditions are unacceptable, a piled bank seat will be the choice (Section 8.4.4).
The abutments need to be designed and detailed to accommodate both sliding and
rocking movements.
A bank pad for construction on rock is shown in Detail 8.4.6-1. The form is similar tothe frame abutment (see Section 8.4.2) but with movement principally accommodated bysliding (and rocking), not flexure. To ensure freedom to slide, a low-friction granular filllayer and slip membrane are incorporated. This detail has, however, not yet received anindustry consensus and is subject to further development.
Bank pad abutment - sliding type
t Abutmeot
Insitu R.C. integral obutment---t--.
2 loyers 'G' ghigh density polyethylenesheet slip membrane'----
Class '6N' granularfill or moss concrete(minimum 300 thick)
H.D.polyethyleneslip membrane
Movementjoint
50 mm blindingconcrete
layer
Uncompacted selectedsingle sized granularbackfill with run on slob
Drainage layerif needed
150 dia. perforated pipew~h 450 x 450 nofines concrete surround
REMARKS
CIRIA C543
•
•
•
•
Arrangement is suitable for both steel and concrete superstructures.
Use of a run-on slab is optional.
Dimension F, extent of fill supporting slip membrane beyond edges of foundation.Typical value 400 mm.
G, gauge of high-density polyethylene sheet, to be chosen to provide requiredseparation between underside of structure and low-friction granular layer. Considerationshould be given to the need to wrap the granular material in a geotextile membrane toavoid washout.
8.25
Detail 8.4.6-2 Slip membrane - chamfer at edge
Slip layer
JOx 150 chamferon edges in contactwith the slip membrane
\,-------.--+--~v-------,
II
Polystyrene packing
REMARKS
8.4.7
8.26
•
•
This chamfer at the bottom corners of bank pad foundations is recommended to helpavoid damage to the slip membrane and to the support at the edges.
The chamfer can be simply formed using polystyrene packing as shown, which is notremoved.
Reinforced soil
Reinforced soil is a quick and efficient form of embankment construction. It can be
useful in locations that have restricted access for plant and where the phasing of
construction work provides insufficient time for more conventional forms of
embankment construction.
The last illustration in Figure 8.2 illustrates how reinforced soil can be used in integral
bridge construction with piling providing the primary support for the bridge. The
reinforced soil reduces concerns about the differential settlement of the embankment.
The use of reinforced soil to support an unpiled bank pad is not considered to have
reached sufficient development.
CIRIA C543
8.5
8.5.1
8.5.2
CIRIAC543
RUN-ON (APPROACH) SLABS
Preamble
Run-on slabs, otherwise known as approach or transition slabs, have been used in bridge
construction for many years with varying degrees of success. Their purpose is to provide
a smooth transition between the relatively f1exible construction of the approach pavement
and the non-flexible construction of the bridge superstructure. They are mostly designed
and detailed as simply supported slabs. Figure X.6 illustrates some examples of their
construction form.
Difficulties have been experienced with run-on slabs, which have created significant
problems for maintaining authorities. Several have failed, in both integral and non
integral bridge types, due to poor design and/or construction.
Most failures have occurred as a result of:
• failure of the connection between run on slab and abutment
• differential settlement ofthe fill supporting the free corners of the run-on slab.
In integral construction, the forces generated by diurnal and seasonal expansion and
contraction of the bridge superstructure will be transmitted through the abutment, thus
increasing the effects on the run-on slab.
Opinion is divided on the advisability of including run-on slabs in bridge work schemes.
Forms of construction
The three forms of construction shown in Figure 8.6 are:
• buried (at depth)
• simply supported
• cantilever.
The most common form is the simply supported version, which, because of the structural
rotations at either end, still requires some sort of carriageway surfacing joint detail.
However, it is preferred that the waterproofing system runs continuously from the bridge
deck across the run-on slab, and this is shown in Detail 8.5.2-1.
The buried type (Option A in Figure 8.6) does away with such carriageway surfacing
joints and still permits waterproofing membranes to be continuous on to the run-on slab.
The inclination of the run-on slab allows for a variation in depth of road construction,
which aids the transition effect. It is not yet known how successful these buried slabs are
in the longer term.
A run-on slab must be designed to span over the fill material. The design should be on a
"simply supported" basis but with effects anticipated as being reversible, with
reinforcement detailed in both top and bottom faces. The run-on slab should always
extend to the full width of the carriageway.
For details of nm-on slab connection and support, see Detail 8.5.3-1.
8.27
Rood base
Weoring course
'lL,
Closed cell polyethylenelow load transfer joint filler,'p' minimum thick, to beplaced after final compactionof sub base
3.1.4-
Movement joint to suitanticipated range (buriedasphaltic plug type shown,see detail 3.1.9-4)
Waterproofing to be wrappedround end of slob -----
'B' blinding
ormation level
Waterproofing membrane withprotective red sand asphalt
>-
~A
rA
8.5.3-2 or 8.5.3-3
Run-on slab - interface with carriageway
.• 0
" .'.
3.1.9~1
Abutment
I
. ~
! L=:===
~-
Detail 8.5.2-1
T
coNco
iI, I \ f ill ~
Longitudinal section through run-on slab
Run on slab
Section A-Ao;;0
»o(J1./:>.W
3.1.4-3
Waterproofing turneddown sides of slob --.,
Detail 8.5.2-1 Run-on slab - interface with carriageway (continued)
REMARKS
CIRIAC543
•
•
•
•
•
•
•
•
The run-on slab is sloped downwards away from the bridge deck. The top surface of therun-on slab, starting at the underside of the bridge deck surfacing, meets the undersideof the highway pavement construction road base at its end remote from the bridge.
Dimension Y, thickness of the run-on slab. Value to be as required for strength to span apotential void beneath.
Sub-base thickness adjacent to the end of the run-on slab to be increased locally, ifnecessary, to match the thickness of run-on slab construction.
Dimension Z, length of run-on slab, to be sufficient to span across hand-compacted oruncompacted fill behind abutment with adequate length of bearing on formation (seeDetail 8.5.2-3), but not less than 3500 mm overall.
Dimension P, thickness of compressible filler at remote end of run-on slab. Value to beappropriate to accommodate designed expansion movement over length of bridge.
Dimension S, thickness of blinding concrete under run-on slab. Value typically 50 mm to100 mm.
Movement joint detail at remote end of run-on slab will need adaptation from bridge deckdetails in Chapter 3 to permit the detail to be incorporated in the road base instead of onthe bridge deck.
For details beneath run-on slab, see Detail 8.5.2-3
8.29
Run on slab constructedot depth (see detail 8.5.2-2)
Uncompactedselected single size
granular fill
Roadconstruction
Waterproofing
Drainagelayer
Joint
(A) Simply supported at depth
In situ R.C.run on slobseparate fromabutment(see detail 8.5.2~1)
ct abutment
Heavy dutypolythene slipmembrane
I~""':?':""",,".--...:~,,"",,~--:::<:""--x--r---r--;r--r--.-J I
IIIIIL -+ _ -+----1
Compactedgranular fill
(8) Simply supported at surface
IIIIIII IL--t----j
CompactedgranUlar fill
Uncompacted selectedsingle sized granularfill
Run on slabmonolithicwith abutment
In situ R.C. integralabutment and run onslab
(C) Cantilever type
Figure 8.6 Run-on slab - construction forms
8.30 CIRIA C543
o55j;oCJ1.I>0.l
Detail 8.5.2-2 Run-on slab - buried type
'z' run on slab
t
<;l
Closed cell polyethylenelow load transfer joint f'iller,'p' minimum thick, to beplaced after final compactionof sub base-------~
standard thickness
Waterproofing membrane
Sub base, standard thickness minimum
'8' blinding
ormation level
Fall--
Wearing course
>-
• J
;J,
Rubber bitumen transitionstrip 400 wide
4.
4 .. 46
3.1.4-2 '\
3. 1.4~ 3>----~~~
8.S.3~2 or--1---~
B.53-]
REMARKS • The run-on slab is sloped downwards away from the bridge deck. The level of the top surface of the run-on slab starts at the underside of thesub-base for the standard road construction thickness and falls at an appropriate slope to assist sub-soil drainage away from the bridgeabutment.
• Sub-base thickness is increased locally to suit slope of slab.
• Notes for dimensions Y, Z, P and B as for Detail 8.5.2-1.co(,).... • For details beneath run-on slab, see Detail 8.5.2-3 .
Detail 8.5.2-3 Run-on slab - fill backing to abutment
Run on slab8.5 ..3-2 or 8.5 ..3-,3----, 8.5.2-1 or
8.5.2-2
~-~- Formation level
'B' blinding
L:J11
3.. ~·~-~~- ~~":.oo.:~q,o
g..o~~b~fJ0°. go
r-------~"-7''----- Porous no-fines concreteto specification clause'S'
Waterproofing -----------7.
Closed cell polyethylenelow load transfer compressiblesheet 'p' minimum thick:------J
Abutment
Soffit ofabutmentbank seot-------'
REMARKS • Depth of soffit of abutment and slope of hand-compacted granular fill will, in conjunctionwith the required bearing length on to embankment formation, define the length of therun-on slab required (see also Details 8.5.2-1 and 8.5.2-2).
• Dimension B, thickness of blinding concrete under run-on slab. Value typically 50 mm.
• Dimension C, width of drainage layer. Value typically 225 mm for a 150 mm-diameterporous pipe.
• Dimension P, thickness of compressible sheet, value to suit expected movement ofbridge.
• Where run-on slab is to be used with a non-integral bridge the compressible sheetshould be omitted and fill not left uncompacted.
• Ref S is to refer to the relevant project specification clause number.
• Refs 6N and 6P are to refer to the project specification class for appropriate granular fillto structures.
• For details above underside of run-on slab, see Detail 8.5.2-1.
8.32 CIRIA C543
8.5.3
CIRIA C543
Connections between slab and abutment
The run-on slab is subject to forces from thermal and flexural movements of the bridge
and the adjacent highway as well as the impact from the wheels of traffic. It is thereforeessential that, where a run-on slab is used, it is anchored positively to the bridge
abutment to avoid the risk of movement of the run-on slab away from the bridge.
Types of connection between run-on slab and abutment that have been found to be most
suitable are shown in Detail 8.5.3-1.
Options A to D have steel reinforcement bars cast in, with the slab resting on a recess orcorbel constructed in the back face of the abutment. Use ofthe recess, rather than a
corbel, simplifies formwork and construction.
Option E is simple in that there are no cast-in details. A "shear key" is created to prevent
horizontal movement.
A basic assumption should be made at the design stage that the surfacing will crack atthe connections and that proper waterproofing and drainage will be necessary. The use
of stainless steel for reinforcement in the area of the connection should be consideredand details should be kept as simple as possible.
Where steel reinforcement crosses the construction joint between run-on slab andabutment the concentration of flexure at the joint dictates that the steel bar crossing the
joint needs to be debonded over a significant length. This will allow excessiveconcentration of strain in the steel bar to be avoided. There is also the potential for a
concentration of corrosion at this point. For this reason, stainless steel is often used.However, if the debonding material also provides a proven protection against corrosion
it should be acceptable for conventional (HY) steel to be used.
8.33
Detail 8.5.3-1
8.5.3-2
Run on slab
Run-on slab - connection types
8.5.3-3
Run on slab
Abutment
. -Ij"'----- --- -·1-
(A) Anchor bars near bottom (8) Anchor bars near top
11----------,------'
\ ---.f_.-----"----_Abu_t_m_ent~>
Run on slab \
\ J
Run on slob
Stainless steelreinforcementfrom abutment
(C) Continuity bars top andbottom
(0) Inclined anchor bars
Run on slab
\
25 thicklow movementjoint filler
Abutment
(E) No anchor bars
8.34 CfRIA C543
PREFERRED • Options A and B, a single layer of horizontal reinforcement providing horizontalanchorage between run-on slab and abutment are preferred.
AVOID
REMARKS
CIRIAC543
•
•
•
•
•
•
•
Short dowels.
Run-on slabs in Options A and B are cast directly against rear of recess in abutment toform a construction joint across which only the anchorage bars are passed.
Anchorage bars are debonded over a short length adjacent to the construction joint toavoid concentration of stresses at the crack that would result from the flexing of the runon slab.
Use of corrosion protection (Denso) tape to provide debonding will permit the use ofconventional reinforcing bar for anchorage. Otherwise stainless-steel bar must be usedfor anchorage.
If stainless-steel bar is used for anchorage the stainless-steel bars must be providedwith electric isolation from the remainder of the structural reinforcement in the bridgeabutment to avoid the effects of electrolytic action between the dissimilar metals.
Reinforcement bar to be fully anchored into run-on slab and abutment.
Bearing shelf for run-on slab typically 200-250 mm wide.
8.35
Detail 8.5.3-2 Run-on slab connection - anchor bars near bottom
Approach slabAnchor bars to bedebanded locallyover extent shownwith Denso tapeor equivalent \
-'D'~~'D'rHigh yield steel
anchor bars
/ I<"''' -r--t-.. - - I---
....l-I 25x25 chamfer
'7 '\Building paper or
\other debondingmembrane 'X'
L'--Bitumen paint
1\ tv--J fv
.... Abutment
REMARKS • Length of anchorage bars to be at least sufficient to develop full anchorage bond into therun-on slab and anchorage, typically 800 mm, from the ends of the debonded length.
• Dimension X, run-on slab bearing, typically 200-250 mm.
• Anchor reinforcement to be positioned to pass just above bottom mat of reinforcement inrun-on slab.
8.36 CIRIA C543
Detail 8.5.3-3 Run-on slab connection - anchor bars near top
Anchor bars to bedebonded locallyover extent shownwith Denso topeor equivalent
'D'
u
'D'
slob
High yield steelanchor bars
0 ..32 Y (min)
----~---\-------
Building paper orother debondingmembrone -+---J
......
15 thickcompressiblemoteriol
Abutment
'x'
25x25 chomfer
Bitumen paint
~~_I_--------,.f
REMARKS
CIRIA C543
•
•
•
•
Length of anchorage bars to be at least sufficient to develop full anchorage bond into therun-on slab and anchorage, typically 800 mm, from the ends of the debonded length.
Dimension X, run on slab bearing, typically 200-250 mm.
Anchor reinforcement to be positioned near the top of the middle third of thickness ofrun-on slab.
Dimension C, height of compressible material in bottom of construction joint to beapproximately half the thickness of the run-on slab and to suit the position of theanchorage bars.
8.37
8.6
8.6.1
OTHER FORMS OF INTEGRAL BRIDGE
Arches
The oldest fonn of integral bridge is a masonry arch. There are numerous archstructures, many of them centuries old, which are still functioning perfectly well eventhough the loadings may have far exceeded those that the designer had in mind, seeFigure 8.7. To a large extent this must be due to the fact that the materials in thesestructures arc in permanent compression and also there is no steel to rust.
Figure 8.7
8.6.2
8.38
Masonry arch (integral) bridge
Another popular form of integral construction uses precast reinforced concrete archsegments, which have been used for culverts, road underbridges and tunnels. However,the details for such bridges, except where proprietary products are adopted for smallerstructures, are developed by the engineers specifically to suit the circ*mstances. Theyhave yet to bc proven by successful use over a significant period.
Today's designer should ask himself whether the site in question would be appropriatefor a masonry or mass concrete arch. When whole-life costings are applied to the variousoptions an arch may be very economic.
Boxes
Another very common fonn of integral bridge is the box, either single-cell or multi-cell,see Section 3.5. These structures, when buried, have no movement joints at road leveland no bearings. When precast units are used, usually as a proprietary product, care mustbe taken with the joint details between adjacent segments.
CIRIA C543
CIRIA Report C543
References
THE HIGHWAYS AGENCY
BD 57/95, Design/or Durahilitv
HMSO, August 1995
2 WALLBANK, E J
The performance o(concrete in hridges
HMSO, April 1989
3 RAY, S S, BARR, J and CLARK, L
Bridges - design/hI' improved buildahilitv
CIRIA Report 155, London, 1996
4 INSTITUTION OF STRUCTURAL ENGINEERS
CONCRETE SOCIETY
Standard method ofdetailing structural concrete
The Institution of Structural Engineers, 19X9
5 HAYWARD, A and WEARE, F
Steel Detailer '.I' Manual
BSP Professional Books, 19X9
6. EVANS, J E and ILES, D C
Steel Bridge Group: Guidance Notes on Best Practice in Steel Bridge Construction
SCI Publication 185, 199X
7. BIDDLE, A R, ILES, DC and YANDZIO, E
integral Steel Bridges - Design Guidance
SCI Publication 163, 199X
8. HIGHWAYS AGENCY
BA 57/95. Design/i)}' Durabilitv
HMSO, August 1995
9. HIGHWAYS AGENCY
BA 42/96. The Design o/lntegral BridgesHMSO, November 1996
10 HIGHWAYS AGENCY
BD 47/99 Waterproofing and Surfacing ofConcrete Bridge Decks
HMSO, August 1999
11. BUSSELL, M N, and CATHER, R
Design and construction ofioints in concrete structures
CIRIAReport 146,London, 1995
12. OVE ARUP & PARTNERSCDM Regulations - work sector guidance/hI' designers
CIRIA Report 166, London, 1997
R1
13. GEDGE, G and WHITEHOUSE, NNew paint systemsfor the protection ofconstruction steelwork
CIRIA Report 174, London, 1997
14. WRIGLEY, R G
Permanentformwork in construction
CIRIA publication C558, London, 2001
15. HARRISON, T A, DEWAR, J D and BROWN, B VImproving freeze-thaw resisting concrete in the UK
CIRIA publication C559, London, 2001
16. KING, E S and DAKIN, J MSpecifYing, detailing and achieving cover to reinforcement
CIRIA publication C568, London, 2001
17. HIGHWAYS AGENCY
The Design Manualfor Roads and Bridges
HMSO,1999
18. HMSO
Construction (Design and Management) Regulations 1994
HMSO, Statutory Instmments 1994 No 3140, March 1995
19. HEALTH AND SAFETY COMMISSIONSafe work in confined spaces, Confined Spaces Regulations 1997
HMSO, HSE books Ll 01, Sudbury, Suffolk, 1997
20. HIGHWAYS AGENCYBA 36/90 The Use ofPermanent Formwork
HMSO, Febmary 1991.
21. PEARSON, Sand CUNINGHAME, J R
Water management jiJr durable bridges
Transport Research Laboratory, Application Guide 33, Crowthorne, 1998
22. Environmental protection act
Legislation (Parliament), London, 1990
23. HSEControl ofSubstances Hazardous to Health Regulations (COSHH)
HSE books, Sudbury, Suffolk
24. BRITISH STANDARDS INSTITUTION
Steel, concrete and composite bridges
Part 10. Code ofpracticeforfatigue
BS 5400: Part 10: 1980
25. CIRIAManual ofgood practice in sealant applicationCIRIA, Special Publication 80, London, 1991
26. HIGHWAYS AGENCYBD 33/94, Expansion Joints for Use in Highway Bridge Decks
HMSO, November 1994.
R2 CIRIA C543
27. HIGHWAYS AGENCY
BA 26/94, Expansion Joint.~for Use in Highway Bridge Decks
HMSO, November 1994
28. BRITISH STANDARDS INSTITUTION
Steel, concrete and composite bridges
Part 4, Code ofpractice for design ofconcrete bridges
BS 5400 : Part 4 : 1990
29. CONCRETE SOCIETY
Durable bonded post-tensioned concrete bridges
Concrete Society Technical Report 47, Crowthome, 1996
30. BALINT,PSandTAYLORHPJ
Rein/iJrcement detailing ofji'ame cornerjoint.~with particular reference to opening
corners
Cement and Concrete Association Technical Report 42.462, London, 1972
31. BRITISH STANDARDS INSTITUTION
Steel, concrete and composite bridges
Part 3. Code ofpractice/iJr design ofsteel bridges
BS 5400 : Part 3 : 1982
32. BRITISH STANDARDS INSTITUTION
Welded, brazed and solderedjoints - Symbolic representation on drawings
BS EN 22553 : 1995
33. EUROPEAN COMMITTEE FOR STANDARDISATION
Eurocode 4 : Design ofcomposite steel and concrete structures
Part 2 : Composite bridges
British Standards Institution for CEN, Brussels, 1997
34. BRITISH STANDARDS INSTITUTION
Steel, concrete and composite bridges
Part 5. Code olpractice/iJr design olcomposite bridges
BS 5400 : Part 5 : 1979
35. HIGHWAYS AGENCY
BA 53/94, Bracing s.vstems and the Use ol U-Frames in Steel Highway Bridges
HMSO, December 1994
36. BRITISH STANDARDS INSTITUTION
Steel, concrete and composite bridges
Part 6. SpecijicationjiJr material and workmanship, steel
BS 5400 : Part 6 : 1999
37. STEEL CONSTRUCTION INSTITUTE
End deflexions in skew spans during construction
"Advisory Desk" AD 079, Steel Construction Today, 1991
38. HIGHWAYS AGENCYBD 7/81, Weathering steeljiJr highvva.v structures
HMSO, August 1981.
CIRIA Report C543 R 3
R4
39. PATERSON, W S
Selection and use offi.'(ings in concrete and masonry: interim update to
CIRIA Guide 4CIRIA Technical Note 137, London, 1991
40. BRITlSH STANDARDS INSTlTUTlON
Highway parapets for bridges and other structures
BS 6779, Parts 1,2,3 and 4
41. HIGHWAYS AGENCY
BD 52/93, The Design ofHighway Bridge Parapets
HMSO, April 1993
42. HIGHWAYS AGENCY
TD 19/85, Saj'ety Fences and Barriers
HMSO,I985
43. HIGHWAYS AGENCY
TD 32/93 Wire Rope Safety Fences
HMSO, December 1993
44. HIGHWAYS AGENCY
BD 30/87 Backfilled Retaining Walls and Bridge AbutmentsHMSO, August 1987
45. HIGHWAYS AGENCY
BD 42/94 Design ofEmbedded Retaining Walls and Bridge Abutments
(Unpropped or Propped at the Top)
HMSO, December 1994
46. HIGHWAYS AGENCY
Specification/i)r High,vay Works
TSO,1999
47. BAMFORTH, P B and PRICE, W F
Concreting deep lifis and large volume pours
CIRIA Report 135, London, 1995
48. HIGHWAYS AGENCY
BD 68/97 Crib Retaining Walls
HMSO, February 1997
49. HIGHWAYS AGENCY
BA 68/97 Crib Retaining Walls
HMSO, February 1997
50. BRITlSH STANDARDS INSTITUTIONCode ofjJractice/i)r strengthened/reinforced soils and otherfills
BS 8006 : 1995
51. NICHOLSON, B ATntegral bridges - report ofa study tour to North America
Concrete Bridge Development Group, Crowthorne, 1997
CIRIA C543
A1
CIRIA C543
Procedure for feedback
Individuals/organisations are encouraged to submit recommendations to improve
existing details in the guide and/or suggest alternative or additional details. The CAD
library on the CD-ROM provided with this book has been designed to be updated easily
and quickly.
CIRIA has established a holding file for contributions. Receipt will be acknowledged at
the time, and the contents of the holding file will be reviewed annually by the Highways
Agency and CIRIA. The address and format for contributions are set out below.
Should a correspondent consider that the implementation of a recommendation they are
making is urgent their submission should be marked URGENT in bold capitals at the
head of the front page.
Address
BRIDGE DETAILING GUIDE FEEDBACK
CIRIA
6 Storey's Gate
Westminster
London SWI P 3AU
Format
ORGANISAnON/NAME
Address
Telephone
Fax
NATURE OF FEEDBACK
l. Modification to existing detail(s) or advice
• identify detail number and/or section number
provide copy of existing detail or advice marked up with recommendations
provide briefbacki:,'TOlmd and/or justification to support the
recommendation/s
2. New detail and related advice
• provide copy of the new detail
• recommend related advice to be included in the guide
• identify the need and justification for each new detail.
Note
Authorship of any new details and/or modifications that are adopted will be
acknowledged.
R5
• •• ..!-".-~.
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September 2001
The UK highways bridge stock has exhibiteddurability problems in recent years, many ofwhich are attributed to poor detailing and a lackof appreciation of buildability by designers.
The Quality Services Directorate of theHighways Agency manages a large researchprogramme that assists the Agency in its primaryrole as network operator for the trunk roadnetwork. The research aims to support theAgency's key objectives by consolidating andimproving their information, knowledge, ideas,tools and technologies for (i) corporate technicalstrategy and (ii) meeting the wider Agencyneeds.
ISBN 0 86017 543 X
Although there are many sources of advice ongood detailing, it is rare for such guidance to becollected together. Organisations engaged inbridge design and/or construction usually havetheir own preferences. As modern massproduction methods are increasingly applied inthe construction industry, details will tend to berepeated within projects and from project toproject. It is therefore important to identify bestpractice and to eliminate deficiencies.
This book has been prepared for use by activemembers of the bridge engineering professionand is intended for consultants, contractors,bridge owners and their maintaining agents. Itwill be of direct use to trainee engineers(including graduates), technicians andincorporated engineers involved in detailinghighway bridge designs. It should also be ofvalue to chartered engineers as they developdesigns, and to site staff, as it provides advice onthe function and relative merits of various details.
The book concentrates on those details thathave proved to be reliable in everyday use fordurability and ease of construction, inspection,maintenance, repair and demolition. Only detailsthat can be clearly defined have been included.Supporting text explains the rationale behind thechoice of each detail and considers durabilityand buildability issues. The details have beenprepared in a way that allows them to be readilyadopted by designers, but care will still beneeded to ensure that the details, anddevelopments from them, are correctlyinterpreted and applied. The details are alsosupplied in .dwg format on CD-ROM.