无粘结预应力筋的极限应力

基于等效变形区长度提出了极限状态下混凝土梁跨中挠度的简化计算方法,继而根据梁的跨中挠度推导了体内和体外无粘结预应力筋极限应力增量的通用计算公式.以受力钢筋的配筋率、预应力筋布置形式、预应力度、跨高比、荷载形式等为参数,对无粘结预应力混凝土梁的受力性能进行了参数分析,依据分析结果,提出了以综合配筋指标和预应力度为参数的等效变形区长度的计算公式.结果表明 :所提出的无粘结预应力筋极限应力增量的计算方法及公式具有较好的适用性;多种荷载形式作用时的等效变形区长度,可取为各种荷载单独作用时等效变形区长度的加权平均值,权值为各类荷载产生的跨中弯矩.

Ultimate Stress of Unbonded Prestressed Tendons

A simple formula was developed for the ultimate mid - span deflection of concrete beams with the concept of equivalent length of the deformation zone, then an analytical model was deduced to analyze the ultimate stress increment in those concrete beams prestressed with external or internal unDonded tendons based on the mid- span deflection. The nonlinear behavior of the beams prestressed with external or internal unDonded tendons were studied by the program developed. Such parameters as the percentage of ordinary reinforcment, amounts and configuration of unDonded prestressed tendons, the ratio of span to depth and the loading patterns were considered. It was shown that the predicted results from the analytical model were in good agreement with the test values and the results from the program. Based on the results, the equations for the eqivalent length of deformation zone on the beams at ultimate were developed, in which the aggregative indicator of reinforcement and index of prestressed tendons were selected for parameters. The equivalent length of those beams under multiple pattern loads could be determined by that of the beams under single pattern load using the weighted arithmetic average, where the moment at mid-span on the beams could be chosen as the weight coefficient.