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  • Adapting the FlexiArch for widening a complex arch bridge

    Long, A., Gupta, A., McPolin, D., & Cook, J. (2018). Adapting the FlexiArch for widening a complex arch bridge.Proceedings of ICE - Bridge Engineering, [1700007].

    Published in:Proceedings of ICE - Bridge Engineering

    Document Version:Peer reviewed version

    Queen's University Belfast - Research Portal:Link to publication record in Queen's University Belfast Research Portal

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    Download date:22. Aug. 2018

    https://pure.qub.ac.uk/portal/en/publications/adapting-the-flexiarch-for-widening-a-complex-arch-bridge(41e77a99-1037-4e93-aba8-46c2ab6a1516).html

  • ADAPTINGTHEFLEXIARCHFORWIDENINGACOMPLEXARCHBRIDGE

    AdrianLongOBE,FREngPhD,DSc,FICE,FIStructE,QueensUniversityBelfast,Belfast,UK

    AbheyGuptaBTech,MTech,MPhil,MacreteIrelandLtd,Toomebridge,UK

    DanielMcPolinBEng,MSc,PhD,QueensUniversityBelfast,UK

    JohnCookMEng,MSc,WSP,Bristol,UK

    Abstract

    The1840sTeewellHillarchbridge,inthesuburbsofBristol,wasnolongeradequateforincreasinglocaltrafficlevelsandneededtobewidened.Severalwideningoptionswereconsideredanditwasconcluded that the innovative FlexiArchwould best accommodate the complex geometry of theexistingstructurewhilstminimisingsocialandeconomicimpacts.Inordertoelegantlyaccommodatethe raked spandrelwallsof the existingbridgeMacrete andWSP |ParsonsBrinckerhoffworkedcollaborativelytoproduceacustomdesignedhighqualityprecastconcreteFlexiArchwhichmatchedthecontoursof theexistingbridge.As theFlexiArchsystemhasnocorrodible reinforcement, it ishighlysustainableandwillresultinreducedmaintenanceasfortheexistingbridge.Theeliminationofcentringandspeedofconstruction(hoursnotmonths)minimiseddisruptiontoroadtrafficandtocyclistsonthecyclenetworkbelowthebridgeakeyprojectcriterionrequiredbytheclient.Thus,inadditiontoaddressinganaccidentblackspot,theFlexiArchsolutionprovidedSouthGloucestershireCouncil(theclient)withanaestheticallypleasingandfullyfunctionalsolutionatacompetitivecost.

    Introduction

    TeewellHillarchbridge,locatedintheStapleHillareaofBristolandconstructedinthe1840srequiredwideninginordertoenhancethesafetyofroadtrafficusersandprovideanimprovedcarriagewayalignment.ThisaestheticallypleasingbridgecarriesabusyroadandspansaNationalCycleroute.AnassessmenthadconcludedthattheexistingmasonrybridgewasabletosustainSVloadingandasaresult, South Gloucestershire Council were keen that a widening scheme which retained anaestheticallypleasingarchformofconstructionwasdeveloped.However,traditionalmasonryarchesarenotoriouslyslowtobuildandthecentringwouldhaveresultedinclosureofthecycleroutebelowthebridgethroughoutthearchconstruction.

    The consultant,WSP | Parsons Brinckerhoffwho had previous experience of using the FlexiArchsystem suggested that it couldpossiblybeadapted toaddress thegeometrical constraintsof theexistingbridge.AtthisstageMacreteIreland,whomanufacturetheFlexiArch,wereconsulted.Themajorchallengeandoneofthekeydesignrequirementstobeaddressedwasthattherakedspandrelwallsandtheunsymmetricalgeometryofthebridgemeantthattheexistingarchvoussoirprofilewas

  • curvedinplan.UsingtheirexperiencegainedfromdevelopingaskewFlexiArchsystemMacrete,incollaborationwithWSP|ParsonsBrickerhoff,designedandmanufacturedcustommadeFlexiArchunits,witheachvoussoirindividuallytailoredtomatchthecontoursoftheexistingarchprofile.UseofthesecustomdesignedFlexiArchunitsresultedinmultiplebenefitsincludingaestheticqualitiesanddurabilitycharacteristicscommensuratewiththeexistingstructure.

    In this paper the background concept of the FlexiArch system will be briefly described beforeexplaining how itwas adapted to solve the particular challenge associatedwith thewidening ofTeewellHillbridge.

    BACKGROUNDTOFLEXIARCHSYSTEM

    Intheearly1990swhenGordonMillingtonwasVicePresidentoftheICEheaskedthefirstauthorthequestion,whyarefewifanyarchbridgesbeingbuiltastheyareaestheticallypleasing,strong,durableand require littlemaintenance?Asexplained ingreaterdetailbyLongetal (2013) thispromptedresearchwiththeaimofansweringthisperceptivequestion.Beamandslabandrigidprecastconcretearch bridges have been found to be vulnerable to reinforcement corrosion and some havedeterioratedafteronly2030years.InreactiontothistheUKHighwaysAgencyrecommendedtheuseofthearchformandalsostatedthatconsiderationbegiventoallmeansofreducingoreliminatingtheuseofcorrodiblereinforcement(HMSO2004).Thechallengethereforewastodevelopanarchsystemwithalltheattributesofanunreinforcedmasonryarchwhich:

    Canbeinstalledasquicklyasalternatives Eliminatestheneedforcentring Usesexistingmethodsofanalysis/design Iscostcompetitive Usesprecastconcreteandissuitableforoffsiteconstruction Hadnocorrodiblereinforcement

    ThepatentedFlexiArchsystem(Long2004)wasdevelopedinresponseandonlyabriefdescriptionofthisinnovativesystemwillbegivenhere,asthemainfocusofthispaperisontheapplicationtothewideningoftheTeewellBridge.

    MethodofManufacture

    TheFlexiArchisconstructedandtransportedtositeinflatpackformusingpolymericreinforcementtocarry the selfweightof thearchunitduring lifting.Once inplace itbehavesasaconventionalmasonryarch.ThepreferredmethodofconstructionofthearchunitisshowninFig1(moredetailinLongetal2013).Forthemanufactureofeacharchunitthetaperedvoussoirsareprecastindividuallythen they are laid contiguouslywith the top edge touching, in a horizontal linewith a layer ofpolymericreinforcementplacedontop.Insituscreed,approximately40mmthick, isplacedontopandallowedtohardensothatthevoussoirsareinterconnected.

  • TheFlexiArchunitscanbecastinconvenientwidthstosuitthedesignrequirements,siterestrictionsandavailablecranecapacity.Whenliftedatthedesignatedanchoragepointsgravityforcescausethewedge shaped gaps to close.Concretehinges form in the screed and the integrityof theunit isprovidedbytensioninthepolymericreinforcementandtheshearresistanceofthescreed.

    TheFlexiArchunitsarethenliftedandplaced,intheirarchedshapedform,onprecastfootingsatthebridgesitewithalltheselfweightthentransferredfromtensioninthepolymericreinforcementtocompressioninthevoussoirs,i.e.itactsinthesamewayasaconventionalmasonryarch.

    Experienceofusingthissystemforover60bridgeshasshownthatithasanumberofadvantagesovertraditionalmethodsofconstructingarches:

    Thevoussoirscanbeaccurately,quickly,andconsistentlyproducedwiththedesiredtaperinrelativelysimpleshuttering.

    Highqualityconcretecanbeutilisedfortheindividualprecastvoussoirs: Toenhancethedurabilityofthearchwhilstinservice. Togreatlyreducethevariability inthephysicalpropertiesnormallyassociatedwith

    naturalstonework.

    InstallationofFlexiArchUnits

    TheprimaryfunctionofthepolymericreinforcementistoprovidesufficienttensilestrengthsothattheFlexiArchunitscanbeliftedsafely;bothfromtheflatcastingbayontoaflatbedlorryandfromthelorryinitsdesignatedarchformintopositionontheprecastsillbeamsatthebridgesite.Greatcareneedstobetakenduringinstallationastypicallya1mwideFlexiArchunitfora15mspanbridgecanweighover10t.However,providedtherecommendedproceduresareadoptedithasbeenfoundthatatypicalunitcanbeaccuratelylocatedonsiteevery15minutes.Asaconsequencemostbridgescanbe installed inwellunder aday, thus affording the FlexiArch enormousbenefits relative toconventionalarchconstruction.

    TEEWELLHILLWIDENINGPROJECT

    TeewellHillmasonryarchbridge,withaspanof12.8mandariseof3m,carriesatwo lanesinglecarriagewayroadandhadanadjacentsteelfootbridgeonthewestsideofthestructure.

    ThebridgeisownedbySouthGloucestershireCouncilandhadbeenconstructedinthe1840sovertheBristolandBathrailwayline(nowadaysapopularcycleroute)inwhatisnowabusyresidentialarea.Thebridgehadbecomeanaccidentblackspotduetotheincreaseinthevolumeoftrafficusingthebridgeandtheinadequateroadalignment.

    AninspectionandassessmenthadshowntheexistingmasonryarchtobeinagoodconditionandabletosustainSV80loading,howeverthesteelpedestrianbridgewasinapoorconditionandrequiredextensivemaintenanceandrepair.

    Followingafeasibilitystudy,thepreferredoptiontowidentheexistingstructurewasbyplacingsixnew FlexiArches, three either side of the original masonry structure widening the bridge byapproximately 4m on each side. This enabled the road alignment improvements and two newpedestrianfootpathsoneithersideofthebridge.

  • TheFlexiArchsystemwaschosenoverotheroptionsasitprovidedanaestheticallypleasingsolution,its circular profilematched the existing form of the structure. Furthermore the units could betransportedtositeonflatbedtrucksandcranedintopositionrelativelyquickly,reducingdisruptiontothepublicandtheprefabricatednatureofthesystemreducedsitetemporaryworks.

    Conventionalmasonry arch extensions to each side, if feasible, would have been exceptionallyexpensive,takenmanymonthstoinstallandtheneedforcentringwouldhavesignificantlydisruptedtheNationalCycleRoute.

    Oneofthecrucialdesigncriteriawastoensureconstructionwouldaccommodatetherakedspandrelwallsoftheexistingmasonryarch.ThereforeMacreteandWSP|ParsonsBrinckerhoffdecided toexplorethepossibilityofdevelopingbespokeFlexi