橋梁畢業(yè)設(shè)計(jì)英文翻譯(編輯修改稿)
2025-01-06 06:32 本頁面
【文章內(nèi)容簡(jiǎn)介】 s 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 unloaded stage can be avoided , and the perstress force selected promarily to produce the desired deflection for a particular loading condition . The behavior of partially perstressed beams , should they be overloaded to failure , is apt to be superior to that fully perstressed beams , because the improved ductility provides ample warning of distress. The design of structural members based on strength requirements is appeali
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