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24straincapacity
552.4应变能力55relationbetweenthedynamicmodulusofelasticitydeterminedbytransversevibrationofcylindersandtheircompressivestrength动态弹性模量之间的关系由横向振动的汽缸、和他们的抗压强度确定itshouldalsobenotedthatnoinfor__tionis__ailableregardingtherelationshipbetweenthestaticanddynamicmodulusofelasticityforconcretewithstrengthinex__ssof8000psi同样应该注意到的是没有信息可以证明关于弹性模量对混凝土强度超过8000psi静态和动态之间的关系24straincapacity
2.4应变能力Theusablestraincapacityofconcretecanbemeasuredeitherincompressionorintension无论在压缩或拉伸的状态下,混凝土可用应变能力可以测量inthecompressionmode在压缩模式下itcanbemeasuredbyeithercon__ntricorec__ntriccompressiontesting应变能力可以通过同心或偏心压缩测试测量inthetensilemode在拉伸模式下thebeh__iorundermultiaxialstressstatesifoutsidethescopeofthischapter.在本章的范围之外的多轴向的应力状态下的行为andonlythebeh__iorunderuniaxialstressconditionwillbediscussed.只在单轴应力状态将被讨论Stressbeh__iorincompression压缩状态下的应力行为Thestress-strainbeh__iorisdependentonanumberofparameterswhichinclude__terialvariablessuchasaggregatetypeandtestingvariablessuchasageattesting,loadingrate,straingra___ntandothersnotedabove应力-应变行为是依赖于大量的参数其中包括材料变量如骨料类型和测试变量如年龄测试,以及其他人上面所提到的加载速率应变梯度来测定Theeffectoftheaggregatetypeofthestress-staincurveisshowninfig
2.32whichindicatesthathigherstrengthandcorrespondingstrainareachievedforcrushedaggregatefromfine-graineddiabaseandlimestoneascomparedtoconcretes__defrom__oothrivergr__elandfromcrushedgranitethatcontainedinclusionsofasoftmineral图32显示相对于由平滑河流砾石和碎花岗岩含夹杂物的软矿物组成的混凝土其总体效果类型的应力斑曲线表明碎骨料从细粒度的辉绿岩和灰岩可以达到更高的强度和相应的应变Au__berofinvestigationsh__ebeenundertakentoobtainthecompletestresscurvesincompression上述饼状图已开展调查并获得完整的应力压缩曲线Axialstress-strainCurvesforconcretewithcompressivestrengthupto14000psi98mpaconcreteasobtainedbydifferentresearchersareshowninfig
2.33图33显示的是由不同的研究人员测量得混凝土抗压强度高达14000psi98mpa混凝土的轴向应力-应变曲线Itisgenerallyrecognizedthatforconcreteofhigherstrength摘要显示一般情况下对于__度的混凝土theshapeoftheas__ndingpartofthecurvebecomemorelinearandsteeper提升部分的形状的曲线越线性越陡峭thestrainat__ximumstressisslightlyhigher,其最大应力应变越高andtheslopeofthedes__ndingpartbecomesteeper并且斜率的下降部分变得更陡Theexisten__ofthepostpeakdes__ndingpartofthestress-straincurvehasbeenthefocusofare__ntpaper邮报的存在峰值下降部分的应力-应变曲线一直是最近一篇论文中争论的焦点itwasconcludedthatthepostpeakbeh__iorcanbequantifiedforinclusioninfiniteelement研究发现该应力应变行为可以被量化后峰值列入有限元56shorttermmechanicalproperties56短期机械性能Fig
2.33effectoftheaggregatetypeontheas__ndingportionofthestress-straincurvesofconcreteat28days图
2.33骨料种类对混凝土的应力-应变曲线的提升效应为28天____ysisandthatitcanh__econsiderableinfluen__onthepredictedstructuralbeh__iorandstrength分析结果可以对和结构强度预测产生较大影响Toobtainthedes__ndingpartofthestress-straincurve.itisne__ssaryto__oidspecimen-testing__chineinteraction.得到应力-应变曲线的下降是必要的以避免试样测试机交互oneapproachistouseaclosed-loopsystemwithaconstantrateofaxialstrainasafeedbacksignalforclosed-loopoperation.另一种方法是使用一个闭环系统的轴向应变恒定速率作为反馈__闭环来操作thedifficultiesofobtainingthepostpeakbeh__iorexperimentallyandmethodsofovercomingthesedifficultiesaredescribedinastudybyAh__dandShah.沙艾和哈迈德的一个研究表明获得结果的困难在于怎么研究确定峰值forveryhighstrengthconcretesit__ybene__ssarytousethelateralstrainsasafeedbacksignalratherthantheaxialstrains.对于非常__度混凝土可能有必要使用横向菌株作为反馈__而不是轴向压力inapaperbykotsovos在一篇由kotsovos写的文章显示itisarguedthatamorerealisticdescriptionofthepostpeakspecimenbeh__ior__ybeacompleteandimmediatelossofload-carryingcapacityassoonasthepeakloadisex__eded.adifferentpointofviewisreflectedinanotherre__ntpaperwhichsuggeststhatthereisusablestrengthforconcreteafterpeakstress.一篇更客观的文章认为一旦超过峰值负载的实验标本立即丧失承载能力一个不同的角度反映在另一篇论文可以用混凝土的强度峰值的来表示basedontheabovementionedexperimentalinvestigations基于上述实验调查different____yticalrepresentationsforthestress-straincurveh__ebeenproposed不同的应力-应变曲线分析显示theyincludeuseofafractionalequation它们包括使用一个分式方程oracombinedpowerandexponentialequationandserpentinecurvethefractionalequationisacomprehensive或结合力量和指数方程和蜿蜒的曲线是一个综合性的分式方程yet______wayofcharacterizingthestress-strainresponseofconcreteincompression.thefractionalequationcanbewrittenas但简单的表明混凝土在压缩状态下的应力-应变响应的分数方程可以写成这个WhereFC’isthecompressivestressatstrainfc’ande’the__ximumstressandcorrespondingstrainFC表示的是压应力应变FC和e“分别表示的是最大应力和相应的应变AandBareparameterswhichdeterminetheshapeofthecurveA和B是确定曲线的形状参数ThevaluesoftheparametersAandBwhichcontroltheshapeoftheas__ndingandthedes__ndingparts这些A和B参数值可以控制形状的升序和降序respectively__ybeesti__tedby分别可以估计WhereFC’isthecompressivestrengthinpsiandwistheunitweightinpcfFC是抗压强度psi和w是pcf的单位重量TheparametersABandEareasrecommendedbyAH__Dandshahandweredeterminedfromthestatistical____ysisoftheexperimentalresultson3*6in参数B和E是艾哈迈德和沙阿决心从推荐的在3*6统计分析来研究实验结果concretecylindersthesecylindersweretestedunderstraincontrolledconditionsinaclosed-looptesting__chineandhadcompressivestrengthsrangingfrom3000to11000psi应变控制的闭环条件下测试的混凝土钢瓶压缩优势从3000到11000psistress-strainbeh__iorintension应力-应变行为在张力thedirecttensilestress-straincurveisdifficulttoobtain直接测得拉伸应力-应变曲线是很难获得duetodifficultiesintestingconcreteindirecttension原因在于测试混凝土直接张力困难比较大onlylimitedandoftenconflictingdataare__ailable只有那些有限的和经常相互矛盾的数据是可用的directtensiletestswerecarriedoutontaperedcylindricalspecimensof
4.7in.di__eterand
11.8in.length直接拉伸试验研究了直径为
4.7和长度为
11.8英寸的.锥形圆柱试件fortheapplicationoftheload对于应用程序的负载steelplatensweregluedtothetopandbottomofthespecimens粘在顶部和底部的钢压板inordertoprovideplane-parallelandaxialconnectionoftheseplatens是那些为了提供平行平面和轴向连接的aspecialgluingpresswasdesigned.这些压板是按特殊的设计比例胶合而成some500directtensiletests300compressiveand300splittingtestswereperformed.一些500直接拉伸试验300抗压和300年__进行了测试Atypicalstress-straincurvewitha95confiden__regionforconcretesu__ectedtodirecttensionisshowninfig
2.34一个典型的应力-应变曲线与95年的置信区域混凝土遭受直接张力显示在图
2.34中thestress-straincurveshowninthefigureisfordryspecimens.应力-应变曲线的图中所示的是干标本theresults__yvaryslightlyforspecimenstestedinmoistconditions在潮湿条件下测试标本的结果可能会略有不同astudyatnorthwesternbyGopalarathamandShahpointsoutthatduetothelocalizednatureofthepast-crackingdefor__tionsintension西北大学的一项Gopalaratham和沙的研究表明产生局部变形的本质是由于内部的先期开裂nouniquetensilestress-strainrelationshipexists.accordingtothisstudy根据这项研究表明没有独特的拉伸应力-应变关系的存在theuniaxialtensilestrengthcanbeesti__tedbyfc单轴抗拉强度可以估计fcandthetangentmodulusofelasticityisidenticalintensionandcompression和切线弹性模量的张力和压缩相同的thestress-strainrelationshipintensionbeforepeakislessnonlinearthanincompression在之前施压状态下的应力应变关系比峰值非线性压缩状态下较平缓laserspeckleinterferometrywasemployedinare__ntstudy在最近的一项研究采用了激光散斑干涉法toinvestigatethebeh__iorofconcretesu__ectedtouniaxialtension来探讨混凝土在单轴拉伸下的状态uniquepost-peakstress-strainandstress-defor__tionbeh__iorwerenotobserved.并未观察到独特的高峰后应力-应变和应力变形行为Thestress-strainresponseofconcretewasfoundtobesensitivetogauge-length混凝土的应力-应变曲线反应的是所发现的混凝土敏感表长度strainsmeasuredwithinagaugelengthinsidethemicrocrackingzoneweretwoordersof__gnitudehigherthanvaluespreviouslyreported.菌株在标距长度测量的内部微裂缝区的两个数量级值高于之前的报道Inare__ntstudy最近的研究显示itwasshownthatwhiletheuseofstraingaugeswouldleadtonon-o__ectiveconstitutivestress-strainrelations结果表明:虽然应变仪的使用会产生非客观的本构应力-应变关系interferometricmeasurementsonnotchedspecimensallowanindirectdeterminationofthelocalstress-strainandstress-separationrelations.在误差允许的范围内干涉测量在切口标本可以间接确定当地的应力-应变关系和应力分离guoandzhangtested29specimensindirecttensionandobtainedcompletestress-derivedforthestress-displa__mentcurves.郭和张测试29标本中直接张力和获得完整的应力派生的应力位移曲线Flexuraltension弯曲张力Whiletheinfor__tiononthestress-strainbeh__iorintensionisseverelylimited尽管这些信息在应力-应变行为在张力是极其有限的virtuallynodataare__ailableregardingthestraincapacityinflexuraltension.几乎没有数据可用关于应变能力在弯曲张力thisisanareaforwhichresearchissorelyneededtoprovideabasisfordesignwhereflexuralcrackingisanimportantconsideration弯曲裂纹是一个迫切需要提供一些基础设计的研究领域
2.5poison’sratio
2.5抑制剂的比率poison’sratiounderuniaxialloadingconditionsisdefinedastheratiooflateralstraintostraininthedirectionofloading.抑制剂的比率在单轴加载条件下的定义是横向应变的比值来应变方向的荷载intheinelasticrangeduetovolumedilationresultingfrominternalmicrocracking在非弹性范围由于体积膨胀产生的内部微裂纹theapparentpoisson’sratioisnotconstantbutisanincreasingfunctionoftheaxialstrain.明显的泊松比不是固定的而是是一个递增函数的轴向应变Experimentaldataonthevaluesofpoisson’sratioforhighstrengthconcreteisverylimited.泊松比的实验数据值显示__度混凝土是非常有限的basedonthe__ailableexperimentalinfor__tionpoisson’sratioofhigherstrengthconcreteintheelasticrangeappearscomparabletotheexpectedrangeofvaluesforlower-strengthconcrete.根据已有的实验信息在弹性范围内出现的__度混凝土的泊松比比得上低强度混凝土预期值范围intheinelasticrangetherelativeincreaseinlateralstrainsislessforhigher-strengthconcretecomparedtoconcreteoflowerstrength.在非弹性范围内相对增加的侧向压力对__度混凝土少相比混凝土的强度较低thatishigher-strengthconcreteexhibitslessvolumedilationthanlower-strengthconcrete.即__度混凝土展品体积膨胀比低强度混凝土要小Thisimplieslessinternalmicrocrackingforconcreteofhigherstrength.这意味着更少的内部微裂缝对混凝土的强度要求更高thelowerrelativeexpansionduringtheinelasticrange__ymeanthattheeffectsoftriaxialstresseswillbeproportionatelydifferentforhigher-strengthconcrete在非弹性范围产生的相对较低相对扩张可能意味着三轴应力的影响将对__度混凝土比例不同forexampletheeffectivenessofhoopconfinementisreportedtobelessforhigher-strengthconcrete.例如有效性的箍约束据说对__度混凝土小Infor__tiononpoisson’sratioofconcretewithstrengthgreaterthan12000psiisnot__ailableintheliterature混凝土的泊松比与强度大于12000的psi并没有在文章中显示。