Experimental and Theoretical Studies on Behavior of Unbonded PC Beams at the Ultimate State

本研究包括两个测试系列。系列A试验的目的是研究基本参数如预应力钢筋用量、非预应力有粘结钢筋用量、混凝土抗压强度和剪跨长度对无粘结预应力钢筋梁的基本抗弯性能的影响，并与有粘结预应力钢筋梁的基本抗弯性能进行比较。在系列B试验中，以侧限配筋率和预应力筋初张应力为主要试验变量，研究了侧限对试件极限抗弯承载力的影响，对无粘结和有粘结预应力梁的最大可达应力和延性进行了研究，结果表明，无粘结预应力梁的应力增量与有粘结预应力梁的延性相差不大，最大抗弯强度的载荷受所有试验变量的影响很大，测量的应力增量与计算值吻合良好。 ...更多信息 当应变协调系数假定为0.2-0.3时，根据剪跨长度，得出1。ACI规范建议的无粘结梁最小非预应力钢筋用量的规定，被证实是非常有效的改善在极限状态下的抗弯性能以及裂缝的分布。高强混凝土的使用可以很好地提高无粘结钢筋的应力增量和抗弯延性。然后，从系列B试验中发现，最大抗弯强度以及最大可达到的钢筋应力显着增加，由于横向约束在无粘结梁相比，粘结梁，这种趋势变得显着，随着降低初始拉应力的钢筋。在无粘结梁中，设置体积分数为1%的侧向约束不能很好地提高预应力筋的应力增量和梁的极限强度，但能显著提高梁的延性。采用上述应变协调系数可以很好地估计无粘结梁在达到最大强度后包括下落分支区域的行为。少

The present study consists of two test series. The purpose of series A tests is to examine the effect of basic parameters such as amount of prestressed steel, amount of nonprestressed bonded steel, compressive strength of concrete and length of shear span on the fundamental flexural properties of unbonded beams without bond of prestressing steel in comparison with those of bonded beams. In the series B tests, on the other hand, the ratio of lateral confinement steel and initial tensioning stress of prestressing steel were chosen as the main test variables and then the effect of lateral confinement on the ultimate flexural strength, maximum attainable stress in prestressing steel and ductility of unbonded and bonded beams were studied.The results of series A tests showed that the stress increment of unbonded steel due to applied load up to the maximum flexural strength is significantly affected by all the test variables and that the measured stress increment agreed well with the calcula … More ted one when the strain compatibility factor was assumed to be 0.2-0.3, depending upon the shear span length. The provision of the minimum amount of nonprestressed steel for the unbonded beams, as recommended by the ACI Code, was confirmed to be very effective for improving the flexural properties at the ultimate state as well as the distribution of cracks. Use of high- strength concrete could increase well both of stress increment of unbonded steel and flexural ductility. And then, it was found from series B tests that the maximum flexural strength as well as the maximum attainable steel stress was significantly increased due to lateral confinement in the unbonded beam compared to bonded beam and that such tendency became remarkable with decreasing initial tensioning stress of steel. In the unbonded beams, the provision of lateral confinement with 1% by vol. could not well increase the stress increment of prestressing steel and the beam strength at the ultimate state but significantly improve the beam ductility. The behavior of unbonded beam including the falling branch region after the maximum strength could be estimated well using the strain compatibility factor as mentioned above. Less