土木工程专业文献选读.ppt

Lesson3PrestressedConcrete预应力混凝土*1.Concreteisstrongincompression,butweakintension:itstensilestrengthvariesfrom(不同)8to14percentofitscompressivestrength.Duetosuchalowtensilecapacity(受拉承载能力),flexuralcracks(挠曲裂缝)developatearlystagesofloading.Inordertoreduceorpreventsuchcracksfromdeveloping,aconcentric(adj.同中心的，轴心的)oreccentricforce(偏心力)isimposedinthelongitudinaldirection(轴向)ofthestructuralelement.混凝土的抗压性能强而抗拉性能弱:它的抗拉强度仅仅是它抗压强度的8%-14%不等.由于它如此低的抗拉承载力,在荷载作用的初期挠曲裂缝就会出现。为了减小或阻止这种裂缝的开展,在结构杆件纵向施加一个轴心或偏心的压力.*Thisforcepreventsthecracksfromdevelopingbyeliminatingorconsiderably(adv.显著地,大大,相当(大，多)地)reducingthetensilestresses(拉[伸]应力，抗拉应力)atthecritical(危险的,临界的)midspan(中跨截面，部分)andsupportsectionsatserviceload(使用荷载),therebyraisingthebending(弯曲,挠曲),shear(剪力，剪切),andtorsionalcapacities(扭转承载力)ofthesections.这个力(预应力)通过消除或大大减少在使用荷载下跨中或支座的控制截面处产生的拉应力,阻止了(该处)裂缝的开展,因此提高了该截面的(抵抗)弯曲、剪切和扭转的承载能力.Thesectionsarethenabletobehaveelastically(adv.弹性地),andalmostthefullcapacityoftheconcreteincompressioncanbeefficientlyutilized(vt.利用)acrosstheentiredepthoftheconcretesectionswhenallloadsactonthestructure.然后,这些截面表现为弹性,并且当所有荷载作用在结构上时,可以通过混凝土全截面受压有效地利用混凝土几乎全部的抗压性能。Suchanimposedlongitudinalforce(纵向力)iscalledaprestressingforce,i.e.(也就是),acompressiveforcethatprestresses(vt.给…预加应力)thesectionsalongthespanofthestructuralelementpriorto(adv.在前,居先)theapplicationofthetransverse(adj.横向的)gravitydeadandliveloadsortransient(adj.短暂的,瞬时的)horizontalliveloads.这样施加的一个纵向力叫做预应力,也就是说,在横(竖)向重力恒载和活载或短暂的水平活载(风,地震)作用之前,沿结构杆件跨度方向的截面预加的压缩力.*Thetypeofprestressingforceinvolved(adj.,有关的),togetherwithitsmagnitude,aredeterminedmainlyonthebasisofthetypeofsystemtobeconstructedandthespanlengthandslenderness(细长度)desired(想得到的).Sincetheprestressingforce(预应力)isappliedlongitudinallyalongorparallel(v平行)totheaxisof