lecture3混凝土结构设计原理-英文课件.ppt

lecture3混凝土结构设计原理-英文课件.ppt

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Lecture3-FundamentalsJune6,2003CVEN444LectureGoalsConcretePropertiesSteelPropertiesConcreteMixingandProportioningQualityWorkabilityEconomicalInthedesignofconcretemixes,threeprincipalrequirementsforconcreteareofimportance:

ConcreteMixingandProportioningQualityofconcreteismeasuredbyitsstrengthanddurability.Theprincipalfactorsaffectingthestrengthofconcrete,assumingasoundaggregates,W/Cratio,andtheextenttowhichhydrationhasprogressed.Durabilityofconcreteistheabilityoftheconcretetoresistdisintegrationduetofreezingandthawingandchemicalattack.ConcreteMixingandProportioningWorkabilityofconcretemaybedefinedasacompositecharacteristicindicativeoftheeasewithwhichthemassofplasticmaterialmaydepositedinitsfinalplacewithoutsegregationduringplacement,anditsabilitytoconformtofineformingdetail.ConcreteMixingandProportioningEconomicaltakesintoaccounteffectiveuseofmaterials,effectiveoperation,andeaseofhandling.Thecostofproducinggoodqualityconcreteisanimportantconsiderationintheoverallcostoftheconstructionproject.ConcreteMixingandProportioningTheinfluenceofingredientsonpropertiesofconcrete.ConcreteMixingandProportioning3.WorkabilitynWorkabilitymeasuredbyslumptest1.Layer1:

Fill1/3full.25stokes2.Layer2:

Fill2/3full.25stokes3.Layer3:

Fillfull.25stokes4.Liftconeandmeasureslump（typically2-6in.）123412”slumpConcreteMixingandProportioningSlumptest-Themeasurementoftheconsistencyofthemixisdonewiththeslump-conetest.Therecommendconsistencyforvariousclassesofconcretestructures.ConcreteMixingandProportioning4.AdmixturesnApplications:

wImproveworkabilitywAccelerateorretardsettingandhardeningwAidincuringwImprovedurabilityConcreteMixingandProportioning4.AdmixturesnAir-Entrainment:

AddairvoidswithbubbleswHelpwithfreeze/thawcycles,workability,etc.wDecreasesdensity:

reducesstrength,butalsodecreasesW/CnSuperplasticizers:

increaseworkabilitybychemicallyreleasingwaterfromfineaggregates.ConcreteMixingandProportioning5.TypesofCementnTypeI:

GeneralPurposenTypeII:

LowerheatofhydrationthanTypeInTypeIII:

HighEarlyStrengthwHigherheatofhydrationquickerstrength（7daysvs.28daysforTypeI）ConcreteMixingandProportioning5.TypesofCementnTypeIV:

LowHeatofHydrationwGraduallyheatsup,lessdistortion（massivestructures）.nTypeV:

SulfateResistingwForfootings,basements,sewers,etc.exposedtosoilswithsulfates.ConcreteMixingandProportioningFailureMechanismofConcreteShrinkageMicrocracksaretheinitialshrinkagecracksduetocarbonationshrinkage,hydrationshrinkage,anddryingshrinkage.ConcreteMixingandProportioningFailureMechanismofConcreteBondMicrocracksareextensionsofshrinkagemicrocracks,asthecompressionstressfieldincreases,theshrinkagemicrocrackswidenbutdonotpropagatesintothematrix.Occurat15-20%ultimatestrengthofconcrete.ConcreteMixingandProportioningFailureMechanismofConcreteMatrixMicrocracks-aremicrocracksthatoccurinthematrix.Thepropagatefrom20%fc.Occurupto30-45%ultimatestrengthofconcrete.Matrixmicrocracksstartbridgeoneanotherat75%.Aggregatemicrocracksoccurjustbeforefailure（90%）.ConcreteProperties1.UniaxialStressversusStrainBehaviorinCompressioncEcou0.45fcfcfc12”6”ConcretePropertiesThestandardstrengthtestgenerallyusesacylindricalsample.Itistestedafter28daystotestforstrength,fc.TheconcretewillcontinuetohardenwithtimeandforanormalPortlandcementwillincreasewithtimeasfollows:

ConcretePropertiesnCompressiveStrength,fcwNormallyuse28-daystrengthfordesignstrengthnPoissonsRatio,nwn0.15to0.20wUsuallyusen=0.17cEcou0.45fcfcfcConcretePropertiesnModulusofElasticity,EcwCorrespondstosecantmodulusat0.45fcwACI318-02（Sec.8.5.1）:

wherew=unitweight（pcf）90pcfwc155pcfFornormalweightconcrete（wc145pcf）ConcretePropertiesComputeEcforfc=4500psifornormalweight（145pcf）concreteusingbothACIequations:

ConcretePropertiesnConcretestrainatpressivestress,owFortypicalcurvesincompressionwovariesbetween0.0015-0.003wFornormalstrengthconcrete,o0.002Ecou0.45fcfcfcConcretePropertiesnMaximumuseablestrain,uwACICode:

u=0.003wUsedforflexuralandaxialcompressionEcou0.45fcfcfcConcretePropertiesTypicalConcreteStress-StrainCurvesinCompressionConcretePropertiesTypesofcompressionfailureTherearethreemodesoffailure.aUnderaxialcompressionconcretefailsinshear.btheseparationofthespecimenintocolumnarpiecesbywhatisknownassplittingorcolumnarfracture.cCombinationofshearandsplittingfailure.ConcreteProperties2.TensileStrengthnTensilestrength8%to15%offcnModulusofRupture,frwFordeflectioncalculations,use:

nTest:

ACIEq.9-10PfrMmax=P/2*aunreinforcedconcretebeamConcreteProperties2.TensileStrength（cont.）nSplittingTensileStrength,