拉筋接触方式对高轴压比钢管混凝土柱抗震性能影响试验研究

高轴压比下的钢管混凝土柱抗震性能较差，端部拉筋能够有效提高钢管混凝土柱的抗震能力，但拉筋与钢管壁焊接施工困难，不利于工程应用。为了研究拉筋笼与钢管壁间接触方式对钢管混凝土柱整体抗震性能的影响，通过对2个圆形和4个方形截面高轴压比端部带拉筋的钢管混凝土柱进行水平低周往复荷载作用下的试验研究，分析不同接触方式对其破坏形态、滞回耗能能力、骨架曲线、弹性刚度、承载力、延性系数、刚度退化和残余变形率的影响规律。结果表明：拉筋笼与钢管内壁焊接能够加强拉筋和钢管对混凝土的约束作用，从而增加构件的整体刚度。同时，塑性铰处钢管鼓曲幅值与局部屈曲长度明显降低，因此获得了更高的弹性刚度、承载力和滞回耗能能力；外径尺寸和其他设计参数相同时，常用拉筋笼约束方式下方钢管混凝土柱比圆钢管混凝土柱具有更大的抗弯刚度、承载力和塑性耗能能力，且破坏时始终表现为塑性压铰，而带拉筋圆钢管混凝土柱在破坏后往往由塑性压铰转变为拉铰。

Experimental study on influence of contact mode between stirrup and steel tube on seismic performance of stirrup-confined concrete-filled steel tube columns under high axial compression ratio

The seismic performance of concrete-filled steel tube (CFST) columns is poor under high axial compression ratio. The stirrup-confinement at column ends can effectively improve the ultimate seismic resistance of the CFST columns. However, the welding between the stirrup and the steel tube wall is difficult, which is not conducive to its application in constructions. To investigate the effect of the contact mode between stirrup cage and steel tube wall on the hysteretic behavior of stirrup-confined CFST columns, a pseudo-static experimental study on two stirrup-confined circular CFST columns and four stirrup-confined square CFST columns under high axial compression ratio and low cycle horizontal loads was presented. The effect of different contact modes between stirrup and steel tube on the failure mode, hysteretic energy dissipation capacity, skeleton curve, elastic stiffness, ultimate bearing capacity, ductility coefficient, stiffness degradation, and residual deformation ratio of the composite columns were analyzed. The results indicate that the existence of the weld connecting between the stirrup cage and the inner wall of steel tube can strengthen the confinement effect of stirrup and steel tube on the infilled-concrete, thereby increase the overall stiffness of the composite columns. Meanwhile, the amplitude of buckling deformation and the length of the plastic hinge region of steel tube are reduced. Therefore, the overall elastic stiffness, ultimate bearing capacity and energy dissipation capacity of the specimens are upgraded. The stirrup-confined square CFST columns with the same outer diameter and other design parameters have greater bending stiffness, ultimate bearing capacity and plastic energy dissipation capacity compared with the stirrup-confined circular CFST columns. During the progress of failure, stirrup-confined square CFST columns show a compressive plastic hinge, while the tensile plastic hinge forms in the final failure mode of stirrup-confined circular CFST columns.