基于拟静力试验的无黏结预应力装配式桥墩接缝转动模型

Joint rotation model of unbonded posttensioned precast bridge column based on quasi-static cyclic tests

为探索无黏结预应力装配式桥墩的抗震性能,进行了此类桥墩及同尺寸现浇桥墩的拟静力加载试验。基于试验过程桥墩变形模式及滞回特性,进行了3种接缝转动模型下桥墩的抗震性能分析。分析模型采用OpenSees纤维单元建立,并计入无黏结预应力的自由伸缩及接缝处弹性转动变形特征。研究结果表明:拟静力加载过程,无黏结预应力装配式桥墩变形模式主要为墩底接缝处的弹性转动。随着加载位移增大,此类桥墩的失效模式表现为过大的接缝张开量及受压区面积迅速退化。不考虑预应力水平协同变形作用时,由于难以计入墩身整体弯曲及接缝转动引起的预应力伸长量,预应力内力计算值偏小,接缝张开量计算值偏大,导致桥墩初始刚度偏低,承载力退化较早。考虑协同变形作用后,桥墩接缝张开量相对减小,预应力增量相对增大。但由于忽略了无黏结预应力在接缝处的竖向刚度贡献,接缝张开量计算值仍大于试验值。采用释放接缝转动自由度、考虑无黏结预应力与墩身预制段协同变形、无黏结预应力对接缝约束作用时,可准确计算此类桥墩的接缝张开过程、预应力内力及滞回性能参数。提出的接缝模型建立方法可供“摇摆体系”桥墩抗震性能研究参考,以期推动此类桥墩在震区工程应用的进步。

To study the seismic performance of precast post-tensioned column(PPTC), quasi-static cyclic tests of cast-in-place(CIP) column and PPTC were conducted. Based on the deformation modes and hysteretic curves, seismic performance analysis of three joint rotation model columns was carried out. With the software OpenSees, the free expansion of unbonded tendons and elastic rotational deformation characteristics of joints were considered. The results show that the deformation mode of the PPTC is mainly controlled by rocking characteristics in joints during cyclic tests. With the displacement increasing, the failure modes are dominated by excessive joint openings and serious decrease of the compression areas. When the horizontal coordinated deformation of prestress is not considered, the calculated value of prestress internal force is too small and the calculated value of joint opening is too large, because it is difficult to include the prestress elongation caused by the overall bending of the column shaft and joint rotation, resulting in low initial stiffness of the column and early degradation of the bearing capacity. Considering the coordinated deformation, the column indicates reduced joint openings and larger prestress forces. However, due to the ignored vertical stiffness supplied by tendons, the calculated values are still larger than the test values. With the free rotational elements, coordinated horizontal deformations and the vertical stiffness using in numerical models, the proposed joint openings, prestress forces and the seismic parameters can be effectively calculated. The method of joint model establishment can be used as a reference for seismic performance research of ‘rocking characteristic’ columns, in order to promote the progress of engineering application of such columns in seismic regions. 1 tab, 14 figs, 22 refs.