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. © 2019, Editorial Office of Journal of Building Structures. All right reserved.