lesson15-土木工程专业英语-秦卫红

CompanynameCompanysloganhereENGLISHFORCIVILENGINEERING土木工程专业英语CompanynameCompanysloganhere|[e-mail]|[phone]|LONGSTREET12345,CITY,COUNTRY演讲陈成ppt制作赵杰翻译赵欣怡陈成赵杰后期整理赵欣怡杨冕夏文娟赵杰赵向东陈成刘闯刘文尤佐成212建筑工程（土木工程）2班第一组任务分配CompanynameCompanysloganhere|[e-mail]|[phone]|LONGSTREET12345,CITY,COUNTRYSOURCESOFPRESTRESSFORCE预应力的来源3Lesson15CompanynameCompanysloganheremainpartThemostobviousmethodofpre-compressing预应力最常用的方法Othermeansforintroducingtheprestressingforce使用预应力的其他方式pretensioningorpost-tensioningsystems先张法和后张法Fordesigner对设计者而言CompanynameCompanysloganherePrestresscanbeappliedtoaconcretememberinmanyways.Perhapsthemostobviousmethodofpre-compressingistousejacksreactingagainstabutments,asshowninFig.15-1a.Suchaschemehasbeenemployedforlargeprojects.Manyvariationsarepossible,includingreplacingthejackswithcompressionstrutsafterthedesiredstressintheconcreteisobtained;orusinginexpensivejacksthatremaininplaceinthestructure,insomecaseswithacementgroutusedasthehydraulicfluid.Theprincipaldifficultyassociatedwithsuchasystemisthatevenaslightmovementoftheabutmentswilldrasticallyreducetheprestressforce.5预应力技术可以通过很多方法应用于混凝土。可能预应力最普遍的方法就是用千斤顶压迫支座，如图15-1a。这种方案已经被用来做大项目。这种方法的变相使用都是可能的，包括用斜压杆取代千斤顶给结构施加所需的压力是可行的，或者把廉价的千斤顶扣在结构中，在某些情况下把水泥浆当做液压油使用。和这个系统相关的最重要的问题是支座的细微变化都可能降低预应力。Themostobviousmethodpre-compressing预应力最常用的方法CompanynameCompanysloganhereBeamJackAbutmentFig.15-1(a)Post-tensioningbyjackingagainstabutmentsCompanynameCompanysloganhereInmostcases,thesameresultismoreconvenientlyobtainedbytyingthejackbasestogetherwithwiresorcables,asshowninFig.15-1b.Thesewiresorcablesmaybeexternal,locatedoneachsideofthebeam;moreusuallytheyarepassedthroughahollowconduitembeddedintheconcretebeam.Usually,oneendoftheprestressingtendonisanchored,andalloftheforceisappliedattheotherend.Afterreachingthedesiredprestressforce,thetendoniswedgedagainsttheconcreteandthejackingequipmentisremovedforreuse.Inthistypeofprestressing,theentiresystemisself-containedandisindependentofrelativedisplacementofthesupports.7在大多数情况下，把千斤顶和钢丝或钢索连接起来可以方便获得同样的数据，如图15-1b所示。这些钢丝或钢索可以放在梁的外边两侧；更常见的是使它穿过埋设在混凝土梁内的空心导管。通常来说，预应力钢筋的一端锚固，在另一端施加全部力。在达到所需的预应力值后，将钢筋束楔紧到结构中，千斤顶设备可以移走以便再次使用。在这种预应力下，整体结构是独立的而且不受支撑物将对位移的影响。Themostobviousmethodpre-compressing预应力最常用的方法CompanynameCompanysloganhereBeamCableJackFig.15-1(b)Post-tensioningwithjacksrectingagainstbeamCompanynameCompanysloganhereAnothermethodofprestressing,thatiswidelyusedisillustratedinFig.15-1c.Theprestressingstrandsaretensionedbetweenmassiveabutmentsinacastingyardpriortoplacingtheconcreteinthebeamforms.Theconcreteisplacedaroundthetensionedstrands,andaftertheconcretehasattainedsufficientstrength,thejackingpressureisreleased.Thistransferstheprestressingforcetotheconcretebybondandfrictionalongthestrands,chieflyattheouterends.Itisessential,inallthreecasesshowninFig.15-1,thatthebeambesupportedinsuchawayastopermitthemembertoshortenaxiallywithoutrestraintsothattheprestressingforcecanbetransferredtotheconcrete.9另一种广泛使用的加预应力的方法，如图15-1c所示。预应力钢索在以梁的形式安装到结构前，在铸造的地方会被巨大的支座拉紧。结构会被放置在拉紧的钢索上，在结构达到足够的强度后，千斤顶的压力就会被释放。预应力通过粘接剂和钢索的摩擦力传给结构并主要在外部结束。如图15-1所示的所有三种情况下，梁的支撑条件必须允许其毫无约束地轴向缩短，以便将预应力传递至混凝土。Themostobviousmethodpre-compressing预应力最常用的方法CompanynameCompanysloganhereBeamCableAnchorageJackFig.15-1cPretensioningwithtendonstressedbetweenfixedexternalanchoragesCompanynameCompanysloganhereOthermeansforintroducingthedesiredprestressingforcehavebeenattemptedonanexperimentalbasis.Thermalprestressingcanbeachievedbypreheatingthesteelbyelectricalorothermeans.Anchoredagainsttheendsoftheconcretebeamwhileintheextendedstate,thesteelcoolsandtendstocontract.Theprestressforceisdevelopedthroughtherestrainedcontraction.Theuseofexpandingcementinconcretemembershasbeentriedwithvaryingsuccess.Thevolumetricexpansion,restrainedbysteelstrandsorbyfixedabutments,producestheprestressforce.11采用预应力的的其他方法正在通过试验性的原理尝试。用电或者其他方法预热钢可以获得加热预应力。当钢材处于广延态，逐渐降温并趋向于收缩的固定到混凝土的末端。此时预应力通过约束收缩已经发展成熟。膨胀水泥在混凝土构件中的应用已经取得很大成功。它体积的膨胀受钢绞线和固定支座的限制而产生预应力。Othermeansforintroducingthederired使用预应力的其他方式CompanynameCompanysloganhere细颗粒膨胀水泥粗颗粒膨胀水泥CompanynameCompanysloganhereMostofthepatentedsystemsforapplyingprestressincurrentusearevariationsofthoseshowninFig.15-1bandc.Suchsystemscangenerallybeclassifiedaspretensioningorpost-tensioningsystems.Inthecaseofpretensioning,thetendonsarestressedbeforetheconcreteisplaced,asinFig.15-1c.Thissystemiswell-suitedformassproduction,sincecastingbedscanbemadeseveralhundredfeetlong,theentirelengthcastatonce,andindividualbeamscanbefabricatedtothedesiredlengthinasinglecasting.13目前使用的绝大多数的施加预应力的方法就像如图15-1b和15-1c所示。这些方法普遍都被归类为先张法或者后张法。对于先张法，钢束在混凝土浇筑之前施加应力，如图15-1c所示。这种体系非常适合批量生产，浇筑长度可以达到数百英尺，沿全长一次浇筑混凝土。再把长的浇筑体分割成所需长度的单个构件。先张法PretensioningCompanynameCompanysloganhere先张法预应力高强度混凝土管桩的生产CompanynameCompanysloganhere乌海项目先张法预应力空心板预制超百16m先张法预应力混凝土空心桥板CompanynameCompanysloganhereInpost-tensionedconstruction,showninFig.15-1b,thetendonsaretensionedaftertheconcreteisplacedandhasgaineditsstrength.Usually,ahollowconduitorsleeveisprovidedinthebeam,through