Inelastic Earthquake Response of Steel Columns with Variable Cross-Section Subjected to Bi-Axial Bending

本课题研究了地震作用下钢柱的弹塑性地震反应。(1)钢桥墩的弹塑性地震反应分析1)采用有限元程序Marc-K62对钢柱进行地震反应分析，输入水平地震动为南北向和东西向地震波分量。2)在南北向和东西向地震共同作用下，柱子承受双向弯曲时，3)较小截面柱的上部塑性变形导致破坏严重，因为抗力弯矩小于柱脚正截面。4)对梁中部发生剪切倒塌的门式刚架结构的破坏机理也进行了数值研究。5)柱脚部位对耗能非常重要。(2)变截面柱脚的弹塑性性能1)变截面悬臂柱的弹塑性性能通过数值和实验研究了恒定垂直载荷和交变水平载荷作用下的塑性变形。2)实验证实，塑性变形沿锥形底座的传播范围很广。这就是为什么抗力弯矩在柱脚部位均匀变化的原因。3)这一事实暗示了使震害减小的可能性，而不是具有等效截面的柱脚部位。4)锥形底座部分的抗震性能受局部屈曲的最终位置的影响很大。5)有必要制定适当的方法来加强锥形底座部分。

This research project studies the inelastic earthquake response of steel columns subjected to earthquake ground motion. Attention is paid to the variable cross-section of column.(1)Inelastic Earthquake Response Analysis of Steel Bridge Piers1)The earthquake response analysis of steel columns was performed by using Finite Element Code MARC-K62, in which the NS and EW earthquake wave components were assumed as the input horizontal ground motions.2)In the case of columns subjected to bi-axial bending which is caused by the combination of NS and EW earthquake ground motions, the damage of columns become severe compared with the damage of columns subjected to which of NS or EW motion.3)The plastic deformation in the upper potion of columns with smaller cross-section results in the heavy damage because the resistant moment is smaller than the column base cross-section.4)The damage machanism of steel portal frames with the shear collapse in the middle of beam were also investigated numerically.5)The column base parts are very important to dissipate the hysteretic energy.(2)Elasto-Plastic Behavior of Tapered Column Base Parts1)The elasto-plastic behavior of cantilever columns with tapered base part is investigated numerically and experimentally under the constant vertical and alternating horizontal loads.2)It was confirmed by experiment that the plastic deformation propagates widely with distance along the tapered base part. This is reason why the resistant moment varies uniformly in the column base part3)This fact implies the possibility of making the earthquake damage decrease rather than the column base part with equivalent cross-section.4)The earthquake performance of tapered base part is much influenced by the final location of local buckling.5)It is necessary to develop an appropriate method for stiffening the tapered base part.