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1、Chapter2Rectangularreinforcedconcretebeamsandslabs:Tensionsteelonly2-1introductionWhenabeamissubjectedtobendingmoments(alsotermedflexure),bendingstrainsareproduced.Underpositivemoment(asnormallydefined),compressivestrainsareproducedinthetopofthebeamandtensilestrainsareproducedinth
2、ebottom.Thesestrainsproducestressinthebeam,compressioninthetopandtensioninthebottom.Bendingmembersmustthereforebeabletoresistbothtensileandcompressivestress.Foraconcreteflexuralmember(beam,wall,slab,andsoon)tohaveanysignificantload-carryingcapacity,itsbasicinabilitytoresisttensile
3、stressesmustbeovercome.Byembeddingreinforcement(usuallysteelbars)inthetensionzones,wecreateareinforcedconcretemember.Whenproperlydesignedandconstructed,memberscomposedofthesematerialsperformveryadequatelywhensubjectedtoflexure.2-1introductionInitially,wewillconsidersimplysupported
4、single-spanbeamsthat,sincetheycarryonlypositivemoment,willbereinforcedwithsteelplacednearthebottomofthebeam.2-2methodsofanalysisanddesignInthebeamexampleinchapter1,weassumedbothastraight-linestraindistributionandstraight-linestressdistributionfromtheneutralaxistotheouterfibers.Thi
5、s,ineffect,statedthatstresswasproportionaltostrain.Thisanalysisissometimescalledelasticdesign.Eventhoughareinforcedconcretebeamwasknowntobeanonhomogeneousmember,formanyyearstheelasticbehaviorapproachwasconsideredtobevalidforconcretedesign,anditwasknownastheworkingstressdesign(WSD)
6、method.ThebasicassumptionsfortheWSDmethodwereasfollows:2-2methodsofanalysisanddesign(1)aplanesectionbeforebendingremainsaplanesectionafterbending;(2)hooke’slaw(stressisproportionaltostrain)appliestoboththesteelandconcrete;(3)thetensilestrengthofconcreteIszeroandthereinforcingsteel
7、Carriesallthetension;(4)thebondbetweentheconcreteandthesteelisperfect,sonoslipoccursBeforediscussingthestrengthdesignmethod,letusreviewthebehaviorofalongspanrectangularreinforcedconcretebeamastheloadonthebeamincreasesfromzerotothemagnitudethatwouldcausefailure.Atverysmallloads,ass
8、umingthattheconcretehasnotcracked
