An Innovative Approach to Wind Strengthening of a Cantilevered Stadium Roof, Yarrows Stadium,

C. Twaddle and R. Van Bergen Beca Ltd, Fitzroy Engineering Group Limited District Council

ABSTRACT: This case study outlines the assessment and innovative retrofit of a large cantilevered stadium roof at Yarrows Stadium, New Plymouth, Taranaki that sustained significant wind related damage in a high wind event in 2012. The stadium roof sustained damage to a significant area of roofing due to a roof fixing failure. However the investigation highlighted a significant change in the wind loading standard associated with cantilevered roofs. Through agreement with the then owner, the Council (NPDC), a roof structure review by Beca was initiated. The review identified that the stadium stand structure, constructed in 2001 had been designed and built prior to the current versions of AS/NZS1170.2 where cantilevered roofs are specifically covered. The upward wind loading of the truss imposed the most significant load in this case where the existing (steel circular hollow section) top chord was subjected to a significant compressive axial load that exceeded the capacity of the member. This risked structural failure at what is considered a wind event with a serviceability probability of exceedance. This meant that the stadium roof structure was subject to a relative risk of failure of 10 to 20 times that of a new roof structure of the same form. This can be considered similar to the relative risk associated with an earthquake prone building. While there is no provision in the building act for retrofitting structures for wind loading, the recent changes to the wind loading standards are specific and significant. Given the level of relative risk and the number of potential affected parties, the NPDC commissioned Beca to design a retrofit to mitigate this risk. A logical retrofit for this roof involved providing a restraint at the middle of the top chord of the truss, with suitable load paths to transfer restraint loads into existing load paths. This would stabilize the strut and protect it from an axial buckling failure. The issues with such a solution that governed the design were: safety, access, environmental issues and work quality. The roof was 14m above ground level making access difficult and risky. The existing roofing system was underslung with fixings that failed under pedestrian/service loading (therefore access was limited to the purlin structure only, at 2.5m centers). The areas of works were exposed to all elements being exterior in nature. The expense and associated risks (safety, works length, quality and cost) of the works suggested an alternative solution that allowed for prefabrication and simple site assembly. The retrofit included: · A bespoke multifunctional innovative steel clamp that accommodated multiple members and alignments; · It could be fabricated offsite and site fitted directly off a bespoke lifting plate assembly; · Access was via Mobile crane lifted work platforms; · A single member type and connection detail to be used for the entire strengthening works. · Tactical use of friction grip bolts to facilitate rapid construction with site tolerance. The retrofit allowed: · Minimizing exposure of contractors to site risks such as height, weather and access. · Improving the quality of the product by offsite fabrication. · Improving the efficiency of all parties onsite including the ultimate cost of the retrofit.

The retrofit design was initially conceived in house and then collaboratively developed further with both the client and the contractor, Fitzroy Engineering Group limited (FEGL). Ultimately, the successful design and collaboration of all parties allowed the installation of 4 tons of structural steel on top of a relatively inaccessible stadium in three and a half working days.

1. BBAACKCK GROUND:UND:

Beccaa IInffrrasasttrructcture Ltd (B(Beca) was comoommmmmmissssiononeoneded by New PlPlyymomoututh DiDistritrict Counoununciill ((NPNPDC)PDC)C) follllowiwingng thetthhehe failiillure of roof sheheeheeettiiinnngg on thehe TSBSB SSttand Roof at Yarrrrooww SSttadiumum, which ooccccurrrreded durriing highgh winds in Aprrilil 220122020101201212. Thehe ssccopeope of our iniititititial engagagememenmeennt waass to innveveststiiggaate the causeauause of faiillure andaannndd aassssist NPDNPPDDDCC to mamakkee aappppropopririate reepepapaiirrs thahat would allow thehe ssttadadiumum to bbee usseeded for eevenvents. As this commmmissssion eevovovolvvevedeedd iitt becaecaamemmee evevidendent thahat assssesesssmmenent was requequiirred of the following: · IItts sttrruccttural condiitition. · Capaaappaaciitity of thehe eexxiststiing roof sttrruuccctture to resist wiwindnd loads relatitivvee to the currrrenent wiwind loadings stanandadard. · Coonnsideratioonn of servicceabeabilliity issssueues relattiing to thehe TTSSBB ststand. Yarrrrow Staaddium is located neneaar the CCBDBD of New Plymouymouth andand is a sporrtts venuevenue caterriing for topop leveevel sporrtittiingng eevenventts,tsss,, predoeedomedddooomminnanananttlly rugbugbyuuggby. IItt sseeaeats apappappprooxximmaattelteelly 2626,000 peopeeoople wiwitthh thehe mamajorritriiitty of speccttators in the ttwwo mmaain ssttandss,, the TTSBSBSB Standandnd andandnd thehe Yarrrrows SSttand. Thheese are lococated on the Eastst andaannd Wesesstt siidedes of thhee mmaain sporrtts fifield reesspeccttiively, which is aliliggnnedneded aappappppprooxximmaately Norrtth to Sououth. Refer to FiFigguure 1 below for a sitite aeaeririal photo.

TSBTSB Stanndd

Yarrows Stand

NorthNorth

FigurFigure 1 – PPllan of Yarrows StStadium Thehe TSTSBTSB SSttand (and Yarrrroowws standand)),, the ssusubuubbjecctt of strtrengthenhening waass consttrrucctteded in 20012020001 in iittss currrrenent form.m. SSiincece July 2013, thhee ownneership of the stadiuumm has residedded with thehe Taranaanaki Regional Counouncilil ((TRTRC)C) and NPDC, wiwwitith Managememenent anandd Oppeeratitiononss undeunderrttaakken byby the NNPDC.PDC. A Joint commommmmittee waass essttablliished (coomompmprising TRC and NPDC) to provide oveoverallll governance and a joint vision.

2. EXEXISTINGNG SSTTAADDDIIUUMM STANNDD DDEESCRIPTION:

Thehe sstteeeell roooof strtructcture aaboveababoboveboovevvee tthhhee top flfloooor leveevel oonn boboth ststanands conconsists of heaheavheheavyavy sstteeeel coluumnummnnss that form a poporrtttall frfraameamme wiwitwith a sstteeeel trtruusussss, which canttilileeveevvevers 22121m1m1m oovovever the bleaeachehers towards thhee mmaain ffiield. Thhee steeeel trussuusss (7.33mm cceenenttrres) is consttrrucctted frfroomm cirircular hollllow sectitiononnss ((CHCHSHS)) witwiwith a ststeeeel universsaal bbeambeaeamm seccttiionon (UBB)) as thehe bobottoomm chohord loccaateded immedmediatellyy aboveaboabobboveooveve thhee undeunderslungunngg roooof, cononssiststiing of profilfiilleded alumuminunumm roooofifingng suppoporrtted below steeeel rectangular hollow seseecctions ((RRHSRHS). The total roofofed area of each ssttandand is in the ordeder of 3,000m2.

For tthehe ppuurpoposes of diissccussssion in later sesectctiionsons, thhee crirrititiccaal sseecccttiions of the roooof steeeel ststrtructcture are iddenentitifified in Figure 2. The same terms appapply whenhen discuscussing the Easast or West StStand roooof ssttrtructures. Thehe enentirtire TSTTSBSB SSttandaannd ststtrruuccture is ssuuppopporrtteded onon pililes aass itit is siteedd near to thehe middle of the oririginnaal ffiiilllll zone of the vavallllleleey. Thiis threeee storeyey ststrtructure hahaass a dodoubdouuble hheeight middlele ssttoreyey. Thehe grounounund flfloor containsns the sportrts faciilitiillliitieess,s, thhee ffifirirst fflloor contains thhee pubpublliic concoouurse andaanndnd thehe top flfloooor coonntainnss thhee memmembeeembembers areaea, knonown aass thehe LegendLLegenLeegendgendds LoLoungenge. Thehe lateral resesisttiing sstttrrucctture coonnsists of a bracceeded sstteeeel strtructcture, wwiwitith both eeccccceennttrricalllly (K-braces) and concentrtricalllly braced (r(rod bracingng), in the nonorrthth-sououth dirireecctctiionon and sstteeeel momomenoommenent resissttiing fraamamemes in the eaastst-west dirireccttiion. Coonnnccrete bleaeachehers are suupuppoppopporrtteded onon rakakiingng ststeeeell beamsams anandandd the suspepenpendedpendpendenddededed fflloors are geneggeeneneralllly cononsststtrrucctted ffrrom hollllowcore precasast concrete uniittss with an in-sititu cononcrete toppooppping slaabbss. A typypical sectctiionon of thhee TTSSB SSttandand is provoviddededed in FiFigure 2.

Strut 1 Main ColumnColumn 20122012 Failluure ZoZone

Transverse Strtrengthngthgtheeenning plane

Figure 2 & 3 – TTSBSSBB SSttand TTyyppiiccal Sectiontionion and Perspective View

3. HIHIGH WINDND DDAAMAAGGE:GE:

In MMaarch 2012201201212, the TSBTTSSB Stanandd suffffered high windnd relateded dadamagedamddamaamagemageagege frfroomm a gustst evenevent(t(s) ffrrom thehe sououth wesest which loadedoaded the uundendenderslung roof such thahat itit caused thehe rooffiinngg to punppuununcctture throoughugh the ffiixings that heheld thehe roooofifing to the undersidede of thehe RRHHSHS pupurlirlrlins. Thehe damddaammaage oocccccuurrrreded oonn thehe SWSW ttiip of the TTSTSBSB SSttaandndnd andandnd cooveovvereded anan areaea of 9090 to 120m1220m0m2. Refer to FiFigure 3 aabbove for an aannonnonnotattioion of the faililure area. During thhee subsseqequentnt invenvestigatition of the roof cladding faililure and insnspectctiion of the bbaaallanance of the roof for dadamagmage,e, it was raiseded to the stadiuumm oowwnener thahat the underststanding of high wind loadads relattiiveve to largege canttilileevever roofs had chanchangchangechangedgeedd sincnce the desiggnn of the orriiginnaal ssttrrucctture. Therefore thehe enginneeeerriingng scope for the ststaadddiiumum wasas exextendedeendenndeddedd to allllow assssesssssmmmemeneennt of thehe prriimmaary sttrrucctture as well. The intent of this was to eesststabablilishsh whether the ssttrruuccture was exexppososed to higher wiwind relatateded risksk thanhan was previoouusslly undeuunundndederssttood andand to theenn bebe abable to mmanmaananage that risskk in aann informmeded mannemannennnnenerr.. This wiwind ssttrructctural asassseessssssmsmsmmeenentt,, the fifindingngs andand aassossossosociated impmpleemenmentattiion is thehe ssuububjececctt of this pappapepapeer.

4. RROOFROOOF ASSSESSSESESSSSSMENT:MENT:MENT:

WWindind Loaddinging StStandards Thehe sttrrucucture was ddeesignedggngneneedd uunnder NZSNZNZS42200033:19921992, which does nnoot speciifificalllly ccooveoovvveer large ccaananttiltiilileveevereded rooffs. Hooweveowewevewweevever an assssumedumeumedd babassis for designgn waass lliikely dederirived ffrroomm onoonene of the exissttiing simiillar caasses witwwiithin the standaaannddaard succhh as for an exppoossseeded roof. Thhee Auusstrtralliian wwiindnd loading standaandard, ASAS1170.2 (1989) initialllly inttrroduuceuccedd proovvisions to coovever larggee canttilileevevered roofsfs in 2002, after research into wind behaavviour around ssttadiuumm, ststand lliikkee largege caannttilileevever roofsfs byby MMeelbournnee aanndd Cheung in 1985. This reseeaarchch, aamongmongst otherss,, suggesstted that thhee net preessssure coeffiiciients around these tyypepes of sttrruccttures were nonotably higheghheer than hadhad bebeen preevviouoususly assssumed.umed. In 220200420000404, New Zeeaalandnd andand Auussttrralia ccoombommbbined their loadings standandaards into AS/NAS/NZS11170170, Appendix D5

off 11701111770.2 (wi(wwiindnd llooaaadddiinnggsgs ssttaandaanandnndadadard for Austrtralilia anandd New Zealandanandd) formmaalilizzeeded thehe ffiindings ffrroomm earlirrllier workskss.. In this standard, the suggesstted nenet preessssure disttririributtiion oonn a large ccaananttililileeveevver roooff was repepreseennteedd byby a tririangnngugular proffiiillee that tapereded to the supporrtt regegion of thhee cantiltileeveveverr.. The pressssure coouuld be eiitther popossiititivvee or negnegaatitiveve, bbuut the mmagnmamagagnagnitituudede of the coefficieennt cchhangedhhanhahangangedangednggededed witwiwith the signgn andandnd witwwiith the relattiivitity of the area concceernedned relatitive to the sttrruccttureses edge.eeddgge.e. In 20201120111 AAS/S/NZSNZS1170.2 Appendppendpendix D5 was revised, due to furtrther wwoork in this area. The signifiificant changecchanghangehangee wasas to iincncreaease thehe net presessssure distritriribubuttiioonn ffrromom a ttriririanguananggular form to thahat of a ttrrapezzooid. This was nottiififieedd by IIPENZPENZ in 22011011 as parrtt of the draft updaupdate of AAS/NZSS/NZS1170.2, andand wwaas the basis for the advice to aasssssessss the roof for wind loading. Thehe currrrenent (and previous) presesssure disttrributtiionon coeoeffificienents for wiwindnd aliligngnedneded toward the titip of thhee cacannttiliilleevever is aass follllows in FiFigure 5:

0.0

1.1 1.5 1.8

FigurFigure 5 – Cantntintilever Roof Wiindnd PPrressurure CoCoefffficientnts iinn 1170.2 Thhee abovabovee illillussttrtrates the increasing mmagnagniittuude of the Cpn for thesese tyyppes of roofs that occurrrred over time andaannd thehe signifiificcaananncce of thehe upupllilifift case which was criritritticaall in this inssttanance. The follllowing was also notable wiwitthin Appendix D5 relevant to thessee tyypepes of roofs: · Downward loads ffrroomm wind are alssoo signiifificant. · Roooof loadoading vvaaririeess relatitivvee to thhee offffset frfromom thehe sidedes of thehe stand. · Thheeesssee signgniiffificant load cases ononly ooccccur wwhenhen the wiwindnd dirirececttiioonn is wiitthin a 90 degree plan arc of the wwiinndd direcection indicated in FFiigguure 5 above, in otheher cases the wiwind loaoadd on the roof is as per other typypical struucctures. Therefore thhee TSSBB Stand roooof is exposeded to governing wind loaddss from the NW, W aandndnd SW direccttiions. · The mmeethod in AAS/NS/NZS1170.2 Appendix D also includudeeses dimmenensional and dynamynanammic aampmplifilificattiion lliimititattiions andand allowances respeccttiively and nonnon-ccoonnformmanancece canan sttillill require wwiind tunneununnnel tesesttiing. · AS/NZS11170170170.2 Appeppenppendndix D doesdoedoess not refereennce lloocacalliizeded preessssure facactors (as per other roooofinngg shapes) for vovorrttices or otheher mechanchanhanisms that are offttenen crritiriiititical for secondary elemenenttss (ie purlrrlilins andand roooof fifixings).). Therefore teststiiinng aandanndnd jududgmgmenenent of thhee engineer isis requequirired in thehese iinnstananncces.es. Assessssessment ofof tthhe Roofoof Structuurere Thhee steel sttrructure of the roof was commpuputer mmodeodelled in spacegass as a 3D fraameme and aassssessssseeded under vavaririous wind loadingng ccaaasses frfromom allll dirireccttiioonsns. The modemmoodel eexxtenent was such thahat thehe veverrtittiiccaal ffrraammes wewere eexxtenddeeded to thehe founoundoundadatitionon leevvevel wiwitth a seennsiititiviitty ananallysysysis applilieded to the leeveevvel of rotatitionaonal reesstrtraint in plane of the trussss/fr/f/frammee poportrtall.. Out of plane thehe mmaain ttrrusssseses of the ststadiumum were half momoddeelllled to assessss strtructctural ccaapaappaaciitty in thhee ttrruusssss out of plane dirirection.on. It was found however that the AS/NZS1170.2 Appendiixx D condiititionons were thehe only case that caused actionsns onon anyany ststrtruccttural elemenementsts succhh thahat theyhey did nonott mmeemeeeeet their currrrent cooddee capaciitty undeunder NZNZSS3404. Detailed AssessAAssssessessment ofof tthhe Critiriticcaal StrSttrrutut In the upliftlift load combombinattiion ddeeppippictpicicteded in Figure 5, SStStrtrtruutt 1 aassssummemeseses a coompmpressssion load. Whenhenen uundnder coompmpressioonn this elemenement is 15m15155mm longong appapppproximmaately (L) ffrromom thehe bottoomm chord intersectctiionon to the mmaain colluumumnmn at thehe higghghehheeessstt popoint of thehe stadiuumm. Thheerefore bubucckklilingng sseeensnsitiitiviitty is the mostst signignificant issue to ddeeririve capacity. In ddooinngg so we ccononsidered: · The potentitial for rotatitionaonal reststrtraint at thehe bobottoomm chohord andaanndd the midsppapanan veverrttical sttrrut. However thessee mmemechanechanchanissmmss were eitithheer weeakeaaakk or govveerned bbyy pooppooooor conneonnectctiions (pupurlrliin to cchhoord). · Thhee ouout of plane ressttraint and ststitiffiffffnesnneessss of thhee mmaain ccooluumnmmnn whehere it canttililileeveevvered ouout of plane aboaboveve the purlin plane to restrtrain StrStrut 1.

· Thhee ababiililility of thehe mmaaiinn ccooluumnmnmn to also offer torsioonaonnanal restrtraint ((iin ppllanan) to SStrSttrut 1, theherebyeby offfferiring an out of plane moment eenendnd conneonnectctiion to strut 1. GiGivvenenen the aboveaaboboveve issssues, the effffeeccttiiveve leengennggth of ststtrrut 1 relatitivvee to compommppreessssionon bucbbuucucckkliling was Ke X L = Le, whehere Ke was in thehe rangeaannggee of 0.85 to 1.0. This was to reflflect the potenenttiial of the boundaboubounndadary condiititioonns to offer soomeomme rotattiiononaal restraint aavavaiillable by the strut end conditionsons. Inndduced mmoomenments wewere also includeduded iin the ananaanaallysysysis,s, but givvenenen the bbebendbenendndinngg ststababiliililiity of thehe secectition andaannd the ssmasmmmaallll momomenoments innvovollvvvededed, coompmpressioonn bubucckkliling gogoveverned. Thhee resultlts of the aasssessesssmmenent wweere asas follows in Table 1, uundender the looadad ccooomombmbinattiionon of 0.9G9G & Wuuppliflliift: Table 1: Strut 1 – Winndd Asssesssessmentnt Resulltsts Ke PPhhi.N.Ncy Phi.hi.MMcycy N*/Phi.NN*/Phi.Ncy + M*/PPhhi.MMccy <= V,des Strutut 1 - AEP (kNm) (kNNm)m) 1.0 (vs 100% ofof 1170.2) ((mm//s) V,allowablble (m/s) 1.00 327 139 1.81 41.0 32.0 17 years 0.85 455 139 1.30 41.0 36.0 76 years 0.50 1,009797 139 0.63 41.0 56.0 >>5,00000 years Coommmenments on thehe aababoveaboboveovvee table are as follllows: · V,des dederirivveded ffrroomm anan IL3L3 wwiinndd eveveeveneveennt (10001000 yeayeaear AAEAEP),EP), aandannndd an MMzz,ccaat = (1515mm,C3) = 0.89. · V,actual deririvveeses ffrromom a gust speedpepeeded that genegenerateess a unitity chehecckk iinn thehe ccaapaappaacity calculattiion. · Thhee AEPAEP deririvveeses fromom a reveveerse calculattiionon of the eequaquation, AS/NAS/NZS1170.2, table 3.1 reeggion A7 to determiinne the evenevent rriisk that wwouwoouould not cacauauusse faililure. See a parrtt exexttrracact from ASAS/NZS/NZS1170 below to dedeppicctt this (note this is for V,r rather than V,dedes)s).

· Therefore the sttrrut hahhadad 10 to 20 ttiimmeeess thehe reellatitivvee ririsskk of a new sstttrrucctture dedesigned to currrrent stanandadards. (This cocouould be considered aass equivvaalent to anan earrtthquake proneonene buiillding ununder seismic loading). Leggiislation As referenencedced aboveabove, iiff the actctiions were derivedved frfrom sseeissmmic loading and the level of rriisk was such that strtrengengngthenhheeneningng would bebe requirireded of the strtruuccture under the Builildingng Act. But, no such legislattiion exists for wind loading. However, bbooth TRTRC and NNPPDPDDCC deedeemdeemedmeded iitt approoppririate to invessttiigate sttrrengthening of the standsandsnds due to the following: · Thhee levevel of incncreasseed relativeve ririssk;k; · Thhee nunumbmber of paparrtitieess thahat mmamayay attttendendnd a large eventeventvent; · The nearbyby residdenential housing;ng; · Thhee ununkknnonown exextent of areaea affffececteedd byby a sttrruccttural faililure of such a largege roof.

5. SSTTRENGTTHHENINING SSCHCHCHEEMEME FrFromom reevview of Table 1 aboaboveve, itit is cleeaar that stababiliilililizingng SSttrtrut 1 lateralllly at iitts midssppanpan is allll that is requirireded to allllow thehe eexxiststiinngg ststrucctture to operate asas close as practcticcaal to a nenew strtrucucture. To stabilililizzee the strut: · A transvsverse sttrrut and brace sysysteemm, and;and; · A lococcaalilizzeedd flfly bracece syststeemm to brace thehe vveertrticcaal strtrut below SSttrut 1 at midsspapan to the RHS purrlirllins to eitither side of the truuss.ss. Thehe ffiririrst opttiionon of thehe twtwo waass selectcted for thhee follllowwiing rattiionaonal: 1. A strtrut andand brace sysysteemm did not clash wiwitth ananoanoother reroooof projecect to be atoopp thehe exexiststiing RHSRHRHSS’s. 2. Thhee fflly bracace syyssteemm uttiliililizzeedd eexxististiing elemenemenents andand connectctiionons that were either weeaak and/or highhlly loaded. 3. Thhee fflly bracace opoptition wouwould hahaveve requeeqququirireded hhoott work vevery close to the eexxiststiingng roooofifing which was alrlreaeeadyadady known to havehave leakaagagege andand durabililliitity isssusssuuees (r(referenencce thehe roofifing faililure). See anan eleevavateedd halflf seccttiion of thhee ttrraannsvsvveersese sttrrut andand braacce sysysteemm adopaaddopopted bebelow in Figugure 6.

Braces ColCollector FFigurigure 6 –TrTransvsveersese Sttrrruut anndd Braacece Strtrenngtgthgtthhenninging ConCoConcept SStrtruts 4. CCONCONNCCEPT DISCUUSSSSION pickck upup ststaabbiliilizing loads (aassssumingng theheyy are Dueue to the locattiioonn of workkss, a nunumbennumumbembeber of isssuesuesues all additive, andaannd of the increemenmental order of bbeeccaamameme more impomporrttant to consider. These were 2.5% of the primamary aaxxial load – reference ggegeneeneneralllly as follows: NZS3404 1997). CConCoonsttruructtioionn Safety · Thehe collllector ststrruts are to then be Thhee workkss were requequiirreded to be ffittitted on top of diagagonaonally braceded to nomnominalllly above the the staaddiuumm roof,f, 14m14m in thehe aiirr and acrosossss bottoomm chord of the trtruss. rooffiinngg thahat hadhad hissttoriccaalllly been subject to · Thehe eexxiststiing verrtittiical sttrrut wiwitthin the truss ddadamagamagemagee by servicememen. The undundeerslung rooffiing thhenen ttrransfers the ststabiliilizing actions to the wasas alrlreadyeady thhee susuubbject of a water ttiigghhtnenesnessss exissttiing roof plane strtruts and braccees, reveview of eexxissttiing leeaaakkkaagege. Thehere wasas anan area of thheerebebyy diststtririributiting acacttiioonnss into an existinngg ageaagge//UUUVV emembmbrriritittltled opoppaaque rooooffiing thhaat separated strtructctural ssyysstteemm that has redundanedunedunddaanncy for the area of worksks frfromom the momore accessssible top this typepe of load combinattiion. fifixedxeedd roofinngg oovever thehe memembers lounge areas. The strtructural braces were seleeccteded as CHS’S’s This areeaa of rooooffiing hadhad a 5m fallll beneath itit for variououss rattiional, such as: witwwiithout meshsh. IItt had also beenbeen inssttalllleded in susucchh · Ease of coating. a mmanneanneanner thhaat repaeeppairir/rir/repeplaceemenment of this roooof · Thehe abilility to aaccccommodaodate signgniifificaannt woouuld be expensensivve.e. coompmpressssion loads aass wellll as tension. CConCoonsttruructtioionn Access · A CHS couulld be consiststeennttlly andand efffificientltly Dueue to the roof height and accessessibilility of thhee used for allll memeembember tyypepepess whilile reemamaining worksks areas, acccceesessss waass reequququiirreded to bebe consisteennt wiwitth the existtiing strtructure. considered earrlly to aassssistst in miititigagattiing ThThe SStrutrutrutt//Br/BrBrace Deessign conssttrructition safety, mmaaintaininngg qualility and Thehe CHS sttrrut desiggnn waass a convenonventtiional planning fofor a reasonaboonnabable consonstructctiion form. The approach (127CHCHS)S), howeveever the conneonnection mmoore awawkkwwaard the accceccesessss, the loongeonngeger mmeethhohodoododolooggygy was job speciificfic, ddeeveveloped with contractors would be expoexpopossed to thhee risskksks of the issues noteded in Sectionon 4 in mindnd. The working on the roof. sttrrut/brace conneonnecctition desiggnn wasas generally as CConCoonsttruructtioionn QuQuality follllows: This was a concern for both exexissttiing ststandandnd · Thehe connectctiion cleat was a kkninife plate shophopop featureess and for anyany new eleemenments. The risk of weldedded into the CHS. conststrructition actctiivitity dadamagmaging ththhee exiexiststiing roof · Conneccttiion of thehe cleat to the connection wasas high, whilile any new worksks upup oonn thehe roof on the primmaary ssttructure was via frfrictioonn griprip wouould bbee of lesser quaqquuaallitity duedue to the eexxttrreemememmee (TF) bboolltiting anandd slotted holes. aaccccessss issuessues. · Thehe slotted holes alloweded for addiititiononal siitte Safety iinn Design tolerance bebeyondnd a sitite meameasuree,, while thhee Dueue to the preceedding issssuuees aandndnd both the TRC TF bolltitingng allllowed for a non-slilip prriimmaary and NNPPDC appreciatiting thehemm, we were abable to load ppaath conneccttiion to accomoommodammodamodate the brriingng in the contraccttor early to deriveve the connonneonnecectition play deriving frfromom thhee slotted benneefifitfitss of the clilienent, oopeperators aandnd thehe holes and the use of boltltss in shear to take contractor (FitFitzzrooyy Engineering GGrroupoup Limititeedd - thhee axaxial ststrrutt//brace loads. FEGGLL) beingng on boaboard witwith a safety in designgn · To mmobobiliilize thehe acaccuumumulateedd ssttabiliilizinngg processss as wellll as speciiffically addreessssing the action loads, the TF boltlt interfrfaaceces utiillized issssueuess aboaboveve. This allllowed a ccoollllaboabboorattiiveve a specific localilized coattiing syststem. The aappappproacchh throughout thhee project life. ststeel to sstteel interfaces were coateded in an inorganic zinc coattiing to boboth provovidede someome 5. DDEETTAAAIILEEDD DESDESIGN: corrrrosion protecectition whiille ssttillill provovidingng a FrFromom eaearly conceptition the intent of the ddeesign high fririccttiion surfrface interrfface to maxmaximize waass to have thhee follllowing feeaatures: the coonnecnnecnnecttiion capaapapaaccitity. · Transsvveerse collllector horriizontal strtruts that · In the eevenvent of actionons exceeding thehe

cononnectnections capaciitty ((wwhich is ssmsmammaallller than the memeembeembmber),rr)), the joint wouould slip ((wwhileile still maintaining the joint TFTF capaciitty) into a nneew positiitionon 11010m00mmmmm offset wherebbyy thehe bboolltiting can thenhenen bbehaehaehave also in single shear asas welll.lll. Therefore the connonneonnecectition can bebe said to havehave considerable redundancy in it.it. The 10m10m0mm deformmaattiioonn in the sttrrut connecoonnnecnecttiions wouould alssoo hahavehavve aassoassssoociated ddeeformations in the restrained Strut 1. Howeveever thehe orddeer of these additiitional moment aaccttiionons is insigniifificant relattiiveve to the length of Sttrrut 1 and can be easilily aaccccoommmmoodated. FigurFigure 7 – Space Gass ClClammpp Mododel · Refer to FFiigure 6 for anan elevationon of the sttrrutt//brace mmeeembemmbeberss,, andand refer to FiFigugure 8 for the conneccttiion dedetails of thehe strtrut/t/braces. ThThe StruStrut/Brace Desiigngn Thhee Sttrructural SStteel claampmmpp adopadopteedd in the dedetaililed desesign is thehe element that allllowed thehe works to prooggress. The clamp design provided for thehe follllowwiinngg cononsidederattiioonsns: · It formmss thhee connonnectctiion of the sttrrututss//braceess to the pririmamary sstttrructure. · Provides vevertirtical cleats for the new strtrut/t/braces, while also allowiwing for clampammpping the conneonnecctition in ttwwo hhaalvvees arououndounnd the exexissttiinngg primmaary strtructure. · Wiitth this scheschechememe the claampammppss, struts/braces are all eeaassiilyly remoemovaovabvabble and able to bebe fulllly fabricated and coated offsiitte. The sucucccceessss of the jointnt relliieses on thhee claampmpingng actctiioonn aroouounoundunndd the exexissttiing vevertical strtrut in the roof trtrusuusssss. To addreesessss this, the follllowwiingng wasas conduonduccted to mamakkee provovision for cononsstttrruuccttiioonn conditions: · Early siitte mmeaeasuriring of thhee 163CHSCHS eexxisting sttrruts was conducctted bbyy FEGFEGL. · An allllowaanncccee for a UV resistanant rubber sleeveeeeeveve waass mademade betwtweeneeeen the eexxiststiingng CCHSHS ououter diaamemeter and the innnneer diaamemmeeter of the clamp.amp. · TF bbooltingng wasas aagaagggaain adopteded to mmobobiliilize a claampmmpping actctiioonn on the 163163CHS. · AAllllll TFTF bolltts also used load indicatiting wasashers to aassssist in site QA. · Refer to FFiigure 8 for andaannndd exexttrracctt of the clampammpp andaanndd sttrrut/brace connonneonnecectition dedetailils useed.d.

FigurFigure 8 – ClClampmp detail drdrawwiinginingg exttrract To asasssessss thehe inflfluenueuenncece of the stabilizing aacccttions and claampmping accttiiononsons on the cllaampmp parrtts as wewellll

as the eexxistingng ssttrrucucture, calculattiions were Theherefore the coattiing system on the clamp is conduonduccted bbyy hanndd then veverirififieedd byby thhee ussee of a mmoore durabable that the surrounding sysysteemms, thheey Space Gass model of the claampammp (refer to FiFigure can also bebe lococalllly remoeemovedmovedveedd to bbee recoated if 7). Thhee finnddings of this exeexercise raised thhee reeququiirred. following: We considdeered using the bobolltiting arrrrangemenangeangemenent to · That thehe clampampingng load as well as aacctition onon ffitfiitt the clampamp and conneonnect the sttrrut, but foundoouounundnd the eexxiststiingng 163CCHSHS vertical strtrut was that thhee needed for highgh ffriricttiionon in thhee sttrrut aaccccceptabable eevenven in considerattiion of the connection and toleranancancce in thehe clampamp fitfittinngg eexxisting looaaadsds in the CCHHHSS ffrrom upplliflliift were incocompaoommpapattiible or overrlly sstttrresssedsseded thhee clamp.mp. accttiionons.s. SSiiggnniifificant interaaccttiion waass conductcteedd bebetween · That thehe loading dissttributition the clamp was Beca andand FFEGEGGLL duringng the eennttiririre detailed vverery sensititiveve to iitts suppouppopportrt cononddiitttiions (i(ie design, the workskshophop drawinngsgs, tessttiing and the ruubbebbebber sleeve and clampamp ststiffiffnessess). fabrication ssttages ultimamately derriviving benefits · That thehe clampamp boboltilting to the exissttiing strtrut durriinngg the ccoonststtrructtiion stage. hahadd to be minimizzeedd closely to thhee design accttiionsons as when TF bolting is torququedqueed to minimumum tension anand the claampammmpp has room to ddeeform, then thhee claampsampmmppss take on siggnnificant load. · To addaadddreessesss eevenevevevenvenen minonor loadoadingng ththe clamps nneneededneedeededeededededed to bbee signiifificanantltly stififfenedenneded in thhee ddeetailileedd deessign, therebbyy takinngg thhee single clampmp hhaallff weigghht to 28kg, and the ddouboubouble clampmp hhaallff weigghht to 50kg. Inssttallllattiion mmeethodohodologgyy becaameme topopical ddueue to diifffificulty mmanmanhanhanhaanndlliing of thehese weights. · The required claampmping load to keep the clampammpp in posiititionon aanandndnd to transfer the vertitical acaccttiiononss into the exexissttiing sttrructcture wasas relatitively minnoor,r, agaagagain this mmeecchhanissmm had redundaneduedunndandancy ssucuch that in the eveeventnt of signgnifiificant loadinngg the claammps could dedeform Figure 9 – FEGLFEGL WoWorkshhooopp ISO ooff Clamp whilile ststillillll mmaaintaininngg theirir clammpping caapapabpababiilliity. · AAllllll TFTF bolltts also used load innddiccaatiting wasashers to aassssist in site QA. Thhee detailileeded design of thehe stadiuumm wind strtreengngngthenheningng included only ttwwo cocomponenmponents, the claampmp and thhee strut. Thehese only vvaaririeded nonomminally by: · LLeLengengengngth, for the sttrruts veversus the braces and siitte mmeaeasureemenment vvaariattiions. · The single veversus thehe doubdouble claampmp that took the braces. A laasst note on the cllaammppss, due to thhee enclosed spacceeses oonn the claampmp bbooltilting ssttitififffening anangngleess,s, the claammps were hot dip galvvaanizeded iniititialllly. Top coattiinngg was via a 2 pot epoepoxyxy paint syssttem. Thheerefore thehe clampammppss hahaveve a vevery long titimmee bebefore proobabbabbable ffiririrst mamaintenanccee is lliikkeely to bbee required. Howevever asas anan aaddedddeddded mmeaeaeasure allll ststiffiffffeneeenners that were lilikkeely to trap water were pititcchhedheed at 7.5 ddedegegreeeeses to thhee horizzoonontal to actctiivveely shed water rather thahann retain iitt and thhee Figurure 10 – FEGLFEFEGGL Shohopp Drawinngg ofof Craned probable aassssssociated chchloride laadden dedepopositits. Acceccessss PPllattfoforms

“bbuuttononss” that dedeform flat at the appropriate bolltt 6. CCONSONSNSTTRRUUCTION: pretensioonn and “squirirtt” out an indndiciicacator mmaark of Thhee workshopkshop drawing, fabricacattiionon aandndnd ccooaoatitings paint. These allllow a rapid reveview of tensiononing andaannd inssttallllation mmeethodologies dederivevedd mmaainly complettiionon to allow work to progogreessss. However itit ffrrom FEEGGL and theheiirr aim to provovidede the best waass found in conjunccttion wwitith FEGEGL thahat on the productct in thhee besstt waayy they ccoouuld. Their claammps witwiwith minnoor deformation (duedue to eexxperriience anandd depth in coombmbinnaattiion witwiwith their tensioning of the clampamp bollttss),), bboolltt nuts do nnoot accttiivvee interactionon in the Safety In Design (SID) activate thehe squiriirtrter bbuuttononsons ifif the nunut is nonot worksksshhopop andand interactctiveve discscuussssionon of ddeetaiill completely ttrrue. This can lead to oveover titightenening andaannd workkss mmeethodologygy led to mmanymanaananyny benenefifittss for of the TTFF bbooltltss in an atttteempmpt to acttiivvaate the the project. A lliikely nonnon-cocoompmpmplete lilisstt of these washers. This was obobserved during the mockup are asas folllloowws: testinngg stageage ((rrefer Figure 12) when FEGL were WorWorkshohopp Drawiningngs: doingng a ppaarallllel cheheckck ususingng a torqueque wrench. AllAllll shophop drawiwings for eveveevery plate and eleemmeeennt Therefore, in this iinnstance, theyhey were useful to were producceeded in SStteeeel PPrro. Theyhehey includeduded confirm a leveevel of tenenssiononingng hadhad beenbeen aacchievveded, coompmplete mmaaterial take offs, weigghhtsts and site but nnoot necesnecesssarilrriily the final tension. Also, the mmeaeasured vvaariatitioonns. Refer to Figure 9 for a claampmp boboltilting to the existstiingng ststtrrutut did nonot saampmple isomettrric shhopop drawiwingng of the clamp.amp. critically nneedeed to bebe at full tension. Theherefore 11000% prprefabbrricattionion and coatting:iing:ng: torque lliimititss were sseeen as coonnservavattiive in this Allll eleemmenentsts were aabble to be shop fabrriicated. case to test on thehe lowoweer siddee of the minimuumsms, Thheerefore weld andand coacoattiinngg qualliity waass high andaannd due to themhem actctiinngg in tension asas wellll as being abable to be fully inspected. No reewowork was pretensiononed.ed. required onon this projecect. FriFrictiontion Griipp boltiing:ng: WorWorkksshhohopop tesestingtiingng of ffitits and bobolltt tensioning: Thehe use of TTFF bolltitingng in both shear andand in A mockckup of the bracceded aassssembemble was tension allllowed the site asseemblmbly of a ddevedeeveveloped in the workkskshosshophhopopp byby FEGL, thereby dimmenensiononaally ssttabable strtruuccture with an allllowwiinngg a test fitfifit scenaenaririo pririor to the elemenemmenents abuabundabunndance of conststruccttiion tolerance, therefore ggeetttiing to siitte. Refer to Figure 12 for phphootosos of aavovoidinngg loosst ttiimeme and roof topop sitite workks.s. the shop aassseembmbly Besespopokkee access plplattformffoorms: Duuee to the inacnaccceessssibiliililiitty and safety concerns of acacccesessssing the roof, FEFEGEGL ddedeveveevveeloppeeded bebeesspoke acacccesessss/w/work platformsms that ssppannedpannedanned purlirlins andand allllowed dissccrete work areaeas at thehe claamampmps to bebe workeedd safely. These platforms,s, 3 in total wewere aabble to be lififted bbyy crannee ffrrom one posiitition to the nnenexext vveery rapidldly. Refer to Figure 10 for an eexxtractct of the shop drawing of these plattfforms CCllammpp liftingtinting jiiggs: ClClampampss were efficieenntltly fifittted bbyy ususe of a set of bebesspoke steel plate liliiftiifftiting jijigs thahat alllloweded the claampammps to bbee lowered byby a spreadeadeer beabeamm, separated ababoveabooveve the toopp chord (Sttrrut 1) and then lowered andand ffiititteded into ppoossitiition around the veverrtittiical 1163166363CCHS.CHSHS.. The craananene cocouuld thhenheenen ffiinenely adadjustst the clampmp heigghhhtts prior to the ffiititttttiinngg bollttss bebeing ttiighteneenedd to ffifitit the clamaampmpmp in place. Once fifititted the jijig/craneane aasseasssesembmble woouuld thenhheen brriing upup the nenext onnee for the nenexnext joint creeaattiingng a reliliable, repeatable, rapid proceoocescessss. Refer to Figure 11 for a sampample of the shop drawwiing of this jijig. LoLoad indiindicator waasshers: LLoadLooadad indiccaator washsheers were adadoptopteedd for ussee onon Figurure 11 – FEGLFEGL Shhoopp Drawingng of Clamp allll TFTF bolltting, sppeeciifficcaalllly “Squirirtter Wasshheers”. Installationon Jigs Thehey are ssoo ccaalllled due to the washheers havhavingng

Figurure 12 – PPhotoPhPhothotootos ffrromromom FFEGFEEGLL’’s workshophohopop depipicttiinngg the momockck assemmblmbblbly ofof comompononenntsts

7. PPRPROROJOJECECTT RERESESULTS:ULTS: FrFromom reevview of the projeeccctt at coompmpletition thhee follllowwiingng can bebe ssuurmisseed:d: · The design intenent acacchhievedeved a robuobubust strengthening ssccheme througoughh collllaboratitivvee early contractor invovolveememenntt, enenaenabableedd by thhee client (TRC/NNPPDDC)C) whoho wawas able to apapppreciate the benefiffitiittss of this processss ffrrom the outssetet. · A safe cocononsttrructctiioonn processss waass essttablilished andand follllowed thrououghougougghh byby the ccoonntrtracactor incluudding bespokkee acccceesss and innsssttallllattiion aasssseemembmblliies. No accidentnts occurrrred during this project. · The coombmbinattiioonn of a considereded dedesiggnn andand consttrruucctition mmeethodohodology mmeeaeaannt a quickck, effificient construction. · OffOffsitite work also protectcted the eexxiststiinngg ststrucctture andand roooof ffrroomm sitite work related damage.dadamddamadamagammage.age.age.ge. · Thhee strengthenheninngg is fuullllly removovaabble and mamaintainable. · High ququaalliity sstteeeel products were achieevedved byby workksshhopop fababricattiionon anandd paintitinngg in ccoombommbbinatitionon with eexpexperienced conttrracactors witwiwith formamal quqquauaalllitity asssusssurance practtiices ((FE(FFEEGGLGL). · 40% cost redueductctiioonn ffrromom esttiimamates based on convenonventtiional connectitioonn methodology. · Funccttiional insnstallattiioonn ooccccurred at 3.5 workingng days for a total of 4T of structural sstteel ovveer a 100100mm ttrranssveverse long truss. Thheerefore contrtracaccttor risksk exexpoxposure titimmee was shorrt.t. · Subsesequenequenquent insnstallllation of the same syststemem on the opposing standandnd was fulllly inssttalllled bebetween engineer’s sitite visitits, albbeeiitt wiwitwith immpprovedoved accessss to thhee work stationonns.s.