8477-88-18[1]

Detremining the dynamic chararcteristics of multi-panel floors • Carbon trading •

Embodied CO2 in construction • Educating structural engineers •

88 (18) 21 September 2010

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The Structural Engineer 88 (18) 21 September 2010 3

The Institution of Structural EngineersRegistered CharityFounded 1908Incorporated by Royal Charter 1934

International HQ11 Upper Belgrave StreetLondon SW1X 8BHUnited Kingdomtel: + 44 ( 0 ) 20 7235 4535fax: + 44 ( 0 ) 20 7235 [email protected]

PresidentNorman C. TrainBScEng, CEng, FIStructE, FICE, FCIArb

Chief ExecutiveMartin Powell

Acting EditorIan FarmerBSc ( Hons )tel: + 44 ( 0 ) 20 7201 9121fax: + 44 ( 0 ) 20 7201 [email protected]

Art Editor & Design Co-ordinatorAdrian JacksonBA ( Hons )tel: + 44 ( 0 ) 20 7201 9112fax: + 44 ( 0 ) 20 7201 [email protected]

Editorial BoardSee the Journal website www.thestructuralengineer.org

All editorial inquiries to:The Institution, at the above addressCopies of ‘Notes for Authors’ available on journal website:www.thestructuralengineer.org

All advertisement inquiries to:Advertisement ManagerSteve JacksonDipMStructural Promotions Ltd12 Lawrance Way, Thurlby,Bourne, Lincolnshire, PE10 0HUUnited Kingdomtel: + 44 ( 0 ) 1778 420 857fax: + 44 ( 0 ) 1778 424 [email protected]

Published twice monthly by The Institution of Structural EngineersAnnual subscription (non-members):£260.00 (UK & international) including 100 years of free archivePrice per copy £16ISSN 1466-5123

News5 Jeremy Vine presents the Structural Awards

2010

6 AGM and Benevolent Fund meetings 8 Disciplinary meeting reports

Features10 Embodied C02 in construction

13 Carbon trading

16 Thoughts on the education of structural engineers

Papers18 Determining the dynamic characteristics of

multi-panel floors

Regulars27 Notices & Proceedings

28 Products & Services

21 September 2010www.thestructuralengineer.org

Cover Image: Newport’s iconic new station building represents a stepchange in transport design with a featherweight plastic covering that isa hundred times lighter than glass and requires a fraction of the steeland concrete support of a normal structure. Passenger facilities, ticketoffices and platform access are split equally between the twoconcourses either side of the tracks. All elements are situated withinterminal buildings constructed of structural steelwork and covered incontinuous ETFE (Ethylene TetraFluoroEthylene) cushions withaluminium-clad spirals. (photo: Atkins Global)

Image: Lucy Sewill

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Report

The Structural Engineer– promotes the learned society role

of the Institution by publishingrefereed papers aimed at advancingstructural engineering which is the science and art of designing and making, with economy and elegance, buildings, bridges,frameworks, and other similarstructures so that they can safelyresist the forces to which they may be subjected.

– provides structural engineersworldwide with information onpractice, design, development andresearch, education and trainingassociated with the profession of structural engineering and offersa forum for discussion on thesematters

– assists The Institution of StructuralEngineers in maintaining itsinternationally recognised highstandards

– provides the membership withworldwide informa tion on recentprofessional and technical activities,headquarters and branch events,and provides a medium for relevantadvertising.

The Institution of Structural Engineersis the only qualifying body in the worldconcerned solely with the theory and practice of structural engineering.

DisclaimerPapers or other contributions and the statements made or opinions ex pressed therein are published onthe understanding that the author of the contribution is solelyresponsible for the opinions ex pressedin it or the accuracy of the resultspresented and that its publicationdoes not necessarily imply that suchstatements and or opinions are orreflect the views or opinions of the TheInstitution of Structural Engineer’sExecutive Board, Council, Committees,members or employees. Whilst allreasonable care has been taken in thepreparation of this publication, noliability is accepted by the Institution’sCouncil or any other Institution’sCommittees for any loss or damagecaused to any person relying on anystatement, opinion or omission in theJournal.

US distribution The Structural Engineer (USPS #017-884) is published every 1st and 3rdTuesday each month for US$375 byThe Institu tion of Structural Engineers.

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© The Institution of StructuralEngineers

Jeremy Vine, author,journalist and newspresenter for the BBC, willbe guest speaker andpresenting the awards atthis year’s StructuralAwards on 5 November atthe Marriott Hotel,Grosvenor Square,London.

Jeremy is known for hisdirect interview style and

exclusive reporting from war-torn areas throughout Africa and he is thecurrent host of the BBC Radio 2 programme, Jeremy Vine, which presentsnews, views, and interviews with live guests. Jeremy will be speaking on theevening about his career as well as handing out the awards at thisprestigious event. It attracts all major design practices, contractors,members of our own and other institutions and journalists from leadingconstruction press. Whether you have entered a project or not, theStructural Awards provides an excellent networking opportunity, and anenjoyable evening!

Bookings are now being taken for the event which acknowledges andrewards the work of the world’s most talented structural designers, theirindispensable contribution to the built environment and showcases projectsthat lead the industry’s development. Whether you have entered a project ornot, the Structural Awards provides an excellent networking opportunity, andan enjoyable evening!

For further details go to www.structuralawards.org to book your place atthe Structural Awards 2010.

Jeremy Vine to be the guest speakerat this year’s Structural Awards

Image: Lucy Sewill

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6 The Structural Engineer 88 (18) 21 September 2010

News

In brief...

Management of Structures

The Management of Structures Study Group hasproduced some guidance to support and assistthose involved in the management of existingstructures, or considering how new structuresshould be designed and information provided tofacilitate their subsequent management.

The guidance refers primarily to permanentstructures, but much of the thinking may apply totemporary structures, albeit taking into account thefact that temporary structures normally have theadded complexity of being dismantled and re-erected at intervals. The guidance is divided into sixsections: Introduction, Legal requirements, Life-careplans, Benefits of whole-life thinking, Inspectionstrategies and Management of moveablestructures.

Further Information: The guidance can bedownloaded from the Study Group’s webpage:(http://www.istructe.org/technical/study_groups.asp?CID=209).

Comments on the guidance are welcome andshould be sent to Alan Gilbertson, convenor of theStudy Group ([email protected]).

Call for papers – Concrete repair conference

Concrete Solutions is holding an InternationalConference on Concrete Repair in Dresden,Germany, in September 2012, in association withTU Dresden, INSA Rennes and The University ofPadova. The call for papers ends in October thisyear, so if you want to submit a paper you wouldneed to act swiftly.

The event is co-sponsored by the ConcreteSociety, the ACI, RILEM and VDB the GermanConcrete Society.

Further information: Professor Michael GranthamConcrete Solutions (email: [email protected]; web: www.concrete-solutions.info).

Call for Papers – Advanced Composites inConstruction 2011

The Network Group for Composites in Construction(NGCC) – the organisers of the AdvancedComposites in Construction 2011 Conference(ACIC) - have launched the search for papers forthe 2011 programme where the event will takeplace from 6 – 8 September 2011 at theInternational Digital Laboratory, University ofWarwick.

The organisers are currently asking forprospective authors to submit a 250 word abstractfor consideration by the international scientificcommittee which is this year led by Dr TobyMottram at the University of Warwick.

Any enquires or abstracts for the conference,which should be sent by 1 November 2010, to theconference organiser, Claire Whysall ([email protected]).

101st Annual General Meeting

.M. Allen, Mr S. M. Craddy and Mr J. D. Parsonswere retiring as trustees by rotation but wereoffering themselves for reappointment. It havingbeen proposed and seconded, it was resolved thatMr Allen, Mr Craddy and Mr Parsons be reappointedtrustees.

The Chairman then closed the 2010 AnnualGeneral Meeting of the Benevolent Fund.

The 15th Annual General Meeting of members of theInstitution of Structural Engineers Benevolent Fundtook place at HMS Belfast, Morgans Lane, TooleyStreet, London SE1 2JH on Thursday 29 July 2010.

Dr Keith J. Eaton, BSc(Eng), PhD, FCGI, CEng,FIStructE, FRMetS, MASCE (nominated as Chairmanof the meeting by the board of trustees) was in thechair. A quorum of at least five members was present.

The notice convening the meeting (published inThe Structural Engineer on 15 June 2010) was readby the Secretary, Dr S. M. Doran BSc(Eng), AKC, PhD,CEng, MICE, ACIS. It being agreed that the minutes ofthe Annual General Meeting held on 20 May 2009(published in The Structural Engineer on 7 July 2009)be taken as read, it was proposed and seconded thatthe minutes be confirmed. The resolution was passed,and the minutes were thereupon signed by theChairman.

The Chairman then referred to the financialstatements and reports for the year 2009 (theavailability of which had been announced in TheStructural Engineer on 15 June 2010.) It wasproposed and seconded that the financial statements,the directors’ and trustees’ report, and the auditors’report for the year ended 31 December 2009 beadopted. The resolution was carried on a show ofhands by members.

It having been proposed and seconded, BDO LLP(Chartered accountants and registered auditors) werereappointed auditors for the ensuing year at a fee tobe agreed with them by the trustees.

The Chairman next reminded the meeting that Mr J

The Institution of Structural Engineers BenevolentFund – 15th AGM

The 101st Annual General Meeting of the Institutionof Structural Engineers was held at HMS Belfast,Morgans Lane, Tooley Street, London SE1 2JH,United Kingdom, on Thursday 29 July 2010 with MrN.C. Train, BSc(Eng) CEng FIStructE FICE FCIArb(President) in the chair. A quorum of more than 10Voting Members was present.

The Chief Executive, Mr D. M. Powell, read thenotice convening the meeting. It being agreed thatthe minutes of the Extraordinary General Meetingheld on 9 October 2009 (published in The StructuralEngineer, 3 November 2009) be taken as read, itwas duly proposed and seconded that they beconfirmed. The resolution was passed, and both setsof minutes were signed by the Chairman.

The Chairman introduced the Annual Report andAccounts for the year to 31 December 2009, theavailability of which had been announced in thenotice of the meeting, and drew attention to majoraspects of the work of the Institution for that year. Hethanked those members who had given of their timeto serve on the Executive Board and the Council ofthe Institution, and on committees, panels, subsidiarycompanies, advisory groups, study groups andregional groups. The Chairman also referred to theconsolidated financial statements for 2009 and theauditors’ report (published with the Annual Reportand Accounts). The motion that the financial

statements and balance sheet for the year 2009together with the auditors report thereon, and thereport of the Executive Board for 2009 be receivedhaving been proposed and seconded, was carried ona show of hands.

The reappointment of BDO LLP, charteredaccountants and registered auditors, as auditors tothe Institution for the ensuing year, at a fee to beagreed with them by the Executive Board, was thenproposed and seconded, and the motion carried.

The Chairman having introduced a motion relatingto annual subscriptions, of which due notice hadbeen given, it was moved and seconded:

‘THAT in accordance with the provisions ofRegulation 3.1, and in confirmation of proposals ofthe Executive Board, annual subscriptions with effectfrom 1 January 2011, and until otherwisedetermined, shall be:

Fellow £348; Member, Associate £268;Associate-Member £174; Technician Member £135;Graduate, Companion, Student £133.’

Upon being put to the meeting, the resolution wasadopted on a show of hands.

With the completion of the formal business, theChairman closed the 2010 Annual General Meetingof the Institution.

Haiti earthquake – RedR report on its reliefsupport training programme – 6 months on

The RedR-Bioforce training programme in Haiti hasbeen providing training and support to aid agenciesand their staff following the devastating earthquakewhich rocked the island on 12 January.

To coincide with the programme winding downafter 6 months, and to highlight the manyachievements, RedR has published a reporthighlighting the organisation’s response and keyprogramme achievements.

When the devastating earthquake hit Haiti, RedRresponded promptly, deploying embers, providingtechnical support frontline aid workers, and settingup a training service to support agencies and theirstaff. 6 months on from the programme start, the in-country team has trained over 1000 relief personnel,helping ensure a more effective and widespreadresponse to the disaster.

To find out more about RedR or download the fullreport go to: www.redr.org.uk



News

Understanding Structural Behaviour (2-day course) 19 and 20 October 2010

At the end of this 2-day CPD seminar, delegatesshould be able to explain the process of structuralmodelling from the real structure through to thecomputer model; identify and explain major systemsof maintaining overall stability, the reduction ofcomplex structures to a simpler form and key modesof failure in structural elements and systems.

Venue: 11 Upper Belgrave StreetTime: 09:30 – 17:00 (Registration: 09:00)Price: Institution member £450 + VAT, Regular £499+VAT

Please register you interest stating full name andcontact details via [email protected] we will thencontact you for payment.

Further information: Events, The Institution ofStructural Engineers, 11 Upper Belgrave Street,London SW1X 8BH (tel: +44 (0)20 7235 4535; fax:+44 (0)20 7201 9151; email: [email protected]).

New EngineeringUK Chairman

EngineeringUK has appointed Dr Paul Golby as itsnew Chairman. He succeeded Sir Anthony Cleaver,who came to the end of his 3 year tenure, on 1September 2010.

A chartered engineer, Dr Golby is a fellow of theRoyal Academy of Engineering, the Institution ofEngineering and Technology, the Institution ofMechanical Engineers, the Energy Institute Counciland a member of the Energy Research Partnership.

Commenting on Dr Golby’s appointment, PaulJackson, Chief Executive of EngineeringUK said, ‘Iam delighted that Dr Golby will be joiningEngineeringUK to build on the transformational workundertaken by Sir Anthony Cleaver over the past 3years. Paul has the background, skills and truepassion for engineering that I am certain will helptake the organisation from strength to strength’

Dr Golby, who had been Chief Executive of E.ONUK since 2002, brings with him a wealth ofexperience of industry and an understanding of thechallenges facing the sector.

On his appointment, Paul Golby said, ‘I lookforward to building on the great work undertaken bySir Anthony Cleaver, Paul Jackson and the team atEngineeringUK. It’s absolutely clear to me thatengineering is fundamental to the re-building ofBritain’s economy – indeed EngineeringUK’s ownfigures show that if we are to succeed, themanufacturing sector needs to recruit over half amillion engineering and manufacturing workers withstate-of the-art-skills by 2017. The work undertakenby EngineeringUK to promote engineering andengineers has an ever more critical role to play inachieving this.’

In brief...Report of the Disciplinary Board(28 January 2010)A Disciplinary Board was convened on 28 January2010 (comprising Mr Christopher Miers BA(Hons),DipArch, MSc(Const.Law), RIBA, FCIArb, MAE[Chairman], Mr A. Pemberton BSc(Hons), CEng, FICE,FIStructE and Mr D. Narro BSc(Hons), CEng, FICE,FIStructE, FConsE, MaPS with Mr P. Newman,LLB(Hons.), LLM(Lond.), FCIArb, DipCRB, Barrister ofLaw [legal adviser]), in respect of a matter referredto it by the Professional Conduct Committee.

The complaint was in respect of alleged breachesof copyright, plagiarism and the undermining ofsafety standards. The complainant alleged that thefollowing articles of the Institution’s Code of Conducthad been infringed: 1 act with integrity and fairness2 have regard to the public interest and to theinterests of all those affected by their professionalactivities3 uphold the reputation of the profession5 undertake only those tasks for which they arecompetent6 exercise appropriate skill and judgment

The Disciplinary Board found, unanimously and

without doubt, that the Member had infringed all ofthe alleged articles of the Code of Conduct: 1, 2, 3,5 and 6.

Having considered all of the evidence, and inaccordance with the Regulations of the Institution,the Disciplinary Board unanimously decided toexpel the Member from the Institution. Inaccordance with Regulation 4.5, the Member isentitled, within 3 months after receipt of theDisciplinary Board’s decision to lodge an appealagainst the decision with the Construction IndustryCouncil Appeals Tribunal. No such Appeal havingbeen lodged, the Disciplinary Board made thisreport to the Executive Board:

Dr MYH Bangash is forthwith expelled from theInstitution of Structural Engineers

In accordance with Regulation 4.4.4.17, thedecision of the Disciplinary Board and the expelledmember’s name is published in The StructuralEngineer.

A Disciplinary Board was convened on 9 June 2010(comprising Mr John Trussler PPCIOB, FRICS, Hon.AIC, FRSA [Chairman], Mrs K. M. Morris BSc, CEng,FIStructE, MICE, Mr J. C. McCormick MSc, BSc(Eng),CEng, FIStructE, MICE, MConsE with Mr P. Newman,LLB(Hons.), LLM(Lond.), FCIArb, DipCRB, Barrister ofLaw [legal adviser]), in respect of a matter referredto it by the Professional Conduct Committee.

The complaint was in respect of the memberhaving persistently delayed completion of work andbehaving arrogantly and unprofessionally towards hisclient and the Institution. The complainant allegedthat the following articles of the Institution’s Code ofConduct had been infringed: 1 act with integrity and fairness2 have regard to the public interest and to theinterests of all those affected by their professionalactivities3 uphold the reputation of the profession

The member admitted the complaint, in part (andspecifically admitted delay). The Disciplinary Boardhaving considered the Complaint as a whole and indetail, based on all of the evidence presented found,unanimously and without doubt, that the Memberhad infringed all of the alleged articles of the Code ofConduct: 1, 2, 3.

In accordance with the Regulations of theInstitution, the Disciplinary Board unanimouslydecided to reprimand the Member, and in doing sohave expressed the serious nature of the reprimandin this case. The Member has confirmed in writing

Report of the Disciplinary Board(9 June 2010)

that he does not intend to Appeal the decision of theDisciplinary Board.

In accordance with Regulation 4.4.4.16, TheDisciplinary Board made an order that the Institutionshould make a contribution of £100 towards theComplainant’s overall costs in making thisComplaint.

In accordance with Regulation 4.4.4.17, thedecision of the Disciplinary Board is published in

The Structural Engineer, without the member’sname being published.

€20 000 prizes for inventive research projectsfor sustainable construction in concrete sector

The parent company behind Lafarge Aggregates &Concrete UK, has launched a new awards scheme,the Lafarge Invention Awards, to championsustainable construction.

They will reward inventive European research anddevelopment projects related to aggregates,concrete, cement and gypsum. Projects submittedshould involve a new product, industrial process,construction method or service, and be based on aninvention less than 5 years old.

Researchers, entrepreneurs, inventors,academics or research team members shouldsubmit entries before 15 October to website:www.lafarge-inventionawards.com.

Further information: www.lafarge.co.uk.



Structural engineers sometimes feel that they have little directinfluence over the sustainability aspects of buildings but a newstudy has shown that the embodied CO2 (eCO2) in constructioncan be affected by the design decisions of the structural engineer.Structural engineers can have influence over two areas: theimpacts of the operation of buildings by facilitating the use of fabricenergy storage and the eCO2 by specification of the material withinthe structural frame. This study shows that a structural engineercan reduce the eCO2 of a medium sized building by their personallifetime carbon footprint.

The Concrete Centre commissioned Arup to do the study intothe CO2 embodied in a structural frame using the materialquantities produced for the cost model studies for schools,hospitals and offices undertaken in 2007. The different framesoptions studied are shown in Fig 1 and were fully designedschemes.

One of the biggest problems facing structural engineers trying toreduce the eCO2 of structures is the lack of clear information. Dataregarding structural materials are available in the public domain butthere is a large range of values to choose from, with little guidanceas to when the values are appropriate. The variation in the inputdata for eCO2 can come from the specification of the material(which the structural engineer can affect), or from the method ofcalculation (which they cannot). The use of standard guidance (egthe recent PAS 2050 standard) does not avoid the variability arisingfrom the method of calculation. Then, if a calculation of the eCO2 iscompleted, there is little information available with which tocompare the results. One of the problems is that different

boundary conditions are chosen for different studies. In this study,the boundary conditions were chosen to be from extraction toconstruction in the UK so that like for like values could be used forthe different materials and the results of the study can becombined with later life cycle stages.

The study found that the eCO2 in the structure of the buildingswas in the order of 200kg/m2. This represented 50 – 60% of thetotal eCO2, significantly more than the percentage found in otherstudies. The study also showed that optimising the eCO2 of thestructure can be done without compromising the efforts of otherdesign team members to reduce impacts (Fig 2).

The structural engineer can effect a real variation in eCO2 of thislarge percentage of the total through careful specification of thematerials used in the construction. The impact of steel cannot beinfluenced through specification in the current market, but thespecification of concrete allows a significant saving in eCO2 of thebuilding:– ±30kg/m2 for a post-tensioned flat slab (15% of structural

impact);– ±60kg/m2 for an rc flat slab (35% of structural impact).

The use of blended cements containing other cementitiousmaterials such as fly ash or ggbs reduces the eCO2 of theconcrete, but delays the setting time, which might impact theconstruction programme. But the study demonstrates benefitsfrom careful specification of concrete and it is hoped that this willencourage engineers and contractors to ensure that practical,workable, minimum impact concrete specifications are adopted on

Report

Embodied CO2 in constructionJenny Burridge, Head of Structures, The Concrete Centre, discusses how designdecisions can have a positive influence

1 Frame options

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projects. Engineers will also be able to use the results of thesensitivity study to take a robust independent view whenconsidering claims with regard to sustainability in comparisonstudies.

Significant differences of roughly 1000t of eCO2 could be madeon each building through design and specification choices. Themajority of the lowest impact schemes examined, such as rc flatslab and hybrid in situ and precast concrete, would also offer theopportunity to mobilise the benefits of thermal mass throughexposed concrete floor soffits and thus reduce the bigger impactof the operational CO2.

In summary, while general rules cannot be recommended, thedifference in embodied CO2 which a structural engineer canachieve on a building is measurable. It has been found that thesedifferences do not correlate directly with cost or mass across therange of schemes. The variation of data in the public domain canbe considered systematically and eCO2 calculations arerecommended. If eCO2 is minimised, the structural engineer willhelp to achieve some of the savings in emissions in the short timeframe set by Government for green-house gas reduction. This canbe combined with facilitating other members of the design team inachieving ongoing reductions in operational impacts.

2 Results for variation in specification and method

Maitland Lecture 2010The Green EconomyBy The Lord Browne of Madingley

Date | Tuesday 5 October 2010 Time | 18:00 Refreshments 18:30 Lecture 19:45 Pre-dinner drinks 20:00 Dinner Venue | The Royal Society, 6-9 Carlton House Terrace, London SW1Y 5AGRegistration is required in advance via [email protected]

About Lord BrowneLord Browne was born in 1948, he joined BP in 1966 and in 1984 he became Group Treasurer and Chief Executive of BP Finance International.

Exploration based in London. In September 1991, he joined the Board of The British Petroleum Company plc as a Managing Director. He was

appointed Group Chief Executive on June 10, 1995. Following the merger of BP and Amoco, he became Group Chief Executive of the combined group on December 31, 1998 until 1 May 2007.

He was voted ‘Most Admired CEO’ by Management Today from 1999 to 2002. He was knighted in 1998 and made a life peer in 2001.

T

A

Lecture and Dinner Booking: Lecture only ticket(s) £10 | Dinner ticket(s) is £65 per person + VAT | Table(s) of 10 @ £550 + VAT (Includes lecture tickets)

The Events Team, The Institution of Structural Engineers, International HQ, 11 Upper Belgrave Street, London SW1X 8BH, United Kingdomtel: +44 (0)20 7235 4535 fax: +44 (0)20 7201 9151 [email protected] Registered Charity with the Charity Commission for England and Wales No. 233392 and in Scotland No. SC038263

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Reduction in carbon emissions is central to the negotiations at theUN COP meetings. Following Copenhagen (COP-15) (seesustainability briefing in The Structural Engineer 88/2, 19 January2010, p10), the negotiations will resume later in 2010 at Cancün inMexico. This note, on carbon trading, has been prepared to helpstructural engineers in understanding this complex topic, toencourage them in following reports and to enable them incontributing to discussions.

In a world where there is an obligation to reduce carbonemissions, Governments could issue an instruction to all carbonemitters that they must reduce emissions by a certain amount.This system of Command and Control makes no distinction,between carbon emitting companies, of the cost of cutting carbon.

What is emissions trading?

Emissions trading is a mechanism devised to regulate and controlcarbon emissions. There are two types of market-driven schemeswhich create forces to incentivise reduced carbon emissions.

‘Price instrument’ using a tax, levied at a fixed price, with thequantity of emissions allowed to float. A carbon tax increases thecompetitiveness of non-carbon technologies compared to thetraditional burning of fossil fuels, thus helping to protect theenvironment while raising revenues.

‘Quantity instrument’ using a fixed quantity allowance andfloating price. In this system a value is created for carbonemissions, which are then either exchanged or traded.Government progressively reduces the size of the fixed quantityallowance, maintaining and increasing the value of carbon credits.This is ‘emissions trading’.

Emissions trading should ensure that emissions reductions aremade at least cost to industry. Such a system is attractive toGovernments, which need to maintain competitiveness of theircountries. This is in contrast to a command and central controlmechanism, where emissions might be reduced by mandate,regardless of cost to the company. It is also more attractive than ataxation system, which requires detailed Government inventionand operation; in contrast a trading scheme, once operating,requires minimal Government intervention.

The effect of incentivising efficient carbon reduction, throughleast cost to industry, is demonstrated by the example in Table 2.

In this example, Company A and Company B are both requiredby law, through an emissions allocation, to either reduce emissionsby 20% or to trade emissions to an equivalent emission reduction.Under the Command and Control system (Table 1), bothcompanies cut emissions – this costs company A more than it

costs Company B and the combined cost is €3400. Under anEmissions Trading System, companies are allowed to buy from themarket if their own emissions cut is insufficient or to sell surplusemissions to the market if their cut exceeds their allocation.

The ability to trade carbon between the companies provides anincentive to the company that can cut carbon more cheaply (in thiscase Company B). Both companies are required to show a savingof 20t of Carbon. The cut is enforced by fines which, to beeffective, must cost the company more than reduction inemissions. Company A reduces its emissions by 10t and buys theother 10t on the market, at €80/t. Company B cuts its emissionsby 30t and sells its surplus of 10t of carbon into the market andreceives €800. Thus, through emissions trading, the saving incarbon is achieved at an overall lower cost (€3100) than a blanketcut of 20t per company.

For the market to be effective in driving lower carbon emissions,there needs to be a shortage of carbon. Shortage drives the priceof carbon credits up, incentivising reduction. Such Governmentmeasures introduced to reduce carbon and to drive up the cost ofcarbon credits are called ‘Cap and Trade’. The Cap is an agreedenforceable limit on emission and Trade is the activity of theCarbon market. To make sure this shortage exists, the allowancesunder the trading scheme must be less than a ‘business as usualscenario’.

History

The Kyoto protocol, which was set to operate in the period 2008-2012, was introduced to achieve ‘stabilisation of greenhouse gasconcentrations in the atmosphere at a level that would preventdangerous anthropogenic interference with the climate system’. Itquantified greenhouse gas emissions targets for ‘Annex 1’ parties(developed countries and countries in transition) and this led to theEUETS (European Union Emissions Trading System), the largestmulti-national trading scheme in the world and a major pillar of EUclimate policy

The EUETS

The EUETS currently covers more than 12 000 installations in theenergy and industrialised sectors, which together account for morethan half of the EU’s emissions of CO2 and 45% of its greenhousegas emissions. This is the largest trading scheme in the world andso it is discussed in some detail.

The EUETS creates a market for carbon emissions, which allowstrading to take place. The trading unit is one unit of carbon dioxideemitted or 1t CO2e – this is called an EU allowance (EUA). Thus

Table 1 Command and control – Government issues an instruction, enforced by fines, that all emitters of carbon should produce a 20% cut in emissions Table 2 Emission trading – Assuming carbon price of €80/t

Sustainability briefing

Carbon trading

Startemissions

Cost ofreduction

Endemissions

Carboncost/credit

Cost ofreduction

CompanyA

100t €100/t 80t – 20 x 100 =€2000

CompanyB

100t €70/t 80t – 20 x 70 =€1400

Total 200t 160t €3400

Startemissions

Cost ofreduction

Endemissions

Carboncost/credit

Cost ofreduction

CompanyA

100t €100/t 90t +10 x80

10 x 100 +800 =€1800

CompanyB

100t €70/t 70t –10 x80

30 x 70 – 800 =€1300

Total 200t 160t €3100

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‘price of carbon’ is the cost of an EUA on the market. Incidentally,the molecular weight of carbon is 12, that of oxygen is 16 and so1t of carbon dioxide (molecular weight 44) contains around 1/4t ofcarbon.

The key to success of the European trading system is settingthe cap on emissions. The cap is set in the National AllocationPlan (NAP), which is submitted by each Member State andapproved (or not) by the European Commission. Clearly in themarket the cap determines the price of carbon, which determinesinvestment in the technology, which leads to an efficient reductionin carbon emissions. Setting the cap too high leads to a price ofcarbon too low to justify investment to motivate emissionreductions.

Features of the EUETS

Applies to specified industry sectors only. At present these includepower, some building materials, oil and gas, iron and steel, pulpand paper and ‘other combustion’ but not transport.

– Phase I – 2005-2007 – learning period;– Phase II – 2008-2012 – Kyoto period;– Phase III – 2013-2020.

– Applies to CO2 only;– Allowances operated through NAPs and distributed through free

allocation and auctions; – Auction volumes limited to 5% in Phase I and 10% in Phase II;– Not all governments auction in Phase II;– 100% auction for power section in Phase III.

The EUETS currently covers 2bn t of CO2 per annum. Powergeneration accounts for around 30% of EU CO2 emissions and65% of emissions covered by the scheme.

EUETS and the rest of the world

EUETS is not a closed loop scheme. Installations can set offemissions by purchasing credits from other countries. The limits tothe amount of trading is set by the Kyoto mechanisms, which aredefined in the Clean Development Mechanism (CDM) and JointImplementation (JL).

Under EUETS, a carbon credit is an ‘allowance’ to emit onetonne of CO2, hence there is an EU Allowance (EAU). UnderCDM/JL, a carbon credit is a guarantee that emissions have beenreduced below a ‘business-as-usual’ level. This leads to CertifiedEmission Reductions (CERs), Emissions Reduction Units (ERUs)

Table 3 Emission trading fails to operate – Assuming carbon price of €60/t – no incentive for Company B

Table 4 Emission Trading fails to reduce carbon emissions – Assumingcarbon price of €60/t and excess of credits in the system

Startemissions

Cost ofreduction

Endemissions

Carbon cost/credit

Cost ofreduction

CompanyA

100t €100/t 85t +5 x60

15 x 100+ 300 =€1800

CompanyB

100t €70/t 75t –5 x60

25 x 70 – 300 = €1450

Total 200t 160t 1600 + 1500= €3100

Startemissions

Cost ofreduction

Endemissions

Carboncost/credit

Cost ofreduction

CompanyA

100t €100/t 100t +20 x60

1200 =€1200

CompanyB 100t €70/t 100t

+20 x60

1200 =€1200

Total 200t 200t = €2400

A guide to terminology and acronyms in carbon trading

Cap and TradeThe principle behind carbon trading. Limit (cap) the amount of emissions legally permitted and allow countries/operators to buy (trade) certified emissionsgenerated by others. The value of the certified emissions is important. If certified emissions (carbon credits) are worth too little, there is little incentive for theircreation.

Contraction and Convergence The industrially developed world generates to many emissions. The industrially under-developed world would like to generate more. Total emissions shouldreduce thus the developed world’s emissions should contract and the combined emissions of the developed and under-developed nations should converge ona total that is less than the present.

EUETS European Union Emissions Trading Scheme Largest multi-national emissions trading scheme in the world.

NAP National Allocation PlanNational emissions cap for EU member state under the EUETS. For the scheme work in cuttingemissions, the allocation must be less than what would have been emitted in ‘business as usual’

EUA EU emissions Allowance A carbon credit (allowance) under the EUETS to emit 1t of CO2 equivalent

JL Joint Implementation Defined in Kyoto Protocol. This produces the ERU

ERU Emissions Reduction Unit Under the JL, one ERU is the successful emissions reduction equivalent to 1t of carbon dioxideequivalent

CDM Clean Development MechanismDefined in Kyoto Protocol. This sets down the Kyoto mechanism for certifying emissions reductions.CERs are issued under the CDM.

CER Certified Emissions Reductions

Under the CDM, one CER is the certified emissions reduction equivalent to one tonne of carbondioxide equivalent. CERs can be bought from the primary market (from the party making thereduction) or from the secondary market (resold in marketplace). These are a form of ‘climatecredit’ or ‘carbon credit’ and are used by countries or by operators to show compliance withobligations under the EUETS

CDM/JL The mechanisms that define trading under the Kyoto Protocol

VER Voluntary Emissions Reductions Carbon credits developed by carbon offset providers, which are not certified



and Voluntary Emission Reductions (VERs).Savings in carbon on a CDM registered project in a developing

country can be transferred to an EU emitter, in exchange formoney paid into the developing country.

SummaryPositives:

– Supports ‘polluter pays’ principle;– Takes in a large number of operators;– Secondary market in carbon developing;– Phase II price helps continuity of CDM investment;– EU companies have gained advantage over competitors in other

countries and have developed links with developing countriesthrough CDM.

Negatives:

– Phase I allocations too high and there was a price crash incarbon in 2006 and 2007 (from €30/t in 2004 to €0.03 inDecember 2007);

– The free allocation led to excess profits and competitivedistortions;

– Current price collapse, due to recession (€30.53 on 1 July 2008to €8 in March 2009 to settle to around €15 during the first halfof 2010) could delay investment in clean technology;

– Carbon trading only relates to supply – it does nothing directly toincentivise energy reduction by the user. If it leads to increase inenergy prices, this clearly encourages energy conservation butthis is an indirect effect;

– If the carbon price is too low the incentive towards carbonreduction is lost – it is cheaper to buy carbon credits than to cutcarbon emissions.

The example in Table 2 used a carbon credit price of €80/t. Ifthe value of carbon credits falls to less than the cost to CompanyB of reducing emissions, Company B has no incentive to sell

credits onto the market. Table 3 shows that it costs Company Bmore to cut emissions that it receives in trading its surplus on themarket. It would be cheaper for both companies to buy credits onthe market.

The emissions trading market was created by allocations ofcarbon credits. Due to the reduced demand for energy caused bythe recession, the market can operate with an imbalance in carboncredits – credits bought do not have to equal credits created byemissions cuts. Table 4 shows how the trading scheme can createa situation where credits are bought in preference to emissionsreductions.

If the emissions trading scheme is to be effective, Governmentmust intervene to tighten the Cap and reduce the availability ofCarbon Credits. Alternatively they could wait for an increase indemand in energy demand to drive up the price of emissions.Some say that the emissions trading scheme is discredited as aneffective mechanism and carbon taxation should be introduced.

Whatever emissions controls are introduced, the structuralengineer will feel the impact of carbon indirectly. If carbonemissions trading is successful, high carbon emitting operators willbe penalised by having to purchase expensive credits. This willlead to a continuous reduction in carbon emissions and, in duecourse, ‘a low carbon economy’. In a low carbon environment,high emission products (generally high-embodied carbon products)will be expensive and the structural engineer will be deterred fromtheir use through the normal process of economic forces.

Further information

This briefing is prepared by the Institution of Structural EngineersSustainable Construction Panel. Contact: Berenice Chan (email:[email protected])

Issue No: 12



I write in response to the Viewpoint by Past President GrahamOwens1. One’s opinion on the structural understanding of newgraduates entering the work force in Scotland will, surely, dependupon what reference time is chosen to start from. In my case myreference is my own college days at Westminster where I attendedon day-release for my HNC in Civil Engineering. For the (younger)university graduates among you it will be a different period with adifferent syllabus, etc.

Back in the late 1950s and early 1960s one could join theInstitutions (Civil and Structural) without a university degree.Because we worked 4 days of the week our employers took akeen interest in what was taught and any ‘fluffy’ subjects werequickly complained of. Several years after I ‘graduated’ the subjectof General Studies was introduced to a howl of protest but theacademic bodies took no notice, persevering with a ‘We knowbest’ attitude.

I fear that this attitude persists among academics, denying thatthe users of the teaching (employers and students) could have anysay in what was taught. The curriculum is set by the academics;the standard is set by the students. Where are the interests of theemployers and clients represented?

The Joint Board of Moderators (JBM) details the relevantGuidelines2. Universities have to measure-up to these Guidelines inorder to be accredited. Emphasis is placed on the ‘understandingof engineering principles’ though I would ask if anyone has setthese down in a recognisable list. Are there differences between‘Principle’, ‘Equation’, ‘Theorem’ and ‘Concept’? Does it help toidentify the use by naming Castigliano’s Theorem or should we betalking about strain energy and deflection?

Again, although the Guidelines are excellent, they are open tointerpretation. Expressions such as ‘In addition, mathematics at ahigh level must form a significant part of the course’, can beinterpreted as meaning that mathematics must be taught by clevermathematicians in the Maths Department as distinct from AppliedMathematics relevant to structural engineering, taught by anexperienced engineer. How much of the mathematics course isever referred to again during commercial work?

In my day we got as far as the Calculus, but I have never used itin all my practical career, could not do it now to save my life, andwill never know if it would have made a significant difference if Ihad used it. I try and keep to the ‘engineering’ and if need be, findsomeone to do the analysis for me – I don’t need to be a stressanalyst to prepare a building scheme. Similarly, I don’t need to bea cement chemist to make good concrete.

I do need to know how the analysis may be done, whatlimitations may be introduced and what effects these may have. Ido need to know how the properties of the mature concrete will beaffected by aggressive surroundings and what cements areavailable to counteract this attack.

It is my perception that universities see their role as‘researchers’, and staff their departments accordingly. Employers,with their commercial necessity, would rather have practicalGraduate engineers who can earn a fee as soon as possible.Although the departmental staff appreciate any help from

practising engineers, they do not have funds with which to rewardsuch input and the commercial organisations cannot afford to givetheir employees free time to go teaching. In former days (day-release) the departmental staff were engaged as teachers, hadchosen to leave full-time commercial work but often maintained acontact and undertook small design tasks. Part-time lecturerscame in to take evening lectures and provide specialist experiencee.g. in quantity surveying. Soil mechanics was taught as a daytimesubject by selected staff of the well-known company of that name,and the company must have had an agreement with the college.They certainly won the admiration of us students and firmlyestablished the name in our minds.

I think that the core of the matter was that we felt that we werebeing taught useful things in a practical manner at the right time.We wanted to be structural and/or civil engineers; we worked onreal projects and were taught appropriate things to allow us to doour work better. Part of the problem now, if there is a problem, isthat candidates go straight from school to university withoutknowing what the job is about. At university they are submerged intheory without having the link to the real work being explained. Avariety of topics are introduced that have very little reason to belearnt this early but have to be crammed into the timetablesomehow.

The problem, as I see it, is that there is a perceived lack ofbasic, essential and manual skills, for example:

– Essential geometry with applications to arches, etc. andmeasuring and setting out.– Ability with approximate methods for sizing and checking. Abilityto prepare hand calculations.– Ability to sketch and draw (without CAD) and visualisation of theproblem using models (requiring patience and a sense of spatiallogic).– Wide knowledge of the various structural framing forms fromwhich to choose the appropriate project structure.– A substantial and wide-ranging knowledge of structuralmaterials, including aluminium, timber and glass.– Real knowledge or experience of how buildings or bridges areconstructed.– Knowing when the job has been completed satisfactorily.

It appears that a ‘wad of good-to-know-about subjects’ havebeen introduced and use-up valuable time without being essentialto being good engineers. Some subjects are taught in too muchdetail – more detail than the average engineer needs for day-to-day work. The following should be considered for relegation ormodification:– leadership and team working,– quality systems,– communication skills,– broadening the appreciation within society,– mathematics at a high level.

Many of these so-called ‘fluffy’ subjects can be incorporated into

Viewpoint

Some thoughts on the education ofstructural engineersBob Wilson (F), one of the Institution’s 12 Chief Examiners and a Marking Examinerfor the CM Exams adds his views to the ongoing debate

SE18 Wilson viewpt:Layout 3 20/9/10 10:52 Page 16

The Structural Engineer (18) 21 September 2010 17

projects where both engineering and communication/social skillsare displayed.

In respect of Higher Mathematics I suggest that it is necessaryto demonstrate the need before asking the student to make theeffort or justify the time in the curriculum.

This brings out the need to ‘teach when appropriate to need’.Demonstrate the need – then it becomes clear why the effort isneeded. A possible sequence may be seen from the format of theInstitution’s examinations:1 Site conditions and client’s requirements, and any matters thatmay be omitted from consideration;2 Loading;3 Alternative framing of roof, floors, beams, columns, andfoundations. Critical connections should be included as these arealways on the load path.4 Preliminary sizing of members, together with analysis andcalculation (manual calculations) to prove fitness for purpose.5 Communication, i.e. manual sketches for instructing the CADoperator about what to draw. Knowledge of the different types ofdrawing – GA, fabrication, reinforcement and setting-out – and thedrafting of letters, specifications and method statements.

What to do about it?

The employers need to set out their requirements or at least listwhat ‘competencies’ are wanted. It will be necessary for the JBMto agree and champion the cause by up-dating the Guidelines2.Graduates need to make themselves employable – taking-up theuseful modules on offer and even taking second degrees insupportive studies like Management, Advanced ConcreteTechnology, Welding Technology, Timber Technology or AdvancedStructural Analysis. It would help if undergraduates informedthemselves better about the industry they were about to enter.

All parties need to re-evaluate the full-time education principlewith a view to re-introducing part-time college attendance,coupled with much greater practical and hands-on apprentice-type

training. However, the present practice of apprentices being calledback to college leaves the employing firm (or sole employer)without the necessary support for substantial periods during theworking year. At present employers find it difficult to anticipate theflow of work and the part-time principle would help a complexsituation.

Government, industry and the Institution need to be morehonest about the distribution of responsibility, opportunities forpromotion and the number of working engineers and technicians.The distribution is wider at the base of the triangle – moretechnicians and Incorporated Engineers – than at the top.Relatively few of us will actually reach the top: most of us will findour level of responsibility, the one we are comfortable with, andstay there, eventually being replaced as we retire. Some crave thetop job, even in a small firm, and become sole practitioners. Veryfew graduates will become a chief engineer or technical director:most will be doing a good but repetitive job in the engineeringoffice as a project engineer.

I think that it is fair to say that the different levels of degree havebecome confused! Could we have three levels of degree? Forexample:1 Basic – entry to Incorporated Engineer,2 Intermediate – entry to Chartered Engineer,3 Higher – for Chartered Engineers wishing to advance intospecialism.

Could we also recognise Incorporated Engineers and CharteredEngineers to be ‘above’ PhD? After all, they have sat and passed aprofessional examination after practical commercial experience.

Reference

1 Owens, G. W.: ‘Structural engineering education in the 21st century: the wayforward, The Structural Engineer, 88/1, 5 January 2010

2 Parke, G. A. R.: ‘Teaching practice and outcomes, a JBM and personal view’presented at the 2009 conference – Structural Engineering Education in the21st Century, 21 September 2009, London

SE18 Wilson viewpt:Layout 3 20/9/10 10:52 Page 17


Synopsis

This paper deals with the determination of the dynamiccharacteristics of multi-panel floors, primarily to provide informationfor calculating their response to human loading. It presents lessonsthat have been learnt by the authors modelling various types offloor. The paper focuses on the low damped, medium to long-spanfloors typically encountered in modern offices. For these floors, theresonant response to rhythmic loading from walking or jumping isthe prime consideration.

To determine the modal properties of a floor a finite elementrepresentation is adopted. This paper considers three commontypes of floor in order of increasing complexity. In each case thereare important factors to be considered. However, with multi-panelfloors there is one further factor which cannot always be modelledaccurately, namely the continuity between panels, and this isdescribed. Damping is an important characteristic, but one whichdoes not fit in comfortably with finite element modelling.This isdealt with separately.

Finally the data determined from a model of a multi-panelcomposite floor are used to evaluate the floor’s response to bothwalking and jumping loads. Several simpler models are providedfor comparison. The calculated responses are then compared withcorresponding measurements to provide an illustration of therange of results that can be encountered.

Introduction

Modern structures often encounter vibration problems and,although safety may need to be examined in some situations,serviceability is usually the main consideration. Consequentlypredicting structural response to dynamic loading is an importantdesign consideration. This paper concentrates on floors; however,the concepts considered are applicable to several other types ofstructure.

When analysing floor vibration there are four key stages:– Determination of the floor’s characteristics;– Selection of the loads to be considered;– Evaluation of structural response to these loads;– Consideration of calculated response in relation to the relevant

acceptability limits.

The authors have published work on the latter three items but ithas become increasingly clear that the determination of a floor’scharacteristics is crucial. However, this is neither easy nor

straightforward. Excessive floor vibrations in response to human loading may be

important in two situations:– Periodical loading that may cause resonance of low damped

floors – often medium to long span floors.– Impact loading from individual footfalls in domestic and allied

structures.

This paper focuses on the first category which includes mostmodern office structures often with many floor panels or bays onone floor level. An example of a typical floor is shown in the planview in Fig 1.

This paper considers three types of floor:1 flat concrete floors;2 beams supporting cast–in-place concrete, or pre-stressed

concrete floors;3 beams supporting composite floors.

Floors will be considered in the above order as they are ofincreasing complexity and the lessons for modelling applicable totype 1 are also applicable to 2 and then to 3. These concepts arenot solely related to dynamic performance but are also applicableto many aspects of static performance.

Parameters required for dynamic evaluation

When considering dynamic response, most engineers wouldinitially think of the structure’s natural frequencies and, for somestructures, there will be a minimum natural frequency above whichdynamic evaluation for human loading will not be required. Whilesuch simplistic guidance may be useful it does not cover everysituation. All structures have many natural frequencies but it isoften the lowest or fundamental natural frequency that is critical.With multi-span or multi-panel structures there will be a wholefamily of modes with relatively low frequencies and it will usually bethe significant lowest frequency mode in the area underconsideration that is important. This will be termed the principalmode for that area. The design concern arises from the possibilityof resonance being generated by rhythmic human loading (typicallywalking or jumping) if the floor’s principal frequency coincides withthe load frequency or with two or three times its value. As thefrequency range for the load is known, it is possible to set aminimum frequency requirement for the floor to avoid resonanceand possible uncomfortable vibrations from these load cases.

The alternative strategy to providing a simple minimumfrequency is one of determining the floor response to variousdynamic loads and assessing its acceptability. This requires anevaluation of the floor’s dynamic characteristics, primarily thefrequency, mode shape, stiffness (or mass) and damping of theprincipal mode, and this is the main topic dealt with in this paper.However it is useful to mention loading and response evaluationmore generally as this illustrates how the various characteristicsare used.

As mentioned earlier there are two main load considerations:walking and jumping. The details of these topics are dealt withelsewhere1, 2, 3 but for serviceability evaluation the mainconsideration for both is determination of resonant accelerationwhen the frequency of the principal mode coincides with theloading frequency (or two or three times that value). To determineacceleration the required equation is of the following form whenonly the load component that generates resonance is considered:

Paper

Determining the dynamic characteristics ofmulti-panel floors

Brian R. Ellis, BSc, PhD, DSc, CEng, MIStructEConsultant

Tianjian Ji, BSc, MSc, PhD, CEng, FIStructEUK School of Mechanical, Aerospace & Civil Engineering, The University of Manchester, Manchester

Emad El-Dardiry, BSc, MSc, PhDFaculty of Engineering, Banha University, Cairo, Egypt

Tianxin Zheng, BEng, MSc, PhDUK School of Mechanical, Aerospace & Civil Engineering, The University of Manchester, Manchester

Keywords: Floors, Vibration, Dynamic loads, Modelling, Panels, Testing, Damping

Received: 10/09: Modified: 04/10; Accepted: 04/10

© Brian R. Ellis, Tianjian Ji, Emad El-Dardiry & Tianxin Zheng

SE18 paper Ellis floors:Layout 3 15/9/10 11:29 Page 18


Where:x = the resulting accelerationF = the modal forceω (= 2πf) is the circular frequency of the principal mode of the floorwhich is the same as the frequency of the applied load or two orthree times that value k = the modal stiffnessζ = the damping ratiom = the modal mass

In the next two sections the calculation of some of thecharacteristics of the floor modes of vibration is examined, i.e.frequency, stiffness and mode shape. Damping is quite different tothe other parameters and is dealt with later in a separate section.

Modelling floors to determine their dynamic characteristics

Initially it is useful to illustrate some basic considerations. Someform of numerical analysis is usually required to model multi-panel

/ 2 /x F k F m22: : : : :~ g g= =: :

^ ^h h floors, typically a finite element (FE) representation. The six lowestfrequency modes of vibration of the floor shown in Fig 1 are givenin Fig 2 and these illustrate the complexity of the problem. It isperhaps stating the obvious, but the whole floor should bemodelled and it is not sensible to consider just one panel inisolation, although this might provide some useful data. The reasoncan be appreciated by examination of the mode shapes showingthat motion in one area often relates to motion in another, notnecessarily adjacent, area. This is quite important in practice, aspeople who experience floor vibrations may find them particularlydisturbing if they cannot recognise the vibration source.

From the finite element evaluation, the natural frequencies of themodes, the mode shapes and the modal stiffnesses (or modalmasses) are determined. Modal stiffnesses may not be given asthe standard output from the FE program but they can beextracted.

Assume that a floor is to be modelled using FE. The followingsections will concentrate on the lessons learnt by the authors inmodelling various types of floors. The work on each type of floorhas been reported separately; hence the main details are not

1 The plan of a typical floor, the panel numbers and the test locations



repeated here, but this information is available in the givenreferences.

One question that often arises is what value to use for themodulus of elasticity in a dynamic analysis. It is usual to describethe value for the modulus of elasticity obtained from dynamicmethods as the dynamic elastic modulus to differentiate it from thestatic elastic modulus based on a load-deflection curve. Jerath4

compared the values of modulus of elasticity of six reinforcedconcrete beams using both dynamic and static test methods andshowed that the ratios of the values from the static method to thedynamic method varied between 0.96 and 1.15. The test resultsdid not indicate that the modulus of elasticity used for dynamicanalysis should be larger than that for static analysis. There aremany other papers investigating the determination of the values ofmodulus of elasticity of materials or structures but these are notconsidered herein.

It is difficult to provide a unique value for the modulus of

elasticity for concrete which has a nonlinear stress–strainrelationship. The value depends on stress level, rate of loading,strength of concrete and concrete ingredients. As small amplitudevibration is a normal assumption when studying serviceabilityproblems of floors, it may be reasonable not to distinguishbetween the values of static and dynamic modulus of elasticity forthe materials. Hence for the work described in this paper the staticmodulus of elasticity has been used.

Flat concrete floors5

Fig 1 provides a plan view of a flat concrete floor supported byconcrete columns. This is probably the simplest type of multi-panelfloor to model. In this case the floor was modelled using thin shellelements and the columns were modelled using 3D thick beamelements.

An initial exercise using different FE meshes showed that even acoarse mesh (6 x 6 per panel) worked well as the mode shape in

2 The first six modes and natural frequencies of the floor-column model

Mode (1) Freq.= 8.25 Hz Mode (2) Freq.= 8.30 Hz

Mode (3) Freq.= 8.53 Hz Mode (4) Freq.= 8.62 Hz.

Mode (5) Freq.= 8.96 Hz Mode (6) Freq.= 9.18 Hz



any one panel is relatively simple. Finer meshes (15 x 15 elementsin this example) improve the mode shape’s visual appearancealthough not radically affecting the natural frequencies.

Including the columns in the FE model is an importantconsideration and to illustrate their importance three differentmodels were used to represent the columns: – simple pin supports at each column position;– fixed supports at each column position;– modelling the columns using FE (with fixed boundary conditions

at the neighbouring storey levels).

The results of the modelling were compared with 11 naturalfrequency measurements made on the real floor and it was foundthat the third representation corresponded best. Models 1 and 2gave frequencies to either side of those found in model 3. For thefundamental mode these were 7.12, 9.26 and 8.25Hz respectively.The corresponding measured value was 8.54Hz.

Beams supporting cast–in-place, or pre-cast concrete floors

A more complex situation occurs when a framework of columnsand beams supports a concrete floor, be it either pre-cast flooringunits or cast in place concrete. The example considered wasanalysed to check whether the principal frequency of a large panelwithin a multi-panel floor was sufficiently high to avoid resonancefrom the third Fourier component of jumping loads.

In this situation the eccentricities of the slab and beams need tobe considered. For this example the neutral axes of several cross-sections were calculated based on the formulae used in Eurocode46 and presented in [ref 7]. In the analysis three situations wereconsidered.– The eccentricities of all the cross-sections were neglected. – The neutral axis was assumed to be located at the mid-plane of

the concrete slab.– The neutral axis was placed at the bottom surface of the

concrete floor.

When no eccentricity was considered, the floor had a calculatedfundamental frequency of 7.92Hz. When the eccentricities of thebeams were taken into account, the fundamental frequency was9.36Hz and when the eccentricity of the floor was considered thefrequency was 9.58Hz. Thus if eccentricity is neglected in themodelling, the calculations will underestimate both natural

frequency and floor stiffness, whereas considering just the beameccentricities is a considerable improvement and not too dissimilarto the full detailed model.

Composite floors8 – an illustrative example

Composite floors that consist of a combination of profiled steelsheet and concrete floor supported by beams and columns areeven more complex. To study this type of construction a FEprogram was used to build up a 3D-model of a 4.5m x 3mcomposite deck panel which was simply supported along fouredges. Two types of finite element were used:– Thin shell elements to model the steel sheet;– 3D-solid elements to model the concrete slab.

The steel sheet and the concrete were first modelled separately;then the two parts were merged to form the composite deck (Fig 3). The compatibility of the two parts was considered whenmodelling the individual parts. A cross-section of the floor is shownin Fig 4.

This example is based on the composite floor used in the steelframed test building at Cardington9. The steel sheet is thin and hasa small cross-sectional area in comparison with that of theconcrete; however, the elastic modulus of the steel sheet is 6 to 7times that of concrete and the location of the sheet is relatively farfrom the neutral axis of the composite section. For the studiedcase, the steel sheet contributes about 16% of the total stiffness ofthe composite floor. Thus the calculation shows that the steelsheet decreases the maximum displacement by approximately16% and increases the fundamental natural frequency by about5%.

Although 3D models are ideal for dealing with profiled compositefloors in research, the complexity and time consumed for themodelling may be beyond the needs for normal engineeringdesign. However, reasonably simple FE models for dynamicanalysis of multi-panel floors can be developed as shown in thenext sections.

An equivalent isotropic flat plate model

To simplify modelling the composite panel, an equivalent isotropicplate will be considered. Based on the theory of isotropic thin flatplates, the maximum central deflection Δmax of a simply supportedplate subject to a uniformly distributed load is known10. The

3 Formation of the 3D composite floor modela) Steel-sheet model (thin Shell elements)b) Concrete slab model (3D Solid elements)c) 3D-Model of a composite floor

3a

3b

3c



displacement of the composite panel subject to a similar UDL canbe calculated using the 3D FE model. Thus for a given Δmax anequivalent stiffness, or thickness, of a flat plate can be determinedto relate it to a composite panel with similar plan dimensions andmass. This uses a sample area as a preliminary to the mainanalysis. It requires detailed modelling but once this has beendone, the flat plate model can be used to represent more complexmulti-span systems.

When the thin plate equivalent was used to model thecomposite panel, it was found that:– The isotropic equivalent flat plate has similar values for the

fundamental frequency, mode shape and maximumdisplacement to those of the composite panel.

– The analysis of the isotropic equivalent thin flat plate model onlytakes about 1% of the CPU time required by the 3D-model.

An equivalent orthotropic flat plate model

As the decking sheet profile differs in the two principal directions,an orthotropic equivalent flat plate model can be developed forwhich a 3D model of a composite floor panel is not required. Thedetailed procedure to determine properties in the two principaldirections is described in the literature8. This involves the followingsteps based on beam theory:1 In the ‘x’ direction, the deck cross-sections parallel to the ‘xz’plane have a profiled shape, which needs to be converted to anequivalent single section. The area and the second moment of theprofiled sections can be determined from standard calculationsand the properties can then be transferred as an equivalentconcrete section.2 In the ‘y’ direction, the cross-sections of the deck parallel to the‘yz’ plane have two different depths which also need to beconverted to an equivalent single section. The calculation involvesequating the predicted maximum deflection with the maximumdeflection of a uniform simply supported beam with the same

length and width but a constant cross section along its length.Both are subjected to the same uniformly distributed load.3 The basic data for the orthotropic plate can then be determinedas follows:

– The bending stiffnesses in the two perpendicular directions(EIx) and (EIy) can be equally expressed by (ExIy) and (EIy), where Ex

= EIx/Iy and E is the elastic modulus of concrete. – The mass density of the equivalent flat plate: that is the ratio of

the total mass of the original floor to the product of the area of thefloor and the equivalent thickness teq.

In this way, the composite plate is converted to an orthotropicflat plate, which can be easily modelled using a commercial FEsoftware package.

Comparing the isotropic and orthotropic models

Comparison between the results of the 3D-model of the compositedeck panel and the two equivalent plate models (isotropic andorthotropic) indicates that the composite deck floor can bemodelled as an equivalent flat concrete floor using either method.The comparison shows that:– The natural frequencies and the displacements of the 3D model

and the two simplified 2D models agree reasonably well.– The isotropic plate agrees slightly better with the composite

model than the orthotropic plate. However, the equivalentisotropic flat plate requires modelling a 3D composite deckpanel.

– Significant savings in CPU time are achieved using theequivalent models.

Modelling a complete multi-panel composite floor8

Based on the information given in the last section an example ofmodelling a real composite floor will now be considered. Theexample is based on the composite floors of the steel framed

4 The profile of the beam modelledusing plane stress elements

5 The plan of the floor and the testareas

4

5



building at BRE’s Cardington Laboratory9 for which measuredcharacteristics of various floor areas are available as well as theresults of tests involving people walking and jumping.

The composite floor

The composite floor system comprised steel down-stand beamsacting compositely with a floor-slab supported by columns. Thefloor slab was constructed using a trapezoidal steel deck andlightweight concrete, and an anti-crack steel mesh 15mm abovethe steel deck. The design depth of the slab was 130mm. A typicalplan of a floor in the third storey and above is given in Fig 5. Atground and first floor levels, the plan arrangements are slightlydifferent with an atrium at the centre of the south of the building.

A survey of the actual slab thickness of one floor area concludedthat it varied quite considerably from specified values; the averagebeing 146mm and the maximum 160mm11,12. Thesemeasurements were not taken on the panels used in the tests.Nevertheless, the two thicknesses were used for modelling thecontinuous upper portion of the concrete slab of the full-scalecomposite floor. The first one is the nominal design depth 60mm(Model 1) and the second is the actual measured overall averagedepth of 76mm (Model 2).

The FE model

A model of the composite floor was created following the conceptsgiven in the section on ‘Modelling foor to determine their dynamiccharacteristics’. This considered the concrete slab, steel sheeting,beams, columns in the upper and lower storeys and thecomposite action between beams and plates. All the columnswere assumed restrained against both translations and rotations attheir connection to the upper and lower floors.

An equivalent isotropic flat plate model was then used to obtainthe equivalent thickness and material density of the floor, for thetwo different concrete slab depths (which turned out to be 107mmand 121mm for Model 1 and Model 2, respectively).

Comparison between frequencies calculated using the FE models andexperimental results

Two panels within the upper floors were used extensively fortesting. These were 9 x 6m corner panels in different locations (theNE and SE corners panels respectively) and on different floors.They were selected because in both cases the principal mode ofvibration was well separated from other modes. The dynamicproperties, which were obtained from forced vibration and statictests, are given in Table 1.

The frequencies of the modes determined using the FE model

are given in Table 2.The peak vibrations induced in each test panel relate to the

vibration mode in which the maximum movement occurs in thatarea, that is the principal mode. Therefore, each of the calculatedvibration modes was examined; and the fourth calculated modeidentified as corresponding to the measurement in the first testpanel and the sixth mode to the measurements in the second testpanel. The comparison between the calculated and measurednatural frequencies of the composite floor is summarised in Table 2.

Continuity

Having progressed this far it had been hoped that the modellingwould be complete; however, there is one further significantproblem. Although the calculated frequencies might be similar tothe measured values it was evident that calculated stiffnesses weremuch higher than the measured values and the measuredvibrations in adjacent floor panels were not as high as thetheoretical model suggested. Examination of the floor revealedcracks on the upper concrete surface above beam supports and itis these cracks, or the lack of continuity that they indicate, thatappears to explain the differences that have been noted.

This is explored in [ref 13]. The floor, which was modelled on thedesign thickness, is divided into separate panels cornered by thecolumns. These panels are linked using rotational springsrepresenting the cracks and continuity between panels. Varyingthe spring stiffness in the model can change it from that of acontinuous system (i.e. that modelled earlier) to a series ofindependent panels. To try to replicate site measurements thespring stiffnesses were determined by comparing the measuredFrequency Response Function (FRF) with an equivalent calculatedvalue. The optimum match, based on minimising the differencebetween measured and calculated FRFs using a least squaresmethod, gave differences between the measured and calculatedprincipal frequency, modal stiffness and static stiffness of 0.23%,0.51% and 5.8% respectively. The FRFs for the optimum matchare shown in Fig 6 along with the measured data and that for thecontinuous model.

While this match may seem very good it must be rememberedthat the spring stiffnesses were determined via a comparison ofmeasurements and calculations but no method of calculating thestiffnesses is provided. Indeed these spring stiffnesses may varyalong panel boundaries and depend upon the loading experiencedby the various panels, thus rendering them impossible todetermine without experimental measurements.

Where then does this lead? Certainly it is not currently possibleto show how to model floors accurately at the design stage,although given an existing floor that can be experimentallyexamined a numerical model can be tuned to correlate withmeasurements. This model can then be used to calculate thestructure’s response to given load scenarios. Nevertheless, theidentification of a critical factor in behaviour, i.e. the continuitybetween panels, is an important step in our understanding of howcontinuous structures behave. Further developments in modellingwill either require a change in design philosophy, e.g. to create aknown flexibility between panels, possibly complete continuity, orto learn more from current designs using a combination ofexperimental testing and numerical modelling.

Damping Overview

Damping, or the ability to dissipate energy, is an importantcomponent of any dynamic system as it limits the amplification ofmotion in a resonant situation. Earlier an equation was given for

ModeNo.

Model 1 (M1)(designthickness)

Model 2 (M2)(actualthickness)

Measurements

1 6.89 7.35

2 7.16 7.67

3 7.24 7.76

4 7.56 8.17 7.58

5 7.57 8.25

6 8.01 8.70 8.49

Floor Force @res. (N)

ResonanceAmplitude(mm)

Best-fit curves for spectra Decay data StaticStiffness(MN/m)Freq. (Hz)

Damping(% crit.)

Stiffness(MN/m)

Freq(Hz)

Damping(% crit)

1 (NE) 213 0.322 8.49 1.65 19.4 8.49 1.59 9.32

2 (SE) 168 0.550 7.58 1.16 13.1 7.58 1.09 10.04

Table 1 Results of tests on principal mode on the two test panels

Table 2 The calculated lowest natural frequencies of Model 1 and Model 2



evaluating a floor’s acceleration ( x ) when subject to resonancehuman loading:

It can be appreciated that the response is inversely proportionalto the damping ζ. The above equation is based on a one degree-of-freedom system, corresponding to one mode of vibration. Thegoverning equation of motion is:

The damping term c in the equation is related to ζ, the ratio ofcritical damping, by the following equation

This model assumes that the damping is viscous, which alignsreasonably well with the observed behaviour of most structures.Damping is often expressed as a percentage of critical damping,for example 2% damping; this is equivalent to ζ = 0.02 when usedin calculations. At resonance for the one degree-of-freedomsystem the inertia term ( mx ) is exactly equal to the stiffness termkx but with opposite direction; hence the two cancel out leavingthe situation where the damping term resists the load, i.e. cx = f(t)As the damping force is usually much smaller than the inertia orstiffness force, a much larger response is encountered atresonance for a similar amplitude input force.

Damping is not a factor which can be determined accurately,since it reflects how a system is constructed as well as what itsconstituent materials are. So, for example, a steel frameworksupporting pre-cast concrete floor beams will have a much largerdamping value than that of the steel frame or the beams bythemselves, the joints between the two materials being a source ofenergy dissipation. Likewise, a bolted steel framework will havemuch higher damping than a similar welded framework. Thusdamping of the structure is greater than that which might bepresumed from the intrinsic damping of the elements from which itis constructed. This suggests that damping is not of a form readilycompatible with finite elements. Instead it is often sensible toestimate the damping value for each mode based uponmeasurements taken on similar structures, although the interactionwith the person perceiving the motion should not be neglected.

The previous paragraphs, and indeed most literature, suggeststhat damping is a constant factor, but measurements show thatdamping does vary with vibration amplitude, the damping generallyincreasing with increasing amplitude of vibration. So dampingvalues should be measured at amplitudes of vibration of a similarlevel to those under consideration.

xk

F2

2

g~

=: :

km

c

2g =

mx cx kx f t+ + =: : :

^ h

Measurements

A number of measurements have been made on various types offloor (at vibration amplitudes similar to those induced by peoplewalking) and are given in Table 3.

The table lists the floors in order of increasing damping so therange of damping values can be appreciated. However these floorpanels did not have any people on them when the tests wereconducted and this important factor will be considered later.

The first point to observe is that there is quite a wide range ofdamping values. Yet damping is the critical factor for determiningwhether resonance due to walking will produce a larger responsethan that from individual footfalls, with a damping level of belowapproximately 3.5% indicating that resonance is critical1. Hencethe resonant loading condition is critical for the modern floorsgiven in Table 3.

The floors with lower damping values have one thing incommon; they have a continuous floor system. The floors built upwith pre-cast concrete panels tend to have higher damping valuesdue to their joints providing an extra damping mechanism. Thefurnished floors also tend to have higher damping values, but it isquestionable whether damping from furnishings can be reliedupon, and it is often the least furnished areas of multi-panel floorsthat encounter problems. The two highly damped floors are bothquite old and of the type of construction including many joints.

It is of interest to consider the effects of fittings and fixtures onfloor characteristics. From experience it can generally be assumedthat the changes which occur when finishes are added to a barefloor will follow a reasonably obvious sequence. False floors willprovide increased stiffness and damping, with these increasesbeing less significant for longer span floors. For areas that havebeen stiffened by significant structural alterations, adding stairwaysetc., significant increases in stiffness will result, hence higherfrequencies. For areas that have just had a significant increase insupported mass, a decrease in frequency will occur. Forintermediate cases which have some stiffening and some addedmass then only small changes in frequency will result. The additionof fittings may also change the mode shapes especially if thedistribution of fittings is not uniform. There will be, however, ageneral trend for all the damping values to increase, albeit some byonly a small amount.

Human-structure interaction

There is one last factor to consider. For serviceability related tohuman acceptance to be of concern, there must be someone onthe floor to feel the vibration. This stationary person must interactwith the floor (otherwise there would be no feeling or perception)and thereby absorb some of the vibration energy, thus alsoincreasing the effective damping. This is quite a complex topictermed ‘human–structure interaction’ which is described in detail14.

6 Comparison between the measured and simulated Frequency Response Functions (FRFs) for the displacement at the centre of the test area

6



However for illustrative purposes consider measurements made onthe first test panel of the composite floor described earlier.

The floor panel, which had a frequency of 8.49Hz and adamping of 1.65% when tested empty, was examined with variousgroups of people. The measured frequency and damping for thevarious sized groups are given in Table 4. The data weredetermined from heel-drop tests which tend to give slightly highervalues of damping than the more accurate forced vibration tests.The values for one person and 32 and 64 people are from one testeach, whereas those for the other groups are average values for anumber of tests with different groups of people. The values for thetests on the two larger groups should be taken as approximate asthe characteristics are derived from very short decays (due to thevery high damping).

From the table it can be appreciated that stationary people adda significant amount of damping to the system, indeed they arevery good vibration absorbers. Thus floors with larger groups ofpeople will tend to limit any resonant build-up. But it is the floorswith individuals present that are important; nevertheless even thestationary individual will still increase the system damping which isespecially significant for low-damped floors. It is possible tocalculate the frequency and damping of a floor with stationarypeople, given a knowledge of the floor characteristics and thenumber of people, and assuming the people have a damping of34%, a frequency of 6.1Hz and a modal mass equal to their actualmass15. This predicts the values in the table and othermeasurements reasonably well.

Practical evaluation of floor response to human loading

Having reached this understanding, it is worthwhile consideringwhat can be done if one cannot believe that an accurate model ofa multi-panel floor can be constructed at the design stage. Anobvious question is whether it possible to consider error bands tohelp evaluate performance in response to human loading. In orderto do this a number of models were examined, all based on thedetailed model of the multi-panel composite floor but imposingvarious restrictions. For each model the key dynamiccharacteristics are calculated and the response of the model totwo load scenarios determined. These two load scenarios are:– One 76kg person walking across the floor at a frequency to

generate resonance. (i.e. the critical pacing rate). – 32 evenly spaced people (of average weight 67.6kg) jumping at

the critical frequency on the floor (i.e. 8.49/4Hz).

The calculation procedures which are described in detail inreferences 1 and 2 were applied to the five models given below.

These examples are chosen as experimental results are availablefor comparison with the calculated values. The models consideredare: 1 The continuous floor model obtained in the section ‘Comparison

between frequencies calculated using FE models andexperimental results’.

2 The optimised model shown in the section on ‘Continuity’ (i.e.the model with springs used to model the lack of continuity).

3 A panel of similar construction but supported at four corners(based on the NE corner of the Cardington building).

4 A panel with simple supports along its four edges.5 A panel with corner supports and simple supports where it links

with other panels.

In each case the damping was taken to be the measured valueof 1.65%. The calculated results are given alongside the equivalentmeasured values.

Not surprisingly the optimised model (Case 2) provides the bestcorrespondence with measurements. The most obvious mismatchin the above table is that for case 4, i.e. a panel with simplesupports along its four edges, and its fundamental frequency ismuch too high thereby giving very high values of acceleration. Forthe other cases, the acceleration values are approximatelyinversely related to the modal mass which is not surprising as theacceleration is dominated by the response at resonance for onemode. The continuous FE model (case 1) underestimates theaccelerations significantly whereas the simple models (cases 3, 4and 5) overestimate the response.

All the calculated displacements due to jumping, have valuesmuch closer to the measurement as the response at the jumpingfrequency has a significant influence and the results are notdominated totally by the resonant response.

The two models 1 and 5 may be considered to provide upperand lower estimates of the structural characteristics and for thiscase the average acceleration is not too far away from themeasured value. This may be a useful first stage in an evaluation. Itis wise to remember that for a multi-panel floor, characteristics maychange with the loading that has been encountered. Thus a newfloor without cracks may be more akin to a continuous floor. In thissituation the loaded area may experience lower vibration levels inresponse to critical loads (as shown in Table 5) but the vibrationswill be transmitted throughout the whole multi-panel area. On theother hand, if the floor area has been subject to high loads anddeveloped cracks it may have characteristics more akin to case 5,and would therefore encounter higher vibration levels than for case1 but these would be restricted primarily to the loaded area. In this

Floor type Frequency(Hz)

Damping(% crit)

Steel beams with composite floor 6.39 0.61

Slimfloor 12.03 0.67

In-situ concrete 11.89 0.86




Steel girders with pre-stressed concrete planks 4.95 1.35

Deep profiled concrete slab 7.43 1.56



Composite steel/concrete beams with pre-cast hollow floor units 7.91 1.81

Steel beams with pre-cast concrete planks and false floor 6.96 1.90


Steel beams with composite floor plus furnishings 9.26 4.45

Sprung wooden dance floor 7.62 4.54

Beam and pot 11.93 5.08

Table 3 Measured characteristics of the principal mode of a single panel for a range of floors

No. of persons Freq. (Hz) Damping (% crit)

0 8.49 1.65

1 8.53 2.66

2 8.54 2.84

4 8.51 3.70

8 8.57 4.37

16 8.59 6.81

32 8.48 15.88

64 8.89 14.97

Table 4 Frequency and damping derived from heel-drop tests for various groups



latter case those feeling the vibrations would be able to recognisethe vibration source which therefore may not be as great aconcern as when the source is unknown. Also the highestvibrations will be nearest the centre of the loaded panel andreduce significantly towards the edges of the panel.

It should also be noted that the measured values in Table 5 inresponse to jumping are average values and a considerablevariation in response magnitudes was observed. The measuredaccelerations and displacements are presented more fully in [ref 2].

Concluding remarks

The serviceability of floors subject to dynamic loading is animportant consideration for modern designs. For floors in modernoffices, which are typically multi-panel systems, it is necessary todetermine their dynamic characteristics. This may involve thecalculation of their fundamental natural frequency as a simplecriterion to avoid problems, i.e. by ensuring it is sufficiently high toavoid problems, or alternatively the calculation of all of the modalcharacteristics to determine their response to a design load. Tocalculate the characteristics of a multi-panel floor it is necessary tocreate a numerical model, typically using finite elements. Butcurrently there is no truly accurate way to model the continuitybetween panels. This paper has considered the numericalmodelling of floors and presents the following recommendations: – The columns, which support or link to the floor, should be

considered in the model.– For floors supported by beams, the eccentricity of the beams

needs to be considered in the analysis. This will provide a morerealistic representation of the actual structure and will increasethe stiffness of the floor. The calculated frequencies are not verysensitive to the location of the neutral axis, but this should beconsidered.

– For a composite floor the profiled steel decking should beconsidered in modelling as it represents a significant part of thesystem stiffness.

– Accurately modelling a composite floor can be complex, butrelatively simple equivalent flat plate models can be developed.These provide significant savings in modelling and CPU time incomparison with developing a detailed model.

– For multi-panel floors the continuity between adjacent panels isimportant, albeit not easy to model accurately. This suggeststhat a variety of different models should be considered.

Although finite element models can be built-up to representquite complex systems, the accuracy may be illusory, moreoverthe predictions of floor acceleration are linked to the selecteddamping value which will not be known accurately. The damping ofthe structure is greater than that of the elements from which it isconstructed, which suggests that damping is not of a form readilycompatible with finite elements. Instead it is sensible to estimatethe damping value for each mode based upon measurementstaken on similar structures, although the interaction with theperson perceiving the motion should not be neglected. Forserviceability evaluations related to human acceptance of vibrationin modern structures a damping value of 2% is recommended to

represent the floor plus the stationary person who perceives thevibration.

It is wise to recognise that some of the data used in modelling afloor may not be perfectly accurate, for example the materialproperties and even the slab depth. Therefore the actualcharacteristics will reflect these imperfections. It should also beremembered that the serviceability limit states are themselvesrelatively coarse indicators of acceptability16, 17.

Finally it is worth considering one factor which is important forserviceability related to people walking. It is the centre of the floorpanel where the biggest response will be encountered so it is not agood idea to have a ‘sensitive’ person sitting there if the floor is‘lively’. Equally walking across the centre of the floor panel createsthe largest vibrations so a major walkway should avoid this area(perhaps through thoughtful positioning of furniture). These twosimple points may help to minimise some problems.

References

1 Ellis, B. R.: ‘On the response of long-span floors to walking loads generatedby individuals and crowds’. The Structural Engineer, 16 May 2000, 78/10,17-25

2 Ellis, B. R. and Ji, T.: BRE IP 4/02. ‘Loads generated by jumping crowds:experimental assessment’, February 2002

3 Ellis, B. R. and Ji, T.: ‘Loads generated by jumping crowds: numericalmodelling’. The Structural Engineer, 7 Sept 2004, 2/17, 35-40

4 Jerath, S.: (1984), Dynamic modulus for reinforced concrete beams, J.Struct. Eng., 110/6, 1405-1410

5 El-Dardiry, E., Wahyuni, E., Ji, T. and Ellis, B. R.: (2002), ‘Improving FEmodels of a long-span flat concrete floor using natural frequencymeasurements’, Computers & Structures, 80/27-30, 2145-2156

6 BS EN 1994: Design of composite steel and concrete structures 7 El-Dardiry, E. and Ji, T.: ‘The effect of eccentricity on free vibration of

composite floors’, Computers and Structures, 2007, 85/ 21, 1647-16608 El-Dardiry, E. and Ji, T.: Modelling of the dynamic behaviour of profiled

composite floors, Engineering Structures, 2006, 28/4, 567-5799 Bravery, P. N. R.: ‘Cardington large building test facility – construction details

for the first building’,1994, The First Cardington Conference, UK 10 Timoshenko, S. P. and Woinowsky-Krieger, S.: Theory of plates and shells,

Second Edition, McGraw-Hill, 195911 Rose, P. S., Burgess, I. W. and Plank, R. J.: ‘A slab thickness survey of the

Cardington test frame’, Res. Rep. DCSE/96/F/7, Sheffield, 1996, Dept. ofCivil and Structural Engineering, University of Sheffield, UK

12 Gibb, P. and Currie, D. M.: ‘Construction loads for composite floorslabs’,1994, The First Cardington Conference, UK

13 Zheng, T., Ji, T. and Ellis, B. R.: ‘The Significance of Continuity in a Multi-Panel Composite Floor’ Engineering Structures, 32/1, 184-194

14 Ellis, B. R. and Ji, T.: ‘Human-structure interaction in vertical vibrations.’Proc. Instn. Civ. Engrs. Structs & Bldgs, Feb.1997, 122, 1-9

15 Pedersen, L.: ‘Floor vibrations – As induced and reduced by humans’. PhDthesis, 2005, Aalborg Univ. Denmark

16 Ellis, B. R.: ‘Serviceability evaluation of floor vibration induced by walkingloads’, The Structural Engineer, 6 November 2001, 79/21, 30-36

17 Ellis, B. R. and Littler, J. D.: ‘The response of cantilever grandstands tocrowd loads. Part 1: Serviceability evaluation’, Proc. ICE Structs & Bldgs,157/SB4, August 2004, 235-241

Case Frequency (Hz) Modal stiffness(MN/m)

Static stiffness(MN/m)

Response to walkingacceleration (%g)

Response to jumpingdisplacement (mm)

Response to jumpingacceleration (%g)

Measured value 8.49 19.4 9.32 2.9 2.39 15.18

1 8.68 54.8 11.31 1.08 1.72 10.23

2 8.51 19.5 9.86 2.90 2.20 17.313 7.45 11.19 9.52 3.80 2.59 19.634 11.31 16.08 14.56 6.45 1.73 30.995 8.33 14.22 12.32 3.81 2.01 19.22

Table 5 Response of various models to walking and jumping loads



At a meeting of the Membership Committee on1 July 2010, the following were elected inaccordance with the Institution’s Regulations:

Elections

Member (1)GUAN, Zhongwei

Graduate (152)Student (7)Student Free (813)

Transfers

Member/Associate to Fellow (6)BAKER, Michael GeorgeBARTON, Robert StanleyCALDER, Leslie StephenCHOWDHRY, Zahid WaheedTULLETT, Andrew BrianWILLIAMS, David Eirwyn

Student to Technician (2)HEGINBOTHAM, LeeYUSUF, Yuhanna Adiyb

Student to Graduate (35)

Reinstatements

Fellow (1)BLACKER, Michael Stewart

Member (7)CLAY, Peter AndrewLAU, Wai Sang RexLEUNG, Wah MingTANG, Louis Wing-YinTSANG, Chun MingWISHLADE, Elliot DuncanWONG, Kwok-Yee

Graduate (7)Student (1)Student Free (41)

NOTICE

Resignations

The Membership Committee has accepted withregret, the following resignations:

Fellow (15)BAKER, John RichardBONNER, Henry JohnDIBB-FULLER, EdwinENGLISH, Charles JohnFLETCHER, PeterGWYNN, JohnKORBUSZ, TadeuszLEGGATT, Alec JamesSEMPLE, Peter JamesSMITH, Richard EmbletonTAGGART, Thomas StanleyUNDERWOOD, ReginaldVENN, John AntonyWRIGHT, John AlfredYOUNG, Frederick Alan

Member (19)AINSWORTH, AlanBROOKES, FrederickBROWN, Roy CharlesCHAN, Boon TeikCLISBY, RobinCOLBERT, Michael GrahamDAVIES, Stephen JohnDAWSON, PeterEDWARDS, Drew HunterHILDITCH, Martyn CliffordHOOD, John RamsayINAYATULLAH, LATHAM, Alan RichardLEWIS, Wanda JadwigaNEWBY, John ChristopherSMITH, AlanTANSLEY, David Arthur HaslamWADE, Frederick RonaldWALTERS, David Alfred

Associate-Member (5)BURNE, MichaelDAVIES, Paul AndrewGOODBY, Peter LloydLAWES, Dennis ArthurSIMPSON, Graham Albert

Technician Member (1)POOL, Lauryn

Graduate (45)Student (8)

Deaths

The deaths of the following are reported withregret:

Fellow (14)ARMSTRONG, James HodgsonBASTEN, John DerrickBROWN, John StewartCHATTERTON, MarjemFAHY, John Francis GerardFOWORA, Amos AdeoyeGREGORY, John James ConradJONES, Owen WilliamNEEDHAM, Frederick HaroldRENNICK, Edward BrianSHOWAN, Andrew MervynSRISKANDAN, KanagaretnamWEAVER, Charles Louis HarryWOOD, Frederick George

Member (9)ACTON, Ian MurrayBEANEY, Thomas PatrickBROCKLEHURST, FrankCARTMAN, Robert DouglasCHAN, Ka YikLEUNG, Chun Sing BorisLINDSAY, John CharlesSEHMI, Niranjan SinghSIT, Edward Tak Wah

Graduate (1)CONNOLLY, Sean Michael

Notices and Proceedings

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Southend studentaccommodationBell & Webster has supplied its structuralprecast concrete rooms system to HollybrookLimited for new student accommodation at theUniversity of Essex. Comprising 561 studentbedrooms, the completed project required atotal of 2251 by Bell & Webster Concrete Ltdfactory engineered concrete units.

With 1296 wall units and a height of 10storeys, the new building has been constructedto create a strong, robust structure that can beinstalled and fixed far quicker than mostalternative building systems for this scale ofbuilding.

The offsite engineered wall units weremanufactured and installed by specialistinstallation teams, helping to speed up theoverall construction and finishing processes.Site costs were kept to a minimum by ensuringthat the initial construction phase including theinstallation of bathroom pods would becompleted on time, making way for followingtrades to install the crucial services needed torun the building.

The construction consists of load bearingcrosswalls supporting single span floor slabs in

reinforced concrete with prestressed concretefor the longer span common rooms andkitchens. The walls are laterally restrained bythe floor slabs. External walls laterally restrainthe building at right angles to the crosswalls.The floor slabs act as a diaphragm and theirplate action carries all lateral loads, from windand notional loads, down through each floorlevel to foundation level in shear and momentactions. Progressive collapse and floorplateaction is provided through cast-in vertical andhorizontal ties.

Further information: Bell & Webster ConcreteLimited, Alma Park Road, Grantham, Lincs (tel:01476 562 277; fax: 01476 562 944; email:web: www.bellandwebster.co.uk).

Free design integrationsoftware available on lineTo complement the latest release of Autodesk’sRevit® Structure, CSC has launched its newRevit integration software. This free Revitintegration software is now available fordownload from the company’s website andenables clients to transfer their models betweenCSC’s steel and concrete building designsolutions, Fastrak and Orion, and the 2011version of Revit Structure.

‘Engineers and technicians can share, makechanges to and synchronise models at anystage of the design process, withoutcompromising existing or new modelling work’,said Kevin Lea, BIM Business DevelopmentManager at CSC.

‘The seamless integration between Fastrakand Orion and Revit Structure improves projectcommunication and significantly increases

productivity. Engineers and technicians canreport and manage incremental model changeseasily with less risk of repetition andinterpretation errors.’

CSC also offers technical support, trainingand consultancy services to help users get thebest from their Revit integration software.

This latest release further consolidates CSC’sposition as an Autodesk Premier StructuralPartner.

Further information: Revit Structure (tel: 0113329 3000; web: www.cscworld.com).

Gifford has trademarked its new Laser AidedModelling (LAM®) process which providescontractors, quantity surveyors, propertycompanies and developers with highly accuratecomputer models of their buildings and thesurrounding landscape.

The novel surveying technique creates avaluable tool for monitoring existing structuresand assessing property portfolios. It is alsovaluable for planning refurbishments and theintegration of existing buildings with new buildprojects. Laser scanning has been used insurveying for the last 10 years producingmeasurements in 3D called point clouds.Building information modelling (BIM) is nowwidely used for the design of new buildings andother structures whereby a 3D virtual model of anew building can be created. Improvements indata collection techniques has enabled Giffordto pioneered this new process, which for the

first time makes possible the comprehensiveinclusion of the entire built environment into thecomputer modelling process.

Applications include the structural modellingand visualisation of new buildings, assessmentof materials quantities, the provision of accurategeometrical measurements for structural andenvironmental analysis and the co-ordination ofnew building projects within and adjacent toexisting buildings.

in addition, Gifford has signed an agreementwith data collection specialist Plowman Craven.The two companies will together provide acombined modelling system for clients that linkssurvey data, via LAM® with a full range ofengineering services such as modelling, design,inspection and monitoring.

Further information: John Rudofsky, HelsenCommunications (tel:020 8786 6699).

Product items on these pages are selectedand edited in good faith from pressreleases supplied by the companies, andthe Journal accepts no responsibility forthe product information supplied.

Investment advances‘cloud computing’ softwareBentley Systems, Incorporated has acquired aminority interest in Charlotte, N.C.-basedBlueridge Analytics, Inc., provider of SITEOPSsite design optimisation technology that utilisescloud computing to save substantial time andcost while improving land developmentoutcomes. SITEOPS is a patented web-basedapplication, empowers civil engineeringprofessionals, real estate developers, and landplanners to perform quickly site configurationsimulations, produce preliminary cost estimates,optimize site designs, and reduce overall costs.The conceptual designs are compatible withDGN, DWG, LandXML, and other file formats.

Mike Detwiler, president and CEO,BLUERIDGE Analytics, said, ‘We are extremelypleased to have Bentley Systems as our largestshareholder. Bentley’s decision to make asignificant investment in our company and helpsupport our ongoing development workvalidates the tremendous potential of our cloud-based land development technology.’

To facilitate information sharing amongSITEOPS and Bentley users, Bentley will add aSITEOPS user community to its Be Communitiesprofessional networking site athttp://communities.bentley.com.

Further information: Jennifer Gaddy (tel: +1704 409 7508; email: [email protected];web: www.siteops.com).

Laser scanning technique for the built environment

Guidance on bond beamsto resist lateral loadCERAM has published a Design Guide forMasonry Reinforced by Bond Beams to ResistLateral Load, which is available free of chargefrom the CERAM website. It outlines the use of abond beam system, commercially known as theWI Beam System, to replace wind posts as themeans of subdividing large walls andstrengthening them against lateral loading. Thereport is the result of a 3-year study to assesslateral load resistance of walls built using thissystem.

The study on which the design guide isbased involved the testing of four walls, each8m long and 5m high, under lateral load.

‘Instead of subdividing the walls using windposts, we used bond beams placed atapproximately one-third and two-thirds of theheight,’ explains Dr Geoff Edgell, Head ofBuilding Technology at CERAM.

‘The system we used in this study introducesshear transfer rods – an innovative method ofproviding additional support for large walls.’Shear transfer rods connect the bond beamwith the blockwork courses above and below it.In this way the three courses act compositely toprovide a stiff reinforcing layer. The study hasdemonstrated that such walls can resistsignificant wind loads, in excess of 6kN/m2

before failure, and it sets out generalrecommendations for the design of concreteblockwork walls using the WI Beam System.

Further information: CERAM (tel: 0845 0260902; web:www.ceram.com/structures).

Striking façade forColchester Arts Centre

The new £26M Colchester Arts Centre buildinghas a striking looking glass façade, designed byacclaimed American architect Rafael Vinoly, thatwas always going to pose an engineeringchallenge. Standing 11m tall by 24m wide, it isconnected to a curved roof surface and walls atthe edges. It is also inclined by 15° outwardsand rotates 5° about its vertical axis, presentinga complicated geometry in design terms.

In addition, the fixing method for the 40tfaçade had to accommodate movements of upto 50mm vertically and 30mm horizontally inthe main steel support structure.

Specialist glazing contractor FA Firman calledin Malishev Wilson Engineers (MWE) to apply itsengineering skills to came up with a two-way,sliding joint detail, which simplified the overallfaçade construction.

The engineers used state-of-the-art 3Dsoftware to translate architectural visuals intoglass fabrication drawings and cuttingschedules for the glass. This allowed highprecision techniques to be applied during siteinstallation. Special analysis was carried out toestablish the true thermal performancecharacteristics of a non-standard façadesystem, which comprised 250mm by 80mmthick solid steel mullions (each weighing nearly2t) and 2.3m by 3.5m high performance,double glazed units (with a weight of about600kg each) fixed to them. Using a heat flowanalysis, MWE established a system U-value of1.4 W/m2 °C for the whole façade, whichcomplied with the architect’s demandingspecification. The glass vestibule of the buildingis fitted into the façade to provide public accessand also for the delivery of large scale artworks,by using integrated sliding and pivoted bespokedoors.

Further information: Gennady Vasilchenko,Malishev Wilson Engineers (tel: +44 (0) 207970 6020; email: [email protected];web: www.malishevwilson.com).

Refurbished swing bridgegets CE Mark

With the aid of services provided by LaidlerAssociates, one of Europe’s leading safety andcompliance consultants, the refurbishedPortumna road bridge in Galway has becomethe first bridge in the Ireland to carry CEmarking. The CE marking was needed becausethe bridge has moving parts – it is a swingbridge – and it therefore falls within the scopeof the Machinery Directive.

Spanning the Shannon River, PortumnaBridge was originally built in 1911 and when itwas decided that the structure needed to berefurbished, Waterways Ireland awarded theorder for design specification, contractpreparation and project supervision to RoyalHaskoning. L&M Keating carried out the buildingand installation work.

Further information: Laidler Associates (tel:0333 123 7777; web: www.laidler.co.uk/).

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