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

为了通过施加竖向预应力提高混凝土桥墩的抗震性能，采用预应力混凝土柱试件进行了静力和拟动力试验。本研究的主要结果如下：1。不粘结预应力筋的预应力混凝土墩（PC墩），当由预应力引起的总压应力和外轴应力小于混凝土抗压强度的25%时，其延性与普通钢筋混凝土墩相同。PC墩具有较高的恢复能力，其残余变形与普通配筋分担挠曲的比例成正比。空心截面PC墩的抗震性能因柱底截面形状的不同而有较大差异。2 .考虑柱底截面刚度的桥墩设计，从基础表面开始用混凝土填充D （D：截面高度）的高度，或者在D/2的情况下，在底部布置额外的钢筋，显示出足够的抗震性能。阐明了预应力混凝土桥墩在不发生预应力混凝土肌腱屈服的情况下，由于混凝土开裂和钢筋屈服导致桥墩的自然周期向较长边转变，从而避免了地震作用下桥墩振动的共振行为。考虑到重力的偏心，只要施加足够的竖向预应力，可以预期PC墩在偏心和普通情况下都有较高的恢复能力。

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.