Civil-Enigneering-Issue-169.Pdf

Civil Engineering

Volume 169 Issue CE3 August 2016

■■ A-frame rocker bearing replacement at Humber Bridge, UK ■■ Evolution of modern mega-buildings in China: innovations and sustainability ■■ Launching of Leigh Road Bridge, Slough, UK ■■ Urbanisation and landslides: hazard drivers and better practices

www.civilengineering-ice.com ISSN 0965 089 X Call for Papers

Proceedings of the Institution of Civil Engineers Smart Infrastructure and Construction Co-Editors: Dr Jennifer Schooling, Centre for Smart Infrastructure and Construction, University of Cambridge, UK Prof Kenichi Soga, Dept of Civil and Environmental Engineering, University of California - Berkeley, USA

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■ smart cities To submit an abstract or to request further information, please contact: ■ smart construction technology Alison McAnena, Journals Development Editor ■ value of sensing T: +44 (0)20 7665 2450 ■ whole-life cost and value E: [email protected] Proceedings of the Institution of Civil Engineers Civil Engineering Volume 169 Issue CE3 August 2016

CONTENTS:August 2016

Contact Information Editor: Simon Fullalove tel: +44 20 7665 2448 Civil Engineering email: [email protected] Journals Manager Ben Ramster tel: +44 20 7665 2242 email: [email protected] EDITORIAL General manager, ICE Publishing: Mike Cookson tel: +44 20 7665 2486 BRIEFING email: [email protected] Advertising: Steve Jackson, Structural Promotions Ltd. PAS 2080: world first specification for cutting carbon dioxide emissions in 12 Lawrance Way, Bourne, Lincolnshire PE10 0HU infrastructure 99 tel: +44 1778 420 857 Cyber threats and civil engineering – understanding the risks 100 fax: +44 1778 424 771 email: [email protected] Improving urban resilience to flooding: a vital role for civil engineers 101 Published by Recycling construction materials – proud tradition and bright future 102 ICE Publishing One Great George Street,Westminster Doubts remain on reliability of concrete chemical analysis methods 103 SW1P 3AA tel: +44 20 7222 7722 fax: +44 20 7538 4101 MONITOR email: [email protected] www.icevirtuallibrary.com Books 106 ICE Publishing is a division of Thomas Telford Ltd, a wholly owned subsidiary of ICE Proceedings 108 the Institution of Civil Engineers ICE review 111 Production editing by Paul Allanson Illustrations by Barking Dog Art TECHNICAL PAPERS Origination by Phoenix Photosetting Ltd, Chatham, Kent Printed in the UK by A-frame rocker bearing replacement at Humber Bridge, UK Garnett Dickinson, Rotherham Using fibre sourced from responsibly J. Collins and D. Smith 113 managed and sustainable forest ISSN 0965-089X (Print) Evolution of modern mega-buildings in China: innovations and 1751‑7672 (Online) sustainability © The authors and the Institution of Civil Engineers, 2016 A. J. Wang 121 Available online at www.civilengineering-ice.com Launching of Leigh Road Bridge, Slough, UK Subscription Information M. O’Connor, M. Attrill, I. Gibb and S. H. Oh 129 Non-members: Subscription enquiries and notification of Urbanisation and landslides: hazard drivers and better practices change of address should be sent to the Customer Services department, E. A. Holcombe, M. E. W. Beesley, P. J. Vardanega and R. Sorbie 137 ICE Publishing, One Great George Street, Westminster SW1P 3AA tel: +44 20 7665 2460 fax: +44 20 7537 2529 email: [email protected] Civil Engineering, 4 issues per year (plus two special issues) 2016 subscription price: UK £191; EU £217; Elsewhere £236 ICE Specialist Engineering Journals Collection (formerly full ICE Proceedings Package), 94 issues per year, 2016 subscription price: UK £4495; EU £5135; Elsewhere £5565 PAGE 119 PAGE 127 PAGE 135 PAGE 138 Members: Subscription enquiries and notification of changes of address should be sent to Membership Registry, CIVIL ENGINEERING EDITORIAL PANEL Institution of Civil Engineers, PO Box 4479, London SW1P 3XB, UK Chairman Emma Kent, CEng, MICE,MIStructE, Cundall, London, UK Sebastian Lewandowski, Atkins, Birmingham, UK tel: +44 20 7665 2227 Andy Alder, CH2M HILL, UK Eva Linnell, MEng, Atkins, Bristol, UK fax: +44 20 7222 3514 J. Dario Aristizabal-Ochoa, National University of Colombia, Andrew Martin, BEng, MSt, CEng, MICE, MIStructE, COWI A/S, email: [email protected] Colombia Kongens Lyngby, Denmark David Atherton, BSc, MSc, CEng, CGeol, FICE, FIMMM, FCIWEM, MCIWM, FGS, David Oloke, Progressive Concept Consultancy Ltd, The papers and articles express the Peter Brett Associates, Reading, UK Walsall, UK opinions of the authors, and do not Philippe Bouillard, BSc, MSc, PhD, Hab, MICE, FAUA, Université Libre Neil Owen, BSc, CEng, MICE, Independent Consultant, necessarily reflect the views of the ICE, de Bruxelles, Belgium Birmingham, UK TTL, or the Editorial Panel. Papers are Yancheng Cai, PhD, MIASS, Meinhardt (C&S) Ltd, Hong Kong, Priti Parikh, PhD, CEng, MICE, FRSA, University College London, UK formally refereed by the editorial panel PR China Dave Parker, Independent Consultant, Bishop’s Stortford, UK whereas, to ensure topicality, Briefing John Clifton, BSc, CEng, CEnv, FICE, FCIHT,MCMI, Independent Consultant, Colin Rawlings, BSc, DIC, MSc, CEng, MICE, MASCE, CGeol, FGS, CH2MHill/HS2 articles are not refereed. Santa Barbara de Nexe, Portugal Ltd, London, UK Civil Engineering is indexed in the Mark Hagger, MA, CEng, FICE,MCIWEM, Environment Agency, UK Stuart Ross, Arup, Hong Kong, PR China Science Citation Index David Hobson, Jacobs, Stourbridge, UK P. J. Rudden, RPS Group, Killiney, Republic of Ireland Siva Kandasami, BE, ME, PhD, MICT, Coimbatore, India Alessandra Villa, CEng, MICE, Dott. Ing., Arup, London, UK

97 Civil Engineering Editorial Volume 169 Issue CE3 August 2016 Bouillard

Editorial

Philippe Bouillard BSc, MSc, PhD, Hab, CEng, MICE, FAUA Professor, Building Architecture and Town Planning Department, Université Libre de Bruxelles, Belgium

This century will certainly be the ‘century of the cities’. Unfortunately, as described in this issue by O’Connor et al. According to reports from the Organisation for Economic (2016), an unforeseen incident occurred during the launch. Co-operation and Development and others, the world’s urban The methodology and successful realignment operation population be around 6 billion by 2050 and 9 billion by 2100, led to some very pertinent learning points for future similar with 85% of our descendants living in cities by the end of the launches. century. And finally, in addition to new delivering new To address this challenge, we will need the skills and interconnecting infrastructure, civil engineers need to keep competences of civil engineers as never before to design, existing infrastructure operational – which can involve some build and operate the increasingly complex structures particularly challenging and large-scale replacement of worn and infrastructure required by our ever-expanding urban parts. In the lead paper of this issue, Collins and Smith (2016) populations. report on a 2-year project to do just that on the world’s In China, where the demographic challenge is already a seventh largest suspension bridge. big one, the government is encouraging a dramatic increase Humber Bridge carries the A15 highway 2·2 km over the in the density of cities through greater use of high-rise Humber estuary between Hessle, East Yorkshire and Barton, buildings. These structures still raise many issues related to North Lincolnshire, UK. An innovative technique was used hazard mitigation against extreme actions and environments, to replace the main span’s four A-frames – which carry up to integrated structural frameworks and facades, complex 1600 t each – with vertical pendels and horizontal wind shoes connections and constructional and energy efficiency. without disrupting traffic. It is likely to inspire similar solutions Wang (2016) presents an interesting review in this issue worldwide. of four recent high-rise building projects in China, discussing I hope you enjoy the papers and articles in this issue; that the evolution in engineering design, construction and they help you appreciate your own role in building a bright management that has been required for their successful and sustainable future; and that they encourage you to share delivery. your experiences of doing so in this and other ICE Proceedings Urbanisation is also crucial in developing countries, where journals. unplanned or uncontrolled development is not unusual – as was discussed in our recent special issue on humanitarian References engineering (Kent and Adler, 2016). Without proper structural and risk analyses, or adequate civil infrastructure, many urban Collins J and Smith D (2016) A-frame rocker bearing replacement at Humber areas are barely liveable. Bridge, UK. Proceedings of the Institution of Civil Engineers – Civil In this issue, Holcombe et al. (2016) address rainfall- Engineering 169(3): 113–120, http://dx.doi.org/10.1680/jcien.15.00066. triggered landslide risk in such urban areas in countries Holcombe EA, Beesley MEW, Vardanega PJ and Sorbie R (2016) Urbanisation where conventional slope stabilisation techniques are often and landslides: hazard drivers and better practices. Proceedings of the unaffordable – and where most risk-reduction investment Institution of Civil Engineers – Civil Engineering 169(3): 137–144, http:// dx.doi.org/10.1680/jcien.15.00044. is currently made post-disaster. Based on studies in the Caribbean, the authors propose a promising and effective Kent E and Adler A (2016) Introduction. Proceedings of the Institution of Civil Engineers – Civil Engineering 169(5): 3, http://dx.doi.org/10.1680/ community-based surface water drainage system based on jcien.2016.169.5.3. bioengineering schemes. O’Connor M, Attrill M, Gibb I and Oh SH (2016) Launching of Leigh Road A recent misrepresentation of urbanisation and mobility has Bridge, Slough, UK. Proceedings of the Institution of Civil Engineers – Civil suggested that European countries no longer need to invest Engineering 169(3): 129–135, http://dx.doi.org/10.1680/jcien.15.00081. in civil infrastructure – and some have already started to rein Wang A (2016) Evolution of modern mega-buildings in China: innovations in spending. The economic reality is that cities need to be and sustainability. Proceedings of the Institution of Civil Engineers – Civil more interconnected than ever, even if this proves increasingly Engineering 169(3): 121–128, http://dx.doi.org/10.1680/jcien.15.00063. difficult. CALL FOR PAPERS: Civil Engineering relies entirely on material contributed by An example in the UK is Leigh Road Bridge in Slough, civil engineers and related professionals. Illustrated articles of 600 words and papers of 2000 to 3500 words are welcome on any relevant civil engineering only the second bridge in the UK to have been launched topic that meets the journal’s aims of providing a source of reference material, across a railway using trailers – and one of the largest promoting best practice and broadening civil engineers’ knowledge, Please structures constructed by this method anywhere in the world. contact the editor for further information

98 Civil Engineering PAS 2080: world first specification for cutting Volume 169 Issue CE3 August 2016 carbon dioxide emissions in infrastructure McAlinden http://dx.doi.org/10.1680/jcien.2016.169.3.99 ICE Publishing: All rights reserved BRIEFING: STANDARDS

PAS 2080: world first specification for cutting carbon dioxide emissions in infrastructure

The UK Green Construction Board launched a new specification in May 2016 to encourage a consistent approach to reducing carbon dioxide emissions related to infrastructure – a world first. Ben McAlinden of the Institution of Civil Engineers introduces PAS 2080.

PAS 2080:2016 Carbon management At the heart of the specification in infrastructure (BSI, 2016) and are strong leadership and governance its associated guidance document to drive positive behaviours and step (GCB, 2016) set out the general changes in design – and to reinforce principles and components of a carbon the message that the greatest dioxide emissions management system opportunity for both capital and for infrastructure supply chains. operational carbon dioxide reduction The UK government’s Infrastructure is at the earliest stages. Other key carbon review of 2013 (HM components of the framework Treasury, 2013) made a number include setting targets and baselines, of recommendations to reduce monitoring, quantification, reporting greenhouse gas emissions related to and continual improvement. infrastructure, including development of a low carbon dioxide specification. Guidance document A publically available specification (PAS) was duly commissioned by the UK The Green Construction Board Construction Leadership Council’s Green has also published a free guidance Construction Board and published by document on PAS 2080 to give practical BSI in May 2016. advice on how to implement the specification. Current good practice is Benefits of specification addressed through worked examples The new PAS 2080 Carbon management and case studies and presented in Leading infrastructure organisations are in infrastructure specification and guidance an engaging style with clear cross- already delivering solutions with reduced document are both available online references to PAS 2080 clauses. carbon dioxide emissions – and therefore In summary, PAS 2080 and its reduced cost – by applying the principles associated guidance document provide and framework set out in PAS 2080. expectations. It has three distinct a consistent approach to deliver Carbon dioxide emissions are an sections: scope and general principles; reduced carbon dioxide, reduced cost excellent proxy for materials and energy the carbon dioxide management process; infrastructure, which when actioned used in constructing and maintaining and assessing emissions reductions and will leave a sustainable legacy for future infrastructure, such that reducing claims of conformity. generations. carbon dioxide equates to reducing A core theme is that each part of The 60-page specification and cost. The specification also sets out the supply or ‘value’ chain can take 82-page guidance document can be collaborative ways of working to drive action to measure, manage and reduce downloaded from the BSI and Green innovation and improve value. carbon dioxide, but it is not until the Construction Board websites, respectively. Overall, the specification aims to whole chain is aligned against common contribute to reducing greenhouse gas principles that significant emissions and References emissions and lead to a more effective cost reductions will be achieved. use of raw materials. It is hoped this in The common and individual BSI (2016) PAS 2080:2016: Carbon management in responsibilities assigned to asset owners infrastructure. BSI, London, UK. See http://shop. turn will enhance the reputation of the bsigroup.com/PAS2080 (accessed 07/06/2016). infrastructure industry, helping to attract and managers, designers, constructors GCB (Green Construction Board) (2016) Guidance new talent and skills. and product and material suppliers are Document for PAS 2080. GCB, London, UK. See http://greenconstructionboard.org/images/ set out, illustrating the organisational stories/ICR/Guidance%20Document%20for%20 Structure and framework capabilities required to be in place. PAS2080_vFinal.pdf (accessed 07/06/2016). Compliance with PAS 2080 can be HM Treasury (2013) Infrastructure Carbon Review. HM Treasury, London, UK. https://www.gov.uk/ PAS 2080 is written in a clear language demonstrated through certification or government/publications/infrastructure-carbon- with well-defined responsibilities and self-assessment. review (accessed 07/06/2016). For further information contact: BSI Tel: +44 345 086 9001 Email: [email protected] Web: www.bsigroup.com

99 Civil Engineering Cyber threats and civil engineering – understanding the risks Volume 169 Issue CE3 August 2016 Jones http://dx.doi.org/10.1680/jcien.2016.169.3.100 ICE Publishing: All rights reserved

BRIEFING: INSURANCE

Cyber threats and civil engineering – understanding the risks

The embarrassment of headline-grabbing information breaches are just the tip of the iceberg when it comes to the growing cyber risks facing civil engineering firms. Karl Jones of UK insurance broker Kerry London says the risks go much further than reputational damage.

From the cyber attack which lost UK include regular stress tests. Civil telecoms firm TalkTalk 100 000 UK engineering firms should also factor in customers last year to the many red the need for anti-virus software and faces caused by international law firm firewall protection, evaluating and Mossack Fonseca’s ‘Panama papers’ protecting systems of high exposure or leak, the importance of cyber security value to the business, and regulation of has never been more relevant – administrative access. particularly for civil engineering firms. Prudent firms should also consider A Department of Business, Innovation buying non-physical business and Skills survey published in May interruption insurance. Essentially this this year (BIS, 2016) found that works in the same way as physical 65% of large and 51% of medium business interruption cover. The cover organisations suffered a cyber breach is designed to indemnify businesses in 2015 – though there is still no for either lost profits or revenue as a obligation to report these. result of a cyber event that damages or interrupts their cyber infrastructure. Knowing the risks Depending on the insurer, the cover could be part of data-breach Civil engineering firms now rely insurance or a standalone policy, and heavily on electronic systems. They Civil engineering firms are at increasing risk can be extended to deal with financial are used for everything from day- from potentially hugely damaging cyber crime. to-day office administration and attacks – all employees and suppliers need to be aware of the danger communications to digital design and Top-level decision engineering, building information modelling, project and supply chain the UK Information Commissioner; According to the Department of management, logistics planning, business interruption; loss of invoicing Business, Innovation and Skills (BIS, satellite positioning, and monitoring systems; being held to ransom to 2016), only 29% of UK businesses and control systems. remove external encryption from have written cyber security policies The consequences of electronic documents; financial fraud; malicious and just 10% have formal incident systems failing or coming under attack alteration of designs or survey data; management processes. are potentially very serious, given the and defamation. Cyber security strategy should be safety-critical nature of structures and decided at the top level of all civil infrastructure and the often large Potential solutions engineering businesses and then sums of money involved. Attacks can integrated into company culture come from a diverse range of sources The Information Commissioner’s through employee policies and including criminals, rogue governments, Office reported that 93% of education. Its success will also depend terrorists, activists, competitors and investigated incidents in the fourth on regular updates to security software even disgruntled employees. quarter of 2014–2015 were caused and procedures reflecting new cyber Attacks generally fall into two by human error. Employee education threats. categories: malicious viruses being should therefore be a high priority, introduced to the network internally along with appropriate controls on References or external network intrusions. If a own-device usage and access to system breach happens, the risks personal web-based email accounts. BIS (Department for Business Information and are many: reputational damage and Employee education and control Skills) (2016) Cyber Security Breaches Survey 2016. BIS, London, UK. See https://www.gov. the ensuing loss of customers; loss should all form part of a comprehensive uk/government/publications/cyber-security- of intellectual property; fines from cyber security strategy, which should breaches-survey-2016 (accessed 02/06/2016).

For further information contact: Karl Jones Tel: +44 7807 194 283 Email: [email protected] Web: www.kerrylondon.co.uk

100 Civil Engineering Improving urban resilience to flooding: Volume 169 Issue CE3 August 2016 a vital role for civil engineers Escarameia http://dx.doi.org/10.1680/jcien.2016.169.3.101 ICE Publishing: All rights reserved BRIEFING: FLOODING

Improving urban resilience to flooding: a vital role for civil engineers

Being resilient against flooding is a key challenge for urban communities – and one for which civil engineers can play a vital role. Manuela Escarameia of HR Wallingford highlights findings of two themed issues of the Institution of Civil Engineers’ journal Water Management on the topic.

Much has been written in recent years of protection measures, emergency scale, describe the design and social about resilience in many sectors of evacuation) and after (reinstatement). impact of resilience technologies such society and, equally, many definitions of They also span a range of technical as temporary flood barriers and set out resilience have been suggested. subject areas which, in addition to mitigation solutions for critical urban In the context of urban resilience to hydrological and hydraulic flood studies, infrastructure during flood events (Balsells flooding, the following definition by van include urban planning and design, urban et al., 2015; Connelly et al., 2015; Veelen et al. (2015: p. 50) is arguably drainage, building construction and asset Escarameia et al., 2016). the most appropriate: ‘Resilience [is] the management of infrastructure networks. Case studies from France, the USA, capacity of a system to buffer natural Thailand, Norway and the UK highlight variations, recover from disturbances Global engineering challenge the importance of collaboration, clear and return to its previous state without vision, an integrated approach, good experiencing changes to the system as A sample of the breadth of engineering organisational structure and good a whole.’ research and practice in the field of flood flood data archives. It is also shown However, when certain thresholds are resilience has been captured in two that public awareness of flood risk and reached (‘tipping points’) systems are themed issues of the Institution of Civil willingness to contribute to long-term no longer able to recover and need to Engineers’ Water Management journal maintenance can be heightened by adapt to face changing circumstances. (168 WM2 and 169 WM2) published in the use of locally tailored sustainable This is what civil engineers need to bear April 2015 and April 2016. They include drainage systems (Everett et al., 2016). in mind when designing and managing contributions from France, Norway, The papers offer only a taster for this infrastructure that limits personal and Thailand, the Netherlands, the UK and ever-expanding and topical subject – it economic damage from flooding. the USA, often through international is hoped they will whet the appetite of collaborative research. a broad range of civil engineers. New approaches needed The papers highlight that new thinking needs to acknowledge uncertainties, References Recent flood events worldwide not least of which is climate change. have brought to light the pressures This has led to the development and Balsells M, Barroca B, Becue V and Serre D (2015) Making urban flood resilience more operational: that increased population, urban promotion of adaptive approaches to current practice. Proceedings of the Institution development and climate change pose flood resilience rather than traditional of Civil Engineers – Water Management 168(2): on existing traditional flood defences. precautionary approaches (Brisley et al., 57–65. Brisley R, Wylde R, Lamb R et al. (2016) Techniques The efficacy of traditional flood defence 2016; van Veelen et al., 2015). for valuing adaptive capacity in flood risk methods is being questioned, with The papers also discuss how to improve management. Proceedings of the Institution of increased efforts and resources being urban flood resilience at a neighbourhood Civil Engineers – Water Management 169(2): 75–84. made available for research into new Connelly A, Gabalda V, Garvin S et al. (2015) approaches that focus on resilience. Testing innovative technologies to manage flood risk. Proceedings of the Institution of Civil The new approaches include Engineers – Water Management 168(2): 66–73. technologies and methodologies that Escarameia M, Walliman N, Zevenbergen C and allow a smoother passage through de Graf R (2016) Methods of assessing flood resilience of critical buildings. Proceedings a flood event and promote faster of the Institution of Civil Engineers – Water recovery, enabling populations to Management 169(2): 57–64. resume their normal activities more Everett G, Lamond J, Morzillo AT, Chan FKS and Matsler AM (2016) Sustainable drainage quickly. The approaches – which are systems: helping people live with water. particularly important for expanding Proceedings of the Institution of Civil Engineers – Stranded aircraft at Don Mueang airport in Water Management 169(2): 94–104. urban areas – span the various stages van Veelen PC, Stone K and Jeuken A (2015) of flooding: before (preparedness, Bangkok, Thailand – civil engineers need to Planning resilient urban waterfronts using find new ways to improve urban resilience to assessment of vulnerability and adaptive pathways. Proceedings of the flooding Institution of Civil Engineers – Water criticality), during (implementation Management 168(2): 49–56.

For further information please contact: Manuela Escarameia Tel: +44 1491 822429 Email: [email protected] Web: www.hrwallingford.com

101 Civil Engineering Recycling construction materials – proud Volume 169 Issue CE3 August 2016 tradition and bright future Sims http://dx.doi.org/10.1680/jcien.2016.169.3.102 ICE Publishing: All rights reserved BRIEFING: MATERIALS

Recycling construction materials – proud tradition and bright future

Salvaging and recycling construction materials, which has gone on for thousands of years, looks set to increase in the future. Ian Sims of RSK Environment reports on the latest trends detailed in a recent themed issue of the Institution of Civil Engineers’ journal Construction Materials.

There is an established tradition for could soon be a new lease of life from salvaging and recycling construction processing recycled iron and steel. materials. Former Roman buildings served as a source of new construction Recycled and reclaimed materials for hundreds of years in aggregates Europe, while demolition waste has long been used in foundations for Certainly it is clear from the range buildings and infrastructure worldwide. and diversity of papers in the themed The clear sustainability benefits of issue of Construction Materials that recycling demolition waste and re- recycling in construction is now the using building elements means it is global norm. now actively encouraged throughout Cumbrian roof slates being assessed for re‑use For example, Soutsos and Fulton the construction industry. The latest after decades in London’s Regent Street (2016) report on the successful developments in recycling were reported programme of re-utilising construction in a themed issue of the Institution of largely beneficial uses in construction. In and demolition waste during recent Civil Engineers’ Construction Materials the mid-twentieth century, clinker from regeneration in Merseyside. In Qatar, journal in April 2016. coal-burning furnaces was routinely Hassan et al. (2016) address the used as concrete aggregate, and today development of new infrastructure Salvaging key elements furnace ash is a common component of ahead of the 2022 FIFA World Cup and precast units. the initiative underway both to recycle Valued building elements – such as Calcium sulfate, also an industrial demolition waste and reclaim usable stone, bricks, slates, lintels and flooring by-product, is used to make gypsum aggregates from excavation arisings. tiles – have always been recovered and plaster by factory blending with fillers Also, Ellis et al. (2016) describe an re-used. Indeed, certain materials are and other constituents, competing exemplary case in south-east London, only available on a second-hand basis, directly with plasters processed from where bricks from a demolished viaduct including stone varieties that are either natural deposits. were innovatively recycled as engineering worked out or no longer viably quarried. fill for the replacement works. For example, in the UK it is often By-product supply shortages It seems construction recycling, which considered preferable to undertake has a long, proud history, also has a very expert selection of second-hand slates The availability of by-products can bright future. for re-use rather than import new fluctuate however. For example, the natural slates or use manufactured ones. architect of a recent London landmark References was originally keen to use floor tiles Employing waste and by- Crockford I, Breton M, McCormick F and Johnson made from the abundant supply of P (2011) Delivering London 2012: the Olympic products television and monitor cathode ray Stadium. Proceedings of the Institution of Civil tubes. Unfortunately, not only were the Engineers – Civil Engineering 164(6): 37–43, http://dx.doi.org/10.1680/cien.2011.164.6.37. There has also been a gradually glassy tiles too slippery, their production Ellis S, Goodwin A, Laycock E and Hurst C (2016) increasing role in construction for was soon compromised by the rapid rise Use of crushed brick in reinforced earth railway redundant or waste products. For of flat screens. structures Proceedings of the Institution of Civil Engineers – Construction Materials 169(2): 93–105. example, the London 2012 Olympic Slag and fly ash might also face Hassan KEG, Reid JM and Al-Kuwari MS (2016) Stadium roof incorporates 2600 t of supply shortages going forward. Some Recycled aggregates in structural concrete – a Qatar case study Proceedings of the Institution redundant steel gas pipes (Crockford former steel-producing countries, of Civil Engineers – Construction Materials et al., 2011). including the UK, are increasingly 169(2): 72–82. Industrial by-products such as ground focusing on specialist rather than bulk Soutsos M and Fulton MC (2016) Recycling of demolition waste in Merseyside Proceedings of granulated blast-furnace slag from production, resulting in reduced slag the Institution of Civil Engineers – Construction steel-making have found extensive and outputs. On the other hand, there Materials 169(2): 54–66.

For further information please contact: ICE Publishing Tel: +44 20 7665 2460 Email: [email protected] Web: www.icevirtuallibrary.com

102 Civil Engineering Doubts remain on reliability of concrete Volume 169 Issue CE3 August 2016 chemical analysis methods Ingham and Barnes http://dx.doi.org/10.1680/jcien.2016.169.3.103 ICE Publishing: All rights reserved BRIEFING: TESTING

Doubts remain on reliability of concrete chemical analysis methods

It was reported over 2 years ago that British Standard methods for analysing hardened concrete give unreliable results. Jeremy Ingham of Mott MacDonald and Richard Barnes of The Concrete Society warn that nothing has changed – and that great care is needed until it does.

Chemical analysis of hardened concrete participated in the trial and the results inevitably continue to change the samples is commonly undertaken during indicated that BS 1881-124 analysis composition of concrete mixes over condition investigation of concrete procedures are insufficiently accurate time. structures, forensic investigation when applied to contemporary concrete On the other hand, the tests may of failures and during research and (Concrete Society, 2014). have been inaccurate or inadequate standards development for concrete An example graph from the trial, for decades. This raises concerns about durability design. showing the range of cement content knowledge of the current and future Such analysis is an important asset results obtained for the four concrete condition of the UK infrastructure stock. management, diagnostic and research mixes, is shown here. It can be seen There are significant implications for tool and so it is imperative the results that the laboratory tests gave results safety, serviceability and sustainability, are accurate. However, despite being ranging from 175 kg/m3 to 400 kg/m3 which also typically increase the whole- shown 2 years ago to give inaccurate for a sample of concrete with an actual life cost of structures (Ingham and results, the methods set out in cement content of 300 kg/m3 – typical Barnes, 2016). BS 1881‑124:1988 (BSI, 1988) are still of the level of inaccuracy found. routinely used in the UK and elsewhere. Recommendations Implications Laboratory trial The Concrete Society recommended The accuracy of the BS 1881-124 2 years ago and continues to call for A Concrete Society laboratory trial in methods are clearly in doubt and this a further, larger laboratory trial to be 2012–2013 investigated the accuracy is a matter of considerable concern undertaken. If the findings concur with of the most commonly used chemical given their extensive and long- the 2012–2013 trial, then a considerable analysis methods in BS 1881-124 – standing use. In the 28 years since the amount of research and development of cement content, chloride content, methods were introduced there have new test methods will be required. sulfate content, alkali content and been considerable developments in In the meantime – and as a stopgap water/cement ratio. Four concrete mixes concrete technology and changes in only – the society has recommended were prepared that included a range of concrete construction practice, which that BS 1881-124 methods continue contemporary concrete ingredients. the tests have not kept pace with. to be used, but in full knowledge of Eleven UKAS-accredited construction This is a problem that will increase as the potential levels of inaccuracy. In materials testing laboratories advancements in concrete technology addition, the analysis of results and any interpretation of their significance

500 Mix 1 should always be undertaken by 3 Mix 2 suitably qualified and experienced 450 Mix 3 Mix 4 specialists, capable of exercising sensible 400 Line of equality engineering judgement. 350 References 300 BSI (1988) BS 1881-124:1988: Testing concrete 250 – Part 124: Methods for analysis of hardened concrete. BSI, London, UK. 200 Concrete Society (2014) Analysis of Hardened Concrete: A Guide to Tests, Procedures and Measured cement content: kg/m 150 Interpretation of Results. Technical Report No. 250 300 350 400 450 32, 2nd ed. The Concrete Society, Camberley, Actual cement content: kg/m3 UK. Ingham J and Barnes R (2016) Briefing: Testing times for concrete structures – is BS 1881- Comparison of actual and BS 1881-124 measured cement contents from the 2012–2013 124 still fit for purpose? Proceedings of the laboratory trial results Institution of Civil Engineers – Construction Materials 168(6): 253–258.

For further information contact: Jeremy Ingham Tel: +44 20 8774 2994 Email: [email protected]

103 Call for Papers

Proceedings of the Institution of Civil Engineers Civil Engineering Panel Chair and Honorary Editor: Emma Kent, Cundall, UK

Civil Engineering, indexed Why Publish with ICE? in Web of Science, is the ICE Publishing has been uniting research and ICE’s flagship journal. practice in engineering and science since 1836. As the publishing arm of the Institution of Civil Practical and diverse in its scope, Engineers, we provide exclusive access to over Civil Engineering publishes overview 80,000 active ICE members in 160 countries. papers for the non-specialist on any subject relevant to civil engineering By publishing with ICE, you will benefit from today. Multi-disciplined in approach, our quality, visibility and advocacy. topics range from landmark projects to philosophical, ethical, QUALITY environmental, management and safety issues. • Rigorous blind peer review by an international panel of experts

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• We work closely with our authors and editors to promote our journals to all relevant audiences, at international conferences, and through engineering social networks Invitation to Authors

To submit an abstract or to request further details, please contact Tel: +44 (0) 207 665 2242, Email: [email protected] To submit a paper, visit www.editorialmanager.com/ce For more information about the journal, including full submission guidelines, visit www.icevirtuallibrary.com Highways and Transportation Books From ICE Publishing

ice textbooks

Transportation Engineering

John Wright

Highways: The Location, Design, Transport Engineering Practical Road Safety Auditing Construction and Maintenance of (An ICE Textbook) 3rd Edition Road Pavements, 5th edition

Coleman O'Flaherty and David Hughes John Wright Martin Belcher, Steve Proctor and Phil Cook Price: £45.00 Price: £30.00 Price: £65.00/$110.00 ISBN: 978 07277 5993 1 ISBN: 978 07277 5973 3 ISBN: 978 07277 6016 6 Format: Paperbound Format: Paperbound Format: Hardbound Extent: 646 Extent: 160 Extent: 208

Highways is a comprehensive textbook on Covering rail, air, road and water, Practical Road Safety Auditing 3rd edition, all aspects of road engineering and the new Transportation Engineering explores the explains the systematic process for checking edition will cover the latest developments in transport of people, goods and information the safety of new road schemes to comply the ﬁ eld, building on the fourth edition which throughout history and considers how with the brand new 2014 update to the Road is still viewed as the leading title in highway transport can meet the needs of the future. Safety Audit Summary, which includes risk engineering, despite now being over ten years It examines the idea that transport needs assessment as a potential part of the Road old. are based on the concept of supply and Safety Audit and the need for the professional demand and that modes of transport must, certiﬁ cation of Road Safety Auditors. Originally published 1974, this book is the therefore, have a “life-cycle”. This book also leading authority on the subject. Highways, Practical Road Safety Auditing ensures that explores the economics of transport and the 5th edition covers road location and plans, all highways schemes operate as safely as is importance of considering price, convenience roadwork materials, surface and subsurface practicable, by minimising future accident and safety of new and existing modes of moisture control, pavement design and numbers and severity. The book aims to raise transport, as well as the impact that the construction, thickness design of bituminous awareness of the safety of all road users, and recession has had on preferred modes of and concrete pavements, and road in particular vulnerable road users such as transport, e.g. an increase in people cycling maintenance and rehabilitation. the visually and mobility impaired, cyclists, instead of driving, using the internet to pedestrians, equestrians, motorcyclists, communicate instead of travelling overseas. children and the elderly.

To order Online: www.icebookshop.com Email: [email protected] Phone: +44 (0)1892 83 22 99

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Books REVIEWS

CDM 2015: It is a little bible that cuts through Successful questions and the myths and uncertainty to give clear, professional answers confident and concise guidance. reviews for civil by Pat Perry, ICE engineers Publishing, 2015, Health and (4th ed.) safety: questions £40, reviewed by Patrick Waterhouse by Eva Linnell, and answers – a and Harry Macdonald Atkins, UK practical Steels, published by approach ICE Publishing, 2015, The third edition (2nd ed.) £30, reviewed by of the UK Construction (Design and by Pat Perry, Sebastian Lewandowski, Atkins, UK Management) Regulations (CDM published by ICE 2015) has applied to all construction This book provides comprehensive Publishing, 2016, guidance on the Institution of Civil Engineers’ projects since October 2015. The revised £35, reviewed by regulations impact the entire project life (ICE) professional review and offers advice David Oloke, Progressive Concept as to how the candidates should comply cycle, but there is increased emphasis on Consultancy Ltd, UK early engagement by the client and on with each of the requirements given in ICE’s the role of the designer in maximising This second edition has built on the professional review guidance. opportunities to eliminate risks. success of the first edition to produce The fourth edition has been updated This is a surprisingly accessible book very good material on a very important to cover the simplified review process about legal responsibilities under CDM subject. It covers a wide range of health introduced by ICE in 2015. The authors 2015, describing health and safety and safety issues in the construction have drawn upon their experience and best practice on construction projects. industry. included a number of practical tips and The format of this book makes it highly The logical presentation makes it easy common mistakes made by candidates readable, with questions and answers to interact with the book. The first five in writing the report and preparing the arranged under easy-to-reference chapters deal largely with concepts, presentation. sections, and interspersed by short case laws and regulations, while the next five Similar to the previous edition, it also studies. chapters relate mostly to human factors describes what to expect on the review The book is split into two parts. including training requirements – which day. While some of the information could Part one is on the regulations, roles are particularly important for health be considered as just common sense, there and duties, describing the legal and safety management and accident is a good amount of useful advice as well. responsibilities of the duty holders and prevention. If you have nearly completed your the recent changes to the legislation. The next 14 chapters cover common initial professional development, I would The second part covers construction questions asked in respect of work recommend you and your supervising safety, with guidance included on the processes and the requirements to civil engineer reach for this book well construction phase health and safety work safely and guarantee the safety before you actually start putting your plan, working at height and asbestos. of others. Significantly, they also cover submission together. Answers reference the relevant the practicality of occupational health For those earlier in their career, looking legislation that forms the legal basis for matters. The last three chapters deal for advice on the initial professional the responsibility. with the unique aspects of stress, lone development process, I would recommend First and foremost, this is a highly working and working with others – Initial professional development for civil practical guide, covering real-world including managing contractors. engineers by Macdonald Steels instead. scenarios so readers can confidently Although readers may tend to see Trust in assess whether they are complying ‘Q&A’ books either as handy quick- with the law. Questions include, ‘the reference guides or non-conventional construction client refuses to accept my advice as textbooks, this book succeeds in bridging projects principal designer, what shall I do?’, that gap. Each chapter contains relevant by Anita Cerić, ‘what type of temporary works should and up-to-date information, templates to published by be medium risk?’ and ‘what is a permit aid application of discussed concepts and Routledge, 2016, to work?’. The book also includes a case studies that can further help the £95, reviewed by range of example forms, including reader. As such it is a good reference for Philippe Bouillard, an appointment letter for a principal students, graduates, trainers and other Université Libre de designer and a hot-works permit. practitioners. Bruxelles, Belgium

106 Civil Engineering Monitor: Books Volume 169 Issue CE3 August 2016

MONITOR:BOOKS

Anita Cerić presents in this book the of people who work together. A team is The book cites existing British result of 4 years of empirical research a group of people who trust each other.’ standards, Eurocodes and US codes, and complemented by a thorough literature covers many different types of structures review. After setting the scene by Structural – including multi-storey buildings, space stating why trust matters in construction structures and bridges. It also contains projects, she analyses the new roles of analysis and detailed information on fire and blast, construction project managers. design to the two forms of extreme loadings The argument of the book is prevent which typically lead to disproportionate straightforward and relevant considering disproportionate collapse. the increasing complexity of current collapse The analysis method is based on projects, particularly in terms of By Feng Fu, published Abaqus software and the author the number of actors involved. It is by CRC Press, 2016, provides the corresponding files for easy supported by much evidence, making £82, reviewed by application. The many applications in the the book very easy to read. Philippe Bouillard, book could also be useful as case studies This is definitely a book that will Université Libre de Bruxelles, Belgium for engineers and students. convince its readers of the importance From a research perspective, the state of trust as an essential project success This book presents a disproportionate of the art is perhaps under-examined factor. Though inspirational in this collapse analysis based on the alternative and references to past publications, regard, the book gives little practical path method initially proposed by including Ellingwood’s, are missing. information on how to build the trust. Ellingwood in 1978. Author Feng Fu, who But it is of major practical interest and I It is nevertheless a significant and useful has 10 years of practical experience before would definitely recommend it for design contribution to support Simon Sinek’s joining academia, has produced a clear engineering offices and lecturers in essential quote, ‘A team is not a group and practical guide for design engineers. structural mechanics.

NEW BOOKS

The ICE library maintains one of the most comprehensive collections of civil engineering books in the world, including all titles from ICE Publishing (shown in bold below). New books received in the past 3 months include the following. 2015 International Building Code illustrated handbook D Thornburg and J Henry £122·99 ACE find a consultant 2016 ACE £70·00 Assessment and management of unexploded ordnance (UXO) risk in the marine environment, Ciria C754 N Cooper and S Cooke £110·00 Building futures: managing energy in the built environment J Powell, J Monahan and C Foulds £34·99 Construction planning (2nd ed.) R Neale, D Neale and P Stephenson £30·00 Deformation and failure mechanism of excavation in clay subjected to hydraulic uplift Y Hong and L Wang £59·99 Delivering value with BIM: a whole-of-life approach A Sanchez, K Hampson and S Vaux £44·99 Engineering geology for underground works P Gattinoni, E M Pizzarotti and L Scesi £117·00 Fit-out environmental good practice on site guide, Ciria C757 S Harris £70·00 Geomechanics in soil, rock, and environmental engineering J Small £57·99 Geomodels in engineering geology: an introduction P Fookes, G Pettifer and T Waltham £35·00 Highway bridge maintenance: planning and scheduling M A Hurt £85·00 Innovative bridges C Broto £44·71 Low car(bon) communities: inspiring car-free and car-lite urban futures N Foletta and J Henderson £41·99 New forms of procurement: PPP and relational contracting in the 21st century M Jefferies and S Rowlinson £95·00 Non-destructive techniques for the reverse engineering of structures and infrastructure B Riveiro and M Solla £99·00 Offshore wind farms: technologies, design and operation C Ng and L Ran £180·00 Railway transportation systems: design, construction and operation C Pyrgidis £95·00 Setting up in business as a mediator S Walker £80·00 Structural analysis and design to prevent disproportionate collapse F Fu £82·00 Structural design of buildings P Smith £49·95 Structural steel design to Eurocode 3 and AISC specification C Bernuzzi and B Cordova £99·95 Structures and their analysis M Fuchs £63·99 The fully integrated engineer: combining technical ability and leadership prowess S Cerri £33·50 Triaxial testing of soils P Lade £125·00 Urban quay walls A Roubos and D Grotegoed £89·00 All books can be borrowed from the ICE library on the first floor of 1 Great George Street, London, SW1P 3AA from 8.30 am to 6.30 pm, Monday to Friday. ICE Publishing titles can also be purchased from the ICE library or ordered by calling +44 1892 832299, emailing [email protected] or by visiting www.icebookshop.com.

MONITOR: PROCEEDINGS

ICE Proceedings

In addition to Civil Engineering, ICE Proceedings includes 17 specialist journals. Papers and articles published in the most recent issues are listed here. Summaries of all these and other papers and articles published can be read free in the ICE Virtual Library at www.icevirtuallibrary.com/content/journals.

Bridge Engineering Smart citizens for smart cities: participating in Temperature in housing: stratification and the future contextual factors Assessing the capacity of existing R. Bull and M. Azennoud M. Baborska-Narozny, F. Stevenson and bridge structures: part 1 Corporate social responsibility at the core of P. Chatterton 169, No. BE2, June 2016, 79–154 new business models Material quantities and embodied carbon On-site assessment of bridges S. Lupini dioxide in structures supported by acoustic emission Governing effective and legitimate smart grid C. De Wolf, F. Yang, D. Cox, A. Charlson, P. Olaszek, J. R. Casas and G. Świt developments A. S. Hattan and J. Ochsendorf Progressive cracking of masonry arch bridges P.-A. Langendahl, M. Cook, S. Potter, H. Roby and Reuse of redundant gravels and phyto- N. Gibbons and P. J. Fanning T. Collins conditioned sewage sludge London Underground – successful outcome of M. S. M. Chan and I. Wolsey bridge assessment programme R. McKoy Assessing the potential value of bridge Engineering and monitoring systems Computational Mechanics Forensic Engineering P. J. Vardanega, G. T. Webb, P. R. A. Fidler and Structural health monitoring C. R. Middleton 169, No. EM2, June 2016, 43–85 169, No. FE2, May 2016, 29–80 Assessment of Tame Valley Viaduct A tablet computer application for Predicting service life from site- C. West conceptual design D. Åkesson and J. Lindemann accessed corrosion rate data Modelling localised fracture of reinforced G. Jones and P. Lambert concrete structures Assessing temporal requirements for SHM Construction Materials F. Liao and Z. Huang campaigns Alkali–aggregate reactions: part II Perforated tunnel exit regions and micro- I. Farreras-Alcover, J. E. Andersen and 169, No. CM4, August 2016, 179–240 pressure waves: geometrical influence N. McFadyen Rilem activities on alkali–silica H. Wang, A. E. Vardy and D. Pokrajac Maintenance of structural integrity using reactions: from 1988–2019 cathodic protection B. J. Wigum, J. Lindgård, I. Sims and S. Beamish, S. El-Belbol and V. Ngala P. Nixon The enigma of the ‘so-called’ alkali–carbonate Engineering History and Heritage reaction Geotechnical Engineering T. Katayama, V. Jensen and C. A. Rogers 169, No. EH3, August 2016, 169, No. GE4, August 2016, Alkali release from aggregates: contribution 109–154 319–380 to ASR Seismic reinforcement of Piled-cruciform attachment E. Menéndez, R. García-Rovés and S. Ruiz historical steel bridges in Japan to monopile head reduces Options for minimising the risk of alkali– H. Isohata, A. Kurebayashi and A. Mori deflection aggregate reactions Accessibility for the 19th century Naarden- M. Arshad and B. C. O’Kelly P. Nixon, B. Fournier and M. D. A. Thomas Bussum railway station, Netherlands Foundation design and construction for store Alkali–aggregate reaction: performance N. den Hartog and M. Brinkhuis in Zagreb, Croatia testing, exposure sites and regulations Failures of US bridge rocker bearings Z. Cabarkapa and P. Smith J. Lindgård, B. Fournier, T. F. Rønning and J. M. Cohen and V. Wetzk An analytical method for a slope reinforced M. D. A. Thomas Civil engineering heritage: country profile – with rigid piles Expansive chemical reactions in dams and Albania Y. Zhuang and X. Cui hydroelectric projects M. D. Gill IDM pressure measurements in a large-scale R. G. Charlwood and I. Sims Civil engineering heritage: country profile – excavation test Mitigation of alkali–silica reaction in US Scotland M. V. Schwager, M. Amstad and A. M. Puzrin highway concrete G. Masterton K. J. Folliard, M. D. A. Thomas, B. Fournier, Cement stabilisation of crude-oil contaminated T. Drimalas and G. Ahlstrom soil I. A. Akinwumi, C. A. Booth, D. Diwa and P. Mills Engineering Energy Sustainability Smart futures 169, No. ES4, August 2016, Ground Improvement 169, No. EN3, August 2016, 91–138 123–168 169, No. GI3, August 2016, Performance comparison of UK Development of thermally 157–233 domestic renewable incentives insulated sustainable building Re-examination of compaction J. R. Snape, P. J. Boait and model parameters of fine-grained soils R. M. Rylatt V. A. Dakwale and R. V. Ralegaonkar G. A. S. Pillai and P. P. Vinod

108 Civil Engineering Monitor: ICE Proceedings Volume 169 Issue CE3 August 2016

MONITOR:PROCEEDINGS

Strength development in fly ash and slag Post-earthquake performance indicators for Urban Design and mixtures with lime sewerage systems Planning A. K. Sharma and P. V. Sivapullaiah M. Liu, S. Giovinazzi and P. Beukman Strength indices of high-moisture soils using Disaster management in Pakistan 169, No. DP4, August 2016, 163–208 handheld gauges M. Malik and H. Cruickshank Understanding identity and F. Vahedifard, I. L. Howard, W. H. Badran, Study for assessment of rainfall duration belonging through incidental W. D. Carruth, M. Hamlehdari and B. D. Jordan inducing landslides spaces The swelling behaviour of lignosulfonate- C. Chhorn, C.-Y. Yune, G. Kim and S.-W. Lee L. P. Rajendran treated expansive soil Workington: a case study in coordination and Urban resilience: the regeneration of the D. P. Alazigha, B. Indraratna, J. S. Vinod and communication Dublin Docklands L. E. Ezeajugh A. Affleck and J. Gibbon A. Doyle Physico-geotechnical properties of peat and its When floods strike close to home Thinking about resilient cities studying Italian stabilisation D. Rowley, M. Buckler and J. Barnett earthquakes P. K. Kolay and Md A. Rahman M. Vona, P. Harabaglia and B. Murgante Properties of soil after surcharge or vacuum Why the urban pattern toward sprawling preloading development? S. Gangaputhiran, R. G. Robinson and R. Karpurapu Structures and Buildings K.-C. Hsu, T.-Y. Lai and C.-N. Li 169, No. SB7, July 2016, 469–546 Comparison of code-specific Management, non‑linear seismic performance Waste and Resource A. Kiani, S. Manie and B. Mansouri Procurement and Law Experimentally based q-factor Management 169, No. MP3, August 2016, 141–186 estimation of cross-laminated timber walls 169, No. WR2, May 2016, Effects of an economic downturn L. Pozza, R. Scotta, D. Trutalli, A. Polastri and 55–92 on construction partnering I. Smith Aerobic treatment of leachate J. Challender, P. Farrell and F. Sherratt Load-bearing capacity of axially loaded circular from municipal solid waste in A chronographic protocol for modelling concrete-filled steel tubular columns Morocco construction projects S. Jegadesh and S. Jayalekshmi M. Abouri, S. Souabi, M. A. Bahlaoui, F. Zouhir, A. Francis Bond–slip behaviour of steel bars in low- M. Baudu, R. Moharram and A. Pala Public–private partnerships for future urban strength concrete Towards recycling and waste reduction in infrastructure S. Ahmad, M. M. Rafi, K. Pilakoutas, Q. uz Zaman Mohammedia, Morocco S. Alim and J. Polak Khan, F. Shabbir and M. F. Tahir A. El Maguiri, I. Laila, B. Kissi and S. Souabi Maximum loads on shores during the Hazardous constituents of e-waste and construction of buildings predictions for India M. Buitrago, J. M. Adam, Y. A. Alvarado, S. Ahmed and R. M. Panwar Maritime Engineering P. A. Calderón and I. Gasch Recovery of lubricant base oils using ionic 169, No. MA2, June 2016, 47–95 liquid processes Spar concrete monolithic design S. M. Grimes and F. Thompson for offshore wind turbines A. Campos, C. Molins, X. Gironella Transport and P. Trubat 169, No. TR4, August 2016, Water Management Assessment of three dredging plans for a 185–246 wave-dominated inlet Calibrating truck characteristics 169, No. WM4, August 2016, D. S. Mendes, A. B. Fortunato and A. A. Pires-Silva into traffic microsimulation 155–200 Chloride penetration of RHA concrete under J. Appiah, B. Naik, L. R. Rilett and An efficient multi-layer model for marine environment S. Sorensen pier scour computations D. S. Jayanti, J. Mirza, R. P. Jaya, B. H. Abu Bakar, Conflicting volume for U-turns at uncontrolled S. Pournazeri, S. S. Li and N. A. Hassan and M. R. Hainin median openings F. Haghighat Non-linear analysis of quay wall combi-pile S. S. Mohapatra, P. P. Dey and S. Chandra Greywater quality changes in a permeable infill sheets Evaluating effects of integrated TDM measures pavement reservoir H. Ahmed and A. Douglas in Nanhai, China R. K. Chowdhury, S. E. Sharvelle and S. Beecham F. Zong, H. Jia, Z. Juan and H. Zhang Stability criterion for people in floods for Size effects of rubblised PCC on HMA overlay various slopes Municipal Engineer performance J. Xia, Q. Chen, R. A. Falconer, S. Deng and Y. Lu and Z. Rong P. Guo Emergency planning and disaster Correlations among railway turnout geometry, Gasification of petrochemical sludge in relief: part I safety and speeds supercritical water 169, No. ME2, June 2016, 63–124 J. Sadeghi, A. Masnabadi and A. Mazraeh L. Zhang, Y. Zhang and T. Zhao Natural disasters: an engineer’s Analytical method for evaluating top-down Predicting flow rate and sediment in perspective in Nepal cracking in pavements bifurcated river branches K. Merrilees Y. Gao Q. Du, H. Tang, S. Yuan and Y. Xiao

In addition to substantial discounts on ICE journal subscriptions, ICE members can also subscribe to the ICE Virtual Journal, offering access to 15 papers from any volume for £40. Visit www.icevirtuallibrary.com/info/icevirtualjournal for more information

MONITOR:PROCEEDINGS

Award-winning papers for free download On 7 October 2016 ICE president John Armitt will present awards to the following papers published in the various ICE Proceedings journals in 2015. Journal editorial panels nominated their best papers and an awards committee, chaired by Nigel Wright, allocated the awards. These award-winning papers can be downloaded for free from the ICE Virtual Library’s ‘ICE Publishing Awards 2016’ page at www.icevirtuallibrary.com/info/awards2016.

PAPER AND AUTHORS ISSUE IN 2015 AWARD Bridge Engineering Design and static analysis of the Taizhou Yangtze River Bridge, China, by Min Zhang, Tianbao Wan and March Mokshagundam Visvesvaraya Yingliang Wang Prize MediaCityUK Footbridge, Salford, UK, by Fabio Gazzola, Steve Thompson and Peter Curran June John Henry Garrood King Medal Civil Engineering High-resolution sonars set to revolutionise bridge scour inspections, by Simon Clubley, Constantino Manes and February Bill Curtin Medal David Richards The News Building, London: design and construction cantilevering over a live transport hub, by Jack Adams, Bart August Coopers Hill War Memorial Lemmens and Matt Massey Prize A review of satellite positioning systems for civil engineering, by Gethin Wyn Roberts, Xu Tang and Chris Brown November Charles Manby Prize Construction Materials Fire performance of metal-free timber connections, by Daniel Brandon, Cristian Maluk, Martin Ansell, August Thomas Howard Medal Richard Harris, Pete Walker, Luke Bisby and Julie Bregulla Energy Delivering safe geological disposal of nuclear waste in the UK, by Cherry Tweed, Alun Ellis and Rob Whittleston November James Watt Medal Engineering and Computational Mechanics Unsteady Reynolds averaged Navier–Stokes simulations of a buoyant plume above a cylinder, by Stig March Thomas Telford Premium Prize Grafsrønningen and Atle Jensen Calculation of fluid–structure interaction: methods, refinements, applications, by Mustafa Can Kara, Thorsten June George Stephenson Medal Stoesser and Richard McSherry Engineering History and Heritage Hinges in historic concrete and masonry arches, by Stefan Holzer and Karen Veihelmann May Benjamin Baker Medal James Newlands and the origins of the municipal engineer, by Sally Sheard May Thomas Telford Premium Prize Engineering Sustainability Towards a sustainable infrastructure company, by Chris Whitehead February Richard Trevithick Memorial Fund Forensic Engineering Release of data following a serious incident in the UK construction industry, by John Carpenter August Thomas Telford Premium Prize Geotechnical Engineering Seismic stability of braced excavations next to tall buildings, by Nick O’Riordan and Ibrahim Almufti February Russell Crampton Prize Ground Improvement Field-scale bio-cementation tests to improve sands, by Michael Gomez, Brian Martinez, Jason DeJong, August Thomas Telford Premium Prize Chris Hunt, Len deVlaming, David Major and Sandra Dworatzek Management, Procurement and Law NEC for DBFO – taking best practice procurement into PPPs, by Richard Patterson and Barry Trebes October Parkman Medal Maritime Engineering Littlehaven promenade and seawall, South Shields, UK, by Nick Cooper, Simon Wilson, Tony Hanson, David March Safety in Construction Medal West and Mike Goodall Impact of managed realignment design on estuarine water levels, by Nigel Pontee June Halcrow Prize Municipal Engineer Investigating ramp gradients for humps on railway platforms, by Taku Fujiyama, Craig Childs, Derrick June James Hill Prize Boampong and Nick Tyler Structures and Buildings Structural development and testing of a prototype house using timber and straw bales, by Daniel Maskell, Chris January Frederick Palmer Prize Gross, Andrew Thomson, Katharine Wall, Peter Walker and Tim Mander Transport Guernsey airport pavement rehabilitation and safety works, by Jonathan Green April William Webb Prize Reassessing the financial and social costs of public transport, by Xucheng Li and John Preston August Rees Jeffreys Award Urban Design and Planning Do sustainability measures constrain urban design creativity?, by Joanne Leach, Christopher Boyko, February Reed and Mallik Medal Rachel Cooper, Anna Woodeson, Jim Eyre and Christopher Rogers Waste and Resource Management Municipal solid waste as a resource: part 1 – specifying composition, by Jade-Ashlee Cox, Michael Mulheron, August Thomas Telford Premium Prize David Jesson, Angela Druckman, Matthew Smyth and Helen Trew Water Management Using climate change projections in UK flood risk assessment, by Ashley Woods August Robert Alfred Carr Prize

MONITOR: ICE REVIEW

ICE review

A review of recent developments at the Institution of Civil Engineers by ICE president John Armitt. For further information please contact the communications office on +44 20 7665 2107, email [email protected] or visit www.ice.org.uk//news-public-affairs.

UK infrastructure body ‘official’ Studying nature’s engineers In May, while setting out the UK A fascinating paper on termite government’s legislative programme for engineering in the April 2016 issue the coming year, the Queen confirmed of ICE’s Environmental Geotechnics that the National Infrastructure journal has been widely covered in the Commission chaired by Andrew Adonis media. Written by the Indian Institute – and of which I am a member – will be of Science in Bangalore, it looked at the formalised in statute. effectiveness of construction techniques Setting the commission on a used by the mound-building termite statutory and independent footing and their potential application in civil will confirm and uphold its role and engineering. purpose. This is an important milestone ICE’s evidence gathering covered all aspects The paper revealed that the well- for UK civil engineering. Certainly of UK infrastructure needs – the findings will documented ‘bio-cementation’ process the mood in the commission is now be published in autumn 2016 used by termites – where grains of soil very positive as we work towards are bonded into balls and then stuck developing proposals for rolling out together – actually makes their mounds Proving UK infrastructure needs the next generation (5G) of mobile ten times stronger than structures built telecommunications networks. Evidence gathering for ICE’s from unmodified materials. We are also looking at providing independent assessment of Britain’s The paper was widely covered infrastructure proposals for the infrastructure needs is now complete. in engineering and construction Cambridge–Milton Keynes–Oxford The findings will be published in trade publications, many of which corridor that will unlock growth, jobs autumn this year and presented to the described the termite as one of and housing. The area contains some National Infrastructure Commission. nature’s top engineers. Stories like of the UK’s fastest growing and most The response to ICE’s nationwide these – where engineers learn and productive places, with global centres call for written evidence and a series of benefit from nature – are important of research in Oxford and Cambridge engagement events and workshops has in engaging the media and public and advanced manufacturing and been huge, providing us with a wealth on engineering. They also show the logistics in Milton Keynes. Our review of evidence and expertise. Over 400 breadth of depth of ICE’s international will recommend how to maximise organisations and individuals from across journal publishing programme – see the potential of the area as a single, the infrastructure sector contributed. www.icevirtuallibrary.com for more knowledge-intensive cluster that The collaborative nature of the project information. competes on a global stage. has played a part, creating a real sense of excitement, and it has been a pleasure for me to chair the executive group. We have a collection of very different organisations – including Pinsent Masons, KPMG and the University of Oxford – working together ultimately to benefit society, grow the economy and drive the shift to a low carbon dioxide future. Research by the Oxford University- led Infrastructure Transitions Research Consortium will also form part of the evidence base, along with other economic and environmental data. Our aim is to Andrew Adonis, chair of the National establish an independent evidence base An ICE journal paper revealed that bio- Infrastructure Commission which is now to cementation processes used by termites become statutory independent body on the UK’s infrastructure needs up to makes their structures ten times stronger 2050 and facilitate more strategic choices.

111 Call for Papers

Proceedings of the Institution of Civil Engineers Engineering History and Heritage Chairan: illiam ddi, Canta,

Engineering ir n Why Publish with ICE? erige is currently ICE Publishing has been uniting research and inviting papers. practice in engineering and science since 1836. As the publishing arm of the Institution of Civil A great many engineers are Engineers, we provide exclusive access to over nowadays undertaking work on our 80,000 active ICE members in 160 countries. existing infrastructure and buildings, work which includes extending By publishing with ICE, you will bene t from the life of existing structures, our quality, visibility and advocacy. refurbishment, conservation and restoration. Heritage structures often QUALITY attract particular attention, but these are only the tip of a large iceberg. • Rigorous blind peer review by an international panel of experts

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To submit an abstract or to request further details, please contact Tel: +44 (0) 207 665 2242, Email: [email protected] To submit a paper, visit www.editorialmanager.com/ehh For more information about the journal, including full submission guidelines, visit www.icevirtuallibrary.com Civil Engineering Proceedings of the Institution of Civil Engineers Volume 169 Issue CE3 Civil Engineering 169 August 2016 Issue CE3 Pages 113–120 http://dx.doi.org/10.1680/jcien.15.00066 A-frame rocker bearing replacement Paper 1500066 at Humber Bridge, UK Received 29/09/2015 Accepted 03/03/2016 Published online 22/04/2016 Collins and Smith Keywords: bridges/steel structures

A-frame rocker bearing replacement at Humber Bridge, UK

1 John Collins MEng, CEng, MICE 2 Daniel Smith BSc, IEng, FSOE, FIPlantE Senior Engineer, Ove Arup, Leeds, UK Senior EPC(m) Project Manager, Fabricom, Great Grimsby, UK; formerly Project Manager, C Spencer Ltd, Hull, UK

1 2

Routine inspections of the A-frame bearing rockers on the Humber Bridge, UK, led to concerns over lack of articulation and potential premature wear. Following design optioneering, an innovative scheme was selected to replace the main span’s A-frames with a pair of vertically orientated pendels and a wind shoe at each tower, thus separating out the horizontal and vertical forces, with benefits for construction and maintenance. This paper describes the design and £4 million, 2 year replacement project. The works were carried out in a very confined environment, and required significant strengthening to the existing bridge to accommodate the new permanent and temporary design elements. The project was completed in 2015, all under live traffic, and has ensured the future integrity of this world-class structure.

1. Introduction ■■ vertical load path for a nominal amount of dead load not carried by the hangers and for a component of traffic load up to Opened in the UK in 1981, the Humber Bridge carries the A15 approximately 90 m from the deck box ends. dual carriageway over the Humber estuary between Hessle, East Yorkshire and Barton, North Lincolnshire, UK. With its 1410 m The total longitudinal displacement accommodated by the main suspended main span, it was the world’s longest single-span bridge span A-frames was approximately 2 m. until 1997 (Figure 1). Through routine inspections, the bridge owner Humber Bridge The highway is carried by a 4·5 m deep steel deck box. Board (HBB) had noted degradation to the main span A-frames. The carriageway is discontinuous at the reinforced concrete towers, Gaps that were present between the rocking A-frame and its passing onto expansion joints. Each end of the deck boxes at the supporting structure had closed, suggesting wear of the pin towers and anchorages were supported by pairs of steel A-frames bearings was taking place (Figure 3). (Figure 2). These elements formed a pinned connection at their In 2011, HBB commissioned designer Arup to investigate apexes – to the deck box at the top and to the tower and anchorage further, recommend a single preferred option for refurbishment abutment at the bottom. or replacement and undertake detailed design. This paper details The A-frames provided several functions this process and describes the resulting 2013–2015 £4 million construction work by contractor C Spencer. ■■ free longitudinal movement of the deck boxes while the supporting catenary above changes shape as traffic crosses the bridge 2. Investigation ■■ free longitudinal movement of the deck boxes against other effects, notably temperature expansion and contraction, static 2.1 Inspection and monitoring and dynamic wind loading Upon inspection of all 12 A-frame bearing rockers, only the four ■■ being of low plan torsional stiffness, free plan rotation of the to the main span were noted to be heavily worn. The two rockers deck box ends under wind loading at Hessle tower were particularly heavily worn. Restraining keys ■■ torsional restraint for the deck box against unbalanced intended to prevent rotation of the pin relative to the tower portal carriageway loading – one A-frame acting in compression, the beam and deck box brackets had been removed. Although the opposed A-frame in tension bearing arrangement prevented full inspection, it was thought and ■■ horizontal restraint to the ends of the deck boxes under wind later proven on demolition that the pin was free to rotate inside the loading connecting brackets, causing heavy wear to the bracket holes.

113 Civil Engineering A-frame rocker bearing replacement at Humber Bridge, UK Volume 169 Issue CE3 Collins and Smith

162.5 mOD MHWST 3.960 mOD

Hessle Barton

280 m 1410 m 530 m CL CL CL CL sidespan Hessle Barton sidespan anchorage tower tower anchorage bearing bearing Elevation 22.9 m 162.5 mOD

CL CL cable and cable and hangers hangers 3 m 22 m Deck box Footway 2 lanes = 7.3 m 34.8 mOD Portal beam A-frames 4.5 m 6.6 mOD Hessle 9.0 mOD Barton 28.5 m 24.4 m Elevation of towers Section through deck box Isometric of A-frames

Figure 1. General arrangement of Humber Bridge and view onto an A-frame rocker bearing

Laser extensometers recording longitudinal displacement of the Temporary Permanent Deck box Original pendel pendel strengthening A-frame main span deck box had been set up (Brownjohn et al., 2012). These concrete were mounted on the tower legs, measuring the varying distance to the deck box corners. For example, passage of a 40 t vehicle After Before results in longitudinal movement over a 20 mm range. Analysis of the resulting data showed good agreement with a computational structural model. Extrapolation from a 4 week monitoring period led to the estimated longitudinal accumulated sliding distance of the main span being 4·5 km/year, or around 130 km prior to the A-frame replacement works (Hornby et al., 2012). Extensometer output demonstrated that the deck box was articulating as per the original design intent. However, due to the relatively large height of the A-frames – at 3·8 m tall – and

Tower leg and Transformer Wind shoe portal beam room

Figure 3. Pin housing at the base of an A-frame (left) and gap closure Figure 2. The main span deck box arrangement at the towers before formed by elongation of the pin’s hole in supporting bracket plates and after the works (right, circled in red)

114 Civil Engineering A-frame rocker bearing replacement at Humber Bridge, UK Volume 169 Issue CE3 Collins and Smith

relatively small horizontal displacements, it was not clear to Refurbishment or replacement like-for-like was ruled out since the naked eye that the frames were rocking to accommodate the existing arrangement only achieved 30 years’ life. Consideration longitudinal displacements. If a pinned bearing were seized, it was given to removing all uplift forces, allowing use of a common is possible that it would form a moment restraint against a free spherical sliding bridge bearing. This could be achieved by filling rocking motion with displacement accommodated by the A-frame the end deck box with concrete. The large quantity of concrete acting in flexure. Such a flexural action on the A-frame would required made this option untenable. The existing pin-in-bush impose a stress range of approximately 90 N/mm² on extreme bearing was identified as a particular weak point not only due to fibres of the frame for each 40 t vehicle crossing the bridge: a their poor wear performance but also the difficulty of replacement stress range which could result in rapid growth of fatigue cracks. now and in the future. To determine whether the A-frames were freely rocking, a Proprietary plane spherical bearings with polytetrafluoroethylene simple but effective monitoring regime was instigated. Moiré (PTFE) sliding surfaces are commonly encountered within the tell‑tales, sensitive to differential movements as little as 0·1 mm, realms of mechanical engineering and were specified. It was were attached across the A-frame pin-housing–lug-plate interface. decided that rather than installing these bearings into new These were visually monitored under displacements imposed A-frames, the horizontal and vertical load components would be by live load. All A-frames appeared to be rocking freely under separated into vertical pendel and horizontal wind shoe elements imposition of live load with the exception of Barton main span’s (Figure 2) to simplify installation and future bearing replacement A-frames. works. From the wear to A-frames at Hessle main span and concerns Pendels (from the German Pendel meaning pendulum) are over the freedom of rotation of Barton main span’s A-frame rocking single-bar linkages, here positioned in place of the bearings, it was decided that refurbishment or replacement of the A-frames and housing a spherical bearing top and bottom. main span A-frames only was required. The wind shoe is a steel box cantilevering from the deck box, with opposed sliding bearings providing horizontal reactions. An inventory of the principal elements is included in Table 1. 3. Option development and design Eurocodes were used for determination of load effects and design of new structural components. Traffic live load to the UK Six possible options were developed and appraised by the implementation of BS EN 1991-2 (BSI, 2008) was found to result designer and the bridge owner (Hornby et al., 2012). Aspirational in load effects and longitudinal displacements far in excess of the design life was 120 years, with 50 years on replaceable parts such bridge’s original design load or its bridge specific assessment live as bearings. loading. Bespoke amendments to the appropriate factors were

Element Item Number Material Total / comments Steel (BS EN 10025 (BSI, 2009a), Temporary pendel 4 S355 8·0 t BS EN 10225 (BSI, 2009b)) Temporary pendel holding-down frame 4 S355 26·5 t 90 mm thick temporary pendel connection plate 4 S355 16·8 t 15 mm thick end diaphragm strengthening plate 4 S355 2·4 t Upper pendel connection bracket 4 S355 16·0 t Pendel 4 S355 and S460G2+M 24·8 t Pendel holding-down frame 4 S355 36·0 t Wind shoe 2 S355 9·8 t Total 140·3 t Threaded connectors BS EN 14399-8 (BSI, 2007) fit bolts >4000 Grade 10.9 Post-tensioned steel bars 144 Macalloy 1030 12·7 t Bearings Spherical: pendel 8 PTFE, stainless steel RBC Lubron supplied 450 mm dia. pins, pendel 8 Mild steel 7·6 t Spherical sliding: wind shoe 4 UHMWPE, stainless steel Ekspan supplied In situ reinforced concrete Deck box strengthening: wind shoe 2 C40/50 11·6 m³ (concrete BS EN 206 (BSI, 2013), Deck box strengthening: upper pendel connection 4 C50/60 24·8 m³ reinforcement B500B/C to BS 4449 (BSI, 2005)) Pendel bottom anchorage 4 C40/50 17·0 m³ Wind shoe plinths 4 C40/50 3·4 m³ Side span A-frame plinths 4 C40/50 2·6 m³ Total 59·4 m³ Electrical 3·3 kV cast resin transformers 4 Air cooled Installed by PCS

Table 1. Summary of principal elements

115 Civil Engineering A-frame rocker bearing replacement at Humber Bridge, UK Volume 169 Issue CE3 Collins and Smith

Bearing Cylinder Sliding To allow removal of the plinth bearing Min. 2 MPa surface A-frames and installation of the new pendel without closing the bridge to traffic, a temporary pendel arrangement was designed and implemented made to develop a live load model representative of the bridge’s capacity (Collins et al., 2013). While predominantly under compressive loads (16·4 MN at ultimate limit state (ULS)), the pendels frequently enter tension (11·5 MN ULS) when forming a torsional reaction. Loads are transferred from the pendels into the tower portal beam by a steel fabricated holding-down frame. To resist uplift, the frame To accumulator is connected by post-tensioned steel bars to the portal beam. This necessitated formation of a reinforced concrete anchorage inside Figure 4. Wind shoe hydraulically preloaded sliding spherical bearing a void in the portal beam which houses the bridge’s electrical arrangement transformers and switchgear. The frame has been designed to take loads from side spans, should the existing A-frames here require future replacement. Opposed sliding spherical bearings are required to the wind shoe The top pin of the main span A-frame was just 225 mm in such that wind-induced loads (2·1 MN ULS including a dynamic diameter. To reduce bearing pressure and increase wear life a larger wind loading) in either horizontal direction can be resisted and 450 mm pin was designed. However, this larger pin is contained transferred into the portal beam through new reinforced concrete within the pendel in a geometrically tight area that was only big plinths. Unless preloaded, the windward side bearing would carry enough for the A-frame’s top bearing. High-strength quenched no load, opening up sliding surfaces to dirt and moisture ingress: and tempered steel BS EN 10025-6 S690QL1 (BSI, 2009a) with highly undesirable if bearing life is to be maximised. Hydraulic enhanced brittle fracture requirements was specified. Specialist preloading of bearings to maintain a contact pressure of at least guidance was sought to produce an achievable performance 2 MPa was specified. specification for the pendel’s spherical bearings. This included While several bearing manufacturers offer bespoke units close consultation with suppliers at design stage and review of incorporating both hydraulic cylinder and bearing, it was felt that load and wear tests. future maintenance and replacement would be made easier if the The top pendel bearing and its connecting plate is attached to cylinder and bearing could be separate, easily procurable items the deck box by post-tensioned bars. The bars are anchored against (Figure 4). Conventional PTFE in sliding surfaces has limited wear the penultimate diaphragm. An existing complex arrangement of life for high movement cumulative displacements and velocities. longitudinal diaphragms in this area is strengthened compositely A silicone-lubricant-impregnated ultra-high molecular weight by reinforced concrete. polyethylene (UHMWPE) was specified. The deck box soffit to To allow removal of the A-frames and installation of the new which the wind shoe was connected was strengthened by placement pendel without closing the bridge to traffic, a temporary pendel of in situ reinforced concrete. arrangement was designed and implemented. It was attached to a new 90 mm thick plate cantilevering from the side of the deck box, immediately adjacent to the tower leg. This is an area of the 4. Construction deck box not designed to take large point loads. Steel strengthening plates 15 mm thick were therefore bolted to the end diaphragm, Construction works commenced in July 2013 and finished in providing additional capacity to transfer loads from the temporary July 2015. The £4 million project was procured under the NEC3 pendel to the A-frame–pendel connection area. Engineering and Construction Contract option A (priced contract To limit the extent of strengthening works required to transfer with activity schedule). The designer was retained as NEC project temporary pendel loads, it was specified that the bridge’s nearside manager and supervisor. lanes (lane 1, the ‘slow’ lane) in both directions would be closed For accurate fabrication and installation, it was essential to traffic while on temporary pendels. The main effect of this is first to survey in three dimensions the faces and edges of the to reduce the torsion on the deck box requiring reaction by the existing structure. What might otherwise be a simple structural temporary pendels. When combined with reduced factors for survey was complicated significantly by the exposed windy the relatively short duration that the temporary pendels would environment and constant movement of the deck box under be resisting live load, ULS loads on the temporary pendels were traffic loads. Surveying was hence at night in calm winds and 6·4 MN compression, 2·5 MN tension. low traffic volumes.

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Weld trials to the originally specified S690QL1 steel were not successful so a new specification for S460G2+M with enhanced toughness and yield strength was developed

The contractor designed and installed temporary pendels, with rotational freedom provided at their ends by pins in bearing bushes of synthetic woven material in a resin matrix incorporating solid lubricants. During the 15 months on temporary pendels, these bearings wore to such an extent that they emitted loud banging noises under deck movements. However, thanks to close monitoring of strain gauges attached to the temporary pendels it could be proven that resulting stresses in steelwork from additional restraint formed by the bearings were of a safe magnitude. Before load transfer to the temporary pendels, the wind shoe Figure 5. Removal of lane 1 carriageway expansion joint and and bearing assembly was installed and commissioned. Output installation of a temporary hinged plate allowed the new fabrications, from a pressure transducer allows the bridge owner to monitor such as the permanent pendel base, to be lifted by Hiab loader crane the hydraulic system remotely. The steel wind shoe was installed and lowered onto the portal beam by lowering it through the temporary expansion plates before transferring the load across the portal beam and under the deck by the use of a series of lifting points with lever hoists. Bespoke brackets were made so that the survey station could The wind shoe and strengthening plates were connected to the be fixed directly to the deck box, allowing it to move with the deck box with M24 fit bolts. The selection of these fit bolts reduces bridge. Two surveys were then created: one of the bridge deck the number of bolts required compared to conventional preloaded box (moving) and one of the portal beam (stationary). These two bolts in normal clearance holes. To ensure the fit bolt shank engages surveys were then brought together by plotting the A-frame’s upper the connected plies in shear, the hole tolerance is just -0/+130 μm. bearing locus. Holes were drilled and reamed on site with magnetic drills, using The main area for the works, the A-frame bearing shelf atop the a match-bored template with undersize holes. Quality control of portal beam, is extremely cramped. Working area was increased hole size was by go/no-go gauges on every single hole. All bolts by a temporary scaffold cantilevering from the face of the portal were fitted with direct tension indicator washers to verify preload beam. Access to the deck box faces was provide by scaffold affixed applied with torqueing by hydraulic wrenches. These performed to the steel box, positioned such that it did not clash with other very well, offering increased control and reduced noise compared bridge elements as the bridge moved longitudinally. to impact wrenches. High-risk operations, such as lifting of the bulky replacement Load transfer to the temporary pendels was carried out under components, were meticulously planned. To reduce risks associated live traffic, albeit at night in calm wind conditions to make for with lifting and working in confined areas, the contractor removed easier monitoring of strain gauges. Taking advantage of the slope the lane 1 carriageway expansion joints above the portal beam. in the A-frame bearings created by 30 years of wear, the bridge was Access for lifting in the large sections of new steelwork was created lifted by jacking up each temporary pendel in turn by two 260 t by temporary expansion plates (Figure 5). These plates could be low-height, failsafe hydraulic cylinder jacks connected in series to independently hinged open to allow the steelwork to be lowered in a hand pump. through the carriageway. The loads in the temporary pendel were monitored by way of Completion of the dimensional survey allowed steelwork strain gauges. Dial indicators monitored the height of lift of the fabrication to start. The pendels’ spherical bearings were chill- A-frame’s bearing housing. When it was determined by reference fitted into the completed pendel arms after fabrication. Aware of to the monitoring equipment that there was no residual load in the the difficulties of welding some of the high-strength steel grades A-frames, they were severed from the deck box by oxyacetylene specified, the designer’s metallurgical expert, fabricator Allerton cutting (Figure 6). This was repeated at all four corners of the deck Steel and the contractor’s material consultant Sandberg worked box over successive nights in September 2014. closely to ensure the high quality of welding and materials With load transfer to the temporary pendels complete, the was not compromised. Weld trials to the originally specified A-frames were demolished (Figure 7). A survey finding was that S690QL1 were not successful and a new specification for BS EN the deck box is significantly non-flat and therefore unsuitable as 10225 S460G2+M with enhanced toughness and yield strength a surface for the clamping reaction formed by the post-tensioned requirements was developed. bars. To overcome this, an ultra-low shrinkage and creep, high-

117 Civil Engineering A-frame rocker bearing replacement at Humber Bridge, UK Volume 169 Issue CE3 Collins and Smith

strength resin, usually used for chocking of marine machinery The new pendel was secured to the portal beam by the base plates, was used to fill the voids after engineering a minimum holding-down frame, each of the four frames held down by gap between the plates. Such a specialist, high-performance resin 14 post‑tensioned steel bars. The 50 mm dia. bars passed through required exacting installation conditions, proven by detailed 75 mm dia. holes, cored 1·3 m through reinforced concrete trials. into the portal beam void. To allow installation of a densely In situ concreting required complex reinforcement fixing and reinforced 1 m deep concrete anchorage block to the ceiling of a highly workable, self-compacting, low-shrinkage concrete. the switch room (Figure 8), C Spencer installed new transformers Extensive trials were undertaken to prove the pouring method into in a temporary location on the bridge footways. This allowed the tight, enclosed spaces of the deck box and switch room. the old transformers to be removed from the working area: an excellent example of the ‘avoid, reduce, control’ hierarchy of risk mitigation. There was inadequate space in the closed lane 1 for a mobile crane to extend its outriggers fully. To transfer the steelwork down between main span and side span deck boxes through the hinged temporary expansion joint, the contractor used a 175 t/m Hiab loader crane, modified with a bespoke ballast box on the rear to carry and install the steel (Figure 5). Off-site trials using test weights proved the machine could safely operate on reduced outriggers. Pendels were manufactured in two halves with a bolted splice in the middle to aid installation and future bearing replacement. Accurate survey discipline throughout the drilling and installation works ensured that when the upper pendel connection was installed above the pendel base, the two pendel halves aligned well within tolerance (Figure 9). Post-tensioned steel bars in the base and upper connection were each prestressed with 1400 kN prior to load transfer from the temporary to permanent pendels. Load transfer was again Figure 6. Oxyacetylene flame cutting at night following load transfer carried out in calm weather on successive nights with the bridge from the A-frame (foreground) to the temporary pendel (background) remaining open to traffic throughout. The bolted splice was installed, followed by immediate lowering of the temporary

Figure 7. Gap left by removal of a main span A-frame, restraint being Figure 8. Portal beam void’s switchroom, showing new in situ provided by the temporary pendel (behind) with strain gauges monitored. anchorage for the holding-down frame’s post-tensioned bars on the An A-frame left unaffected by the works can be seen on the right ceiling and new transformer in the background

118 Civil Engineering A-frame rocker bearing replacement at Humber Bridge, UK Volume 169 Issue CE3 Collins and Smith

Figure 9. The lift of the upper pendel connection (left) and achieving perfect alignment of top and bottom parts of the pendel (right)

Figure 10. Views from the three-dimensional computational model of lifts (left) and photographs of the lifts (right), showing temporary pendels, dropping the bridge onto the permanent pendels. This pendel deck plate (top) and permanent pendel base (bottom) time the jacking operation had the benefit of strain gauges providing data for both the temporary and permanent pendels to determine when all of the load had been transferred. The strain gauges continue to monitor loads on the pendel, providing Brown, 2015). From the unsuccessful specification of this grade useful data to the bridge owner during unusual wind or traffic in the works, caution would be advised over its use in bridgeworks events. with their often demanding fracture toughness requirements coupled with the heightened risk of hydrogen embrittlement (Dainelli and Maltrud, 2012). 5. Use of three-dimensional modelling Difficult access prevented a pre-works survey of the deck box to which new plates were to be bolted. The existing deck box Design was aided by, and contract drawings created from, a was found to be significantly non-flat: in fact it did not meet the three-dimensional computational model. This model was passed to tolerances specified in the 1970s fabrication drawings. This led to the contractor and greatly aided site planning including complex protracted discussions and analysis to understand whether bolts lifts (Figure 10), explaining works to the client and operatives in would safely draw plates together and use of a chocking resin task briefings. around post-tensioned bars. With hindsight, the cost of creating access for a pre-works survey would have been less than the actual costs ultimately incurred. 6. Discussion 6.2 Project successes 6.1 Learning points The project was full of unique challenges and their successful With increasing awareness of high-strength steels, especially solutions. Of particular note are the following. due to its inclusion in Eurocode standards, there is likely to be increased specification of grades such as S690 (Baddoo and ■■ The client understood the complexities of their bridge and allowed adequate time to investigate and understand bridge behaviour, develop options and design. ■■ Inclusion of third party knowledge by early engagement with The existing deck box was an excellent independent checker who was present when found to be significantly crucial detailed design decisions were made. ■■ Continuation of design staff to site roles with rapid response to non‑flat, eventually leading to site queries. ■■ Meticulous planning of site works, aided and communicated use of a chocking resin. With by the same building information model used by the hindsight, the cost of creating designer. ■■ Low impact on the public: the bridge remained open throughout access for a pre-works survey the works. would have been less than the ■■ Experienced and innovative contractor’s design team leading to versatile, well-detailed temporary works such as the temporary actual costs ultimately incurred pendel and temporary expansion joint.

119 Civil Engineering A-frame rocker bearing replacement at Humber Bridge, UK Volume 169 Issue CE3 Collins and Smith

■■ Highly skilled and disciplined site operatives, able to undertake The complex structural works a wide variety of complex tasks accurately to the required quality. exhibit the difficulties and ■■ Use of a predominantly Yorkshire-based supply chain, demonstrating the wide ranging ability of local resources on a novel solutions required when project of high complexity. working with existing bridges

The unique challenges addressed by this project have been 7. Conclusion recognised by industry through award of the Institution of Engineering and Technology’s Sir Henry Royce Award for Young The finished arrangement of pendel (Figure 11) and wind shoe to Professionals 2012 to the Arup author; the Institution of Civil the Humber Bridge’s main span play a critical part in the continuing Engineers’ Yorkshire & Humber Smeaton Award 2015; and safe operation of the bridge. shortlisting for the British Construction Industry Civil Engineering The works undertaken were the most complex structural works Project of the Year (up to £10 million) Award 2015. undertaken on the bridge to date. They exhibit the difficulties and novel solutions required when working with existing bridges. Close work between designer and contractor, with meticulous planning Acknowledgements and care while implanting on site, resulted in works befitting one of the UK’s most spectacular structures. The authors are grateful for the support of Humber Bridge Board in writing this paper. The independent checker for the design was AECOM. Eadon Consulting Ltd provided design services leading to the bearing specifications. The steel fabricator was Allerton Steel Ltd and electrical works were by Pennine Control Systems.

References

Baddoo N and Brown D (2015) High strength steel. New Steel Construction 23(8): 24–26. Brownjohn J, Koo KY, Scullion A and List D (2012) Operational deformations in long span bridges. In Bridge Maintenance, Safety, Management, Resilience and Sustainability: Proceedings of the Sixth International IABMAS Conference, Stresa, Lake Maggiore, Italy, 8-12 July 2012 (Biondini F and Frangopol DM (eds)). CRC Press, Boca Raton, FL, USA, pp. 20–26. BSI (2005) BS 4449:2005: Steel for the reinforcement of concrete. Weldable reinforcing steel. Bar, coil and decoiled product. Specification. BSI, London, UK. BSI (2007) BS EN 14399-8:2007: High-strength structural bolting assemblies for preloading. System HV. Hexagon fit bolt and nut assemblies. BSI, London, UK. BSI (2008) NA to BS EN 1991-2: 2003. UK National Annex to Eurocode 1: Actions on structures – Part 2: Traffic loads on bridges. BSI, London, UK. BSI (2009a) BS EN 10025-6: 2004+A1: 2009. Hot rolled products of structural steels. Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition. BSI, London, UK. BSI (2009b) BS EN 10225: 2009. Weldable steels for fixed offshore structures. Technical delivery conditions. BSI, London, UK. BSI (2013) BS EN 206:2013: Concrete. Specification, performance, production and conformity. BSI, London, UK. Collins J, Hornby SR, Hill P and Cooper J (2013) Humber Bridge A-frame rocker bearings replacement. IABSE Symposium Report 99(1): 2037–2044. Dainelli P and Maltrud F (2012) Management of welding operations with high strength steels. Soudage et Techniques Connexes 66(7–8): 37–42. Hornby SR, Collins J, Hill P and Cooper J (2012) Humber Bridge A-frame refurbishment/replacement. In Bridge Maintenance, Safety, Management, Figure 11. One of the four completed pendels, attached to a new Resilience and Sustainability: Proceedings of the Sixth International IABMAS Conference, Stresa, Lake Maggiore, Italy, 8-12 July 2012 bracket at the top, holding-down frame post-tensioned to the portal (Biondini F and Frangopol DM (eds)). CRC Press, Boca Raton, FL, USA, pp. beam at the bottom. A bolted strengthening plate can be seen top left 3170–3177.

120 Civil Engineering Proceedings of the Institution of Civil Engineers Volume 169 Issue CE3 Civil Engineering 169 August 2016 Issue CE3 Pages 121–128 http://dx.doi.org/10.1680/jcien.15.00063 Evolution of modern mega-buildings in Paper 1500063 China: innovations and sustainability Received 19/11/2015 Accepted 16/02/2016 Published online 22/04/2016 Wang Keywords: composite structures/concrete structures/ design methods & aids

Evolution of modern mega- buildings in China: innovations and sustainability Aaron J. Wang PhD, CEng, CPEng, FICE, FIStructE, FCIOB, MRICS, MIEAust Director, CapitaLand Management (China) Co., Ltd., Shanghai, China

China’s construction boom over the past few decades has led to growing demand for high-rise and ‘mega- scale’ buildings. Such structures feature sophisticated building services, unique elevations, seamless connection to infrastructure and high safety levels. Design and construction challenges include hazard mitigation against extreme actions and environments, integrated structural frameworks and facades, complex connections and overall constructional efficiency. Civil and structural engineers add value, enhance engineering efficiency and achieve overall environmental and cost-effectiveness for modern mega- buildings in China. This paper introduces the design and construction of four of such projects. It reviews the evolution of modern mega-buildings, including aspects of integrated engineering design, construction technology, value engineering and overall sustainability.

1. Introduction ■■ Raffles City Chengdu – this mixed development consists of five 110 m bespoke high-rise towers including offices, hotels, With the booming construction industry in China, the demand serviced apartments and a four-storey shopping mall plus a for high-rise and ‘mega-scale’ buildings has increased over the past four-storey basement car park. The project is complete and has few decades. The main features of such mega-buildings include: been open to the public since 2012 (Wang and Hong, 2015). being big in scale with more integrated building functions and ■■ International Trade Centre, Tianjin – this is a brownfield a more significant carbon dioxide footprint; open and tailored development based on an unfinished building of 18-storey steel building elevations with a better incorporation into the community; frame works and half-completed basement works. The new seamless linkage to municipal infrastructures; and higher levels of design includes a total of one 250 m tall steel hotel tower, two building safety provision and hazard mitigation. 180 m tall composite office wers,to a five-storey commercial The design and construction of such modern mega-buildings podium and three-storey basement. The re-development need to conquer engineering challenges in hazard mitigation against includes the re-use of a large portion of the existing structural extreme actions and environment, integrated structural frameworks frameworks and the associated strengthening works. and facades, complex connection and overall constructional efficiency. Civil and structural engineers add value, enhance overall Looking at the engineering design, construction and management engineering efficiency and achieve overall environmental and cost- on these four projects, the evolution of modern mega-buildings effectiveness for modern mega-buildings in China. is considered. This covers the aspects of integrated engineering This paper introduces the design and construction of four such design, construction technology, value engineering and overall mega-developments situated in different major cities of China, as sustainability. follows.

■■ Raffles City Hangzhou – the project is located in the central 2. Value through engineering business district of Hangzhou, China, and consists of two 60-storey 250 m tall super-high-rise twisting towers, a Value engineering is a systematic method to improve the ‘value’ commercial podium and three-storey basement car park. of goods or products and services by using an examination of The overall construction floor area of the project is 390 000 m2. function. Value, as defined, is the ratio of function to cost. Value ■■ Raffles City Chongqing – designed by architect Moshe Safdie, can therefore be increased by either improving the function this top-end mixed development project includes a total of or reducing the cost (Cooper and Slagmulder, 1997). Value six mega-high-rise towers, ranging in height from 250 m to engineering in a building project does not simply mean a cost 370 m and including offices, hotels, residential and serviced reduction, but also an enhancement in building performance and apartments, a sky conservatory, a four-storey shopping mall construction productivity from a whole-life cycle point of view. and a four-storey basement car park. The overall completed Structural engineers create value through rigorous engineering floor area of the project is over 1 million 2m . approaches.

121 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

In Raffles City Hangzhou, a composite moment frame plus Table 2. Thus, option 3 was selected to be the outer moment frame concrete core structural system was adopted for the 250 m tall of the tower structures, with a relatively low cost, controllable tower structures. A total of three outer frame forms were studied as constructability and reasonable building functions. follows Figure 1(a) shows the structural frameworks of the tower structures. Figure 2 shows the site construction of the main ■■ option 1: steel floor beams together with concrete-filled steel structure. The main structure of the project was completed in late tubular columns 2014. It was demonstrated that a 5 d cycle was achievable in typical ■■ option 2: concrete floor beams together with steel-reinforced floors with the adopted structural form. concrete columns ■■ option 3: steel-reinforced concrete beams together with concrete-filled steel tubular columns. 3. Joints – the frontier to conquer

Cost comparison and work breakdown analyses were conducted The detailing of joints is always a frontier to conquer during the for a typical tower floor; the results are shown in Tables 1 and 2, design of modern high-rise composite buildings. The rigidity and respectively. It was concluded that option 3 – steel-reinforced ductility requirements of composite joints are covered in various concrete floors beams together with concrete-filled steel tubular prevailing design codes (AISC, 2005; Brockenbrough and Merritt, columns – and the reinforced-concrete-dominant option 2 2006; BSI, 2005; MHURD, 2010, 2011; SCI and BCSA, 2002). shared similar low construction costs. On other hand, the overall construction cycle of option 3 was much lower as a result of breaking through the critical path of column construction with Option 1: steel floor Option 2: reinforced Option 3: steel- permanent formworks of steel tubular columns. The construction beams plus concrete- concrete floor beams reinforced concrete filled steel tubular plus steel-reinforced floor beams plus cycle per typical floor was estimated to be 5 d, as shown in columns concrete columns concrete-filled steel tubular columns Work Days Work Days Work Days Item Option 1: Option 2: Option 3: steel- breakdown breakdown breakdown steel floor reinforced reinforced beams plus concrete floor concrete floor Erection of steel 0·5 Circular column 1 Erection of steel 0·5 concrete-filled beams plus beams plus tubular columns formwork tubular columns steel tubular steel-reinforced concrete-filled Erection of edge 0·5 Column 1 Erection of edge 0·5 columns concrete steel tubular beams reinforcement beams columns columns Erection of floor 1·5 Erection of edge 0·5 Erection of floor 1·5 Concrete: m3/m2 0·54 0·97 0·97 steel beams beams steel beams Reinforcement 110 117 102 Reinforcement 1·5 Erection of floor 1·5 Reinforcement 1·5 tonnage: kg/m2 in slab and walls steel beams in slabs and Steel tonnage: kg/m2 118 62 68 walls Formwork: m2/m2 0·97 2·1 2·1 Concrete 1·0 Reinforcement in 1·5 Concrete 1·0 pouring slabs and walls pouring Profiled steel 0·82 – – decking: m2/m2 Concrete 1·0 pouring Overall cost ratio 149% 100% 105% (option 2 = 100%) Total 5·0 Total 6·5 Total 5·0

Table 1. Cost comparison of structural options at Raffles City Table 2. Time comparison of options for typical floor construction at Hangzhou Raffles City Hangzhou

(a) (b) (c)

+ + =

Concrete Composite Concrete core moment frame beams & slabs

Figure 1. Raffles City Hangzhou: (a) tower structural system; (b) views of composite moment frame; (c) completed tower

122 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

■■ Lapped reinforcement bars: all the longitudinal reinforcements were lapped around the flanges of the steel corbel, so that both the loads and stress could be transferred from the longitudinal main reinforcements onto the corbel in the connection region.

Physical tests under both static and cyclic loads were conducted to investigate the load-carrying capacities and deformation characteristics of this new type of composite connection according to both ASTM (2011) and CABR (1997) specifications. Figure 3(a) shows the overall set-up of the tests. Various structural responses were examined in detail, including load–deformation characteristics, the development of sectional direct and shear strains and the history of cumulative plastic deformation and energy. A three-dimensional (3D) finite-element (FE) model built up with solid elements was also proposed and carefully calibrated incorporating the material, Figure 2. Construction of Raffles City Hangzhou twin towers boundary and geometrical non‑linearities, as shown in Figure 3(b). Figures 4(a) and 4(b) present the results of the monotonic In Raffles City Hangzhou, the structural design of the composite tests on specimens SP1 and SP2. A close observation on the connection between concrete-filled steel tubular columns and steel- strain development also shows that the direct tensile strain at the reinforced concrete beams needed to safeguard the overall structural top flange is 30–50% higher than the compressive strain of the stability through fully rigid connections as well as maximise bottom flanges due to the contribution of the concrete material. internal space. The conventional ring-beam-type composite It is noted that the shear strain in the web is significantly smaller connection was considered to be bulky and not suitable because than the strain in the flange, which is just above the yield strain. of its inference with facade erection and interior decoration. This is preferred for a high-rise building in a seismic-sensitive An innovative and high-performance corbel-type composite region like Hangzhou, where the project is located (Lou and Wang, connection was proposed to achieve a fully rigid connection with 2015). The quasi-static cyclic loading tests were conducted on both a minimum intrusion into the interior space (Lou and Wang, 2015; specimens SP3 and SP4. Figures 4(c) and 4(d) present the load– Wang, 2015). The proposed corbel-type composite joints include deflection and moment–rotation curves of specimens SP3 and the following key components, as shown in Figure 3. SP4. The cumulative plastic deformations of both specimens SP3 and SP4 are 0·3 and 0·24 rad respectively, which correspond to 88 ■■ The corbel and ring stiffener was butt-welded to the concrete-filled and 80 times the first yield rotation of the composite connections. steel tubular column: to ensure a full-strength rigid connection, the This, again, demonstrates the high ductility and energy-absorbing I-section corbel was enlarged and stiffened together with a ring capacities of the corbel-type composite connections. stiffener welded inside the steel tube, so that the overall rigidity To study the structural behaviour of the corbel-type composite and load-carrying capacity of the connection is not less than that connection, a generalised non-linear 3D FE model was set up using of a typical steel-reinforced concrete beam section. the commercial FE package Ansys 12.1 (Ansys, 2011). The meshes ■■ The tapered section from the corbel to the steel beam: to ensure of the FE model are shown in Figure 3(b). To simplify the problem a smooth loading and stress transfer from the corbel in the joint and save computational time, only half of the specimen was modelled. region to the ordinary steel-reinforced concrete beam, a tapered The FE simulation gave a quite close prediction of the load– steel section was proposed with a slope of 1:6. deformation characteristics in the connection regions, which was ■■ The steel section in the steel-reinforced concrete beam: the demonstrated through the comparison of the load–deformation curves ordinary I-steel section in the composite steel-reinforced at the end of the connection corbel (Lou and Wang, 2015; Wang, concrete beam was fully connected to the outer edge of the 2015). Both the experimental and numerical studies demonstrated corbel through full bolted joints on both flanges and webs. the high rigidity, strength and rotation capacities of the corbel-type

(a) (b)

Figure 3. Connection test and numerical simulation: (a) test set-up; (b) finite-element models

123 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

(a) (b) 350 350 300 300 : kN : kN 250 250 200 200 150 150 100 End of the cantilever (inclimometer 6) 100 End of the cantilever (inclimometer 6) Applied load, P End of the corbel (inclimometer 3) Applied load, P End of the corbel (inclimometer 3) 50 50 End of the tapered section (inclimometer 4) End of the tapered section (inclimometer 4) 0 0 0 25 50 75 100 125 150 0 25 50 75 100 125 150 Deflection: mm Deflection: mm (c) (d) 400 400

300 300

200 200 : kN : kN 100 100

0 0 –150 –100 –50 50 100 150 –150 –100 –50 50 100 150 –100 –100

Applied load, P –200 Applied load, P –200

–300 –300

–400 –400

Deflection, Δb: mm Deflection, Δb: mm

Figure 4. Load–deflection curves: (a) specimen SP1; (b) specimen SP2; (c) specimen SP3; (d) specimen SP4 composite connections, and gave detailed structural understanding for pendulum bearings are adopted between the decking structures and engineering design and practice. As such, the corbel-type composite supporting tower structures. A friction coefficient of 5% was chosen joint was verified to be of high strength, rigidity and ductility and after detailed consultation with the bearing suppliers. The bearings suitable for high-rise buildings in seismic regions. work with viscous dampers and disperse the seismic energy on the occurrence of various levels of earthquake and relative movement between the tower and the conservatory. The overall engineering 4. Engineering against the extreme design also uses the mass of the conservatory to disperse the seismic energy and control the lateral deflection of the tower structures – as The design and construction of high-rise buildings in China such, a ‘mass damping’ mechanism is facilitated. require a rigorous consideration of earthquake and wind actions. Figure 5(b) shows the overall effectiveness of a mass-damping In current national seismic design codes (MHURD, 2010, 2011), effect on the base shear onto towers at various levels of earthquake. performance-based design approaches are introduced, which Generally, 35–40% of the base shear is reduced due to this innovative require a structurally complex building to meet the corresponding configuration between the conservatory and tower structures, which stringent requirements under minor, moderate and major leads to significant saving in building materials in columns and core earthquakes with 50-year exceedence rates of 63%, 10% and 2–3% walls. The steel-reinforced concrete structural moment frame together respectively. ‘Dual system’ requirements also need to be met for with the core wall system was adopted for all of the 250 m towers in tall buildings in many circumstances. Wind is another concern Raffles City Chongqing. The structural design of the project tackled for many Chinese coastal cities, where typhoons are normally an multiple structural irregularities in an intensity 6·5 seismic zone. issue. The structural engineer normally faces the double challenges Shaking table tests were conducted on the linked towers to verify of extreme loads from both wind and earthquakes, and needs to the effectiveness of mass damping and the structural adequacy of the achieve both overall structural and spatial efficiency. Energy- buildings under moderate to extreme earthquakes. Figure 6(a) shows dispersing devices, like dampers and isolating bearings, are the test set-up under various levels of earthquake, while Figure 6(b) becoming more commonly used in high-rise buildings to enhance shows the bearing details adopted in a 1:25 scale physical model. the overall structural performance under disastrous loads. An innovative type of steel–concrete hybrid outrigger truss was The engineering design of the sky conservatory in Raffles City also developed in two 370 m tall mega-high-rise towers in Raffles Chongqing allows for semi-continuous connection between the City Chongqing (Wang, 2015), in which the steel truss is embedded conservatory decking structures and four of the tower structures into the reinforced concrete outrigger wall as shown in Figures below. Figure 5(a) shows the overall structural configuration. Friction 7(a) and 7(b). Both the steel truss and concrete outrigger wall work

124 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

(a) (b) 600 Level 3 500 Level 2 Secondary truss 400 Level 1 Capacity Main truss of top of wall 300

200 Base shear: MN 100 Wind 0 shear

Bearings damping damping with damper Option 1 – fixed Option 2 – fixed Option 3A – FPB 5% Option 4A – FPB 5% Option 3B – FPB 15% Option 4B – FPB 15%

Figure 5. Raffles City Chongqing sky conservatory mass damping arrangement (a); effect on base shear (b) (FPB, friction pendulum bearing)

(a) (b)

Figure 6. Shaking table tests on linked towers at Raffles City Chongqing compositely to enhance the overall structural performance of the (a) (b) (c) tower structures under extreme loads. Meanwhile, low-yield steel dampers were also adopted as a ‘fuse’ device between the hybrid outrigger and the mega-column. The dampers were designed to yield first under moderate to severe earthquakes to protect the structural integrity of important structural components of the hybrid outrigger. As such, no brittle failure occurs in the reinforced concrete portion of the hybrid outrigger system. Figure 7(c) shows the numerical simulation of the hybrid outrigger system under earthquake loading. The design allowed the contractor to break through the critical path of the time-consuming welding on the steel outrigger trusses Figure 7. Hybrid outrigger system: (a) hybrid outrigger; (b) reinforced in the floors, and ‘shoot’ the core first by leaving the construction concrete outrigger wall; (c) numerical simulation under earthquake joints between the core and the outrigger walls. This helps to shorten the overall construction period of the tower. As per verification actions. The hybrid outrigger system exhibits sufficient ductility tests, low-yield steel dampers work effectively under level 2 and 3 under seismic actions under the effective protection of the fuse earthquakes and enhance overall structural performance. Both FE device of low-yield-steel dampers. Figure 8(b) shows the results of modelling and physical component tests were conducted to verify the 3D FE simulation. This demonstrated sufficient ductility at the the effectiveness of the hybrid outrigger system. Figure 8(a) shows fuse device while cracks in the concrete outrigger wall were well the overall test set-up and load–deflection curves under cyclic controlled, even under the action of a severe earthquake.

125 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

(a) 800 600

400

: kN 200

–200

Applied load, P –400

–600

–800 –8 –6 –4 –2 0 2 4 6 8 Deflection: mm (b)

Figure 8. Study on hybrid outrigger: (a) physical tests test set-up and load–deflection curves; (b) finite‑element modelling

5. Integrated building facade and digitalised between reinforcement and steel sections. Both construction design mock-ups and a 3D computer tool were adopted to assess buildability, allowing for reasonable construction tolerances and working space. Stiffener and gusset plates were adopted to transfer Modern computerised design tools allow the designer to break the loading from the reinforcement into the joint region without through the barrier of conventional modular design and work on sacrificing structural continuity and rigidity. Figure 10 shows the a 3D platform. Nowadays, more free-form tailor-made building construction mock-up and computer visualisation model. facades can be achieved in a more creative way. Structural engineers Building information modelling (BIM) was adopted in both are now equipped with 3D design technology such that they can Raffles City Chongqing and Raffles City Hangzhou to sort out produce structural frameworks suited to the building facade. the complex building shapes and possible conflict at particularly As shown in Figure 1(b) for Raffles City Hangzhou, structural complex locations such as the basement, plant floors, cores and members are tailored to support the facade outer skin, and form the conservatory. A BIM protocol was set up among the various modern appearance of the building. Both the structural engineer design parties and contractor to streamline management and main contractor worked collaboratively on a 3D platform to procedures, and a BIM manager was employed to administer the establish the setting-out information on site. daily model operation and design coordination. The civil and Raffles City Chengdu used high-strength light-colour in situ structural BIM model was issued to the tenderers as part of the concrete in its outer frame, which forms part of the facade system tender documents to assess the possible major dynamic conflicts together with the window wall as shown in Figure 9 (Wang and in the complex site logistics, like installation of major steel Hong, 2015). The unit cost for the concrete was higher than works and facade panels. ordinary concrete, yet the integrated design greatly reduced the glass coverage areas. As such, overall cost-effectiveness was achieved for the facade system. Several trial mixes were conducted in the tendering and construction stages to ensure the finish and 6. Overall sustainability and brownfield projects concrete colour met the architectural design intent, and the mechanical properties met the engineering design requirements. All the previously discussed aspects and technologies facilitate In addition, durability tests such as chloride penetration tests and a more efficient and better-integrated engineering design and concrete curing tests were also performed to ensure an alkaline- construction. This will contribute positively to the overall dominant concrete mixture with acceptable crack width. sustainability of the building construction and development through The project also faced another challenge of composite joints the reduced usage of building materials and less tedious effort and in the steel-reinforced concrete columns, beams and diagonal energy consumption in site implementation. As such, the overall members, leading to special complexity and possible conflicts carbon dioxide footprint throughout the building development can

126 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

Maximising possible reuse of existing structural frameworks is always a priority in a brownfield development. This not only leads to more cost-effective design, but is also an energy-efficient engineering solution. Necessary alteration and strengthening works need to be conducted to fit the newly defined building functions and general layout plans. For steel frameworks, de‑rusting, corrosion treatment and fire-proofing need to be redone. The International Trade Centre, as shown in Figure 12, is an example of a brownfield development that CapitaLand undertook in the downtown area of Tianjin. The engineering and construction of the project is being carried out on an unfinished steel skeleton with half-finished basement concrete works. Rigorous de-rusting work was conducted with visual mock-ups regarding finished surfaces. The strengthening works involved both enlarged member sizes on existing steel beams and columns and concrete works in the basement. Both metal and viscous dampers were designed and installed to ensure the overall structural stability and integrity under wind and seismic actions. Figure 9. Raffles City Chengdu be reduced accordingly. Some of the key issues that need to be 7. Conclusions considered through the engineering of mega-projects include This paper introduces the design and construction of four mega- ■■ controlled building footprint and aspect ratio building projects in China. Looking at the evolution of engineering ■■ proper composition of concrete, reinforcement and steel design, construction and management on these projects, the materials to achieve optimal embodied carbon dioxide emissions following conclusions are reached. ■■ possible use of seismic- and wind-energy-dispersing devices to Value engineering in a building project does not only mean a prevent over-sized structural members and enhance the overall cost reduction, but an enhancement in building performance and engineering efficiency construction productivity from a whole-life point of view as well. ■■ consideration of carbon dioxide footprint from material supply Structural engineers can create value through rigorous engineering and transportation, especially for some precast concrete and approaches. structural steel components Structural engineers need to face the double challenges of ■■ reuse of existing buildings and structural framework through resisting extreme loads from both wind and earthquakes, and brownfield development. ensure the overall structural and spatial efficiency at the same time. Energy-dispersing devices, like dampers and isolating bearings, are Figure 11 shows a computer program developed to carry out becoming more commonly used in high-rise buildings to enhance structural design optimisation towards the most cost- and energy- the overall structural performance under high environmental loading. efficient structural layouts on typical residential blocks. Multiple Detailing of joints is always a frontier to conquer during the design constraints on structural member sizes and reinforcement ratios can of modern high-rise composite buildings. The rigidity and ductility be assigned as input conditions, and the computer program, linked requirements of composite joints need to be met. Three-dimensional with commercial structural analysis software, can interact and reach computer tools, verification tests and construction mock-ups should a structural layout dually optimised for cost and energy effectiveness. be used for some especially complex composite joints.

(a) (b) (c)

Figure 10. Raffles City Chengdu composite facade joints: (a) under construction; (b) construction mock-up; (c) screenshot of computer model

127 Civil Engineering Evolution of modern mega-buildings in Volume 169 Issue CE3 China: innovations and sustainability Wang

Nowadays, free-form bespoke building facades can be achieved of building materials and less effort and energy consumption. in a more creative way through digitalised working platforms. As such, the overall carbon dioxide footprint throughout a building Structural engineers need to equip themselves with 3D design development can be reduced accordingly. technology, and produce structural frameworks compatible or integrated with building facades. All the above-introduced aspects of evolution facilitate a more References efficient and better-integrated engineering design and construction. AISC (American Institute of Steel Construction) (2005) ANSI/AISC 360-05: This contributes positively to the overall sustainability of the Specification for structural steel buildings. AISC, Chicago, IL, USA. building construction and development through reduced use Ansys (2011) User’s Manual Version 12.1. Ansys Inc., Canonsburg, PA, USA. ASTM (2011) E2126-11: Standard test methods for cyclic (reversed) load test for shear resistance of vertical elements of the lateral force resisting systems for buildings. ASTM International, West Conshohocken, PA, USA. Brockenbrough RL and Merritt FS (2006) Structural Steel Designer’s Handbook. American Institute of Steel Construction, Chicago, IL, USA. BSI (2005) BS EN 1993-1-8:2005: Eurocode 3: Design of steel structures, Part 1.8: Design of joints. BSI, London, UK. CABR (China Academy of Building Research) (1997) JGJ101-1996: Specification of test methods for earthquake resistant building. CABR, Beijing, China. Embodied carbon Cooper R and Slagmulder R (1997) Target Costing and Value Engineering. Productivity Press, Portland, OR, USA. Lou GB and Wang AJ (2015) Studies into a high performance composite 987654321 121110 151413 181716 connection for high-rise buildings. Steel and Composite Structures 19(4): Cycle number 789–809. MHURD (The Ministry of Housing and Urban–Rural Development) (2010) GB50011-2010: Code for seismic design of buildings. The Ministry of Housing and Urban–Rural Development, Beijing, China. MHURD (2011) JGJ3-2010: Technical specification for concrete structures of tall buildings. The Ministry of Housing and Urban–Rural Development, Beijing, China. Cost SCI and BCSA (The Steel Construction Institute and the British Constructional Steelwork Association Limited) (2002) Joints in Steel Construction. The Steel Construction Institute, Ascot, UK. Wang AJ (2015) Re-engineering composite connections for a higher construction and cost effectiveness. In Proceedings of the 11th 987654321 121110 151413 181716 International Conference on Advances in Steel and Concrete Composite Cycle number Structures, Tsinghua University, Beijing, China (Han LH, Li W and Lam D (eds)). Tsinghua University Press, Beijing, China, pp. 538–543. Wang AJ and Hong Y (2015) Raffles City Chengdu, China: achieving a sunlight- Figure 11. Examples of numerical optimisation of embodied carbon influenced design. Proceedings of the Institution of Civil Engineers – Civil dioxide and construction cost Engineering 168(2): 81–88, http://dx.doi.org/10.1680/cien.14.00062.

(a) (b) (c) (d)

Figure 12. International Trade Centre, Tianjin: (a) before de-rusting; (b) after de-rusting; (c) protection to surroundings; (d) project graphic

128 Civil Engineering Proceedings of the Institution of Civil Engineers Volume 169 Issue CE3 Civil Engineering 169 August 2016 Issue CE3 Pages 129–135 http://dx.doi.org/10.1680/jcien.15.00081 Launching of Leigh Road Paper 1500081 Bridge, Slough, UK Received 25/11/2015 Accepted 11/01/2016 Published online 03/03/2016 O’Connor, Attrill, Gibb and Oh Keywords: bridges/steel structures/temporary works

Launching of Leigh Road Bridge, Slough, UK

1 Mike O’Connor BEng, MSc, CEng, MICE 3 Iain Gibb BSc, CEng, FICE Technical Manager, Osborne, St Albans, UK Design Team Leader, Peter Brett Associates LLP, Reading, UK 2 Malcolm Attrill BSc, MSc, CEng, FICE 4 Soon Hee Oh BEng (Hons), MSc Engineering Manager, Osborne, Reigate, UK Engineer, Peter Brett Associates LLP, Reading, UK

1 2 3 4

Leigh Road Bridge, a road-over-rail bridge crossing the Great Western route in Slough, UK, is believed to be only the second bridge in the country to have been launched across a railway using trailers. It is also one of the largest structures constructed by this method anywhere in the world. During the sliding stage of the launch a significant unforeseen incident occurred when the launch structure nose suddenly slid laterally, damaging some of the key temporary works. The project team worked collaboratively to restore the position and complete the launch without disruption to rail traffic and open the scheme to road traffic on time. Both the methodology and the successful realignment operation led to important conclusions and learning points for future launches of this type.

1. Design of permanent works and launch design development gained the client’s acceptance. To satisfy the structure alignment profile and associated highway network tie-ins a vertical curve profile was required for the permanent span. Multiple railway Slough Trading Estate, UK, is Europe’s largest trading estate possessions could not be accommodated for the construction phase in single ownership. At present the owner, Segro plc, has a due to coincident Crossrail works (the east–west rail link being redevelopment programme running. The estate is bisected by the constructed across London) planned through the site. Therefore, four east–west tracks of the Great Western route of Network Rail the delivery team worked to devise a detailed method for a (owner and maintainer of Britain’s heavy rail network). The railway launched structure and began the necessary initial consultations is crossed by an existing 1836 Brunel brickwork twin-arch with the various parties, particularly Network Rail. bridge owned by Network Rail at Leigh Road, which provides a As early as 2004 the contractor had been involved in developing sub-standard, narrow, signal-controlled single-way crossing for the concept of a trailer-based launch of a proposed bridge near traffic with no segregated provision for pedestrians and cyclists. Hemel Hempstead, UK, which did not happen at the time, but The vision to improve this situation required the owner to promote is now being progressed. This concept was incorporated into the a scheme to provide a safer and more accessible route through the methodology described in a paper by Marples and Richings (2014), central core of the estate by way of a new adjacent overbridge which which proposed best practice following an overline bridge launch would be adopted by Slough Borough Council, which also acted as at the A406 North Circular Road in 2010. the technical approval authority under BD2/12 (HA, 2012). The available site for the scheme required demolition in advance Design concept considerations were influenced not only by of provision for a large site compound (Figure 1). To minimise rail the tight vertical highway alignment constraints, but also the interfaces the supports for the permanent bridge were positioned construction methodology. Peter Brett Associates and Osborne, outside the Network Rail boundary, resulting in edge girders the owner’s appointed design consultant and civil engineering 52·95 m long and having a 51 m span at a 15° skew (Figure 2). contractor, respectively, formed a design-and-build team under Weathering steel was chosen to avoid costly future maintenance the NEC3 Engineering and Construction Contract option A form painting over the railway. To accommodate the prescribed carriageway, of contract. Initially three superstructure forms were considered: a cycleways and footways the edge girder webs were positioned 15·3 m crane-lifted lattice arch; deck beams involving multiple lifts; and a apart. This girder spacing, span, road vertical curve profile and launched through-girder deck. precamber for the dead load deflections resulted in variable-depth Further considerations showed the third option to have the lowest edge girders with a maximum height of 3800 mm enabling their webs operational rail disruption impact and cost estimate. The resulting to be sourced from standard weathering steel plate depth.

129 Civil Engineering Launching of Leigh Road Bridge, Slough, UK Volume 169 Issue CE3 O’Connor, Attrill, Gibb and Oh

(a) 51 000 mm skew

Great Western main line

Buildings demolished to enable new road (b) construction 2000 mm 1500 mm 7000 mm 1500 mm 2000 mm Proposed bridge location adjacent to the existing bridge min.

Extent of works 1:401800 mm

1:40 130 mm 325 mm 1:40 1:40 Site compound and bridge assembly area A4 Bath Road

Figure 2. Bridge elevation (a) and section (b)

(a)

Figure 1. Aerial view of site in the centre of the Slough Trading Estate 878 mm 1300 mm The deck of the permanent bridge was steel/concrete composite construction with a 250 mm concrete slab (Figure 2). It was formed on permanent steel plate between deck cross-girders, which provided

a closed construction platform over the railway once launched. 8230 mm 17 485 mm 56 758 mm To launch the structure, the contractor had engaged specialist 14 000 mm expertise for moving large and heavy loads using self-propelled (b) modular transporters. A 16 m long temporary tail supporting the required 380 t counterweight and a torsionally stiffened 27 m long temporary nose were added to the permanent steelwork. The resulting all-steelwork launch structure had an overall skew length of almost 96 m and weight of 1122 t (including counterweight), which could be assembled in an area 250 m from the final bridge position. 27 000 mm 52 950 mm 16 000 mm Launching required a structure capable of cantilevering 57 m (c) (Figure 3) to enable the transporters to get close to the south abutment and land the nose onto rubber slide bearings on jacks on the north side. Once the leading transporter was removed the launch structure became simply supported with a span of almost 91 m for advancing by sliding. The UK design document recording the basis for scheme detailed design methods and checking (approval in principle) for the permanent highway structure was accepted by Slough Borough Council in early 2013. It was also necessary to satisfy Network Rail standards and, as the method of installation was classified as novel, its common safety method on risk evaluation and assessment Figure 3. Cantilever launch in (a) elevation, (b) plan and (c) isometric (NR/L2/RSE/100/02 (Network Rail, 2012a) and PAN/S&Sd/ CD/INS/0081 (Network Rail, 2014). For certifications both the permanent and launch structures were subject to category 3 the chosen fabricator’s factory set-up. Because of the torsional checking by Tony Gee & Partners. susceptibility of the main bridge structure without its composite The permanent and launch structures were analysed using the deck, the nose of the all-steelwork launch structure was made Midas Civil three-dimensional finite-element package. The nose torsionally robust with lateral and top and bottom longitudinal plan and tail were also formed using plate girder edge members to suit bracing (Figure 3).

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Nevertheless, launch model analysis revealed significant It was vital that the delivery team (contractor/launcher/designer/ deflections during both cantilever and simply supported checker) had a combined understanding of all the mechanisms conditions due to the skew spans and the hydraulic performance affecting the launch methodology. Deformations within the of the transporters. It therefore became important to predict the launch structure and its supports were recognised as critical deflection profile of the structure to assist planning of the launch for the operational integrity to achieve the launch geometry methodology and ensure that the resulting levels of the launch constraints. Consequently, regular launch workshops were held by structure could be adjusted for transportation, landing, transporter the contractor and attended by the launch contractor, the design removal and jack down. consultant and the checker. The layout of the self-propelled modular transporters enabled a stable, statically determinate three-point support system to be 2. Launch preparation and method development devised throughout the launch. The hydraulic linkages within and between the transporters also allowed the complete launch The self-propelled modular transporters offered the most structure with its transporter supports to deform such that no advantageous method to move the launch structure from the unacceptable additional dead-load stresses arose. It was essential assembly yard to the permanent supports. The installation method to model this feature such that these deformations could be had been used in the Hanger Lane project referred to in Section 1.2 confidently evaluated to predict the associated geometrical above (Marples and Richings, 2014). behaviour of the combined mechanism and to enable clearance The outline launch sequence (Figure 4) had been included for the self-propelled modular transporters to be removed. in the approval in principle process to the council and the final scheme was detailed in the subsequent submissions for launch methodology, launch embankment, slide bearing and lateral restraint for the additional certification process with Network Rail. Other aspects of the launch also requiring consideration were the design of the bottom flange of the nose edge girders, which entailed a change of width from 1000 mm to 1500 mm at a point 15 m from the leading edge (Figure 5). This required a ‘hold point’ during the slide to reposition the lateral restraints on the slide bearing jacks. Furthermore, the bolted connection between the horizontal nose section and the precambered main bridge required a bottom flange splice with a bolt-free central zone to enable progress of this joint across the slide bearing jacks to reach the permanent bearing positions (Figure 6).

(a) Bridge Nose Tail Figure 5. Launch nose flange width change North South abutment abutment

(b) Bridge Nose Tail

North South abutment abutment

(d) Lower Bridge Tail

North South Split splice plates abutment abutment to allow launch Slide bearing jack slide through arrangement

Figure 4. Launch sequence: (a) initial launch, (b) slide, (c) nose removal and (d) jack down Figure 6. Slide bearing jack and split splice area allowing slide through

131 Civil Engineering Launching of Leigh Road Bridge, Slough, UK Volume 169 Issue CE3 O’Connor, Attrill, Gibb and Oh

This theoretical geometry was captured and summarised in a 3. The launch series of drawings with tables for the various stages of the launch. During the workshop process it was agreed that the predicted A ‘rules of the route’ possession had been arranged for the deformations associated with both the maximum launch cantilever early hours of Sunday 8 February 2015. Over a 2 h period the and simply supported state analyses should be demonstrated in a initial cantilevering launch structure was slowly moved along trial launch in the assembly yard. Support packing and transporter the predetermined path (Figure 7) on the self-propelled modular stroking (raising or lowering) adjustments had been devised for the transporters (two at leading positions under the permanent main launch and these could also be reviewed. This would serve to verify span edge girders and one combined set beneath the tail and for the team the geometric intricacy of the launch methodology and counterweight) from the assembly yard to where the cantilevered enable the launch contractor’s team to familiarise themselves with nose reached the south abutment. the actual structural behaviour. Once the possession had been handed to the contractor, the In parallel with the workshop process the contractor arranged cantilevered structure was incrementally steered over the railway regular meetings with Network Rail representatives to establish a on the self-propelled modular transporters along the permanent professional relationship to provide confidence and assurance in bridge centreline until the tips of both nose edge girders were the development of the launch methodology. This forum was also directly over the receiving slide bearing jacks on the north used to discuss the contingencies risk assessment schedule and abutment. The jack heights and the self-propelled modular agree the principles for the certification of the launch and other transporter strokes were adjusted until the launch structure could temporary works required under NR/L2/CIV/003 (Network Rail, be simultaneously landed on both jacks – that is, taking account 2012b). of the greater vertical deflection of the western tip of the nose as Mabey Bridge fabricated and then assembled the launch structure induced by the skew. at the site. The two lengths forming each main bridge edge girder Within just over 1 h of the possession the nose was landed and were butt-welded on site; all other main connections (nose, tail, measured as being within 1 mm of the intended absolute touchdown cross girders) were site bolted. The temporary trestle support position, thus allowing the possession to be handed back. The tail positions for the assembly were devised to allow subsequent self- counterweight could then be reduced and the leading self-propelled propelled modular transporter positioning, removal and trial launch modular transporters removed, leaving a simply supported 91 m sequences to be executed. span launch structure sitting over the railway. The route for manoeuvring the 96 m launch structure from the Having removed the leading self-propelled modular assembly area to the initial cantilever touchdown launch position transporters the launch structure could be advanced, steered was carefully planned from the launch workshop meetings and is by the tail transporters over the polytetrafluoroethylene-coated shown in Figure 7. This identified where conflicts would arise with rubber slide bearings on the two jacks to maintain the three-point existing street furniture and services requiring protection. support arrangement. The jacks incorporated lateral restraints The final launch workshop took place shortly before the actual with a 30 mm clearance from the leading nose girder flange.This launch and comprised the full-scale trial and calibration of the major tolerance enabled the bottom flange to be largely unstiffened. launch movement conditions for maximum span, forward slide, ‘hold It was noticed that, unlike during the trial slide, contact was point’ restraint adjustments and for the maximum cantilever. This being made with the western restraint requiring continuous small enabled verification of the methodology for controlling the steering corrections to direction and level to assist guidance while the and restraint of the structure and of the predicted deformations. slide advanced. It also allowed the launch subcontractor to demonstrate the ability satisfactorily to slide the nose splice connection with the main bridge 3.1 Unforeseen slide incident and immediate aftermath over the temporary slide bearings. All aspects of this technical trial During the subsequent restraint repositioning ‘hold point’, the and geometry check proved satisfactory. launch structure suffered a sudden and unforeseen uncontrolled

(a) (b)

Figure 7. Launch route (a) and initial cantilever condition (b)

132 Civil Engineering Launching of Leigh Road Bridge, Slough, UK Volume 169 Issue CE3 O’Connor, Attrill, Gibb and Oh

(a) (b)

Figure 8. Damage at north-west slide bearing plinth (a) and slide bearing jack (b)

300 mm lateral movement to the west on the slide bearing jacks. 3.2 Assessment and realignment The nose immediately slid laterally, resulting in a significant impact Prior to structural assessment, welds around the deformed against the restraints and ejecting one of the rubber slide bearings zones were subjected to magnetic particle examination and the on the western jack. The launch contractor quickly lowered the bolted joints were closely examined to ensure no defects had jacks landing the leading nose area onto the north embankment arisen. Monitoring of longitudinal and vertical movement of the to stabilise the structure. Despite the large forces generated in this structure was initiated immediately and continued throughout the incident, the lateral restraints performed their function and no- recovery process. Observations demonstrated that there was no one was injured. The launch nose and the temporary slide bearing unwanted restraint to thermal movement or any locked-in stresses supports were damaged, but there were no restrictions or delay due to the sudden impact. An emergency plan and protocol was imposed on the railway. prepared, which was to be implemented if any movement trigger Immediately after the incident an initial visual condition levels were breached. inspection was undertaken by the delivery team. It was clear Hydraulic pressure readings from the slider jacks were that the bottom flanges of both east and west nose girders had stable and indicated that they had equal support reaction loads deformed locally at the slide bearing jack positions. The slide of 82·5 t. Although the affected nose girder flanges were still bearing pads were deformed on the jacks and the bolted in tension, it was initially decided to discount any strength connections of the western restraint had been overstressed. provision provided by the deformed flange section, resulting in The jacks were fixed around and in front of the 900 mm high a J-section rather than I-section assessment along the affected north abutment permanent bearing plinths and the western plinth panels. had been damaged due to the torsional effect of the dynamic The analysis structure is shown diagrammatically in impact through its fixing to the jack. Figure 9. The resulting assessment was formalised in combined By landing on the north embankment the nose had effectively certification to Network Rail and formed the basis of further re-established the stability of the launch support system. There was modelling for the certification of subsequent recovery no damage to the permanent structure and there appeared to be no operations. visible effect on the splice connections to the nose or tail sections It was important to achieve the recovery and realignment as from the impact. Figure 8 shows some of the damage. Additional quickly as possible to restore the final structural integrity safely lateral restraint at the nose was quickly installed utilising ballast- and to contain contract overrun and additional expenditure. filled skips to the east of the north embankment. Several constraints were already evident: availability of Following these initial assessments an urgent meeting was appropriate recovery equipment; any likely requirement for convened with Network Rail’s representatives on site who had railway possessions; and designs, checks, repairs, certification and witnessed the incident. It was vital to assess the stability and acceptance by Network Rail. integrity of the structure on its temporary supports, then to assure Network Rail that it was safe to continue operation of passenger 6.0 m 7.5 m and freight trains through the site. The meeting discussed this initial assessment and the actions required in order to assess fully the structural integrity for the Support point – current state and for the proposed recovery plan. An initial Support point – Support point – slider jacks . centre of group 1 realignment plan had already been conceived and the combined temporary (approx. 82 5 t per jack) self-propelled delivery team set about their respective tasks in order to embankment modular transporters demonstrate and assure Network Rail that the structure was safe, and would remain so during the proposed recovery plan to Figure 9. Post-incident support arrangement complete the bridge installation successfully.

133 Civil Engineering Launching of Leigh Road Bridge, Slough, UK Volume 169 Issue CE3 O’Connor, Attrill, Gibb and Oh

Network Rail appointed an independent reviewing consultant The bearing plinth was repaired by breaking back to undamaged (Aecom) to provide additional assurance on structural integrity and original concrete surfaces and recasting. proposed recovery methodology. It also deemed that recovery of The key proposal for lateral realignment entailed the assembly the structure could only be conducted within possessions. and installation of a skid shoe system under the nose edge girders Before the slide could be resumed the main physical challenges (Figure 11) as the mechanism for restraining and then sliding the to the delivery team involved bridge laterally. These were positioned north of the permanent bearings and damaged girder zones to provide alternative ■■ repairs to the slide bearings and jacks temporary support during all the repairs to the jacks, permanent ■■ repairs to the deformed flange areas to resume slide bearing plinth and nose edge beams. continuation Once the realignment corrections and the modifications were ■■ enhanced lateral restraint for the repaired nose bottom flange at completed the structure was lowered onto the repaired slide the slide bearing jacks bearing jacks again before resuming the longitudinal slide. ■■ repairs to the damaged bearing plinths These arrangements were devised by the delivery team, certified ■■ lateral realignment. and reviewed, including a revised contingency risk assessment schedule, before being accepted by Network Rail in time to The team was confident that the original slide and bridge complete the slide successfully during a possession on 29 March positioning could be continued as originally planned once all these 2015, only 7 weeks after the incident. challenges were overcome.

3.3 Addressing the physical challenges The slide bearing and jack repairs comprised replacement bolt fixings for the overstressed lateral restraints and replacing Launch nose damaged slide bearings. The damaged girder panels had already been treated as J-sections for structural strength provision but the bottom flanges required reinstatement of flat running surfaces Jack for the resumed slide. This entailed fixing a 3 mm plate beneath Push/pull rams the central cross-section of the damaged flange zones and filling the void between the damaged and replacement slider plates with Stool epoxy mortar. Enhanced lateral restraint was accomplished by welding new plates to the nose bottom flanges at the damaged section to increase the flange width from 1000 mm to 1500 mm, thus Direction of skid travel taking out the width transition and providing immediate restraint across that zone when the slide bearing jacks were Skid track re-engaged. This was accomplished by way of local stiffeners attached to the new widening plates and welded to the damaged girder flange and its web. Both these flange modifications are Figure 11. Skid shoe system shown in Figure 10.

(a) Nose flange (b) widening and New stiffeners stiffening Narrower nose flange

Edge restraint

3 mm running plate Direction of resumed slide Flange widening plates

Figure 10. Nose flange modifications – (a) repaired flange at slide bearing jack and (b) plan showing flange widening for resumed slide

134 Civil Engineering Launching of Leigh Road Bridge, Slough, UK Volume 169 Issue CE3 O’Connor, Attrill, Gibb and Oh

4. Bridge installation completion When the ‘hold point’ for the planned change of inner steel packing at the restraint position was reached (to allow the transition Once the launch structure was finally correctly aligned over the between narrow and wide nose flange sections, resulting in a permanent bearings, the nose could be unbolted and slid over the period of removal of close lateral restraint) any such induced lateral temporary scaffold tube roller arrangement on the embankment movement tendencies had temporarily increased the potential ready for dismantling and recycling. movement range from beyond the maximum intended close control The initial intention was to lower the bridge deck onto the 40 mm value provided when the restraints were in place to 250 mm. four permanent bearings using hydraulic jacks and demountable In turn, as the nose was slid forward to capture the wider nose towers of stacked hardwood timbers. A facility to jack the deck flange this further unrestrained increased eccentricity subsequently longitudinally and laterally was also needed to achieve the required deformed the bottom flanges of the nose girders. Combined with plan tolerance of ± 10 mm. the bearing deformation, this significantly increased the transverse To minimise the need for such complex plan jacking an gradient causing rapid lateral acceleration, but was instantaneously alternative method was devised using the self-propelled modular halted on impact with the outer restraint system resulting in the transporters and the temporary slide bearing jacks to manoeuvre damage occurring during the rapid deceleration. and lower the deck to 300 mm above the permanent bearings and It was still concluded that close collaborative teamwork between within ± 40 mm of plan location. At this point the bearings were all parties enabled thorough safe incident recovery to proceed re-centred and grouted prior to the final stage of lowering using swiftly. The full engineering trial of the launch gained confidence the self-propelled modular transporters (southern end of deck) and and assurance in the analysis associated with the method and climbing jacks (northern end). support arrangement for launching. The additional plan tolerance was created by using the clearance From the experience of the incident it was concluded that of the bearing anchor bolts in the grout pockets. The deck was ■■ horizontally restrained at all times through contact friction with continuous close lateral restraint should be provided at all self-propelled modular transporters and jacks. Once jacked down times during the slide phase of a bridge launch ■■ the tail could be unbolted and withdrawn on the self-propelled where possible, any need to change a close lateral restraint modular transporters for its own dismantling and recycling. position during the slide should be eliminated ■■ Completion of the remaining bridge, embankment and highway where such a change cannot be avoided, a suitable construction was reprogrammed to minimise the time lost to the supplementary restraint mechanism should be provided during incident, resulting in the scheme opening to traffic on time on transition of the close restraints ■■ 22 September 2015, the original contract completion date (Figure 12). in addition at any transition zone, the structure should be made sufficiently robust to accommodate the most eccentric lateral load case movement that could be generated from the overall 5. Conclusions and learning points system at any time. Application of these conclusions and learning points would Several conclusions leading to learning points and the root cause assure that bridge installation by the method used on this project of the unforeseen lateral movement incident in the slide phase were remains viable and suitable. identified by the team. Lateral alignment corrections required at the western restraint during the slide phase to overcome the tendency for the nose to References move west were due to a transverse weight component induced on the supports by the skew effect of the nose girders and this HA (Highways Agency) (2012) BD2/12 – technical approval of highway condition gave rise to a transverse deformation of the low-friction- structures. In Design Manual for Roads and Bridges. Highways Agency, Guildford, UK. rubber slider jack bearings. Marples F and Richings JD (2014) Improving management controls for the launching of bridges. Proceedings of the Institution of Civil Engineers – Bridge Engineering 167(2): 131–142. Network Rail (2012a) NR/L2/RSE/100/02: Safety Verification. Network Rail, London, UK. Network Rail (2012b) NR/L2/CIV/003: Engineering Assurance of Building and Civil Engineering Works. Network Rail, London, UK. Network Rail (2014) PAN/S&Sd/CD/INS/0081: Guidance to Projects on Compliance with the Common Safety Method on Risk Evaluation and Assessment. Network Rail, London, UK. What do you think?

If you would like to comment on this paper, please email up to 200 words to the editor at [email protected]. If you would like to write a paper of 2000 to 3500 words about your own experience in this or any related area of civil engineering, the editor will be Figure 12. Aerial view of completed bridge happy to provide any help or advice you need.

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ICE Journals-Ad-Jan14.indd 1 06/01/2015 11:46 Civil Engineering Proceedings of the Institution of Civil Engineers Volume 169 Issue CE3 Civil Engineering 169 August 2016 Issue CE3 Pages 137–144 http://dx.doi.org/10.1680/jcien.15.00044 Urbanisation and landslides: hazard Paper 1500044 drivers and better practices Received 31/07/2015 Accepted 11/01/2016 Published online 03/03/2016 Holcombe, Beesley, Vardanega and Sorbie Keywords: developing countries/disaster engineering/ geotechnical engineering

Urbanisation and landslides: hazard drivers and better practices Elizabeth A. Holcombe MSci, PhD Paul J. Vardanega BE, MEngSc, PhD, MASCE, MIEAust Lecturer in Civil Engineering, University of Bristol, Bristol, UK Lecturer in Civil Engineering, University of Bristol, Bristol, UK Mair E. W. Beesley MEng Rachel Sorbie BEng, PGCE Postgraduate, Civil Engineering, University of Bristol, Bristol, UK Former undergraduate, Civil Engineering, University of Bristol, Bristol, UK

Rapid unplanned urbanisation is driving increasing rainfall-triggered landslide risk in low-income communities in tropical developing countries. Conventional slope stabilisation techniques are often unaffordable and most disaster-risk-reduction funding is currently spent post-disaster. However, experience in the Caribbean has changed local engineering practice and World Bank policy, demonstrating that community-based surface water drainage is affordable and effective in mitigating urban landslides. New evidence presented in this paper identifies specific informal construction practices generating further landslide hazards and bioengineering schemes most effective for landslide mitigation. A dynamic hydrology–slope stability model is used to simulate the factor of safety response of nine slope classes (angle and soil strength) to progressive vegetation removal, slope cutting and loading, for six design storms. The effectiveness of 76 bioengineering schemes for improving stability is modelled. Key recommendations are that deforestation should be limited and slope cutting avoided as cutting is most detrimental to stability. Site-specific modelling is needed to identify where deep-rooting, lightweight trees might add stability, whereas grasses are beneficial in all locations.

1. Introduction development (Wamsler, 2007); and a significant lag in funding for ex-ante disaster mitigation (de la Fuente, 2010), despite evidence Landslide hazards and impacts are increasing globally. that it is more cost-effective than post-disaster actions (World Developing nations experience the highest economic losses relative Bank, 2010). to gross domestic product and the majority of fatalities – over half Effective risk reduction requires that risk drivers are identified of which are estimated to occur in urban areas (Petley et al., 2007). and appropriate actions are taken to reduce hazards and/or High-intensity and high-duration rainfall events are the consequences (exposure and vulnerability). The top-level drivers of dominant landslide trigger in the humid tropics (i.e. Köppen the increasing landslide risk are urban migration and population classification: tropical rainforest and monsoonal climates; Peel growth as cities in developing nations expand rapidly. et al., 2007) where deeply weathered residual soils render slopes Over 900 million people now live in overcrowded, poor-quality particularly susceptible to failure (Lumb, 1975). High-magnitude housing with inadequate infrastructure, making them highly events, with hundreds of landslides triggered, can set back vulnerable to both small- and large-scale disasters (Satterthwaite the economic growth of developing countries by several years et al., 2007). Often these settlements are built on hazard-prone land (Peduzzi and Deichmann, 2009). such as marginally stable slopes. Informal construction means that However, until recently the impact of small-scale, high-frequency slopes and structures are not assessed or designed for safety; and landslide events on development has not been recognised. Such high housing density increases exposure to landslides. Landslide ‘everyday’ hazards contribute to an accumulation of risk which hazard is increased further by localised changes to vegetation, compromises livelihoods at community levels, erodes economic topography, drainage and loading (Figures 1 and 2). growth and indicates systemic lack of resilience (Bull-Kamanga In this context controlling exposure to landslides using et al., 2003). Risk accumulation is part of a vicious spiral in which, planning policies alone is impractical, since urbanisation often ‘disasters put development at risk... [and] development choices... outstrips regulation and 30–50% of the population already can generate new disaster risk’ (UNDP, 2004: p. 1). live in informal, low-income settlements (Satterthwaite Unfortunately current top-down disaster-risk-reduction policies et al., 2007). Vulnerability reduction thus presents a complex struggle to address the highly localised physical and human drivers socioeconomic challenge; and landslide hazard drivers are not of everyday hazards such as urban landslides. Two examples of being systematically addressed. this disconnection between policy and practice are: the limited Delivering conventional slope stabilising works is technically delivery of practical interventions on the ground, despite challenging due to the localised scale of instability drivers, statements that disaster risk reduction is required for sustainable widespread distribution of urban landslide hazards and high costs

137 Civil Engineering Urbanisation and landslides: hazard drivers and better practices Volume 169 Issue CE3 Holcombe, Beesley, Vardanega and Sorbie

Figure 1. Typical informal housing on a landslide-prone slope in Castries, Saint Lucia, Eastern Caribbean (photograph by Holcombe, 2011) of geotechnical data, engineering expertise and construction. Furthermore, unless informal construction practices are modified, landslide hazard will continue to accumulate. Experts in the built environment are being called upon to develop innovative ‘global solutions and local actions’ to increase community resilience (IISD, 2014: p. 6).

1.1 A platform for delivering community-based landslide mitigation Figure 2. Rainfall-triggered landslide in an informal community Just such a community-based engineering approach to urban (photograph by Holcombe, 2004) landslide hazard mitigation has been developed by Anderson and Holcombe (2006). Known as ‘management of slope stability in communities’ or ‘Mossaic’, it engages residents, community development practitioners and local engineers in identifying 800 homes). There have been no subsequent landslides reported localised drivers of slope instability and implementing appropriate in these communities despite the exceptional rainfall associated drainage measures. with hurricane Tomas in 2010 (>500 mm in 24 h in Saint Lucia), Lack of geotechnical data and a limited budget for conventional whereas previously even 1 in 2 year rainfall events would trigger site investigation are overcome by combining information from multiple small slope failures (Anderson and Holcombe, 2013). several sources: residents’ descriptions of slope materials, By involving residents at all stages of mapping, design and runoff, seepage and previous landslides; mapping of house plot construction there is evidence that both residents and local scale slope features; elicitation of local engineering knowledge engineers have incorporated better slope drainage practices into of soils; and reference to previous direct shear tests of similar subsequent construction (Holcombe and Anderson, 2010). local soils. This method provides detailed information on topography and surface drainage, and enables estimation of soil 1.2 Understanding and mitigating future hazards depths, categorisation by weathering grade and determination of Mossaic addresses the hydrological drivers of rainfall-triggered relative strength with respect to other local soils (Anderson and landslides where urbanisation has already occurred. Its uptake by Holcombe, 2013). international disaster risk reduction funders, local practitioners and The physically based modelling software – Chasm (Combined communities provides a unique platform to extend the analysis of Hydrology And Stability Model; see Section 2.2) – is then used urban landslide hazards and identify additional practical solutions. to diagnose dominant instability processes. Where surface water To this end, this paper presents numerical simulations of infiltration is shown to drive instability, networks of open drains are designed to intercept runoff at critical locations and convey water ■■ dynamic slope stability responses to progressive urbanisation, to existing drains. Roof guttering and rainwater tanks are installed enabling identification of the most detrimental informal to intercept rain, supplement water supplies and attenuate peak construction practices drain flows. ■■ modified urbanisation scenarios to determine the effectiveness Between 2004 and 2011 three Eastern Caribbean states of actions by residents and engineers in offsetting accumulation implemented Mossaic in 12 low-income urban communities (over of new landslide hazards.

138 Civil Engineering Urbanisation and landslides: hazard drivers and better practices Volume 169 Issue CE3 Holcombe, Beesley, Vardanega and Sorbie

2. Modelling urbanisation and landslide Precipitation Slip search grid Evaporation hazard drivers Computational point at centre of cell Runoff Informal urbanisation of slopes typically involves removal of natural vegetation and excavation to create flatter sites for house Saturated cells Slip circle Mechanical and construction (Smyth and Royle, 2000). Cut slopes are often at hydrological effects of vegetation angles of 60° or steeper (Diaz, 1992) and may initially remain Slope profile for hydrology model stable due to the high negative pore pressures that can develop in Slope profile for stability deep tropical residual soils, only to fail later as rainfall infiltrates model (Anderson, 1983). The first houses are often built at the base of slopes adjacent to urban centres in valleys and on coastal plains. Water table

Informal settlements extend up slopes over time, and housing 1 x 1 m Soil type 0 mesh Soil type 1 density increases as infilling occurs and houses are extended. cells Soil type 2 2.1 Mechanical and hydrological processes Figure 3. Representation of a slope cross-section for analysis in Chasm Deforesting and cutting slopes are known to increase the incidence of landslides (Glade, 1998). Vegetation has mechanical and hydrological effects on slope stability, including root fibre reinforcement and anchoring, load transfer of self-weight and wind three soil types) to typical stages of urbanisation observed in the forces, rainfall interception, evapotranspiration and preferential Eastern Caribbean and similar humid tropical locations (Smyth and flow pathways created by roots. Slope cutting alters the load Royle, 2000). Starting with a fully forested slope, urbanisation was distribution on potential shear surfaces within the wider slope, and represented as a sequence of three construction steps – vegetation can generate localised instability of the cut section. removal, slope cutting and site loading – repeated at four sites Altered surface cover and topography also affect runoff, on each slope, to give a total of 12 urbanisation stages (Figure 4, infiltration and drainage, leading to raised or perched water tables. Table 1). Landslides become more likely to be triggered by rainfall as negative For each slope three material strata were defined using the Hong pore pressures are lost and material shear strength reduced. While Kong weathering grade classification for tropical residual soils the individual effects of different vegetation types, slope angles (GEO, 1988), and assuming no previous landslides had occurred. and hydrogeological conditions have previously been investigated Strata depths and parameter values for soil cohesion cʹ and drained (Anderson et al., 1997), the impact on slope stability of the friction angle were based on direct shear tests on 25 undisturbed combination of the dynamic mechanisms that relate to progressive residual soil samples from un-failed cut slope faces in Saint Lucia urbanisation and the effect of retaining or replanting vegetation in (Anderson and Kemp, 1985; Holcombe, 2006). the changing urban environment have not been established. The mean peak strength values (grade VI residual soil: cʹ = 14 kPa, ϕʹ = 25°; grade V: cʹ = 21 kPa, ϕʹ = 30°) were in accord 2.2 Experiment design and data with those obtained from an extensive programme of triaxial To model dynamic slope stability processes, the physically testing in Hong Kong on similar undisturbed tropical residual soils based model Chasm was used to represent rainfall infiltration, derived from volcanic bedrock (GCO, 1982). Such soils typically groundwater flows, negative and positive pore pressures and exhibit apparent cohesion due to the formation of high negative slope factor of safety (F) over time. Chasm has proven reliable in pore pressures, chemical bonding and the persistence of structures predicting the safe/failed condition of tropical residual soil slopes inherited from the parent material (c.f. Wesley, 1990). for given rainfall events (e.g., Anderson, 1990; Holcombe, 2006) The parameter values of ϕʹ = 25° and cʹ = 2, 5 and 10 kPa and for indicating the benefits of Mossaic drainage interventions selected for modelling are thus conservative with respect to these (Holcombe et al., 2012). Slopes are represented by a regular two- data, reflect uncertainty surrounding apparent cohesion (negative dimensional mesh of columns and cells with specified material pore pressures are represented in Chasm), and support the aim of parameters (Figure 3). investigating the stability response of typical slope classes. A forward explicit finite-difference scheme solves Richards’ and Further studies investigating specific slopes, and with resources Darcy’s equations (Darcy, 1856; Richards, 1931) for unsaturated and for additional geotechnical data, would allow revision of these saturated flows in which cell moisture contents and pore pressures values as appropriate. However, it should be recognised that, as are updated every time-step (usually 60 s). Once the initial water with all such numerical models, these parameters are lumped at table has equilibrated, a rainfall of a specified intensity and duration the grid-scale (1 m2 in Chasm), effectively incorporating sub-grid is imposed. Every hour pore pressures are incorporated into a limit- mechanisms such as apparent cohesion. equilibrium analysis (Bishop’s circular (Bishop, 1955) or Janbu’s Two sets of simulations were carried out. The first analysed the non-circular (Janbu, 1954)) in which the minimum F slip surface is impact of a 12-stage ‘business as usual’ urbanisation scenario identified using a search algorithm. The hydrological and mechanical on each slope class to identify construction practices most effects of vegetation and the unit weight of houses can be included in detrimental to slope stability. For each simulation the minimum the analysis (see Wilkinson et al. (2002a) for model equations). F and associated critical slip surface location were determined A series of Chasm simulations was designed to represent the in response to Saint Lucia’s 1 in 50 year, 24 h storm (based on stability response of different slopes (classified by three angles and an unpublished report from 1995 by Klohn-Crippen ‘Roseau

139 Civil Engineering Urbanisation and landslides: hazard drivers and better practices Volume 169 Issue CE3 Holcombe, Beesley, Vardanega and Sorbie

24 h design storm Sequence of construction steps 12 mm/h intensity modelled per house plot 50 year return period

Original forest cover

4th house (i) Deforestation 2nd house 60° α° Definition of slope classes 3rd house (ii) Cutting by slope angle and grade V–VI soil strength 9 m α: ° 20 30 40 1st house Grade V–VI soil 8 kPa c’: kPa 2 5 10 2 5 10 2 5 10 (iii) Loading ϕ’: ° 25 25 25 25 25 25 25 25 25 Grade III–IV weathered material Class a b c d e f g h i 6 m Grade I–II rock 52 m

Figure 4. Representation of a typical progression of tropical slope urbanisation used in the Chasm model (12 construction steps in total, from 100% forest cover to 100% urbanisation)

Urbanisation stage 0 1 2 3 4 5 6 7 8 9 10 11 12 Forest % 100 75 75 75 50 50 50 25 25 25 0 0 0 Total cuts 0011122233344 Total houses 0001112223334 a Slope angle = 20° cʹ = 2 kPa 2·07 1·89 0·62 b 20° 5 kPa 2·34 2·19 0·89 c 20° 10 kPa 2·57 2·54 1·30 1·30 1·30 1·30 1·30 1·25 1·27 1·27 1·26 1·22 1·22 d Slope angle = 30° cʹ = 2 kPa 1·45 1·34 0·63 e 30° 5 kPa 1·69 1·58 0·89 f 30° 10 kPa 1·91 1·91 1·33 1·33 1·33 1·30 1·30 1·22 1·12 1·12 1·12 1·12 1·12 g Slope angle = 40° cʹ = 2 kPa 1·11 1·02 – 1·01 1·01 – 1·01 0·98 h 40° 5 kPa 1·26a 1·22 – 1·20 1·17a – 1·16a 1·10a – 1·09a 1·00a – 0·99a

a a a a a a a a a Factor of Safety for each slope class i 40° 10 kPa 1·38 1·34 – 1·34 1·28 – 1·27 1·21 – 1·20 1·11 – 1·10 Decrease in F relative to previous construction step ΔF ≤ 0·05 0·15 ≥ ΔF > 0·05 ΔF > 0·15 Increase in F relative to previous construction step ΔF ≤ 0·05 0·15 ≥ ΔF > 0·05 ΔF > 0·15 Bold font indicates F > 1·4; a planar slip surface (Janbu) at base of top strata, otherwise failures are rotational (Bishop); – no cut geometrically possible.

Table 1. Urbanisation stages and associated factors of safety for each slope class for a 1 in 50 year storm, delivering a total of 288 mm of rainfall in 24 h

Dam and ancillary works. Tropical storm Debbie, final report 3. Simulation results on hydrology’, held by WASCO in Saint Lucia – see the online supplementary data for rainfall intensity-duration-frequency data). Table 1 presents the lowest F for each slope class and The second set of simulations tested the potential benefits of urbanisation stage in response to the 1 in 50 year design storm. modified urbanisation scenarios: the impact of deforestation alone; In total, 62 simulations were run; if a slope failed at a certain the exclusion of the most detrimental construction practices; and stage then no further urbanisation stages were imposed. Cuts were bioengineering. omitted from 40° slope simulations as they are not geometrically A series of design storms of increasing intensity and return period viable and houses on such slopes are often constructed on stilts. (from 1 in 5, to 1 in 200 years) were also simulated to identify the critical storms rendering each slope ‘unsafe’. A threshold level 3.1 Effect of slope cutting on stability of F > 1·4 was adopted ‘as an acceptable number to guard against Table 1 aligns with observations that progressive urbanisation failure in a high-risk slope’ (Hencher, 2012: p. 280). tends to reduce slope stability. Changes in F relate to the type of

140 Civil Engineering Urbanisation and landslides: hazard drivers and better practices Volume 169 Issue CE3 Holcombe, Beesley, Vardanega and Sorbie

construction activity and its location on the slope. Cutting is the (α = 40°) are inherently marginally stable and are considered dominant instability driver giving reductions in F of up to 1·30. unsafe for urbanisation. Here, only soils modelled with cʹ = 10 kPa The greatest stability decrease due to deforestation is 0·18; and maintain F > 1 throughout the urbanisation process. For slopes of housing loads have a negligible impact regardless of their position. α = 20° or α = 30° the first cut produces consistent decreases in For slope classes ‘a’ to ‘f’ the maximum impacts occur during the F and indicates that the landslide mechanism transformations are first construction sequence at the base of the slope. geometrically similar. For slopes of these angles with the highest At the start of the urbanisation process, critical failure surfaces cohesion soils (i.e. c and f) the critical surface becomes localised typically encompass a large part of the slope and penetrate less- to one of the cut slopes and F remains relatively constant after the weathered material (Figure 5). Cutting at the toe of the slip third cut. Here, cut slope geometry outweighs the influence of the surface (Figure 5, stage 2) removes a large proportion of the original slope angle in determining slope stability. shear resistance and reduces the stability condition of a shallower None of the fully urbanised slopes meet the specified safety slip surface. The first cut produces the greatest reduction in F, threshold of F > 1·4. Therefore, the scenario of ‘urbanisation triggering shallow rotational failure in soils modelled with low without cuts’ was modelled for slope classes in which cutting led to cohesion (cʹ = 2–5 kPa). F < 1 (classes a, b, d and e). The results for this scenario (Table 2) Of the remaining stable slopes, following the second cut, the show that slopes a, b and e maintain F > 1·4 throughout the design slip surface radius typically decreases further due to stress relief storm, while d remains marginally stable (1 < F < 1·4). at its crest, and relocates to a more critical position downslope (Figure 5, stage 5). Removal of residual soil by cutting exposes 3.2 Effect of targeted bioengineering on stability less-permeable material and locally reduces rainfall infiltration. While slope cutting dominates decreases in F, reintroducing Additionally, cutting introduces an angle (60°) greater than the vegetation to slopes, or limiting deforestation, is one way of effective angle of friction (25°). Progressive urbanisation of slope mitigating the impact of urbanisation. However, despite the classes c and f ultimately leads to localised circular slip surfaces on recognised benefits of bioengineering for reducing soil erosion, the face of each cut with critical or near-critical F values. ‘its ability to stabilise slopes...is less well proven, and certainly Slope angle and soil strength strongly influence stability of the less well quantified’ (Campbell et al., 2007: p. 13). This is because natural slope and the impact of urbanisation. The steepest slopes the effect of vegetation on slope stability is strongly related to the location of roots with respect to the critical slip surface; and there is uncertainty regarding the mechanical and hydrological influences Stage 0: F = 1.91 Pressure head: m of vegetation and natural variations in plant properties (Norris and Black lines: critical 24.3469 3.5816 Greenwood, 2006). slip suface . . 20 1939 –0 5714 The importance of the mechanical effects of vegetation, such as Blue lines: water table 16.0408 –4.7245 and perched water 11.8878 –8.8775 root–slip surface interaction and root tensile strength, was evident 7.7347 –13.0306 in simulations of the urbanisation process. Table 1 indicates a Remove vegetation Cut slope Add house loading reduction in F if tree roots interact with the critical slip surface Stage 1: F = 1.91 Stage 2: F = 1.33 Stage 3: F = 1.33 prior to deforestation. Where the sliding mechanism is translational (slopes g and h) successive stages of deforestation lower F in

Slope Business as Modified urbanisation scenarios definition usual : ° c : Class 100% Urbanised 100% Urbanised Tree Grass Stage 4: F = 1.33 Stage 5: F = 1.30 Stage 6: F = 1.30 α ʹ kPa forest with cuts deforested without cover cover cuts 20 2 a 5 b 10 c AA Stage 7: F = 1.21 Stage 8: F = 1.12 Stage 9: F = 1.12 30 2 d BB 5 e 10 f AA 40 2 g BB 5 h BB Stage 10: F = 1.12 Stage 11: F = 1.12 Stage 12: F = 1.12 10 i BB Dark shading: F < 1·0, failed; light shading: 1·0 < F < 1·4, critical; no shading: F > 1·4, stable; diagonal strike through: not considered. Modelled bioengineering schemes: A, cut slopes, one tree at crest of each cut, complete grass cover; B, uncut slopes, five trees between houses, complete grass cover Figure 5. Chasm visual output of pore water pressure, critical slip surface and F at progressive stages of simulated urbanisation at time Table 2. Summary of stable, critical and failed slopes for a 1 in 50 year, steps corresponding to the lowest factor of safety (slope class f) 24 h design rainfall (12 mm/h)

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approximately equal steps because each tree contributes an equal tensile strength and surcharge for each plant type were used to fraction of shear resistance. For rotational slides the critical assess the sensitivity of F to variations in properties of grass and slip surface extends up the slope as F decreases (e.g., stage 6–7, trees (see Table 3, the online supplementary data and Sorbie and Figure 5), suggesting that trees force the critical slip surface Beesley (2013)). The most effective planting schemes were then outside the rooting zone prior to removal. Slopes with soils applied to the remaining critical slopes (see Table 2). The design modelled with lower cohesion (cʹ = 2–5 kPa) are more sensitive to values chosen for the modelled bioengineering schemes are given initial deforestation because the cohesion added by roots (taken as in table S8 of the online supplementary data. 6 kPa for the deforested trees (c.f. Wu et al. 1979)) is greater than Table 3 shows that trees potentially produce the greatest the ‘bare-soil’ value. increases in F if there is a large degree of interaction between To test the impact of bioengineering the three urbanised slope the roots and slip surface (e.g., roots of 4 m depth located at the classes with the greatest response to vegetation removal for their crest of cuts), and if the roots have a high enough root area ratio to soil type were selected (d, f, h). Two types of bioengineering increase cohesion significantly. However, cut slopes are particularly scheme were modelled: grass (uniform distribution) and trees (at sensitive to surcharge due to trees (2 to 5 kPa) positioned on the the crest and toe of cuts and downslope of houses). Vegetation crests, which reduces F by 0·89 and triggers failure during the effects represented in Chasm included: rainfall interception, design storm. The effectiveness of trees is thus highly dependent evapotranspiration with root water uptake, increased hydraulic on their location and properties. In contrast, all three slopes (d, f, h) conductivity, root reinforcement, and surcharge (Wilkinson et al., were found to respond positively to grass cover in every simulation, 2002b). Additionally, ranges of root area ratio, root depth, root with increases in F of at least 0·13.

Rd: RAR: T r: S: Added cʹ: α: 30°, c′: 10 kPa α: 40°, c′: 5 kPa α: 30°, c′: 2 kPa m 1 × 10-3 MPa kPa kPa ΔF F ΔF F ΔF F m2/m2 Trees 1 0·1 50 2 6 0·05 1·17 0·03 1·02 0·01 1·29 Max. ΔF = 0·39* 2 0·1 50 2 6 0·09 1·21 0·03 1·02 0·03 1·31 Mean ΔF = 0·14* Coefficient of 4 0·1 50 2 6 0·22 1·34 0·06 1·05 0·05 1·33 variation (COV)* Mean (SD) 0·12 (0·09) 0·04 (0·02) 0·03 (0·02) range: 0·27–0·74 Mean COV = 0·52 4 0·1 50 2 6 0·22 1·34 0·06 1·05 0·05 1·33 *Excludes effect 4 0·5 50 2 30 0·39 1·51 0·18 1·17 0·20 1·48 of variation in S 4 1 50 2 60 0·39 1·51 0·34 1·33 0·30 1·58 Mean (SD) 0·33 (0·10) 0·19 (0·14) 0·18 (0·10) 4 0·1 20 2 2·4 0·17 1·29 0·05 1·04 0·03 1·31 4 0·1 50 2 6 0·22 1·34 0·06 1·05 0·05 1·33 4 0·1 100 2 12 0·29 1·41 0·09 1·08 0·09 1·37 Mean (SD) 0·23 (0·06) 0·07 (0·02) 0·06 (0·03) 4 0·1 50 2 6 0·22 1·34 0·06 1·05 0·05 1·33 4 0·1 50 5 6 -0·89 0·23 0·04 1·03 0·06 1·34 4 0·1 50 10 6 -0·92 0·2 0·01 1 0·07 1·35 Mean (SD) -0·53 (0·65) 0·04 (0·03) 0·06 (0·01) Grass 1 0·1 20 0·0008 2·4 0·34 1·46 0·13 1·12 0·17 1·45 Max. ΔF = 0·37 2 0·1 20 0·0008 2·4 0·34 1·46 0·13 1·12 0·18 1·46 Mean ΔF = 0·22 COV range: 4 0·1 20 0·0008 2·4 0·22 1·35 0·16 1·15 0·21 1·49 0·00–0·38 Mean (SD) 0·30 (0·07) 0·14 (0·02) 0·19 (0·02) Mean COV = 0·18 1 0·02 20 0·0008 0·48 0·34 1·46 0·13 1·12 0·13 1·41 1 0·1 20 0·0008 2·4 0·34 1·46 0·13 1·12 0·17 1·45 1 0·5 20 0·0008 12 0·34 1·46 0·16 1·15 0·37 1·65 Mean (SD) 0·34 (0·00) 0·14 (0·02) 0·22 (0·13) 1 0·1 4 0·0008 0·48 0·34 1·46 0·13 1·12 0·13 1·41 1 0·1 50 0·0008 6 0·34 1·46 0·13 1·12 0·17 1·45 1 0·1 75 0·0008 9 0·34 1·46 0·15 1·14 0·31 1·59 Mean (SD) 0·34 (0·00) 0·14 (0·01) 0·20 (0·08)

Table 3. Sensitivity of slope factor of safety (F) to rooting depth (Rd), root area ratio (RAR), tensile strength (Tr) and surcharge (S) (see Table 1 for colour key)

142 Civil Engineering Urbanisation and landslides: hazard drivers and better practices Volume 169 Issue CE3 Holcombe, Beesley, Vardanega and Sorbie

Again, high values of root area ratio increase the effectiveness of landslide hazard could be mitigated in slopes a, b and e. To offset grass, particularly in soils exhibiting low cohesion. Furthermore, risk accumulation in existing urbanised slopes, both modelled F is generally less sensitive to variation in grass parameters than bioengineering schemes are viable (classes c and f). tree parameters, and significant increases in F were observed The value of integrating better practices is demonstrated by without roots interacting with the critical slip surface. This the response of slope class d, where a combination of informal suggests that the thatch effect, by which long grass intercepts and urbanisation without cuts and with bioengineering reduces sheds rainfall, improves slope stability by way of a hydrological landslide hazard to below that of the original forested slope. mechanism (reduced infiltration). The consistently beneficial effect of grass makes it a ‘no regrets strategy’ in bioengineering schemes. Table 2 compares the selected tree and grass bioengineering 5. Summary and recommendations schemes with current and modified urbanisation scenarios. For slopes of 20° and 30° both schemes improve slope stability From the simulations reported in this paper, slope cutting to F > 1·4; and for the 40° slopes the ‘urbanisation plus design is shown to be the dominant instability driver; aligning with tree cover’ scenario stabilises slope i. These results rely on the observations that high-frequency rainfall events (<1 in 5 years) design tree root area ratio of 1 × 10-3 m2/m2 (see table S8 in the often trigger multiple cut slope failures in informal urban hillside online supplementary data) – a parameter to which the slope shows communities. The retention or reintroduction of vegetation can be significant sensitivity (Table 3). In comparison, complete grass effective in mitigating some of this hazard, and grass is found to be cover does not increase F sufficiently for any of the 40° slopes beneficial in all cases. to be considered stable, although there is less uncertainty in the Site-specific bioengineering schemes can be identified for each effectiveness of grass schemes. slope class. However, given that the critical factor of safety is sensitive to the modelled cohesion of the soil and the mechanical effects (and location) of trees, a thorough ground investigation, 4. Discussion – urbanisation and landslide physics-based modelling of site hydrology and stability mechanisms hazard and selection of local tree species with beneficial characteristics (e.g., Greenwood et al., 2006) is required to reduce the uncertainty The change in landslide hazard for slopes under alternative in F related to tree-planting schemes. These general and site-specific ‘business as usual’ and ‘modified urbanisation’ scenarios is actions would be suitable for application in combination with other summarised in Table 4. In all cases current construction methods improved construction and slope drainage practices. increase the frequency of rainfall-triggered landslides to return periods of at least 1 in 5 years, affecting multiple cut slopes. This aligns with observations of ‘everyday’ landslide hazards in Acknowledgement informal urban communities in the humid tropics. The steepest slopes are considered unsafe for urban development The authors wish to thank Professor Malcolm Anderson who – again reflecting the known unsafe locations inhabited by many developed the Mossaic approach in collaboration with the first such communities. These results emphasise the detrimental effect author and who reviewed early drafts of this paper. The online of slope cutting; yet by constructing without cuts (e.g., using pier supplementary data file can be downloaded from the ICE Virtual foundations as recommended by AGS (2007)), the increase in Library website.

Slope definition Business as usual Modified urbanisation scenarios α: ° cʹ: kPa Class 100% forest Urbanised with 100% deforested Urbanised Tree cover Grass cover cuts without cuts 20 2 a 1 in 200 >1 in 5 1 in 200 1 in 200 N/C N/C 5 b 1 in 200 >1 in 5 1 in 200 1 in 200 N/C N/C 10 c 1 in 200 >1 in 5 1 in 200 N/C 1 in 200 1 in 200 30 2 d 1 in 100 >1 in 5 >1 in 5 >1 in 5 1 in 200 1 in 200 5 e 1 in 200 >1 in 5 1 in 200 1 in 200 N/C N/C 10 f 1 in 200 >1 in 5 1 in 200 N/C 1 in 200 1 in 200 40 2 g >1 in 5 N/C >1 in 5 >1 in 5 >1 in 5 >1 in 5 5 h >1 in 5 N/C >1 in 5 >1 in 5 >1 in 5 >1 in 5 10 i >1 in 5 N/C >1 in 5 >1 in 5 1 in 200 >1 in 5 N/C, not considered. Modelled tree and grass covers are defined in Tables 2 and 3. 24 h rainfalls with return periods of 1 in 5, 10, 20, 50, 100 and 200 years were simulated. Rainfall intensity, duration, frequency data used to define the critical storms are provided in the online supplementary data.

Table 4. Return periods of 24 h storms causing F < 1·4 (‘>1 in 5’ indicates F < 1·4 for a storm with a return period of 1 in 5 years or lower)

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