a partial look at concrete - a very good book
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This is an uncontrolled copy. Ensure use of the most current version of this document by searching the Construction Information Service at http://uk.ihs.com
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Aa t concrete
John G. Richardson
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A practical lookat conc rete
John G. Richardson FlCT
The Concrete SocietyL
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A practical look at concrete
John G. Richardson
ISBN0 946691 83 5
Ref: CS 132
John G. Richardson
Design and Production: Jon Webb
Published by The Concrete Society, 2002
Further copies and information about The Concrete Society, including membership, may beobtained from:
The Concrete Society,Century House, Telford Avenue,Crowthorne, Berkshire RG45 6YS, UKTel: +44 (0)1344 466007, Fox: +44(0)1344 466008Email: [email protected],www.concrete.org.uk
All rights reserved. Except as permitted under current legislation no part of this work may bephotocopied, stored in a retrieval system, published, performed in public, adapted,broadcast, transmit ted, recorded or reproduced in any form or by any means, without theprior permission of the copyright owner. Enquiries should be addressed to The ConcreteSociety.
Although The Concrete Society (limited by guarantee) does its best to ensure that any advice,recommendations or information it may give either i n this publication or elsewhere isaccurate, no liabil ity or responsibility of any k ind (including liability for negligence)howsoever and from whatsoever cause arising, is accepted in this respect by the Society, itsservants or agents...
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Contents
The issue of Concrete in which the page first appeared is shown in italics
A few words abou t Cubco manfew words abo ut the author
Publishers Note
vi
vii
viii
EXCELLENCEExcellence 1Excellence 2StandardsQuality assuranceEfficient co nstructionTestingM ore testing
Th e Conc rete SocietyAwards
Jub/Atgust 1991Sep teniberl October 1996Stpteniber 1982Azgust 1981Jub/August 200Jatzuary/ February 1993Jub/At/gr/st 1996
January 2000October 2002
12345678
910
C O MM UN CAT10 NS A ND DETA1LDrawings November I98 1Geometry 1 Janiiary 1982Geometry 2 February 1982Detail: the need for comm unication October 1983Detail: people’s inpu t April 1981Detail: concrete March 1981Methods and com munication Jub 1979Panel joints June 1980Computers in construction March 1999
11121314151617181920
ComputersCom puters and design
Jub/Aigi ~st 993 21June 1997 22
FORMWO RK AN D FALSEWORKSetting-out points January 1979Detail: form work June 1984Kickers 1 Septenzber 1977Kickers 2 October 1977Nibs an d corbels November 1977Cores and formers December 1977Ramps and intersections February 1978Staircases June 1983Circular work August 1979Props and propping December 1980Striking formwork August 1982Aluminium forms November 1980Trough and waffle floors October 1980GRC formwork March 1983Formwork failure January 1981Formwork March/Aprill992Formwork systemsFalsework 1Falsework 2Falsework 3Form work and falsework1Formwork and falsework2Formwork and falsework3
March/Aprill996October 1982November 1982Deceniber 1982March 1998May 2001June 2002
2324252627282930313233343536373839
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40414243444546
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REINFORCEMENTReinforcement 1Reinforcement 2Reinforcement 3
Reinforcement 4Reinforcement, fittings and accessoriesReinforcement and accessoriesCast-in fixingsLocating inclusionsTiesReinforcement accessoriesFibres
Jatiuay I999JanuaryylFebruary 1994October 1978
M q 1979M q 2002March 2001Janualy 1978September 1983Jub1984M q 2000September 2002
47484950
5152535455565758
PRODUCTION A ND PLACING
Preparingto
concreteTh e pre-concrete check 1Th e pre-concrete check2Production, plant and equipmentCon struction jointsProduction and handlingPlacing concrete 1Placing concrete 2BatchingConc rete mixing and batching plantReady-mixed con crete1Ready-mixed concre te2Ready-mixed concre te3Ready-mixed concre te4Slab constructionFlatworkHot- and cold-weather concretingWinter workmgConcrete in adverse conditionsPlacing, compa cting and caringSelf-compacting concrete
February 1979March 1979April 1979Februay 2001November 1978Jub/August 1994Ju b 1978January 1983Jub/August 1998September 1997February 1997September/ October 1992February 200 1June 1999M q 1981September 2000Juh/Aigust 1999September 198 1Mq/June 199sApril 2000March 2002
59
606162636465666768697071727374757677787980
SURFACE FINISH
Surface finishes 1Surface finishes 2Surface finishes 3Surface finishes 4Surface finishes 5Surface finishes 6Fixing to concreteSurface retardersArchitectural conc reteCon crete surfacesMaintaining conc rete finishesProtecting concrete
Cleaning concreteWeatheringRepairs and remedial work
M q 1977June 1977Mq/June 1993AuguJt 1977September/ October 1993ANgtlst 1980September 1980September 1979November/December 1998September/ October 1995February 1999January/Febmay 199s
Januay 1998June 1981December 1978
81
828384858687888990919293
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HA NDL ING AN D SAFETYLiftingLifting equipmentSafety
Sitesafe '83Moving loadsSupervisionCranesCranes - ommunicationsGetting things movingErgonomicsSafe working with small dum pers
December 198June 1982October 1979
Februay 1983Jub 1980October 1981August 1983December 1979J M ~983Murch 1984December I983
Precast concrete: samples and prototy pesPrecast concrete 1Precast concrete 2Precast concrete 3Prestressed concrete1Prestressed concrete2Prestressed concrete3Prestressed concrete4Con crete moulds for precastingMould designPolymer moulds and linersFlexible mould sConc rete ingredientsConcrete as a mould materialPrecast erection 1 - generalPrecast erection 2 - site factorsConc rete sculptureDecorative concrete and finishesLightweight and foamed concreteglass fibre-reinforced concreteTil t-up constructionSlipform an d tilt-up constructio nBridge constructionBridges
PRECAST A N D PRESTRESSED CONCRETEOctober 2001October 1999Nolieniber/ Deceniber 1991Februay 1984M y 1978March 1980M q 1997Mq 1982June 1978April 1980March 1982A p d 1982Mq 1998March 1978Noveniber 1979Januuy 1980Noiieniber/ December 200 0Jtily/August2002Noveniberl December 1996
9798
99100
101102103104105106107108
109
110111112113114115116117118119120121122
123124125126127128
April 1984 129April 1983 130March 2000 131Noveniber/ December 2001 132Noveniberl Deceniber2002 133
INDEX 134
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A few words about Cubco manCubco man was employed by Cube CompanyLimited (trade name Cubco). Cubco originated inthe Leonard Trotter* series of articles published
in the JournalPrecast concrete(nowQualityconcrete)in1972. The firm was a small (imaginary) manu-facturing concern whose entrepreneurial spiritsforesaw a market for concrete specimens of sucha standard tha t they would havea 99.9% chance ofmeeting any given specification. Rumour hasitthat, long before fibres of any kind were usedelsewhere in any concrete application, Cubcointrod uced micro-fine and virtually invisible fibresinto the specimens they produced, therebyensuring the required pass rate for the product.
Jack Barfoot, then editor of Concrete, saw theseillustrations as a means of conveying practical information to his readers and the page wasbor n. Since May 1977, in the pages entitledIlookingatitpractka/&,we have attemptedto conveythe practicalities of the use of conc rete in constru ction . We have detailed meth ods fo r forming ,casting, handling and finishing concrete, and touched o n planning and organisationas well ascritical details of safety. Early pages consistedof simple details, with few- f any - people tobe seen in the illustrations. In 1978, the need arose to intro duc e the human element and C ubc oman was pressed into service.
Cub co man has developed with age.It could be said that his character has become rounded overthe years. Initially he was con cerned with t he intimate details of construc tion, kickers, starter bars,stripping fillets, noggings and suchlike. Thes e days, while still maintaininghis interest in the finerd et d s, h e is involved with greater things, industry-wide. Cubc o man today appreciates such thingsas the advantages to be ob tained from new materials and m ethods, the benefitsto be gained byapplying techniques suchas networking and value analysis and even the use of computers indesign. Although his ability to appreciate the marvels of new technology and the seeminglyinfinite range of products designed to speed construction and improve quality has advanced overthe years, he sull retains an essentially practical attitudeto such developments:a ‘feet upon theground’ approach,as he would p ut it.
Th e pageLookingatitpractica4 has been used as a training aid by major contractors. Th e authorused it as such for many years in the course of nearly20 years working as a lecturer inconstruction topics at the Cement& Concrete Association (now BCA) Training C entre atFulmer Gra nge . near Slough, Berkshire. As wellas these applications, Cu bco m an has variously:advertised the Advisory Serviceof T h e C onc rete Society, appeared in exh ibitions, illustratedresearch reports and information bulletins, popped-up ina series of C D Roms for ContinuingProfessional Education of Engineers, and instructed site personnel on the installation ofprecast elements.
Since 1978, he has go ne from s treng th to strength to th e point wh ere his image isto be foundon notice boards on construction sites, within works, offices and laboratories. The pages areoften annotated with names of persons with whom , in the mind o f the viewer, he has beenassociated by deed o r action.
Ov er th e years, several people have suggested thata compilation of the pages would makeauseful book , recording t he practicalities and intro ducin g possibilities of emerging techniques tothe reader. T h e suggestion was taken up w ith enthusiasm by Nick Clarke, Publications Manager
and Managing Edito r of Concrete.So here it isJohn G . Richardson FICT High Wycombe, Buckinghamshire Nov emb er2002
*Pen name of Philip L. OwensHNC, MPhil, FICT, MCIWM, and n o connection with DelBoy or any of hisfamily
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A few words abou t the authorO n leaving school, and before joining the Royal Engineers, John worked brieflyas a narchitectural drau ghtsm an, meanwhile studying architecture which in th ose days involved tuitionin mechanical and still life drawing Followingan introd uction to army life with the Infantry, and
the Mons Officer Training School, the FE16 RE OCTU at Newark provided an education inconstruction, erection and demolition.
After the army, employment as adraughtsman and study at the renownedBrixton School of Building served to feedJohn’s interest in concrete work andprompted a specialisation in formwork.During this time, further education wasreceived from contact with his all-timehero, Cyril Parry, a formwork consultantwhose works included the floating jetties
used in the Norman dy landings of WorldWar I1 and the notorious Sellafieldchimneys.
Formwork design and detai l ing withHolland, Hannen and Cubitt , a majorcontractor of the time, embraced moulddesign for precast and prestressedconcrete leading to a move in to precastingas a mould shop supervisor. What seemeda natural progression led through sitesupervision of formwork with Scaffoldmg
(G rea t Britain) 1,td to fo rm wo rk man u-facture and then employment as aproduction engineer with Trent ConcreteLimited, at Colwick and HoveringhamWorks, Notting ham .A move to the lectur-ing staff o f the Cement & ConcreteAssociation followed som e yearsas worksmanager for Concrete Limited at Iver,Bucks. Th ese latter employments a fforde dthe opportunity to study works manage-ment at evening classes and as a day-release studen t.
Con curren t with the service at the C&CAand during the following ten yearsas aself-employed consultant and lecturer,John worked as Technical Assessor fo r theBritish Standards Institution in theirFirms of Assessed Capability Scheme.Avaried (somewhat chequered) career hasprovided a wealth of conta ct with allmanner of people in construction, fromthe man on the job to top management,from steelfixer to designer and from
consultant to concretor, bothon site andin works. Indee d, much of these worthies’knowledge has been incorporated in thepages Lookingat itpractical4 in Concrete
John at work on Cubcoman ...
... and Ctlbco man returns the compliment
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Publisher's note
John R~chardson's Looking atit practica& pages published in Conmete magazinesince 1977 cover a wide range of topics and present a wealth of advice on safe,practical concrete construction. Some of the pages were prepared to drawattention to a new code of practice or guidance document, and new editions ofsome of these documents have since been published. Some of the site practices,materials and systems shown in these pages may also have been replaced orimproved by more efficient approaches. Mmor amendments to the captionshave been incorporated to highlight these but as far as possible the pages havebeen retained essentially in their original format, reproduced from the printedpages of Conmete magazine.
Readers should make sure that any standards, codes or guides they refer to arecurrent and relevant to their situation.
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EXCELLENCE
he general acceptance of quality assurance in construction processes and productshas focussed Cubco man’s attention on standards of performance, Unlike the pastT here h s only measure of accomplishment was comment - or, even worse, lack
of comment - on his product or outputs, there are no w published procedures he observes.His work is carried out using these and incorporating h s suggestions. No longer are thngsdone the way that ‘our Mr Smith or our Mr Jones always did’.
In his home life, he has become accustomed to awards and award ceremonies foreverything from television soaps to good housekeeping, so that the existence of accoladesfor ‘Excellence in concrete’ comes as no great surprise. Cubco man has always felt pride in
his work. He is aware that, as well as earning his living using concrete to build a bridge,hospital, or somethmg as down to earth as a road or drainage scheme, he is contributingto the welfare of the community as a whole. Thus an award for ‘Excellence in concrete’seems wholly appropriate and more meaningful than many other awards.
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Excellence 1
111 /i,& of n i e Coi ic re te SocietyAwards, our bnejivas t o consider EXCELLENCEinputs necessaryt o achieve the standards exliibitedb y the i u i u n i t ~ ~ qrqer ts
We pondered t l i r. .
ENCIh‘EERI iVGsk i l l sand a b i l i t y E X T E N S I V Eplaizirin~qvidencedb y die outcomeof d i e operations . .
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Excellence 2
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Standards
\
No, don get excited - we know the word‘sturidard is e.rtrenielveniolive
We are using the word in the uppearuncecorite.rt..
._. nd , while a lot is said ut nieeriiigs aridlectures..
.._ we clre well u w r e that people aresomet imes disuppoirited wheiithey see thereal thing
_.. about the dangers o sniull samples-productso the sample-makeri skills ..
The Formwork Report* has some goodadvice to off..
Where there are speciul detui ls , feattires,dayjoints, tie holes. kickers. strrrters.retirrris ctnd so on ...
U niodel shotrld he mude to emitre that
iE.speciullyrvheri they have takencoruideruhlecure over desigii m i d detail.
. . it reconinieiid.y that. using site riiuterialsctnd t h e intended equipn~ent..
Of cotme. not every job cuii ,qet (111 rnvard -.._. specially the skillson site. . stundurds are establishedfo r cletuil,Jeuture
und iriish. ucceptahle staiiclurdsare.but at least evetyoiie knows whatt h e
* ConcreteSociety Technical Report No.13. Since revised as ‘Forinwork- U guide o good practice ’, The ConcreteSociery, 1995.
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Qu ality assurance
F i r m wisliingto becomeregi.stererlJrin.s ofassessed cupubiliijvwithin /lie BSI scheiiiefirst tlrrash out [heirquulity po1icie.sandnominute resporuihle people.
Theri an ussessnient of the conrpuny s people.
proc/uct.sr i nd systeiiis wil l be nifideto ensure thut.
... clruwingoffice uric1orguriizutionof qiiulityprocednres [ire in orcler:
4 7... loucling proceciiires,mid the ..
Theqiirrlity niuiiiiul produced by /lie hiIias to he ~sirbinitted..
eyuipnrentis up to scrcrtcli.
Tliut routine testing
... rrnd upproved by BSI Qiroli t)~AsslrrunceDepurtrnent.
... /he qirulity coritrol systemof checks isripercitedus it shoirld he ..
.slrlckirlg.stocks.
. . segreplion und disposul of.suhstondurdunits w e ull curried out in the upprovedIJlrInnel:
The resir// s Certificutiori - und N continuingsurveillarice to ensiire [lieniuintenunce of ureudysupply of Q u r r l i ~ ~ ~ssirrecl prooclrrctsf o rspeedy und economic constr~rctiori
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Efficient cons truction
Wi th developmentsin informatio n technology and coinpiiterapplications proceeding apace, never has our mail beenso aiuareo f t h ePOWof informationi n the desigii and planning stages ofa Contract...
... nor has h e enjoyed SiiCh high levels of comnniriicationoi i site.Indeed, the term ‘informatio n overload’ mayyet appear in hisle.xic01i of comtriictioii terms
Rationalised details are ensuring speedy reitiforcement installationand eco nomic reiise of expensive for mw ork iuithII rediicedlearning cycle for...
Materials obtained fr om ap proved,quality-assit redsripplierscontribute to th e maintenance of qiiality standards...
All these fentitres make for sotind and efficient comtriiction.ensiiring that gainful wor k f or all disciplines is available throrighoiitthe uarioiis stages of the constrrictiori process.
... the skilled workforce, ma ny ofwhom are certificated, andoperating sophisticated eq iiipnient at previoiisly tinimaginedolitpllts.
... con1biningat site ivith ‘state o ft h e art’ technology iuhere, forexample, magnetic impulse arid iiltrasonicpiilse readings provideimmediate rneasiires of performance.
As a resiilt o f t h e rediiced incidence of ‘snags’on completion, andwith less cutting and re-remaking during construction, theuse ofelectric h am mers and ciittirig tools hasbecome something of alostart to oiir niflti
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Testing
TTiere appears to be tio end to t h e tests w e arerequired 10 apply to corrcretei n irs various states.. .
break it, in a variety ofititeresrirg ways
, i 11 $,
We may have to 'slump i r ' . . . 'Juiii test' i r ,
Orr site u x may be called upotr to buzz thirgs Jigq' i t . .through i t . .
Botrtice thirgs o j i t , and getrerally mistreat it It's a salutary thought, however, that although weput a lo t ofstore by the results ... atid whatever theboy$rrs come up with next ,
as u d l as the samp lirg procedures, uh at we mostlytest is.. . the specimen producer/selector, the testerand the test equipment
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More testing
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The Concrete Society
Although his firm had not yet won an award for excellence inconcrete...
our man was prompted to find orrt more about The ConcreteSociety. I n the magazine CONCRETE, he found descriptionsofthe varied activities...
such as site visits to prestigious contracts around the coimtr y(safe. bitt not always fo r the faint-hearted ) along with...
He noted that seminars and meetings were held both locally andnationally, often in cooperation with other profcssional bodies, andthat th e Society participated in, and coordinated, research anddevelopment programmes.
and that the chap who had come onto site the day he had aprobleni had been an engineer fromThe Society's AdvisoryService
exhibitions and deminars providing a forum for demonstrationsof methods and eqiiipment.
He realised, to o, that ma nyof the reports and current practicesheets tha t had provedso helpful with his knowledgeof concretetesting and interpretationof results were Concrete Societypiiblicatioris
...
Wi th all these benefits in mind, our m an decidedto join and, notbeing inclined t o hang abo ut, filled in his memb ership applicationfo rm and posted it straight away
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Awards
Learniiig of the factorsassessed by the judges while consideringsubmissions for Concrete Society Certificates of Excellertce, our m anvisualised...
On sire, it is unlikely that the ground worker, impressivei n act ion, ...
. . ...
the difficultiesrbey would experiencein comparing the (excellent)achievemeittsof one t e a m of architects, erigitieersand coiistructors, withthose o f similnr teams
or the crane driver. workiiig withhis bauksmnn and slinger tomeet t h ed em an ds of th e ~ ~ ~ i ~ t r i i c t i o ~ ieam, ...
or the team members busy ‘assistrng’ the rendy-nti.ued truck driver todeliver the rightmix to the right place at the right time..
or the fnlseworkrrsarid formuiorkers, together providing safe support,
the completed structure,...access arid working co?lditlonS atid determirlhg theShflpe and fiplishO f
or even the concretors, responsible for sound compaction, wouldhavehad muchtime during construction to consider the importance of theircontr ibution to theexcellenceo f the s tructure.
But, of course, whatever their task, everyone involvedin a ConcreteSociety award-whining project will he proud tohave shared in theachievementmid will enjoy thereflected glory
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COMM UNICA TIONS A N D DETAIL
uring h s working life, our man has seen great changes in the way contracts areorganised and the skills of the individual are developed. He worked on site forD ome time before he was told how to judge good compaction, and longer before
he was instructed on the importance of weighng the constituents of the concrete mixrather than batching by volume. Much of the learning process and acquisition of skills,apart from trades such as those of the carpenter, depended on observing the work ofothers, not always the best s u e d examples
The tide has turned and these days many employers carry out training on site as well asencouraging training by sending staff on courses. Certification is now an essential
requirement of many facets of construction, particularly where the safety of othersdepends upon satisfactory performance.
Our man is aware that knowledge is strength and is always keen to learn of new materialsand techniques. Technical representatives of the firms servicing the construction industrymake a major contribution here by demonst rating their wares, instructing o n their use, andproviding a follow-up to their supplies.
Computers have become an essential tool in the construction process and are used byworkers at all levels. Th e batcherman, the designer and the production engineer all usecomputers in the course of their day. Cubco man still has his reservations but has to admitthat drawings and schedules are more legible than in his youth, that goods are deliveredwhen required and machme maintenance is better organised than ever before. It seems thateven his wages are dispensed more accurately than when they were calculated by atimekeeper with a calculator in his hand and a pencil behind h s ear
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Drawings
17t 1
‘Wcbt bs,k?\ dmA T‘b ML.4
We trust you w il l excuse our presrmiption inwarning against such things as redundantdimensions.. .
.._ uti-informative n otation and revisioii - utthis stage uiiarchy sets in
Handing was always a problem. And the iiote which said ‘al l us MK13 RHbut ... ’
It ivas often /ielpJirl o t ry to sketch the item wehad u s t drawn to eiisure enough informationhad beeii given.
Riiririirig dimensions were usefirl whe re linearwork was concerned.
Try to remember that the draughtsnian (ordraughtsperson) ca iiriot possibly foresee a ll thesite problems.
Ajier a l l . of ten the only t ime theyget to siteis when there are diJfic‘cUlties.
12
Our e igh t yews 11 the drawing boardwarned of the dangers of over-riotatioii- he c r i t i cu l bit might be missed
We were sometimes ca ught out by the thicknesso a h e .. oii a 1.1 scale things (ire a littlediffereii t .
We learned that the check in the oJke ~ v u sa reusier than the o i i e made 11 site. Often thefirsttime a drawing is checked is rvheri the carpenterconstructs his orni
Such as when some unintended geometrycreeps into the system.
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Geometry 1
TzzIzI=_
As we were saying... i t k sonietiines rlifficulitovisualisethe inzplicaiionsof a line on thedrawing.
Change / h e section ( /he engineer willbe niirchhappier with this thickeningat tlze rooi of tliecuniilever).
Well,w e could either construcispiral
cohrniris. set them on an a.ri.7 ind ependent of/he tower geometry- or make iheni circulur:
Well,le/ s remind hini to look b r t r ue lines anddimensions: these undsonie carejirl thoughtallow develop nient of&zce.s.
Crrreful sectioning reveuls we ’ve ained two morefirces than were originullyuppureni -plus soniefbrniworkproblems.although tlze resirlis in theReading Centre are excelleni.
Take a balcony- quure in p h i wiihupsiand wall - niodifythe plan (tlieurcliiiect j. prerogative )
The result - fnot ccrrejiilly p lu m ed- s problems inconsirlrciion.
Le: :s wuich our circulur work. However; setting
constnrction fab ricnornzal o /he uxis avoids iricln,form munilfaciitre, such as developmentof ellipsesc z n dbevelledmembers.
Nowj u s t fo r f i rn , design somefiwniworkfor this -cas/ in two 1iJi.s.Eusy withour nice ~lastic’, ,fieslzconcrete. We ‘ve o niuke euch ac e icleniicul inuppearance.
Let :s go back to an old bogey ... rakingcolirnins on U ‘cooler ’ ._ liere:s a /raphere
We ‘re rlealing wiih well knowii (to us)
principles ... how /houghcan we he lp theform worke r?
OK,so now i fs puzzle time - how do weproduce /hesuine appearance wiihhvoseparuie precust elenienis A & BY(Possible but highly iniprobable )Answeron nexi page.
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Geometry 2
I \
Continuing from the previous pag e... youcould precast them this way. Possible butimprobable- he trick is the diagonal doubledovetail We could improve the oin t bytapering the dovetails.
Moisture curing silicone rubber sealantapplied by gun can be usedto seal betweenmould sides and concrete, andso on. Carefirlabout waste- t’s expensivest~@‘
There’s no right answer, but an essential
feature is a stable base which ifcom bined witha side or sides governs geometty.
Steel m u s t be accurately locaterl- ocketsbolted to sides and ends can position lacerbars - ailing that, there are always plasticspacers - hoose the right shape and niuterial.
Seriously though -previous precastingof thecritical bits ofienresolves tricky problems.
The cured rubber strip can b e peeled fronithe concrete. When the casting is completed,the concrete will be unmarked.
7-
Stopends deterniine the section and length.Seals are iniportant, particularly in mouldsfortning visual concrete.
Precasting today implies mechanisulion insome orm or other - watch the geonietty-hinged cornponentsniu.st c l e w US in doorgeometty.
The precast pieces are assenibled into the baseof the main mould, Here we are casting thebottom block upside down.
Now let’s consider the nuts and bolts. Yousee,when precasting we con (structural clesignpermitting)cust elements inU variety of ways.to overconieproblenis ofj inish , cornpaction.etc.
Lijiing eqtiipinent is a separute topic-precasting is a mechanical hoiidlirig-iritensiveoperation.
A good casting t e r m coupled with a rigid QCarrungement and our main worty will bewhere to stuck the product
* ‘Themanager :s responsibility f or safety’, The Industrial Society, London, 1979.
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Detail : th e need for communication
Whuitoe board? Whaiv ihe extension? The salesniun said it was hixotropic
Whens the nexi sire nieeiing?
4 d d Q Y 0
d o o
Areyou sure ihe dosagewus 5000ml?
1
The nianual said 7 tonnes
These high-frequ ency vibraiors niakeall ihe diference io ihe produci
Who checked ihe drawings? Theren n i s t he ano ihe r type
Hard whai? Whereb the nieihodstaietneni? Perhaps iik ihe plunib bobihai b ' ou r ' .
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Detail: people’s input
Of course there has ulwaysbeeri the problemof ideiitrjcation withthe product
Of coiirse formwork isan urtfonii in its ownright..
We doget a bit “blosi” however. Thepassingcomnieiitwas - “ l f l was pimping 25m3/hour1 d want to know where the other end is. I
16
Althoughsuch sitiratiorisdo provide u nexercise in coriiniunications
It must be renternbered howevertliut trrilikeother iridiistrieswhere =+0. 05 nim will“do”, w e ave to be spot on
. ._
.-
And the s l~upeshat the dedicatedsteel mancan achieve have to be seeii to be believed
and compact it, huve a vital impact on hefinishedproduct
The commenthere was - “ I said all alongit said ntmiher 5 1 ”
i -.
Regarding concrete.. the way wemix it ..
Otrr service iridirstry issecond to n o m ; thisdespatcher was calculuting the lady :sreqrrirernerits o r her j s l y ~ o r i d
Whenall is said and done, how eve^ we huvea great spirit of cooperation.
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Detail: concrete
1n
Badly-locateddrips can causea loi ofproblenis - etisweadequate space oraggregate and sufficientsubstarice toavoid damage during striking.
Slightly undersize kickers allow insertionof oam gaskei to ensure groui-tighi joiniwheri casting column.
The 'joiriersfiietid', ihe quirk, isa usefir1device to help in curtailing exposedaggregaie - watch coricreie cove<however:
Recessed kickers canlook well andsolv e diJficirliiesof colutnri/kicker oint.
Norniul variabiliv canupset the mostnieticulousof details. remember formsaridmould spread arid growili ' down alwuysoccur outwards.
Filled iie boli holes look well whenjilliskeptj u s i belowsu r juce -plastic filler plugsget pinched' and are noi reconinierided
Surface reiurder011 face offeutures whichure Iaier to be iooled ea.ses stripping andfrrcilitates tooling.
,
J
Forrners casting deep ji.aiures suchus lightrecesses,cable entries andso on, strip eusierwith returder appliedby brush or roller:
A layer ofresiri-itipregiiatedglass niat onply nioulcl aces assisis in reducing crazing,otherwise occurring on sniooihfaces.
The implication o f ines on drawings spring tolight on site- we don r u i e the chances ofsurvival oft h i s deiuil very highly
Talkinguboi r t pinching- watch out f o r groovesund features whichtrap fornis - xpensivedamage rnay result. to o rmf ace and concrete.
An odd one rom ihe deseri Plastic downpipeproiects plirnib line froin wind - what aboutdanipirig bob in ja r ofwatec then
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Methods and communication
The most inipressive chart isuseless i itcannot readily be interpreted by thesiniplest per.son to be infornied.
Cliarts are conipletely uselessi out ofdate or not niaintuined
Out-of datedrawingsare dangerous,inark tlienicareful1,v- keep onesetfo r reference.Histograms identifypeaks and are easy 10
understand.
To checka drawing orfull informationtvy to draw the elenient or detailfroniinforniution given.
\ .I
, , , , . , , , . . . . , , . . . . . , _ ,Don 'r leave stairs behind, however- h eaniount of deck r apidly diniinishes.
Siniplicity improvescornni~rnicatiorinuniber 1ij i .sand operationsan mastersheet, rind use numbersus reference inconversation.
Overlaps ensuring continuityof workare essential
Keep those 'dim books and site diariestoo -they w e vuluablesources of basic d i m .
Work at sever ullevelsu t one timeensurescontinuityor all trades.
A method statenierit or hundbookavuilable toall provides the knowledgeessential to safe working.
Even U blackboardon the wall inthe siteoffice is a start towards more conipleteconimunication
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Pa ne1 joints
Rugged treatinerit of c o r n e r s will resrilt inrugged uppearunce ofjoints- someurchitects like this.
The use of chunfers rind margins 'tidies lipjoints ' und makes for N better production.
I
Regurdirig jo ints- we shotild renieniher t h a tinaccuracy i n any one panel may afect t h eperforniunce of any of t h e 24 other panels o relenients.
Where seulurits [ire used, defects cuused by t l~emoulds uhsorbing conipactiveefort aridcuusingeritrapnierit of air arid writer: niust befil led anda siiituhleprimer applied.
Drflerentiul citririg resultingfroniorientation intlte stuck can res i i l t in iricicciiracies.
Movenienrsare mother considerution. Wehuve been aniozed how IJiohikconcretecun be in e.rtrenies of teriiperatiire. how itcifects o t h e r eleiiierits.
Joints whichare nurrow do not necessurilywork well- he sealants cuii onlvucconiodateniovenients of about 25% of their owii width.
Norniul vuriubilityof production can also be a
prohleni. Look u t t h e nianufiicturing dates -pre-groding of panels is possible- and"visucil adjtistnient will avoidlocalexceptionuljoints (if it was OKfor LondonBridge it niiist he acceptable elsewhere )
The iritrodiictioriofcliunlfersc indbitllnozing alsoa v o i h ragged edge.s -allowing aggregute to il l t h e nioiild - hecorners are ulso susceptible to duniage.
A n d how it bows when restruined... thesemoverrieiits must he considered i n designofjoints.
Wherepossible.serilunt set into thes t ructure thus, works well.
Use the snnie .sealant teain throughout theconstrnction. Their pride in their work isS O I J ~ ~guaruritee of sulisfactoniwork
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Computers in construction--_--------
Our man is impressed by computer-aided design techniques,but hopes that the people in the officeful ly understand theimplicationsof their outp ut.
1 . 1 I t , / .
He is aware'that databases ease the work of the estimato...
while realising the economics achieved b y computerised stock
control of the product of repetitious processes, such as flooring andblock manufacture, as well as in warehousing and similar tasks...
and element checking in precasting- can be computer controlled,our man is at aloss to know why..
He appreciates the ease with which d etails can be produced (andmodified) and wishes that revisions could be madeon site withjusta click of a mouse
and has always done his utmost to work within the rates they set,as well as meeting the production demanded by the networkexperts. However...
and noting that many demanding operations- such as comparing
process data in the courseof slipforming operations...
as they are in industry, com puters aren't ableto predict the lotterynumhers that wo uld transform his role fro m that of producertoclient
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Computers
The irripact that niicroprocessorsivoiild have ori oiirindiistry becariie opparerrtwith t h e f i r s t aritorrraticbatclziryarid iiiuirlg plnri t
I I L, ,k
Sirice tlieri a i i tor i ia ied cirttirg arid beridir qriiachirres..
arid die skil lsof the rriari sprayiyy- t rpGRC be ingriiiirirriised b y r oh t i c s , a r earrrorg app/icatioristhathave cor rriied t h e i rpoteritid.
Nor ori ly lras C A D revoliiiioriisedthe d ra iv i ryl ce.. .
At tlreforrnworkfabricators, the CAD systerii trotorily prodrices desigrr and derail..
. .~.6irl also coritrols triadiirres i r i t h e works , re-ordersriiaterialsarid plaris t h e i i s e o f ~ ~ c i i t s
- ". . * I ,
co r r rp i i t e rcor?mil/edarid recordedchecks or1 precasrelerrieirts..
With all this, it ioor i /dr i '~ e siirprisirtqtofirid oi i rclrap o r i site 6 q y i t i r i i r gto ivoiideriiil~eri he is to bereplacedb y a 'chip'
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Computers and design
Our man k briefJlirtatio,i with his home PChad come to an end an d, although they were-to his way of thinking -par t of 'hewtechnolog '.
... when engineers used thetechriolog of theday - lide-rules arid calcula torsin manysliapes and sizes - all claimingto get the bestapproximatioii to a result
..,he had to admit to a srieaking admirationfo r the CAD operators hemet i n his workOn efir m had seveii C AD statioris operatedon shifis
His thoughts went backto the days whenmost design arid detail work was donelorig-hand...
He only hoped the present-day CAD mancould recognisean approxiniatioriwhen heeiicoimtered on e.
The last approximutiori ourman had met waswhile coririectirigup a p i p e behveeri silos
Mainl,v, however: he recognised thebenefitso computer output suchas handy-sizeddrawings (many including the bending
schedule)..
.._ uch a pleasant chungefroni thedrawingsof yesterday, especially in hadweather or exposed conditions.
He thought tohimself ' I should Jirid outmore about tablets. layer s, overlrrys cudsoo n . The way things are going,a little bit of
extra know-how wills tand me iri good steadfor theJirttrre '.
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FORMWORK AND FALSEWORK
ur man has seen reports produced by experts on all manner of formwork andfalsework matters such as safe loads on props, the development of concrete
ressures, achievement of surface finish, wind and friction loadmg and so on.These and many other topics previously comprised the ‘folk lore’ of formwork. H e believesthat the publication of the collective knowledge of such committees must have made thesite a safer place to work.
As well as seeing permissible lift heights change from a few feet to many metres, he haswitnessed the emergence of sophisticated equipment and methods. He estimates that, as aresult of the adoption of equipment such as table forms, jump forms and slipforms,
outputs per man-hour have increased more than tenfold. Safety, particularly at heights, hassimilarly improved.
Much of his work has been simplified -b y kickerless construction, for example, and by theadoption of expanded metal stopends in even the largest lifts of slab and wall. In thesimplest of construction tasks, he is aided by the huge range of accessories such as smallpanel systems including ties and spacers as well as disposable forms for use in the ground.
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Setting-ou t po ints
Perhaps we may he excused ormetitioning the3, 4, 5 tria ngle iriestuhlishing right-angles
_.. he batten to plot arcsof largeradius kriowirig the chordlengtli andrise.
When usirig builderk leveland aboard to traii.fer datum s. rotatehoard to average out anydiscrepa ncy in either.
C
Conesmid caps are easily developedusirig radii ah and ac - visualiseunrolling slieathirtg until lengthof topliiie equals circunference.
And theuse ofun equi-marked battento divide spaces intoequal purls.These are well known techniqu es arldvery practical.too.
fWe haveseeii checks o r squaremade hymeasuring diagonals The small figur e hasequal diagonals, check side lengths as well
Perhaps less wellknown is thep l ysquare used to descr ibe semi-circles0 1 1a given radius and..
The lewingsurface is widely misunderstood,where one coriter is out ofplurle of the othertliree theii we have aflewingsurface. Watch out-fo rm s and coristructioii are expensive.
When setting up datunts. initialanddate your level and record meaningA record ofirzaccuraciesmay savetime in months to come.
With hoppe rsand mitshrooms rememherto deal with tr ue lerigths- he splaycut atX i s determined by90' cut set out a j k rtop arid bottom bev els have beert struck.
Ellipsescaii he plotted by intersectionsofhorizontals and verticals runi -om points wherecomnioii radii cross circunferencesof circles busedon major and miiior axis- therwiseuse a tratnmelwith ama and am i marked and travel these pointsa long vertical and horizontalaxes.
Tlie mortardot 11 concrete improves lineaccuracy and thecost of a permuiient opticulbase willofreri he amply repuid hyease ofsetting out. Provide lockable cover to keepintruders away
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Detail:formwork
There's nota lot to say,for the results ofIplanted chamfer fillet
Precastersfind the extruded plastic orallo,vsections idealf o r orming small chamfers.
Built-in featu res. wliile morecostly originally,cast crisper detail and provid e grout-tightjoints. than paste.
Bull-nosedcorners can he neatlyforiiiedand the orrises illed with aggregate rather
Featurefillet jus t blanted ' onto tlieforni,facebecomes displaced arid trapped by infiltrationofpaste but .._
... a secondaiy layer o thin plyor hoardavoids the problemand provides butt jointsto resist grout. The )>encil'roundshelp in
striking operations.
Where illet must remain in thecoiicretefi)rsonie tinie,saw kerfing aids eventualrenioval.
I fsquare sides clre speciJiedto recesses,atwo-piece ornieE . .
LULarger oriners,Jirhricated and bolted to t h eforniface using tapped platesor plates withwelded nutsat the concrete/form interface..
... eau he ieer l afler inairiform reniovalbyreinserting bolts. The acking action againstthe concreteJuce gently yet j rm ly s t rips,former: Renieniberend splay or draw
... aid.s striking.Half the eature reniairisf ixedto the orni and the reniaiiider isstripped out as a secondatyoperation.
Detai1er.s can assist in uchievingexcellenceb,v m asking horizon tal joi nts instriatedwork in the shadow o a recess but theyninst he alert to maintenance o cover
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Kickers 1
Kicker forinationis an ersentral part of the"constriictioii process. Whenever possiblekickers should be cast monolithic with slabs
Shallow kickersof what wouldbe scrapconcreteform possible points offuiliire.15Onini + depth of kicker allows correctcoinpaction. Ruled join ts should beincluded i a fe n iireof generalconstruction.
Kickers broughtto iiniforni level help tosimply$ succeedinglijis.
Kickers are essential in circular andgeometric work -providing a check011accitracy of setting out arid governin g line offornis above.
Where coniplicated columns are seton rake,kickers provide acciirate location and simplifyfornis above.
. .. .
Siinple cast criiciform concrete bloc ks..
Kickers provid e restraint. ensure grout-tight1 of orni and assist in locating openings.
Kicker blocks set in blinding canhe used
Depth o kicker provides scopefor levellingforni.
... o provide bearingfor props and pages
Space forms arid governloor zone as wellas...
Providing Jixingor urigle steel kickerfornier.s.
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Kickerforiiis coil be siiiiplysecuredbv V-slottedply cleots driveii onto
reinforceiiieiit.
4
9A soc~iidlyonstrircted re-usohlekickerforiiipuys oflwlieii iiioii,v kickers liuve to be foriiied.
Kickers2
A plute bolted iiito tie udjoceiit to kicker eusesjbriiilocutioii.
steel reiiiuiii us periiiuiieiit foriiiwork.
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Ni bs and corbels
Nibs are to walls as kickersare to slabs -they provide grout-tightpurchase or returnbay formwork..
Nibs C U I I be simply formedwithin irst layerof for m carcass.
Corbels in precast elements presentdf jcul t ies in i l l .
_.. at cross-wall locations
Corbels ofren determine the horizontulcons/riictionjoint position. Corbels at top of
lift ullow good compuctionand control ofsleel location.
Rotate the unit to bring corbelto top: mouldmust be ree to drop away u s urrowed.
. __ nd wherespandre1.sspari betweencolumns.
I n precast arid i n - s i t ~ i onstruction, it is oJenpermissibleto insert previouslycust corbelsinto the
main casting.
JScastface down, mould must allowunit toslide whenfo rm is rota/edfor stripping.
Striking pieces allowthe in-situ orm to bestruck largely by own weight..
,.. s o slow clownfillarid inspect fo rcompaction frequentlyin locality of corbeland don 'I orget strippingJllet
Boltedpcids within main for m allow corbelcasting without damageto mainform. Thirip1,v for m s templa teto locate projectingsteel.
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Cores and formers
Tiniberjilleis ciiid p l y diuphrugiiisforiiieconomiccores: pins ihrough hoiiseclbuiieii preveiii tiplift.*
Coiicreie blocks loccrie siressed wires: U wruppiiigo polytheneor crujk puper conipleiescore. *
Sieel iuhes u n d ubricuied c0re.s reniovedh v o hours cfter cusiirig orni cuvities ecoiioniicullyfithe ishvisied to strike. Boih c m be pulled itsirig ‘rutcheibourd’ mid lever:
Tiinber,fornierdepend.7on wedgiiig actioriwitliiiiorrii uperture to inuiriiuin shup e.Eusy to strike.
Fouiii-plusiic-filledpo[viheiie iuhe restruined bysiressiiig wires.*
Coricreie blocks w e ridestriictihle. The wruppirigo ihiri e.vpuiidedpolysiyreriesimplifiesrelease.niper erisiires ihui block does i ioi full ihroirgli sluh ut time ofstriking.
*Puier i ied
Meiulpluies locuied ( I ) by ritbber inotrldirigsmid (2) by irljlaied iubes, ure eusily collupsed
for recovety*
Throitgliholes cuii he oriiied usiiig iiniberbohhiris, dowelreduces size of hole in ormSpiral woirrirlcurd iiibe peels from wuriii
greeii coiicreie.
Expuiideleclpolysiyrer ie wruppedwith plusiicbourd resists inipuciof pokers. Adequuieresirairit is esseritiul.
Oiiejor the iiiriovuior Root veg shririks oiri USciiririg proceeds.Sirgur retards fuce of cuviiy
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Ramps and intersections
Formsfor spiral ramp sof i tsare dif icul t ,especiallywhen splayedsofJt is involved.
i
Simple standard tr usses of timberuiid plv cull heprefabricated on siteor in yard.
Where specialunit or table type orms arerequired,constnrctiori is eased by assemb1,v o ver Jiill-sizeset-out on slabor plv deck.
Set radialb, thetrusses resolve the geometryand simplifyshealhirig operation s.
Tumielinlersection s withshujis cari present problemsof ormworkgeometty.Here an oflset intersectioriis set out uwuyfrom theactual job. ProJles spot tuririel hi e s relative to sectionof shaJlirling.*
Tumiel orme rsbuilt over projles allow sheuthiiig-sh(~tlining iiiter.section tohe plotted urid shearhing
developed.
Chocksgenerate otherwise difficult-to-generute airing. Fairing is sheathed usiiig multi-layers ofthiiip ly orhardhourd.
*The uuthoris indebtedfor this to E Consdale of EdmimdNuttall Lid.
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Staircases
/ ‘On a riuniher ofsite.s, stuir constructiongoverns overall progressin constructioii
so a capuhle sraircusehand is riecessary
highlighringthe needfor eurly provisiorioft he drawings
/
He has experienceon his sideand niunytricks up his sleeve. Keep an eye on thewuyhe achieves support, however
To avoid rhe prohlenis resuliingf,.oni theuse offornisas a ‘rightof ~ q ~ ’ , . ,
and the useof reiiforceinent as,footholdsAlternativenieuiis of uccess should heindicated
Precasting offers econoniy inspeed as well assimpifying th e inclusion of special finis hes,riles, Iread~s, arborunduni fo r n on-slippurposes
Edge casting eiisures two a ces andonestriiig of ex-niould finis h,as well as allowinggang casting about afixed centre fo rmDoliforget rheflrr t-lij points by th e wa,v
415 4
Geonietry aiid varying thickness of headfinish are traps or theU I I M J U ~ ~ffectingconcrete profile...
Machiiied or pressed sectionscan save tinieaiid iniprove coricrete profile where it iscritical
Our friend ishest used as a specialisr. movedfioni job to o b os he is needed
Site precasting is best carriedout where itprovides ‘hospital’work and where concreteconhe siniply placedfro ni the truck, or example.
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Circularwork
Although we understand thotthe Romansused greut heaps ofeurth ..
__ .imber arid ply or camhers,concrete
fo r skewedcamhers.
Ply or liardboard. a double diugorial hoardover radial ribs gives double curvature-spun steelskeet providesmould liners.
Thin sheet glass-reinforced plast icandglass-reinforcedcement, either usedasstandalone materials orbacked withconcre te, provide excellentmoulds o rshuped elementsand products.
._. oday, even with all our urniouty ofmateriuls and techniques, i rst sightof thedrurvirigs is oJen startling
The carpenterhas many ways of deulingwith corners arid curves.
Modern materials, extrudedhollowsectiorisarid polyurethanecan he used to cast detailwork. The casting poly allowsus to eaturesphericul sheathing.
For barrels and arches, theproprietarysupplier provides an econom ical solutioii...
However,we have managed fo r years usingtraditional lined rib arid lag girigforms...
Recently we even smv ‘Iiorsed concretenioiildsfo r special elenients.
At the other end of th e scale, lightweightexpanded plastic coated or sheatlied witli deriseplastic is great fo rlarge voids, trans itions, etc.hiit watch out fo r Jloration and displace ment.
,.. and when it gets real1,v repetitiousorcomplicatedwe mustri forgetthe speciulformw ork sup plier with his electronics aridhydraulics
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Props and propping
Huving seenthis x i - l i p recently we thought alook at props could behelpjiil
And this - riuils und re-bar just won ? do
System props providea b i d in assiiratice -
spucing, lacing arid bracing are provided fo r
Good oundutions arecriiical -plenty ofspikes arid w henever possible siipport fro mmature concrete.
Huvirig tuken u close look - we withdrewto iliink ihe iopic over
Oiri-ofplumband eccentricully loadedprops lose about 50% of their cupacity
Commonprops niiisi be laced and hruced -
large diuriietercouplers are needed on ouiertubes.
Pltonb-in one or two props in euchdireciion and eye-inthe rest. The wellcalibraied eyeball is remarkablyacciirate
Thisconvinced us ofih ewisdomof ourflclions
-c
The ilted pins o f specialsteel niust be used toenstire that liublishedSWLcall he swiained.
Alwaysconstilt the makers inutiuul. Soinetitnes
the height io which U prop can be closed is asirnportanias thai to which it can he extended.
Firidly - ake adviceon strikingand easingprops iri tnulii-storeywork. You buildso quicklythese duy.s tha t problenislend io get huili in *
*See ‘Forniwork- u guide to good pructice ’, The ConcreieSociey, 1995
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striking formwork
OK. So theconcrete is OK - what aboutthe orniwork
Ideallyfornis should he freeto drop onrelease of ties.
Moirld treatments are best appliedasmist sprays.
Avoid the use ofcranes in striking rutherthan handling- he man who swings theblock is a dangerto hiniselfaridtoothers- nd the concrete element.
A great deal of lieart-searching goeson overtypesof release agents andso on.
The thin 'dog ? tail' wedge, whilst beingirridesirahlein other operations,helps b,v allowingair in to break thevaciiiini at the orni/concreteinterface.
Precasters frequently m op off after ap plicationto leave then i e r e s t j i l n i at the suflace.
d
Openings affordciccess or wedgingreluctant forms - avoid the pinchbar though.
Tight ointsmid nice points of o rmconstruction [ireul.so most importantto resistgrout infiltration.
Earlv striking (conihined withan approvedcuring reginie) avoids hang-ups caused byshrinkage and swelling.
Rollers providee.rcellerit applicators o r releaseagentsand returders.
Hydraulicsto the rescue - everalJirmsmarket sniull potent jack s which usedstrutegica lly ease the striking imniensely.
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Aluminium forms
Bit / there k little doiiht t h a t lightnes.scan p a yoff- 2 orms can he handled at (I timefo re,r.rcIniple..
A lot of the odvertisingniutericil is reminiscent oja n advertfor a well known Irish )ick-nie-iip '.
Available systems canbe usedfor both wallsarid floor forms. t h e .stiff.sections rillowsiihstantial support and tie spcicings.
They iise chemical releaseagents to avoid
'gassing', ind piit 011 a coat o lacquer every10-12 uses in case of di,fjicult,v
We 've lookedclose1,vat sites where altnniniiniisystems have been iisedfor months (in one casemore than a yeor) arid haveyet to spot Ndcimagedsection. The niaferialis clerin to workwi th too.
There s beenthe pro :s and con :s of ~ilaininiani.
lot o disciissiori regrirdirig
Some of the system cornporient.sare
compatible with timber:SectionsincludetimherJ7llet.sf o r p(v or shecithirtgJ7.rinring.
A hit dfferent to timber where we'veseenmen clciniber over piles o short ends tojinda long lengtli - o clit down to size
And t h e size of tribles in ol i i rni i i i i in i have 1he seen to he believed
And of coiirse /lieAiiiericans mid Canadahuve been iising 'ulli f . ryears.
Circiilrr work can he curried out using the
Jrriiig pieces rind .substrintirilplates bolted10 webs.
P
They'11 hove (i job with this olwninitins -hope the suw i s a borrowed one.
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Trough and w aff le floo rs
A Concrete Society working party workedhard to produce a guide...
Formers are extremely robu st althoughsometimes almost transparent.
. . .
Uneveri application of striking fo rce cunjamb ormers and cuuse hang-ups.
The air vent is not a gimmick, air hastopercolate into interface or for me r sta,vs put.Don t forget to tape the vents prior to illing.
A s to sections and sizesm i d the coderequirements- here is however plentyofscope o r specials.
They canbe phy.sically designedhutdeflections ure criticalrrnd cc117 affectstriking. The specialists have this 'weigh ed-up ' of course.
We've seensuperb results, from varieddepthsof w@'e f o re.raniple.
Care is required regarding choice ofrnateria1.s irt those countries which see thesun.
Excessive local application o f release agetithas been known to cause retcrrdationt h u snegating lead allowed011 former: Controlthe application whichmust be by mistspray.
111case of sticking very thin wedges allow air/ o irifiltrcrte arid fre e or me r -g iv e it timehowever:
Quickstrip is easedin 'traditional ' supportsby providing 1mm+ clearance overjoistdimension. System supports of course ullownormal quickstrip action with support atintersections of ribs.
0
Rentemberto irljorm this chapcrboirt care orequipment,/ S l l , O O Oof u s readers cl0 it themessage must get through
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GRC formwork
Glass-reinJorcedcement permanent orm s allow thedesigner coitsiderable freedornas regurd.s te.xture arid
features.
The use of GRCform punels allows the provision ofspecial finish es- white cementarid exoticaggreguteswithout resorting to through-mixes in horizontal,verticalm i d slopingfaces.
PuneIs can be clesignerlto reduce or eliminatesupport requirements.
Pre-inspection offornl purielsensuressatisfactory ii1islie.s to concrete structuresbejbre ariy concrete is placed.
In conjunctionwith polymerform liner.s,interesting testure.s can beprovided: no rieeclf o r lead and draw here
Eliminutionof striking operatiori free.s menjormore productive work.
Location of distributionsteel isgoverned by h0.u stfleners on formpanels.
,
\-=-----The GRC punels canbe munuallyhundled witheuse: impact re.sistanceisgood.
Munr~acttrre s relativelystraigliqonvard usingsimple mouldstogenerate many o rm units, , .
... mid QC nieusures using'bag m i d bucket forexumplemaintoin adequate control.
As well usformwork,moulr1.sfo r precast (andGRC) are i d e d products.
A soon-to-be published design manual from t h eGRCA* will prove invuluableto specifyinguuthorities, designers and producers.
*Guide to GRCperincriieiitformw~~rk.ew edition in prepurution (2002). See also Permanentforinworkin construction. CIRIA PublicationC558.
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Formworkfailure
. .. ..
Not all fo rm ailures are drarnatic-although thisis how the authork interest informwork cameabout
Failures of the lessdramatic kind happenquite a lot - speciallyin other people:sconcrete
oh) u A L L
Once we recognise the symptonis (such aslocal sheathing deflectiori at ove rlaps)wecui1 takesteps to correct them.
Anotherold chestnutis the nibcriused bysecond deflection wherewe stop-offa pour
part way upN o r m - an anchor or pigtail inthe j r s t part of the lifi securesform.
Stopends rarely get the attentionnecessuyto achieve goodresults. A s much as 60% oflabour can be in stopendsand dayjoints -care in designcan make substantial savingsand a void unsightly defects.
Similar deflections causenibs under dayjoirits and construction oint s in slabs.
It 5 amazinghow heat (h ydration ), pressure andntoisture cause quiltirig,but then that 5 how w e
make bent-woodchairs Reduce spacing ofbackingmembers.
A t the risk of being boring we must mentionhigh incidenceoffiles caused byflutterinduced by vibration und darkening at cornerscruised by leakage.
Quite apart fro m th e initiul urgeto dosomething aboutthem...
We can overcome theproblem by insertingana t r a backing member at the oint withpreviouslycast concrete.
Fewform s areseldom quite "correctto lineand level", it k the second layerof carcassirig
whichcontrols line.
A little time in stackingor rucking ormsbetween usescan provide r ed econornies interms of enhanced reuse.
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Formwork
CL--- ---\-Time to get down to some detail CONCRETEpresents a commentaryon the skills em ployed,for ever Nfter
Have no ear Help is available in Thelnstitiition of Strirctitral Engineers an d TheConcrete Society publication 'Formwo rk- aguide to good practice'... It's a "good read" forwet days in the office
Special form wo rk manufacturer.s have someneat details fo r sealing joints(A). In traditional
workfoani strip can be effective (b)...__utbeware displacement.For critical work one-part, moisture-curing sealants are effective(C).
Sheathing deflectionscon occur at s t o p e d slocated within contirnrous fo rm s,and in slabconstruction against previously cast bays.111both instances it is unlikely that join ts co incidewith backing members. Avoid "curtains" byinserting extra "noggingsI.
-.___.
Stopends. seldom designed or detailed,must sustain the same pressuresas the restof theform. Deflections here will beevidenton the inished face.
I~ fo rma t ionrom the "Guid e with inputfrom the practical man on site ensureattention to critical detuil such as..
I nJust tracking ond less critical work.forms maybe located employing kicker-
less techniques... using proprietaryfittings(A), />recastblocks in slab(B), spacer.s(C&D ). external plates (E)o r plasticchannel spikedto slab (F).
Sheathing must be soiindlyfixedtobearers, flutt er causesupset to vibration,the resultant lineof which can bererid onthe&rce and may proveto be up to 50mmdeep when the ace is tooled.
O~~eriirigormer.s are anotherkey area ..pressrrres fro mplacementbuild up, causingsurprising orces,
... importanceof kickers in geometricalaridvisirul work, providing locutionarid a sealagainst grout loss .. provided the support isapplied correctly.
Stopendsshould be ixed through intobacking m emb ers, e.yternal tiessupport
wide stopends r om form carcass. Jointrulefillets are as effective hereas they a re athorizontal joints.
Of coiirse concrete placenientand vibratorytechniques inlist be m atchedto the ormdesign and method....we will lookat thisanother time
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Formw ork systems
L e a v i t ghis collea~rres o nraintain the wntc/r./or‘ b r i g s ’i n the cotnlniter, oiirman th r r tn l~ed h r o i g ha brochrrredcscribiii,yproprieetaryforriru4,rk~irk ystems
He rccaalledthe ‘rrenr mortal co rir l~ t’ ndrrredin nsirgw h a twas ahvays knorvnas tradit ional urmrvork
He ~ r o t ~ dhat srcppliersivouldprovide proditctsiipportbased rrpon experiencep i n e d in the course~Jpr estigio irs contractsaboirt t h e world
Proprietary equipment* he learned,corrlds i g n f i c a d yredttcethe number of thro i rqhties reqirired. 771ispleased h i m os he h a d experiencedsome problemsi nthe past, particrrlarlyhen extracting toper tiest h ine n d j r s t )
Althorrglr the d a z z l i n gormoirry o f components
available fr om the catalogneumuld obvioirsly presenth i m toithplenty of opt ions ons i t e . . .
The cost ofmaki i ;yformioarkivoirld also be rediiced.For example,i n circrtlarand taperedi va / / i igsteeledyin‘gs, soldier m enibe rs,fork armsarid tribes arc’iisedin c o i ~ i i n c t i o nwith tu rn biicklesso that plyfac inys canbe radinssedto match a template - n o more expens iveshaped r ibs or rolledsections
1t1brochrrre illrrstratiotrs,he noted that thefabr ico fm n c / rproprietary formumrk permitssrrbstontial sectionsto be handledwithout dismantliirgberiveerruses, thusreducirg workcontent a n d speedirg the constructioncycle. The ivork i igplalformstraveltoo
the technicali i?forination, drawiqsarid method
statementspttblished bythe supplierm(fh twellpreventsome problem inthe coi rrse ofs t r ik i rgfo rms . ..j o m a c a n r il e v er, fo r i n s ta n ce
Readen will appreciate that our man finds it difficult to identify any specific supplier’s equipmentunless, that is, he can see the colour of the paint
Bearing in m i n dhis concretetechtiology,oi ir man
reckonedthat , by capitalisingon the b e n e j t so fproprietaryf o r m w o r ki n combination uith sound crrringpracticeand establishmento fstriking times r r s i r ~ yreinperature-inatclled specimens, considerable savingsint i m e and @rt ivoir/dbe achieved onfrctrtre contracts
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Falsework 1
A greui deal ofhord committee work..
T-It rnukes gripping reading- udvisingumongother things...
._. nd emerge some time laier withasertsible form work design
I -
... and some considerable public commentpreceded...
._. he ~JUh~iCaliOnfthe newCode BS5975: 1982Falsework.
.- .
... the uppointineittof a falseworkeo-ordinuior directly responsibleiothe site ntunuger: The Code seems to be devisedso that a
suitable yiraliJedpersoit coulddisappeur intoa site office ..
The Codepoints out ihai every detuilofthe sclieme must be considered.....and decisions madeon method.
The muterials are usually second-hand and soneed partictilar1,v carefiil inspection.
We are told tkuifalsework failuresure ofrensideways und that we should identify the loadpatterns and takesteps io contain them.
Oh, and that's usi the beginning.
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Falsework 2
Reverting to the Code, FalseworkBS5975: 1982,we are reminded ofsafeworking loads or adjustable props..
.._ are warned against drilling milituty trestles.. .._ are given useful guidance on windforces..
_.. and on ensuring the stability (andqualiry) of individual members.
Puzzle corner? Figure25 dealing withconcrete pressures gives plenty of oo dfo r thought.
I-- ? TL .\J
Table 31 raises some iniportant points onuristiffened webs acting as columns.
\ r
No, not an advert fo r 'Juw s 11'but a source oinformation on wave forces for the advancedfalsework designer:
Figure 10 is representative of a lot ofjob swe've seen- even as a r as the 'Kam ikazedumper driver:
This rings abell somewhere- a w arning bellperhaps.
We are also warned of th e dungers ofimpact ron i floating objects and theneed to avoid a build-up of debris.
Regarding impact loading, we are advised thatthe larger the loa d, the more carefully it is likelyto b e placed.
There is also a warning about the eflectsof vibration
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Falsework 3
The codeBS 5975: 1982 reminds us tocheck extensionsat thefoot ofstandards..
... may pronipt LIS to seek a glass of thewellknown cider advertised in Figure28A (Oh no, it is a coninient on rotationaland positiorial restraint).
It wus nice to see our old friend Figure13:the code wouldbe incomplete withoutit ..
and a t the head
The commenton spilluge addingI.Skg/ni othe niass of tube mqvprovide a solutionto theage-old problem of where the estiniator .s 5%w s t e went
so much nicer thuii this uttenipt
Expeviencingthe accumulation of debrisfromfrrie cleaning/boilerscalirtg wliicli inayhave aclensit,v of 1600kg/m' (andthus imposesubstantial loadingon platforms).
A-
Wetliougkt 'BaileyBridge Fatigue' was a i larmy complaint warruntingM + D until weread pag e 59
v
The codestresses the iniportanceof details -otnissiorio f a bolt o r wedge ..
.._ or failure to tightenN bolt could l e d tolocal instabilitythat might endanger thestructure
We havefound the prototypefor the map the~veathermurihows us on TV (notice howeveiything revolves around London).
All irreverence aside.however;there can heno doubt that the code providesa sound basisf i r those designing,constructingandcheckingJiilsework.
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Formworkand falsework 1
Wi th safety In mi nd, our ntan reflected upo nthe nature of the work of the steeplejack“Nothing.” he thotrght “ Could induce meto go u p there ” But, remembering someof the hazards encountered at site andhighlighted in Th e Concrete Society?best-selling guide‘-
such as formwork detail that had escapedthe eagle eyes of th e foreman carpenter...
out -of- plum b props and sirbstandard pins,the despair of the site engineer...
rrnbraced and unlaced supports, not inaccordance with the proprietary suppliersmanual...
support taken from po or foundations,to be discovered, we h ope, in thepre-concreting check...
changes in placing m ethod. made with outreference to the planning engineer and theformwork designer...
and striking procedures other than thoseset down in the method statement-
he thought that, all things considered, hemight be safer up a chimney...
Formwork - a guide to good practice.2nd Edition. The Concrete Society. 1995
44
then he thought again
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Formwork and falsework 2
Wheir forniruork a i d falseruork corisrstcdi m r r i l y of ncres ofp/ywood aird stmidnrds of tiriiber sripported by n seii of props,riiitch of t h e iiiaterriil ruas rirorrhoirdled hetiueeii uses.
W i t h falsework,the cnpncityof props ruas siidly overestiriiated.Apart frotit forriiiirgair nccident bazrrrd, propstbnt ruere~ ~ r t t - o f - p l i t ~ r r l ~ ,cce,itrically loaded or wer-c.uteridcd caitsedprohleiirs of displacemerit nird loss of litre and level.
A/thorrgbmo st coristrrictioirs iiiere robitsta i d strrtctrtrally sort id.r i in r iy left irtirch to be desired. The iiioir on the 106 drew O I I Iiiscsperieiice h i t ofteiiium rtriniurrre of t h e prcssrrres mid forcesd C l W / l J p e d l U / J C I l COlICl’efelWS / ) / i lced.
Fai/rtrrs ocused the nttott ioiiof reports, stniidnrdsmid codes,midcsseritid cl~eckirigvd ccrtificntioir tuere ititrodrtcetl.As n resitlt, tue1iotii haiic skilled sofc ciird efficieirtuse ( J / O vast rouge of materinls midtechriiqiies.Spoce perittits orily o fciv e.uniirples h t t it is cielrr thn t ...
... iiieclJniiicnlhaiidlitig 110s iiicrensed oritpiits.as IJns slipforiiiiiig-particrt lnrly j i inipfo r~ni~ig .ulieru iritegral platforms improve accessarid rvorkiiig coitditioris.
T l ~ corii