压-弯-剪-扭复合受力钢筋混凝土L形截面柱抗震性能试验研究

为研究压-弯-剪-扭复合受力下钢筋混凝土L形截面柱的抗震性能,以扭弯比、轴压比为变化参数,设计6个钢筋混凝土柱试件在恒定轴力和反复弯-剪-扭复合作用下的加载试验.观察试件的破坏过程和形态,得到其扭矩-扭转角滞回曲线和荷载-位移滞回曲线,以及试件的开裂点、峰值荷载点和破坏点等特征参数.基于试验数据,分析扭弯比和轴压比变化对钢筋混凝土L形截面柱的压碎区高度、钢筋应变、承载力、位移延性、层间侧移角、耗能能力、承载力及刚度退化等抗震性能指标的影响.结果表明:低周反复压-弯-剪-扭钢筋混凝土L形截面柱破坏形态表现为弯曲、弯扭和扭剪破坏,滞回曲线呈捏拢的S形,随着扭弯比的增大,柱根部压碎区高度变小,翼缘裂缝发展更为完善,纵筋应力增大,箍筋应力减少,开裂荷载和受扭承载力均有提高,试件扭转延性提高但位移延性降低,初始刚度较小且退化更为平稳;而轴压比则与受扭承载力和弯曲刚度密切相关,轴压比越大,受扭承载力越大,弯曲刚度提高;试件弯曲耗能的等效黏滞阻尼系数在0.08~0.28之间,扭转耗能的等效黏滞阻尼系数为0.13~0.23,试件耗能占比由初期扭转耗能为主向弯曲耗能转变,L形截面柱性能水平对应的层间位移角均能满足相关规范要求.扭矩的存在对试件抗震性能削弱较大.

Experimental study on seismic behavior of reinforced concrete L-shaped column under compress-flexure-shear-torsion combined action

To study the seismic behavior of reinforced concrete L-shaped column under compress-flexure-shear-torsion combined action, a total of six reinforced concrete columns with varying parameters of torsion-bending ratio and axial compression ratio were designed and tested under constant axial compression force and quasi-static reversed cyclic loading. The failure process and patterns were observed. The hysteretic loops of torsion moment-torsion rotation angle and load-displacement were obtained respectively. The crack, yield, peak, and failure points of specimens during loading test were acquired as characteristic values. Based on the experimental data, the effects of torsion-bending ratio and axial compression ratio on the seismic behavior indexes like height of crushing region, strain of reinforcement, bearing capacity, displacement ductility, story drift, energy dissipation, bearing capacity and stiffness degradation of specimens were analyzed. The test result shows that the failure patterns of L-shaped specimens present as bending failure， bending-torsion failure and torsion-shear failure. The hysteretic curves show a pinched “S”. With the increase of torsion-bending ratio, the height of crushing region at the bottom of the specimens is lower, the cracks on the flange develop more complete, the tensile stress of longitudinal steel bars increases, the stress of stirrups decreases, the cracking load and the ultimate torsion bearing capacity both improve, the torsion ductility increases but the displacement ductility decreases, and the initial stiffness is relatively small and degrade slowly. The ultimate torsion bearing capacity and bending stiffness are closely related to the axial compression ratio. The bigger axial compression ratio, the greater ultimate torsion bearing capacity and bending stiffness. The bending equivalent viscous damping coefficient of the specimens is between 0.08~0.28. The torsion equivalent viscous damping coefficient is between 0.13~0.23. With the increase of load, the large proportion of the energy dissipation turns into the bending energy dissipation from the torsion energy dissipation. The average of the story drift ratio of L-shaped column meets the requirement of chinese code based on seismic performance. The presence of torque contributed to the decrease of the seismic performance of the specimens.