如何在桩基设计规范中定量考虑施工检测的作用

XX大学,XX年XX月XX日

Constructioncontrolandsafetyofpilefoundations

如何在桩基设计规范中定量考虑施工检测的作用

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xx大学土木与环境工程系1HKUSTContentsIntegratedesignandconstructionqualityassuranceProposeaproceduretoinvestigatetheeffectofconstructioncontrolonthesafetyofdrivenpilesProvidetheoreticalbasistoderivefactorsusedtoconsidertheeffectofconstructioncontrolindesigncodes2HKUSTConstructioncontroltestsoranalysesManytypesofconstructioncontroltestsoranalysesareroutinelycarriedoutasameanstocopewithuncertaintiesFinalsettestsDynamictestsusingpiledrivinganalyzers(PDA)WaveequationanalyseswithmeasurementsBlowcountanddrivingenergymonitoringStaticloadingtests3HKUST4HKUSTPDAtest5HKUSTExample:aseven-stepprocessforselectingdrivingcriteria

(Belletal.2002)1

Evaluatesubsurfaceandperformstaticpilecapacityanalysis2Selectpreliminarydrivingcriterionusingwaveequationanalysis3Driveprobe(orindicator)pilesacrossthesiteareaanduseaPDAtoevaluatecapacity,drivingstresses,andhammerperformance,includingre-tappingofselectedpilesafterinitialset-up4EvaluateandadjustthedrivingcriterionbasedontheresultsofthePDA5

Drivestatictestpile(s)usingthereviseddrivingcriterion6

Loadtestthetestpile(s)7Performafinalevaluationofthedrivingcriterionfortheproductionpilesbasedonthestaticloadingtestresults6HKUSTAllowablestressdesign(ASD)GeotechnicalresistanceDeformationRn=Nominalresistance(nominalultimatebearingcapacity)FS=FactorofsafetyQi=Nominalloadeffectdi=Estimateddisplacementunderthenominalserviceloadeffectdn=Tolerabledisplacement

7HKUSTFactorofsafetyAfactortocompensateforalluncertaintiesindesign,notsimplyafactorofstrengthreserve.Allfoundationmayfail!Theproblemishowlikely.FOSdependson:

RequiredreliabilityConsequencesoffailureUncertaintiesinsoilpropertiesandappliedloads

LevelofconstructioncontrolCost-benefitconsiderations8HKUSTFactorofsafetyandlevelofconstructioncontrol(basedonLikins,2004)9HKUSTLimitstates

Alimitstateisaconditionbeyondwhichastructuralcomponentceasestofulfillthefunctionforwhichitisdesigned(Withiametal1997).Strengthlimitstates(ultimatelimitstates)GeotechnicalresistanceStructuralresistanceServicelimitstates(functionofstructureunderexpectedserviceloads)Deformations,vibration,cracking,localdamage,deterioration(durability)10HKUSTSomeultimatelimitstatesforfoundations11HKUSTProbabilitydensityfunctionfQ,fRQ,R_Q_RAreaprobabilityoffailureLoadeffectQResistanceRProbabilityoffailure,pf=P(R<Q)ConceptofreliabilitybaseddesignMeanFS=/NominalFS=Rn/Sn_R_QQnRn12HKUSTLimitstatedesignUltimatelimitstates(MOC2002)Tobecheckedindesignofalltypesofstructures&loadcombinationsServiceabilitylimitstatesTobecheckedonlyforimportantordifficultfoundations13HKUSTGeotechnicalresistance:Servicelimitstate:(sameasASD)Rn=Nominalresistancef=Resistancefactor,asafunctionoflevelofconstructioncontrolQi=Loadeffectgi=Loadfactor,definedinsuperstructuredesign=Factortoaccountforeffectsofductility,redundancyandoperationalimportance,>0.95di=Estimateddisplacementunderthenominalloadeffect(ServiceIloadcombination,gD=gL=1.0)dn=TolerabledisplacementLoadandresistancefactordesign(AASHTO)14HKUSTTargetreliabilityindex(MOC2001)UltimatelimitstatesFailuretypeGeotechnicalcategoryCategoryICategoryIICategoryIIIDuctilefailureBrittlefailureServiceabilitylimitstatesbT=0ifthedisplacements,cracks,localdamagesetc.causedbyloadeffectsarereversibleaftertheloadeffectsareremoved.bT=1.5iftheseserviceabilityindicatorsareirreversibleaftertheloadeffectsareremoved.15HKUSTResistancefactorsforgeotechnicalstrengthlimitstateofaxiallyloadedsinglepiles(fromAASHTO1998)16HKUSTValuesoflvforvariousmethodsofpileconstructioncontrol(fromAASHTO1998)17HKUSTReliabilitymethodtoconsidereffectofconstructioncontrolEstimateempiricalstatisticsofadesignmethodReducethevariabilityofthedesignmethodgiventheoutcomeofacontroltestoraseriesofcontroltestsObtainnewstatisticsofthedesignmethodObtainnewpartialfactors/resistancefactorstoachievetargetreliability18HKUSTUncertaintyofdesignmethods19HKUSTBiasfactorandcoefficientofvariationforvariousdesignmethods*Note:20HKUSTWhathappensiftestpilespasscontroltests?–Bayesianregressionanalysisx=measuredpilecapacity/predictedpilecapacityxfollowsalognormaldistributionEmpiricalstatisticalvaluesofxmeanmstandarddeviationsTakethemeanmasavariableApilepassesnconsecutiveconstructiontestsatx=xT,thentheprobabilitythatallofthentestpilesdonotfailatxTis(Zhang,2004)isThedistributionofxisthenupdatedUpdatedstatisticsforx:largermandsmallers21HKUSTExample:DesignbasedonaSPTmethod(Meyerhof1976)andverifiedbyprooftestsattwicethedesignloadlR=1.30COVR=0.5022HKUSTExample:Updatedbiasfactorandcoefficientofvariationasfunctionofpilecapacity23HKUSTCalculatingresistancefactorbasedonupdatedpilecapacitystatisticsCOVR,COVQD,andCOVQL=coefficientsofvariationofresistanceR,deadloadQD,andliveloadQL,respectively;lR,lQD,andlQL=biasfactorsofresistance,deadload,andliveload,respectively;DandL=loadfactorsfordeadloadandliveload,respectively;bT=targetreliabilityindex24HKUSTEffectofconstructioncontrolonsafetyfactorRequiredfactorofsafetyafterverificationbydifferentlevelsofconstructioncontrolatbT=2.025HKUSTRequiredfactorofsafetyafterverificationbydifferentlevelsofconstructioncontrolatbT=2.5Effectofconstructioncontrolonsafetyfactor26HKUSTTherequiredFScanbesubstantiallyreducedthroughcarefulconstructioncontrol.TherequiredFScanbereducedfrom3.50forthestaticanalysismethodbasedontheSPTto1.42atbT=2.0,andto1.80atbT=2.5forthesameanalysisthatisverifiedwithtwoCAPWAPanalysesplustwostaticloadingtests.TherequiredFSdecreaseswiththelevelofconstructioncontrol.Forinstance,usingtheSPTmethod,therequiredFSstoreachbT=2.5are2.24,2.03and1.80,respectivelyafterverificationbytwoPDAtests,twostaticloadingtests,andtwoPDAtestsplustwostaticloadingtests.TherequiredFSsfordifferentdesignmethodstoreachtherequiredtargetreliabilityaredifferentbecauseeachmethodisassociatedwithdifferentbiasandCOV.ThusitisnotreasonabletospecifythesameFSfordifferentdesignmethodsifthesedesignmethodsarenotsufficientlyverifiedbycontroltesting.Afterverifiedbysufficientconstructioncontroltesting,therequiredFSsfordifferentdesignmethodsarenotsensitivetotheaccuracyoftheindividualmethods.Forexample,therequiredFSsforthefivedesignmethodsafterverificationbytwoPDAtestsplustwostaticloadingtestsfallintonarrowranges1.44-1.55and1.80-1.88.27HKUSTEffectofconstructioncontrolonresistancefactorRequiredresistancefactorafterverificationbydifferentlevelsofconstructioncontrolatbT=2.528HKUSTTherequiredfincreaseswiththelevelofconstructioncontrol.ForthedesignbasedontheSPTmethod,therequiredfafterverificationbytwoPDAtestsonly,twostaticloadingtestsonly,andtwoPDAtestsplustwostaticloadingtestsare0.61,0.69,and0.75,respectively.Aftersatisfyingsufficientconstructioncontroltestsoranalyses,therequiredfvaluesforthefivedesignmethodsarenotsensitivetotheaccuracyoftheindividualmethods.Forinstance,afterverificationbytwoPDAtestsplustwostaticloadingtests,therequiredfvaluesforthesedesignmethodsfallintoanarrowrange0.72-0.75.29HKUSTValuesoflvafterverificationbydifferentlevelsofconstructioncontrolatbT=2.5Note:TakethosewithCAPWAP+Loadtestas1.0030HKUSTRequiredfactorofsafetyafterverificationbydifferentconstructioncontrolmeasures31HKUSTAsexpected,therequiredFSdecreaseswiththenumberofcontroltestsoranalyses,particularlybythefirstfewtestsoranalyses.Aftersatisfyingasufficientnumberofcontroltestsoranalyses,therequiredFSvaluesforallthefivedesignmethodsappeartobesimilar.Thisindicatesthatthesafetylevelofadesignverifiedbysufficientconstructioncontrolislessinfluencedbytheaccuracyoftheoriginaldesignmethodused.32HKUSTRequiredfactorofsafetyafterverificationbymultipleconstructioncontrolmeasuresAcosteffectiveplanforconstructioncontrolcanbemadebasedontheanalysis.Combinedstatic&dynamictests?33HKUSTConclusionsDesign