Study on enhancement in seismic performance of concrete piers by applying vertical prestressing

为了通过施加竖向预应力来提高混凝土桥墩的抗震性能，进行了预应力混凝土柱试件的静力和拟动力试验。主要研究结果如下：1.无粘结预应力混凝土桥墩（PC墩）在预应力和外轴应力的总压应力小于混凝土抗压强度的25%时，具有与普通钢筋混凝土桥墩相同的延性。试验结果表明，预应力混凝土桥墩具有较高的恢复能力，残余变形与普通钢筋在受弯部位的分担率成正比.空心墩的抗震性能随柱底截面形状的不同而有较大差异。考虑柱底截面刚度设计的桥墩，在距基础面高度为D（D：截面高度）处填充混凝土，或在D/2的情况下，在柱底布置附加钢筋，均表现出足够的抗震性能.研究表明，在地震作用下，混凝土开裂和钢筋屈服导致自振周期向长边方向变化，而预应力混凝土筋不屈服，从而避免了桥墩的共振现象.可以预期，PC桥墩具有较高的恢复能力偏心条件下，以及正常条件下，如果适当的垂直预应力安装考虑到重力偏心。

In order to enhance seismic behavior of concrete piers by applying vertical prestressing, static and pseudo-dynamic tests using prestressed concrete column specimens were carried out. The main results obtained from this study are described as follows :1. The prestressed concrete pier (PC pier) in which the prestressing tendons were unbonded had same ductility as an ordinary reinforced concrete pier when the total compressive stress due to the prestress and external axial stress was less than 25% of the concrete compressive strength. Also, it was shown that the PC pier had high restoration capability, and that the residual deformation was proportional to the sharing ratio of ordinary reinforcement in flexure.2. The seismic performance of PC pier having hollow cross section were differed largely according to the shape of cross section at the column bottom. The pier which was designed considering the stiffness of the cross section at the column bottom in such a way that height of D (D : height of cross section) from footing surface was filled up with concrete or, in the case of D/2, additional reinforcing bars were arranged at the bottom showed sufficient seismic performance.3. It was clarified that the PC pier could avoid the resonant behavior of vibration under seismic motion due to the fact that the natural period changed to longer side due to the cracking of concrete and yielding of reinforcement without yielding of PC tendons.4. It can be expected that the PC pier has high restoration capability under eccentric condition as well as ordinary condition if vertical prestressing was adequately installed considering the eccentricity of the gravity.