外文翻譯---預應力混凝土

1、<p><b>　　外文翻譯</b></p><p>　　INTRODUCTION TO PRESTRESS CONCRETE</p><p>　　Basic Concepts of Prestressing</p><p>　　Prestressing concrete is basically concrete in whi

2、ch internal stresses of suitable magnitude and distribution are introduction so that the stresses resulting from external loads are conteracted to a desired degree .in reinforced concrete members, the prestress is common

3、ly introduced by tensioning the steel reinforcement.</p><p>　　The earliest examples of wooden barrel construction by force-fitting of metal tyres on wooden wheels indicate that the art of prestressing has be

4、en practiced from ancient times .the tensile strength of plain concrete is only a fraction of its compressive strength and the problem of it being deficient in tensile strength appears to have been the driving factor in

5、the development of the composite material known as “reinforced concrete”.</p><p>　　The development of early cracks in reinforced concrete due to non-compatibility in the strains of steel and concrete was per

6、haps the starting point for the development of a new material like “presstressed concrete “.the application of permanent compressive stress to a material like concrete ,which is strong in compression but weak in tension

7、,increases the apparent tensile strength of that material ,because the subsequent application of tensile stress must first nullify the compressive prestress</p><p>　　1. Nessity of using high steel and concre

8、te.</p><p>　　2. Recognition of losser of prestress due to various causes.</p><p>　　he early attempts to use mind steel in prestressed concrete were not successful since the working stress in mil

9、d steel of 120 N/MM2 more or less completely lost due to elastic deformation ,creep and shrinkage of concrete.</p><p>　　The nomore loss of stress of stress in steel is generally about 100 to 240 N/MM2 and it

10、 is apparent that if this loss of stress is to be a small portion of the intitle stress, the stress in stress in steel in the intitle stages must be very high , about 1200 to 2000N/MM2.there high stress ranges are possib

11、le only with the use of high strength steel.</p><p>　　High strength concrete is necessary in prestressed concrete since the materirail offers high resistance in tension , shear ,bond and bearing stresses bei

12、ng higher ,high strength concrete is invariably preferred to minimize cost.high strength concrete is less liable to shrinkage cracks ,and resulting in a smaller loss prestress in steel .the use of high strength concrete

13、result in a reduction in the cross sectional dimensions of prestressed concrete structural elements . Whith reduced dead weight</p><p>　　ADVANTAGES OF PRESTRESSED CONCRETE</p><p>　　Prestressed c

14、oncrete members posses improve resistance to shearing forces, due to the effect of compressive ,which reduces principal tensile stress .the use of curved cables ,particularly in long span members helps to reduce the shea

15、r forces developed at the support section.</p><p>　　A prestressed concrete flexural member is stiffer under working loads than a reinforced concrete member of the same depth.</p><p><b>　　H

16、owever,</b></p><p>　　after the onset of cracking,</p><p>　　the flexural behavior of a prestressed member is similar to that of a reinforced concrete member.</p><p>　　The use o

17、f high strength concrete and steel in prestressed members results in lighter and slender members than could be possible by using reinforced concrete.</p><p>　　the two structural features of prestressed concr

18、ete ,namely high strength concrete and freedom from cracks , contributes to the improved durability of the structure under aggressive environmental conditions .Prestressing of concrete improves the ability of the materia

19、l for energy absorption under impact loads. The ability to resist repeated working loads has been proved to be as good in reinforced concrete.</p><p>　　The economy of prestressed concrete is well established

20、 for long span structures. According to Dean , standardlized precast bridge beams between 10 and 30 m long and precast prestressed piles have proved to be economical than steel and reinforced concrete is economical for f

21、loor , roofs and bridges of spans up to 30 and for cast in suit work , it applies to spans up to 100 m. in the long span range , prestressed concrete is generally economical in comparison with reinforced concrete and ste

22、el co</p><p>　　Prestressed concrete has considerable resilience due it its capacity recovering from substantial effect of overloading without undergoing any serious damage. Leonhardt points out than in prest

23、ressed concrete elements, cracks which temporarily develop under occasional overloading will close up complete when the loads are removed .since the fatigue strength of prestressed concrete is comparatively better than o

24、f other materials, chiefly due to the small stress variations in prestressing steel , it</p><p><b>　　預應力混凝土</b></p><p><b>　　預應力的基本概念：</b></p><p>　　預應力混凝土是通過設

25、計乃應力的大小和分布以抵消外荷載產(chǎn)生內(nèi)應力達到設計要求的混凝土中的最基本要求的一種形式。在鋼筋混凝土構(gòu)件中，預應力是通過長拉鋼筋產(chǎn)生的。</p><p>　　最早期在輪子上裝輻條的例子表明預應力在遠古時代就已被應用，素混凝土的抗拉強度遠不如抗壓強度，抗拉強度的不足促使鋼筋混凝土這種組合材料的發(fā)展。</p><p>　　鋼筋混凝土早期裂縫的發(fā)展歸因于鋼筋和混凝土發(fā)展的不協(xié)調(diào)，這也許正是預應力

26、混凝土這樣的新材料發(fā)展的原因。對于混凝土這種抗壓強度大而抗拉強度小的材料，在其內(nèi)部施加永久預應力可明顯增大材料的抗拉強度，因為后期的壓應力必須抵消已存在的預壓力。1904年，F(xiàn)reyssinet是試圖在混凝土中永久性作用下的彈性作用力，不久這種想法就發(fā)展為“預應力”。</p><p>　　高強度鋼筋和混凝土的需要：</p><p>　　開展預應力混凝土低強鋼筋不很理想。因為鋼筋中應力會由于

27、彈性變形，混凝土收縮和徐變損失不少，一般的鋼筋中應力損失大約在100到24N/MM2之間。并且如果這樣的應力損失只占內(nèi)應力的一小部分。那么鋼筋中的初始應力就必須特別高，大約再1200到2000N/MM2。這樣的高應力范圍只可能通過使用高強鋼筋來實現(xiàn)。</p><p>　　因為高強混凝土具有較高的抗拉強度，抗剪強度，約束力和承載力，錨固區(qū)的混凝土應力會更高。高強混凝土不宜產(chǎn)生收縮裂縫，有較高的彈性模，產(chǎn)生較小的徐變

28、，產(chǎn)生較小的鋼筋預應力損失。高強混凝土研究工作的重要性在于：</p><p>　　1、利用高強鋼筋和混凝土的必要性。</p><p>　　2、對于各種原因引起的預應力損失有了一定的認識。</p><p>　　3、在預應力混凝土中利用的使用可以減小預應力混凝土構(gòu)件的截面尺寸。自重的減小使大跨結(jié)構(gòu)在技術上和經(jīng)濟上實用。</p><p>　　預應力

29、混凝土的優(yōu)點：</p><p>　　在壓力作用下與其他結(jié)構(gòu)如鋼筋混凝土結(jié)構(gòu)和鋼筋結(jié)構(gòu)形式相比預應力混凝土有很大的技術上的優(yōu)點。在正常荷載作用下全預應力混凝土構(gòu)件不會出現(xiàn)拉應力。與帶裂縫工作的普通鋼筋混凝土構(gòu)件相比預應力混凝土的截面能被充分利用。在一定的范圍內(nèi)，通過增大預應力結(jié)構(gòu)構(gòu)件的預加偏心力可以抵消永久荷載的作用，因此可有效的節(jié)約材料。</p><p>　　預應力混凝土構(gòu)件群可提高抗剪強

30、度，這是因為預壓應力的存在減弱了拉應力的作用。特別是在大跨結(jié)構(gòu)中彎曲預應力的存在使加強截面減弱了剪力的作用效果。</p><p>　　在相同的荷載作用下，預應力混凝土受彎構(gòu)件比普通鋼筋混凝土構(gòu)件更不易變形。但是當裂縫出現(xiàn)以后，預應力混凝土構(gòu)件與鋼筋混凝土構(gòu)件的受力性能將會相同。</p><p>　　高強混凝土和鋼筋運用在預應力構(gòu)件中，可使其重量截面比普通鋼筋混凝土構(gòu)件都小，被命名為高強混凝

31、土和無裂縫預應力混凝土的兩種結(jié)構(gòu)形式在各種環(huán)境作用下其耐久性明顯優(yōu)于鋼筋混凝土構(gòu)件，語音里混凝土提高了沖擊荷載作用下構(gòu)件的吸能能力。試驗證明抵抗反復荷載的作用能力預應力構(gòu)件和鋼筋混凝土構(gòu)件同樣具有很好的性能。</p><p>　　對于大跨結(jié)構(gòu)預應力混凝土的良好經(jīng)濟性更加表現(xiàn)出來，在美國按照Dean的說法，預制橋梁10到30米長預應力混凝土梁比鋼梁和鋼筋混凝土梁經(jīng)濟效果都好。</p><p>

32、;　　按照Abeles所說，預制預應力混凝土應用在樓板，屋面和跨度在30m以上的橋梁中會明顯顯示出優(yōu)越的經(jīng)濟性。在大跨結(jié)構(gòu)中，預應力混凝土通常比鋼筋混凝土更經(jīng)濟。</p><p>　　因為預應力混凝土在遇到超載作用時不會產(chǎn)生任何嚴重的破壞，所以預應力混凝土具有相當大的彈性變形能力。Leonhardt指出在預應力混凝土構(gòu)件中，裂縫會在偶然荷載作用下發(fā)展，但當荷載恢復，裂縫又會完全閉合。與其他材料相比，預應力混凝土的

33、疲勞強度比較大，這主要歸因于混凝土中鋼筋應力變化比較小，因此適應承受動荷載的結(jié)構(gòu)。如鐵路橋和機器基礎。因為利用了混凝土的受拉區(qū)，預應力混凝土與鋼筋混凝土相比能節(jié)約15~20%的混凝土。鋼筋的節(jié)約會更大，60~80%這也要取決于預應力鋼筋中允許應力的大小，盡管在材料方面與鋼筋混凝土結(jié)構(gòu)相比，預應力混凝土結(jié)構(gòu)有很大的節(jié)約量，但經(jīng)濟上卻節(jié)約甚少。這主要因為預應力混凝土中要求使用高強混凝土，高強鋼筋，錨具和其他零件。盡管如此，預應力結(jié)構(gòu)中的來說