stadium roofs

8/6/2019 Stadium Roofs

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F O O T B A L L S T A D IAA D V I S O R Y D E S I G NC O U N C I L

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ISSU E 5 A P R I L 1992

S T A D I U MR O O F S

CONTRII3UTORSB. K. Bardhan-Roy

Stephen MorleyBill Reid

John ThorntonEDITOR

Callum MurraySERIES EDITORSimon Inglis

This publication has been endorsed by theInstitution of Civil Engineers

TH E FOOTBALL STADIA AOVJSORY DESIGN COUNCILFOOTBALL

ASSOCIATION


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All rights reserved.No part of this publication may be reproduced,

stored in a retrieval system or transmitted, in any form or by any means,electronic, mechanical, photocopying, recording or otherwise,

without the prior written permission of the publishers.

1992

T H E F O O T B A L L S T A D I AA D V I S O R Y

D E S I G N C O U N C I LISBN 1 873831 15 3

Typeset by Groundwork. Design by Gregory Brown. I llustrat ions by Lloyd Raworth.Printed in Great Br itain by Castle Pr inters (London) Ltd.

The information contained in this publication is intended to provide useful guidance, but is not adef ini tive statement applicable in all c ircumstances. Independent profess ional adv ice should be

obtained before taking any action or refraining from taking any action on the basis of thisinformation. Further adv ice can be obtained f rom the Football Stadia Advisory Design Counci l.


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Contr ibutors 4Introduction 5 CONTENTSG lo ss ar y o f t erm s 6

1. 0 D es ig n a nd c on stru ctio n is su es a ffe ctin g s ta diu m ro ofs 71 . 1 U n o bs tr uc te d v ie w in g1 . 2 Plann ing cons idera t ions1 . 3 W i nd u p lif t1 . 4 W in d tu nn el te stin g1 . 5 F ir e r a ti ng s1 . 6 D e s ig n li fe1 . 7 M a in te na nc e a nd f ut ur e o pt io ns1 . 8 T im in g o f c o ns tr uc tio n1 . 9 Costs2 .0 H o w d o d iffe re nt ro of fo rm s a ffe ct s pe cta to rs ? 92 . 1 Columns2 2 R o o f lin e2 . 3 S he lte r fro m th e e le me nts2 . 4 S ha ding from th e s un3 .0 H ow d o diffe rent ro of fo rm s affec t th e env iro nm en t? 123 . 1 P l ay in g s u rfa ce3 . 2 W i nd f lo w3 . 3 T ele vis io n a nd ra dio r ec ep tio n4.0 W hat a re the app rop riate fo rm s o f s tad ium roo f? 134 . 1 P ost and beam form4 . 2 S pa n form (or 'g oa l p os t')4 . 3 C a n ti le ve r fo rm4 . 4 T e ns ile f or m4 . 5 S p e cia l r oo f s tr uc tu re s5 .0 W hat other facto rs need to be cons idered? 175 . 1 S u p po rt lo c at io n s5 . 2 Drainage5 . 3 F ire a nd s mo ke5 . 4 R ela tiv e p os itio ns o f ro of c ov erin g a nd s up po rtin g s tru ctu re5 . 5 Robustness5 . 6 C on stru ctio n a nd m ain te na nc e c os ts o f d iffe re nt ro of fo rm s6 .0 W h at m ateria ls c an be u se d fo r th e s tru ctu ra l e le m en ts ? 196 . 1 Stee l6 . 2 Concrete6 . 3 Timber6 . 4 Aluminium6 . 5 S t ai nle s s s te e l7 .0 W hat m ateria ls can be u se d f or r oo f c o ve rin g ? 207 . 1 M e ta l s h ee tin g7 . 2 Concrete7 . 3 Timber7 . 4 R i gi d p la s ti cs7 . 5 Fabrics7 . 6 T ra ns lu ce nt o r o pa qu e?8 .0 Add ing a roo f to an exis ting s tand 238 . 1 A p pr ais in g a n e xis tin g s ta nd8 . 2 M o dif yin g a n e xis tin g s ta nd8 . 3 M o dif yin g a n e xis tin g t er ra ce8 . 4 R o of d ev elo pm e nt o ptio ns8 . 5 E xte nd in g a n e xis tin g r oo f8 . 6 E ff ec t o n f ou n da tio n s8 . 7 S t ru c tu ra l t yp e s8 . 8 P h a sin g o f c o ns tr uc tio n9 .0 The aesthe tics o f roo f design 251 0.0 F utu re d ev elo pm en ts in ro of d esig n 27


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C O N T R I B U T O R S

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The F SA DC w ould like to thank the fo llow ing m em bers o f itsE ng in ee rs' W o rk in g P arty fo r th eir sp ec ia lise d c on trib utio ns to th ed ra ftin g o f th is d es ig n g uid elin e:B. K Bardhan-Roy B E F IC E F IS truc tE M ConsE is a partnerw ith Jan B obrow ski and P artners , C onsu lting E ng ineers . H isex pe rie nc e in th e d esig n a nd c on stru ctio n o {g ra nd sta nd s in clu desth e R OU BS ta nd , W a tfo rd , th e W e st S ta nd , S t J am es' P ark , N ew ca stle,the Sou th S tand , Tunckenham and the hosp ita lity su ite and gym -nasium , H ighbury . H e has a lso w orked on a num ber o f race-coursegrandstands, inc lud ing Sandow n P ark , C heltenham and a t venuesin the UAR . Bardhan-Roy was a m ember o f the W orking Party o fth e In stitu tio n o f S tr uc tu ra l E ng in ee rs w h ic h p ub lis he d th e 'A pp ra is alo f S p orts G ro un ds ', is th e a uth or o f th e b oo k 'T he P re str es se d C on cr eieD e sig ne r's H a nd bo ok ' a nd c o-a uth or o f th e p ap er 'T he D e sig n a ndA n aly sis o { G r an ds ta nd S tr uc tu re s, p ub lis he d in S tru ctu ra l E ng in ee r.Stephen Morley BSc H ons CEng M IS truc tE FFB is a d irec tor o{Y RM A nth on y H un i A sso eia tes , S tru ctu ra l a nd C iv il E ng in ee rs .H aving w orked on pro jec ts in Austra lia and P apua N ew G uinea , hejo ined h is presen t firm to w ork on the design o f'the tension assis tedtrussed roo ffo r the Sw indon L ink C en tre , and subsequen tly on an um ber o f c om m ercia l, le isu re a nd p ub lic b uild in ,q s, in clu din g th eprize-w inn ing T ruro L aw C ourts . N ow based in Sheffie ld , M orleyw as responsib le fo r the D on V alley S tad ium w ith its innova tive m em -b ra ne ro of stru ctu re , d esig ne d fo r th e 1 9 9 1 W o rld S tu de nt G am es.Bill Reid BSc CE ng M IC E M IS truc tE M IH T is a d irec tor o fT ho rb urn P LC , C on su ltin ,r} B nq in ee rs. H is in vo lv em en t w ith sta diabegan w ith the redeve lopm en t o tIbro P ark in 1 9 7 9 , { ollo we d b yw ork on th e design and construc tion o f the E ast S tand , M urray fze ldand the N orth S tand , W indsor P ark (B elfa st). H e is curren tly co -o rd in atin g T ho rb ur n's c on tr ib utio n to r ed ev elo pm e nt p ro po sa ls fo rH am pden P ark , M urray fze ld , the C ity G round (N ottin gham ), S tJam es' P ark , N ew castle and the new M illw all s tad ium at Senega lF ie lds. R eid has a particu lar in terest in the assessm en t o f the e ffec to f s tand structures on the env ironm en t in and around stad ia , and isau tho r o f a paper, 'W ind T unn el T esting o f Sports S tad ium s'.John Thornton B Sc C Eng M IS truc tE is a d irec tor o f' O ve Ar u pa nd P ar tn er s, C o ns ultin g E n gin ee rs . K no w n w id ,e ~y as th e s tru ctu ra le ng in ee r fo r th e L lo yd 's B uild in g in th e C ity o f L on do n, T ho rn to nw as e ng in ee r o f th e a ccla im ed M o un d S ta nd , w ith its lig htw eig htte nsile ro of stru ctu re , a nd a lso o f th e C om pto n a nd E dric h sta nd s, a lla t L ord 's C ricke t G round , L ondon . H e w as invo lved in the design o f'B ari S tad ium , one o f the 1990 W orld C up venues in Ita ly , and anum ber o f o ther stad ia in A frica H e is the au thor o f a pape1~ 'T heD esign o f C ab le S tayed R oo{s ', p ub lished in th e joum al o f theIn stitu tio n o f S tr uc tu ra l E n gin ee rs , a nd c o-a uth or o f a te ac hin gp ac ka ge fo r a rc hite cts o n th e u se o f str uc tu ra l s te el.T he F SADC is a ls o g ra te f'u l to th e fo llo w in g c on su lta nts fo r th eirc omm e nts a nd s ug ge stio ns : M a rtin B ar na rd (T ra ve rs M o rg an ),E dm un d H ap po ld , Ia n L id de ll a nd M ic ha el D ic kso n (B uro H ap po ld ),J oh n S im p so n (M o tt M a cD o na ld ), D a vid M a rs ha ll (G . M a un se ll &P tn rs), A nth on y H op kin s (S ir W illia m H alc ro ui & P t nr s) , B r ia nP ritc ha rd (W ,S Atk in s), Jo hn T allis (P arktn an S tru ctu re s). T hein te re st a nd su pp ort o f th e In stitu tio n o f C iv il E ng in ee rs a nd th eIn stitu tio n o f S tr uc tu ra l E n gin ee rs is a ls o g ra te fu lly a ck no w le dg ed .


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C on stru c tio n o f a n ew co ve re d s ta n d is o n e o f th e c le a re s ts ta tem en ts a c lu b ca n m ake a b o u t its e lf a n d its re la tio n sh ipw ith th e c om m un ity . A g ra n d s ta n d ro o f is o fte n th e m os td om in a n t s tr u c tu re in a lo c a li ty , a n d is lik e ly to b e a fo o tb a llc lu b 's g re a te s t v is u a l l in k w ith i ts su rro u n d in g s . T he d e s ig n o fa n ew g ra n d s ta n d ro o f th e re /o r e o f fe r s a ra re o p p o r tu n ity toe n h a n c e a c lu b 's s ta tu s , a n d a s su c h d em an d s c a re fu l th o u g h t .In th e w ea th e r c o n d itio ns o f th e U n ited K in g d om , s ea tsn eed to b e u nd er c ov er u ih ere ue r p ra ct ic ab le . U lk er e o pe nte rra cin g is b ein ,q re pla ce d w ith sea ts , o r w he re n ew se atin gtie r s a r e b e in g a d d ed to m a in ta in e x is tin g ca p a ci ty le v e ls , it isth e re fo re in e v i ta b le th a t m an y n ew ro o fs w il l h a ve to b e b u il t.C lu b s sh o u ld b ea r in m in d th a t ca p i ta l c o s ts a re n o t th eo nly c on sid era tio n w h en a ss ess in g th e c os t o f ro of c on stru ctio n.'W h ole li le ' co s ts - th a t is , o p era tin g a n d m a in te n a n c e c o s ts inre la tio n to th e a n tic ip a ted l ife o f th e s tru ctu re - a re ju s t a simpo r t an t .Im po rta n t to o is th e p ro v is io n o f u n ob s tr u c ted v iew in g fo rsp ec ta to rs . T he e lim in a tio n o f ro o f co lum ns fr om n ew d e s ig n sn e ed n o t b e a s co s tly a s is o fte n th o u q h t, p ro v id in g so u n dp ro fe ss io na l a do ic e is so ug ht.A n ew ro o f s h o u ld n o rm ally h a v e a d e s ig n li fe o f a t lea s tfifty y e a rs , so its a p p e a ra n ce , n o t ju s t o n co mp le tio n b u t a fte rm an y y ea r s o f u se a n d o f e xp o su re to th e e lem en ts , de se roe sc l o se c o n s id e r a t io n .E qu a lly , a p o o r ly o r in a p pro p r ia te ly d e s iq n e d ro of c a nco mp rom is e th e o v e ra ll a pp ea ra n c e o f a s ta dium fo r y ea r s ,th ,e re by u pse tt in g lo nq -c he ris he d p erc ep tio ns o f b oth th e v en uea n d th e c lu b .T he in fo rm a tio n g iv e n in th is , th e 3rd F SA D C gu id e l in ep u b lic a tio n, is r e le v a n t to a n y c lu b , la rq e O f sm a ll, s e e k in g top ro v i d e a ro o f o ve r a se a tin g tie r , o r to co v e r a n ex is tin gs ta nd in g te rra ce b efo re th e in sta lla tio n o f s ea ts .'S ta d iu m R oo fs ' s h o u ld n o t b e re g a rd ed a s a c om pre h e n s iv ete c h n ica l m an ua l o n th e d e s ig n a nd co ns tr u c t io n o f s ta d iumro o fs . I ts p u rp o se is to g iv e g e n e ra l in fo rm a tio n a b o u t th era n g e o f o p tio n s a v a i la b le , a n d to w arn a g a in s t th o s e th a tsh ou ld b e a vo id ed .T he re is , a s a lw ays , n o su bs ti tu te fo r co nsu lt in gex p e r ie n c ed p ro fe s s io n a l a d v is e r s , ju s t a s th ere ca n b e n oex c u se fo r sp en din g la rg e sum s o n in a p p ro p r ia te d e s iq n w hich m ig h t b u rd en th e c lu b fo r m an y y ea r s to com e.

T he F oo tb al l S ta dia A dv iso ry D es ig n C ou nc il w a s e s ta blish edin A ug u s t 1 990 o n th e rec om m en d a tio n o f L ord J u s tic e T a y lo ra n d is fu n d e d jo in t ly b y th e F oo tb a ll L e a g u e a n d th e F oo tb a llA sso c ia t io n . I ts a im , in p u b lish in g b o o k le ts s u ch a s th is a n d b yd ev elo pin g fu rth er r e se arc h, is to e nc ou ra ge im p ro ve m en ts ins ta n d a rd s a n d a g re a te r aw are n e s s o f s ta d ium d es ig n . F orm ore in /o rm a tio n a b o u t th e F SA D C p le a se r e fe r to p a ge 28.

I N T R O D U C T I O N

F O O T B A L LS T A D I A A D V I S O R YD E S I G N C O U N C I L

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GLO SS AR Y O F TE RM SCantilever: a beam supported at one end only,with all of the loads applied to the beam beingcarried back to this one end.Design life: the minimum period for which astructure or element of structure is designedto last.Fire rating: a value accorded to a structuralelement in building regulations, indicating thelength of time it is able to resist the effects ofa fire of a standard intensity and in a standardenvironment.Galvanising:: a system for protecting steelfrom corrosion by coating it with zinc.Glulam: glue-laminated timber, normally in theform of a beam, which is made up of smallerstrips of t imber glued together.'Goal post' (span form): a beam that issupported at each end, but not at intermediatepoints in between.Piling: a type of deep foundation, consisting ofa buried vertical pillar, usually of concrete.Plastisol: a type of plastic-based paintPost and beam: a beam that is supported atintermediate points along its length.Reversal of forces: the application of a loadwhich is opposed to that which a structurenormally withstands - for instance, wind upliftas opposed to gravity.

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Ring beam: a continuous, horizontal, circularor elliptical band of support, used to help tosecure the roofs of 'bowl' stadia.Robustness: resistance to widespread damageliable to be caused by the failure of a keyelement of structure.Roof line: the point of a roof structure mostlikely to affect views of the playing surface.Space deck: a lightweight, two-way spanningstructure, inthe form of a steel lattice whosemembers are interconnected by diagonal bracing.Span form: see 'Goal post'Superstadium: a term applied to large stadia,developed as complete enti ties, often as bowlstadia and sometimes with fixed or moveableroofs covering the spectator accommodation.Tensile structure: a structure designed toresist al l loads through tension alone, andcharacterised by highly curved shapes.Terrace: a sloping area for standing spectators.Tier: a sloping area for seated spectators.Wind tunnel: a tunnel or large duct throughwhich air can be blown at high speeds by a fanto simulate the effects of a real wind.Wind uplift: uplift caused by the pressure ofwind underneath, and the suction of windpassing over, a roof.


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1.0 DES IGN AND CO NSTRUCTIO N IS SUES AFFECT INGS TAD IUM R OO FSIn providing a roof, a club's first responsibilityis to the spectators, who are entitled toexpect reasonable standards of comfort,safety and viewing in return for the price ofadmission.Basic requirements for spectator comfortwere addressed in the FSADC's firstguideline booklet, 'Seating' (for details seepage 28), which made recommendations forsight lines, seat dimensions and seat types.This publication should be read inconjunction with 'Seating', particularly whereboth roofs and seats are to be provided inthe same project.Throughout this document, it is assumedthat grandstand roofs consist of twoseparate elements: Roof structure - the structural elementswhich support the roof (i.e. the columns,beams or trusses of a traditional stand) Roof covering - the material which issupported by the structure, and whichprovides shelterHowever, roof covering and structure may beintegral in some concrete roofs and inlightweight structural fabric membranes(see Section 4.4).Also throughout this guideline, as notedin the glossary (see facing page), a bank ofstanding accomodation will be referred to asa 'terrace' or as 'terracing', while the word'tier' will be used in relation to seatedaccomodation, whether at ground level orabove.1 .1 U n o bs tru cte d v ie w in gThe need to conform with all-seatingrequirements places heavy financial burdenson many clubs. However, this is unlikely tobe regarded, either by the spectators or bythe regulatory authorities, as an excuse forrepeating the viewing mistakes of the past.This guideline seeks therefore todescribe ways of designing roofs so thatviews of the pitch are not obstructed.1 .2 P la n n in g c o ns id e ra tio n sLocal planners will inevitably take a keeninterest in any proposed development, andtheir views and co-operation should besought as early as possible.Traditionally, British football stadia havebeen located in densely developed urbanand residential areas, from which supportwas easily attracted. Nowadays, however,local residents can no longer be expected toidentify unquestioningly with the ambitions

of the club, particularly if those ambitionsinvolve the construction of a tall, bulky orotherwise intrusive new grandstand roof.Therefore, it is essential that clubsconsult with representatives of localcommunities before, not after, the decisionto proceed with a development proposal."Failure to do this may alienate thecommunity to such an extent that the localplanning committee feels unable to grantplanning permission. In such Circumstances,the club may have to develop alternativedesigns. This will cost time and money.The general rise in conservationawareness also means that the demolitionof older grandstands of high design merit isincreasingly controversial, even where thosegrandstands are not listed buildings.Similarly, any new developments may berequired to take account of thecharacteristics of existing stands and/orlocal architectural styles, so that thecompleted stadium does not appear as anuncomfortable mix of separate, unrelatedstructures and does not clash with neigh-bouring buildings. For further comments onaesthetics, see Section 9.Detailed information on planningapplication procedures will be given in aforthcoming FSADC Guideline.1 .3 W ind u p liftA major consideration in the design of allgrandstand roofs is how to resist 'winduplift', a force which can easily exceed thatof the structure's own weight.Wind uplift happens when the windrushes over a surface, generating upliftforces, as with an aircraft wing. Theseforces should not be underestimated.Of the few grandstand roofs which havefailed, more have blown away than havecollapsed. So the problem is not just one ofholding the roof up, but also of tying it down.All supporting systems should thereforebe able to withstand a reversal in thedirection of the forces bearing on them. It ispossible to make the roof constructionheavy enough to resist a reversal of forces.But this solution is often disproportionatelyexpensive because uplift forces have to beresisted only occasionally, whereas thosebearing down on the structure are permanent.Although cladding/fascia panels are notgenerally load-bearing, they need to transmitlocal wind forces to their support structures.Such panels may become semi-structural,and can be designed to act as stiffeners tocontrol vibration, or to ensure betterperformance of the structure against lateralforces.

1. For guidance on howto establish consultationwith local communities,clubs may wish tocontact:The Federat ion ofStadium Communities,c/o Paul Weston,Anfield House,1-13 Holme Lane,Sheffield S64JP.Tel. 0742 322474.

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2. By N.J.Cook.Publ ished byButterworths, 1985.ISBN 0408 00870 9.

3. Contact:BRE, TechnicalConsultancy Unit.Garston,Watford WD2 7JR.Tel. 0923 664 664.

4. Appraisal of SportsGrounds, page 32,Chapter 6.Published 1991 by theInstitution of StructuralEngineers, price 45.00.For details contact ISE,11 Upper Belgrave St.,London SW1X 8BH.Tel. 071 235 4535.

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1 .4 W in d tu nn el te stin gThe best way to ensure that a proposedstructure will withstand wind uplift is to builda model and subject it to wind tunnel tests.Wind tunnel tests can also help to deter-mine the effect of the proposed structure onthe quality of the pitch and on surroundingproperty (see Sections 3.1 and 3.2).Certain universities and researchestablishments possess the necessary windtunnel testing equipment and expertise. Afull list of these is reprinted in thepublication 'The Designer's Guide to WindLoading of Building Structures. Part One'.2For example, the Building ResearchEstablishment has three wind tunnels, formeasuring wind loading on buildings and theeffect of buildings on the environment.For the former tests, a special model isrequired. For environmental tests anarchitect's model may sufflce.fCharges, based on hourly rates, plususe of the tunnels and computer analysis,can amount to between 5 - 20,000, butthis expense should be set against the likelysavings a more efficient structure willcreate.However, tests on models have to beused with extreme care to avoid erodingnecessary safety margins when applyingresults to actual structures.The complete process of wind tunneltesting takes from 4 - 10 weeks.1 .5 F ire ra tin gsStructural elements are given 'fire ratings' inBuilding Regulations, according to how longthey are able to resist the effects of a fire ofstandard intensity and in a standard environ-ment.Building regulations or by-laws normallyspecify the degree of fire resistance requiredfor a construction.The object is to ensure the safety of theoccupants by encouraging: The use of materials and designparameters that will delay the growth ofa fire and prevent it from spreading The provision of adequate escape routes Easy access to fire fighting equipmentand efficient operation of rescue proceduresMaterials used for the structural elements ofa stand or stadium (beams, slabs, columns,walls etc) should offer inherent fire resistancefor the specified period.If they do not, protective coatings will beneeded.The design of a roofmay also influencethe movement of smoke following a fire.Section 5.3 of this guideline providesfurther details.

1 .6 D es ig n lifeDesign life is the minimum period for whicha structure or element of structure isdesigned to last. Normally the design life ofa stand is specified by the client (footballclub, local authority etc.) but in the absenceof a specification, architects and engineersare likely to assume a design life of 50 years.It should be noted that a structure mayincorporate elements which are not intendedto last the full length of the structure'sdesign life, provided that these elementscan be easily replaced.1 .7 M a in te na nc e a nd fu tu re o ptio nsEven the best designed roof cannot beexpected to last the full length of its designlife, unless a regular programme of maint-enance is drawn up and budgeted for. Designlife, or periods covered by guarantee, mustnot be thought of as periods during whichelements can be left completely unattended.The FSADC advises that a maintenanceprogramme should allow for an inspection ofthe building fabric on an annual basis atleast (in any case, this is often arequirement of the licensing authority).Further information on inspection andmaintenance of stand structures is given inthe booklet 'The Appraisal of Sports Grounds' .4Looking to the future, clubs should beaware that their chosen roof design solutionwill have other long-term implications. Theyshould, for example, consider the future pos-sibility that a new roof structure may have tobe strong enough to support the extra loadingimposed by a TV position, commentary box,floodlights or electronic display board.1 .8 T Im in g o f c on stru ctio nFrom an engineering point of view, the besttime to begin ground works is in the springor early summer. From a footballing point ofview, the summer is normally the mostsuitable time for construction. Where otherconstraints have to be overcome, however,the chances of completing all of the work ina single close season are reduced.Ideally therefore the process of agreeingcontracts, securing planning permission andthe supply of all materials should begin ayear in advance of construction.1 .9 C o s tsIt is impossible to generalise about thecosts of providing a grandstand roof, evenwhere the spectator capacity is given. Costsdepend on a number of variables, includingground conditions, space constraints andthe structural form chosen (see Sections 4and 5). Only when these factors have beenprofessionally assessed can a cost estimatebe achieved. (see also Diagram 2 opposite)


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2.0 H O W D O D IF F E R E N T R O O F F O R M S A F F E C TS P E C T A T O R S ?

A number of factors in the design of a roofhave an effect on the comfort and safety ofspectators. These include: the impact of columns on slghtllnes the impact of roof lines on viewing angles exposure of spectators to the elements exposure of spectators to direct sunlightNowadays, computer software is available tohelp architects and engineers to assess thenumbers of seats affected, and to evolvecost-effective solutions.2.1 Co lumnsUnobstructed viewing of the playing surfaceis, of course, the ideal design solution.Paragraph 176 of the Guide to Safety atSports Grounds (the 'Green Guide')5 states:"All spectators should have a clear,unobstructed view of the whole of theplaying area. Designs should ensure thatsightlines are such that spectators areencouraged to remained seated (whereseats are installed) and do not have tostrain or stretch to view the playing area."The FSADCendorses this requirement,and adds that, in view of advances inconstruction technology, roof supportingcolumns placed between the spectator andthe pitch should nowadays be regarded asunacceptable in new stands, and as highlyundesirable in modified or upgraded stands.The extent to which the spectator's viewis obscured by columns is governed by thecolumn dimensions and the relative positionsof column and spectator. Diagram 1 (aboveright) illustrates the detrimental effect that

D iagram 1. The effect o f co lum ns on v iew ing

even a small number of columns can haveon spectator viewing.Obviously, the first concern in seeking toprovide a column-free roof will be the cost.It is generally assumed that a columnsupported roof will be much cheaper, butexperience actually indicates that, for a comp-lete new stand, a column-free roof design mayincrease the overall project cost by as littleas 2 - 4 per cent (see Diagram 2). In smallstands, there may be no increase at all.At present many clubs voluntarilyoperate a different pricing policy for seatswith views particularly restricted by columns.In future however any club which comesunder the jurisdiction of the FootballLicensing Authority will , as a condition of thelicence, have to state on tickets whether theseat in question has a partially restrictedview (although it remains up to the club todetermine the pricing level).6

Shading shows areas of stand with partially restricted views, according toplacement of columns. Column dimensions need also to be considered.

free sb'ucbJreadds2-4%of total cost

D ia gram 2 . C os t a na ly sis o f a n ew g ra nd sta nd 's e ng in ee rin g a nd b uild in g e le me ntsFixtures/ fitnAnt~-----,Seating -----,

Prelims ----'Finishes ----__j

Superstructures

Cladding --------''-----------Substructures

5. Chapter 11. CoveredStanding and SeatedAccommodation. GreenGuide - the Guide toSafety at SportsGrounds. HMSO1990.

6. The FLAdraws adistinction betweenseats where a roofsupport restricts theview (and thereforestanding up makes nodifference) and seatswhere spectators arepositively encouraged tostand up in order toobtain a better view. Inthe latter case the FLAmay refuse to licencesuch seating. Forfurtherguidance see the FLA'snotice to FootballLeague clubs concerning'Seating with aRestricted View'(30.3.92), from the FLA,27 Harcourt House,19 Cavendish Square,London W1M 9AD.Tel. 071491 7191.


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1m above crossbar

D ia gram 3 . E ffe ct of ro of lin e o r o ve rh an gin g tie r o n v is ib ility o f h ig h b all

12 -18m~-! " -~ -- -- -- -- -- -- -- -- -

l _ _ _ ~ ~ ~ , . @ ~_ m'_~~"_=',~, - _ , _ " , ~ _ , _ , w _ , _ _ ,_,_''_'_=_=="",_k-l__-----_2l_-'-----'-~~=~o PtchHigh ball visibility from stands at side of pitch

7. In stadia designed forrugby, unobstructedsight lines to high ballsare essential. Thereforeroof lines should allowviewing to at least 15mabove each goa/line.

8. TaylorReportinto Hills-borough Disaster, HMSO,Cm962, Jan 1990.9. Meteorogical OfficeCommercial ServicesDepartment:London Road, Bracknell,Berks. RD12 2SZ.Tel. 0344420242 ext.6307.

10

High ball visibil ity from stands behind the goals

2 .2 R oo f lineWhere roofs overhang tiers or terraces, thespectators' view of a ball kicked high intothe air can be impaired. Diagram 3 aboveillustrates the maximum height at which ahigh ball is visible to the worst affectedspectators, ie. those at the back of the tier.While it is appreciated that viewingdisruption is lessened because the ball is inuniform flight during the period it is lost toview, the FSADC advises that for new standsroof lines should allow viewing to 12mabove the centre Circle, and if possibleideally 18m.Under no circumstances should the mini-mum viewing standard fall below 3m abovethe far touchl ine or 1m over each crossbar. 7The same comments apply to tiers orterraces located under the overhang of anupper tier.2 .3 S he lter from the e lem en tsParagraph 63 of Lord Justice Taylor's FinalReport8 states that 'Seating is only regardedas more comfortable than standing if coveris provided ... So, increased seating doesrequire that cover be provided.'However, covering seats or a terracewith a roof is no guarantee that all spectatorswill be protected from the elements (seeDiagram 4 below).The vulnerability of a particular seat tothe elements depends on six factors:

the height of the front of the roof relativeto the seat the overhang of the roof relative to theseat the direction of the wind relative to the

orientation of the stand the probability that winds blowingtowards the spectator will be rain orsnow bearing the extent of gable end cladding wind turbulence, especially where astadium has open corners.

Predicting the vulnerability of a particularseat to rain or snow is not easy, becauseclimatic conditions vary significantly fromlocation to location.Guidance can however be provided fromIocal meteorological data on rain and snow-fall incidences for various wind directionsand speeds.Basic local data is available, for anominal fee, from the MeteorologicalOffice's Commercial Services Department.fWhere appropriate, clubs installing seatsin uncovered or partially covered areasshould consult beforehand with the Footballlicensing Authority (see note 5, page 9).Note also that Football Trust does notgrant aid uncovered seating installations.

In this example, even seats in rows situatedbehind the front edge of the roof cannot beguaranteed protection from the elements. Goodprotection can only be assured for the rearmostrows. Yet however deep the roof span andhowever apparently protected the seats mayappear, the influence of adjacent structures, theheight of the roof above the tier, the prevailingwind direction or wind turbulence must be takeninto account. These factors must also beconsidered before extending a roof, the benefitsof which may prove only marginal where certainconditions prevail.

D iag ra m 4. E xte nt o f p ro te ctio n o ffe re d b y ro of


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2.4 S had ing from the sunSpectators in stands which face towards thesouth or west are vulnerable to sunlightglare and dazzle.This is why, at many stadia, the mainstand is the West Stand, which faces east(see Diagram 5 below)This effect can be reduced by a standstructure configuration which casts ashadow on the seating tier below.Computer software is available todetermine at the design stage the extent ofshadow cast by a roof (for example, there isa program called 'Shadow Pack'), but most

large building services engineers havedesigned their own programs to perform thistask.The Meteorological Office (see previoussection) can provide statistical data on theprobability of sunshine occurring at a givendate and time for particular site locations.Spectators (and television viewers) mayalso be affected by patterns of brightsunlight and deep shadow cast on the pitchby stand structures.Using a transparent or translucentmaterial to cover the roof overhang may helpto reduce this problem (see Diagram 6below and also Section 7.6).

D iagram 5 . Path o f the sun on a S atu rday a fte rnoon

North15.38 hrs

16,27 hrsThis is a hypothetical example of the pattern of the sun as it affects a typical football stadium, with sun casting shadows infront of the West (main) Stand.Of course the pattern will vary according to the season of the year and the stadium's latitudinalposition. This sun path information can be calculated by a computer program, based on data obtained from the MeteorologicalOffice. Further advice on sun paths can be found in various publications available from the Building Research Establishment'sTechnical Consultancy unit (for detai ls see note 3, page 8).

East

South 17.34 hrs

West(main)

16.57 hrs

D ia gra m 6 . E ffe ct o f u sin g tra ns pa re nt o r tran slu ce nt ro of c ov erin g

The use of transparent or translucent covering on the front of the south and west stands may helpto reduce the depth of shadow cast on the pitch. However shadows cast by the roof or by fasciapanels may, as a result, form distracting patterns on the pitch.

11


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10. Sports TurfResearch Institute canprovide telephoneadvice to designers onmatters relating topitches.Contact: STRI,Bingley,West Yorkshire,BD161AU.Tel. 0274565131.

11. The Confederationof Aerial Industries isable to provide a list ofapproved specialists.Contact CAl, FultonHouse, Wembley Park,Middlesex, HA9OTF.Tel. 081 902 8998.

12

3.0 HOW DO DIFFERENT ROO F FORM S AFFECT THEENV IRONMENT?The previous section examined the effectsof roof design upon spectators and viewingstandards. This section explains how thedesign of a stand roof can also influence: the playing surface the effect of wind flow on neighbouringproperties television and radio reception in thenelghbourhood3 .1 P lay in g su rfac eThe layout and design of stand structurescan have a major effect on the condition ofa grass playing surface.Roof structures on east, west and southsides cast shadows on the pitch whichdiminish the quality of grass, and retardboth natural drying and the thawing of frostand snow. The areas affected by shadowvary with the time of year (see Diagram 5 onprevious page), but can be identified withthe aid of computer software and models.Shading can be reduced by incorporatingtransparent or translucent sheeting at thefront of the roofs (see Diagram 6 onprevious page). The efficiency of transparentor translucent sheeting in promoting growthof grass below has not been fullyresearched, however, and further study ofthis important aspect of stand design isrequired (see Section 7.6).Much discussion has taken place on themerits of open cornered stadia, as opposedto the 'bowl' design which is considered bymany to be the more desirable solution. Bowldesigns allow larger numbers of spectators

within a given stadium perimeter but mayinhibit wind flow at pitch level.It is generally accepted that acombination of shading from sunlight andreduced airflow at pitch level has an adverseeffect on the durability and quality ofgrass.Further information on this subject isavailable from the Sports Turf Research

rnstltute.t? Playing surfaces will also formthe subject of a forthcoming FSADCbooklet.3 .2 W ind F lowLarge stand structures affect the natural pat-terns of wind flow on the pitch, on adjacentstands and may, for example, generate down-draughts which interfere with emissionsfrom the chimneys of nearby houses.Wind tunnel tests (see Section 1.4) willshow the influence of differing stand layoutson the environment, thereby helping designersto minimise disruption.3 .3 T ele vis io n a nd ra dio re ce ptio nAny large building is capable of affectingtelevision and, to a lesser extent, radioreception. The building can block the signalfrom a transmitter, putting houses in a radioor television 'shadow', or it can reflect atelevision signal so that the receiver showsa 'ghost'.Both effects are made worse if thebuilding is steel framed and metal-clad;concrete affects signals less. Diagram 7below illustrates the problem.Where stadia are being developed closeto residential areas, it is therefore advisableto involve speclallsts to establish whetherreception will be affected.11

D ia gra m 7 . E ffe ct o f s ta nd s tru ctu re o n ra dio a nd te le vis io n s ig na ls

. ... . . . .

transmitter transmitterA B

As can be seen, if the signal is coming from Transmitter A it might be reflected by the standstructure, causing 'ghosting'. If coming from Transmitter B it might be blocked altogether.


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4.0 W H A T A R E T H E A P P R O P R IA T E F O R M S O FS T A D IU M R O O F ?

For convenience the types of roof structurecommonly used in stadia have been dividedinto five simple categories, detailed below.It should be noted, however, that standroofs can combine elements of more thanone type.4 .1 Pos t and beam fo rmThis is the simplest and perhaps the oldestform of roof bearing structure.In football stands, a row of columns,running parallel to the edge of the pitch, hascommonly been positioned at the leadingedge of the roof cover, to support anarrangement of beams or trusses (seeDiagram 8 below).The FSADCstrongly advises that this solu-tion should now be regarded as unacceptable,for both new and upgraded stands.An alternative arrangement of the postand beam form is to place columns part waybetween the front and rearmost seating, andthere may be occasions, especially inupgraded stands, where this solution isunavoidable owing to space constraints orthe structure of the existing tier or terrace.In such cases, it should be rememberedthat the further back the columns areplaced, the less the disruption to specators'viewing.Nevertheless, the FSADC recommendsthat this alternative arrangement only beemployed as a last resort.Angled or raked columns may also helpto minimise viewing disruption, but are lessefficient structurally.Note that providing column-free roofsmay not be as costly as is often imagined(see Diagram 2).Before resorting to the use of columnsexpert professional advice should besought.

D iag ram 9 . S pan o r 'g oa l p os t' fo rmAs a general guide, a depth equivalentto1/12of the length is consideredto be aneconomic ratio for the main supporting girder

~~~

4 .2 S pan fo rm (o r 'goa l pos t')Strictly, this is a refinement of the post andbeam form, and not a separate roof type. Atfootball stadia, where its use is increasinglypopular, the difference is that this variantprovides column-free viewing. It is oftenreferred to as the 'goal post' form.In this form, the main spanning elementof the structure runs parallel to the edge ofthe pitch - as it does in the post and beamform - but is supported at the ends only,and not at intermediate points in between(see Diagram 9 above).The form works best when little or nocorner seating is required so that the lengthof span need be no greater than that of thepitch itself.The depth of the main supporting girderwill vary in proportion to its length, but as ageneral guide a depth equivalent to 1/12 ofthe length is considered to be an economicratio, ego10m depth for 120m long girder.As the entire roof structure dependsupon this single girder, regular inspectionand maintenance is especially important.

D iag ram 8 . Pos t and Beam fo rm

Leading edge Mid - point

Post and beam with columns positioned along leading edge.Althoughthis is the form of roof constructiontraditionallyused at manyBritishfootballstadia, theFSADCstronglyadvisesthat with advancesin technologythe postand beamform as illustratedshouldnowbe regardedas unacceptable,for both newand upgradedstands. 13


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D ia gra m 1 0.Cant i leverfonn

c a n ti le v er s p a n

T he c an tile ve r ro of atW i nd so r P ar k, B el fa st,s h ows t he s tr uc tu ra l

e le m en ts c le ar iy . N o teh ow s uc h roofs requirem ore roo m at the rear,a lth ou gh th is m ay be

i nf ill ed w it h fa cil it ie s fo rspectators.

14

4 .3 C an tile ve r fo rmThe cantilever is the standard solution to theproblem of providing unobstructed viewing.The cantilever is a structural elementsupported at one end only, with all of theloads applied to the structure being carriedback to this one end (see Diagram 10).A number of these structural elementscan be set at right angles to the edge of thepitch and linked together to form a standroof. Thus the roof can be supported at theback only, leaving the front free of intrusivesupporting columns.

The obvious advantages of this must bebalanced against the following considerations: There must normally be space availablefor the supporting end of the cantileverstructure behind the rearmost row of seating.Cantilever roofs may therefore require moreroom, although the spaces between the

cantilever supports can be filled by facilitiessuch as refreshment bars or executive boxes. Because a cantilever roof's highest pointis normally at the stand's rear, this formmay appear taller and more visually intrusiveto local residents than other forms.

Theoretically there is no limit to thespans which can be achieved by cantileverstructures (ie. the distance from the rear ofstand's spectator accommodation to theroof's leading edge). As of 1992, theworld's largest cantilevered roof span at asports stadium is believed to be 48m, at theHusky Stadium, Seattle (USA).In the UK the largest spans are to befound at the North Stand, Twickenham(39m) and the new North and South stands,Murrayfield (43m). Both PSV Eindhoven(Netherlands) and FC Barcelona (Spain)have cantilevered roofs spanning 38m.Spans of 50m or more have beenproposed, but where the rearmost row ofseating is required to be a long way backfrom the pitch, using the 'goal post' roofform has often been found to be moreeconomic than cantilevering the roof outfrom the back of the stand.The reversal of forces caused by winduplift in a cantilevered roof demands specialconsideration. The outer, supporting staysat the back of a cantilevered roof, normallythought of as being in tension, will besubject to compression as the roof is liftedby the wind.Therefore small diameter, high strengthcables which might otherwise lighten theappearance of the structure - and hencegain favour with local residents and planners- will not normally work unless analternative means of resisting uplift isprovided.


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4 .4 T en sile fo rmTensile structures are not easily describedbecause of their intrinsic fluidity of form.They are designed to resist all loads throughtension alone. The need to resist forces inboth upward and downward directionsresults in highly curved shapes. (seeillustrations below)There are two types of tensile form roof: Cable net, where the roof coveringmaterial is supported by a network ofcables. The most famous example ofthis is the Munich Olympic Stadium andsports complex. Structural membranes, where the roofcovering material forms both thestructure and the enclosure. A recent

example of this type is the Mound Standat Lord's Cricket Ground in London.In the UK, lightweight membranestructures have been little used at stadia.However, the Mound Stand, Lord's, and theDon Valley Stadium,Sheffield, display someof the possibilities of lightweight membranestructures (see illustrations below).Although tensile structures may appearless heavy and bulky than other options,they are technically sophisticated and insome forms demand additionalmaintenance. They should therefore beconsidered with caution, and the advice of astructural engineer with experience of theform should be sought as early as possible.For more information on the materialsused in tensile forms of roof, see Sections7.5 and 7.6.

Lightweight membrance roofstructures have been used at boththe Don Valley Stadium, Sheffield(left) and Lord's Cricket Ground,London (bottom), both designedprimarily for use at summer events.One of the most ambitious tensileroof forms, using acrylic panelssupported by cables, wasconstructed at the Munich OlympicStadium (below).Such roof forms, while aestheticallypleasing, may demand moremaintenance than other forms.


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4 .5 S p ec ia l ro of s tru ctu re sWhere there is the opportunity to develop acompletely new bowl stadium - eitherelliptical or circular in plan - a 'threedimensional' roof form can be considered.At the Olympic Stadium in Rome 'ring'beams (continuous supports encircling thepitch concentrically) are integrated into theroof, giving it the appearance of beingsupported only at the outer edge (see photobelow). Looking something like the surfaceof a giant doughnut, this form can allow aspan of roof which extends a great distance

from front to back (52m in Rome). It is alsopossible with this form to minimise theexternal profile of the structure, reducingthe visual impact of the stadium.Other forms of three dimensionalspanning structure, common in coveredarenas, are domes - perhaps of crossedarches - grids or space decks (as at Milan,see photo below).Certain forms permit the addition of apermanent or removable roof cover over theplaying area. For further comments onpermanent and removable roof covers, seeSection 10.

R om e's O lym pic S tad iu m (ab ove ! h as th e larg est ten sio n s tru ctu re in E uro pe. T he c en tra l rin g o f 12 en cas edc ab le s h old s th e 7 8 ra dia l 'ca ble tru sse s' an d lo ad -b ea rin g b eam s o ut an d, w ork in g w ith th e co mp res sio n rinl~above , s top the roo f from tw isting inw ard and d ow nw ard . Th is fo rm can on ly be used at b ow l s ta dia . T he ro ofc ove rin g a t R om e is T eflo n, w hich is b oth lig htw eig ht a nd allo ws lig ht to p en etrate th ro ug h to th e se ats b elo w.

A t th e S an S iro S tad ium , M ilan (above! th e space deck ro of has been form ed by a grid o f fou r enorm ous s teella ttic e b ea ms w hic h s up po rt a re tic ula r a lu min iu m n etw ork , c ov ere d b y v au lte d tra ns lu ce nt p oly ca rb on ates he etin g. A n e xp en sive so lu tio n w hich c reate s in trica te s had ow p attern s o n th e p itc h, th e ro of fo rm m ay b ep artly re sp on sib le fo r th e p itc h's s ub se qu en t g ro wth p ro ble ms .6


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5.0 WHAT O THER FACTO RS NEED TO BE CO NS IDERED?Section 4 outlined the main forms of con-struction used for stadium roofs. Thissection details other design factors whichneed to be considered.Note that in Section 1.3 it was stressedthat one of the most important factors in thedesign of a stand roof is its ability to resistwind uplift. This will remain a major designconsideration, whichever type of roofstructure is adopted.5 .1 S u pp ort lo ca tio nsThe locations available for supporting theroof cover will have an important bearing onthe choice of the most appropriate structuralform.For instance, where a stand backsimmediately onto another development,restricting the space available for thesupporting end of a cantilever, other formsmay be more appropriate.Where seating or other structures existat the corners of a stadium, there may notbe space to locate the supporting ends of a'goal post' structure, and again a differentform may be required.Equally, the choice of the goal post formmay rule out the future addition of seating(because of sightline disruption) in thestadium corners.Constraints such as these need to beidentified as early as possible in thedevelopment of a design, with dueconsideration being given to their effect onsight lines, seating positions and access.5 .2 D ra in ageMethods of draining rain water from the roofare an important consideration in the choiceof roof form.The simplest method of drainage is asloping roof, which allows the water to flowaway by gravity. Where gravity drainage isused, no point on the roof's surface shouldbe lower than the gutter.Column-free roofs are usually designedto slope away from the playing surface, toavoid the need for a series of downpipesdropping from the front edge of the roof.Where roofs of the post and beam typeslope down towards the pitch, guttersnormally run along the roof's leading edgewith downpipes running alongside the roofsupport columns.Where a forward sloping roof on acolumn-free structure is considered anecessity it may be possible to install asystem of non-mechanical syphonicdrainage.In this system, flow in the verticaldownpipes draws water along the horizontalsections of pipe, according to the principle

D ia g ram 1 1. P o te n tia l s m o ke re se rv o irs

Potential smoke reservoirs, formed by the roof or by overhangingtiers and affecting the rearmost rows, as in this example, should betaken into account when considering the design and location ofescape routes and emergency exits.

of the syphon. Thus only a single downpipeat each end of the stand is required.For this arrangement to function, all thepipes must be airtight and regularmaintenance is required.In bowl stadia and in some forwardsloping cantilever roofs where there may beno opportunity of introducing downpipes,mechanical pumps will be required to drainaway water.Such pumps are expensive and requireregular maintenance, but have been usedwith success at certain large stadia.5 .3 F ire and sm okeThe design of a roof may influence themovement of smoke following a fire. Thisshould be considered in relation to theposition of escape routes and emergnecyexits.There are various ways of controlling themovement of smoke.Roofs which slope upwards towards thepitch will tend to disperse smoke naturally.Roofs which trap smoke (see Diagram11) may need some form of venting to limitthe lateral spread of hot smoke and gases.This will not be required in every case andexpert advice should be soughtEmploying a fire engineer at the designstage to avoid roof configurations which arevulnerable to the effects of fire and smokemay save money in the long run.It should be noted that where the newstand is close to neighbouring buildings,according to Building Regulations the type ofroof covering material used must notencourage the spread of flames bythermalradiation (see Section 7 and table on page22.) 17


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D ia gra m 1 2. R o of c ov erin g

Roof covering suspendedbeneath roof supports

Roofcoveting placed on top ofroof supports

5 .4 R e la tiv e p os itio ns o f ro of c ov erin ga n d s u pp o rtin g s tr uc tu reMost roof configurations present thedesigner with a choice of suspending theroof covering beneath, or laying it on top of,the supporting beams spanning above theterrace or seating tier (see Diagram 12).There are many factors to take intoaccount before deciding whether the roofsupporting structure should lie above orbelow the roof covering.a. Where the roof covering is fixed abovethe supporting structure: A sheltered environment is provided for thestructure. The life of a concrete or paintedsteel structure may thereby be prolonged. Fixing of the covering is relativelystraightforward. This can be done whollyfrom above, with fixed areas of coveringnormally providing a stable platform fromwhich to continue fixing. An uncluttered form can be producedwhich may be more acceptable to bothplanners and designers, particularly wheresmaller stands are concerned. Access for inspections and maintenance ofthe supporting structure has to be from below- perhaps by scaffolding, involving cost andtiming difficulties. Bird droppings may be a nuisancebecause of the number of perches providedby the roof supporting structure.b. Where the roof covering is fixed beneaththe supporting structure: Concrete and painted steelworkstructures are more exposed to the weather Fixing of the covering may be much moredifficult, unless it is pre-fixed to sections ofthe structure before erection.8

The bulk of larger stands may appear tobe reduced. This will be advantageouswhere planners are likely to demand areduction in the visual impact of the stand. Inspections and maintenance of thestructure are easier, at least for elementswithin hand reach of the roof coveringsurface, which can be used as a platformfrom which to work The number of places where birds canperch is reduced.There is no single solution to the positioning ofroof covering and structure in relation to oneanother. Eachcase needs to be assessedcarefully on its merits, taking the context intoaccount, before a decision is reached.5 .5 R obus tnessRobustness, or resistance to widespreaddamage, is important for large structures -particularly those, such as grandstands,which are intended for use by the public.For a public building with a roof span ofgreater than 9m, Clause A4 of the BuildingRegulations 1991 (England and Wales)requires that the failure of any part of theroof or its supports should not causecollapse disproportionate to that failure.Given the nature of stand roofs thisrequirement is likely to apply in almost everycase to the various forms of designdiscussed in Section 4.While disproportionate collapse iscovered by the Building Regulations, it maystill be open to interpretation, both bydesigners and Building Control officers.Where a small number of supports carries alarge area of roof, however, as in the endposts of a 'goal post' structure, it is likelythat these supports will be designated 'keyelements', and will need to be designed towithstand the effect of damage throughexplosion, vehicle impact (whereappropriate), and so on.5 .6 C on stru ctio n a nd m a in te na nc ec os ts o f d iffe re nt ro of fo rm sIt is difficult to compare the costs of thevarious roof forms, as these will varyaccording to the parameters of the stand inquestion. Suffice to say that the costincreases rapidly with the increase of the freespan - that is, the distance between supports.When comparing different roof forms, allassessment should always be made of aroof's "whole life" costs (i.e. its operatingand maintenance costs over its projectedlife), as well as its capital costs. Where aroof operates efficiently, and requires littlemaintenance, significant annual savings canoften be made for a relatively small increasein the initial cost.


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6.0 W H A T M A T E R IA L S C A N B E U S E D F O R T H ESTRUCTURAL ELEM ENTS O F A ROO F?As was emphasised in Section 1, throughoutthis document it is assumed that grandstandroofs consist of two separate elements: Roof structure - the structural elementswhich support the roof (i.e. the columns,beams or trusses of a traditional stand) Roof covering - the material which issupported by the structure, and whichprovides shelter

This section deals with the materialused for the roof structure.Materials for structural elements shouldbe strong and durable, and should be stiffenough to satisfy the safety and service-ability requirements of the structure.Roof elements do not normally need anyspecific fire rating (see Section 1.5) unlessthey are intended to provide overall structuralstability. Where a localised fire in an elementmay cause a disproportionately large area tocollapse, however, fire protection for a givenperiod may be required, even though theelement does not provide overall stability.Steel or concrete (reinforced or pre-stressed) are the most commonly usedmaterials for structural elements. Bothpossess the required properties and providea reasonably cost-effective solution.Timber, a popular structural material inthe past (particularly for smaller standroofs), is rarely used now. Rare also is theuse of aluminium and stainless steel forstructural elements.Only after balancing the pros and consof each material, including respective costs,will the final choice be made, unless ofcourse, the choice is already dictated by thechosen structural form of the roof.Maintenance costs, as well as the initialcapital cost, need to be considered whenmaking a comparison (see Section 1.7).6.1 SteelSteel usually provides both a relatively lightstructure and an appearance of lightness.But it should be remembered that wherewind uplift is a problem, a light constructionmay not always be an advantage (seeSection 1.3).Where a 'goal post' construction iscontemplated steel will almost certainlyhave to be used.With advances in paint technology,protecting exposed steel work againstcorrosion and fire (where necessary) is notdifficult. Some of the disadvantagestraditionally associated with steelconstruction are thus reduced.

Because paint applications have alimited life, a long-term maintenanceprogramme will be required. The samecomment applies to galvanised (zinc-coated)steel, although the galvanising process mayoffer more long-term protection than painting.Self-weathering steel is sometimes usedfor reduced maintenance. With exposure, afilm of rust forms, protecting the steel fromfurther corrosion or rusting. The appearanceof the rust film may, however, be consideredunacceptable.6.2 ConcreteMouldability is one of the main advantagesof structural concrete. Where the productionprocess is skilfully handled, a wide range ofshapes and forms, textures and finishes,can be produced relatively cheaply. It is,however, vital to specify the correct concretefor the structure concerned.Because properly made, high-qualityconcrete provides good protection forembedded steel, external protection work isunnecessary, and maintenance work isreduced to a minimum. Concrete hasinherent fire resistance, and so may besuitable where a fire rating is required.Concrete can be made with normal orlightweight aggregates. As well as lightness,lightweight aggregates usually provide betterinsulation and fire resistance, withoutsacrificing strength. The unit cost oflightweight aggregate is, however, higherthan that of normal.To ensure better quality control and ahigher standard of finish, and also to saveconstruction time on site, concrete roofelements are often brought to the site inpre-cast form instead of being poured in-situ.6.3 TimberNowadays, timber is only ever likely to beconsidered for the roof supporting structureof a small stand. For longer spans, it isnormally too expensive.There are two categories of timber forengineering: hardwoods and softwoods.Because of a world-wide shortage andgrowing awareness of the need forenvironmental conservation, the use ofhardwoods for structural purposes is nowrare and limited to the occasional detailonly.Softwoods can be used in exposedsituations, such as in a stand, if they areproperly treated with preservative againstinsect attack and/or fungal decay.Protection work is also necessary to inhibitfire and the spread of flames. 19


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Notwithstanding their expense, it can beargued that softwoods are more attractiveecologically than energy-intensive materialssuch as steel.Following recent technological advances,glue-laminated timber (glularn), if properlydesigned and detailed, may be consideredas appropriate material for structuralpurposes.6.4 Alumin iumAluminium in alloy form is a viablestructural material and is used mainly

where a high strength-to-weight ratio isneeded. Its use as a structural element ina stand is rare, however, because it is notnormally competitive in price with a steelstructure.6 .5 S ta in less s tee lOwing to its comparatively high cost, theuse of stainless steel as a primarystructural element is very rare.However, stainless steel cables havebeen used successfully for stands whichhave a cable-stayed roof construction.

7 .0 W HAT M ATER IALS CAN BE U SED FO R RO O FCOVER I NG?Materials used for roof covering need to belightweight, tough, water-tight, incombustible,aesthetically acceptable, cost-effective anddurable enough to withstand the effects ofoutdoor weathering, including ultra-violetlight. They should also be strong and stiffenough to span between secondary orprimary structural elements, supportingsnow and other superimposed loads,including wind forces.Over the facility areas of stands andstadia, such as private boxes, kitchens,restaurants and toilets, the roofconstruction may require additional thermaland/or acoustic insulation.Materials used for roof covering includemetals, concrete, timber and plastics, in avariety of shapes and forms.For a comparison of the properties andcosts of these materials, see page 22.7.1 Me t al s h ee tin gMetal sheeting is by far the commonestform of roof covering for stand roofs,because it is cheap and easy to fix.Manufactured from thin sheets of metalformed into various corrugated or troughprofiles, it has a very high strength-to-weightratio and is accepted as being incombustible.The two most commonly used metals are: Steel: different types of steel sheeting areavailable, marketed by a number of firms, tosuit different spans and loading conditions.The steel is generally galvanised (zinc-coated), painted or otherwise coated toprovide corrosion resistance. A range ofcolours is available.

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Aluminium: sheets of aluminium alloy arealso marketed in corrugated or troughshaped profiles by a number of firms.Although lighter in weight, visually thismaterial is almost indistinguishable fromsteel at a distance.

Aluminium has a built-in resistance toatmospheric attack, because an inert oxidefilm on its surface inhibits corrosion.Aluminium sheeting is supplied in a plainor mill finish. Colour finishes are alsoavailable for aluminium, but may differ fromthose available for steel. Plain finishaluminium requires treatment to preventdiscolouration by oxidisation.Aluminium suffers electrolytic corrosionwhen in contact with other metals orconcrete, and chemical corrosion when incontact with wood which is frequently wetted.In these cases, separation membranes willbe required at the contact points.7.2 Concre teFor roofing purposes concrete can be pre-cast in slab or shell form, and used to spanbetween primary structural elements.The problem with concrete is that it isgenerally heavier than other roof coveringmaterials. For longer spans, however , concretemay be a cost-effective roofing material ifmade in curved forms and cast in a lightweightaggregate to reduce its weight. Concrete mayalso incorporate decorative features.Concrete has a tendency to streak orstain, although current silicone treatmentscan help to prevent this.If properly designed, constructed anddetailed, concrete elements should requirelittle maintenance.7.3 T Imbe rNowadays, timber is usually discouraged asa roof covering material owing to concernsover combustibility and durability.The spread of flame can be reduced withflame resistant coatings or sprays, but inoutdoor situations the life of such coatingsis limited, requiring frequent reapplication.Timber roofing needs to be covered withfelt or a similar waterproof membrane.


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7 .4 R ig id p la stic sFor roof covering purposes, plastic can takethe form of acrylic (including perspex), PVCor polycarbonate. Of the three types, poly-carbonate is the most expensive, at almosttwice the price of PVC (see table opposite)

Plastic is translucent, waterproof,corrosion-free and strong. It can withstandrelatively large deformations withoutshowing any structural distress or damage,and has high impact resistance.Some plastics, like PVC, tend to degradewith exposure to ultra violet light. Thisproblem is less acute in the U.K. than insunnier climates, but even without the ultraviolet effect PVCtends to become brittlewith prolonged exposure to the atmosphere.Polycarbonate is considered durable underultra violet light.PVC and polycarbonate are both self-extinguishing, while acrylic catches andspreads fire rapidly, unless the edges areprotected.Glass Reinforced Plastic (GRP) is also aviable roof covering material, but it tends tobecome brittle and less translucent with age.7 .5 F ab ric sFabrics are used as roof covering materialsin tensile structures (see Section 4.4). Thetwo main types of structural fabrics suitablefor use in external conditions are: PVCcoated polyester fabric PTFE(Teflon) coated glass fibre fabric.PVCcoated polyester fabric is easy to handle

and erect, but is unlikely to last more thanabout fifteen years, mainly because of thedegradation of PVC in ultra violet light. Withage, the surface of PVCcoated polyesteralso becomes sticky and collects dust,requiring frequent cleaning. Polyester fibrestend to slacken, causing the material to sagwith time.PTFEcoated glass fibre fabric has areasonably long life, and has the advantageof being to some extent 'self cleaning' - aproperty it shares with Teflon coated, non-stick frying pans.However, it is the more expensive of thetwo types of structural fabric, and is alsoexpensive in comparison with other forms ofroof construction. Once again, 'whole life'costs should be considered in any comp-arative costing of roof covering materials.Careful detailing of guttering is requiredto drain fabric roofs.7 .6 T ra ns lu cen t o r o paq ue ?Apart from the obvious advantage of giving amore open feel to the seating tier,translucent roofs can reduce the shadingwhich degrades the quality of grass on thepitch and interferes with televisiontransmission (see Sections 2.4 and 3.1).Glass is the most transparent medium,but among the rigid plastics, polycarbonateand GRP both provide 85% light transmission.PVC coated polyester fabric and PTFEcoated glass fibre fabric are also translucentto varying degrees.Examples of the successful use oftranslucent roofs in major stadia includeMunich, Split, Twickenham, Watford (seephoto below) and Wembley.

W atfo rd 's R o us S ta nd s ho ws th e u se o f tra ns lu ce nt tr ip le -s kin ne d PV C va ulte d s he lls s pa nn in g th ep re -ten sio ned lig htw eig ht co ncre te ro of b eam s. T he PV C sh ee ts are ac tu ally tin ted p in k to p ro vid e aw arm er am bien ce to th e lig ht en te r in g th e u pp er tie r.

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stadium roofs

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