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在线教务辅导网HTTP/WWWSHANGFUWANGCOM更多课程配套课件资源请访问在线教务辅导网41FLEXURALBEHAVIOROFREINFORCECONCRETEBEAMRC受弯构件正截面性能2018/1/102NPLAINCONCRETEBEAMAREINEFFECTIVEASFLEXURALMEMBERSBECAUSETHETENSILESTRENGTHINBENDINGISASMALLFRACTIONOFTHECOMPRESSIVESTRENGTHNASACONSEQUENCE,SUCHBEAMSFAILONTHETENSIONSIDEATLOWLOADSLONGBEFORETHESTRENGTHOFTHECONCRETEONTHECOMPRESSIONHASBEENFULLYUTILIZEDNREINFORCEDCONCRETEBEAMSTEELREINFORCINGBARSAREPLACEDONTHETENSIONSIDEASCLOSETOTHEEXTREMETENSIONFIBERNINSUCHAREINFORCEDCONCRETEBEAM,THETENSIONCAUSEDBYTHEBENDINGMOMENTISCHIEFLYRESISTEDBYSTEELREINFORCEMENT,WHILECONCRETEALONEISUSUALLYCAPABLEOFRESISTINGTHECORRESPONDINGCOMPRESSIONREINFORCEDCONCRETEBEAMUNDERLOADREINFORCEMENTPLACEMENTINCONTINUOUSBEAMSORSLABSNSUCHJOINTACTIONOFTHETWOMATERIALSISASSURED,IFRELATIVESLIPISPREVENTEDNTHISISACHIEVEDBYUSINGDEFORMEDBARSWITHTHEIRHIGHBONDSTRENGTHATTHESTEELCONCRETEINTERFACE,AND,IFNECESSARY,BYSPECIALANCHORAGEOFTHEENDSOFTHEBARSDEFORMEDBARSANCHORAGEDEFORMEDBARRIBRELATIVESLIPBETWEENCONCRETEANDSTEELISPREVENTEDBYUSINGDEFORMEDBARSWITHTHEIRHIGHBONDSTRENGTHATTHESTEELCONCRETEINTERFACENTHREETYPESOFREINFORCEDCONCRETEBEAMSASINGLYREINFORCEDRECTANGULARBEAMS单筋梁BDOUBLYREINFORCEDRECTANGULARBEAMS双筋梁CSINGLYORDOUBLYREINFORCEDTBEAMST形梁NTHEREINFORCEMENTRATIOARATIOOFAREASOFSTEELANDCONCRETEREPRESENTTHERELATIVEAMOUNTOFTENSIONREINFORCEMENTINABEAMH0BASREINFORCEDCONCRETEBEHAVIORMODERATEREINFORCEDBEHAVIOR适筋适筋OVERREINFORCEDBEHAVIOR超筋超筋LIGHTLYREINFORCEDBEHAVIOR少筋少筋MODERATEREINFORCEDBEHAVIOR适筋NWHENTHERELATIVELYMODERATEAMOUNTOFREINFORCEMENTAREEMPLOYED,ATSOMEVALUEOFTHELOADTHESTEELWILLREACHITSYIELDPOINTFUFYOYIELDPOINTCRUSHINGOFTHECONCRETEENSUESATALOADONLYSLIGHTLYLARGERTHANTHATWHICHCAUSEDTHESTEELTOYIELDTHETHREESTAGESOFTHEBEAMSTEELYIELDCONCRETECRUSHTHEEXTERNALLOADPCAUSETHEBOTTOMFIBERSTOEQUALTOTENSILESTRENGTHOFTHECONCRETETHETENSILESTRENGTHOFTHECONCRETEEXCEEDSFTANDCRACKSDEVELOPCONCRETELOSESTENSILESTRENGTHANDSTEELSTARTSWORKINGEFFECTIVELYANDRESISTSTHEENTIRETENSILELOADTHEREINFORCEMENTYIELDSFAILUREOFTHEBEAMNATTHATSTRESSYIELDPOINT,THEREINFORCEMENTYIELDSSUDDENLYANDSTRETCHESALARGEAMOUNTANDTHETENSIONCRACKSINTHECONCRETEWIDENVISIBLYANDPROPAGATEUPWARD,WITHSIMULTANEOUSSIGNIFICANTDEFLECTIONOFTHEBEAMWHENTHISHAPPENS,THESTRAININTHEREMAININGCOMPRESSIONZONEOFTHECONCRETEINCREASESTOSUCHADEGREETHATCRUSHINGOFTHECONCRETEENSUESAT跟着发生ALOADONLYSLIGHTLYLARGERTHANTHATWHICHCAUSEDTHESTEELTOYIELDTASFSCCU0003CRUSHINGFUFYOSTRETCHESALARGEAMOUNTCRUSHINGOFTHECONCRETENEFFECTIVELY,THEREFORE,ATTAINMENTOFTHEYIELDPOINTINTHESTEELDETERMINATESTHECARRYINGCAPACITYOFMODERATELYREINFORCEDBEAMNSUCHYIELDFAILUREISGRADUALANDISPRECEDEDBYVISIBLESIGNOFDISTRESS恶化,损坏,SUCHASTHEWIDENINGANDLENGTHENINGOFCRACKSANDTHEMARKEDINCREASEINDEFLECTIONOVERREINFORCEDBEHAVIORNCONCRETEFAILSBEFORETHEYIELDOFSTEELDUETOTHEPRESENCEOFAHIGHPERCENTAGEOFSTEELINTHESECTIONONTHEOTHERHAND,IFLARGEAMOUNTSOFREINFORCEMENTORNORMALAMOUNTSOFSTEELOFVERYHIGHSTRENGTHAREEMPLOYED,THECOMPRESSIVESTRENGTHOFTHECONCRETEMAYBEEXHAUSTEDBEFORETHESTEELSTARTSYIELDINGOVERREINFORCEDBEHAVIORNCONCRETEFAILSBYCRUSHINGWHENSTRAINSBECOMESOLARGETHATTHEYDISRUPTTHEINTEGRITYIN5TERITI完整性OFTHECONCRETENCOMPRESSIVEFAILURETHROUGHCRUSHINGOFTHECONCRETEISSUDDEN,OFANALMOSTEXPLOSIVENATURE,ANDOCCURSWITHOUTWARNINGFUFYOSTEELDOSENOTYIELDCRUSHINGOFTHECONCRETENFORTHISREASON,ITISGOODPRACTICETODIMENSIONBEAMSINSUCHAMANNERTHATSHOULDTHEYBEOVERLOADED,FAILUREWOULDBEINITIATEDBYYIELDINGOFTHESTEELRATHERTHANBYCRUSHINGOFTHECONCRETELIGHTLYREINFORCEDBEHAVIORNFLEXURALSTRENGTHOFTHECRACKEDSECTIONISLESSTHANTHEMOMENTTHATPRODUCEDCRACKINGOFTHEPREVIOUSLYUNCRACKEDSECTIONNBEAMFAILSIMMEDIATELYANDWITHOUTWARNINGOFDISTRESSUPON紧接着FORMATIONOFTHEFIRSTFLEXURALCRACKLIGHTLYREINFORCEDBEHAVIORNTOENSUREAGAINSTTHISTYPEOFFAILURE,ALOWERLIMITCANBEESTABLISHEDFORTHEREINFORCEMENTRATIOBYEQUATINGTHECRACKINGMOMENT,COMPUTEDFROMTHECORRESPONDINGPLAINCONCRETEBEAM,TOTHESTRENGTHOFTHECRACKEDSECTION钢筋混凝土梁的MY素混凝土梁的受弯承载力MCRDESIGNOFREINFORCEDCONCRETEBEAMSTRENGTHDESIGNOFRECTANGULARBEAMWITHTENSIONREINFORCEMENTONLYSINGLYREINFORCEDBEAMNBASICASSUMPTIONS1SECTIONSPERPENDICULARTOTHEAXISOFBENDINGTHATAREPLANEBEFOREBENDINGREMAINPLANEAFTERBENDING平截面假定THISASSUMPTIONENSURESTHATTHECROSSSECTIONOFTHEMEMBERDOESNOTWARPWCP使翘曲DUETOTHELOADSAPPLIEDITFURTHERMEANSTHATTHESTRAINATANYPOINTONTHECROSSSECTIONISDIRECTLYPROPORTIONALTOITSDISTANCEFROMTHENEUTRALAXISNSTRAINATANYPOINTONTHECROSSSECTIONISDIRECTLYPROPORTIONALTOITSDISTANCEFROMTHENEUTRALAXISBASICASSUMPTIONSN2APERFECT5PEFIKTBONDEXISTSBETWEENTHEREINFORCEMENTANDTHECONCRETESUCHTHATTHESTRAININTHEREINFORCEMENTISEQUALTOTHESTRAININTHECONCRETEATTHESAMELEVEL钢筋的应变和相同位置处混凝土的应变相同假定混凝土与钢筋之间粘结可靠N3CONCRETEISASSUMEDTOFAILWHENTHECOMPRESSIVESTRAINREACHES00033THISISACLEARLYDEFINEDLIMITINGSTRAINOFCONCRETEINBENDINGCOMPRESSIONBEYONDWHICHTHECONCRETEWILLBETAKENASREACHINGTHESTATEOFCOLLAPSEITISVERYCLEARTHATTHESPECIFIEDLIMITINGSTRAINOF00033DOESNOTDEPENDONTHESTRENGTHOFCONCRETECOLLAPSEOFCONCRETELIMITINGSTRAINOFCONCRETEN4THEACCEPTABLESTRESSSTRAINCURVEOFCONCRETEISASSUMEDTOBEPARABOLIC抛物线的,像抛物线的混凝土受压时的应力应变关系U0OCFCCN5THETENSILESTRENGTHOFCONCRETEISIGNOREDCONCRETEHASSOMETENS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