建筑结构设计与预算外文翻译文献Word文档下载推荐.docx

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Thepaperquestionsthevalidityofthegenerallyacceptedviewthatforareinforcedconcretestructuretoexhibit"

ductile"

behaviourunderincreasingloaditisnecessaryforthestressstrainrelationshipsofconcretetohaveagraduallydescendingpost-ultimatebranch.Experimentaldataarepresentedforreinforcedconcretebeamsinbendingwhichindicatethepresenceoflongitudinalcompressivestrainsonthecompressivefaceinexcessof0.0035.Itisshownthatthesestrains,whichareessentialfor"

behaviour,arecausedbyacomplexmultiaxialcompressivestateofstressbelowultimatestrengthratherthanpostultimatematerialcharacteristics.Thepresenceofacomplexstresssystemprovidesafundamentalexplanationforbeambehaviourwhichdoesnotaffectexistingdesignprocedures.

1.INTRODUCTION

The"

planesections"

theorynot,onlyisgenerallyconsideredtodescriberealisticallythedeformationresponseofreinforcedandprestressedconcretebeamsunderflexureandaxialload,butisalsoformulatedsothatitprovidesadesigntoolnotedforbothitseffectivenessandsimplicity[1].Thetheorydescribesanalyticallytherelationshipbetweenload-carryingcapacityandgeometriccharacteristicsofabeam by considering the equilibrium conditions at critical cross-sections.Compatibilityofdeformationissatisfiedbythe"

planecross-sectionsremainplane"

assumptionandthelongitudinalconcreteandsteelstressesareevaluatedbythematerialstress-straincharacteristics.Transversestressesandstrainsareignoredforthepurposesofsimplicity.

Thestress-straincharacteristicsofconcreteincompressionareconsideredtobeadequatelydescribedbythedeformationalresponseofconcretespecimenssuchasprismsorcylindersunderuniaxialcompressionandthestressdistributioninthecompressionzoneofacross-sectionattheultimatelimitstate,asproposedbycurrentcodesofpracticesuchasCP110[1],exhibitsashapesimilartothatshowninfigure1.

Thefigureindicatesthatthelongitudinalstressincreaseswiththe

distancefromtheneutralaxisuptoamaximumvalueandthenremainsconstant.Suchashapeofstressdistributionhasbeenarrivedatonthebasisofbothsafetyconsiderationsandthewidelyheldviewthatthestress-strainrelationshipofconcreteincompressionconsistsofbothanascendingandagraduallydescendingportion（seefig.2）.Theportionbeyondultimatedefinesthepost-ultimatestresscapacityofthematerialwhich,Typicalstress-strainrelationshipforconcreteincompression.asindicatedinfigure1,isgenerallyconsideredtomakeamajorcontributiontothemaximumload-carryingcapacityofthebeam.

However,arecentanalyticalinvestigationofthebehaviourofconcreteunderconcentrationsofloadhasindicatedthatthepost-ultimatestrengthdeformationalresponseofconcreteundercompressivestatesofstresshasnoapparenteffectontheoverallbehaviourofthestructuralformsinvestigated（[2],[3]）.Ifsuchbehaviouristypicalforanystructure,thenthelargecompressive

strains（inexcessof0.0035）measuredonthetopsurfaceofareinforcedconcretebeamatitsultimatelimitstate（seefig.1）,cannotbeattributedtopost-ultimateuniaxialstress-straincharacteristics.Furthermore,sincethecompressivestrainattheultimatestrengthlevelofanyconcreteunderuniaxialcompressionisoftheorderof

0.002（seefig.2）,itwouldappearthatarealisticpredictionofthebeamresponse

14

underloadcannotbebasedsolelyontheascendingportionoftheuniaxialstress-strainrelationshipofconcrete.

Inviewoftheabove,theworkdescribedinthefollowingappraisesthewidelyheldviewthatauniaxialstress-strainrelationshipconsistingofanascendingandagraduallydescendingportionisessentialfortherealisticdescriptionofthebehaviourofareinforcedconcretebeamin flexure.Resultsobtainedfrombeamssubjectedtoflexureundertwo-pointloadingindicatethatthelargestrainsexhibitedbyconcreteinthecompressionzoneofthebeamsareduetoatriaxialstateofstressratherthantheuniaxialpost-ultimatestress-straincharacteristicsofconcrete.Itisshownthattheassumptionthatthematerialitselfsuffersacompleteandimmediatelossofload-carryingcapacitywhenultimatestrengthisexceedediscompatiblewiththeobserved "

structural behaviour as indicated by load-deflexion ormoment-rotationrelationships.

2.EXPERIMENTALDETAILS

2.1.Specimens

Threerectangularreinforcedconcretebeamsof915mmspanand102mmheightx51mmwidthcross-sectionweresubjectedtotwo-pointloadwithshearspansof305mm（seefig.3）.Thetensionreinforcementconsistedoftwo6mmdiameterbarswithayieldloadof11.8kN.Thebarswerebentbackattheendsofthebeamssoastoprovide compression reinforcement along the whole length of the shearspans.Compressionandtensionreinforcementalongeachshearspanwerelinkedbyseven3.2mmdiameterstirrups.Neithercompressionreinforcementnorstirrupswereprovidedinthecentralportionofthebeams.Duetotheabovereinforcementarrangementallbeamsfailedinflexureratherthanshear,althoughtheshearspantoeffectivedepthratiowas3.

Thebeams,togetherwithcontrolspecimens,werecuredunderdamphessianat

20~forsevendaysandthenstoredinthelaboratoryatmosphere（20oC~and40%

R.H.）forabout2months,untiltested.FulldetailsoftheconcretemixusedaregivenintableI.

2.2.Testing

Loadwasappliedthroughahydraulicramandspreaderbeaminincrementsofapproximately0.5kN.Ateachincrementtheloadwasmaintainedconstantforapproximately2minutesinordertomeasuretheloadandthedeformationresponseofthespecimens.Loadwasmeasuredbyusingaloadcellanddeformationresponsebyusingboth20mmlongelectricalresistancestraingaugesanddisplacementtransducers.Thestraingaugeswereplacedonthetopandsidesurfacesofthe

beamsinthelongitud{nalandthetransversedirectionsasshowninfigure4.Thefigurealsoindicatesthepositionofthelinearvoltagedisplacementtransducers（LVDT'

s）whichwereusedtomeasuredeflexionatmid-spanandattheloadedcross-sections.

Themeasurementswererecordedbyanautomaticcomputer-baseddata-logger（Solatron）capableofmeasuringstrainsanddisplacementstoasensitivityof2microstrainand0.002ram,respectively.

3.EXPERIMENTALRESULTS

Themainresultsobtainedfromtheexperimentstogetherwithinformationessentialforabetterunderstandingofbeambehaviourareshowninfigures5to14.

Figure5showstheuniaxialcompressionstressstrainrelationshipsoftheconcreteusedintheinvestigation,whereasfigures6and7showtherelationshipsbetweenlongitudinalandtransversestrains,measuredonthetopsurfaceofthebeams（a）atthecross-sectionswheretheflexurecrackswhicheventuallycausefailurearesituated（criticalsections）and（b）atcross-sectionswithintheshearspan,respectively.

Figures6and7alsoincludethelongitudinalstraintransversestrainrelationshipcorrespondingtothestress-strainrelationshipsoffigure5.

Figure8showsthetypicalchangeinshapeofthetransversedeformationprofileofthetopsurfaceofthebeamswithloadincreasingtofailureandfigure9providesaschematicrepresentationoftheradialforcesandstressesdevelopingwithincreasingloadduetothedeflectedshapeofthebeams.Typicalload-deflexionrelationshipsofthebeamsareshowninfigure10,whereasfigure11depictsthevariationoncriticalsectionsoftheaverageverticalstrainsmeasuredonthesidesurfacesofthebeamswiththetransversestrainsmeasuredonthetopsurface.Figure12indicatesthestrengthanddeformationresponseofatypicalconcreteundervariousstatesoftriaxialstressandfigure13presentsthetypicalcrackpatternofthebeamsatthemomentofcollapse.Finally,figure14showstheshapeofthelongitudinalstressdistributiononthecompressivezoneofacriticalsectionatfailurepredictedonthebasisoftheconceptsdiscussedinthefollowingsection.

翻译

在多向应力作用下从混凝土的特性看受弯钢筋混凝土梁

变化的一个基本试验

M.D.Kotsovos 伦敦皇家科学与技术学院土木工程系

本文所探讨的问题是通常认为在荷载递增下钢筋混凝土结构呈现弹性状态，这必须是因为混凝土的应力-应变关系有一个逐渐递减的临界部分的真实性。

试验数据显示受弯钢筋混凝土梁会在受压面的纵向压应变超出0.0035。

这表明这些应变是钢筋混凝土结构的本质，它是由于一个比极限强度小的复杂多向的应力状态而不是塑性材料的特性引起的。

一个复杂应力系统的存在为梁的状态提供了一个基本试验，而不是想象的一个现有设计过程。

1.引言

“剖面”理论不仅是通常认为能很真实地描述钢筋混凝土梁和预应力混凝土梁在弯矩和轴向荷载下的变形，而且能确切地阐述，所以它提供了一个设计工具，因为它的有效和简单而闻名[1]。

假设在临界横截面伤是均衡的，这个理论分析地描述了一个梁的承载能力和几何特性之间的关系。

变形协调必须满足“水平横截面荏苒水平”的假定和纵向混凝土和钢筋的应力是通过材料的应力-应变的特性来估算的。

为了简化计算，忽略横向的应力和应变。

受压混凝土的应力-应变特性认为能够被混凝土试块的变形充分地描述，例

如在极限的有限状态下，棱柱体或圆柱体在横截面的受压区受单轴压力和应力，就像现行规范所建议的CP110[1]，显示出一个与图1相似的形状。

图1表明纵向应力随着与中和轴的距离增加而增加至最大值，然后保持不变。

这个分布图已经达到安全性和受压混凝土的应力-应变关系的广泛观点，由上升和逐渐下降的两部分组成（如图2所示）。

超出极限的部分，材料的塑性应力能力如图1所示，被认为对梁的最大承载能力有较大的作用。

图1.临界面破坏建议CP为110的应力和应变分布 图2.受压混凝土结构的标准应力-应变关系

然而，最近关于在集中力作用下的混凝土的变化的一个分析性调查表明，在压应力作用下混凝土的极限强度变形没有对所有被调查的结果形式的变化产生明显的影响（[2],[3]）。

如果这个变化对任何结果都是典型的，那么在钢筋混凝土梁的顶面被测的很大的压应变（超出量0.0035）在它的极限有限状态下（如图1），不能对极限单轴应力-应变特性产生作用。

因此，因为压应变在单轴压力下的任何混凝土的极限强度等级下为ε=0.002（如图2所示），在混凝土的单轴应力-应变关系下降部分，将出现一个在荷载作用下梁变化的现在可行的预测。

根据以上的观点，本文的描述都在以下的评价中，广泛的支持观点的一个单轴应力-应变关系由一个上升的和一个逐渐下降的部分组成，对受弯的根据混凝土梁的变化的真实描述是非常必要的。

这个结果是从梁在两点荷载作用下弯曲得到，表明很大的应变的通过梁受压的混凝土呈现的，由于三维应力而不是一味的混凝土极限应力-应变特性。

这表明材料本身受到一个完整和直接的承载能力损失，当极限强度被超过的假定与弹性结构的变化并存的，通过偏心荷载或瞬间旋转关系表明的。

2.试验细节

2.1试块

三根矩形钢筋混凝土梁，跨度915mm，横截面为102mm51m