橋梁畢業(yè)設(shè)計(jì)英文翻譯-展示頁(yè)
2024-12-13 06:32本頁(yè)面
【正文】 te beams They would certainly be less pleasing to the eyes and often more expensive than the prestressed concrete beams . These school buildings have a strong , simple architectural appeal and will be a pleasure to look at for many years . The most important parts of a precast prestressed concrete beam are the tendons and the concrete . The tendons , as the name implies , are the cables ,rods or wires of steel which are under tension in the concrete . Before the concrete . has hardened (before transfer of stress ) , the tendons are either unstressed (posttensioned prestressing ) or are stressed and held by abutments outside the concrete (pretensioned prestressing ) . While the concrete is hardening it grips each tendons more and more tightly by bond along its full length . End anchorages consisting of plates or blocks are placed on the ends of the tendons of posttensioned prestressed units ,and such tendons are stressed up at the time of transfer , when the concrete has hardened sufficiently ,In the other type of prestressing , with pretensioned tendons , the tendons are released from external abutments at the moment of transfer . The factory precasting of long prestressed concrete beams is likely to bee more and more popular in the future ,but one difficulty will be road transport .As the length of the beam increases the lorry bees less and manoeuvrable until eventually the only suitable time for it to travel is in the middle of the night when traffic is at a minimum . The limit of length for road are straight or curved . Precasting at the site avoids these difficulties 。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
公司管理相關(guān)推薦
鄂ICP備17016276號(hào)-1