第8章鋼筋混凝土構(gòu)件的變形裂縫及混凝土結(jié)構(gòu)的耐久性

會計(jì)學(xué)1第8章鋼筋混凝土構(gòu)件的變形裂縫及混凝土結(jié)構(gòu)的耐久性Whenthematerialishomogeneous,thestiffnessofsectionisconstant.Curvatureislineartothebendingmoment.MFeatureofstiffnessofsection第1頁/共21頁MyMuMcrEcI0MStageⅠStageⅡStageⅢReinforcedconcreteisnothomogeneous,sothestiffnessofsectionchangeswiththeincreaseinbendingmoment.Featureofstiffnessofsection第2頁/共21頁1、Curvatureofsection8.1.2Short-timestiffnessofflexuralmemberBs第3頁/共21頁2、Strainofsteelandconcreteatthecrackedsection

CompressiveareaofconcreteStrainatcrackedsection第4頁/共21頁3、Averagestrain4、Expressionforshort-timestiffnessStiffnessformula第5頁/共21頁5.Expressionofparameters(1).Leverarmcoefficient(3)第6頁/共21頁8.1.3FlexuralstiffnessofcrosssectioninflexuralmemberStiffnesswilldecreaseundersustainedloadCreepofconcreteSlipbetweenconcreteandsteelStiffnessformulaStrainofconcreteatcrackedsectionincreasesStrainofsteelatcrackedsectionincreases第7頁/共21頁8.1.4Principleofminimumstiffnessandcomputationofdeflection1.PrincipleofminimumstiffnessAlongthelengthofspaninsimplebeam,deflectioniscomputedapplyingthestiffnessatthemaximum-momentsection(maximumstiffness),basedonmechanicalformulanotconsideringthesheardeformation(在簡支梁全跨范圍內(nèi)，按彎矩最大處的截面彎曲剛度，即最小的截面彎曲剛度，用材料力學(xué)方法中不考慮剪切變形影響的公式來計(jì)算撓度。)2.Computationofdeflection3.DiscussionHowtocontrolthedeflection第8頁/共21頁8.2CrackcontrolofreinforcedconcretememberCausesofcracksandtheircontrolCrackscausedbyloadsOthercracksTensileforceBendingmomentshearTorqueVerticalanddiagonalcracksMaincauses第9頁/共21頁8.2.1mechanismofcrackingDevelopmentlength1.OccurrenceofcrackingDevelopmentlength第10頁/共21頁2、Numberofcracksisstable（裂縫出齊）IfthedevelopmentlengthisL，themaximumspacingbetweencracksis2L，andtheminimumspacingL，averagespacingLm＝1.5L第11頁/共21頁8.2.2AveragespacingbetweencracksLmisrelatedtothediameterofsteelbar,effectivereinforcementratioandtheconcretecover第12頁/共21頁8.2.3Averagecrackwidth第13頁/共21頁ChineseCode:8.2.4maximumcrackwidthSustainedloadeffectRandomicityofcracks第14頁/共21頁8.3Ductilityofsectionforreinforcedconcretemember8.3.1conceptofductility1、Definition：Thedeformationabilityofsectionthroughoutitsyieldingtoreachingultimateload2、Functionofductility：AbsorbandconsumeseismicenergyAvoidsuddenfailurewithoutwarningAdjustthestructuraldeformationmakingitaccommodatedtothedifferentsettlementandthermaldeformation.Achievethefullredistributionofinternalforce.第15頁/共21頁8.3.2DuctilitycoefficientofsectioncurvatureinflexuralmemberDuctilitycoefficientofsectioncurvature第16頁/共21頁FactorsaffectingtheductilityofsectionUltimatecompressivestrainofconcrete、yieldstrengthofreinforcement、strengthofconcrete、reinforcementratio。Ductilityincreaseswiththeincreaseincuandareaofcompressivereinforcements.Ductilitydecreaseswiththeincreaseinareaoftensilereinforcements.第17頁/共21頁8.3.3Ductilityofsectioncurvatureineccentriccompressionmember1.FailuremodeofeccentriccompressionmemberSmalleccentriccompressionfailureBrittleLargeeccentriccompressionfailureDuctileAxialforceratioAvoidsmalleccentriccompressionfailure2.Axialforceratio第18頁/共21頁8.4Durabilityofconcretestructure8.4.1generalconceptsofdurabilityDefinitionThestructurecanmeettherequirementsofserviceandsafetythroughoutitslifetimewithoutmajorrepairundernormalmaintenance.FactorsaffectingdurabilityInternalfactorse