预应力混凝土Prestressed-Concrete大学毕业论文外文文献翻译及原文

1、9毕业设计（论文） 外文文献翻译文献、资料中文题目：预文献、资料英文题目：Prestressed Concrete文献、资料来源：文献、资料发表（出版）日期： 院（部）:专 业： 班 级： 姓 名： 学 号： 指导教师： 翻译日期： 2017.02.14毕业设计（论文）外文资料翻译外文出处:The Concrete structure附 件：1 外文原文；2、外文资料翻译译文。指导教师评语：签字：年 月曰1、外文资料原文Prestressed ConcreteConcrete is strong in compression, but weak in tension: Its tensile

2、strength varies from 8 to 14 percent of its compressive strength. Due tosuch a Iow tensile capacity, fiexural cracks develop at early stages ofload ing. In order to reduce or preve nt such cracks from develop ing, aconcen tric or ecce ntric force is imposed in the Ion gitud inal directi on of the st

3、ructural eleme nt. This force preve nts the cracks from develop ing by elim in at ing or con siderably reduci ng the ten sile stressesat thecritical midspa n and support secti ons at service load, thereby rais ing the bending, shear, and torsi onal capacities of the secti ons. The sect ions are the

4、n able to behave elastically, and almost the full capacity of the con crete in compressi on can be efficie ntly utilized across the en tire depth of the con crete secti ons whe n all loads act on the structure.Such an imposed Iongitudinal force is called a prestressing force,i.e., a compressive forc

5、e that prestresses the secti ons along the spa n ofthe structural eleme ntprior to the application of the transverse gravitydead and live loads or transient horizontal live loads. The type ofprestressing force invoIved, together with its magnitude, are determined mainly on the basis of the type of s

6、ystem to be con structed and the spa n len gth and sle ndern ess desired. Since the prestress ing force is applied Ion gitud in ally along or parallel to the axis of the member, the prestressi ng prin ciple invo Ived is com monly known as lin ear prestress ing.Circular prestressing, used in liquid c

7、ontainment tanks, pipes,and pressure reactor vessels, essentially follows the same basic principles as does linear prestressing. The circumferential hoop, or "hugging" stress on the cylindrical or spherical structure, n eutralizes the ten sile stresses at the outer fibers of the curvili ne

8、ar surface caused by the internal contained pressure.Sec. CilndividyEi $LongilLrdihaEprcsBrcssinfElevatkirtibrcc：(s)A 谢uixkn barrel(d)m preshessinj; prtnciple in linear incfFigure 1.2.1 illustrates, in a basic fashi on, the prestress ing action in both types of structural systems and the result ing

9、stress resp on se. In( a), the in dividual con crete blocks act together as a beam due to the large compressive prestressing force P. Although it might appear that the blocks will slip and vertically simulate shear slip failure, in fact they will not because of the Iongitudinal force P. Similarly, t

10、he wooden staves in (c) might appear to be capable of separati ng as a result of the high internal radial pressure exerted on them. But again, because of the compressive prestress imposed by the metal bands as a form of circular prestress in g,they will remai n in place.From the preceding discussion

11、, it is plain that permanent stresses in the prestressedstructural member are created before the full dead and live loads are applied in order to eliminate or considerably reduce the net tensile stresses caused by these loads. With rein forced con crete, it is assumedthat the tensile strength of the

12、 concrete is negligible and disregarded. This is because the ten sile forces result ing from the bending mome nts are resisted by the bond created in the rei nforceme nt process. Crack ing and deflect ion are therefore esse ntially irrecoverable in rein forced con crete once the member has reached i

13、ts limit state at service load.The rei nforceme nt in the rein forced con crete member does not exert any force of its own on the member, contrary to the action of prestressing steel. The steel required to produce the prestressing force in the prestressedmember actively preloads the member, permitti

14、 ng a relatively high con trolled recovery of crack ing and deflecti on. Once the flexural tensile strength of the concrete is exceeded, the prestressed member starts to act like a rein forced con crete eleme nt.Prestressedmembers are shallower in depth tha n their rein forced con crete counterparts

15、 for the same span and loading conditions. In general, the depth of a prestressedconcrete member is usually about 65 to 80 percent of the depth of the equivale nt rein forced con crete member. Hen ce, the prestressed member requires less con crete, an d,about 20 to 35 perce nt of the amount of rein

16、forceme nt. Unfortun ately, this sav ing in material weight is bala need by the higher cost of the higher quality materials needed in prestressing. Also, regardless of the system used, prestressing operations themselves result in an added cost: Formwork is more complex, since the geometry of prestre

17、ssed sect ions is usually composed of. flan ged sect ions with thin-webs.In spite of these additi onal costs, if a large eno ugh nu mber of precast un its are manufactured, the differenee between at least the initial costs of prestressedand rein forced con crete systems is usually not very large. An

18、d the in direct Ion g-term sav ings are quite substa ntial, becauseless maintenance is n eeded;a Ion ger work ing life is possible due to better quality control of the concrete, and lighter foundations are achieved due to the smaller cumulative weight of the superstructure.Once the beam spa n of rei

19、n forced con crete exceeds 70 to 90 feet (21.3 to 27.4m), the dead weight of the beam becomes excessive, resulting in heavier members and, consequently, greater Iong-term deflection and cracking. Thus, for larger spa ns, prestressed con crete becomes man datory since arches are expe nsive to con str

20、uct and do not perform as well due to the severe Ion g-term shri nkage and creep they un dergo. Very large spa ns such as segme ntal bridges or cable-stayed bridges can only be con structed through the use of prestress ing.Prestressdc on crete is not a new con cept, dati ng back to 1872, whe n P. H.

21、 Jacks on, an engin eer from Califor nia, pate nted a prestress ing system that used a tie rod to con struct beams or arches from in dividual blocks see Figure 1.2.1 (a). After a long lapse of time during which little progress was made because of the unavailability of high-stre ngth steel to overcom

22、e prestress losses, R. E. Dill of Alexa ndria, Nebraska, recog ni zed the effect of the shri nkage and creep (tra nsverse material flow) of con crete on the loss of prestress. He subsequently developed the idea that successive post-te nsioning of unbon ded rods would compe nsate for the time-depe nd

23、ent loss of stress in the rods due to the decrease in the len gth of the member because of creep and shrinkage. In the early 1920s,W. H. Hewett of Minneapolis developed the principles of circular prestressing. He hoop-stressedhorizontal reinforcement around walls of concrete tanks through the use of

24、 turnbuckles to prevent cracking due to internal liquid pressure, thereby achieving watertightness. Thereafter, prestressing of tanks and pipes developed at an accelerated pace in the Un ited States, with thousa nds of tanks for water, liquid, and gas storage built and much mileage of prestressed pr

25、essure pipe laid in the two to three decades that followed.Lin ear prestress ing continued to develop in Europe and in Fran ce, in particular through the ingenu ity of Euge ne Freyss in et, who proposed in 1926-1928 methods to overcome prestress losses through the use of high-stre ngth and high-duct

26、ility steels. In 1940, he in troduced the now well-k nown and well-accepted Freyss inet system.P. W. Abeles of England introduced and developed the concept of partial prestress ing betwee n the 1930s and 1960s. F. Leon hardt of Germa ny, Mikhailov of Russia, and T. Y Lin of the United States also co

27、ntributed a great deal to the art and scie nee of the desig n of prestressed con crete. Lin's load-bala ncing method deserves particular mention in this regard, as it considerably simplified the design process, particularly in continuous structures. These twentieth-century developments have led

28、to the exte nsive use of prestress ing throughoutthe world, and in the United States in particular.Today, prestressed con crete isused in build in gs, un dergro und structures, TV towers, floating storage and offshore structures, power stations, nuclear reactor vessels, and nu merous types of bridge

29、 systems in cludi ng seg nen tal and cable-stayed bridges, they dem on strate theversatility of the prestress ing con cept and itsall-e ncompass ing applicati on. The success in the developme nt and con struct ion of all these structures has bee n due in no small measures to the adva nces in the tec

30、h no logy of materials, particularly prestressing steel, and the accumulated knowledge in estimat ing the short-a nd Ion g-term losses in the prestressi ng forces.2、外文资料翻译译文预应力混凝土混凝土的力学特性是抗压不抗拉：它的抗拉强度是抗压强度的8% 14%混凝土的抗拉强度如此低，因此在加荷的初期阶段就产生弯曲裂缝。为了减少或防止这种裂缝的发展，所以在结构单元纵向施加了一个中心或偏心的轴向力。 这个力的施加消除或大大减少了工作荷载

31、下结构中最危险的跨中和支柱截面处 的拉应力，阻止了裂缝的发展。也因此提高了截面的抗弯、抗剪和抗扭能力。这样，构件能表现出弹性性质，当全部荷载作用于结构时，混凝土构件的全部断面 的抗压能力都能够被充分有效的发挥出来。这个强加于构件的纵向力就叫做预应力，就是在构件承受横向的重力恒载和 活载或水平向的瞬时活载之前，沿着结构单元跨度方向预先给截面施加一个压 力。预应力的类型及大小主要是根据要建造的系统类型、跨长和构件细长度的需要来决定。由于预应力是沿着或平行于构件的轴向纵向施加的，因此这种施加预应力的原理一般被称做直线预应力法。环形预应力法应用于建造盛放流体的构筑物中，如储水池、管道和压力反应 堆容器

32、等，它本质上和直线预应力法的基本原理相同。 这种柱形或球形结构的环 向箍力或围压就抵消了由内部压力在结构外表面引起的环向拉应力。Scc C Set. A. U.(b)I 工-T prstr-e-SHin呂卫rliaHplie in aineur and -cinzulsir pmWeN点n吕如图1. 2. 1用基本模型描述了在两种结构系统类型上的预应力作用及应力 反应结果。图(a)是在大的预压应力P下单个的混凝土块组成的梁模型。虽然它 可能出现混凝土块间的滑动或在竖向剪切力下滑动破坏，但实际上由于纵向压力P的存在这种情况是不会发生的。同样，图(c)所示木制木桶的木板似乎会由于 施加在它上面的内

33、部的径向高压力而分裂开，但是同上面情况一样，由于金属箍预先施加的力在木桶外周形成一种环向的预压应力，使木板纹丝不动。从前面的讨论中可以清楚地看出，为了消除或大大减少荷载在预应力结构单 元上引起的纯拉应力，在它们承受整个的恒载和活载前，就预先给它们施加一个 永久的预压应力。在一般的钢筋混凝土结构中，通常认为混凝土的抗拉强度是可 以不加考虑、忽略不计的，这是因为弯矩产生的拉应力由加筋处理后的黏合层来 抵抗。也因此，钢筋混凝土结构在工作荷载下达到极限状态后产生的裂纹和挠曲变形不可恢复。和预应力钢筋的作用相反，普通钢筋混凝土构件中的钢筋不给构件施加任何 力。在预应力构件中，钢筋要通过预应力作用给构件主

34、动施加预载，使构件对裂缝和变形有相对较高的恢复控制能力，一旦预应力构件受力使混凝土超过了其弯 曲抗拉强度，贝U构件开始表现出钢筋混凝土构件的性质。在同等跨度和相同荷载条件下，预应力构件要比一般钓钢筋混凝土构件要 薄。一般来说，预应力混凝土构件的厚度通常约是同等钢筋混凝土构件厚度的 65% 80%。因此，预应力构件需用的混凝土量要少，约占钢筋混凝土构件需 用量的20%一 35%。不幸的是，在材料重量方面节省的花费与在预应力措施中 使用的高质量材料的较高费用抵消掉了。 同时，不管什么样的结构体系，预应力 混凝土的模板都比较复杂，因为预加应力的截面的几何形状通常由带薄腹板的翼 形面组成，这样就会造成大量附加费用。尽管有这些附加的费用，通常情况下，如果生产的顿制构件在数量上足够 多的话，预应力构件和钢筋混凝土构件相比，至少最初直接成本的差异不是太大。 但因为预应力构