受扭构件的扭曲截面承载力.ppt

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1、Chaper7Torsionalstrengthofmembers7.1Introduction7.2Experimentaboutpuretorsionmember7.3Torsionalcapacityofmembersunderpuretorsion7.4Torsionalcapacityofmemberundercombinedflexure,shearandtorsion7.7Detailingrequirements7.1IntroductionTwotypesoftorsionEquilibriumtorsion

2、(平衡扭矩)：staticallydeterminatetorsion;primarytorsionItisdeterminedbasedonstaticequilibrium,andnotrelatedtothetorsionalstiffness.Compatibilitytorsion(协调扭矩)：staticallyindeterminatetorsion;secondarytorsionItcannotbedeterminedbasedonstaticequilibriumalone,andrelatedtothet

3、orsionalstiffnessanddeformationofmembers.7.2Experimentofpuretorsion1.MechanicalanalysisofpuretorsionbeforecrackWhentheprinciplestressesexceedthetensilestrength,cracksformatthemiddlepointoflongersideandextenddiagonallyalong45°linetotheneighboringfaces.Finally,cracksa

4、respiralwhenconcreteinonesidecrushes.Spiralcracks2.TorsionalreinforcementsStirrupsLongitudinalbars2.FailuremodesoftorsionalmemberswithtorsionalreinformentsFailuremodesarecloserelatedtotheratioofreinforcements.scarce-reinforcedmemberTensionfailureUnder-reinforcedmemb

5、erBendingfailureUnder-reinforcedmember,scarce-reinforcedmember,Over-reinforcedmember,Over-reinforcedmemberWhenmemberisadequatelyreinforced,thereinforcementsyieldbeforeconcretecrushes.CalculationoftorsionalstrengthWhentorsionalreinforcementsareinadequate,membersfaila

6、ssoonascracksform.MinimumamountoftorsionalreinforcementsPartiallyover-reinforcedmemberOver-reinforcedmemberCompressionfailureWhentwotypesoftorsionalreinforcementsareexcessive,thereinforcementsdonotyieldbeforeconcretecrushes.Whenonetypeoftorsionalreinforcementsisexce

7、ssive,theexcessivereinforcementsdonotyieldbeforeconcretecrushes.ChecktheminimumdimensionofsectionControltheratiooflongitudinalbarstostirrups（）7.3Torsionalresistanceofmemberunderpuretorsion1、CrackingtorqueTcr45°F1F2F3F4PrinciplestressIfconcreteisidealplasticmaterial

8、,membercrackswhenprinciplestressesatallpointsofsectionexceedtensilestrength2、Torsionalcapacityofmemberwithtorsionalreinforcements(1)Mechan