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CIRIA C764

London, 2017

Hidden defects in bridges Guidance on detection and management J Collins, D Ashurst Arup J Webb, P Sparkes AECOM A Ghose Waterman (formerly AECOM)

Griffin Court, 15 Long Lane, London, EC1A 9PN Tel: 020 7549 3300

Fax: 020 7549 3349

Email: [email protected]

Website: www.ciria.org

Summary The UK and Ireland’s bridges are central to the countries’ economies and societies. When a bridge has a weight restriction or an emergency closure imposed, the consequences can be severe. The body of case studies in the guide provides evidence that these events are often caused by hidden defects. The existing methods of managing risks associated with hidden defects in bridges are reviewed and critiqued. A proposal for a proactive approach is made. With a focus on superstructure, detailed practical guidance on commonly encountered hidden defects categorised by structural element is given. The guidance is extensively cross-referenced to other sources of good practice and includes input from a broad spectrum of the bridge engineering industry. It will prompt all those involved with the UK and Ireland’s bridge stock whether owner, operator, maintainer, designer, inspector or contractor to assist in reducing risks associated with hidden defects. Hidden defects in bridges. Guidance on detection and management Collins, J, Ashurst, D, Webb, J, Ghose, A, Sparkes, P CIRIA C764

© CIRIA 2017

RP1013

ISBN: 978-0-86017-779-1

British Library Cataloguing in Publication Data A catalogue record is available for this publication from the British Library Keywords Asset and facilities management, environmental management, health and safety Reader interest

Classification

Ground engineering, ground investigation and characterisation, embedded retaining wall, ground movements, piling, retaining wall, soil-structure interaction

Availability

Unrestricted

Content

Advice/guidance

Status

Committee-guided

User Design, specification, construction, managers, clients and supervising engineers involved in civil and geotechnical works

Published by CIRIA, Griffin Court, 15 Long Lane, London, UK EC1A 9PN This publication is designed to provide accurate and authoritative information on the subject matter covered. It is sold and/or distributed with the understanding that neither the authors nor the publisher is thereby engaged in rendering a specific legal or any other professional service. While every effort has been made to ensure the accuracy and completeness of the publication, no warranty or fitness is provided or implied, and the authors and publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from its use. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature. If you would like to reproduce any of the figures, text or technical information from this or any other CIRIA publication for use in other documents or publications, please contact the CIRIA publishing for more details on copyright terms and charges at: [email protected] or tel: 020 7549 3300.

Front cover images Main cover photo: Forth Road Bridge inspecting and installing monitoring equipment at the failed north-east main span truss end link (courtesy Chris Waite) Bottom left: Hammersmith Flyover Bridge Bottom right: Plank Lane Lift Bridge (courtesy Rod Howe)

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Acknowledgements CIRIA was approached by the Bridge Owner’s Forum (BOF) whose members identified the need for this guide, which is the result of CIRIA Research Project (RP) 1013. Many members of BOF subsequently cofunded part of the project and kindly provided input and review of the guide as members of the project steering group.

Authors John Collins MEng(Hons) CEng MICE John is a senior engineer at Arup. He works predominantly with existing bridges undertaking assessments, inspections, investigative works, strengthening and refurbishment. In 2016 he was named as a RAEng Engineers Trust Young Engineer of the year, predominantly in recognition of his work on the Humber Bridge (Case study A1.13) and Forth Road Bridge (Case study A1.37).

David Ashurst BSc CEng MICE David has worked for Arup since 1985 and is an associate director. His main focus is in structural investigation – determining the causes of structural problems and in the appropriate rehabilitation. He was a member of the PSG for CIRIA’s guidance on iron and steel bridges (Tilly et al, 2007).

John Webb BEng CEng MICE John has worked on a wide range of construction, repair and maintenance projects over many years – the last 30 with AECOM (formerly Maunsell). He was a co-author on Guidance on the design, assessment and strengthening of masonry parapets on highway structures (DfT, 2012).

Amrit Ghose BA BAI MSc CEng CEnv FICE Amrit is a framework director at Waterman (formerly regional director at AECOM) responsible for bridge management, maintenance and design services. He is a member of a number of national bridge and structures committees setting policy and standards for the industry.

Peter Sparkes BSc Hons Civ Eng MICE MIStructE Peter is an associate director at AECOM with over 40 years’ experience in bridge design, assessment and construction. His area of expertise lie in the condition and behaviour of bridges, particularly masonry structures.

Hidden defects in bridges – guidance for detection and management

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Project steering group The PSG consisted of industry leading experts, many of whose organisations contributed to funding of the project and report content. The authors are grateful to all members for their extensive and detailed contributions to the guide. They provided comments, ideas, content and case studies: Matthew Anderson

Strainstall

Chris Brock

Atkins

Graham Cole

Graham Cole Consultancy Ltd

Barry Colford*

AECOM (formerly Forth Estuary Transport Authority)

James Collins

Ramboll

Matthew Dronfield

Freyssinet

Ken Duguid (retired)

Formerly of Transport for London

Richard Fuller*

Environment Agency

David Gibson*

Mott MacDonald

Jamie Harrison*

Osborne

Rod Howe

Canal & River Trust

John Iliff

Transport Infrastructure Ireland

Paul Jackson*

Ramboll

Lee Kelly

CIRIA

Dr Donald Pearson-Kirk (chairman)

Mouchel (now part of WSP|Parsons Brinckerhoff)

Liz Kirkham*

Gloucestershire County Council

John Lane*

Rail Safety and Standards Board

Neil Loudon

Highways England

Dr Hazel McDonald

Transport Scotland

John McRobert*

Transport NI

Cam Middleton*

University of Cambridge

Rabinder Phull*

Institution of Civil Engineers

Colin Richardson*

Environment Agency

Chris Sheppard

Balfour Beatty

John St Leger*

Strainstall

Julian Staden

Network Rail

Andrew Stevenson*

Scottish Canals

Kevin Stoakes

Tube Lines (London Underground Limited)

Guy Szomi

Environment Agency

Derek Thornbill*

Osbourne

Alan Tovey*

Concrete Bridge Development Group

Kieran Tully

CIRIA

Ben Wilkinson*

Network Rail

Elfyn Williams

Welsh Government

Saeed Ziaie*

WSP|Parsons Brinckerhoff

*corresponding members

Other contributors The following provided additional contributions to the guide: South Yorkshire Passenger Transport Authority, Amey plc at the Forth Road Bridge, David Millar. Arup: Hunisha Patel, Khurram Nazir, Richard Fletcher, Nicola Talbot, Oliver Riches, Ann Jones AECOM: Fiona Pick, Jack Rose, Sayf Bakr.

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Specialist technical guidance was provided by Arup’s materials specialists: Graham Gedge (corrosion and protection systems), Simon Cardwell (fracture mechanics), Bryan Marsh (concrete). Dave Ward and Keith Harwood assisted with review. Details for some of the case studies and photographs were provided by Chris Armstrong, Dave Ward, Sonam Norbu, Steve Kite, Pat Moore, Dara McDonnell and Paul Baralos. Detailed technical input was provided by AECOM’s experts: George Lawlor (steel bridges), Mark Bulmer (cable-stayed and suspension bridges), Charles Cocksedge (cable-stayed and suspension bridges), Beverley Urbans (timber bridges), David Dunne (concrete technology), Christian Christodoulou (repair methods, corrosion), Simon Caswell and Ryan Cobbs (inspection methods).

Funders Environment Agency Freyssinet Structural Repairs and CCSL Ltd Highways England Institution of Civil Engineers Research Enabling Fund Mouchel (now part of WSP | Parsons Brinckerhoff) Network Rail Ramboll Strainstall Transport Infrastructure Ireland (TII) Transport NI Transport Scotland Welsh Government The authors’ employers AECOM and Arup fully supported the project. In addition to the funds provided directly to CIRIA by industry organisations and suppliers, AECOM and Arup provided substantial funding from internal research and development sources.

CIRIA project team The initial project director for the guide was Chris Chiverrell, and project manager Victor Zasadzki. Lee Kelly

Project manager

Kieran Tully

Project director

Clare Drake

Publishing manager

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Foreword The need for this guidance became clear to bridge engineers following a number of specific incidents where significant deterioration of hidden components of bridges led to closures, emergency works or major disruption, despite established inspection and maintenance regimes being in place. Many of the most critical defects in bridges are often hidden from sight, either inaccessible or not obvious on first observation. Examples of failures include Plank Lane Bridge, a bascule bridge where the counterweight weighing several tonnes fell onto the carriageway below whilst unrelated maintenance to the mechanical components was being carried out (2006). Fortunately there were no injuries in this instance, although the counterweight narrowly missed causing serious injury to the maintenance crew. The significance of hidden defects and their ability to cause significant loss of life is illustrated by high profile failures including the de la Concorde collapse (2006) and the Forth Road Bridge truss end link failure (2015) which resulted in closure until emergency works were carried out. The guide aims to share such knowledge to avoid these issues in future through the illustration of hidden defects and how to detect or design them out. The production of the guidance has been steered by a governance group comprising bridge consultants, contractors and suppliers, academics and UK and Ireland bridge owners. The guide provides methods to identify, investigate and manage many known hidden defects, illustrated by a significant number of well documented case studies and comprehensive reference list. This guide fills in some important gaps in knowledge and is complementary to existing bridge inspection guidance. It is essential reading and reference material for the Bridge Inspector Certification Scheme, graduates under training and all professionals involved in bridge engineering and management. Dana Skelley Chair of UK Bridges Board

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Executive summary The UK and Ireland’s bridges play a critical role in support of their countries’ economies and societies. As evidenced by the rarity of bridge failure or closure, they are generally well managed and fulfil their operational requirements. This guide collates a group of case studies demonstrating that hidden defects do exist in critical bridge components. In some cases they have threatened safety to the travelling public. In extreme cases they have resulted in the collapse of bridges without warning. If the risk posed by hidden defects is not managed appropriately then the likelihood of encountering such failures will increase. Chapter 2 of this publication records general existing practice. Following collapse of a bridge at Stewarton in 2009, Network Rail has successfully implemented a national programme of inspection and remedial works of hidden critical elements. This method is described and developed in Chapter 3 with recommendations on use of structural risk assessments and failure mode effect analyses to form guidelines for bridge managers. The remainder of the guide presents the technical details of various hidden bridge components and their potential defects. It provides a brief description for their inspection, identification and maintenance and offers some suggestions for how to limit risk through design. Common themes identified for management of hidden defects in bridge components include: Inspection: before visiting the site, a thorough desk study is vital. By identifying uninspected or uninspectable areas, the desk study should ask ‘what is not recorded?’. Similarly, once on site the inspector should not only record what can be seen, but ask the question ‘what cannot be seen?’. There is generally no method as informative and reliable as visual inspection from within touching distance by direct line of sight. It is appreciated that this may often involve destructive works and be expensive and time-consuming. However, without such inspection by a knowledgeable, suitably qualified inspector then unknown levels of risk over the hidden component will remain. Non-destructive testing (NDT), endoscopic, drone and remote monitoring methods of inspection may provide some useful information, but are not necessarily an appropriate substitute. Identification: good quality interpretation of the inspector’s findings is required to determine if a defect to a hidden component threatens the bridges’ function and safety. The inspection findings can inform a numerical assessment if needed. Maintenance: given the extensive efforts that may have been made to gain access for inspection, the opportunity may also exist to remediate the defect. Not only should the defect be repaired if required, but the cause should be confidently identified and addressed. In some cases the primary cause of a hidden defect may be inadequate maintenance. For example, routine maintenance or timely replacement of waterproofing, expansion joints, drainage, paintwork etc may obviate hidden degradation. Such issues are often used in considering whole life cost at design stage, but the principles are not always adhered to during service life. Design: the Construction Design and Management Regulations 2015 (CDM 2015) may oblige the designer to manage the risk associated with hidden defects. Specific requirements should be included in contract terms and/or design basis documents. Where a hidden component cannot be avoided, bespoke specification and often specialist material/protective systems advice may be required to minimise the likelihood of defect development. As with all bridge details, a preference towards simple, robust details should be adopted. Low or zero maintenance choices are preferred to mitigate risks of maintenance not being undertaken during service life. Means of access for inspection, maintenance and, where relevant, replacement should be considered at the design stage. While currently only an emergent technology in the bridge industry, structural health monitoring systems offer great potential in assisting management of hidden defects.

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Preface This has been an illuminating and enjoyable guide to write. There is much interest in the subject. Altruistic professionals from across the civil engineering sector have been keen to provide opinions, ask challenging questions and share knowledge. CIRIA embodies much of the construction industry’s spirit of openness for general betterment of all, and this guide offers an outstanding example. By definition, experience-based guidance requires input from more experienced practitioners. However, this guide has had a high level of input from enthused younger engineers whose own experiences and viewpoints have been valuable. While there has been concerted effort to ensure the most commonly encountered hidden defects and bridge types are included, this guide is not all encompassing. It is not definitive guidance and some aspects such as substructure and design of new bridges to reduce risks posed by hidden defects would be worthy of more information. However, this guide encourages the reader to consider hidden bridge components that are hidden where visual inspection alone may not be enough. Some of the photographs and defects in this guide are striking. However, in the authors’ experience, severe deterioration shown in parts of this guidance is not commonplace on the UK and Ireland’s bridge stock. There has been substantial improvement in design details, construction quality and products over the last few decades. Combined with risk-based management techniques such as that outlined in this guide, it is hoped that engineers in the future will be less likely to uncover or manage adverse consequences of hidden defects in bridges. John Collins, Dave Ashurst, John Webb, Amrit Ghose, Peter Sparkes

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Contents Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Executive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii How to use this guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

Part 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1 Who is the reader? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2 What is a defect? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 1.1.3 What is a bridge? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1.4 What is a hidden component? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Management of hidden defects in bridges, existing practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Existing UK and Ireland highway bridge management practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 General – UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.2 General – Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3 Condition performance indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1.4 DMRB standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1.5 Highway bridge management – other guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1.6 Existing highway bridge practice: discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Existing UK and Ireland railway bridge management practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3 Planning and undertaking an inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.4 Legislative, contractual and code of practice considerations during the design phase . . . . . . . . . . . . . . . . 12 2.4.1 Legislative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4.2 Contractual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4.3 Codes of practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.5 Discussion of existing practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3 Management of hidden defects in bridges, recommended practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.1 Approach to management of hidden defects in bridge components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2 A risk-based approach to managing hidden defects in bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2.1 Risk review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2.2 Risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.3 Risk management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.3 Starting a hidden defects programme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.3.1 Portfolio overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.3.2 Hidden defects investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.4 Bridge inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.5 Inspection tools – role of technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.6 Structural health monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4 Components and defects in bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Part 2 Technical guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 5

Iron and steel bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Hidden components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Steel components under ballast/surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2 Protected steel surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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6

7

8

9

x

5.1.3 Insides of boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 5.1.4 Members behind non-structural components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 5.1.5 Abutting structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 5.1.6 Deck/buckle plates, jack arches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 5.1.7 Suspension bridge main cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 5.1.8 Suspension bridge hangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.1.9 Cable stays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 5.1.10 Components deemed too difficult to inspect/missed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5.1.11 Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5.2 Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 5.2.1 Metallurgical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 5.2.2 Section loss from corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 5.2.3 Latent weld defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 5.2.4 Fatigue cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 5.2.5 Brittle fracture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5.2.6 Bolting and rivets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Concrete bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 6.1 Hidden components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6.1.1 Within the concrete body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 6.1.2 Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 6.1.3 Prestressing wires/strands and anchorages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 6.1.4 Voided and cellular structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 6.1.5 Half-joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 6.1.6 Obscured surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 6.1.7 Concrete hinges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 6.1.8 Temporary works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 6.2 Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.2.1 Alkali–silica reaction (ASR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 6.2.2 Sulfate attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.2.3 Chlorides in concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.2.4 Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 6.2.5 Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 6.2.6 Reinforcement/prestressing corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.2.7 Missing/inadequately fixed reinforcement/prestressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Masonry arch bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 7.1 Hidden components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 7.1.1 Arch barrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 7.1.2 Spandrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 7.1.3 Masonry piers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 7.2 Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 7.2.1 Hollowness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 7.2.2 Mortar loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 7.2.3 Masonry deterioration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 7.2.4 Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Timber bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 8.1 Hidden components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 8.1.1 Timber interior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 8.1.2 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 8.2 Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 8.2.1 Biological attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 8.2.2 Splitting, checks and shakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Bearings and expansion joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 9.1 Hidden components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 9.1.1 Poor access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 9.1.2 Uninspectable details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 9.1.3 Inspection at the ‘wrong’ time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 9.2.1 Metallurgical and corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 9.2 Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 9.2.2 Bearing seizure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 9.2.3 Sliding interface deterioration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

CIRIA, C764

9.2.4 Elastomeric deterioration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 9.2.5 Bearing installation errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 9.2.6 Other bearing defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 9.2.7 Expansion joint hidden defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 10 Durability components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 10.1 Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 10.2 Waterproofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 10.3 Paint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 10.4 Galvanising . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 10.5 Sealants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 10.6 Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 11 Safety components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 11.1 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 11.2 Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 11.3 Access/walkways/gantries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 12 Other bridge components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 12.1 Moveable bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 13 Ancillary components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 13.1 Services, bays and ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 14 Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 14.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 14.2 Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 14.3 Identification and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 14.4 Design guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

Part 3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 15 Further research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 16 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 16.1 Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 16.2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 16.3 Further learning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 16.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Part 4 Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 A1 Case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 A2 Extract from BS 5400-10:1980 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 Statutes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

Boxes Box A1.1 Extract from Queensferry Crossing’s design requirements highlighting the importance of design approach for access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

Case studies Note that Case studies A1.27 and A1.28 are not bridges, but are of interest to infrastructure managers. These studies both form clear examples of the importance in understanding condition of hidden areas on assets with very little redundancy. A1.1

A1.2

A1.3 A1.4 A1.5

Hidden critical elements programme, Network Rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.1.1 Defining the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.1.2 Desk-based study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.1.3 Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.1.4 Ongoing management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.1.5 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge collapse, corrosion of buried girder web, Stewarton, Ayrshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.2.2 Bridge design/articulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.2.3 Factors leading to the collapse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.2.4 Inspection history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1.2.5 Network Rail’s response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Box girder section loss due to corrosion, components behind masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel box girder bracing detail, Midland Links viaducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bolt failure and dropping of counterweight, Plank Lane bridge, Lancashire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hidden defects in bridges – guidance for detection and management

215 215 215 215 219 219 220 220 220 221 221 222 223 224 225

xi

A1.6 A1.7 A1.8 A1.9 A1.10 A1.11

A1.12 A1.13 A1.14 A1.15

A1.16 A1.17 A1.18 A1.19 A1.20 A1.21 A1.22 A1.23 A1.24 A1.25 A1.26 A1.27 A1.28 A1.29 A1.30 A1.31 A1.32 A1.33 A1.34

A1.35 A1.36 A1.37

A1.38 A1.39

xii

A1.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 A1.5.2 Factors leading to the collapse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 A1.5.3 Subsequent actions and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Weld cracking, Boston Manor Viaduct, west London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Strengthening and refurbishment, High Level Bridge, Newcastle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Hidden section corrosion loss and replacement, Southend High Street bridge, Essex . . . . . . . . . . . . . . . . . . . . . . . 230 Cracks to bearings, Thelwall Viaduct, Warrington . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Approach viaduct bearing replacement, Forth Road Bridge, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Post-tensioning deterioration, Hammersmith Flyover, west London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 A1.11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 A1.11.2 Chronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 A1.11.3 Description of the structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 A1.11.4 Works before strengthening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 A1.11.5 Strengthening part I – interim measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 A1.11.6 Strengthening part 2 – phase 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 A1.11.7 Strengthening part 2 – phase 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Rail underbridge bearing condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 Main span bearing replacement, Humber Bridge, East Yorkshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 Half-joint failure, Pont de la Concorde, Laval, Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Deck hinge joints – investigation techniques, M4, South Wales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 A1.15.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 A1.15.2 Nature of the challenge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 A1.15.3 Investigation programme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 A1.15.4 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 A1.15.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Concrete components, Midland Links motorway viaducts, Birmingham . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Thaumasite sulfate attack, M5 Bridges, Gloucestershire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Hidden defects programme, Transport Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Hidden defect identification, D46 bridge, Middlesex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 Roller-shutter joints, Forth Road Bridge, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 Failure of a stainless steel tie bar, southern England . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Corrosion to girders supporting jack arch at bridge D3, Harrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Main cable internal inspection and dehumidification, Humber Bridge, East Yorkshire . . . . . . . . . . . . . . . . . . . . . . . 257 Design approach to hidden components, Queensferry Crossing, Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Scour of abutment causing partial collapse, Bridge RDG1 48, west London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Expansion joint replacement, St George’s Bridge, Doncaster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Cladding collapse, Sasago Tunnel, Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 Overhead line equipment supporting post failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 Hidden arch defects, Belcoo Bridge, Northern Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Hidden spandrel defects, Crystal Palace Subway, south London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Hollow pier, Releagh Bridge, Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Rail masonry arch bridge hidden brickwork detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Defects in metallic parapet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Fatigue assessment of deck hinge joints, M4 motorway Usk River Bridge, South Wales . . . . . . . . . . . . . . . . . . . . . 272 A1.34.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 A1.34.2 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 A1.34.3 Findings of fatigue assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 A1.34.4 Approach limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 A1.34.5 Laboratory testing at Cardiff University . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 A1.34.6 Lessons learnt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Investigation of timber bearing pads, Royal Albert Bridge, Cornwall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Cladding failure, Denmark Hill, south London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Truss end link failure, Forth Road Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 A1.37.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 A1.37.2 Series of events, December 2015 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 A1.37.3 Failure analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 A1.37.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Parapet defects, Gallows Corner, Romford . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Fatigue cracking to track girders, North Bridge, Hull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

CIRIA, C764

Figures Figure 3.1 Risk-based approach to management of hidden defects in bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 3.2 Two key questions to ask when reviewing historic information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 3.3 Two key questions to ask on site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 3.4 Structure risk assessment and failure mode effect analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 3.5 Starting afresh on a hidden defects programme for an entire stock of bridges . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 3.6 Drones may be a useful tool in assisting inspections, but are no replacement for full inspection to within touching distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 3.7 SHM on Stonecutters Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 3.8 The main considerations when examining whether or not to employ SHM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Figure 4.1 Hidden components of a concrete bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figure 4.2 Hidden components of a steel bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figure 5.1 Girder on Manchester Metrolink, UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Figure 5.2 Highway bridge in East London, UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Figure 5.3 Buried girders (circled in red) of a half-through rail underbridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Figure 5.4 A standard haunch detail to a reinforced concrete slab providing further moment capacity and protecting the web from ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Figure 5.5 Timber boarding against steelwork of web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Figure 5.6 Ballast plates, here with removable lids to aid inspection as part of a new FRP arrangement . . . . . . . . . . . 49 Figure 5.7 The top surface of a cross girder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Figure 5.8 Main components as boxes, a girder (a), and truss chords (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Figure 5.9 Closed stiffener components, troughs (a), and bearing stiffener (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Figure 5.10 Inspection by endoscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Figure 5.11 Endoscopic inspection output: can be difficult to interpret. Detailed accompanying commentary is important . 53 Figure 5.12 Failed bolt heads inside a box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Figure 5.13 Cabling obscuring a steelwork parapet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Figure 5.14 Girder end at abutment hidden by screening brickwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Figure 5.15 Severe corrosion to steelwork uncovered during a Network Rail HCE inspection . . . . . . . . . . . . . . . . . . . . . . 55 Figure 5.16 Viaduct composed of simply supported girders – standing over an intermediate pier . . . . . . . . . . . . . . . . . . 56 Figure 5.17 An example of adjacent bridge decks to the side, Leeds, UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Figure 5.18 Z-type bridge used on UK rails includes asymmetric girders that help limited inspection to one side of girders between tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Figure 5.19 Sagging buckle plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Figure 5.20 Jack arches, here spanning transversely between longitudinal beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Figure 5.21 Compilation of the suspension cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Figure 5.22 Cable access platform on suspension cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Figure 5.23 Wedge location in cable and encapsulated cable exposed for inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 Figure 5.24 Cable dehumidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Figure 5.25 Suspension bridge hangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Figure 5.26 Vibration dampers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Figure 5.27 Comparison of parallel strand, parallel wire and locked coil stays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Figure 5.28 Parallel strand anchorage details at deck (a) and tower (b) illustrating the difficult of inspecting hidden elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Figure 5.29 Generic stay termination socket for parallel wire stays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Figure 5.30 A rail bridge in West Yorkshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Figure 5.31 Spandrel wall tie bars exposed during removal of fill to masonry arch bridge . . . . . . . . . . . . . . . . . . . . . . . . . 72 Figure 5.32 The back of a pattress plate exhibiting corrosion suggesting water ingress to tie (a), the location of the pattress plate before its detachment from tie strand failure due to corrosion (b) . . . . . . . . . . . . . . . . . . . . . . 72 Figure 5.33 Tie bars to be buried as part of an abutment construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Figure 5.34 Location of failure of anchor bars to shear keys forming part of the bearing arrangement of the San Francisco–Oakland Bay Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Figure 5.35 Cause of damage to 128 bridges in East Germany since 1945 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Figure 5.36 Microstructure of wrought iron showing dark slag inclusions linear from the rolling process . . . . . . . . . . . . 75 Figure 5.37 Details susceptible to lamellar tearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Figure 5.38 Corrosion to hidden area, Brunel swivel bridge, Bristol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Figure 5.39 Design features inhibiting the development of corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Figure 5.40 Crack within ground back weld material, MPI to improve crack visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Figure 5.41 Crack started as fatigue growth from weld toe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Figure 5.42 Consequence of brittle fracture, Diefenbaker bridge, Canada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

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Figure 5.43 An example of a bolted connection between cross girder (left) and main longitudinal girder (right) with a shear connection detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Figure 6.1 Concrete bridge with difficult access to many components, Hammersmith Flyover, west London . . . . . . . . 88 Figure 6.2 Concrete from a demolished structure showing the matrix comprising aggregate, fines and cementitious binder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Figure 6.3 Strain gauge to be cast in a concrete member for SHM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Figure 6.4 Congested reinforcement at lap joint positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Figure 6.5 Congested reinforcement at a concrete protrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Figure 6.6 Stainless steel used for reinforcement in combination with carbon steel in the region up to the top of the estuary splash zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Figure 6.7 External post-tensioning on Hammersmith Flyover, west London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Figure 6.8 Grout and tendons exposed after opening of a duct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Figure 6.9 Recessed, but exposed and unprotected, post-tensioning anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Figure 6.10 Interior of a box beam bridge deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Figure 6.11 Bridge deck soffit showing access portals into the interior of Figure 6.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Figure 6.12 A typical half-joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Figure 6.13 Significant structural degradation of a Type A half-joint due to chloride-induced corrosion . . . . . . . . . . . . . . 98 Figure 6.14 Types of half-joints in accordance with their access onto the bearing shelf (a), and typical detail of a bridge half-joint (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Figure 6.15 Close-up inspection showing the condition of the hidden bearings of a half-joint using an endoscope for metal (a) and elastomeric (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Figure 6.16 Typical example of an inverted ‘T’ crosshead forming a half-joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Figure 6.17 Beams on thin elastomeric bearings on an abutment bearing sill with blocked sill drain . . . . . . . . . . . . . . . 101 Figure 6.18 Freyssinet hinge at the base of a bridge pier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Figure 6.19 Mesnager hinge, showing detail of the ‘scissor’ reinforcement crossing the throat . . . . . . . . . . . . . . . . . . . 102 Figure 6.20 Exposed mesh reinforcement in the cell soffit. Note evidence of corrosion on the far left . . . . . . . . . . . . . 104 Figure 6.21 Broken and unstable formwork left inside the cell after construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Figure 6.22 Typical ‘map’ style cracking pattern in unrestrained concrete resulting from ASR . . . . . . . . . . . . . . . . . . . . 106 Figure 6.23 ASR gel leaching from crack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Figure 6.24 ASR crack in pre-tensioned concrete beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Figure 6.25 Sulfate attack in concrete showing a tank that had held materials containing sulfates . . . . . . . . . . . . . . . . 108 Figure 6.26 Thaumasite attack displays layers of deposits around the aggregates in concrete . . . . . . . . . . . . . . . . . . . 108 Figure 6.27 DEF is characterised by visible displacement and cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Figure 6.28 Mechanism by which attack reduces the integrity of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Figure 6.29 Extreme chloride attack damage to a motorway support cross-beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Figure 6.30 Chloride attack damage, showing localised severe pitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Figure 6.31 A half-cell test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Figure 6.32 Reinforcement corrosion due to carbonation in reinforced concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Figure 6.33 Typical phenolphthalein staining test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Figure 6.34 Cracking in concrete, highlighted here with leachate staining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Figure 6.35 Longitudinal cracking and rust staining in a reinforced concrete beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Figure 6.36 Close-up view of exposed reinforcement in the soffit of a beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Figure 6.37 Inadequately fixed reinforcement in a post-tensioning blister component . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Figure 7.1 Bridge with arch barrel incorporating rib arches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Figure 7.2 Stability of an arch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Figure 7.3 A ‘flat’ masonry arch bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Figure 7.4 Spandrel wall [...] above the arch barrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Figure 7.5 Spandrel and arch barrel ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 Figure 7.6 Open spandrels at Pontypridd Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Figure 7.7 Masonry pier with loose rubble filling. Note the absence of mortar between stone units . . . . . . . . . . . . . . 127 Figure 7.8 Mortar (and masonry) loss from the arch barrel extrados . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Figure 7.9 The centre span [...] of a railway masonry arch bridge strengthened by partially replacing the arch barrel intrados with a concrete lining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Figure 7.10 Masonry deterioration due to a change in structural behaviour because of initial deterioration . . . . . . . . . 135 Figure 7.11 Classic case for longitudinal crack formation under back face of spandrel wall . . . . . . . . . . . . . . . . . . . . . . 137 Figure 8.1 Timber decking spanning longitudinally over cross girders to the High Level Bridge, Newcastle . . . . . . . . . 138 Figure 8.2 Wood cross-section. Bark (a), sapwood (b), heartwood (c), growth ring (d), knot (e), and examples of extraction patterns that could govern timber properties (f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Figure 8.3 Mechanically-laminated timber (using rectangular shear key blocks) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Figure 8.4 Good quality core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

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Figure 8.5 Collapsed core from poor quality timber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Figure 8.6 Connection with hidden metal components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Figure 8.7 Connections in a stress laminated timber bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Figure 8.8 Typical decay resulting from fungal attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Figure 8.9 Surface marks from insect activity that indicate interior decay has occurred . . . . . . . . . . . . . . . . . . . . . . . . 146 Figure 8.10 Riverine environment at Dutton Horse bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Figure 8.11 Checks, shakes and splits in timber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Figure 9.1 A weathering steel girder end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Figure 9.2 Expansion joint showing corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Figure 9.3 Mechanical component pot bearing (a) that contains many components of various materials (b) . . . . . . . 150 Figure 9.4 Modular expansion joints consist of multiple parts, forming a formidable piece of mechanical engineering in their own right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Figure 9.5 Precast concrete beams sitting on elastomeric bearings that are obscured by lighting units and sealant . . . . 151 Figure 9.6 Cast iron piers housing bearings within a decorative shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Figure 9.7 Endoscopic bearing inspection inside a half-joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Figure 9.8 Removal of a grease box (a) encasing a bearing which identified a misaligned roller (b) . . . . . . . . . . . . . . . 152 Figure 9.9 A PTFE disc removed from a bearing (a) compared to its new replacement (b) . . . . . . . . . . . . . . . . . . . . . . . 153 Figure 9.10 A carefully detailed contemporary nosing joint with incorporated drainage . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Figure 9.11 Monitoring data of the longitudinal position of the Humber Bridge main span recorded over 24 hours – extensometers measuring the gap between tower and deck box to an arbitrary datum . . . . . . . . . . . . . . . 154 Figure 9.12 Extensive corrosion focused at bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 Figure 9.13 Longitudinal translational freedom should be questioned for this heavily corroded roller bearing . . . . . . . 157 Figure 9.14 Extreme wear of a sliding interface on a bridge support bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Figure 9.15 Stainless steel sliding surface deterioration with a ‘tide mark’ of debris at the extreme range of the sliding surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Figure 9.16 Powdered PTFE working its way out of a bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Figure 9.17 A PTFE plate extruded out from a bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Figure 9.18 A sliding bearing that was notably misaligned against the bearing stiffener compared to other bearings on the bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Figure 9.19 A temporary concrete block used to take precast beam load while epoxy mortar cures to the elastomeric bearing behind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 Figure 9.20 An example of a grouting trial to a bearing base plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 Figure 9.21 Bearings of a Type 6 multi-element modular joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Figure 10.1 Subsurface drainage is inherently hidden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Figure 10.2 A new dual carriageway viaduct being waterproofed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Figure 10.3 Residual red lead paint left after paint removal for weld inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Figure 10.4 Around 20 layers of paint in a sample from the Royal Albert Bridge, London . . . . . . . . . . . . . . . . . . . . . . . . . 172 Figure 10.5 Galvanised ‘Armco’-type corrugated steel buried culvert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Figure 10.6 Newly galvanised surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Figure 10.7 Weathered galvanised surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Figure 10.8 A joint between an integral bridge span (left) and wingwall (right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174 Figure 10.9 Cladding to arch soffit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Figure 10.10 Rust staining and corrosion to fixings that should be investigated further . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Figure 10.11 Example of cladding panel (circled) that (subjectively) provides little aesthetic purpose . . . . . . . . . . . . . . . 176 Figure 11.1 Parapet exhibiting evidence of vehicle impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Figure 11.2 Parapet cast-in anchorage on Hogarth Flyover deck replacement using appropriately-graded stainless steel components for fixings prone to corrosion (a), embedded threaded bars had been used to secure a base plate (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Figure 11.3 High containment parapets (H4a) on a Manchester Metrolink underpass showing the difference between what is externally visible (a) and the hidden critical components (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Figure 11.4 Replacement parapets on Hogarth Flyover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Figure 11.5 Precast concrete parapet with [...] bolted anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Figure 11.6 Poor fixing to an access ladder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 Figure 11.7 Clear access to whole cross section without specialist techniques required, Queensferry Crossing central tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Figure 13.1 A manhole cover without a seal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Figure 13.2 A groove had been cut in the arch extrados to facilitate a gas main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Figure 13.3 Ducts to be cast into a deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Figure 13.4 Pipes are accessible and visible, but protected between the bridge’s girders . . . . . . . . . . . . . . . . . . . . . . . . 185

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Figure 14.1 At first glance, the back of platforms may be identified as the overhead bridge’s abutment (a). Platform wall is built in front of structural abutment (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Figure 14.2 A familiar form of bridge on a UK motorway with overhanging abutments (a), consulting as-built drawings reveals the presence of a hidden void (shown in red) found to the back of the abutment (b) . . . . . . . . . . . 188 Figure 16.1 Two key questions in preparation for inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Figure 16.2 Two key questions while inspecting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Figure 16.3 As-built record of arch widening from 1904 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Figure 16.4 Intrusive investigation may be disruptive and time consuming, but is usually the most reliable method to determine condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Figure 16.5 Mechanical removal of concrete required to positively identify reinforcement arrangement for confirmation of a NDT survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Figure 16.6 Aging bridge, demanding loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Figure A1.1 Extract from internal guidance on inspection of HCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Figure A1.2 Intrusive works specified for HCE inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Figure A1.3 East elevation of bridge (a), and west elevation (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 Figure A1.4 Cross section of the ballasted deck with waterproofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 Figure A1.5 The heavy band of corrosion at mid-height of the web on the centre girder after collapse . . . . . . . . . . . . . 221 Figure A1.6 Detailed survey of the eastern girder after collapse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 Figure A1.7 Cross section through bridge. Note the back-to-back universal beams (UBs) forming the outer girders . . 223 Figure A1.8 Elevation onto bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Figure A1.9 View inside a box beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Figure A1.10 Schematic of bracing detail showing poor fatigue detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Figure A1.11 Strain gauges installed to remotely monitor hidden component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Figure A1.12 Before collapse, Plank Lane bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Figure A1.13 Counterweight at Plank Lane Bridge taken on 22 March 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 Figure A1.14 End of counterweight showing sheared off bolt ends that were in threaded holes in the counterweight end plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Figure A1.15 Bolts from the bridge’s counterweight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Figure A1.16 The central truss spans of Boston Manor Viaduct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Figure A1.17 A crack discovered in an electro-slag weld to the edge of a plate girder flange . . . . . . . . . . . . . . . . . . . . . . . 227 Figure A1.18 The High Level Bridge, Newcastle-upon-Tyne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 Figure A1.19 A cast iron beam spanning between columns (a), and a new steel over-beam installed above the cast iron beam (b) to create a new load path if the cast iron beam fails from fatigue . . . . . . . . . . . . . . . . . . . . . . 228 Figure A1.20 The carriageway deck is hung from the arch by wrought iron hangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Figure A1.21 A section through a cast iron component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Figure A1.22 A crack in a fascia plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Figure A1.23 Before removal of ballast plate lids, Southend High Street bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Figure A1.24 Heavy corrosion visible to web once ballast lids [...] are removed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Figure A1.25 Northbound carriageway elevation of Thelwall Viaduct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Figure A1.26 North view of the Forth Road Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Figure A1.27 Viaduct bearings, seized (a) and damage (b) to supporting concrete, Forth Road Bridge . . . . . . . . . . . . . . . 232 Figure A1.28 Elevation on the Hammersmith Flyover, west London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Figure A1.29 Segmental deck construction and post-tensioning layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 Figure A1.30 Voids through deck formwork (a) and hessian wadding (b) following construction . . . . . . . . . . . . . . . . . . . . 235 Figure A1.31 Graphic model showing locations of wire breaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 Figure A1.32 Radiographic image of strands in ducts leading from the upper anchorages and density analysis of area of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 Figure A1.33 Temporary span propping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Figure A1.34 Discovery of complete severance of a strand that led to bridge closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Figure A1.35 Replacement permanent post-tensioning solution (top flange at pier locations) . . . . . . . . . . . . . . . . . . . . . . 238 Figure A1.36 Layout of new post-tensioning in the deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Figure A1.37 New internal tendons in wax filled ducts, at mid-span deviator (a) and pier deviator (b) . . . . . . . . . . . . . . . 239 Figure A1.38 Bearing at principal inspection, bottom part obscured by ballast/leaf litter (a), and bearing arrangement (b) . . . . 240 Figure A1.39 Bearing once clear of debris (a) and detail on racking frame pins (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 Figure A1.40 A pin bearing at an A-frame apex (a), and detail showing a closed gap [...] (b) . . . . . . . . . . . . . . . . . . . . . . . . 241 Figure A1.41 Moiré tell-tales installed to A-frame bearings to monitor movement (a), interference patterns generated by movement across the measured interface, here indicating the A-frame was safely accommodating displacement from thermal effects by rocking (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 Figure A1.42 Diagram of a spherical bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

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Figure A1.43 Aerial view of the de la Concorde overpass partial collapse (a), and a hole and crack during a visual inspection an hour before the collapse occurred (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Figure A1.44 Chair bearing support reinforcement, as designed (a) and as-built (b). The difference is small, but demonstrates the lack of robustness of this detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Figure A1.45 Standard thrust-hinge in solid slab bridges (Type A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 Figure A1.46 Beam and slab deck (Type B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 Figure A1.47 Semi-intrusive methods used to inspect reinforcement at throat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Figure A1.48 Pitting corrosion to Type A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Figure A1.49 Pitting corrosion to Type B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Figure A1.50 Example record of observed pitting corrosion and radial position of defects . . . . . . . . . . . . . . . . . . . . . . . . 246 Figure A1.51 Typical arrangement of MLMV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Figure A1.52 Typical chloride attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Figure A1.53 Cathodic protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Figure A1.54 Exposed foundation column showing white mush of attacked concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Figure A1.55 Concrete testing underway on affected structures as part of the remediation work . . . . . . . . . . . . . . . . . . 249 Figure A1.56 Hidden critical components of bridge D46 prone to defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 Figure A1.57 Installation of Forth Road Bridge’s carriageway expansion joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 Figure A1.58 Evidence of and views during inspections of worn components at moving interfaces . . . . . . . . . . . . . . . . . 252 Figure A1.59 Cross section through bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Figure A1.60 Failed tie bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Figure A1.61 View onto soffit of bridge D3 (a) and corrosion to bottom flange of a girder with temporary restraining bracket (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Figure A1.62 Brickwork removal uncovering hidden steelwork in good condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Figure A1.63 Humber Bridge, East Yorkshire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Figure A1.64 The main cable inspection gantry (close to mid-span) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Figure A1.65 Rusting on the cable surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Figure A1.66 Cable wrapping system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Figure A1.67 Unwrapped cable, with inspection wedges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Figure A1.68 A proprietary elastomeric wrapping material used as an air-tight covering for the Humber Bridge main cable dehumidification system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Figure A1.69 Stainless steel manifolds with location of injection and exhaust sleeve . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Figure A1.70 Injection sleeve after installation, together with the associated housing for the continuous monitoring equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 Figure A1.71 Typical results from three of the monitoring points, with long-term control of the relative humidity (RH%) . . 259 Figure A1.72 Typical output from acoustic monitoring report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Figure A1.73 Illustrated acoustic output of a typical wire break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Figure A1.74 Queensferry Crossing under construction in October 2015 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Figure A1.75 Inside the tower at stay cable anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 Figure A1.76 Damage caused by scour to the east abutment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Figure A1.77 A rubber mat reinforced elastomer joint (a), and, finger joint (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Figure A1.78 Removal of original joints (a), and new finger joint being installed (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Figure A1.79 The Sasago Tunnel before collapse with ceiling panels visible (a) and visualisation of the collapsed panels (b) . . 264 Figure A1.80 The failed post (a), and heavy corrosion on the post length embedded in foundation concrete (b) . . . . . . 265 Figure A1.81 Elevation showing the three semi-elliptical arch spans on the Belcoo Bridge . . . . . . . . . . . . . . . . . . . . . . . . 266 Figure A1.82 Clearly visible sag in the string course and parapet coping on the eastern elevation . . . . . . . . . . . . . . . . . . 266 Figure A1.83 ‘Dropped’ stones in masonry arch barrel intrados on the east side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Figure A1.84 Extraction of core samples from arch barrel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Figure A1.85 Internal vaulted arches of the subway supporting the carriageway above (a), and detail of the arches and fan vault under the road footway (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Figure A1.86 Trial pit excavations revealing cohesive (a) and granular (with visible standing water) spandrel fill (b) . . . . 268 Figure A1.87 Releagh bridge (a) and its pier with internal rubble fill exposed (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Figure A1.88 The viaduct elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Figure A1.89 The bridge with fill removed, exposing hidden brickwork detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Figure A1.90 BACO parapets with evidence of minor vandalism to facing mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Figure A1.91 Hairline cracks were observed around the base weld (a) and the parapet identification marking (b) . . . . . 271 Figure A1.92 M4 Usk River Bridge, South Wales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Figure A1.93 Deck hinge detail showing ‘C’ bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Figure A1.94 External face of the deck hinge, centred on a construction joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Figure A1.95 Free body equilibrium conditions implicit in the shear strength analysis of reference . . . . . . . . . . . . . . . . . 274 Figure A1.96 Elevation showing the locations of timber bearings under the truss tubes at the piers, Royal Albert Bridge . . . 277

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Figure A1.97 Cross-section of the bearings at each pier (a) and showing arrangement of the bearings (b) . . . . . . . . . . . Figure A1.98 Deteriorated timber bearing (a) and with worm infestation (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure A1.99 Extracted cores showing a solid, but damp sample (a) and a fragmented sample (b) . . . . . . . . . . . . . . . . . Figure A1.100 Resistance micro drilling – drill detail (a) and general use (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure A1.101 Cladding failure at Denmark Hill, cladding installation (a) and failure mode (b) . . . . . . . . . . . . . . . . . . . . . . . Figure A1.102 Cross section of cross girder of main span illustrating the location of the truss end links . . . . . . . . . . . . . . Figure A1.103 Truss end link detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure A1.104 North-east main span outer truss end link crack-like indication revealed by MPI . . . . . . . . . . . . . . . . . . . . . Figure A1.105 The fractured northeast main span inner truss end link (a), and showing the fracture surface to the 1’’ plate with possible chevron shaped tide marks (b and c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure A1.106 Splash panel fixings to parapets (a) and breakdown of corrosion protection system on parapet (b) . . . . . . Figure A1.107 Severe loss of area to a heavily rusted bottom rail of the parapet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure A1.108 North Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

277 278 278 278 279 280 281 282 282 284 284 285

Tables Table 1.1 Selected bridge collapses in the UK and Ireland since 1800 where a hidden defect may have played a key role . . . 2 Table 1.2 The six principal sources of defects in bridges and examples, with further suggested defect sources . . . . . 4 Table 2.1 Suggested sections of design basis documents in which to record aspects relating to hidden components . . . 13 Table 3.1 Structure risk assessment example for a selection of illustrative items, consequences, control methods and outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 3.2 Failure mode effect analysis examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Table 3.3 Summary of advantages and disadvantages of SHM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Table 4.1 Components and typical defects. Blue references are sections in this guide . . . . . . . . . . . . . . . . . . . . . . . . . 33 Table 5.1 Bolt identification marks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Table 6.1 Summary of concrete testing methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Table 9.1 Hidden defects encountered within common expansion joint types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Table 9.2 Hidden defects in expansion joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Table 10.1 Drainage components and their hidden defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 Table 11.1 Typical hidden components in parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Table 15.1 Suggestions for further research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Table A1.1 List of case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 Table A1.2 The 42 types of HCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 Table A1.3 Specified frequency of inspection of a wrought iron HCE – a risk-based approach . . . . . . . . . . . . . . . . . . . . 219 Table A1.4 Summary of findings associated with the various investigation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Table A1.5 Summary of a desk study identifying the number of hidden defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Table A2.1 Classification of details: non-welded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Table A2.2 Classification of details: welded details other than at end connections of a member . . . . . . . . . . . . . . . . . 287 Table A2.3 Classification of details: welded details at end connections of member . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

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Glossary Abutments

End support structure of a bridge.

Acoustic monitoring system A monitoring system that detects and records acoustic emissions in real-time, caused by materials deterioration, often at the microstructure level. Admixtures Additional chemical components other than Portland cement, water and aggregate, which are added to the mix immediately before or during mixing. Arch ring

Load bearing curved part of an arched structure made of voussoirs.

Bascule bridge A bascule bridge (sometimes referred to as a drawbridge) is a moveable bridge with a counterweight that continuously balances a span, or ‘leaf ’, throughout its upward swing to provide clearance for boat traffic. It may be single or double leafed. Bridge failure

Collapse of all or part of a bridge such that it can no longer carry load.

(Cementious) binder The total content of cementitious material in the concrete, including Portland cement and any additions such as fly ash, ground granulated blast-furnace slag, limestone powder, silica fume or metakaolin. Construction (Design and These Regulations apply to construction work undertaken in Management) Regulations England, Scotland and Wales. They place duties upon defined parties (CDM) 2015 with designated roles within the design and construction process and management of a facility. For the purposes of this guide, Northern Ireland CDM 2016 and the Republic of Ireland’s Safety, Health and Welfare at Work (Construction) Regulations 2013 are taken as being analogous. Component In this guide, a distinct part of a bridge. Used in preference to ‘element’, which is only used where it has a specific meaning, eg Network Rail’s hidden critical elements programme. Degradation

Loss of function or safety to a component, brought on by deterioration.

Delayed ettringite formation Denotes the formation of ettringite in a concrete, mortar or cement paste that has been subjected to a temperature high enough to destroy any that was earlier present. The effect can cause expansion or cracking. It could also occur in concrete that has been heated adventitiously through the heat evolved on hydration, or from an external source during service. Detailed examination Term used by Network Rail for an inspection within touching distance to all exposed components. Used in this guide only when directly referencing Network Rail procedures. See also Principal inspection. Deterioration Physical, chemical and/or biological mechanism(s) that lead to a reduction in desirable material characteristics and/or volume over a period of time. DMRB Design manual for roads and bridges. This manual provides current standards, advice notes and other documents relating to the design, assessment and operation of trunk roads, including motorways. This is a UK-based publication, but it is also adopted in Ireland.

Hidden defects in bridges – guidance for detection and management

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Environmental hydrogen See Stress corrosion cracking. General inspection An inspection made without any special access arrangements, ie areas readily accessible on foot only. This term is used throughout the guide with direct equivalence to Network Rail’s routine examination. Glued laminated timber A type of structural engineered wood product comprising a number of layers of dimensioned lumber bonded together with durable, moisture-resistant structural adhesives. Grade 10.9 bolts The higher of two grades (the other being 8.8) of bolting material typically encountered in bridges. Historically referred to high strength friction grip (HSFG) ‘higher grade’ (as opposed to ‘general grade’ for 8.8). Half through bridge A bridge in which the lower truss chord/girder flange carries the vehicular or pedestrian traffic. Hidden A component that would not usually be visually inspected as part of a principal inspection (see Section 1.1.4). High strength friction grip (HSFG)

This term for preloaded bolts is outmoded, but remains in common use in UK.

LIDAR A detection system that works on the principle of radar, but uses light from a laser. Mechanically laminated timber Laminated timber where the laminations are joined with mechanical fasteners. Principal inspection A detailed inspection to within touching distance of all visible components. This term is used throughout the guide with direct equivalence to Network Rail’s detailed examination. Routine examination Term used by Network Rail for an annual inspection made without any special access arrangements (ie from ground level/trackside only). Used in this guide only when directly referencing Network Rail procedures. See also General inspection. Scour Removal of soil, fill or other material to a bridge substructure by hydraulic action. Stress corrosion cracking Crack growth in a corrosive environment under tensile loads in ductile metals. Thaumasite sulfate attack (TSA) A form of sulfate attack in which there is significant damage to the matrix of a concrete or mortar as a consequence of replacement of cement hydrates by thaumasite. Ultrasonic Testing (UT) A NDT technique based on the propagation of ultrasound in the object or material tested. Voussoir

A wedge-shaped or tapered stone used to construct an arch.

Walkover inspection/survey Visual inspection (on foot) of a bridge. Usually conducted as a preliminary inspection to understand a bridge’s general arrangement. Weathering steel Structural steel that, in certain environmental conditions, forms a stable rust patina that adheres to the steel surface. The patina protects the steel from further corrosion, which may negate the need for painting. Also known as Corten.

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Abbreviations and acronyms ADEPT Association of Directors of Environment, Economy, Planning and Transport AEM Acoustic emission monitoring AIP Approval in principle ASR Alkali–silica reaction BINDT British Institute of Non-Destructive Testing BICS Bridge Inspector Certification Scheme BMS Bridge management system CDM 2015 Construction (Design and Management) Regulations 2015 CPI Condition performance indicator CROSS Confidential Reporting on Structural Safety CSS County Surveyors Society (now subsumed by ADEPT) DEF Delayed ettringite formation DMRB Design manual for roads and bridges FE Finite element FEA Finite element analysis FoS Factor of safety FRP Fibre-reinforced polymers GGBS Ground-granulated blast-furnace slag Glulam Glued laminated timber GPR Ground penetrating radar H&S Health and safety HCE Hidden critical element (Network Rail) HSFG High strength friction grip LUL London Underground Limited LVDT Linear variable differential transformer Mechlam Mechanically laminated timber MEWP Mobile elevated working platform MPI Magnetic particle imaging NA National Annex (Eurocode) NCCI Non-contradictory complementary information (Eurocode) NDE Non-destructive examination NDP Nationally determined parameters (Eurocode) NDT Non-destructive testing NHSS National Highways Sector Scheme NMM Network maintenance manual (UK Highways Authority) NRA National Roads Authority (Republic of Ireland) OLE Overhead line equipment PTFE Polytetrafluoroethylene PTSI Post-tensioned concrete bridge special inspections RAIB Rail Accident Investigation Branch SCOSS Standing Committee on Structural Safety SHM Structural health monitoring TII Transport Infrastructure Ireland TfL Transport for London UB Universal beam UHMWPE Ultra high molecular weight polyethylene UKRLG UK Roads Liaison Group ULS Ultimate limit state UT Ultrasonic testing

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How to use this guide This guide has four main parts: Part 1 Introduction including recommendations on risk appraisal and management. Part 2 Technical guidance. Part 3 Summary and further areas of research including references. Part 4 Appendices (containing detailed case studies).

Purpose

Principal audience

1

Introduction

Background and purpose of the guide.

All

2

Management of hidden Existing practice for the appraisal and management of defects in bridges, risks associated with hidden components and defects. existing practice

3

Management of hidden Recommended practice for the appraisal and defects in bridges, management of risks associated with hidden components All recommended practice and defects.

4

Components and defects in bridges

For all commonly encountered bridge types, defines components and where to find further guidance in Part 2.

5

Iron and steel bridges

6

Concrete bridges

7

Masonry arch bridges

Details of hidden components and defects based on the primary construction material of the bridge. Where over two pages, left hand page is a summary, right hand page further detail. Details provided are by: „„

description

8

Timber bridges

„„

inspection and investigation techniques

9

Bearings and expansion joints

„„

identification and maintenance

„„

design guidance.

10

Durability components

11

Safety components

12

Other bridge components

13

Ancillary components

14

Substructure

3 Conclusions

Part Chapter

15

Future research

16

Conclusion

A

Case studies

Summary of project aspects relevant to this guide.

All

B

BS 5400-10:1980

Tables including useful fatigue diagrams included.

Inspectors and designers

2 Technical guidance

1 Introduction

Title

4 Case studies

The processes in Chapter 3 are central to the guide. These processes form recommended practice for managing bridges that may contain hidden defects. The reader is aided through the navigation of this guide by distinct formatting presented in the key. A summary table is also provided to help direct the reader to relevant content. Each section is extensively referenced to help the reader find further information.

xxii

Bridge owners and managers

Inspectors, maintenance engineers and designers

Discussion of hidden defects in typical bridge components.

Potential research opportunities to complement or further All the goals of this guide. All

CIRIA, C764

Where works to or around a hidden defect or components pose an unusual or higher risk health/safety hazard, this is highlighted using the ‘Take note’ symbol. These boxes are not exhaustive and are to prompt the reader into considering health and safety (H&S) risks. In addition, The technical guidance in Part 2 is divided into two sections: guidance is provided in ‘Further information’ boxes. „„ Hidden components (dark blue) are associated with that section’s bridge type. Information for the reader

Part 1 Introduction and Part 2 Technical guidance include short summary boxes at the start of each chapter to assist the casual reader.

„„

i

Hidden defects (dark red) describe those that may be encountered in that section’s bridges.

Part 3: Summary of information including detailed references. Part 4: Appendices containing 39 case studies and further guidance for the reader.

Take note

Further information

Cross references are highlighted in bold blue throughout the guide.

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Introduction

Part 1 Introduction

Technical guidance Summary Appendices

Hidden defects in bridges – guidance for detection and management

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Introduction

1 Introduction

Loss of life resulting from failure of a component is the worst-case scenario that can occur on a bridge. Bridges are managed to mitigate risks to avoid this tragic event and other adverse societal, economic or environmental consequences. The risks can only be efficiently mitigated if they are known, and hidden defects may increase the likelihood of this scenario occurring. Sadly, there is a history of bridge collapses in the UK and Ireland resulting from hidden defects (Table 1.1).

In 2009, the Stewarton rail bridge, Ayrshire (Case study A1.2) collapsed during passage of a freight train. Corrosion to half-through girder webs was so severe that complete loss of section had occurred in areas of high shear load. The corroded areas were hidden under ballast and had not been inspected.

„„

The A4 Hammersmith Flyover on one of London’s busiest roads (Case study A1.11), had been subject to limited inspections of its post-tensioning tendons since the mid-1990s. During investigation works in 2011, two of the eight tendons over one particular pier were found to be badly corroded and the flyover was closed while further investigation of the remaining six tendons and assessment was undertaken. The flyover was reopened with restricted traffic loading while emergency strengthening works were undertaken before the implementation of a full strengthening scheme. The full strengthening works, plus bearing and joint replacement, were completed in 2015 at a cost in the order of £120m.

Prompted by these and other cases, the Bridge Owner’s Forum (BOF) identified the need to define good practice for inspecting, identifying and maintaining bridges with hidden components. This guide undertakes this exercise, as well as providing guidance on how to avoid the potential for such defects in design. Some information is presented to highlight aspects of defects in hidden components before referring the reader to more definitive texts. Risk assessment techniques are proposed to be incorporated into management. In gathering the case studies for this guide, it has become apparent that they may have an important secondary function. As a collation of interesting and often difficult works to existing bridges, the case studies provide useful background reading for bridge professionals and those wishing to understand the daily technical challenges faced by the industry.

Hidden defects in bridges – guidance for detection and management

1

Appendices

„„

Summary

Two high profile cases in recent years have emphasised the importance of defects in hidden bridge components. Indeed, while writing this guide, a further prominent and very disruptive temporary bridge closure occurred at the Forth Road Bridge in Scotland as a result of a hidden defect (see Case study A1.37).

Technical guidance

Bridge owners and operators, together with bridge engineers such as designers, assessors and maintainers play key roles in bridge management. A core component of a bridge management programme is a thorough review of records followed by on-site examinations by a competent bridge inspector, which may include limited targeted testing. These inspections are central to determining bridge condition and are used by bridge owners to ensure defects are identified and rectified within reasonable timeframes as well as identifying larger maintenance works. When coupled with an accurate numerical assessment of capacity, the risk posed by a bridge and/or individual components the continuing safe use or operation is defined. Generally, this works well in the UK and Ireland. However, the success of the process is, among other items, very sensitive to the quality of the inspections. These inspections should see an increase in quality with the introduction of the Bridge Inspector Certification Scheme in 2016 (Lantra, 2015). If an inspection does not include all components because, for example, they are hidden and not easily examinable, the adverse effects can be significant or in the worst cases catastrophic.

Table 1.1

Selected bridge collapses in the UK and Ireland since 1800 where a hidden defect may have played a key role

Bridge

Date

Section

Further reading

Dynamic effects of marching soldiers 20 injuries resulted in bolt failure

5.2.6

Taylor and Philips (1831)

Cast iron beams prestressed by wrought iron tie rods

Poor design philosophy and Five deaths construction. Fatigue failure

5.2.4

Lewis (2007)

Two deaths

5.2.4

Tyler (1861)

None

5.2.1

Lewis (2007)

5.2.4

Lewis (2004)

Arrangement

Reason for collapse

Broughton Suspension Bridge, 12 Apr 1831 Manchester

Suspension bridge

Dee Bridge, Chester

24 May 1847

Wooton Bridge, Warwickshire

11 Jun 1860

Cast iron girders

Crack growth (likely fatigue) from a bolt hole used to attach strengthening component

Bull Bridge, Derbyshire

26 Sep 1860

Cast iron girders

Web and flange casting defect not previously observed

Casualties

Tay Bridge, Dundee 28 Dec 1879

Poor design including inadequate Wrought iron truss on consideration of wind 75 deaths cast iron piers load. Fatigue growth in cast iron pier detail

Inverythan Bridge, Aberdeenshire

27 Nov 1882

Cast iron girder

Hidden defect from casting process

Five killed, 17 injured

5.2.1

Marindin (1882)

Norwood Junction, London

1 May 1891

Cast iron girder

Hidden defect from casting process

One injury

5.2.1

Hutchinson (1891)

Bury Knowsley Street Station Footbridge, Bury

19 Jan 1952

Timber superstructure, wrought iron substructure

Heavy corrosion, including of joints hidden under superstructure

Two deaths, 173 injured

5.1.4, 5.1.5, 5.2.2

Langley (1952)

Ynys-y-Gwas Bridge, West Glamorgan

4 Dec 1985

Segmental post-tensioned construction

Hidden corrosion of inadequately protected posttensioning tendons

None

6.1.3, 6.2.6

Woodward and Williams (1988)

Glanrhyd Bridge, Camarthenshire

19 Oct 1987

Steel half through on Swept away in flood masonry abutments waters and piers

Four deaths

14

Cooksey (1990)

Ness Viaduct, Inverness

8 Feb 1989

Masonry arch rail viaduct

Upstream scour of foundations to pier

None

14

Scott (1995)

Stewarton Bridge, Ayrshire

27 Jan 2009

Wrought iron half through rail bridge

Corrosion to web buried under ballast

None

5.1.1

RAIB (2010a)

Malahide Viaduct, Co Fingal

21 Aug 2009

Wrought iron lattice girder on masonry piers

Scour to pier

None

14

RAIU (2010)

Cumbria bridge collapses

21 Nov 2009

Masonry arch bridges

Foundation scour, One death scour of masonry units

14

Collins et al (2013)

Tadcaster Bridge, North Yorkshire

29 Dec 2015

Masonry arch bridge

To be determined

N/A

N/A

2

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1.1.1

Introduction

1.1 SCOPE Who is the reader?

This guide is intended for bridge owners and operators, together with bridge engineers such as designers, maintainers and inspectors looking for guidance on hidden bridge components in the UK and Ireland. As a subject area, defects in hidden bridge components influence many aspects of these professionals’ activities, including: specifying design requirements

„„

developing inspection and management regimes

„„

appraising defects

„„

evaluating the most appropriate course of action for defect mitigation

„„

writing contract documents

„„

producing operation and maintenance documentation including hazard registers

„„

referring to precedent to justify remedial works.

The reader is assumed to have a basic technical understanding, familiarity with engineering materials, and knowledge of structural behaviour. It is assumed the reader is aware of the arrangement and terminology associated with most commonly encountered bridge types.

1.1.2

What is a defect?

“…risks the ability of the bridge to be defined as meeting service level and safe for use criteria. The defect can be defined in terms of severity and extent. The defect may have arisen because of: 1 Inadequate structural capacity or clearances. 2 Naturally occurring damage (environmental). 3 Accidental or deliberate damage.

Summary

Working largely from definitions by the UK Roads Liaison Group (UKRLG, 2016), the Association of Directors of Environment, Economy, Planning and Transport’s (ADEPT) (now including the County Surveyor Society) bridge inspection proforma method and the Highways Agency (2007a), this publication defines a defective bridge component as one that:

Technical guidance

„„

4 Structural materials deterioration. 5 Structural elements functionality. 6 Other sources, including poor detailing in design or inaccurate historic records.”

Unfortunately, the most common time a defect is found is once the component has failed. Defects can be formed or become apparent at any time in the structure’s life: „„

construction including off-site manufacture or material production

„„

operation

„„

maintenance

„„

repair, refurbishment, strengthening

„„

only apparent on decommissioning.

Hidden defects in bridges – guidance for detection and management

3

Appendices

The designer has the opportunity to affect the likelihood of defects occurring from any of these sources. Table 1.2 provides further details and examples of these six defect sources and cross references to other parts of this guide. Often, formation of bridge defects in the UK and Ireland have unwanted water ingress as a key feature. Effective water management and associated maintenance can significantly increase bridge life and reduce the risk of defect formation and development. Further possible defect sources identified while writing this guide are also suggested.

Table 1.2

The six principal sources of defects in bridges and examples, with further suggested defect sources

Defect source

1

2

3

4

Description

Inadequate structural capacity or clearances

Naturally occurring damage (environmental)

Accidental or deliberate damage

Deterioration of structural materials

5

Functionality of structural components

6

Other potential sources

1.1.3

Example

„„

inadequate design

„„

inadequate construction including materials

„„

inadequate maintenance

De la Concorde collapse (Case study A1.14)

„„

excessive loading or overstress

„„

sub-standard layout

A4 Hammersmith Flyover (Case study A1.11) where de-icing salt use not foreseen

„„

change in use, increased loading

„„

lack of protective measures.

„„

unforeseen movement

„„

water seepage

„„

scour

„„

freeze-thaw

„„

erosion

Bridge collapses in November 2009 Cumbria flood event (Collins et al, 2013)

„„

vegetation

Malahide Viaduct (RAIU, 2010)

„„

debris, silt blockage

„„

pollution

„„

climate change.

„„

fire

„„

impact

„„

vandalism.

„„

steel corrosion

„„

concrete deterioration

„„

masonry cracking.

„„

seizure of moving parts

„„

drainage provision/capacity.

„„

poor detailing in design

„„

missing historic records.

Fire damage to Dean’s Brook Viaduct, M1, London (Wheatley et al, 2013) Stewarton bridge collapse (Case study A1.2) Hammersmith Flyover (Case study A1.11) Plank Lane Bridge (Case study A1.5) Ynys-y-Gwas (Woodward and Williams, 1988) Humber Bridge bearing replacement (Case study A1.13) Dee Bridge (Lewis, 2007)

What is a bridge?

For brevity, this guide uses the term ‘bridge’ in its main title. This is an inadequate descriptor of all the infrastructure of interest to bridge owners. Transport structures may be more accurate. In an attempt to encompass the most commonly encountered UK definitions (Highways Agency, 2012a and Network Rail, 2011a) for this guide, a bridge is: “A structure of one or more spans greater than or equal to 0.9 m. Its prime purpose is usually to carry traffic or services over an obstruction or gap. This includes bridges, subways, underpasses and footbridges. Also included is the bridge’s superstructure, substructure, foundations and bridge furniture.” The guide predominantly focuses on bridge superstructures. Substructures and foundations are only briefly covered. Similarly, other transport structures such as culverts, pipe bridges, aqueducts, retaining walls and gantries are not explicitly covered though aspects of this guide may be appropriate.

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i

What is a hidden component?

Introduction

1.1.4

This guide adopts a definition of ‘hidden’, which is wider ranging than a typical dictionary definition. In a bridge, a hidden component is one that would not usually be visually inspected as part of a principal inspection. A hidden component is not identified from normal principal inspection techniques such as: „„

visual inspection from within touching distance

„„

using access techniques such as mobile elevated work platforms (MEWPs), roped access etc

„„

hammer tapping.

Components are hidden if they are inaccessible for inspection without excavation or removal of material or other structural components.

An element may be largely visible, but could have partially hidden components. For example: „„

Half-through girders may be largely visible except for sections of web buried under surfacing or ballast.

„„

Reinforcement is a hidden component within a concrete element.

This is largely a technical document. The main chapters of the guide (Chapter 4 onwards) define engineering aspects of individual defects in hidden components. Good practice in mitigating risk associated with individual defined hidden defects is given with respect to: „„

inspection

„„

identification and maintenance

„„

design and detailing.

1.3 LIMITATIONS This guide is primarily confined to bridge superstructure components although some are also applicable to substructure. Defective substructures and other transport structures may also suffer from some of the deterioration mechanisms described in this guide and benefit from being managed in the manner described.

Examples of defects in hidden components are included, which may be critical to the safe use or operation of a bridge. However, determination of whether the defect is critical should ultimately be quantitatively assessed on a case-by-case basis. Novel or unusual structures/components require careful consideration. While the guide offers general principles and advice, specialist guidance from a suitably qualified and experienced engineer is recommended. Structural materials that are not considered in detail include stainless steel, aluminium and glass/fibre-reinforced polymers (GRP, FRP). The former two are not commonly encountered as principal structural elements, while the latter materials are seeing increasing use, particularly abroad and notably in the Netherlands (Smits, 2014). As GRP/FRP becomes more widely used, their susceptibility or otherwise to hidden defects will become apparent. However, there is little evidence in the UK and Ireland’s bridge stock to produce general guidance on these materials as structural components.

Hidden defects in bridges – guidance for detection and management

5

Appendices

Efforts have been made to cover all commonly-encountered hidden components in UK and Irish bridge stock. Regional differences in detailing, construction quality and environmental triggers for defects exist, which will need to be carefully considered if this guide is used in other parts of the world. Also, in a world of rapid social, economic, technical and environmental change, defect characteristics or perception of risk may change with time.

Summary

This technical guidance for individual components can be used by bridge operators in the broader context of managing a bridge portfolio using a risk-based approach. Chapter 3 comments on the general impact on risk management of defects in hidden components.

Technical guidance

1.2 PURPOSE

The remainder of this guide provides practical guidance to defining, inspecting, investigating, maintaining, and identifying design-related issues for defective hidden bridge components. It is intended to provide an overview only and is not an all-encompassing, definitive text. However, together with the extensive referencing, an understanding of good practice can be developed. A key aspect where this guide does not go into great detail are methods for remedial works to a hidden defect. Generally, this is because remediating the hidden defect is no different to a non-hidden defect, and cross-reference to guidance by others should be followed. Also, in many cases there will not be a single type of remedial work that will be appropriate for all instances. Employment of suitably qualified and experienced designers and contractors working to a well thought-out scope is vital to ensure that the most appropriate solution is implemented.

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CIRIA, C764