EXPERIMENTAL STUDY ON SEISMIC PERFORMANCE OF STEEL-REINFORCED CONCRETE COLUMNS UNDER COMPRESSION-FLEXURE-SHEAR-TORSION COMBINED ACTIONS

In order to reveal the seismic behavior of steel-reinforced concrete (SRC) columns under compression-flexure-shear-torsion combined actions, twelve SRC columns and one reinforced concrete(RC) column were tested by comprehensively considering the cross-sectional dimension of the column, the steel ratio, the reinforcement ratio, the stirrup ratio and, the welded stud location. The failure characteristics of specimens under composite torsional conditions were observed, and the influence of different parameters on the seismic indexes of SRC columns were analyzed, such as hysteric curve, stiffness degradation, energy dissipation and ductility. The test results indicate that the failure patterns of specimens mainly appear as the bending-torsion composite failure occurs. The load - displacement hysteric curves present full spindle shapes, and the torque-torsion angle curves are in “S” shapes with obvious pinching. The torsional and flexural bearing capacity of SRC columns can be effectively improved by increasing the section size or reinforcing ratio. Before the peak load, the degradation rate of torsional stiffness is significantly faster than that of flexural stiffness and, increasing the steel ratio and reinforcement ratio can delay the degradation of SRC column stiffness. The bending energy dissipation capacity of SRC columns is better than the torsional energy dissipation capacity, and the torsional ductility is greater than the bending ductility. SRC columns with rectangular cross-sections have better torsional deformation capacity than those with square cross-sections. Welding studs on I - shaped steel flanges can effectively improve the seismic behavior of SRC columns. According to the current seismic code and test data, some suggestions of structural measures of SRC columns and empirical formula of torsional energy degradation are put forward.