The Structural Engineer January 2016

TheStructuralEngineer

January 2016

Volume 94 | Issue 1

The flagship publication of The Institution of Structural Engineers

TUNED MASS DAMPERS REPAIRING MISSILE DAMAGE PI CLAIMS: NOTIFICATION DYNAMIC ANALYSIS STEEL QUIZ

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NEW LEASE OF LIFE A case study in timber repair at Tyneside’s historic Dunston Staiths

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Contents

PAGE 22 VIBRATION ABATEMENT WITH TMDS

TheStructuralEngineer January 2016

PAGE 28 REPAIRING DUNSTON STAITHS

3

PAGE 42 DYNAMIC ANALYSIS WITH TMDS

TheStructuralEngineer Volume 94 | Issue 1

Upfront

Project focus

Opinion

5 6 8

22 Vibration abatement of rectangular, trapezoidal and irregular-shaped joist-framed floors, using tuned mass dampers 28 Conservation compendium. Part 14: Dunston Staiths, Gateshead – a case study in timber conservation and repair 32 Baghdad missile-damaged building brought back to life

50 Book review: Best Construction Methods for Concrete Bridge Decks – Cost Data 51 Book review: Acoustic Emission (AE) and Related Non-destructive Evaluation (NDE) Techniques in the Fracture Mechanics of Concrete: Fundamentals and Applications 52 Book review: Design of durable concrete structures 53 Verulam

Professional guidance

At the back

Editorial Institution news: President’s end-of-year report Institution news: Council election 2016 Election of members of the Board for 2016–17: second poll David Brohn awarded President’s Award

10 Institution news: Institution election/transfer/reinstatement list: December 2015 Young professionals excel at Teambuild 2015 12 Institution news: Recognising the contributions of reviewers 14 Industry news

36 Engineer’s Guide to PI Claims. Part 1: Notification to insurers 38 Managing Health & Safety Risks No. 47: Safe excavation

Technical

Features 16 Constructing the future – the role of bearings

56 58 60 61 63 64

Diary dates Spotlight on Structures And finally… Products & Services Services Directory TheStructuralEngineerJobs

42 Simplified dynamic analysis of beams and slabs with tuned mass dampers

Front cover: ©Kari Vickers The Structural Engineer PRESIDENT Alan Crossman CEng, FIStructE, FICE, MCIWEM CHIEF EXECUTIVE Martin Powell EDITORIAL HEAD OF PUBLISHING Lee Baldwin EDITOR Robin Jones t: +44 (0) 20 7201 9822 e: [email protected] EDITORIAL ASSISTANT Ian Farmer t: +44 (0) 20 7201 9121 e: [email protected]

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www.thestructuralengineer.org ADVERTISING

EDITORIAL ADVISORY GROUP

DISPLAY SALES Patrick Lynn t: +44 (0) 20 7880 7614 e: [email protected]

Project focus: Allan Mann, FIStructE Features: Don McQuillan, FIStructE Technical: Chris O’Regan, FIStructE Opinion: Angus Palmer, MIStructE Professional guidance: Simon Pitchers, MIStructE

RECRUITMENT SALES Paul Wade t: +44 (0) 20 7880 6212 e: [email protected] DESIGN SENIOR DESIGNER Craig Bowyer CREATIVE DIRECTOR Mark Parry PRODUCTION PRODUCTION EXECUTIVE Rachel Young

Price (2016 subscription) Institutional: £390 (12 issues incl. e-archive, p&p and VAT) Personal: £125 (12 issues incl. p&p) Personal (Student Member): £40 (12 issues incl. p&p) Single copies: £35 (incl. p&p)

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© The Institution of Structural Engineers. All non-member authors are required to sign the Institution’s ‘Licence to publish’ form. Authors who are members of the Institution meet our requirements under the Institution’s Regulation 10.2 and therefore do not need to sign the ‘Licence to publish’ form. Copyright for the layout and design of articles resides with the Institution while the copyright of the material remains with the author(s). All material published in The Structural Engineer carries the copyright of the Institution, but the intellectual rights of the authors are acknowledged. The Institution of Structural Engineers International HQ 47–58 Bastwick Street London EC1V 3PS United Kingdom t: +44 (0)20 7235 4535 e: [email protected] The Institution of Structural Engineers Incorporated by Royal Charter Charity Registered in England and Wales number 233392 and in Scotland number SC038263

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Presidential Inaugural Address 2016 “THE ART OF THE POSSIBLE” Alan RL Crossman CEng, FIStructE, FICE, MCIWEM

We are delighted to announce that Alan Crossman CEng FIStructE FICE MCIWEM has been appointed 2016 President of The Institution of Structural Engineers. Alan will give his inaugural address to the Institution at its Bastwick Street Headquarters in London on 15 January. The theme of his address will be “The Art of the Possible”. During his address Alan will discuss his own education and formative career, and REmECTONHOWITCOMPARESTOTODAYSEDUCATIONANDCAREERROUTES He will then outline his priorities as President, which include the importance of promoting OPPORTUNITYANDmEXIBILITYINCAREERDEVELOPMENTTHE)NSTITUTIONSVITALGLOBALROLEINCLUDING HISOWNINTERESTINFORGINGNEWLINKSWITHTHEPROFESSIONIN)NDIA ANDTHENEEDTO make sustainability a vital key element in the profession’s thinking.

Date Time Venue

Price

Friday 15 January 2016 17:30 for 18:00 start The Institution of Structural Engineers, International HQ, 47-58 Bastwick Street, London, EC1V 3PS Free

Annual Institution Events

Conferences & Seminars

programme of conferences and seminars The Institution’s key annual events, many of Awhich have been organised by the Institution and industry partners

running for several decades.

Special Interest Series

Technical Lecture Series

A series of lectures organised in partnership by the Institution and other leading organisations.

A series of technical lectures based upon a key theme, which in 2013 is Materials

Registration is required in advance. To book your place, please visit the events section of the Institution website, www.istructe.org and register before Thursday 7 January lecture theatre. If you have any questions please contact the Events Team at [email protected]

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Upfront Editorial

TheStructuralEngineer January 2016

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Upfront In with the new Robin Jones Editor

With the holidays behind us and New Year’s resolutions made, I hope that readers are looking forward to the opportunities and challenges that 2016 will bring. At The Structural Engineer, we are starting the year with a revamp of the magazine’s “At the back” section. As well as “Diary dates” (page 56), you will now also find “Spotlight on Structures” (page 58) here, along with periodic updates on other Institution services and a new, lighter feature – “And finally…” – where we hope to exercise your mind each month. We begin with a steel quiz (page 60). In addition, Professional guidance sees the launch of a new series for 2016. Following on from last year’s articles on risk and contractual liability, insurance broker Griffiths & Armour will be providing a series of articles examining the life of a typical professional indemnity claim. We begin by looking at matters requiring notification to one’s insurers (page ge 36). As ever, feedback on these changes is welcome.

present an article showcasing the use of sophisticated bearings systems (page 16), while Project focus also features the latest part of the Conservation compendium – a case study of timber repair at Dunston Staiths (page 28) – and an article from Baghdad on repairs to the steel frame of a building damaged in a missile strike (page 32). We also bring you a number of letters to Verulam (page 53), with a focus on May 2015’s Project focus article on the Grand Parade balustrade in Bath. I will also take this opportunity to remind regional groups about the Sir Arnold Waters Medal, which is awarded each year to the best paper to have won a regional group prize during the session. If your group would like to submit a paper for consideration, please send it to me at [email protected] by 11 January.

Elsewhere in this issue, we have two articles on tuned mass dampers – one in Project focus (page 22) and one in Technical (page 42). In Features we

The Structural Engineer  provides structural engineers and related professionals worldwide with technical information on practice, design, development, education and training associated with the profession of structural engineering, and offers a forum for discussion on these matters  promotes the learned society role of the Institution by publishing peer-reviewed content which advances the science and art of structural engineering  provides members and non-members worldwide with Institution and industry related news  provides a medium for relevant advertising

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The Institution has over 27 000 members in over 100 countries around the world  is the only qualifying body in the world concerned solely with the theory and practice of structural engineering  through its Chartered members is an internationally recognised source of expertise and information concerning all issues that involve structural engineering and public safety within the built environment  supports and protects the profession of structural engineering by upholding professional standards and to act as an international voice on behalf of structural engineers 

Finally, following on from Will Arnold’s photo Fi in the November issue, Bob Astley has sent in this th picture in which he enjoys his copy of The Structural Engineer in front of the Burj Al Arab S in Dubai. Keep the images coming! Perhaps we can c come up with a prize for the best entry at the t end of the year.

The Structural Engineer (ISSN 1466-5123) is published 12 times a year by IStructE Ltd, a wholly owned subsidiary of The Institution of Structural Engineers. It is available both in print and online.

Contributions published in The Structural Engineer are published on the understanding that the author/s is/are solely responsible for the statements made, for the opinions expressed and/or for the accuracy of the contents. Publication does not imply that any statement or opinion expressed by the author/s reflects the views of the Institution of Structural Engineers’ Board; Council; committees; members or employees. No liability is accepted by such persons or by the Institution for any loss or damage, whether caused through reliance on any statement, opinion or omission (textual or otherwise) in The Structural Engineer, or otherwise.

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TheStructuralEngineer January 2016

Upfront Institution news

President’s end-of-year report Tim Ibell FREng, CEng, BSc(Eng), PhD, FIStructE, FICE, FHEA 2015 President of The Institution of Structural Engineers

It hardly seems possible that I am writing my end-of-year report as the 2015 President. By the time this article is published, roast turkey and all the trimmings will already be a distant memory, and Alan Crossman will be our 96th President. I know that Alan is extremely excited about the role, and that he will lead the Institution with immense energy and distinction. I would like to take this opportunity to wish Alan all the very best for 2016, and to thank him personally for all his support during 2015. As you might imagine, one of the most frequent questions I received as President was: “Are you enjoying your year?” And, predictably, you will not be surprised to hear that I loved it. I shall miss it greatly, and I recommend the role to you unreservedly! It’s a fabulous privilege to play a senior role, albeit temporarily, in such an extraordinary institution. We enjoy a unique and exceptional reputation worldwide, and we should be very proud of this indeed.

Creativity is fun One of the strengths of our profession is that we lie within the Venn diagram intersection between the professional engineering institutions and the built environment institutions. This wonderful positioning gives us the opportunity to lead collaborations and to influence many more sectors than is usually possible for most professions. This has always been true, but I believe that the accelerating changes which the digital revolution is driving represent potent opportunities for our profession, ensuring that creative invention is paramount. At our International Conference in Singapore in September 2015, Chris Wise suggested that humans should do that which humans are good at. This wonderfully pithy comment could not be truer as a signpost for our profession. Creativity is central to all we do as structural engineers, and will only continue to grow in importance in defining our success in future. But there are two other profoundly important reasons why creativity is so crucial to the underpinning education of the next generation of structural engineers. Firstly, creativity is fun, and “fun” is attractive to all of society. Diversity in our profession starts with understanding the talents which we should be looking for among schoolchildren who might wish to be structural engineers. Are they really only Maths, Further Maths and Physics? I suggest not. I suggest that a breadth of outlook, underpinned, of course, by sound numerical aptitude, is increasingly representative of the sort of talent set which our

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profession must attract if it is to stay relevant through the digital revolution. Secondly, profound and deep learning of structural engineering can only take place if students are happy and inspired. Uninspired students require teaching, which will not penetrate. Learning and teaching are different concepts. The embedment of creativity as the bedrock of all student activity ensures inspiration to learn, such that deep technical learning is possible. Without creativity as the bedrock, teaching is necessary, and learning is shallow.

Emerging leaders It was such a pleasure back in November, both in Hong Kong and in London, to shake the hands of new professionally qualified members of the Institution, and to welcome them. What strikes me is that these new members will, in all likelihood, have been transferring skills to some of their senior colleagues since the

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CREATIVITY IS CENTRAL TO ALL WE DO AS STRUCTURAL ENGINEERS, AND WILL ONLY CONTINUE TO GROW IN IMPORTANCE IN DEFINING OUR SUCCESS IN FUTURE

day they arrived in the workplace. It is likely that the most prevalent examples of this would include the ins and outs of particular types of software and the exploitation of social media. When I arrived in industry as a fresh graduate, I couldn’t teach my senior colleagues anything at all. The transfer of skills occurred from the top down only. Times have changed. This is a new era. Transfer of skills is now also taking place from the bottom up. This is a critical break with the past, and we must recognise it. Our young members are not the future of the Institution. They are already the Institution. The digital revolution requires us to be fleet of foot, and I am quite sure that one such agile requirement is to ensure that our young members are seen as emerging leaders within the Institution in a profound way. I believe that this is crucial for our profession and for the Institution, and I greatly look forward to our emerging leaders playing an ever-increasingly important role. In order for our young members to emerge as leaders in the Institution, however, they need to have wanted to stay in the Institution and make the step from Student to Graduate member. During my year, I was keen to see ideas tabled to ensure that an increasing proportion of new graduates transfer their membership from Student to Graduate grade. I feel we have made real headway in this with the Structural Behaviour Course. Now that it has gone live, all members of the Institution, but particularly Student and Graduate members, can take the online Course as often as they like. In fact, I am using the Course as part of the learning material (and assessment) for first-year students, and I would encourage all academics to consider doing likewise. I am sure that the Structural Behaviour Course will quickly become another compelling reason why our younger members should wish to retain membership of the Institution during their Initial Professional Development. Why wouldn’t they want to demonstrate core competence in structural behaviour to their employer?

President’s Award The concept of ensuring that our graduates have a profound understanding of structural behaviour has a long and interesting history within the Institution. But in the more

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modern era, there is one member of the Institution who stands out as a visionary. Dr David Brohn pioneered the “Brohn Test”, as it is affectionately known, in the early 1970s. By evidence-based tracking of the level of understanding of structural behaviour among graduates over several decades, and by relentlessly pursuing the goal to ensure that structural behaviour is learned in universities in an appropriate manner, David has led the way in this quest. His passion for the importance of this issue across the industry was far ahead of its time, and now that the Institution has the Structural Behaviour Course firmly in place, it seems so fitting that David be recognised appropriately for his pioneering work. Therefore, it is with the greatest of pleasure that I have decided that Dr David Brohn should receive the President’s Award for 2015. It is a rare honour, and richly deserved.

Encouraging Fellowship Despite the fact that I am clearly championing the involvement of our younger members in everything we do in the Institution, there is another group of membership which deserves a special comment. It is that group of Members who should really be Fellows. On all my visits around the regional groups in 2015, during which I was treated fabulously without exception, I came across large clusters of highly experienced Members who had not yet submitted their forms to become Fellow. This is the written reminder to my verbal chivvying! We have exceptional Members all over the world, so if you feel that you might be ready for Fellowship, please contact our Membership Department and undertake the upgrade. Our staff will help you through the process, which has become far more streamlined over the years.

Fabulous team Speaking of our staff, I would like to take this opportunity to thank every one of them for their extraordinary commitment to the Institution. Under the leadership of Chief Executive, Martin Powell, and his Directors, we have a fabulous team. I can vouch for that first hand. So, thank you for the daily efforts you put in to ensure that the Institution continues to grow successfully. I know that 2016 will be no different, so a very Happy New Year to all our staff and members!

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TheStructuralEngineer January 2016

Upfront Institution news

Council election 2016 Nominations are sought for candidates for election as: • Vice-President 2017–18 • Ordinary member of Council 2017–19 Information about the role and operation of the Council may be found at: www.istructe. org/about-us/organisation-structure/ council The electoral regions in the UK and the Republic of Ireland are based on Institution regional groups – a map of which can be accessed from the website at: www. istructe.org/near-you/europe/unitedkingdom The regions are: 1 Lancashire and Cheshire 2 Scottish, Northern Ireland and Republic of Ireland 3 Yorkshire and Northern Counties 4 Bedfordshire and Adjoining Counties, East Anglia and East Midlands 5 Midland Counties and Wales

6 Devon and Cornwall, Western Counties and Southern 7 Thames Valley and Surrey 8 North Thames 9 South Eastern Counties 10 Rest of Europe, Middle East, Africa and the Americas 11 Hong Kong 12 Asia and Pacific The minimum number of ordinary members (continuing in office in 2017 and to be elected) from any electoral region is one (apart from region 11, where because of the size of the electorate, it is two). To fulfil this requirement, at least one ordinary member of Council from each of Region 7 and Region 11 must be elected. Chartered and Incorporated Structural Engineers and Technician Members (who have submitted a current Institution Continuing Professional Development return) are invited to consider standing for election as an ordinary member of the Council

Election of members of the Board for 2016–17: second poll

David Brohn awarded President’s Award

Voting by members of Council 2015 to resolve the tie for the election of the third member of the Board for 2016–17 (reported on 12 November 2015) closed at 12 noon GMT on 2 December 2015. The result is as follows:

Institution Fellow Dr David Brohn CEng has been awarded the President’s Award by the Institution, in recognition of his visionary approach to the education of students and graduates in structural engineering. It is only the second President’s Award ever made. David’s “Brohn Test” is used by educators and employers across the UK to measure and embed an understanding of structural behaviour in students and employees, and his extraordinary efforts have underpinned the Institution’s own new Structural Behaviour Course. Institution President, Professor Tim Ibell, said: “The concept of ensuring that our graduates have a profound understanding of structural behaviour has a long and interesting history within the Institution. But in the more modern

Number of eligible voters: 83 Number who voted: 61 Turnout: 73.5% Glenn R Bell 31 Simon J Pitchers 30

Elected

Susan M Doran Company Secretary and Director of Regulations 2 December 2015

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2017–19. Fellows (who have previously served on Council and who have submitted a current Institution Continuing Professional Development Return) are invited to consider standing for election as a Vice-President 2017–18. Nomination papers (which must be completed by the candidate and ten other Voting Members) are obtainable from Dr S M Doran and must be submitted by Monday 15 February 2016. Candidates must also complete a candidate information form and supply a photograph. Completed nomination documents can be returned by e-mail to [email protected] or by post. In due course, voting documents will be issued and you will be able to vote either electronically or postally. The results will subsequently be published in The Structural Engineer, in the e-newsletter and on the website. Dr S M Doran Company Secretary and Director of Regulations

era, there is one member who stands out as a visionary. “Dr David Brohn pioneered the ‘Brohn Test’, as it is affectionately known, in the early 1970s, leading the way in evidence-based tracking of the level of understanding of structural behaviour amongst graduates, ensuring that structural behaviour is learned in universities in an appropriate manner. “His passion for the importance of this issue across the industry was far ahead of its time, and now that the Institution has its own Structural Behaviour Course firmly in place, it seems fitting that David be recognised appropriately for his pioneering work. It is with the greatest of pleasure that I have decided that Dr David Brohn should receive the President’s Award for 2015. It is a rare honour, and richly deserved.” Dr Brohn said: “I have been a member of the Institution for over 50 years and it has been a major part of my professional life, so I am pleased and honoured to receive this Award.” Dr Brohn will receive the award at the Institution’s Annual People and Papers Awards Luncheon to be held in London during June 2016.

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TheStructuralEngineer January 2016

Upfront Institution news

Institution election/transfer/reinstatement list: December 2015 At a meeting of the Membership Committee on 3 December 2015, the following were elected/transferred/ reinstated in accordance with the Institution’s Regulations: ELECTIONS Fellow via Eminent Persons Route (3) BASHEER, Paliakarakadu Assen Muhammed ROMO, Jose YOUSEFI AZIMI, Saeed Members (2) GHOSH, Somnath MACMILLAN, Colin Richard Callum Graduate (95) Student Employed (10) TRANSFERS Member/Associate to Fellow (7) BARTON, Ian BUCKLEY, Stephen Philip KELLY, Fergal Shaun LOHMANN, Timothy Gerard SCOTT, Thomas Findlay SPELLER, Dominic Gavin THOMAS, Neil Graduate to Member (1) KIM, Boksun

TREASURE, Paul TSANG, Chiu Wai UDAGAMA PALLEWATTHE, Athula WINTERBOTHAM, Andrew

MURRISH, David

Student Employed (1) BAMSEY, Timothy

Associate-Member (3) BROTHWOOD, Kenneth Reginald GREENWAY, John Charles HARRIS, Richard John

Student Free (44) RESIGNATIONS The Membership Committee has accepted, with regret, the following resignations: Fellow (5) AUBREY, William Harry BROOKS, Robert Anthony MARECHAL, Roger Vernon RICHARDS, Malcolm Alexander SMITH, Richard Anthony Member (13) ALLISON, Robert William BROWN, Gary James CANTY, Leslie Esmond COOKSEY, David Mervyn DALL, James Balfour ECHETA, Chinedum Bennett HARLEY, Robert Anthony HARPER, John Frederick JOHNSON, Brian KELLY, Daniel Herbert KWONG, Shun Hang LEUNG, Chi Ming

Associate (1) FULLARD, Andre

Graduate (6) DEATHS The deaths of the following are reported with regret: Fellow (10) CARTER, Raymond Fred Sidney DEAKIN, Neville Teare DUPENOIS, Charles Emilien FORSBREY, Leonard William JOHNSON, John Richard PETITT, Anthony Leslie TOLBUTT, Alan John TYPROWICZ, Tadeusz WEBSTER, Rodney Michael YOUNG, Richard Charles Member (5) BURTON, Alexander Charles HUMPHREYS, Robert JENKINSON, Anthony Richard OAKLEY, Anthony George SPICE, Reginald Walter

Student to Graduate (85) Student to Student Employed (1) Free Students (976) REINSTATEMENTS Member (11) BLACKMORE, Mark CHAN, Kwong Yan CHAN, Yat Hei CHAU, Kaki DRUMMOND, William George HURLEY, Brian LAI, Chi Kin LAM, Chi Leung MCDAID, Pauric Gerard NG, Hoi Lun STRONG, David Associate-Member (2) PRICE, Richard Albert John THOMSON, Russell Mcdonald Graduate (17) BRADLEY, Fiona Foyer HERBERT, Alexander HINKSON, Christopher HUGHES, Graham KNEVITT, Clayton John KUNG, Wilson Wing Kin MARIANO, Priscillano Jr. MCCLERNON, Marta Karolina MORTIMER, Giles Lewis RAD, Taghi RUSH, David Ian TAI, Chin Keung THOMPSON, David

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Young professionals excel at Teambuild 2015 Teambuild 2015, a construction challenge sponsored by The Institution of Structural Engineers’ Educational Trust, was a big success again this year. The objectives of Teambuild focus on developing skills in leadership, communication and coordination, helping to identify ways to improve teamwork in the construction industry. Eleven teams representing 24 UK top construction firms competed in this year’s competition, which took place in November. Teams were challenged with a brief dominated by infrastructure investment and SMARTcities innovation. The teams were asked to plan, design and present hypothetical proposals based around “Edinburgh gateway” – the complex interchange at Gogar, west of Edinburgh, connecting road, tram, rail and air transport.

In line with the SMARTcities concept, teams were required to make data management and IT a key driver in their schemes. The winning team was “Blue Steel”, with team members drawn from Arup, Price & Myers, Max Fordham and Balfour Beatty. All the team members were under 30 and the majority women. Congratulations to the team, who won a prize of £2000. Competition Judge, John Brennan, FCIOB, Project Director at Skanska Plc, said: “Teambuild is a great event, and it has been very rewarding to observe the teams get together over the demanding tasks. Very similar to real-life project situations, this is a great learning experience for all those taking part.” Entries for the 2016 competition will open in June. Read more about Teambuild at: www.teambuilduk.com

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TheStructuralEngineer January 2016

Upfront Institution news

Recognising the contributions of reviewers The Structural Engineer

Brian Uy

Yao Cui

Richard Henry

The Institution is grateful to the following for their work in reviewing articles published in The Structural Engineer during 2015.

Pedro Vellasco

Xianghe Dai

Stephen Hicks

Ahmer Wadee

Mario D’Aniello

Chao Hou

Yong Wang

Antony Darby

Yuner Huang

Chien Ming Wang

James S Davidson

Jianwei Huang

Don White

Buick Davison

Jing-Si Huo

Hua Yang

Dina D’Ayala

Hassan Ibrahim

Ronald Ziemian

Nele De Belie

Ragip Ince

Alphose Zingoni

Jorge de Brito

Mehmet Inel

Adel Abdelnaby

Francisco De Caso y Basalo

Aimar Insausti

Sigrid Adriaenssens

Flavia De Luca

Jeppe Jönsson

Sheida Afshan

Juan Jose del Coz Diaz

Prakash Jain

Cinitha Ajith

Gaetano Della Corte

Michal Jandera

Mitsuyoshi Akiyama

Rajesh Prasad Dhakal

Xiaodong Ji

Mehmet Akköse

Luigi Di Sarno

Huanjun Jiang

M. Shahria Alam

Fabio Di Trapani

Lin Jing

Nicholas A. Alexander

Daniel Dias-da-Costa

Venkatakrishnan Kalyanaraman

Yu-Feng An

Florea Dinu

Hemant Kaushik

Sivakumar Anandan

Samir Dirar

Surendra Kumar Kaushik

Ioannis Anastasopoulos

Sekhar Dutta

Liao-Liang Ke

Mahmud Ashraf

Matthew Eatherton

Zbynek Keršner

Farhad Aslani

Evangelos Efthymiou

M Reza Kianoush

Francis TK Au

Wael El-Dakhakhni

Peter Koteš

Ashraf Ayoub

Ana Espinos

Merih Kucukler

Arash Azadeh

Mark Evernden

Sashi Kunnath

Yu Bai

Ciro Faella

Thomas Löhning

Patrick Bamonte

Jiansheng Fan

Nikos Lagaros

Cilmar Basaglia

Cheng Fang

Dominik Lang

Alemdar Bayraktar

Ahmed Farghaly

Deuck Hang Lee

Jurgen Becque

Mohamed Farhat

Sutat Leelataviwat

Abdeldjelil Belarbi

Behzad Fatahi

Janet M Lees

Rita Bento

Peng Feng

Christian Leinenbach

Adriano Bernardin

Jian Feng

Bing Li

Sherif Beskhyroun

Miguel Fernández Ruiz

Kefei Li

Turhan Bilir

Paulo Flores

Guochang Li

A. H. M. Muntasir Billah

Julio Florez-Lopez

Wei Li

Colin Billington

Dora Foti

Fei-Yu Liao

Luke Bisby

Stavroula D Fotopoulou

Abbie B. Liel

Leon Black

Michalis Fragiadakis

J Y Liew

EDITOR-IN-CHIEF

Dionysios Bournas

Raoul Francois

Andrew Liew

Leroy Gardner

Franco Braga

Fernando Fraternali

Gian Piero Lignola

Jianguo Cai

Khaled Galal

James Lim

ASSOCIATE EDITORS

Alfredo Camara

Wei Gao

Peiyang Lin

Mark Bradford

Colin Caprani

Francois Gautier

Xinpei Liu

Lin-Hai Han

Sandro Carbonari

Siddhartha Ghosh

Siwei Liu

Tim Ibell

Donatello Cardone

Agathoklis Giaralis

Alessandra Longo

Jason Ingham

Katherine Cashell

R Ian Gilbert

Sergio Lopes

Sara Cattaneo

Indrani Gogoi

Adelino Lopes

GUEST EDITOR

Liborio Cavaleri

Charles H Goodchild

Joseph Loughlan

Nuno Silvestre

Omar Chaallal

Zdzisław Gosiewski

Paulo Lourenco

Tak-Ming Chan

John Graham

Xinzheng Lu

REVIEWERS

Sylvain Chataigner

Rishi Gupta

Yaozhi Luo

Mike Banfi

Siauchen Chian

Madhar A Haddad

Colin C. MacDougall

Mark Bradford

Jiunnshyang Chiou

Muhammad Hadi

Lorenzo Macorini

Dinar Camotim

Chang-Geun Cho

Ehab Hamed

Gregory MacRae

Dennis Lam

C Z Chrysostomou

Trey Hamilton

Gennaro Magliulo

Janet Lees

Felice Colangelo

Hong Hao

Mahen Mahendran

Guo-Qiang Li

Marco Corradi

Jiping Hao

Damodar Maity

Jeffrey Packer

Mauro Corrado

Mohammad Amin Hariri-Ardebili

Triantafyllos Makarios

Esther Real

Joao Correia

Kent Harries

Christian Malaga

N E Shanmugam

Daniel Cox

Richard Harris

George C. Manos

Jin-Guang Teng

Jacques Cuenca

Amin Heidarpour

Justin Marshall

EDITORIAL ADVISORY GROUP Allan Mann Don McQuillan Chris O’Regan Angus Palmer Simon Pitchers REVIEWERS Tony Bassett Angus Cormie Brian Ellis David Evans Ian Feltham Peter Finnegan Ian Firth Richard Harris John Lyness Ali Manafpour David Rolton Geoff Sellors Brian Smith Dimitris Theodossopoulos Peter Walker

Structures The Institution would also like to thank all of the following who have contributed to the Structures peer-review process during 2014 and 2015.

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José-R Martí-Vargas

Adrian Page

Anastasios Sextos

Aneta Ustrzycka

Joao Martins

Kevin Paine

Bahram Shahrooz

Christina Völlmecke

Mark Masia

Dan Palermo

Therese Sheehan

Hamid Valipour

Fabio Mazza

Alessandro Palmeri

Gang Shi

Els Verstrynge

Finian McCann

Peng Pan

Nadeem Ahsan Siddiqui

Paulo Vila Real

Jason McCormick

S Pantazopoulou

Josivan Silva

Phillip Visintin

Gabriele Milani

Chris Pantelides

Nuno Silvestre

Francesco Vivio

Thomas H Miller

Honggun Park

Bhrigu Singh

Marco Vona

Kyungwon Min

M Pecce

Scott Smith

Zora Vrcelj

Cristopher Moen

Fernando Pelisser

Eleni Smyrou

Yuan-Qing Wang

Massood Mofid

Carlo Pellegrino

Chongmin Song

Facheng Wang

Bashar Mohammed

Yong-Lin Pi

Tian Yi Song

Xiuyong Wang

George Morcous

Rui Pinho

Luigi Sorrentino

Jan Wastiels

Guido Morgenthal

Marco Pisani

Dan Stancioiu

Brad Weldon

Christopher Morley

Amir Poursaee

Mark G Stewart

Rou Wen

Evgeny Morozov

Marco Preti

Tim Stratford

Lydell Wiebe

Masoud Motavalli

Raffaele Pucinotti

Mingzhou Su

Chengqing Wu

Giuseppe Muscolino

Mohamad Qatu

Mei-Ni Su

Yufei Wu

Aman Mwafy

Sertong Quek

Luis Suarez

Lili Xie

Farzad Naeim

Karthik Ramanathan

Haluk Sucuoglu

Pei-Yu Yan

Roberto Nascimbene

Maria Ramirez

John Summerscales

Jun Yang

Mohannad Naser

Gianluca Ranzi

Zhiguo Sun

Jie Yang

Giacomo Navarra

Kim JR Rasmussen

Andrea E Surovek

Kang-Sheng Ye

David Nethercot

Prishati Raychowdhury

Alberto Taliercio

Yong Ye

Charles D Newhouse

Ghani Razaqpur

Zhong Tao

Stylianos Yiatros

Hasan Nikopour

Paolo Ricci

Andreas Taras

Hao Zhang

Taichiro Okazaki

Fey Rob

Arturo Tena-Colunga

Bill Zhang

Kutay Orakcal

Manuel L Romero

Solomon Tesfamariam

Guodong Zhang

John Orr

Ana Ruiz-Teran

Marios Theofanous

Jun Zhang

Ashraf Mohamed Osman

Daisuke Saito

Tetsuo Tobita

Ou Zhao

Yu-Chen Ou

Tatsuo Sawada

Timothy H Topper

Zuo-Zhou Zhao

Togay Ozbakkaloglu

Kostas Senetakis

Jean-Michael Torrenti

Alexandr Zhemchuzhnikov

Osman Ozbulut

Junwon Seo

Alireza Ture Savadkoohi

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TheStructuralEngineer January 2016

Upfront Industry news

SCOSS Alert – Wind Adjacent to Tall Buildings SCOSS has published a new alert – Wind Adjacent to Tall Buildings – because reports to CROSS have raised concerns about the design of temporary works to resist wind loading in urban environments. This alert is aimed at those who design or commission temporary structures that are subject to wind loading and adjacent to tall buildings. Although reports relate to urban environments, temporary structures adjacent to tall buildings in exposed locations may also be adversely affected. Read the full alert at: www.structural-safety.org/media/386216/scoss-alert-wind-adjacentto-tall-buildings-december-2015-final-2-.pdf The Structural-Safety website (www.structural-safety.org) combining CROSS (Confidential reporting on structural safety) and SCOSS (Standing committee on structural safety) has newsletters, a database of reports, information on how to report, alerts and other publications.

Leeds firm first structural engineers to achieve BRE BIM certification A Leeds-based firm of civil and structural consulting engineers is celebrating becoming one of just four companies in the country, and the first practice of civil and structural consulting engineers, to be awarded with a coveted certification. The Building Research Establishment (BRE) Building Information Modelling (BIM) Level 2 Business Systems Certification has been awarded to Adept following a stringent assessment process. The firm is therefore recognised as successfully being able to implement and utilise advanced 3D modelling tools in strict compliance with the Government’s strategy. Adept’s managing director, Erol Erturan, a

BRE BIM Accredited Professional, said: “BIM is a great way of demonstrating to clients that we have the right procedures in place at every level to deliver what are very rigorous Government requirements. It also simplifies the tendering process, as once a business is BIM certified its competence levels are guaranteed. “We are now one of just a handful of firms that have achieved this top BIM certification, which is a fantastic achievement – especially as the majority of small to medium-sized businesses are not at all prepared for the introduction of BIM Level 2 and face being frozen out of Government contracts as a result.”

National BIM survey launched NBS has launched its sixth National BIM Survey, which has become recognised as the industry’s most comprehensive look at the use of Building Information Modelling (BIM). The survey is supported by a broad range of professional bodies. Since 2011, the NBS National BIM Survey has charted the rise in the use and awareness of BIM, as well as highlighting the challenges people face. This year’s survey has been timed in order to get a real picture of how the Government mandate has affected that adoption. A vital resource for UK construction

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professionals and policy makers, the 2015 survey found awareness of BIM was almost universal at 95%, yet the adoption figures reported a slight fall – from 54% to 48%. The report suggested that this could be because the “Late Majority” are late to follow on from the Early Adopters and Innovators, so it will be interesting to see if adoption has accelerated in the last 12 months as the mandate starts to loom. You can complete this year’s NBS National BIM Survey at http:// surveys.ribaenterprises.com/wh/s. asp?k=144777062858. The results of the

NBS survey finds construction disputes still as prevalent as ever NBS has revealed the results of its third major survey into construction contracts and related legal issues. The results show that despite market buoyancy the number of disputes within the construction industry remains unchanged in recent years. In 2012, 90% of respondents thought the number of disputes in the construction industry had increased or stayed the same, and in the 2015 survey that figure was the same, with extensions of time being cited as the main cause. Other aspects of the results were more encouraging, with 62% of respondents reporting that they have been involved in some collaborative working in the last 12 months and most (81%) believing it enabled information sharing and reduced the number of disputes that arose (65%). Building Information Modelling (BIM) has been introduced to address one of the major barriers to collaborative working – the lack of clear definition of responsibilities – but the report suggests that the legal framework needs to evolve to recognise and accommodate the changes this brings. Only 14% of those taking part in the survey currently have BIM fully integrated into contracts. The research also concluded that there have been significant changes in the forms of appointment that people use. The use of bespoke contracts has risen from 42% in 2011 to 51% in 2015 and use of the NEC Professional Services Contract has risen from 15% to 37% over the same period. Organisations are increasingly using contracts that are better suited to higher value, collaborative projects. Figures provided by NBS suggest that there has been an increase in the use of NEC and FIDIC contracts, while use of JCT contracts has fallen. The full report can be viewed at: www.thenbs.com/pdfs/nbs-contracts-andlaw-report-2015.pdf

survey will be published in Spring 2016. The results and commentary from last year’s survey are available at: www.thenbs. com/topics/bim/articles/nbs-national-bimreport-2015.asp.

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Features Articles with a broad scope often accompanying a significant Institution award or event.

16 Constructing the future – the role of bearings In this article, Phil Burge of SKF (U.K.) Ltd describes how sophisticated bearings systems are helping to keep a variety of cutting-edge civil and structural engineering projects in working order: whether it’s adjusting an enormous telescope, ensuring that a church bell keeps ringing, or moving the immense doors on an aircraft hangar, each comes with a challenge of its own.

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Feature Use of bearings

Constructing the future – the role of bearings Phil Burge Country Communication Manager, SKF (U.K.) Limited

Civil engineering projects – whether a church bell or a drawbridge – are built on a grand scale. As such, they often require very special bearings. The general perception of bearings is tiny silver balls, whizzing around very quickly in fast-moving industrial machinery such as spindles, fans and drives – or in consumer products such as roller skates and skateboards. However, bearings are not always fast and small. In civil and structural engineering, they are usually the exact opposite – large, slow-moving and capable of supporting huge loads (Figure 1). Some of the most sophisticated bearings systems are helping to keep a variety of cutting-edge projects in working order: whether it’s adjusting an enormous telescope, ensuring that a church bell keeps ringing, or moving the immense doors on an aircraft hangar, each comes with a challenge of its own.

Sliding doors The UK’s Building Research Establishment (BRE) houses the largest enclosed



Figure 1 Bearings for civil engineering are capable of supporting huge loads

laboratory in the world in the Cardington Airship Hangar. Built in 1928, it can accommodate huge structures – such as the enormous R100 airships that were designed by Barnes Wallis. Following a refurbishment programme, BRE engineers began to experience difficulties sliding open the southern hangar door, which is 55m high and 24m wide and weighs 470t. BRE needed an urgent solution, because the door needs to be opened and closed almost every day. To begin with, the doors – which run on a twin-track system using four sets of fourwheeled bogies mounted on each track – were raised using eight 110t hydraulic jacks, which allowed the wheel bogies to be removed. It took one week to remove each one. An inspection of the bogies on the inner track revealed that the existing bearings had degraded, which had created flats on some of the 760mm diameter wheels, due to them skidding rather than rotating. One bearing was removed, and found to be a poorly

constructed needle roller bearing design that had disintegrated. Most rollers were in a similar condition, while the side plates were almost entirely worn away. BRE could have tried to replace the bearing arrangement with a similar system, but was concerned about the degree of wear on the side plates. So rather than fit an identical system, which might go the same way as the original, it adopted a new design using heavy-duty spherical roller bearings. Adapting and reusing some of the existing bogie components helped to make the new arrangement cost-effective. Engineering analysis revealed that the inner bogies were carrying three-quarters of the door’s weight, equivalent to a load of 33t on each wheel. Track measurements showed that the side plate wear was caused by a difference of 20mm in the height level of the inner and outer rail tracks. To accommodate these massive loads, the refurbishment included detailed redesign plus shaft, housing and wheel re-machining, plus complete assembly of wheel units. By the end of the project, all 16 wheels on four bogies – for one door – had been refurbished, and 32 new bearings fitted. To further save cost, existing shafts and wheels were incorporated into the new design where possible. The new arrangement ensured that all loads were held within the wheeled units – containing both lateral forces and high static loads. This prevented a repeat of the original wear problems. Careful coordination of the removal and re-machining of the wheel sets ensured that the door remained in operation during the redesign. The huge doors now open and close easily, with bearings that are likely to last for at least another 50 years.

Lifting boats On an even larger scale, slewing bearings play a huge part in an enormous water wheel that transfers boats between two canals in Scotland.

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Figure 2 The Falkirk Wheel uses a pair of 4m diameter, three-row slewing bearings

The Falkirk Wheel (Figure 2), the only structure of its kind in the world, is the centrepiece of the Millennium Link – a £78m project that reconnects the Forth and Clyde Canal with the Union Canal between Glasgow and Edinburgh. It does this by raising and lowering boats by 25m, a process that takes four minutes. The two canals were originally linked by a series of locks, but due to a reduction in commercial traffic they fell into disrepair and it was not feasible to restore them. Instead, a giant water wheel – shaped similarly to a double-headed axe – rotates in a continuous circle, lifting and lowering two 22m long caissons. Each can hold a payload of 300t, which is enough for four boats and the water for them to float on. Supporting the wheel required a new bearing that uses a pair of 4m diameter, three-row slewing bearings – one positioned at either end of the wheel, with outer rings bolted to the support structure and inner

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rings bolted to the arms. The inner ring of one bearing has gear teeth to transmit the drive to the wheel. Each slewing bearing has three rows of cylindrical rollers: one is for the radial load; and two – with smaller rollers – are for the axial loads. This was an unusual solution, because slewing bearings are usually used in applications with heavy axial loads such as large cranes. They were designed to be positioned on a horizontal axis, and cope with the specified combination of radial and axial loads. When fully loaded, the wheel weighs 1800t – producing a radial load of 9095kN per bearing. The wheel is turned by 10 hydraulically driven gearboxes via the geared slewing bearing. The low friction torque of the antifriction bearings means that a rated torque of only 2972kN is needed to rotate the wheel. What’s more, the energy needed to turn the wheel through a half-turn is just 1.5kWh – the amount required to boil eight

kettles of water. The bearings are supplied with their own integral seals and have a life expectancy of 120 years. Additional seals, of 4m and 2.5m diameter, are designed to withstand the heavy-duty conditions, and prevent water ingress. To reduce wear on bearings and other moving parts, operators ensure that the wheel alternates between clockwise and anti-clockwise rotation. As well as the slewing bearings, the design also includes cross-roller bearings to support idler gears that keep the caissons level at all times. The caissons themselves run on a wheel arrangement on circular rails, with each wheel mounted on two sealed spherical roller bearings.

Bridging the gap Spherical roller bearings are supporting a 40t, 30m opening deck on the Pont Y Werin Bridge in South Wales. The bearing units are part of a hydraulic system that can lift

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Feature Use of bearings

The safe, efficient way in which the span moves relies heavily on the bearing units (Figure 3), which must take almost the entire load of the span and withstand the effects of wind forces – which can be very high when the span is fully opened. They must also resist extremes of temperature and the effects of both rain and salt water. Efficient contact seals help to retain internal grease and exclude moisture and other contaminants.

Ringing the bell

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Figure 3 Spherical roller bearing units on the Pont Y Werin Bridge must take almost the entire load of the span and withstand the effects of wind forces

the bridge deck to a vertical position of 75° in just two minutes, in wind speeds of up to 25m/sec. The 130m bridge comprises four equal sections, of which one is a lifting span that maintains a clear 20m navigational channel below. Engineering consultancy KGAL designed a mechanism to control the movement of the lifting span based on two hydraulic

rams, whose base end is hinged by pairs of 440mm diameter spherical roller bearings set into a specially engineered deck trunnion. Extra bearings are fitted at the top of the hydraulic rams, allowing them to pivot smoothly as the span opens and closes. The bearings used for the bridge have symmetrical rollers, two window-type steel cages and an inner ring centred via a floating ring between the two rows of rollers.

Even highly traditional engineering structures need an occasional makeover in order to cope with the modern world. A swinging church bell, for example, can exert a force equivalent to four times its own static weight. Whites of Appleton, the UK’s oldest continually trading bell-hanging company, has a number of high-profile installations, including St Paul’s Cathedral in London, Windsor Castle and Canterbury Cathedral. According to Whites, headstock design has changed enormously over the last century – with timber increasingly replaced by steel and cast iron. What has not changed is the need to choose the right bearing according to bell weight.

Correcting errors – and preventing them What happens when things go wrong? Engineers should not forget that the Titanic was dubbed “unsinkable”, while the ultra-modern (for 1940) Tacoma Narrows Bridge in the USA oscillated in heavy wind and collapsed four months after it was built. Sixty years later, pedestrians walking across the new Millennium Bridge in London caused it to wobble – though in this case, the problem was fixed by retrofitting fluid dampers. Root cause analysis (RCA) is a tried and tested method for identifying the reason behind an engineering problem (Figure 4). Usually, it is applied in response to an accident, but it can also be used as a way of designing out failure – or at least minimising its risk. It is very much a proactive operation. It splits into five main areas: problem identification/understanding; possible cause generation; data collection; possible cause analysis; and cause-and-effect analysis. The first – problem identification – requires tools such as flowcharts and performance matrices to get to the root of the problem and its causes. Using this

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information, a list of possible causes can be generated through methods such as brainstorming – which can identify both problems and their possible solutions. Further to this, methods such as sampling, surveys and check sheets are used to collect reliable RCA data. Possible causes can be analysed through data visualisation, which often reveals that a small number of causes account for the bulk of the problem. The final stage, cause-and-effect analysis, shows that multiple causes can lead to the same problem. The trick is to determine the actual root cause. If sufficient data are available, a probabilistic approach could identify the most likely root cause. The tools available to put RCA into practice are extensive, but the most important thing is to use its principles as a proactive way of introducing necessary actions to prevent accidents and solve problems. At the root of it all is recognising that a problem exists in the first place: if a Figure 4 problem is seen as normal, the situation will Root cause analysis is a tried-and-tested method for never improve. identifying the reasons behind an engineering problem

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At the horizontal position of the swing, the bearings experience a force equivalent to 2.5 times the bell’s static weight. At bottom dead centre, this rises to four times the static weight. This means that bell weight immediately determines what size of bearing is needed. Depending on the exact application, Whites uses one of a number of variants of selfaligning ball bearing – supplied with tapered bores and adapter sleeves for easy mounting and dismounting. These are particularly suited to applications that show misalignment in either the shaft housing or bearing seat. They offer low friction and operating temperatures, reduced vibration and noise levels and – a particular advantage for this type of application – low lubrication needs. The bearings and housings support the bell via two gudgeon pins that extend from either end of the headstock. The assembly is lubricated using a general purpose industrial bearing grease, and completed with Type C felt seals. These suit the semi-external environment and the shaft deflection, and are very good at keeping out pigeon droppings – though this has yet to appear on any specification. It goes to show that, sometimes, a

bearing’s capabilities go beyond the call of duty.

Simulating the High Roller Modelling and simulation can be a key factor in getting the design right, and this was evident in the spindle-and-hub design for the largest observation wheel in the world – the 168m tall High Roller in Las Vegas (Figure 5). Simulation tools were used to evaluate the many factors that influence system behaviour, such as clearance in the assembly, misalignments, supporting structure flexibility and different boundary conditions. The High Roller wheel rotates on a pair of custom-designed spherical roller bearings, each weighing approximately 8.8t. Each bearing has an outside diameter of 2300mm, a bore of 1600mm and a width of 630 mm. The double row spherical roller bearings have 30 rolling elements per row – and a simulation model was used to determine the optimal radial bearing clearance. The structure is based on a 143m diameter tension wheel. As well as the two bearing assemblies, it has four steel support legs, a single braced leg, fixed spindle, rotating hub, tubular rim that is 2m in diameter and 112 locked coil cable

assemblies as spokes. Passenger cabins are mounted on the wheel’s outboard rim and are individually rotated by electric motors to maintain a horizontal cabin floor throughout each full rotation. For the spindle and bearing, there are heavy loads and large housing deformations to be considered: on the observation wheel, loads are 1350t per end; for each of the 56 bottom radial cables, the tension is 132t; for the top 56 cables, it is 47t. Total radial cable tension is 4600t. Design and analysis was split into four phases and used extensive modelling and analysis software to evaluate the complex interaction of all the components in the system and identify key performance indicators. Particular attention was dedicated to the evaluation of the effects of loadings and deformations to the bearing performance in terms of forces and motion. After defining the project and collecting design data in Phase 1, the project moved on to simulation analysis in Phase 2. With a configuration in mind, analysis of bearing performance was carried out using simulation models. The model was built by connecting all types of machine components, such as bearings, shafts, gears and housings. An arbitrary combination of



Figure 5 Engineers on the High Roller in Las Vegas evaluated the effects of loadings and deformations on the wheel’s bearing performance using simulation models

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Ensuring a tight fit Tightening bolts is a mundane – through critical – part of putting together huge structures. Getting this wrong can be a major cause of failure. To try and overcome this, devices such as hydraulic bolt tensioners – either manual or automatic – can ensure it is done in a reliable, repeatable way (Figure 6). The Falkirk Wheel, for example, contains more than 15 000 bolts that are matched up with 45 000 bolt holes. Each of them was tightened by hand. It was originally put together in Derbyshire, dismantled, transported to the site and reassembled. Hydraulic bolt tensioning applies a predetermined axial load to the bolt or stud, and helps to ensure consistency in the face of differing friction coefficients in threads and contact surfaces. Poor assembly is the major cause of assembly failure. In particular, bad or irregular tightening contributes to 30% of all assembly failures, and this rises to 45% when fatigue life is concerned. Potential benefits of using the hydraulic principle to tighten bolts include the facts that: • the tightening preload is accurate and well known, and can be close to the bolt’s elastic limit • it enables simultaneous tightening • tensioners are easier and safer to use than torque wrenches • it lends itself well to automatic machines • it enables good care for the bolted joint assemblies and components • it enables reduction and optimising of bolt diameter • it results in better fatigue behaviour

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Figure 6 Manual or automatic hydraulic bolt tensioners apply a predetermined axial load to ensure that bolts and studs are tightened correctly

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Feature Use of bearings

forces, displacements and rotational velocities can be used to define the loads on the components – which can be special (non-linear) elements, as well as arbitrary elements such as shafts and housings. The latter must have a linear behaviour, and their stiffness and damping properties are obtained using the finite element method. Special reduction methods are applied to reduce the number of degrees of freedom, and so reduce the calculation time for analyses. After this, the modelling looked at the effect of structural flexibility on bearing performance, which involved adding the hub and spindle as fully flexible components to the model before performing further simulations. A key part of the design project was to ensure that the bearing assembly would be able to live up to the conditions expected in the real world – so during Phase 3 the sensitivity of the bearing to changes in boundary conditions and internal geometry was performed. Initial optimisation runs identified the possibility of life improvements by varying the roller profile and the shaft/hub stiffness. An optimal design was chosen, after which further simulations of the various loading conditions were evaluated. At the end of the project, the results of all simulations were used to determine the procedures and equipment needed for the installation. Installation procedure simulations were almost identical to actual field assembly. As predicted, the installation needed hydraulic injection assist in order to mount the bearings properly. The predicted axial drive-up that was required to achieve the final mounted internal clearance was within 2% of the calculated value – a very accurate result given the complexity of the hub design.

Staring into space Making astronomical observations is expensive – and it’s not just a case of scouring the sky in the hope of finding something of interest. Research telescopes must be closely controlled, and frequently repositioned: another job that is improved by accurate bearings. Telescope Technologies Limited (TTL), a spin-off from Liverpool John Moores University, has designed a scaled-down telescope with a 2m reflective mirror, which relies on hydrostatic shoe bearings in its horizontal (azimuth) and vertical (altitude) axis positioning system. The bearings are designed to carry heavy loads – with the three used for the horizontal axis supporting 24t. On this axis, two torque motor drives, with 100:1 gearboxes, move the telescopes no faster than 5°/sec. Two altitude axis bearings carry a load of 12t. Meanwhile, a secondary mirror – which is moved in order to change the focal plane – uses recirculating ball bearings to give free-flowing axial movement. A third moving part of the telescope also needs accurate positioning. The acquisition and guidance box contains all the scientific instruments – and directs light to the appropriate one. It does this by constant – and accurate – repositioning, called the science fold mechanism. A specially machined threaded ball screw gives a repeatability to within 3m. These examples are just a selection of the many and varied applications of bearings in construction. In almost every case, their size, accuracy and load-bearing capability win out over speed – and this is unlikely to change. SKF is a leading global supplier of bearings, seals, mechatronics, lubrication systems, and services which include technical support, maintenance and reliability services, engineering consulting and training. Web: www.skf.com

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Project focus Peer-reviewed papers focusing on the structural engineering challenges faced during the design and build stages of a construction project.

22 Vibration abatement of rectangular, trapezoidal and irregular-shaped joistframed floors, using tuned mass dampers 28 Conservation compendium. Part 14: Dunston Staiths, Gateshead – a case study in timber conservation and repair 32 Baghdad missile-damaged building brought back to life

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TheStructuralEngineer January 2016

Project focus Vibration abatement with TMDs

Vibration abatement of rectangular, trapezoidal and irregular-shaped joist-framed floors, using tuned mass dampers Reza Kashani PhD, PE, DEICON, Inc., USA

Synopsis

A tuned damping solution was developed to mitigate walkinginduced vibration of joist-framed floors in 25 rectangular, trapezoidal and irregular-shaped rooms in an educational facility. The make-up of the floors was concrete on metal deck, supported by open-web steel bar joists. The floors came in various sizes (800–1200sq.ft) and shapes, with the first resonant frequencies in the 6.5–7.5Hz range. Following the measurement of vibration and finite element analysis of the floors, 50 tuned mass dampers (TMDs) (two for each room) were designed, manufactured and installed to effectively address the vibration challenges of the first structural modes of the floors they were designed for. After installation of the TMDs, the effectiveness of the tuned damping solution was evaluated via further measurements. TMDs effectively dampened the first structural modes of the floors in various rooms and lowered their walking-induced vibration to acceptable levels.

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Introduction Wide column spans, along with the use of high-strength material (less of which would provide the required structural integrity), tend to make modern composite and noncomposite floors flexible and oscillatory. Walking (as well as other human activities) can induce high levels of vibration in such floors. When the traditional floor vibration control solutions, such as adding architectural features, mass and/or stiffness to the floor, are either not practical or ineffective, reactive damping provided by tuned mass dampers (TMDs) is used for quieting vibrating floors. A high level of effectiveness, negligible weight penalty and ease of installation make TMDs a cost-effective and non-intrusive vibration control solution for both new and existing floors. In addition, contrary to the damping that can be provided by nonstructural elements such as partitions, raised floors and panelling, which is not readily quantifiable and may not be an option for a space in which a light fit-out is required, TMDs provide predictable damping and can easily be retrofitted. The installation of TMDs on existing floors is the least disruptive (to the occupants) of any floor vibration control solution. Although by no means exhaustive, a sample of research and applied work in tuned damping of floor vibration is cited here. In a laboratory floor structure, Lenzen (1966)1 used a TMD to add damping to a

single mode. Shope and Murray (1994)2 and also Rottmann (1996)3 used several TMDs to control a few modes of an office floor. Others, such as Setareh and Hanson (1992)4 and Webster and Vaicaitis (1992)5 used TMDs to suppress steady-state floor vibration in a number of applications. Setareh (2002)6 studied the use of semi-active TMDs to control floor vibration. Setareh et al. (2006)7 presented the results of the analytical and experimental studies of a pendulum TMD to control excessive floor vibration. Kashani et al. (2014)8 used TMDs to dampen the first two modes of three large balconies in a performing art centre. In addition to the more traditional passive TMDs, active TMDs and proof mass actuators (also known as active mass dampers) have been recently proposed and used for abating floor vibration9,10. These active devices tend to be more lightweight than an equivalent passive damper (with the same effectiveness). Active devices can also be tuned, and add damping, to multiple modes of vibration of the structure. Moreover, they can readily be re-tuned (either automatically using a self-tuning algorithm or manually) to maintain their optimal tuning in the face of change in natural frequencies of the structure. Successful implementation of tuned damping for a floor requires thorough understanding of the system dynamics, including identification of the dominant modes of vibration in terms of their

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Figure 1 First two modes of trapezoidal-shaped floors

of the floors, perceptible vibration was felt, when a single person was walking across and near the middle of the rooms. Stiffening solution As an initial attempt to alleviate the floor vibration issue, the joists in a sample of the rooms were stiffened. This was done by attaching W8 beams to the bottom chord of the joists (similar to adding queen post hangers as suggested in the AISC Design Guide). As in any floor stiffening solution, the goal was to increase the stiffness of the floor and, in turn, raise its natural frequencies. Despite the fact that this solution raised the natural frequencies of the test floors by around 20%, e.g. from 7.4 to 9.1Hz in one of the floors, and thus made the vibration caused by walking less perceptible than before, it did not make it imperceptible. Following this unsuccessful attempt in abating floor vibration sufficiently, a damping solution using TMDs was pursued.



Figure 2 Power spectral densities measured at two locations on floor of room A202

natural frequencies and shapes. Such understanding requires the development of experimentally verified numerical models, which in turn leads to proper sizing and placement of the TMDs. Acceptability of floor vibration The levels of vibration that can be felt strongly by human occupants of structures are generally of no concern to the integrity of the structure. The primary goal of controlling vibration is to ensure comfort of the occupants. The levels that are deemed acceptable vary depending on environment, usage of the space and the individual sensitivity of occupants. Since it is acceleration that causes a force to be felt in the body of the occupants of a structure, the perceptibility of floor vibration is commonly described in terms of accelerations (expressed in terms of the acceleration due to gravity, g). The peak measured and predicted levels of vibration on construction of the joistframed floors, in response to a single person walking, were higher than would be deemed

TSE49_22-26 Project Focus v1.indd 23

acceptable in a typical office/classroom. According to American Institute of Steel Construction (AISC) guidance11, the target performance of the worst-affected areas of the floors, in office-like environments, in response to one person of average weight walking, is 0.5% g. The case where a number of people are present on the floors, sitting or standing, could be less problematic considering the fact that human bodies add damping to the floor.

Description of floors The floors were made up of 2.75in. of concrete on metal deck, supported by open-web steel bar joists spaced at 3ft on centre. The floors came in various sizes (800–1200sq.ft) and shapes (rectangular, trapezoidal and irregular), with the first resonant frequencies between 6.5 and 7.5Hz, falling in the frequency range where human bodies are most sensitive in perceiving vibration. The large joist spacing and small concrete thickness made the floors susceptible to undesirable vibration. Upon construction

Dynamic analysis and testing In order to design and specify the TMDs, reasonably accurate estimates of the dynamic properties of the floors were acquired numerically (using finite element analysis) and experimentally. Shell elements were used to model the floor (concrete) rigidly offset from beam elements used to model the floor joists. The offset is half the joist depth plus the height to neutral axis of the concrete decking. The dynamic modulus of elasticity was used for the concrete. Finite element modal analysis of the floor models allowed for the prediction of the natural frequencies, their corresponding mode shapes and modal masses. On-site testing enabled the structural model to be verified (and adjusted if need be) and the inherent level of damping in the structure to be measured. The correlated model was then used to assess the effectiveness of the proposed solution. When developing a finite element model of a floor for such purposes, it is good practice to include adjacent structure from the floor area that is being investigated8. The extent of this inclusion depends on the floor system itself. Once the model is built, this assumption can be checked by looking at the modes and the areas that respond in each mode. If the modes of interest do not have significant participation at the boundaries of the model, then the extent of the adjacent structure included in the model can be deemed sufficient. If not, then more adjacent structures should be added until the modes of interest are no longer affected by further additions to the model.

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Project focus Vibration abatement with TMDs



Figure 4 Measured (blue/solid line) and identified second-order FRF of TMD

S

Figure 3 Schematics of viscous damper’s

a) Maxwell model

b) TMD suspension

c) TMD

TSE49_22-26 Project Focus v1.indd 24

The finite element models of the floors were experimentally verified by measuring the natural frequencies of their lowfrequency modes. A heel-drop simulator was used to perturb the floors at locations where the perturbation coupled most effectively with the target modes. At each excitation location, heel-drop perturbations were repeated three times, and accelerations at two locations on the floor were measured simultaneously (and averaged to produce statistically valid data). Figure 1 shows the shapes of the first two modes and their corresponding frequencies for the floors of the two adjacent, trapezoidal-shaped classrooms, predicted by finite element analysis. The modal masses (normalised to maximum vertical displacement of the mode) were 8 tons for both modes. The measurement locations, A (at the centre of the floor) and B (at ¼–¼ point on the floor), are also highlighted on Fig. 1. Figure 2 shows the power spectral densities of acceleration measured at the two locations of A and B, shown in Fig. 1, in one of the trapezoidal rooms (room A202). Note that point A is almost at the centre of the room and point B is located halfway between point A and the long wall of the room. The presence of both modes, especially at location B, is quite clear from Fig. 2. The natural frequencies of all the floors, including those of room A202, measured experimentally, were in very good agreement with those predicted

numerically. The floor system’s mode shapes were not expected to be particularly different from the predicted one shown in Fig. 1. A certain amount of variation could be expected in terms of degree of participation of connected areas, but not to a degree that would significantly affect the results. The purpose of matching the model to the results was to have an updated analytical platform to work from when assessing the effectiveness of a potential solution. Matching the frequencies of the modes was therefore deemed sufficient, and was achieved by varying the modulus of elasticity of the concrete, which can be expected to vary in practice depending on the amount of cracking.

Design and realisation of TMDs Once the floor finite element models had been verified against the initial testing, they were used to determine the required parameters of each TMD according to the following procedure: • Choose a TMD mass. A larger mass will generally yield more damping and higher bandwidth (to provide robustness in a potential off-tuned case), but an optimal choice that balances requirements, buildability and cost can be made by studying predicted achievable damping for various amounts of mass. Equations for achievable damping can be found in work by Den Hartog (1956)12, among others, which relates to the optimum parameters for adding damping to undamped systems. These equations are

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Figure 5 Installation of two TMDs underneath floor of room A202

shown in Fig. 1 – it was felt that two smaller TMDs were a better option than one large TMD. Additionally, the use of two smaller TMDs alleviates the concern over the overloading of the bar joists.

also appropriate for use with lightly-damped structures. • Calculate the optimum frequency for the TMD, given the mass ratio (the ratio of the mass of the TMD to the modal mass of the target mode of the structure) and the damping inherent to the structure. • Calculate the optimum damping ratio for the TMD, using the tuning frequency and mass ratio of the TMD. • Adjust the optimum parameters according to experience to ensure robustness of the solution. The optimum, perfectly tuned parameters may not be the best when considering that the frequencies of the structural modes may drop somewhat, for reasons such as further cracking of the concrete slab, over the life of the structure. For this reason, the optimum damping calculated using the procedure outlined above was in the 23–28% range.

Make-up of TMDs The TMDs were made up of a stack of 1in. steel plates constituting the mass and a suspension system comprising of eight precompressed coil springs and two laminar flow viscous dampers. The spring rates were specified to deliver the desired tuning frequencies. Adequately high damping ratios ensured that enough energy dissipation capability is built into the TMDs so that they effectively damp the vibration of their target modes across an acceptable range of tuning frequencies. The laminar flow viscous dampers consisting of a moving part immersed in a highly viscous, nearly temperatureindependent fluid, were used to deliver the required damping; see Kashani et al. (2012) for more on such viscous dampers8. Laminar flow viscous dampers exhibit mainly viscoelastic, frequency-dependent dynamic behaviour, the parameters of which depend on both the properties of the viscous fluid and the geometry of the device. The Maxwell model of Figure 3a was used to mathematically describe

such dampers. The parameters of this model were evaluated experimentally. Figure 3b depicts the parallel combination of the spring (k) and damper (c and k2) making up the suspension of the TMD; and Figure 3c shows the schematic of the TMD. Fabrication and tuning Following the assembly of each TMD, it underwent testing to evaluate its damping ratio and natural frequency. The evaluation was done by a) experimentally measuring the frequency response function (FRF) mapping the force perturbing the mass of the TMD to the acceleration of the mass; b) comparing it with the frequency response of an analytical, viscoelastically damped, second-order system; and c) adjusting the parameters of the second-order system until the analytical FRF had a near perfect fit to the measured FRF. The natural frequency and damping ratio of the analytical model that resulted in a match between the two FRFs were considered to be the natural frequency and damping ratio of the TMD under evaluation/testing. Figure 4 shows the experimentally measured and analytically identified FRFs for one of the TMDs. Note that the frequency at which the phase angle lags 90° behind the low-frequency phase angle is viewed as the natural frequency of the TMD.

S

Figure 6 Power spectral densities and corresponding time traces of acceleration, without and with TMDs operational, measured at points A (centre point on floor) and B (¼–¼ point on floor) of room A202

Two TMDs were specified for each of the 25 rooms (50 TMDs total), varying in size from 250kg to 500kg, depending on the size of the floors they were assigned to. These TMD sizes provided the mass ratios (TMD mass to the first modal mass of the floor) large enough to offer good robustness against the possibility of the dampers becoming detuned if the frequencies of the floors were to shift, as may occur due to additional cracking caused by loading of the floors by large classroom sizes. Since TMDs work best when placed as close as possible to the points of maximum motion of their target modes – in the case of room A202, in the vicinity of points A and B

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Due to the tight tolerances on the stiffness of the springs and to having accounted for the viscoelasticity of the laminar flow viscous dampers, the natural frequencies of the TMDs were measuring very closely to their desired tuning frequencies. The slight deviation of the theoretical and measured frequencies in some of the TMDs was addressed by adding/removing small 7kg tuning plates to/from the TMDs. The damping ratios of the TMDs were between 19 and 25% critical, depending on their mass ratio, which complied with the design specification. Following the completion of the evaluation/adjustment of the TMDs at the shop, they were tagged for their corresponding installation location, locked and shipped to the site, where they were installed underneath their corresponding floors at designated locations. Figure 5 shows a pair of 400kg TMDs installed underneath the floor of the trapezoidal room A202.

Project focus Vibration abatement with TMDs

Acknowledgements The author would like to thank Nicholas Constantine PE of PERDA, Inc. and Ron Spade PE of MKC Associates for fruitful discussions during the course of the project and also the design of the installation scheme of the TMDs.

References E1

Lenzen K.H. (1966) ‘Vibration of steel joist-concrete slab floors’, Eng. J. AISC, 3 (3), pp. 133–136

E2

Shope R.L. and Murray T.M. (1994) ‘Using tuned mass dampers to eliminate annoying floor vibrations’, Proc. Structures Congress XIII, Boston, USA, 2–5 April, New York, USA: ASCE, pp. 339–348

E3

Rottmann C. (1996) The use of tuned mass dampers to control floor vibrations, M.S. thesis, Blacksburg, USA: Virginia Polytechnic Institute and State University

E4

Setareh M. and Hanson R.D. (1992) ‘Tuned mass dampers for balcony vibration control’, J. Struct. Eng., 118 (3), pp. 723–740

E5

Webster A.C. and Vaicaitis R. (1992) ‘Application of tuned mass dampers to control vibrations of composite floor systems’, Eng. J. AISC, 29 (3), pp. 116–124

E6

Setareh M. (2002) ‘Floor vibration control using semi-active tuned dampers’, Can. J. Civil Eng., 29 (1), pp. 76–84

E7

Setareh M., Ritchey J.K., Baxter A.J. and Murray T.M. (2006) ‘Pendulum tuned mass dampers for floor vibration control’, J. Perform. Constr. Facil., 20 (1), pp. 64–73

E8

Kashani R., Pearce A. and Markham B. (2014) ‘Tuned damping of balcony vibration’, J. Perform. Constr. Facil., 28 (3), pp. 450–457

E9

Hanagan L. and Murray T. (1997) ‘Active control approach for reducing floor vibrations’, J. Struct. Eng., 123 (11), pp. 1497–1505

E10

Hanagan L.M., Murray T.M. and Premaratne K. (2003) ‘Controlling floor vibration with active and passive devices’, The Shock and Vibration Digest, 35 (5), pp. 347–365

E11

Murray T., Allen D. and Ungar E. (1997) Steel Design Guide 11: Floor Vibrations Due to Human Activity, Chicago, USA: AISC

E12

Den Hartog J.P. (1956) Mechanical Vibrations (4th ed.), New York, USA: McGraw-Hill

In situ verification of TMDs As the installation of the TMDs on each floor was completed, the TMDs were fine-tuned (by adding/removing small 7kg steel plates) using the following procedure: 1. With both the TMDs locked, the accelerations at two points (the centre of the room and halfway between the centre and the long wall) on the floor in response to heel-drop perturbations (at the vicinity of the centre of the room) were measured. 2. The TMDs were unlocked, one at a time, and the accelerations at the same locations in response to the same perturbations as those of step 1 were measured. These measurements were used to judge if any finetuning was needed. Figure 6 shows the power spectral densities and time traces of the measured acceleration on the floor of the trapezoidal room A202, with two TMDs installed, in response to heel-drop perturbation. The TMDs were locked first and then unlocked one at a time. The damping effect of unlocking the first of the two TMDs can be seen by comparing the red and blue traces in Fig. 6. Comparison of the red traces (corresponding to having only one TMD unlocked) and black traces (corresponding to having both TMDs unlocked) indicates that bringing the second TMD online doubled the damping effectiveness of the treatment. The careful specification, extensive analyses of the floors with and without TMDs, precise manufacturing and shop tuning of the TMDs ensured that they arrived on site with near optimal tuning. Due to the flexibility built into the design of the TMDs, it was possible to add/ remove a small amount of mass to/from some of the TMDs on site to optimise their performance even further. It is evident from Fig. 6 that the TMDs quieted their target modes very effectively. The measured data on the floors of the other 24 rooms, following TMD installation, showed the same effect. In addition to the objective experimental evaluations shown in Fig. 6, the effectiveness of the TMDs was subjectively evaluated by having different people walking (at different paces) on the floors and seeing whether different subjective evaluators standing at the centre of the floor perceived any vibration. None of the subjective evaluators perceived any objectionable vibration.

Summary The application of tuned damping for quieting the perceptible floor vibration of 25 classrooms at an educational facility was presented. Numerical and experimental studies of the floors were conducted, and the results were used to size the TMDs. Fifty passive TMDs were built and installed underneath the floors of the 25 classrooms (two TMDs per room). The TMDs effectively absorbed the oscillatory energy of the structure and dissipated it internally, lowering the walking-induced vibration to acceptable levels.

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Project focus Dunston Staiths

Conservation compendium Part 14: Dunston Staiths, Gateshead – a case study in timber conservation and repair

This article forms part of the Conservation compendium, which aims to improve the way engineers handle historic fabric through the study of historic materials, conservation philosophy, forms of construction and project examples. Articles in the series are written by Conservation Accredited Engineers. The series editor is James Miller.

coal from railway wagons into ships, and the Dunston Staiths (Figures 1 and 2) were the largest timber structure in Europe at the end of the 19th century. Their repair history has been reasonably well documented2 and so they provide a good case study for timber deterioration, selection of repair species and strength analysis. Construction of the North Staiths was completed in 1893 on the south side of the River Tyne just upstream from Gateshead. There was berthing for three ships on the riverside. In 1903 increased demand required three more berths to be constructed on the south side. This included duplicating the first Staiths and excavating a large tidal basin between the first Staiths and the riverbank, which allowed several ships to moor while waiting to load. Output from the Dunston Staiths in 1938

Charles Blackett-Ord CEng, FICE, Engineer Accredited in Conservation (CARE) and Director of Blackett-Ord Conservation Limited, Cumbria, UK Introduction The previous article in the Conservation compendium provided an introduction to common repairs and strengthening of structural timbers in historic buildings1. This article continues by illustrating how structural timber fared at the Grade II listed Dunston Staiths in northeast England. The River Tyne has been a major discharge port for coal from the UK’s Northumberland and Durham coalfields for centuries. Staiths were constructed near the mouths of navigable rivers as a means of discharging

RIVER TYNE

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Figure 1 General arrangement of Dunston Staiths

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TIDAL BASIN

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SOUTH STAITHS

was around 4M tonnes each year; this dropped to 2M tonnes by 1943, and by the early 1970s to less than half a million tonnes. The North Staiths were extensively repaired in the 1970s, but the National Coal Board decided to close the Staiths in 1980. By 1984 the Staiths were totally derelict, and in 1985 one of the conveyor gantries collapsed and the structure suffered badly from arson attacks and neglect. Feasibility studies and structural appraisals were undertaken throughout the 1980s with a view to dismantling parts of the structure and re-using the reclaimed timber to repair the remainder, and this culminated in a major repair scheme which was completed for the Gateshead Garden Festival in 1990. However, subsequent lack of maintenance and more arson attacks allowed further decay to take hold. The Tyne & Wear Building Preservation Trust took over ownership, and in 2012 a further repair programme was planned with funding from English Heritage and the Heritage Lottery Fund. This programme is now virtually complete.

CYCL

SILT LEVEL ROCK & SHRUB

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NORTH STAITHS

Description

PLAN ON STAITHS

0

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100m

SOUTH STAITHS

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LONGITUDINAL ELEVATION OF NORTH STAITHS DUNSTAN STAITHS GENERAL ARRANGEMENT FIGURE 1

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Dunston Staiths are a scheduled monument and a Grade II listed building. The Gateshead Garden Festival left the structure in sound structural condition and safe for public access. The work at that time included the demolition of most of the South Staiths, including withdrawing all the associated piles, and providing a low-level access deck on the part that was retained. The North Staiths remain largely complete. Steel and timber stairs were provided in two locations to give access to the top of the North Staiths from the low-level deck of the remaining parts of the South Staiths. It is the North Staiths that have been the

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MODERN STEEL STAIRCASE

GROUND LEVEL

GREENHEART PILES

CROSS-SECTION THROUGH FRAME 4 (LAND BASED)

TYPICAL REPAIRS

subject of the recent repair programme. The Staiths comprise a simple structural framework of 98 trestle frames on timber piles at 5.3m centres, supporting a timber deck spanning between the frames, with a width varying between 8m and 12m. There are additional intermediate frames to carry six steel discharge gantries and hoppers. The deck is inclined upwards from the land end at a gradient of 1 in 90, and the height of the furthest end above the water is about 12m. There is cross-bracing in both directions, the longitudinal bracing taking in three frames, which results in some very long lengths of timber, although some are in two parts spliced together. The main frames are composed of four or more vertical or inclined posts 305mm × 305mm in section on 325mm × 325mm timber piles. The main crossheads at deck level and the main longitudinal sections are two layers of 305mm × 305mm timber, and the secondary edge beams, bracings etc. are 305mm × 150mm or 225mm × 150mm. The deck is formed from 305mm × 75mm thick planks, nailed to the longitudinal beams. Structurally, the design is well thought out, in that there is a cross-beam on top of the piles, which is the base beam of the trestle, and the cross-head sits on top of the posts, so all the loads on the trestle are in compression only, apart from the crossbracing, which is bolted onto the side of the frame. The timbers are held together with iron straps and bolts.

Repair programme The recent repair programme has been carried out by Owen Pugh Ltd as the main contractor, under Blackett-Ord Conservation

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W

CROSS-SECTION THROUGH FRAME 36

Engineering’s design and direction, with input from BM TRADA on the timber testing. The work is partly based on the recommendation of an earlier report by Royal Haskoning, prepared in 2012. It was accepted at an early stage that it would be impossible to fund repairs to the whole structure, so of the 98 frames only frames 1–8, which are land based, and frames 32–39, which are near to the stairway put in for the Garden Festival, would be repaired at this time (Figure 3). The areas selected for repair were those that had been damaged by fire and timber decay and included the lower parts of the frame posts at the land

Figure 3 Typical repairs

KEY

TIMBER TO BE REPLACED

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Figure 2 General view of North Staiths

end (Figure 4) and the main deck beams and frame cross-heads of frames 32–39 (Figure 5). In the latter case, a major cost was the scaffolding and crash deck required to be built beneath the deck, and the need for dismantling parts of the deck and upper structure in order to get at the frames below (Figure 6). A micro-drill survey of the deck structure was carried out by BM TRADA. This was chiefly required so that the deck could be analysed for its capacity to carry construction loads during the repair programme, and small fire appliances in the future. A visual inspection had confirmed that the deck

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could carry the anticipated pedestrian loads that would be required for public access, in part because the deck planks were in good condition and could, if necessary, span over defective beams. Also taken into account was the original design loading, which was for fully laden coal wagons on two rail tracks, which was substantially more than any possible future loading. It soon became apparent that timbers that looked sound externally could have very considerable internal decay. In some cases this resulted from the previous preservative treatment only penetrating a few millimetres, and rot setting in from the exposed end grain. This was particularly evident in the Douglas fir balustrading fence posts and handrailing (Figure 7), which – away from end grain exposure – were perfectly sound. The rot in the main deck beams started from the top, where the 20mm gap between the deck planks allowed water to sit. BM TRADA’s condition survey with a micro-drill tested main deck support beams by drilling down from deck level (there being no access below). The main deck beams comprised two 305mm × 305mm beams on top of each other, and an extended drill bit allowed the lower one to be tested also. The survey tested 206 upper deck beams in 752 locations: severe decay was noted in 17% of these locations; but severe decay was found in at least one location in 36% of the beams. The lower beams were tested in 100 locations and this revealed 14 positive results where the upper and lower beams had severe decay in the same locations (in the centre or at the ends). In some locations there was

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Figure 4 Repairs to land-based frame

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Project focus Dunston Staiths

severe decay on the lower beams where the upper beams were sound, which is more relevant to the shear strength at each end of the upper beams, rather than their bending strength. Following this testing, it was found to be possible to fence off areas of doubtful strength so that construction traffic could be confined to the less severely decayed areas. Timber decay can be very localised, particularly at the bearing ends of beams where there may be exposed end grain, and micro-drilling, of necessity, has to be selective. With timber of this size, up to half a dozen drillings may be needed for complete satisfaction that there is sufficient sound timber remaining in any one location. In fact, in spite of several visual inspections and the micro-drilling, one of the cross-head beam ends failed unexpectedly under its own weight during the course of the repair contract. Where possible, the deck beams were replaced as whole beams, spanning between the frames, and this necessitated taking up the deck. The cross-head repairs did not usually need whole beam replacement and so halved joints were used between the old and the new, as was the case with the vertical posts, and these were bolted with stainless steel bolts. Diagonal bracings were repaired using scarf joints. A significant number of repairs were required where the frame cross-bracing was fixed to the frame posts, where corrosion of the bolts had split the timber. In most cases the old bolts could be removed and replaced with stainless steel, with a secondary cross-

bolt to close the split. Where it was not possible to remove the old bolt, new ones were inserted close by. Where it was not possible to insert the secondary bolt, where access for drilling was impeded by other members, large, toothed timber connectors were used under the plate washers to help hold the split together. Where corroded bolts were left in situ there remained a risk of future corrosive expansion, and hence more splitting of the timber, but for the medium term this was prevented by the cross-bolting.

Selection of timber species Considerable thought was given to the timber species to be used in the repairs. The original timber was greenheart for the piles and Baltic pine or pitch pine for the superstructure. The repairs in the 1970s and 1980s used Douglas fir. The Heritage Lottery Fund required new timber to be sourced from sustainable forests, which restricted the species available, and there is published guidance on species selection3. It was very noticeable on the structure that the decking, for instance, was in excellent condition (apart from a few isolated planks that needed replacement) whereas the lowerlevel walkways, which were evidently in sound condition at the time of the Garden Festival, had decayed to the point of collapse. It was concluded that the difference was due to the presence or not of preservative treatment. Although Douglas fir is not now generally considered to be receptive to preservative treatment, the deck planks had a chromated copper arsenate (CCA)-type preservative and

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Figure 5 Typical timber decay in deck support structure

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Figure 7 Rot in handrail post

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Figure 6 Repairs to deck in progress

the main beams a creosote preservative. This appears to have been effective in the deck planks, which are 75–100mm thick, but not in the larger sections, from the fence posts (100mm × 150mm) upwards, where superficial treatment had allowed internal decay to take hold. Both of these treatments are now restricted by European Directives. Consideration was given to using Douglas fir in the repairs. It would be structurally strong enough, but its durability would be in question for the sort of time frames suitable for a scheduled monument. Greenheart is available from a sustainable source, but pitch pine is not. Greenheart is difficult to work and would have been difficult for the joint configuration and drilling that would be required. Second-hand pitch pine was sourced, but cutting it to size was thought to be problematic because of the likelihood of embedded metalwork, so it was not considered suitable. The quarter-century since the Garden Festival had allowed extensive timber decay and this equates with a quoted design life of exposed softwoods of around 20 years. For a monument such as this, it was felt that a 50-year life would be more appropriate. The timber finally selected was ekki, which is hardwood from a sustainable source in West Africa, imported through the Netherlands. The handrail timber selected was opepe, which has similar strength characteristics to ekki, but is easier to work to the profile required. The main downside of using ekki is its relatively high movement values with

TSE49_28-31 CC v1.indd 31

change in moisture content. This may require connecting bolts to be checked regularly and tightened as necessary.

Repair philosophy Where timbers are being replaced, thought has been given to the detailing so as not to leave exposed end grain or surfaces where water can sit. Where end grain has to be exposed – e.g. between the handrail sections – an air gap has been left. Where possible, spaces allow water to drain rather than being trapped. All new fixings are stainless steel, which is now much more readily available than it was in the 1980s, although the galvanised fittings and bolts used for the Garden Festival works are still in good condition. The principals of timber conservation and repair are in many ways more relevant with softwoods, as at the Staiths, than with hardwoods, as would be used in, for instance, medieval timber-framed buildings. With hardwoods, the aim is to maintain suitable environmental conditions so as to ensure that wet and dry rot or insect infestation will not occur. Such timber must be protected and detailed such that there are no water traps or contact surfaces where water cannot drain away – the positioning of structural timber on top of a damp-proof course is a case in point. At the Staiths, the most vulnerable area is where there are gaps between the deck boards which allow water to sit on top of the support beams. These water traps should be kept clear, or alternatively filled with slips of timber.

With an exposed structure such as the Staiths, however, the environmental conditions cannot be controlled – it is a fully exposed structure in a marine environment – so careful detailed design and selection of the most durable species of timber is a more important consideration. Regular inspections are essential, using micro-drilling and roped access, and a fifth of the structure will be inspected in this way every five years, to give a continuous record of the rate of decay.

References E1

Miller J. (2015) ‘Conservation compendium. Part 13: Common repairs and strengthening of structural timbers in historic buildings’, The Structural Engineer, 93 (12), pp. 45–49

E2

Skill D.R. (1989) ‘Dunston Coal Staiths, Gateshead’, Conservation of Engineering Structures, London, 13 March, London, UK: Thomas Telford, pp. 33–49

E3

Crossman M. and Simm J. (2004) Manual on the use of timber in coastal and river engineering, London, UK: Thomas Telford

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Project focus Repairing missile damage

Baghdad missile-damaged building brought back to life Nabeel A. Ibraheem Senior Structural Engineer, Ministry of Science & Technology; PhD Research Student, Dept. of Building & Construction Engineering, University of Technology, Baghdad, Iraq

Synopsis

This short article describes the rehabilitation of an office building in Baghdad damaged by a missile strike during the 2003 Iraq War. The author briefly sets out the damage to the building’s steel frame, explains how a structural model Introduction The Al-Mansour Building (Figure 1) in Baghdad, Iraq, is a seven-storey office building designed and constructed by a consortium of three Japanese companies in 1982. Later, it was one of many buildings damaged in the 2003 war, when it was targeted by five smart missiles which drilled through its roof. Two of these missiles exploded within the second to third floors, while the other three continued punching through successive floors down to the basement, where they exploded. Severe damage was caused. Given the amount of column damage in particular, a redistribution of forces had clearly taken place to prevent total collapse. Survival was obviously aided by the absence of live load and removal of much of the concrete flooring weight. Figures 2 and 3 show the main framing of the steel structure, identifying the worst affected location. This area included two main columns within the middle building plan, extending from the first up to the fourth floor, along with their surrounding main beams and joists (these originally supported concrete floors).

was created to enable the design of a supporting steel frame, and describes the installation of the temporary supporting frame and new steel columns using hydraulic jacks to raise the building’s upper stories.

preliminary site visit, followed by a detailed survey, which recorded the damage to each steel member. This work was complemented by collation of all available technical reports and the original design calculations. The explosion of missiles within the second to third floors of the building’s interior resulted in heavy damage to the surrounding area; the most severe was inflicted on the two main columns. These were virtually shredded, to an extent that prevented them from effectively supporting

floor beams. Many girders and joists, along with their concrete floor panels and steel decks, were also damaged in degrees ranging from slight to heavy. The main strategy for rehabilitation was therefore removal of the two damaged columns followed by their replacement. To accomplish this, it was necessary to inset some temporary steel to bypass the damaged columns, and use this to transfer load down from the fourth to the first floor, and then to remove the damaged steel and replace it.



Figure 1 Al-Mansour Building, Baghdad

Rehabilitation proposal Following the war, many investigations had been conducted and proposals for repair submitted, but none were specific, practical or economical enough to be adopted. In late 2013, the author made a

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Most damaged area

"Given the amount of column damage in particular, a redistribution of forces had clearly taken place"



Figure 2 Structural framing arrangement identifying most damaged internal areas



Figure 3 View of most damaged steel framing where supporting steel frame would later be placed (1st to 4th floors)

Based on the detailed site survey of the damaged steel frame, and working with the original design calculations, a structural model was prepared using STAAD.Pro. All existing components were represented whether damaged or not, but their actual condition was modelled. For example, some members were only partially damaged through their webs or flanges, so reduced section properties were considered appropriate. Techniques used included decreasing sizes or thicknesses, or introducing suitable intermediate releases to simulate any weakening that had taken place. Several structural models were prepared for the building to cover: • the theoretical as-built steel frame • the existing damaged steel frame • the steel frame after eliminating the most heavily damaged members (i.e. from the first to the fourth storey) • the steel frame after introducing a supporting frame

Repair work The restoration plan called for the introduction of a supporting steel frame (Figure 4) through the void made by the explosion (three stories high), starting from the first floor and rising up to the fourth floor, to replace the load-carrying capacity of the damaged main columns (Figure 5). The supporting frame columns were laterally braced with square tubes at

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Figure 4 Supporting steel frame after installation

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Figure 5 Replacement steel frame and load path

E

Figure 6 Connections between old and new columns (bolted on lower side, welded on upper side)

Existing columns retained

Two jacks

E

Figure 7 Hydraulic jacks in position

COLUMNS IN RED ARE TEMPORARY PARTS OF SUPPORTING FRAME TO BE DISMANTLED LATER

Damaged columns removed

BEAMS IN MAGINTA ARE NEW REPLACED ONES AND AT THE SAME TIME SERVE AS PARTS OF SUPPORTING FRAME

COLUMNS IN BLUE ARE ONES REPLACED

COLUMNS IN BLUE ARE ONES REPLACED

Temporary frame

E

Figure 8 Renovated framing

Beams to remain as part of the permanent structure but act as temporary restraints during rehabilitation

each floor level. Then, at the frame top, two hydraulic jacks were inserted to lift the upper building stories. This was necessary in order to introduce gaps at the contact points between the top of the damaged columns (i.e. above first-floor level) and the bottom of the new columns erected above, so that a steel plate could be inserted firmly at the two positions. The connection was completed by bolting plates to the lower columns and welding the plates to the upper replacement columns (Figure 6). The frame was designed to transmit forces from the upper floors (seventh to fourth) down to the undamaged part of the

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original main columns at first-floor level. Once the frame was installed, the damaged parts of the columns were dismantled; new columns were fabricated to measured lengths and inserted in place so that their tops just touched the original cut parts of the fourth-floor columns. Many damaged steel members (girders, beams, joists) were also removed and replaced with newly fabricated members within the surrounding area. Structural calculations and analyses showed that the minimum required jacking force required to lift the upper building floors was about 1500kN at each of the two jacking points. Figure 7 shows the jacks in position and Figure 8 shows the renovated framing. The lifting operation was performed in early 2015 and the upper (old) columns with their floors were lifted vertically by about 12mm at each of the two contact points using a hydraulic jacking force of 1100kN. A 12mm thick plate was then inserted between the column bearing end plates, and hammered in, before the predesigned connection was fitted and welded. The last step was to release the hydraulic jacks so that the new replacement main columns became active and carried their share of load, restoring the integrity of the framing system.

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TheStructuralEngineer January 2016

35

Professional guidance Articles that provide information and advice on everyday matters affecting the practising structural engineer.

36 Engineer’s Guide to PI Claims. Part 1: Notification to insurers 38 Managing Health & Safety Risks No. 47: Safe excavation

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› Part 1

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TheStructuralEngineer January 2016

Professional guidance PI claims

Engineer’s Guide to PI Claims Part 1: Notification to insurers A new series from insurance broker Griffiths & Armour on professional indemnity claims begins by advising engineers on what requires notification to their insurer.

In this new series of articles, we loosely follow the life of a typical professional indemnity (PI) claim against an engineer, pausing to comment on various issues which might typically arise: from notification to insurers to defence and settlement. The first article in the series is an introduction to the issues surrounding notification to insurers.

Claims-made cover PI insurance operates on a claims-made basis, meaning that the policy which pays out in the event of a claim is the policy which was in force when the matter was first notified. This is always true, irrespective of when the work giving rise to the claim was undertaken by the engineer and even if the claim is not concluded until many years after it was notified. This might sound like an arbitrary arrangement, perhaps allowing the insured engineer a degree of control over which of a

series of annual policies they would like to trigger, potentially to their advantage if there were any substantive difference in successive policy terms (e.g. an increased limit of indemnity or a lower excess). There are two reasons why this is not the case: 1. Crucially, all PI policies contain conditions requiring the insured to notify the insurers of any “claim” (usually a defined term, as explained later) or any circumstances which might give rise to a claim of which they first become aware during the period of the policy. 2. Shortly prior to the inception of the policy, the engineer will have signed some form of undertaking on a proposal (a “no claims declaration” or NCD), effectively stating that having made full enquiries the proposer is not aware of any circumstances that might give rise to a claim against the practice other than those that have already been reported to current or previous insurers. This statement forms part of the proposal and therefore the basis on which the insurers make their offer of cover to the engineer. It therefore also forms part of the contract between the parties if the engineer accepts the terms offered by the insurer. Absent any special policy terms dealing with non-disclosure by the insured, the consequences of having signed an NCD when it was not strictly true can be very serious indeed. Claims can be uninsured as a result.

Obligation to notify insurers The first of these two points raises a number of issues worthy of a brief discussion – subject always to the fact that we can only discuss general principles here. All policies operate subject to their bespoke express terms, which will take precedence over any general comments in this article. “Claim” will usually be a term defined in the policy, typically extending well beyond obvious instances such as court proceedings to something much broader, including any demand for damages. A formal pre-action protocol letter of claim (in relevant jurisdictions) would also fall within this definition, but so would any other allegation of negligence or breach of contract, regardless of its merits and even if it were to consist of no more than a couple of sentences in an apparently unofficial email from the project manager. What amounts to a “circumstance which might give rise to a claim”, on the other hand, is notoriously much more widely open to interpretation and is only rarely defined in express policy terms. The safest course of action for any engineer is to give this term a wide interpretation. Common sense must however be allowed to prevail, otherwise a disproportionate amount of time can be spent notifying every possible conceivable problem, including some imaginary ones. By way of illustration, Box 1 presents three very brief examples of where engineers innocently made the wrong judgement call

Box 1: Making the wrong judgement Example 1

Example 2

Example 3

Fees were being withheld from an engineer, ostensibly because the client thought that a loss had been incurred as a result of design changes. The client said nothing beyond precisely that and volunteered no information until very much later, either in respect of the alleged loss or the changes that had supposedly caused it.

During excavations it came to an engineer’s notice that ground conditions were different from those assumed by her foundation design. She didn’t think that this would cause a problem, but she also recognised at the time that there was a small risk that she could be wrong about this. No one approached her for a contribution to the associated additional cost until the end of the project some 18 months later.

An engineer submitted some design information later than had been expected by his contractor client. The project was already in delay by that stage such that he was confident that his own tardiness had not in practice made matters any worse. Our forensic programming experts were later able to prove that his view was correct, but significant defence costs had to be incurred in reaching that stage.

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and failed to notify their insurers of relevant “circumstances which might give rise to a claim”. Fortunately these engineers all benefited from the safety net provided by the innocent non-disclosure arrangements which we have in place with our key insurer partners; but in principle (and for the purposes of instruction) they amounted to a failure to notify pertinent circumstances within the relevant policy period and therefore a breach of policy conditions.

Small vs larger firms Each of the cases presented here involved small practices with only a handful of technical staff and two or three principals. The principals were closely involved in every project undertaken by the firm and they were fully aware of all developments as they happened. Larger firms of engineers, on the other hand, are faced with the additional challenge that while actual claims probably find their way onto the management radar, there may be a risk that mere “circumstances” do not rise to the surface quite so quickly. The time interval could be critical if it spans a policy renewal date. The NCD on the proposal form is usually worded specifically to say that the proposer has undertaken full enquiries before giving the relevant undertaking, but even without that specific wording the proposer is in effect saddled with the risk that notifiable circumstances wide of their own knowledge are known only to individuals elsewhere in the firm. The fact that the individual signatory completes the proposal form in good faith is not in itself sufficient to alter the fact that PI operates on a claims-made basis – and this is why it is vital for all consultants to make proper enquiries throughout the firm in the lead-up to their renewal dates.

Multiple heads of loss Coverage disputes can arise in cases where claims or circumstances have been correctly notified but then develop in such a way as to expand beyond what was in the engineer’s contemplation when that notification was made (e.g. what started out as an issue over a single under-sized beam having to be removed and replaced later morphed into a more fundamental criticism of the entire roof design). In these cases some insurers will seek to argue that the latest developments form a separately notifiable set of circumstances which belong in the current period of insurance rather than forming part of what was originally notified. This will have the less-than-desirable result that what is essentially one claim

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against the engineer is treated as more than one claim for policy purposes, exposing the engineer to more than one policy excess. If the engineer should fail to make additional notifications promptly when further issues arise, then the risk of uninsured losses once again raises its head. The law in this area is notoriously difficult to condense into simple terms, and its application in practice is further complicated by the effects of different policy wordings and very different factual scenarios. This is where the potential for coverage disputes lies. Engineers should, however, be aware that it can be an issue and that some insurers in the market take a more engineerfriendly approach to the matter than others. Once a matter has been notified, it should be kept under careful review with this in mind.

Continuity of insurer In practice, the issues briefly outlined here are more likely to lead to problems in cases where the engineer has purchased PI cover with a number of different insurers over successive policy periods. Continuity of provider is much more valuable in the context of PI than in many other classes of cover. This is because insurers are much less likely to investigate cases of apparent non-disclosure and late notification (with a view to refusing to pay claims) if in reality they were on risk when the matter in question might otherwise have been notified, and therefore in reality they have suffered no prejudice.

Specific claims conditions Insurers are particularly sensitive about the need to be advised immediately in circumstances where they need to act quickly in order to best protect their interests in meeting procedural deadlines. This is particularly the case in relation to adjudication proceedings, currently more established in some jurisdictions than in others and shortly to come into effect in the Republic of Ireland. For this reason many policies contain specific requirements that insurers be notified within, say, 48 hours of an adjudication notice being received. Crucially, these terms are often expressed as conditions precedent to indemnity being provided, meaning that if the policyholder fails to satisfy that condition then the claim will not be paid, irrespective of whether the insurers can demonstrate having suffered prejudice as a result. It is therefore vitally important that where such conditions form part of the policy, all staff should be made aware that they exist.

Griffiths & Armour is a leading independent and privately owned UK insurance broker and risk management adviser. For further information, scan the QR code or visit www.griffithsandarmour.com. Griffiths & Armour is authorised and regulated by the Financial Conduct Authority.

Key points • Read your PI policy and ask your broker for advice on claims conditions so that you are fully aware of what your duties are and what the consequences of breach might be. • If you are in doubt as to whether or not something is notifiable, you should take advice from your broker. Bear in mind that if you are asking yourself whether something is notifiable, even on a purely precautionary basis, then it nearly always will be. • Do what you can to foster an open, blame-free culture within your organisation so that your staff feel able to raise concerns, however minor, as soon as they arise. Quite apart from the insurance issues briefly outlined in this article, you will be far better placed to monitor and manage problems with early warning than you would be if you were to find out about them only at a later stage. • Never admit liability to a claimant or discuss making a financial contribution without the prior approval of your insurers, even if you are of the view that you have no defence available. Most PI policies contain specific conditions to this effect and you could find yourself in difficulty if your insurers feel that your actions have prejudiced their ability to defend or mitigate the claim. • More generally, upon receipt of any intimation of a claim against the practice, avoid giving any response at all, even by way of acknowledgement, without advice from your brokers.

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TheStructuralEngineer January 2016

Professional guidance Health and safety

Managing Health & Safety Risks No. 47: Safe excavation Introduction All excavation work is potentially hazardous; the collapse of excavation faces can have serious consequences, both for life and purely as an economic loss. For example, in one incident, an experienced ground-worker on his first day on a site with a new company was killed when a trench collapsed. The trench was 2m deep; spoil had been heaped to each side and tamped down with a bucket near to a fence in order to make it easier to walk along the top of the heap for access to the site (Figure 1). Despite the potential risk to life, the need to avoid damage to adjacent buildings, roads and services will usually impose a greater restriction on the designer’s freedom of choice, since it will dictate a greater limitation on face

movement than would be required simply to avoid danger. The risk to buildings is illustrated by another incident, in which a contractor departed from the sequence set out by the temporary works designer when forming an excavation for a new basement. They undermined the gable wall of the adjacent property, causing a collapse and the loss not only of the building but also of the inhabitants’ possessions.

Why is excavation dangerous? Any slope steeper than the angle of repose of the material is unstable; the question is not “if” but “when” it will collapse. When there is a need to excavate, the designer must gather information from the site investigation about the likely short-term stability of earth faces and pass it on to the contractor. Where the ground is likely to be highly unstable in the short term, the need for earth face support must be clearly spelled out and should be scheduled in the tender documents.



Figure 1 Two views, one from each end of excavation, of trench which later collapsed

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Implementing excavation work All excavation work must be planned before work commences on site. This is essential if the work is to be carried out safely and at least cost. Before work starts there should be sufficient suitable materials on site to support the length of excavation expected to be open in normal circumstances, together with a buffer stock. Work on site should be supervised by a competent person. They must have authority to make any decisions necessary to ensure the safety of the operatives, the excavation and its surroundings. Any face support must be installed without delay as the excavation progresses, and strutting completed before the ground relaxes significantly. The operatives doing the work should be given clear instructions, preferably recorded as drawings or sketches, and the work must be inspected regularly. Figure 2 shows a hazardous 3m deep excavation in sand and gravel where entry had to be made into the excavation in order to erect the support for the walkway. The support scheme used may be specifically prepared for the job by a designer. The work supervisor should be aware of the assumptions made in the design of the support and should carefully monitor the actual situation on site. Any changes from the assumed conditions

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should be reviewed, using tables/charts in the case of a standard solution scheme. In the case of a scheme prepared by a designer, any changes should be referred back to the designer for their consideration and comment.

FURTHER READING: Construction Plant-hire Association (2013) Good Practice Guide for the Management of Shoring in Excavations. Part 1 - Management Process [Online] Available at: www.cpa.uk.net/freedownload/?STIG%252 0Publications~~~CPA-STIG-Be-Safe-ShoreGPG-130601.pdf (Accessed: December 2015)

Personal safety when visiting site Excavations away from adjacent structures that no one needs to enter may be unshored. However, bear in mind that the sides could collapse when someone is close by and they could be engulfed. Also, beware of excavations with no edge protection (as it is possible to fall in). What was commonly known as the “four-foot rule”, where excavations shallower than 1.2m did not need to be shored, is no longer current. A collapse trapping a person at waist level can still lead to asphyxiation as return blood flow from the legs is blocked. The salient point is the risk of collapse, not the depth of the excavation. This guidance note has been prepared by The Institution of Structural Engineers’ Health and Safety Panel.

Construction Plant-hire Association (2006) Safety in Shoring: The Proprietary Shoring and Piling Equipment Manual [Online] Available at: www.cpa.uk.net/freedownload/?STIG%2520 Publications%7E%7E%7ECPA-STIG-Safetyin-Shoring-Manual-060701.pdf (Accessed: December 2015) Construction Plant-hire Association (2004) Safety Guidance: Risk Assessment for Shoring & Piling Operations [Online] Available at: www. cpa.uk.net/freedownload/?STIG%2520Publ ications%7E%7E%7ECPA-STIG-0403-RiskAssessment-for-Shoring-Equipment-040901. pdf (Accessed: December 2015)



Figure 2 Excavation in sand and gravel requiring entry to erect support for walkway

Construction Plant-hire Association (2002) Safety Guidance: Selection of Proprietary Shoring Equipment [Online] Available at: www.cpa.uk.net/freedownloa d/?STIG%2520Publications%7E%7E%7E CPA-STIG-0201-SG-Selection-of-ProprietaryShoring-Equipment-020701.pdf (Accessed: December 2015)

If you are aged 28 years or under, you are invited to enter the Kenneth Severn Award 2016. To enter, please answer the following question, set by 2016 Institution President, Alan Crossman:

Society’s consideration of sustainability within the built environment and infrastructure will have an ever-increasing impact on the day-to-day role of the structural engineer. How can this be developed as a core element of our design processes, become a key differentiator for our profession within the design team and be conveyed on a wider public platform? Answers should be in the form of a written paper (max. 1500 words) and may include relevant imagery that supplements the text. The judges will be looking for originality, value to the structural engineering profession and clarity of presentation. Please submit your entry online at: www.istructe. org/events-awards/people-and-papers-awards/ kenneth-severn-award

2016

The closing date for entries is 31 January 2016.

The winner will: Be awarded the Kenneth Severn Diploma Receive a cash prize of £500 Have their paper considered for publication in The Structural Engineer Entrants must be 28 years of age or under on 1 January 2016. Entry is NOT restricted to members of the Institution.

Alan RL Crossman

CEng, FIStructE, FICE, MCIWEM Institution President 2016 Registered with the Charity Commission for England and Wales No. 233392 and in Scotland No. SC038263

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Structural-Safety works with the professions, industry and government on safety matters concerned with the design, construction and use of building and civil engineering structures. We provide an impartial expert resource to share and to learn from the experiences of others. You can participate by reporting concerns, in confidence, to the website. Reports are anonymous and de-identified before being published. Reports can also lead to Alerts which influence the safety of existing and new structures. Visit the website to register for Newsletters and Alerts and to view the database of reports.

www.structural-safety.org CROSS Confidential reporting on structural safety | SCOSS Standing Committee on structural safety

Sponsored by

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TheStructuralEngineer January 2016

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Technical Articles that are technical in nature; focusing on methods of analysis, material properties and aspects of design of structures.

42 Simplified dynamic analysis of beams and slabs with tuned mass dampers

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TheStructuralEngineer January 2016

Technical Dynamic analysis with TMDs

Simplified dynamic analysis of beams and slabs with tuned mass dampers Andrew Robertson MSc, CEng, MIStructE, MICE, Independent Civil and Structural Engineering Consultant, Bergerac, France Introduction As structural material properties are enhanced and structures become lighter and considerably more flexible, with lower structural damping, excessive dynamic response in the form of large displacements or accelerations becomes more commonplace. The dynamic loading may come from high-energy dance or exercise activities (Figure 1) within buildings, or synchronised groups of pedestrians on bridges. Such activities can occur over a range of frequencies coinciding with the fundamental natural frequency of the structure or structural element, thus causing resonance effects. Typically, structures with fundamental natural frequencies in a range of 1.5–4Hz would be at risk. Such undesirable effects may be addressed by modifying the structure, either by changing its stiffness, increasing the overall structural damping or by the addition of a tuned mass damper (TMD) device. Understanding the dynamic response of a structure or structural element can be a daunting task, particularly for practising engineers normally only concerned with the static design of structures. Many structural engineers will be familiar with the dynamic response of simple single-degree-of-freedom (SDOF) models. However, very few structures will correspond directly to such a form, which usually means computerised solutions are embarked upon, structures are radically altered, possibly needlessly, or problems passed to dynamics specialists. This paper simplifies the analysis to provide arithmetic solutions and a means of understanding the dynamic response of a structure. It also provides a means to verify computer modelling and estimate the characteristics (mass, stiffness and damping) of a TMD to address any residual problematic dynamic response. This enables the design provision for the additional weight attached to

the structure and the required space, if a TMD is deemed to be necessary. A worked example of a simply supported welded steel box girder footbridge is presented. Structural beams and slabs generally consist of uniformly distributed mass and stiffness, with many possible modes of vibration of increasing frequency. However, most dynamic response problems are associated with a single, usually primary, mode of vibration with the maximum displacement, for example, at or close to the mid-span of a simply supported structure with a sine wave shape or function or the end of a cantilever with an ‘inverted’ cosine shape function (Figure 2).

Simplified approach The proposed simplified approach assumes that: • the mode shape (Eigenvector) is a sine wave, sine/cosine function or the deflected shape for the associated static loading • the dynamic load (human dynamic input) is also in the form of a sine wave at the same frequency as the natural frequency of the structural mode of vibration being assessed. This will simulate resonance, which will result in the maximum response • the structure is idealised as a SDOF system using generalised mass, damping and stiffness values (Figure 3) The circular frequency of the SDOF system ω is given as1

(1) The natural frequency f is then given by1

(2)





Figure 1 Floor slab subject to dynamic loading

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ALAMY

Figure 2 Idealised principal modes of vibration for beams

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Box 1: Evaluation of generalised mass and stiffness for simply supported beam

W

Figure 3 Idealised singledegree-of-freedom dynamic model for beams and slabs

where k* and m* are the generalised or equivalent stiffness (N/m) and mass of the structure (kg) for the particular mode of vibration of interest. The generalised damping c* (kg/sec) is usually assigned an average value for the structure. The generalised stiffness and mass may be determined by either adopting an assumed deflected shape function2 or calculating the deflection from the closed-form bending moment formula for the structure1. This enables cross-checking of the evaluated parameters where both methods can be used, i.e. beam elements. As closed-form formulae are not available for slabs, only the assumed deflected shape function method can be used. The assumed deflected shape function is used by equating the external virtual work performed by the external loads with the internal work, so that the generalised stiffness and mass can be defined as follows2: (3)

(4)

where E is Young’s modulus, I is the moment of inertia of the structure at position x along the structure, f(x) is the shape function (Eigenvector) and f’’(x) is the second differential of the shape function, m is the mass/metre, mi is the discrete mass at xi and ki is the discrete spring stiffness at xi. The shape function (Eigenvector) is dimensionless and so the maximum displacement y should be taken as unity. The generalised mass and stiffness values can be determined for various beam and slab spanning conditions as follows. For a simply supported beam of uniform mass and stiffness, assuming a sine wave deflected form, sin π x/L (Figure 2a), Equations 3 and 4 yield the following generalised mass and stiffness:

(derived as for simply supported beam)

Similarly, for a built-in beam of uniform mass and stiffness, assuming a shape function of ½ {1 – cos (2π x/L)} (Figure 2c), gives the following generalised mass and stiffness values:

(see Box 1 for derivation)

For a cantilever of uniform mass and stiffness, assuming a shape function of 1 – cos (π x/2L) (Figure 2b), gives the following generalised mass and stiffness2:

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Figure 4 Idealised principal modes of vibration for slabs

Technical Dynamic analysis with TMDs

S

Figure 5 Typical details for tuned mass damper

1 Reinforced concrete deck

For a simply supported isotropic slab, a similar approach may be used, assuming the following shape function2:

2 Main steel beams 3 Adjustable steel mass 4 Adjustable vertical steel springs 5 Adjustable damping elements

where a and b are the slab spans in the x and y directions, respectively (Figure 4). The generalised mass and stiffness are then given by the following formulae2:

where D = the flexural rigidity of a uniform slab = E h3 / {12 (1 – ν2)} per unit width of slab, E is Young’s modulus, h is the slab depth and ν is the Poisson’s ratio. Alternative composite or other slab forms would need to be evaluated as an equivalent flexural rigidity. If the slab is orthotropic, e.g. using precast concrete or steel beams, the slab will probably behave more like a one-way spanning slab for which a beam-analogy approach should provide a reasonable estimate of the generalised parameters. Similarly, a large-aspect-ratio (length/width) isotropic slab will also predominantly behave like a one-way spanning slab. For a simply supported slab, evaluation of the formulae described earlier yields the following generalised mass and stiffness:

The condition of full fixity for slabs and beams would require continuity into substantial adjacent structures and so does not occur that often in practice. Hence, in general, for built-in beams and slabs, some intermediate values would need to be estimated. Alternatively, and indeed more accurately for beams, the generalised or equivalent mass and stiffness may be determined by considering the deflected shape based on the bending moment along the length of the beam1. By equating the strain energy stored in the spring to that stored in the beam as follows:

and

For a built-in slab, the methodology can be extended by assuming the following shape function (Figure 4):

This results in the following generalised mass and stiffness values:

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By integrating twice and using the end conditions to resolve integration constants, the deflection y can be determined. The shape function is then found by equating the deflection to unity. The results this yields for various beam support conditions are shown in Table 1 (corresponding estimate from assumed shape function given in parenthesis). The effect of point loads at mid-span and in-plane loads can also be incorporated by extension of the methodology1 described here to calculate the associated generalised or equivalent mass and stiffness. As there are no simple closed-form solutions for bending moments across a slab structure, it would be necessary to adopt

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S

Figure 6 Idealised model of structure and tuned mass damper

Table 1: Summary of generalised mass and stiffness values for beams1 Beam condition

m*, mL

k*, EI/L3

Cantilever beam

0.257 (0.227)

3.20A (3.04)

Simply supported beam Built-in beam Continuous beamB

0.504 (0.5)

48.15 (48.7)

0.406 (0.375)

204.8 (194.8)

0.162

165.9

Note A: The value of ‘16’ quoted in the reference1 is believed to be a typographical error and should in fact have been given as ‘16/5’, i.e. 3.2 Note B: The continuous beam consists of 4 equal spans with one end built in1. Alternative continuous beam arrangements could be assessed using the same methodology

the approximate solutions presented here assuming sine, cosine or similar shape functions. The damping in a structure is typically assumed to be an equivalent viscous damping ratio, i.e. damping proportional to velocity, and taken as a generalised or average value rather than with discrete dashpots or other damping devices. The damping ratio is defined in terms of the logarithmic decrement δ which can be related to the damping ratio ξ as follows:

The generalised damping c* can then be found from:

Damping is also often given as a proportion or percentage of critical damping (ξ = 1), which is defined as follows:

Typical values for logarithmic decrement δ are given in Eurocode 8, Part 23 and in various texts for percentages of critical damping4. The dynamic pedestrian loading can be modelled approximately as a sine wave and is given in the UK National Annex to Eurocode 1, Part 25, where the amplitude of the harmonic loading (sine wave) is given as follows:

F0 is given as 280N for walkers and 910N for joggers. The factor k(fv) takes account of realistic pedestrian numbers and sensitivity to the mode frequency. γ is a factor to take account of the unsynchronised nature of a pedestrian group and the bridge effective span. N is the number of pedestrians in accordance with clause NA.2.44.25. Crowd loading is dealt with in a similar manner to provide a uniformly distributed vertical pulsating harmonic load w (NA.2.44.55). In order to model this in a simplified SDOF system, it is suggested, as an approximation, that the proportion of the total distributed pulsating load w is taken as the same as the proportion of the generalised mass to the total mass, e.g. approximately 0.5 for a simply supported beam. The equation of motion6 for the simplified SDOF system subjected to a harmonic dynamic load (Fig. 3) is then:

TSE49_42-47 Tech TMD v1.indd 45

Solving this equation7 yields the following deflection and accelerations:

As the structure’s natural frequency is a function of structural stiffness and mass, investigations may be carried out using the formulae presented here or a computer model of the structure in order to modify the stiffness of the structure to achieve a sufficiently increased natural frequency and/or reduced acceleration. However, it may be found that significant changes to the dynamic response of the structure are not possible without substantial modification of the structure. It may therefore be concluded that by far the most pragmatic solution to reduce the acceleration response would be to fix a TMD to the structure and effectively dampen out the unacceptable displacements and accelerations. Once the decision to incorporate a TMD has been taken, either provisionally or otherwise, the analysis could be carried out by hand calculation as described later in this article or by using suitable structural analysis programmes incorporating dynamic analysis. However, many structural computer programmes that incorporate dynamic analyses only allow a single generalised damping parameter rather than discrete damping elements. So the analysis method described here for the inclusion of a single discrete TMD with associated damping may be the only option available to determine the combined structure/TMD dynamic response without recourse to the purchase of the appropriate specialised software. TMDs normally contain a vertically oscillating deadweight, usually solid steel, supported on springs. In parallel to the springs, damping elements are arranged, which can be adjusted to the required damping ξ (Figure 5). The relatively small mass of the TMD oscillates with a larger magnitude and just out of phase with the larger mass of the structure, which has the effect of suppressing the motion of the beam or slab. The TMD can be bolted to the structure in the most effective location. The device would be custom designed to fit in the available space within or underneath the structure. The most effective location for a TMD would clearly be close to the location of maximum displacement indicated in Fig. 2. It

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Technical Dynamic analysis with TMDs

is possible that excessive displacements may occur at different locations due to other modes of vibration, in which case it may become necessary to add several TMDs to deal with each problematic mode of vibration. Extending the SDOF simplification for the structure, the effect of adding a TMD can be modelled as indicated in Figure 6, where ct, kt, mt and yt are the respective damping, stiffness, mass and displacement of the TMD. The equations of motion are then given by the following simultaneous differential equations6:



Figure 8 Welded steel box girder footbridge section

The solution7 yields the following result for the displacement and acceleration of the structure:

where:

The most effective frequency of the TMD is usually as close as



Figure 7 Tuned mass damper installed under footbridge deck

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possible to the natural frequency of the mode of vibration causing the excessive dynamic response. It is important, therefore, that the frequency of the structure is estimated accurately, otherwise it may prove difficult to fine tune the TMD on site to achieve the desired results. The frequency of the TMD is adjusted by changing the mass or modifying the springs. The damping can also be adjusted to optimise the effectiveness of the TMD. TMDs can have masses in the range of 10 to 500 000kg, but for footbridges, beams and slabs will typically range from 500 to 5 000kg. The damping will typically be between 8 and 15% of critical, with a wide range of applications, including seismic resistance and stabilisation of high-frequency machinery. The resulting natural frequency of the TMD can be between 0.3 and 100Hz, although to effectively dampen the motion of a structural element, it is likely to be of the order of 1.5–4Hz. An acceptable displacement or acceleration can be determined by substituting the estimated structural properties and a range of TMD properties into the equations presented here. A typical TMD7 (mass 2000kg, spring stiffness 420 500N/m and damping 4350kg/sec as supplied by GERB), is shown in Figure 7. Resonant amplitudes of the order of several centimetres may be reduced to a millimetre or less, which would normally be virtually imperceptible. A trial TMD mass, say 5–10% of the structure’s generalised mass, can then be selected, which will dictate the TMD spring stiffness determined from Equations 1 and 2. The process should then be repeated until the target maximum displacement or acceleration has been achieved. Once the mass of the TMD has been determined, the structure can be designed for the additional static weight and space requirements or provision made for its possible inclusion. Likewise, existing structures can be strengthened accordingly, if necessary. The final TMD design will be carried out by the TMD supplier using parameters provided by the structural designer, but the effects on the structure in terms of materials, dimensions and costs can be planned well in advance, so the structural designer can retain greater control over the design process. Worked example: Simply supported steel box girder footbridge Architectural demands for footbridges in high-profile locations are likely to result in relatively slender solutions. A welded steel box girder solution may satisfy such requirements. This could be fabricated with a pre-camber to eliminate the self-weight sag with just the live load deflection affecting the in-service appearance. An assumed steel box girder footbridge, simply supported over a 30m span, is shown in Figure 8.

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Bridge properties (Units – N, m, kg, sec): Span Deck plate Web plate Flange plate Edge beam Section area Mass Moment of inertia Modulus of elasticity Logarithmic decrement

30m 2.0 × 0.02m thick 0.85 × 0.012m thick 0.6 × 0.02m thick 0.3 × 0.25 x 0.015m thick fabricated angle 0.0889m2 1004kg/m, including parapets and surfacing 9.955 × 10-3m4 205 × 109N/m2 0.02, for welded steel section3

Using the formulae for generalised mass, stiffness and damping for a simply supported beam yields the following dynamic properties: Generalised mass m* 15 057kg Generalised stiffness k* 3.681 × 106N/m Generalised damping c* 1499kg/sec Natural frequency fb 2.489Hz from formulae presented here Circular frequency ω 15.636 With reference to the National Annex to Eurocode 15 the amplitude of the dynamic sinusoidal input loading F can be determined as follows: Fo 280N, Table NA.8 K(fv) 0.48, Table NA.8 γ 0.24, Table NA.9 N 16, Table NA.7, assumed access to major public facility F 288N, using the given formula Applying the solutions given in the text, the maximum deflection and acceleration due to resonance are as follows: Max. acceleration 3.01m/sec2 Max. amplitude deflection 12.3mm In a prestigious high-profile location, i.e. for access to a major public assembly facility, the above response is unlikely to be acceptable (exceeds maximum acceleration limit of 2.0m/sec2 given in NA.2.44.65) and so the application of a TMD would be an economical solution. In this example it should be possible to locate the TMD in the box at mid-span with an appropriately stiffened access opening. The natural frequency of the TMD should be relatively close to the bridge natural frequency and assuming a mass of approximately 10% of the generalised mass would lead to TMD properties approximately as follows: TMD natural frequency ft 2.60Hz (selected) TMD mass mt 1500kg (selected) TMD stiffness kt 400 984N/m (from ft = (kt/mt)0.5) TMD damping ct 3679kg/sec (from TMD manufacturer) Applying the formulae for a TMD modified structure gives the following factor values: P -1.484 × 1011kg2/sec4 Q 9.872 × 106N kg/sec2 R 2.029 × 1010kg2/sec4 S 1.658 × 107N kg/sec2

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M N

–0.080mm.sec –0.101mm.sec

This yields the composite sinusoidal response as follows:

The amplitude and acceleration could be plotted or tabulated at, say, 0.01 second intervals to determine the maximum response as follows: Max. acceleration 0.03m/sec2 Max. amplitude deflection 0.13mm This should, under normal circumstances, be acceptable, but if more or less onerous conditions need to be satisfied, the mass, stiffness or damping properties of the TMD can be adjusted to suit the client’s requirements. Acknowledgements Thanks to Peter Knight, Robert Carr, Anne Yam and Steve O’Brien for reviewing the text and preparing figures.

References E1

Buchholdt H.A. and Nejad S.E.M. (2011) Structural Dynamics for Engineers (2nd ed.), London, UK: ICE Publishing

E2

Clough R.W. and Penzien J. (1993) Dynamics of Structures (2nd ed.), New York, USA: McGraw-Hill

E3

British Standards Institution (2005) BS EN 19982:2005 Eurocode 8: Design of structures for earthquake resistance. Bridges, London, UK: BSI

E4

Willford M.R. and Young P. (2007) A Design Guide for Footfall Induced Vibration of Structures, London, UK: The Concrete Centre

E5

British Standards Institution (2008) NA to BS EN 1991-2:2003 UK National Annex to Eurocode 1. Actions on structures. Traffic loads on bridges, London, UK: BSI

E6

Beards C.F. (1996) Structural Vibration Analysis: Modelling, Analysis and Damping of Vibrating Structures, London, UK: Hodder Headline

E7

Robertson A.S. (2013) ‘Retrofitting Eagles Meadow Bridge with a tuned mass damper’, The Structural Engineer, 91 (7), pp. 24–28

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James Sutherland History Lecture THE GOTHIC TOWER OF FREIBURG MINSTER: STRUCTURAL ANALYSIS AND REPAIR The 116m high tower is dated to about 1300 AD and its 45m high spire is unique in terms of architecture and building technique. This lecture will report on the extensive investigations and research PROGRAMS WHICHWEREUNDERTAKENINORDERTODEVELOPANEFlCIENTANDMINIMISEDREPAIRCONCEPT

Rainer Barthel is a structural engineer, he is a partner in the company Barthel & Maus, Consultant Engineers in Munich, a Professor at the Technical University of Munich, and specialises on the repair of historic structures. After studying structural engineering at the University of Stuttgart he was awarded his Doctorates degree at the University of Karlsruhe. He has gone on to work as a project manager for Ove Arup in London, has been a Professor at the Technical University of Munich ANDHASFOUNDEDHISOWNOFlCETOGETHERWITHAPARTNER

Annual Institution Events

Conferences & Seminars

Date | Thursday 18 February 2016 Time | 17:30 for a 18:00 start Price | Lecture: Free Dinner: £70 Venue | International HQ 47-58 Bastwick Street

Special Interest Series

Technical Lecture Series

The Institution’s key annual events, many of which have been running for several decades.

Registration is required in advance as space is limited. To book your place, please visit the events section of the Institution website, www.istructe.org . If you have any questions please contact the Events Team at [email protected].

Structural Behaviour Course A free online course for our Academic Community and Student Members. This exciting new course offers 200 questions which assess elements of structural behaviour, with 20 questions presented to you at random each time you log in. You can take the course, free of charge, as many times as you like. Go to www.istructe.org/resources-centre/structural-behaviour A year’s access to the Course is also available to other members of the Institution for just £5 in the UK (or less, depending on VAT outside the UK).

p48_TSE.01.16.indd 48

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Opinion Letters or longer articles written from a personal perspective, on topics of current interest that offer a particular opinion and often encourage further discussion and/or debate.

50 Book review: Best Construction Methods for Concrete Bridge Decks – Cost Data 51 Book review: Acoustic Emission (AE) and Related Non-destructive Evaluation (NDE) Techniques in the Fracture Mechanics of Concrete: Fundamentals and Applications 52 Book review: Design of durable concrete structures 53 Verulam

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Opinion Book reviews

Reviews This new technical guide provides a useful source of cost data for pricing concrete bridges – particularly formwork and falsework – explains Matthew Myerscough, who has trialled it himself on a recent project.

Best Construction Methods for Concrete Bridge Decks – Cost Data Author: Simon Bourne Publisher: Concrete Bridge Development Group  Price: £95.00 ISBN: 978-1-904-48285-6

It has been stated that the twin obligations of a bridge engineer are to use a client’s money wisely and to produce a structure for society that will enhance the built environment1,2. As the title suggests, this latest publication from the Concrete Bridge Development Group (CBDG) provides guidance on selecting a cost-effective type of concrete bridge deck to help ensure these obligations are satisfied. To make a successful choice, the bridge engineer must have a good appreciation of the construction methods available to place and form the concrete for a new bridge deck, as such practices have a major effect on the final cost of a scheme. However, such knowledge alone is not sufficient, as preliminary schemes can only be compared if they have been reliably priced. It is therefore the intention of this technical guide to provide sufficient cost data to enable the initial pricing of any type and size of concrete bridge. With a total length of 120 pages, this glossy A4-sized publication is divided into four chapters plus a detailed 50-page appendix. Following a concise introductory chapter, the second chapter contains

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three sections which cover conceptual, general and particular choice of bridge deck. Conceptual choices include decisions concerning aesthetics, sustainability and durability, while bridge layout, span arrangement and articulation are discussed in the general choices section. Here, the use of reinforced or prestressed concrete is introduced, plus the more unusual partial prestressed bridge form which utilises external cables. While it is not the intention of this guide to describe the merits of preand post-tensioned concrete, some basic details are provided. This section concludes by outlining some benefits of high-strength, lightweight and self-compacting concrete, and the importance of good water management through careful detailing.

The final part of chapter two introduces 15 types of concrete bridge deck, which range from in situ solid slabs and balanced cantilever bridges, to whole-span precast box girders. In my opinion this section best explains the purpose of the book. On page 26, the reader discovers that while bridge deck quantities can be readily determined and priced, the difficulty with accurate cost prediction lies with pricing the formwork and falsework needed to construct the bridge. The novel content of the guide is contained within the third chapter, where several pages are dedicated to each of the 15 bridge deck types. A common format for each type includes a summary table, deck description, and typical formwork and falsework rates in £/m2 for a range of bridge lengths, e.g. 50m, 150m and 600m. These rates include costs relating to casting, transport and erection, and have been published alongside total deck and typical production rates. Usefully, the appendix contains a detailed breakdown of all the summary rates in tabular format, which would allow figures to be adjusted to suit overseas markets. One concern with such a publication is that the cost data are likely to become outdated in the near future. However, it is stated in the guide that a series of indices/factors will be published on the CBDG website in late 2015 so costs can be adjusted pro rata over time. During my review I read the guide from start to finish in a few days and found the content very readable and not

Matthew Myerscough MEng (Hons) Matthew Myerscough is a Bridge Engineer at Cass Hayward. He studied Civil Engineering at University College, Durham, and is currently enrolled on the Bridge Engineering MSc at the University of Surrey. Matthew has a particular interest in long-span structures and won the Institution’s Husband Prize in 2014 for his suspension bridge paper.

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overcomplicated. It is certainly not the sort of text where the reader becomes saturated with complex concepts and formulae. There is, however, some repetition in the first two chapters, e.g. the parameters affecting the choice of bridge deck are discussed on pages 1, 3 and 17. Most pages are well illustrated with colour photographs or neat hand-drawn diagrams, and the tabulated rates in the appendix are presented clearly. I found the cost data straightforward to use when trialled

on a current project, and particularly liked the rules of thumb such as those concerning reinforcement detailing and effective deck thickness on pages 16 and 24 respectively. Although the guide is intended for professionals, the comprehensive explanation of the range of concrete bridge decks would be useful for students with an interest in the subject. In summary this new technical guide is an excellent addition to the range of publications already available from the CBDG.

References E 1) Benaim R. (2008) The Design of Prestressed Concrete Bridges, Concepts and Principles, Abingdon, UK: Taylor & Francis E 2) Bourne S. (2013) ‘Prestressing: recovery of the lost art’, The Structural Engineer, 91 (2), pp. 12–22

This book provides a valuable snapshot of the recent state-of-the-art in this important field, says John Bungey, and will be useful to students, researchers and forward-thinking practising engineers alike.

Acoustic Emission (AE) and Related Nondestructive Evaluation (NDE) Techniques in the Fracture Mechanics of Concrete: Fundamentals and Applications Editor: Masayasu Ohtsu Publisher: Woodhead Publishing  Price: £175.00 ISBN: 978-1-782-42327-0

This book comprises 13 chapters based on a specialist conference session held in Spain in 2013, and is edited by a widely recognised international authority in the field. The chapters focus on recent findings related to innovative non-destructive assessment methods associated with fracture mechanics which are under development for concrete, with particular emphasis on acoustic emission (AE). Ultrasonics, X-rays and thermography also feature. The 32 contributors are from a wide range of countries, including Japan, India and the USA, as well as a strong European input – although, sadly, there is no UK participation. There is a very useful introduction by the Editor explaining the basic principles of AE at an easily understandable level. This includes recommendations for applications to in situ concrete based on recent RILEM work which cover standardisation of measurement, damage quantification and

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crack classification. The majority of chapters are largely theoretical in nature, dealing with analysis and interpretation of results, supported by laboratory studies. AE testing involves the detection of sudden strain energy release from localised sources, such as crack development, and alternative analysis approaches for use on concrete are discussed and compared. Some chapters include details of equipment development, while there is a strong emphasis on monitoring situations, including the use of wireless sensing systems. These range from AE detection and classification of earthquake damage, to corrosion of reinforcing and prestressing steel, low-level load testing, fire damage and creep effects. The potential for use of artificial neural networks to assist analysis of AE results for corrosion monitoring of post-tensioned concrete is also considered in detail in one chapter, while another describes interesting preliminary

studies into thermographic imaging of corroding reinforcing bars. Unfortunately only limited examples are provided of application outside of the laboratory. Among these are laboratory X-ray CT scanning of cores cut from earthquake-damaged concrete for crack visualisation, and AE monitoring of a historic masonry structure during seismic activity, showing clear correspondence of observed data. AE has been proposed for testing concrete for many years, and is already an established laboratory tool. This new document contains a wealth of references, both historic and recent, and provides a valuable snapshot of the recent state-of-the-art in an important and ever-developing field. The general standard of content and presentation is high, with relatively little repetition between chapters. The book will be particularly useful for students and researchers, as well as engineers seeking to move innovative research forward from the laboratory into practical on-site applications, including structural health monitoring.

John Bungey John Bungey is Emeritus Professor of Civil Engineering at the University of Liverpool, and a chartered engineer with more than 40 years of teaching, research and consultancy related to nondestructive testing of concrete. John has published over 150 relevant papers and a textbook on Testing of Concrete in Structures. He is a former chair/member of numerous UK and international committees.

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Review Chris Shaw finds this to be a well-presented and useful book, but one that is let down by a series of omissions which he would like to see addressed in the next edition.

Design of durable concrete structures

Author: Stuart Matthews Publisher: IHS BRE Press Price: £95.00 ISBN: 978-1-848-06175-0

Concrete is the most widely used structural material around the world, and will continue to be. Most of the concrete used is reinforced concrete and durability is an essential requirement. This book looks at most of the different factors involved in achieving durability, and the text layout is good, as are the photos and figures. The author draws heavily on fib documents, and other published work, and draws attention to the advances in analysis and design which have not been matched by improvements in the knowledge and skills of the construction operatives. Structures are still being built to the lowest initial cost, without regard to their lifetime cost, particularly their durability. The author covers most of the issues involved in the selection of the durability factors, but there is no mention of the political influences or personal preferences of designers, both of which can have a significant influence on the choice of the final design. It is good to see the “Common Law of Business” reproduced on page 26, as this is all too often overlooked when selecting the successful tender for the work. The inclusion of the “soft” factors (page 8 etc.) is also welcome, as these have a significant effect on the quality of the finished structure, and more attention needs to be paid to them.

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The author rightly makes many mentions throughout the book of the problems resulting from the failure to achieve the specified cover to the reinforcement in ordinary steelreinforced concrete, but fails to make any mention of BS 7973 or the very relevant papers published as part of the Proceedings of the 6th, 7th, and 8th International Conferences on Concrete. This is a serious omission because, as Sections 1.3 and 1.4 explain, the problem of misplaced reinforcement is the single biggest cause of durability problems in ordinary steel-reinforced concrete. There is only one short section (13.10) on this subject, and this has an error in it with regard to the plastic spacer text. The concreting sub-plan (page 372), and reinforcement plan (page 375) are good ideas, but need to specifically include the spacer and chair requirements. The author makes reference to “negative cover” (page 21), but unlike for other terms in the book, makes no acknowledgement of the originator of the term. On page 129, three of the four “C”s of concrete are mentioned. It would have been very helpful if the four “C”s of concrete had been included and explained, as they are all equally fundamental to achieving durable concrete structures. The section that starts on page 278 deals

with the use of galvanised reinforcement in some detail. However, there is no mention made of the need to passivate the galvanised reinforcement before it is fixed and the concrete poured. This has been known about for many decades, so it should have been included. There is a section that deals with corrosion of reinforcement in some detail, but it is disappointing that it does not mention longitudinal cracking of corroded steel reinforcing bars, which can greatly reduce the strength of the structure. Other terms such as “minimum cover” and “mesh” were discontinued a long time ago and should not have been included in the text, especially “minimum cover”, which has resulted in so many of the problems that continue to be seen, even on new structures. It would have been useful to include a section on flexible detailing as this can overcome many of the problems associated with poor durability due to misplaced and corroding steel reinforcement. Similarly, a section on the use of hybrid reinforcement would have been useful. This is a potentially useful book, especially with regard to the concrete itself, but users need to be aware of the omissions and errors, which need addressing in the next edition.

Chris Shaw Chris Shaw is a consultant chartered civil and structural engineer, with several decades of experience in achieving durable concrete, especially reinforced concrete. He is known worldwide for his expertise in developing sustainable reinforced concrete designs, and has written and contributed to many articles and publications on achieving durable reinforced concrete.

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Opinion Letters

TheStructuralEngineer January 2016

Verulam

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Send letters to… All contributions to Verulam should be submitted via email to: [email protected] Contributions may be edited on the grounds of style and/or length by the Institution's publishing department.

Topics of importance openly discussed

Packing the right force? In May 2015 we published an article on assessing the capacity of the historic Grand Parade stone balustrading in Bath, UK. A number of readers have concerns about the validity of the forces used in the assessment. The first contribution is from Ken Wiseman, who writes:

The paper by Collins and Cooke (May 2015, pages 26–31) suggests that an international rugby side scrummaging against a parapet, as shown in their Figure 9, would exert a force of only 1.4kN. That seemed to me to be intuitively wrong. The pack weights of international teams are typically over 800kg (916kg for the England team in the 2015 Six Nations tournament). Can packs of such weight convert only 17% of their body mass into a forward thrust? The 1.4kN figure is apparently taken from a paper by Preatoni et al1, which appears to be misinterpreted – the forward thrust of international packs indicated in their Table 2 is 16.5kN at peak (approximately 200% of pack weight) and 8.3kN sustained

"AS KEEN RUGBY FANS, WE WERE SURPRISED THAT AN ELITE INTERNATIONAL SCRUM COULD ONLY GENERATE A SUSTAINED FORCE OF 1kN, AS STATED IN THE PAPER"

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(about 100% of pack weight). The 1.4kN force quoted by Collins and Cook is what Preatoni et al describe as “lateral force” – by which they mean the force exerted by the scrum at 90° to the line of action of the scrum. Collins and Cooke are surely correct to point out that unthinking application of code requirements is not always (if ever) appropriate in structural design, but it is a little worrying to think that design might instead be based on misinterpretation of research which has been undertaken for a completely different purpose. The paper by Dickie and Wanless on “Spectator terrace barriers”2 is not cited at all by Collins and Cooke, but this paper reports theoretical and experimental research that is more directly applicable to balustrade design.

And a second letter from Steve Buckley…

My colleagues and I were intrigued by the paper about the in situ testing of the historic Grand Parade balustrades and, in particular, the justification for the test load that was adopted. As keen rugby fans, we were surprised that an elite international scrum could only generate a sustained force of 1kN, as stated in the paper, and a 1.4kN peak force from a group of men weighing around 1t seemed very low. Looking at the referenced paper quoted as the source of this information1, it gives the peak force from an international scrum of 16.5kN and a sustained force of 8.3kN (when not normalised for pack weight). Even when distributed across the nominal width of the front row, this would give something of the order of 4kN/m peak and 2kN/m sustained. It appears the Grand Parade paper has mistakenly quoted the standard deviations for these values, which are given in the source paper as 1.4kN at

peak and 1.0kN for sustained loading. None of which is to say that the adopted load is not appropriate for the testing that was completed, but it does rather negate the published justification for it. One is also to hope there are no mischievous rugby packs lurking in Bath willing to put the paper to the test!

In the same vein, Sam Polson, writing from Christchurch, New Zealand, adds:

As a structural engineer and rugby fan, I was excited by the cover article of the May 2015 issue of The Structural Engineer. The use of a rugby forward pack to check the structural strength of a balustrade seemed too good to be true. So I was surprised to learn from the article that the peak lateral force generated by a male international scrum is only 1.4kN. Given that we are talking about a group of eight exceptionally strong athletes, most of whom weigh over 1.0kN, this force seems far too small. A quick internet search will show that All Black prop forward Ben Franks can squat a total of 2.4kN on his own. Upon reviewing the University of Bath research into scrum loads1, it appears that the 1.4kN peak force and 1.0kN sustained force quoted in the article are actually the standard deviation, with the correct average peak force being 16.5kN and the average sustained force being 8.3kN. Regardless of the above, the article was fascinating and I congratulate the authors on applying some interesting real world science to a complex problem. Although I believe there is little chance of the English forward pack, or any forward pack for that matter, setting a scrum against the Grand Parade balustrade, perhaps in the interests of safety a “Strictly No Scrummaging” sign should be clearly displayed!

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And finally from Stuart Marchand…

I refer to the article “Grand Parade, Bath: in situ load testing of a historic structure to avoid unnecessary intervention”. While researching a separate but similar issue, I referred back to the research carried out by the University of Bath on rugby scrum loadings1. I discovered that the figures given in the paper are incorrect and misleading. A male international rugby scrum can exert a peak force of 16.5kN, not 1.4kN, which is the quoted standard deviation. Similarly, the sustained load is 8.3kN with a standard deviation of 1.0kN. References 1) Preatoni E., Stokes K., England M. and Trewartha G. (2012) ‘Forces generated in rugby union machine scrummaging at various playing levels’, IRCOBI Conference Proceedings, Dublin, Ireland, 12–14 September, pp. 369–378 2) Dickie J.F. and Wanless G.K. (1993) ‘Spectator terrace barriers’, The Structural Engineer, 71 (12), pp. 216–222 It is welcome that the paper was read by so many readers, who all seem to have a common view. While supportive of a riskbased approach to practical problems, they all think the force examples quoted were too low.

Playing it too safe? Alastair Hughes questions Alasdair Beal’s reply (November 2015) to his original Viewpoint article (July 2015) on structural safety margins.

Alasdair Beal’s response was a most interesting one, if somewhat tangential, because what concerns him is the erosion of safety margins across the board. He would, if I understand his drift, be content to see not only γM1 but also γM0 increased to 1.1. Perhaps γM2 should be 1.3? And similarly, for concrete, presumably 1.2 for rebar, to keep the playing field level?

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Opinion Letters

"I WOULD TAKE SOME CONVINCING THAT WE NEED 10% MORE METAL IN EVERY (STRENGTHLIMITED) BEAM AS WELL AS EVERY COLUMN"

(i) In BS 449:1969, web buckling at the end of a beam was calculated based on a length of web equal to the stiff bearing length plus a 45° spread up to mid-height; and the permissible stress was based on column permissible stresses with L/r = (d3√3)/t, where d3 is height between root radii (ii) BS 5950:1985 used a similar approach but L/r was increased to 2.5d3/t (iii) BS 449:1988 was amended to bring it into line with BS 5950:1985 (iv) BS 5950:2000 changed to a completely different calculation

It is certainly true that the ice we skate on has been getting thinner, and pretty obvious that we cannot carry on at this rate for ever. Whether by processes akin to competitive devaluation or to make complexity palatable, official minimum margins of structural safety have been allowed to decline, and Alasdair is surely not alone in his view that this has gone too far. However, I would take some convincing that we need 10% more metal in every (strength-limited) beam as well as every column. In order to avoid an overcorrection, I suggested that any increase to 1.1 should be in tandem with a redefinition of characteristic yield strength.

If we take the example of a 533 × 210@ UB made from grade S355 steel and with a stiff bearing length of 23mm, the allowable web buckling loads in accordance with these codes are:

As ever, collective views are welcome.

Beam web buckling – discrepancies in standards Finally, regular correspondent Alasdair Beal writes in with yet another query on code discrepancies, this time on the topic of steel web buckling at beam supports.

(i) BS 449:1969: 376kN (unfactored) (ii) BS 5950:1985: 324kN (factored) = 216kN (unfactored) (iii) BS 449:1988: 206kN (unfactored) (iv) BS 5950:2000: 173kN (factored) = 115kN (unfactored) The allowable loads in later codes show dramatic reductions. The permissible working load to BS 5950:1985 was less than 60% of the BS 449:1969 figure. BS 5950:2000 reduced this even further: it allows only 53% of the load permitted by BS 5950:1985 and only 30% of the load permitted by BS 449:1969. This is worrying, as seating cleat beam connections were very common until the 1970s and countless thousands of beams must have been designed to the BS 449:1969 recommendations. Does anyone know the reason for these large reductions in allowable web buckling load in recent codes? Are beams designed to BS 449:1969 and BS 5950:1985 unsafe, or is BS 5950:2000 over-conservative? If anyone understands the corresponding Eurocode 3 recommendations, how do these compare? As usual, Alastair invites feedback from those who might be in the know.

I recently had to compare beam web buckling at supports to various different editions of BS 449 and BS 5950 and found surprising results:

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At the back The home of diary dates, the latest from Structures, updates on Institution services and other miscellanea, plus products, services and jobs.

56 Diary dates 58 Spotlight on Structures 60 And finally… 61 Products & Services 63 Services Directory 64 TheStructuralEngineerJobs

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TheStructuralEngineer January 2016

At the back Diary dates

Diary dates

Unless otherwise stated, technical meetings start at 18:00 with refreshments from 17:30 - they are free of charge to attend, unless stated otherwise. Registration for evening technical meetings is required via [email protected]

MEETINGS AT HQ

Speakers: Martin Powell, Hunter Lyden, Philip Nelson 1864 Suite, Lancashire County Cricket Club, Old Trafford, Manchester 18:30 for 19:00

Note that more current information may be available from the Institution website: www.istructe.org/events-and-awards

47–58 Bastwick Street, London EC1V 3PS, UK Friday 15 January President’s Inaugural Address 2016 – The art of the possible Alan Crossman 17:30 for 18:00 start (prior registration required)

Wednesday 27 January Design of steel connections with the new CBFEM method (workshop) Prof. Frantisek Wald (Prague University) and Lubomir Sabatka (CEO of IDEA-RS) Details: http://idea-rs. uk/?p=16061 Start: 09:00; finish: 13:00 (Note meeting time)

Wednesday 6 April Young Researchers’ Conference 2016 Prof. Ian Kinloch 09:00 for 09:30 start

HISTORY STUDY GROUP Tuesday 12 January Annual Meeting Tuesday 2 February Restoration work at Dyrham Park, near Bath Margaret Cooke and Kim Collins

Thursday 18 February Sutherland History Lecture – The Gothic Tower of Freiburg Minster: structural analysis and repair

Saturday 30 January IStructE CRG 8th Annual Secondary Schools “Design & Build” Competition JFK Auditorium, University of the West Indies, St Augustine Campus, Trinidad & Tobago 08:15–14:30 Details: Ms Tiffani de Verteuil (istructe. [email protected])

Rainer Barthel

East Anglia

REGIONAL GROUPS

Monday 11 January Forensic investigation and learning from past mistakes

Bedfordshire and Adjoining Counties Wednesday 20 January CDM Regulations Andy Childs Holiday Inn Hotel, London Road, Newport Pagnell MK16 0JA 18:00 for 18:30 Secretary: Tony Hales ([email protected])

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Caribbean

Dr Stuart Matthews Park Farm Hotel, Hethersett, Norwich NR9 3DL 18:30 for 19:00

Monday 15 February Designing in the Historical Environment Ray Makin Suffolk Golf Hotel & Spa, Fornham St Genevieve, Bury

History Study Group meetings start at 18:15 with refreshments from 17:45. Registration is not required for History Study Group meetings except for the Annual business meeting held in January.

Regional Group Committee members should submit details of forthcoming events to: [email protected]

St Edmunds IP28 6JQ 18:30 for 19:00

Wednesday 16 March Offshore Wind – Meeting the Challenges (Joint meeting with ICE) Rob Mattholie & James Rinkel The Oaklands Hotel, 89 Yarmouth Road, Norwich NR7 0HH 18:00 for 18:30 Secretary: Paul Wilson (tel: 01603 614 834; email: [email protected])

Lancashire and Cheshire Monday 18 January Structural BIM (Joint meeting with ICE Merseyside)

Tuesday 16 February Engineering victory: structural advances in WWI & II Allan Mann University of Manchester, Renold Building, Manchester 17:45 for 18:30

Tuesday 8 March 125 years of steel bridges in Britain Alan Hayward University of Manchester, Renold Building, Manchester 17:45 for 18:30

Thursday 17 March Annual General Meeting

Jayne Dooley & Dennis Kristensen Liverpool John Moores University, Liverpool 18:00 for 18:30

Philip Nelson Lancashire County Cricket Club, Old Trafford, Manchester 18:00 for 18:30

Tuesday 19 January Inaugural Meeting and Hot Pot Supper

Secretary: Ian Tickle (email: [email protected])

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on Progressive Collapse

Northern Counties (Tyne Centre) Tuesday 12 January The new Forth Road Bridge (Joint meeting with ICE) Speaker: TBA Crowne Plaza Hotel, Stephenson Quarter, Forth Street, Newcastle-upon-Tyne NE1 3PF 17:45 for 18:15 Details: [email protected]

Tuesday 2 February Designing in the Historic Environment Speaker: TBA Central Square, Forth Street, Newcastle-upon-Tyne NE1 3PJ 17:45 for 18:15 Details: C.Vemury@tees. ac.uk

Tuesday 1 March Royal Engineers Speaker: TBA Central Square, Forth Street, Newcastle-upon-Tyne NE1 3PJ 17:45 for 18:15 Details: C.Vemury@tees. ac.uk

Tuesday 5 April President’s Visit followed by Skill and Care vs Compliance with Specifications Robert Langley Central Square, Forth Street, Newcastle-upon-Tyne NE1 3PJ 17:45 for 18:15 Details: C.Vemury@tees. ac.uk

Northern Counties (Tees Centre) Tuesday 19 January AGM followed by a talk

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John Carpenter Stephenson Building, Teesside University, Middlesbrough TS1 3BA 17:45 for 18:15 Details: joe@structural. org.uk

Tuesday 9 February Maintaining Transport Structures (Joint meeting with ICE) Stephenson Building, Teesside University, Middlesbrough TS1 3BA 17:45 for 18:15 Details: joe@structural. org.uk

Tuesday 8 March Brazil Olympics: design of water slalom (Joint meeting with ICE) Stephenson Building, Teesside University, Middlesbrough TS1 3BA 17:45 for 18:15 Details: joe@structural. org.uk

Tuesday 12 April Joining of composite materials Chris Worral Stephenson Building, Teesside University, Middlesbrough TS1 3BA 17:45 for 18:15 Details: joe@structural. org.uk Secretary: Trevor Little (tel: 0191 255 7300; email: [email protected])

Street, Glasgow G1 1RD (NB: New venue for Glasgow) 17:30 for 18:15 Hon. Secretary: Danny Wright (email: honsec@ istructescotland.org)

Surrey Monday 11 January The Role of the Professional Engineer & CDM Eur Ing Chris Weston Lecture Theatre M, Surrey University, Guildford, Surrey GU2 7XH 18:00 for 18:30 Details: edward.bromhead@ btinternet.com

Monday 8 February Design – Hidden Dangers Dr Stuart Matthews Lecture Theatre M, Surrey University, Guildford, Surrey GU2 7XH 18:00 for 18:30 Details: edward.bromhead@ btinternet.com

Monday 7 March Designing in the Historic Environment Andrew Burns & Ray Makin Lecture Theatre M, Surrey University, Guildford, Surrey GU2 7XH 18:00 for 18:30 Details: edward.bromhead@ btinternet.com

Monday 11 April Report Writing

Scotland Tuesday 12 January The Future of Structural Engineering Glenn R. Bell Technology and Innovation Centre, University of Strathclyde, 99 George

Brendan Brophy John Galsworthy Building, Kingston University, Penrhyn Road, Kingstonupon-Thames, Surrey KT1 2EE 18:00 for 18:30 Details: edward.bromhead@ btinternet.com

Secretary: Andy Green (thegreenhouse1@ btopenworld.com)

INTERNATIONAL CONFERENCES

Johannesburg, South Africa Western Counties Thursday 21 January Site inspection duties – how long is a piece of string? Stephen Hargreaves Queen’s Building, Bristol University, Bristol BS8 1TH 18:00 for 18:30

Thursday 18 February Construction Products Regulation and CE Marking Update Dr David Moore Arup, 63 St Thomas St, Bristol BS1 6JZ 18:00 for 18:30

Tuesday 8 March Structural behaviour – do you know your hogging from your sagging? Dr AJ Crewe Queen’s Building, Bristol University, Bristol BS8 1TH 18:00 for 18:30

Thursday 17 March Forensic engineering and learning from defects, failures and damage Colin Richardson Arup, 63 St Thomas St, Bristol BS1 6JZ 18:00 for 18:30

Friday 13 May Annual dinner (black tie event) Ashton Court Mansion, Long Ashton, Bristol BS41 9JN 18:30 Price: tickets from £35.00 Secretary: Mahara Booshanam (maharabooshanam@gmail. com)

Wednesday 27–Friday 29 January Advances in Cement and Concrete Technology in Africa 2016 Details: ACCTA2016 Conference Office, BAM Federal Institute for Materials Research and Testing, Unter den Eichen 87, Berlin 12205, Germany (email: [email protected]) Registration details: TBA

Newcastle, UK Wednesday 26 October–Friday 28 October Novel Structural Skins – Improving sustainability and efficiency through new structural textile materials and designs Newcastle University, Newcastle-upon-Tyne, Tyne and Wear, UK Details: Alison Bird (email: [email protected])

Brisbane, Australia Thursday 22 November– Sunday 25 November Australasian Structural Engineering Conference (ASEC 2016) – The roles of structural engineers Speakers: Tristram Carfrae, Dr Sean Brady Brisbane Convention & Exhibition Centre (BCEC), Brisbane, Australia Details: asec2016.org.au

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TheStructuralEngineer January 2016

At the back Spotlight on Structures

Spotlight on In this section we shine a spotlight on papers recently published in Structures – the Research Journal of The Institution of Structural Engineers. Structures is a collaboration between the Institution and Elsevier, publishing internationally-leading research across the full breadth of structural engineering which will benefit from wide readership by academics and practitioners. Access to Structures is free to Institution members (excluding Student members) as one of their membership benefits, with access provided via the “My account” section of the Institution website. The journal is available online at: www.journals.elsevier.com/structures

Update for members From January 2016 we are introducing changes to the way Institution members access articles published in Structures. During 2015 all content in Structures was available free of charge to both Institution members and non-members. From January 2016 non-members will require a subscription to access the journal, or can purchase individual articles on a pay-per-view basis. See www.elsevier.com/journals/structures/2352-0124/order-journal for details. From January 2016 Institution members (with the exception of Student members) will continue to receive free access to Structures. However, members will now need to access the journal via the “My account” section of the Institution website (www.istructe.org/log-in) where you will find a link to Structures. By following this route, the journal website will recognise you as an Institution member. Students wishing to read articles in Structures may have access via their university library. See www.elsevier.com/journals/ structures/2352-0124/order-journal or contact your library for details.

Special Issue Steel Structures: Mechanics, Simulation and Testing Guest Editors: Nuno Silvestre and Leroy Gardner This Special Issue of Structures contains updated and extended versions of a selected collection of papers presented at the MiniSymposium on ‘Steel Structures: Mechanics, Simulation and Testing’, held within the 9th European Solid Mechanics Conference (ESMC), Madrid, 6–10 July 2015. A new approach to modal decomposition of buckled shapes Jurgen Becque Interactively Induced Localization in Thin-walled I-section Struts Buckling About the Strong Axis Elizabeth L. Liu and M. Ahmer Wadee

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A GBT Model for the Analysis of Composite Steel–Concrete Beams with Partial Shear Interaction Gerard Taig, Gianluca Ranzi, Daniel Dias-da-Costa, Giuseppe Piccardo and Angelo Luongo Local–Distortional Interaction in Cold-formed Steel Columns: Mechanics, Testing, Numerical Simulation and Design André Dias Martins, Dinar Camotim, Pedro Borges Dinis and Ben Young Structural modeling of cold-formed steel portal frames Xi Zhang, Kim J.R. Rasmussen and Hao Zhang Experimental Study on Ferritic Stainless Steel RHS and SHS Cross-sectional Resistance Under Combined Loading I. Arrayago and E. Real Experimental study of stainless steel angles and channels in bending M. Theofanous, A. Liew and L. Gardner On the influence of the load sequence on the structural reliability of steel members and frames Andreas Taras and Stefan Huemer Advanced materials for concrete-filled tubular columns and connections Ana Espinos, Manuel L. Romero, Antonio Hospitaler, Ana M. Pascual and Vicente Albero Numerical investigation on I-beam to CHS column connections equipped with NiTi shape memory alloy and steel tendons under cyclic loads Wei Wang, Tak-Ming Chan and Hongliang Shao

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Articles in press The following articles ‘in press’ have recently been made available online:

c Ecole Centrale Paris, 92290 Châtenay-Malabry, France http://dx.doi.org/10.1016/j.istruc.2015.11.002

Effect of concrete compressive strength on transfer length Alberto T. Ramirez-Garciaa, Royce W. Floydb, W. Micah Halea and J.R. Martí-Vargasc a Department of Civil Engineering, University of Arkansas, Fayetteville, AR 72701, USA b School of Civil Engineering and Environmental Science, Norman, OK 73019, USA c Universitat Politècnica de València (UPV), València, Spain http://dx.doi.org/10.1016/j.istruc.2015.10.006

An experimental study on the effect of PET fibers on the behavior of exterior RC beam-column connection subjected to reversed cyclic loading Comingstarful Marthonga and Shembiang Marthongb a Civil Engineering Department, National Institute of Technology Meghalaya, Shillong, India b Earthquake Engineering Research Center, International Institute of Information Technology Hyderabad, Gachibowli, India http://dx.doi.org/10.1016/j.istruc.2015.11.003

Behavior of GFRP bridge deck panels infilled with polyurethane foam under various environmental exposure Hesham Tuwaira, Jeffery Volzb, Mohamed ElGawadya, Mohaned Mohamedc, K. Chandrashekharac and Victor Birmand a Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO, USA b School of Civil Engineering and Environmental Science, The University of Oklahoma, Norman, OK, USA c Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, MO, USA d Engineering Education Center, Missouri University of Science and Technology, Rolla, MO, USA http://dx.doi.org/10.1016/j.istruc.2015.10.008

Bond behavior of smooth and sand-coated shape memory alloy (SMA) rebar in concrete A.H.M. Muntasir Billah and M. Shahria Alam School of Engineering, University of British Columbia, Kelowna, BC, Canada http://dx.doi.org/10.1016/j.istruc.2015.11.005

On the improvement of buckling of pretwisted universal steel columns Farid H. Abed, Mai Megahed and Abdulla Al-Rahmani Department of Civil Engineering, American University of Sharjah, Sharjah, UAE http://dx.doi.org/10.1016/j.istruc.2015.10.012 Application of Intelligent Passive Devices Based on Shape Memory Alloys in Seismic Control of Structures Behrouz Asgarian, Neda Salari and Behnam Saadati Civil Engineering Faculty, K.N. Toosi University of Technology, Tehran, Iran http://dx.doi.org/10.1016/j.istruc.2015.10.013 Buckling and Vibration of Functionally Graded Material Columns Sharing Duncan’s Mode Shape, and New Cases Isaac Elishakoffa, Moshe Eisenbergerb and Axel Delmasc a Department of Ocean and Mechanical Engineering, Florida Atlantic University, Boca Raton, FL 33431-0991, USA b Faculty of Civil and Environmental Engineering, Technion, Israel Institute of Technology, Technion City, Haifa, Israel

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Lateral Cyclic Behaviour of RC Columns Confined With Carbon Fibres Pedro Faustinoa, Pedro Fradea and Carlos Chastrea,b a Department of Civil Engineering, Universidade NOVA de Lisboa, Portugal b CEris, ICIST, Department of Civil Engineering, Universidade NOVA de Lisboa, Portugal http://dx.doi.org/10.1016/j.istruc.2015.11.004 Analytical approach of anchor rod stiffness and steel base plate calculation under tension Konstantinos Daniel Tsavdaridisa, Mohamed A. Shaheenb, Charalampos Baniotopoulosc and Emad Salemb a Institute for Resilient Infrastructure, School of Civil Engineering, University of Leeds, Leeds, UK b Department of Civil Engineering, Al-Azhar University, Cairo, Egypt c School of Civil Engineering, University of Birmingham, Birmingham, UK http://dx.doi.org/10.1016/j.istruc.2015.11.001 Highlights • Anchor rod stiffness and steel base plate under tension • Extensive parametric study using finite element analysis • Parameters: diameter of anchor plate and anchor rod, and length of anchor rod • Proposed equation represents the headed anchor bolts by massspring models • Calculated stiffness used to commercial available structural software

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TheStructuralEngineer January 2016

At the back And finally...

And finally...

The place to test your knowledge and problem-solving ability. If you would like to submit a quiz or problem, contact [email protected]

We launch this new section with a steel quiz brought to you by the SCI. This month’s topic is galvanising. Answers will be published in the February issue. Question 1

Question 2

Is it necessary to remove the galvanising from faying surfaces in joints using tension-control bolts?

In environments where greater corrosion resistance is needed, is it better to increase the weight of galvanising or add a supplementary coat of “paint”?

Question 3 Why is through-deck welding of shear studs acceptable, but welding to galvanised supporting steel beams is not?

SCI is the leading, independent provider of technical expertise and disseminator of best practice to the steel construction sector. www.steel-sci.org

The Institution is proud to publish authoritative books and technical reports that provide essential, accurate information for structural engineers.

The Institution of Structural Engineers February 2008

Manual for the design of plain masonry in building structures to Eurocode 6

Each publication and report is subjected to an exacting peer review procedure and reviewed by at least two external assessors, and where appropriate, subjected to a legal review. As such, these publications are a valuable addition to any practising structural engineer’s reference library. The Institution bookshop also stocks books from other publishers which are relevant to the discipline of structural engineering and, in many cases, the Institution offers a special discount to members on these publications.

Manual for the geotechnical design of structures to Eurocode 7 May 2013

shop.istructe.org

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Institution Structural Engineers

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PRODUCTS & SERVICES

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Ancon backs CARES campaign against nonapproved re-bend continuity systems CARES, the Certification Authority for Reinforcing Steels, has expressed concern at the continued use of non-approved re-bend reinforcement continuity systems by the UK Construction Industry. To address this issue, CARES is running a high-profile information campaign in a number of trade journals including New Civil Engineer, Construction News and Concrete, highlighting the unrivalled assurances given by its Technical Approval scheme. As manufacturer of the CARES-approved Eazistrip continuity system, Ancon gives this campaign its full support and is keen that the industry recognises the stringent quality standards met by this product. Further information: Ancon (tel: 0114 275 5224; web: www.ancon.co.uk)

Structural Concrete Alliance announces 2015 award winners The Structural Concrete Alliance has announced the winner of the 2015 Structural Concrete Alliance Award for Repair and Refurbishment as Concrete Repair Association member Bersche-Rolt, for its concrete repair and coating works to the Barry Island Eastern Shelter, Vale of Glamorgan, in September 2014. The award was presented by broadcaster Huw Edwards during the Concrete Society Awards held at the Grosvenor Hotel, Park Lane, London on 4 November 2015. Second place was awarded to Sika Ltd for Britannia House, a 1930s building with a concrete-encased steel frame in Bradford city centre. Balfour Beatty Concrete Repairs was awarded third place for its repairs to the Sherborne Footbridge in Salford. Further information: Structural Concrete Alliance (tel: 01420 471614; web: www.structuralconcretealliance.org.uk; email: [email protected])

New Demag V-type double girder crane launched Following the launch of the innovative Demag V-type single girder crane, Terex Material Handling has extended the range to include V-type double girder overhead travelling models. V-type double girder cranes are available with load capacities of up to 50t and are offered with spans of up to 35m as standard, with longer girder lengths available upon request. Advantages of the double-girder crane include: it is easily adapted to existing building structures; it offers improved precision for its crab runway; and the design allows more light to pass through, creating a safer working environment. Further information: Demag Cranes & Components Ltd (tel: 01295 676100; fax: 01295 271408; email: [email protected]; web: www.demagcranes.co.uk)

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TheStructuralEngineer January 2016

Reveal hidden slab strength with LimitState:SLAB Limitstate:SLAB speeds up slab analysis and reduces the costs of building refurbishment. Determining the true strength of reinforced concrete slabs is crucial in many rehabilitation projects. The yield-line method excels at identifying slab strength, and LimitState:SLAB is the only software to systematically automate the method. It rapidly finds the critical failure mechanism for problems of any geometry. A Concrete Centre report on the subject states that yield-line design is “a great opportunity for more competitive structures” and engineers can benefit from it with LimitState:SLAB. Further information: Limitstate (email: [email protected]; web: www.limitstate.com)

New design guide from Lindapter The steel connection specialist has launched a 76-page product guide for engineers and other professionals involved in the design of structural and secondary connections. The document features popular products such as the Girder Clamp for quickly connecting I beams without drilling or welding and the Hollo-Bolt®, the original expansion bolt for Structural Hollow Sections (SHS). The new guide has been designed to make it faster for engineers to select the solution to their connection requirement and includes a helpful product comparison table, typical applications and independently approved safe working loads. New products are also introduced such as the Type AAF high slip resistance clamp and Type ALP adjustable lifting point. Further information: Lindapter (web: www.lindapter.com; email: [email protected]; tel: +44 (0)1274 521 444)

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TheStructuralEngineer January 2016

ANALYSIS & DESIGN

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TheStructuralEngineerJobs Telephone 020 7880 6212

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MANAGING DIRECTOR Structural & Civil Engineering Consultancy Central London

Six figure salary + Bonus + Equity opportunity + Benefits

The Role

Experience

Our client is a highly regarded, multi-disciplinary consulting engineering firm which has recently established its first UK office in central London. It is an ambitious overseas company which is seeking to expand in the London/South East market.

‡ Candidates for this position must be self-motivated and highly entrepreneurial. ‡ A Director with strong business development and work-winning experience is required with a track record of growing a consulting engineering business in buildings, structural engineering or civil engineering consultancy – having grown a consulting business to at least £2.0 million fee income per annum. ‡ The MD will need to have strong strategic and business development skills along with an established business network amongst developers, contractors and architects in the London/South East market. ‡ Candidates will have built new partnerships, secured frameworks and developed new client relationships for buildings, structural engineering or civil engineering projects. ‡ Suitable candidates will have had team leadership experience, probably managing at least 20 multi-disciplinary project staff, who have delivered structural engineering or civil engineering consulting projects successfully. ‡ The MD will have a degree and chartered status in either Structural Engineering, Civil Engineering, or Project Management with evidence of further career development and training. An understanding of the whole life cycle of building management would be particularly relevant. ‡ This position will offer an attractive six figure base salary, plus bonus and the opportunity for equity in the new UK business.

This company is seeking to appoint a Managing Director to build a UK engineering consultancy business focusing on structural engineering, civil engineering and project management services in London and the South East. The parent company’s specialist teams currently provide technical structural design services for projects in the UK. The MD will be utilising staff from the parent company and recruiting a local team to build up the technical consulting capability of the London office. Initially, the UK business will be targeting, winning and delivering mainly Commercial, Residential and Educational building projects in London and the South East. Further markets for development could include Sports & Leisure facilities and regional Airports/Airfield developments. The MD will have full P&L responsibility for the London office. The successful candidate will be overseeing business development, work-winning, building new partnerships, securing frameworks, developing new client relationships and ensuring the successful delivery of all UK projects.

Interested candidates should contact, or email a CV in confidence to the retained consultant for this position:Rohan Mitchell, Partner, The Perseus Partnership, Executive Search Consultants. (Tel: 01483 230450 or Mobile: 07973 254577) E-mail: [email protected] Closing date for applications: Monday, 25th January 2016

We are a small and ambitious practice employing 5 chartered, two near chartered and two graduate engineers working on a variety of projects, designing new build, alterations and extensions to residential, commercial and industrial buildings of all types, together with some unusual and unique projects. Our range of services include providing Structural Engineering and Geo environmental Reports together with Party Wall advice. Due to an expanding workload, we require: Chartered Engineer who will be expected to take responsibility for seeing smaller projects through from quotation to completion as well as working as part of a team on larger projects. Experience of preparing Structural Engineering Reports, confidence on site with other construction professionals and an innovative approach to problem solving are pre requisites. Knowledge of MasterSeries, TEDDS and AutoCad would be an advantage. Future opportunities exist for engineers to progress to director/ shareholder level.

Our structural workload is expanding and includes projects in Asia, Europe, Central America and the United States. We are seeking structural engineers at Senior, Associate and Associate Partner level, with strong technical skills and experience, to lead the delivery of complex international projects. To apply please visit: www.fosterandpartnerscareers.com and upload your CV and covering letter to the relevant vacancy.

Salary offered £45,000 - £55,000 dependent on experience. Graduate Engineer with 3 or more years’ experience nearing chartered status. Salary range £24,000 - £30,000 dependent on experience. CAD technician: experienced structural technician in AutoCAD. Knowledge of REVIT an advantage but future training would be given to the right candidate. Salary range £26,000- £30,000 dependent on experience. We pride ourselves on providing excellent solutions, a high quality of presentation and first class customer service in a supportive and friendly working environment where discussion of the best solution is encouraged. We are very flexible and operate 2 incentive schemes which give an opportunity to earn more than a basic salary. We are based in the attractive village of Marple Bridge at the edge of the Peak District but within easy reach of Stockport (6 miles) and Manchester (12 miles). Good public transport links exist via rail and bus and there is plenty of free parking nearby. Please apply to offi[email protected] with CV and brief email.

www.rhodesandpartners.co.uk

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TSE Rec Jan16.indd 65

17/12/2015 09:52

TheStructuralEngineerJobs Telephone 020 7880 6212

Register to receive latest jobs by email - visit www.thestructuralengineer.org/jobs.

Email [email protected]

SENIOR STRUCTURAL ENGINEER DUBLIN

SENIOR STRUCTURAL ENGINEER LEICESTER

PROJECT ENGINEER DUBLIN

Techrete is a leading manufacturer of precast architectural concrete throughout Ireland and the UK. These positions offer the opportunity to work with high profile teams on challenging and exciting buildings. Suitable candidates will enjoy working with detail and have experience of façade engineering. Senior Structural Engineers Dublin (1) & Leicester (1) The candidates will be experienced chartered structural engineers, probably 10 years’ experience, fluent in the design of concrete structure and experience in leading a successful team. Excellent prospects for ambitious persons. Project Engineer The candidate will have up to 5 years post graduate design experience and be chartered or working towards chartership.

Conisbee are an award winning practice looking for dynamic and enthusiastic Structural and Civil Engineers to join our expanding teams in London, Cambridge and Norwich.

From experienced graduates to principal-level engineers, we are seeking individuals to join us on projects spanning across all major building types; with a particular emphasis on residential, educational and historical buildings. For the right candidate there will be the opportunity to take on real responsibility in order to help develop and manage new projects and business growth. For more information or to submit your CV please contact Bob Stagg – [email protected]. or visit www.conisbee.co.uk

Reply in confidence to [email protected]

STRUCTURAL ENGINEERING VACANCIES IN OXFORD 2x Senior Project Engineers 2x Project Engineers 2x Graduate Engineers 2 x R E V I T / C A D Te c h n i c i a n s

AKS Ward is a structural and civil engineering design consultancy who, following an increase in workload, have an immediate requirement for structural engineers at all levels. ‘Premier projects and prestige clients without the daily London commute’ Visit www.aksward.com for more information and further vacancies in other offices, and apply by email with your CV to [email protected]

TSE Rec Jan16.indd 66

WANT TO ADVERTISE YOUR VACANCY HERE? To advertise here contact Paul Wade on 020 7880 6212.

TheStructuralEngineer The flagship publication of The Institution of Structural Engineers

17/12/2015 09:52

www.thestructuralengineer.org

Structural Project Engineer Central London Ref: 50708 Up to £47,500 + Benefits

knowledge based recruitment in structural engineering consultancy

ALFRISTON SCHOOL SWIMMING POOL C

Rapidly-expanding niche consultancy based in Bermondsey has a requirement for a Structural Project Engineer to join the busy London studio working on a wide range of highprofile projects up to £75million. Candidates will need to be near or recently Chartered with IStructE and/or ICE, educated to MEng/MSc level and must be passionate about sustainable design & good architecture.

BELIEVE IN BETTER BUILDING C

STAGE BY THE SEA

Chartered Senior Structural Engineer

W

Central London Ref: 50565 Up to £47,500 + Benefits No 1 Structural Engineers in the UK has a ELLIOTT WOOD requirement for a Chartered Senior Structural Engineer to join the London studio to working on a number of new dynamic, cutting-edge 2 Principal international commissions. Candidates will Structural Engineers need to be recently Chartered with IStructE and will have worked for another London & Cambridge Ref: 50728-29 premier London consultancy on Up to £52,500 + Benefits high-profile, challenging, designLeading multi-sited consultancy has a focused projects requirement for 2 Principal level Chartered Structural Engineers to join both their Central INTESA SANPAOLA TOWER London & Cambridge offices as they continue to win new work. Candidates will need to be W Chartered with IStructE and must be capable of running their own projects and project team, undertaking design as well as offering support to Associate Team Leader.

ENGENUITI & ARUP ASSOCIATES

Chartered Civil Infrastructure Engineers Greater London Ref: Various Up to £55,000 + Benefits EXPEDITION OTKRITIE ARENA (SPARTAK STADIUM)

Walker Dendle Technical has several positions across Central & Greater London for Chartered Civil Infrastructure Engineers in various premier, niche and mainstream consultancies. Candidates should be Chartered with ICE, be educated to MEng/MSc level, have good civil infrastructure design and project-running skills in roads & drainage and associated infrastructure works.

CENTRAL LONDON STONE STAIR

Structural Project Engineer

C

Central London Ref: 50669 Up to £47,500 + Benefits EXPEDITION & STUDIO OSSOLA

Niche consultancy based in Southwark has a requirement for a Structural Project Engineer to join the expanding London studio working on exciting new commissions with top Architects Associate and helping to develop the brand. Candidates Director will need to be a Graduate or just Chartered member of IStructE and/or Central London Ref: 50629 ICE as well as being educated to Up to £65,000 + Benefits MEng/MSc in Civil, Structural or Leading international premier rapidlyArchitectural Engineering. expanding consultancy has a requirement for an Associate Director to join the London studio as SAN BERNARDINO JUSTICE CENTRE it continues its expansion working on both UK & international commissions. Candidates will need to have extensive post-chartership (IStructE) experience in design, project and team-running consultancy combined with an affinity with high-profile architecture. AECOM

Chartered Senior Structural Engineer Central London Ref: 50529 Up to £52,500 + Benefits Niche multi-sited rapidly expanding consultancy has a requirement for a Chartered Senior Structural Engineer to join the London studio as it continues to develop and expand working on high-profile UK and international commissions. Candidates will need to be Chartered with IStructE and/or ICE and will have worked for another London-based niche or premier consultancy.

WEBB YATES ENGINEERS CHICHESTER FESTIVAL THEATRE

STRUCTURAL AWARDS

WINNERS 2015

For the fifth year running we were a proud sponsor of The Structural Awards by IStructE and this year we sponsored the “Award for Community or Residential Structures”. Well done to all the winners and see featured iconic projects by some of this year’s successful nominees and clients of Walker Dendle Technical Recruitment.

Walker Dendle Technical Recruitment would like to congratulate Expedition on their two winning projects featured with a W and Elliott Wood, Engenuiti & Webb Yates Engineers PRICE & MYERS for their commended projects with a C in their categories at the Structural Awards 2015. For the 9th year running we had a table for the night with guests from Conisbee, Eckersley O’Callaghan, Engenuiti, Expedition, Price & Myers, Sinclair Johnston, Techniker & Webb Yates Engineers. IMAGES SHOW RECENT PROJECTS

UNDERTAKEN BY SOME OF OUR CORE CLIENTS

TSE Rec Jan16.indd 67

SKIDMORE OWINGS & MERRILL

T 020 8408 9971 E [email protected]

uualkerdendle.co.uk

17/12/2015 09:52

p68_TSE.01.16.indd 68

Analysis

Concrete

Steel

Composite

Timber

Masonry

Retaining Walls

Drafting

Lite Suite

14/12/2015 16:31