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

本研究计画系探讨钢柱在地震动作用下之弹塑性地震反应。对变截面柱的设计进行了研究。（1）钢桥墩的非弹性地震反应分析1）采用有限元程序MARC-K62对钢柱进行了地震反应分析，其中将NS和EW地震波分量作为输入水平地震动。2）在由NS和EW地震波组合引起的双向弯曲柱的情况下，3）由于柱的抗力矩小于柱脚截面，截面较小的柱上部的塑性变形导致柱的严重破坏通过数值模拟，研究了钢门式刚架在梁中剪切破坏时的破坏机理。5）柱脚部位是耗能的重要部位。（2）变截面柱脚的弹塑性性能1）对变截面柱脚悬臂柱在恒定垂直荷载和水平荷载交替作用下的弹塑性性能进行了数值模拟和实验研究。2）实验证实，塑性变形沿变截面柱脚沿着距离广泛传播。3）这一事实意味着降低地震破坏的可能性，而不是等效截面的柱脚部分。4）锥形基础部分的地震性能很大程度上取决于局部屈曲的最终位置。5）有必要开发适当的方法来加强锥形基础部分。

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.