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

《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》由會(huì)員上傳分享，免費(fèi)在線(xiàn)閱讀，更多相關(guān)內(nèi)容在行業(yè)資料-天天文庫(kù)。

Chapter8DuctilityanddurabilityandcheckofcrackanddeflectionDurabilityserviceabilitySafetyServiceabilitylimitstatedeformationCrackwidthDetailingrequirementsFunctionalrequirementsofstructureUltimatelimitstateStrengthdesignofmembers 8.1Checkofdeflectionofreinforced-concreteflexuralmembersFlexuralstiffness-bendingmomentneededforunitcurvatureofsection.Itshowstheabilityofsectionagainstdeflection.8.1.1Conceptofflexuralstiffnessofsection Whenthematerialishomogeneous,thestiffnessofsectionisconstant.Curvatureislineartothebendingmoment.M?Featureofstiffnessofsection MyMuMcrEcI0M?StageⅠStageⅡStageⅢReinforcedconcreteisnothomogeneous,sothestiffnessofsectionchangeswiththeincreaseinbendingmoment.Featureofstiffnessofsection 1、Curvatureofsection8.1.2Short-timestiffnessofflexuralmemberBs 2、StrainofsteelandconcreteatthecrackedsectionCompressiveareaofconcreteStrainatcrackedsection 3、Averagestrain4、Expressionforshort-timestiffnessStiffnessformula 5.Expressionofparameters(1).Leverarmcoefficient(3) 8.1.3FlexuralstiffnessofcrosssectioninflexuralmemberStiffnesswilldecreaseundersustainedloadCreepofconcreteSlipbetweenconcreteandsteelStiffnessformulaStrainofconcreteatcrackedsectionincreasesStrainofsteelatcrackedsectionincreases 8.1.4Principleofminimumstiffnessandcomputationofdeflection1.PrincipleofminimumstiffnessAlongthelengthofspaninsimplebeam,deflectioniscomputedapplyingthestiffnessatthemaximum-momentsection(maximumstiffness),basedonmechanicalformulanotconsideringthesheardeformation(在簡(jiǎn)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(lái)計(jì)算撓度。)2.Computationofdeflection3.DiscussionHowtocontrolthedeflection 8.2CrackcontrolofreinforcedconcretememberCausesofcracksandtheircontrolCrackscausedbyloadsOthercracksTensileforceBendingmomentshearTorqueVerticalanddiagonalcracksMaincauses 8.2.1mechanismofcrackingDevelopmentlength1.OccurrenceofcrackingDevelopmentlength 2、Numberofcracksisstable（裂縫出齊）IfthedevelopmentlengthisL，themaximumspacingbetweencracksis2L，andtheminimumspacingL，averagespacingLm＝1.5L 8.2.2AveragespacingbetweencracksLmisrelatedtothediameterofsteelbar,effectivereinforcementratioandtheconcretecover 8.2.3Averagecrackwidth ChineseCode:8.2.4maximumcrackwidthSustainedloadeffectRandomicityofcracks 8.3Ductilityofsectionforreinforcedconcretemember8.3.1conceptofductility1、Definition：Thedeformationabilityofsectionthroughoutitsyieldingtoreachingultimateload2、Functionofductility：AbsorbandconsumeseismicenergyAvoidsuddenfailurewithoutwarningAdjustthestructuraldeformationmakingitaccommodatedtothedifferentsettlementandthermaldeformation.Achievethefullredistributionofinternalforce. 8.3.2DuctilitycoefficientofsectioncurvatureinflexuralmemberDuctilitycoefficientofsectioncurvature FactorsaffectingtheductilityofsectionUltimatecompressivestrainofconcrete、yieldstrengthofreinforcement、strengthofconcrete、reinforcementratio。Ductilityincreaseswiththeincreasein?cuandareaofcompressivereinforcements.Ductilitydecreaseswiththeincreaseinareaoftensilereinforcements. 8.3.3Ductilityofsectioncurvatureineccentriccompressionmember1.FailuremodeofeccentriccompressionmemberSmalleccentriccompressionfailureBrittleLargeeccentriccompressionfailureDuctileAxialforceratioAvoidsmalleccentriccompressionfailure2.Axialforceratio 8.4Durabilityofconcretestructure8.4.1generalconceptsofdurabilityDefinitionThestructurecanmeettherequirementsofserviceandsafetythroughoutitslifetimewithoutmajorrepairundernormalmaintenance.FactorsaffectingdurabilityInternalfactorsexternalfactorsStrengthofconcrete,water-cementratio,chemicalgradientcontentEnvironmentalconditionsConcretecarbonationandsteelcorrosion Short-termstiffnessBs