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Wind

By June Ramirez,2014-09-22 13:00
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Wind

    Wind

    Vo1.18No.2JournalofSouthwestJiaotongUniversity(EnglishEdition)Apr.2010 ;ArticleID:10052429(2010)02-0112-06

    ;WindTunnelTestontheWind-ResistantBehaviorof

    ;aLong--SpanCable--StayedBridgeduringErection

    ;MACunming(马存明),LIAOHaili(廖海黎),TAOQi(陶奇)

    ;ResearchCentreforWindEngineering,So~hwestJiaotongUniversity,Chengdu610031.China ;Abstract

    ;InordertoinvestigatetheaerodynamicbehavioroftheSutongbridgeoverYangtzeRiverduringerection,

    a1:50sectional

    ;modelofthebridgedeck.al:100fullaeroelasticmodelofthefreestandingpylonanda1:125fullaeroelasti

    cmodelforthemaxilll

    ;cantileverconfigurationwerebuilt.Thetestresultsshowthattherewasnoseriousvortexinducedvibra

    tionatthebridgedeck.and

    ;thatthefreestandingtower.themodelscaleandtheturbulenceintensityinfluencedstaticloading.Thebuf

    fetingresponsesduring

    ;themaximumcantileverconfigurationdidnotaffectthesafetyofthebridgeunderconstruction.

    ;KeywordsCablestayedbridge;Erectionstage;Aerodynamicbehavior;Windtunneltest ;Introduction

    ;Long?spancable-stayedbridgesaresusceptibleto

    ;dynamicwindactions,andthustheiraerodynamic

    ;stabilityduringservicinganderectionhasrecentlyre

    ;ceivedconsiderableinterest.Thedesignwindspeed

    ;ofbridgesduringerectionissmallerthanthatafter

    ;bridgeconstruction.Thestiffnesslossofthebridges

    ;intheerectionphasereducesthetorsionalandvertical

    ;naturalfrequencies,andconsequently,theaerody

    ;namicstabilitylimit.Itiscommonlyacknowledged

    ;thaterectionstageisoftenlessfavorabletotheaero

    ;dynamicstabilityoflong-spancable--stayedbridges

    ;comparedtothecompletedstate.

    ;Todate,comprehensiveinvestigations[]have

    ;identifiedsomeimportantfactorsgoverningtheaero

    ;dynamicstabilityofsuspensionbridgesduring

    ;erection,includingdynamiccharacteristics,structural

    ;ReceivedNov.27,2009;revisionacceptedJan.22,2010

    ;FoundationitemsTheNafionalNaturalScienceFoundation

    ;ofChina(Nos.50808148and90815016)

    ;Correspondingauthor.Te1.:+86-28-87601843;Email:

    ;mcm@swjtu.edu.cn

;stiffnessanddamping,finitedecklength,erectionse

    ;quence,theprovisionofeccentricmassandartificial ;dampers,etc.Thewindresistantbehaviorofthesu

    ;perlongcablestayedbridgesduringerection,howev

    ;er,lacksthoroughinvestigation.

    ;Inthispaper,wepresentthemainresultsofwind ;tunneltestsONasectionalmodelandthefullaeroelastic ;modelsoftheSutongBridgeatthefreestandingpylon ;stageandthemaximumcantileverstage. ;1IntroductiontoSutongBridge

    ;TheSutongBridge,locatedatNantong,Jiangsu ;Province,China,istheworld’slongestcable—stayed

    ;bridgewithacenterspanof1088m.Initserec

    ;tionstage,thecantilevermethodwasusedandthe ;girderstretchedasmuchas540matmid?spanside ;beforetheclosingofthecenterspan(seeFig.1). ;Here,thewindresistantpropertiesofthebridge ;inerectionstageincludingvo~exinducedoscillation,

    ;flutter,buffeting,etc.,wereinvestigatedcomprehen

    ;sivelywithan1:50sectionalmodelofthebridge ;deck,an1:100fullaeroelasticmodeloffreestanding ;pylonandan1:125fullaeroelasticmodelforthe ;maximumcantileverstage.

    ;MACunmingeta1./WindTunnelTestontheWindResistantBehaviorofaLongSpanCableStayed...113

    ;

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    ;Nantong

    ;一誊.

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    ;:

    ;.,;

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    ;Fig.1GeneralviewofSutongBridgeunderconstmcfion(unit:cm)

    ;Thetestsofthebridgedecksectionmodelwere ;conductedintheXNJD.1windtunne1.Thefu11aero

    ;elasticmodelsforfreestandingpylonandthemaxi

    ;mumcantileverstageweretestedintheFL13tunne1.

    ;BothtunnelsarelocatedatChinaAerodynamicsRe ;searchandDevelopmentCene.

    ;2SectionalModel

;Ageometricalscaleof1:50waschosentosimu

    ;(a)

    ;latethedetailsofthegirder.andtoyieldthemaxi

    ;mumblockagelessthan4%.Generally.theblockage ;shouldbelessthan5%forthewindtunneltesting. ;Thelengthofthemode1Lis2.1m.thewidthB

    ;0.6mandthedepthH0.0585m.Theratioof

    ;lengthtowidthis3.5,greaterthan2.5,whichsaris- ;tiestheminimumrequirementE10.Fig.2showsthe

    ;modelinthewindtunne1.

    ;(b)

    ;Fig.2The1:50sectionalmodelinwindtunnel ;2.1Vortex.inducedvibration

    ;Theobjectiveofthevortexinducedvibrationtestis

    ;todeterminetheonsetwindspeedatwhichthevortexin-

    ;ducedvibrationaroundthedeckoccllrsduringerection. ;Table1summarizestheonsetwindspeedforvor- ;texinducedresonanceduringerection.InTable1.UF ;denotesuniformflowandTFturbulentflow.Whenthe ;,vindattackanglewas+3..torsionalvibrationwasob- ;served.Inothercases,novortexvibrationwasfound. ;Thevortex-inducedresponsevaryingwithwind ;speedfordifferentdampinglevelsanddifferentflow ;typesisshowninFig.3.Itwasfoundthatthestruc

    ;turaldampingcallmitigatethevortexresponse,and ;themaximumamplitudesofresponseswerelessthan ;thosedesignedinChinesecode[...Thissuggeststhat ;SutongBridgewasnotaffectedbyanyseriousvortex

    ;inducedvibrationduringerection.

    ;Table1Parametersandonsetwindspeedsm/s ;Note:Theverticalfrequencyis0.3759Hz;thetorsionalfie- ;quencyis0.9814Hz;/ft=2.61;theunitmassis37.86t/m;the ;rotationalinertiaperunitlengthis5338.41t?m./m;thealong.wind

    ;turbulenceintensityis0.055.

    ;建一?Tl_..,......?...000n

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    ;0.025

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    ;JournalofSouthwestJiaotongUniversity(EnglishEdition) ;01O2O3O40

    ;Windspeed/(m’S)

    ;(a)Uniformflow

;OlO2O3040

    ;Windspeed/(m?s-1)

    ;(b)Turbulenceflow

    ;Fig.3Tortionalvortex-inducedresponseduring ;themaximumcantilevererection

    ;2.2Staticforces

    ;Themeanstaticforces,reflectingthesteady ;windeffectsonbridgedecks,areusuallyexpressed ;bydimensionlessforcecoefficients.Thestaticwind ;forcesactingonabridgedecksectioncanbedefined ;inbodycoordinatesystem(xoy)orwindcoordinate ;system(oy)(seeFig.4).

    ;Inthewindcoordinatesystem,threeforcecoef- ;ficients(drag,rift,andmoment)aredefinedas: ;C.()=

    ;CL(O1)=

    ;2FD(O1)

    ;pU2HL’

    ;2FL()

    ;pUZBL’

    ;c)=

    ;whereOtistheattackangleoftheincomingflow;Uis ;thewindspeed;Pistheairdensity;FD(),FL(O/) ;andMz()aredrag,lift,andmomentonthedeck ;inthewindcoordinatesystem,respectively.Trans

    ;formingFH()andFv()inthebodycoordinate ;systemintoFD()andFL(),thedragcoefficient ;CH()andliftcoefficientCv()canbecalculated. ;Notethatthemomentcoefficientskeepunchangedfor ;thebothcoordinatesystem.

    ;Fig.4Definitionofwindloadingandcoordinatesystem ;Toinvestigatethepossibleeffectofwindcharac- ;teristics.b0ththeuniforillflowandturbulentflow ;weretested.ThedragcoefficientsCD,lifccoefficients ;CIandmomentcoefficientsCMvaryingwiththe ;attackanglesaregiveninFig.5,wherethecoeffi

    ;cientstestedinturbulentflowdiffermuchfromthose ;inuniforlTlflow.

    ;2.O

    ;1.5

    ;1.O

    ;0.5

    ;0.0

    ;

;0.5

    ;.

    ;1.0

    ;(a)Uniformflow

    ;-

    ;10.50

    ;Attackangleofwind

    ;(b)Turbulentflow

    ;Fig.5Forcescoeffici

    ;Ageometricalscale1:100waschosentosimu

    ;latetherequireddetailsandtoyieldablockageofless ;than1%.Thefullbridgemodelwasdesignedand ;manufacturedusingtheconventionalaeroelasticmodel ;technology.Thus,thestructuralstiffnesswasprovid

    ;edbyametalspineassembly:theexternalshapeby ;claddingelementsandmassbylumpingcomplimenta

    ;ryballastelementsinthecladdingstructure.Withthis ;technology,theexternalstructuraldisplacementswere ;measuredusingdisplacementoraccelerationtransduc

    ;ers,andsectionalforcesweremeasuredusingstrain ;gaugesattachedtothespinestructure. ;Twotypicalerectionstageswereselected:free ;standingpylon(CaseI)andfreestandingpylon ;withaMD3600crane(Case1/),asshownin ;Fig.6.ThemodelparametersarelistedinTable2. ;(a)CaseI

    ;(b)Case1/

    ;Fig.6Fullaeroelasficmodeloffreestand

    ;ingpylon

    ;Table2Parametersoffullaeroelasticmodelforfreestandingpylon

    ;Note:windspeedratiois1:6

    ;Fig.7showsthedynamicdisplacementsatdiffer

    ;entwindspeeds,whereyawanglevariesfrom0.to ;90.andthedamperratiois0.5%.Intests.vortex

    ;inducedvibrationswereidentifiedwhentheincoming ;flowwasalongbridge,yawanglewas0.andtheon- ;setwindspeedwas14.2rn/s.Therewasnoexplicit ;vortexinducedvibrationwhenyawanglesvariedfrom ;15.to90..IftheMD3600cranewasconsidered.the ;vibrationwasreduced.

    ;Fromthewindtunne1tests.theStrouhalnumber ;ofpyloniscalculated

    ;LD0.1498×(9to15)==

    ;l4.20.095to0.158,(2)

    ;where,visthevibrationfrequency;Disthewidthof ;thepyloncolumn(9isthewidthofupperpyloncol

    ;umnand15isthewidthoflowerpyloncolumn). ;ThisvalueisconsistentwiththeStrouhalnumberof ;thesquaresectioninRef.[2].Toinvestigatethe ;effectofwindturbulence,theturbulentwindfield ;wassimulatedwithspires,fencesandroughness ;cubes.Fig.8showsthemeanspeedprofileandturbu

    ;lentintensityprofile.Theturbulenceintensityinthe ;testwas50%ofthatrequiredinthecode~... ;Fig.9showstheeffectofthedamperratioand ;turbulenceintensity.Thevortexvibrationisstrongly ;affectedbythedamperratioandturbulenceintensity. ;4

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