橋梁畢業(yè)設(shè)計(jì)英文翻譯-免費(fèi)閱讀
【正文】 這一公式可以被重新整理，使其能直接求解需要的混凝土尺寸和受拉鋼筋面積。 以強(qiáng)度要求為依據(jù)的構(gòu)件設(shè)計(jì)是受人歡迎的，因?yàn)椋隽藰O罕見(jiàn)的情況以外，結(jié)構(gòu)唯一最重要的性能就是結(jié)構(gòu)的強(qiáng)度，它確定了設(shè)計(jì)中所體現(xiàn)的安全度。 部分預(yù)應(yīng)力有很大的有點(diǎn)，它需要較小的預(yù)張拉力，因此可以減少預(yù)應(yīng)力筋和錨具的數(shù)量。 在目前的設(shè)計(jì)實(shí)踐中，明顯地傾向于采用部分預(yù)應(yīng)力梁。 隨著時(shí)間的增加，混凝土（同時(shí)還有鋼筋）還會(huì)產(chǎn)生進(jìn)一步的縮短。與預(yù)應(yīng)力混凝土梁相比，它們當(dāng)然會(huì)顯得不夠美觀而且成本往往更高一些。在橋臺(tái)能承受推力的橋梁中，橋體混凝土中沒(méi)有鋼筋也能施加預(yù)應(yīng)力。二在鋼筋混凝土中，這通常是不可能的，因?yàn)檫@將導(dǎo)致構(gòu)件嚴(yán)重開(kāi) 裂，開(kāi)裂會(huì)影響美觀，而且如果造成鋼筋生銹的話(huà)，還會(huì)發(fā)生危險(xiǎn)。it may be expensive ,but it has often been used for large beams. There is a distinct trend in current design practice tward the use of partially perstressed beams, in which flexural tensile stress or even cracking is permitted in the concrete in the service lode stage or for occasional overloads. Cracks, if the occur,are usually small and well distributed, and normally close pletely when the load that produced them is removed. It is argued convincingly that cracking has long been an accepted feature of reinforced concerte members and that there is no reason to penalize prestressed concerte desinge by requiring that cracks be eliminated pletely ,even though this is possible .Furthermore,the condition of no tension or limited tension in a preastressed structure rarely exise. If bined effects including shear and torsion are taken into account, the calculated principal stresses usually exceed the tensile strength of the concrete. In regions of concentrared loads , load transfer , or anchorage of tendons, Tensile stresses cannot be avoided . Also, in most cases , a struture is prestressed in only one direction , so that in the transverse direction it acts as ordinary reinforced concrete . In vivw of these facts , it is hard to justify a requirement for no fiexurel cracking . The advantages of partial prestressing are important . A smaller prestress force will be required , permitting reduction in the number of tendons and anchorages. The necessary flexural strength may be provided in such cases either by a bination of presstressed tendons and nonprestressed reinforcing bars , or by an adequate number of hightensile tendons prestressed to a level lower than the permitted limit . In some cases a bination of stressed and unstressed tendons is used . Since the prestressing force is less, the size of the bottom flange , which is required mainly to resist the pression when a beam is in the unloaded stage , can be reduced or eliminated altogether . This lerds in turn to significant simplification and cost reduction in the construction of forms ,as well as resulting in structures that are more pleasing esthetically . Furthermore , by relaxing the requirement for low servise load tension in the concrete , a significant improvement can be made in the member in the unloade
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