EXPERIMENTAL STUDY ON SEISMIC BEHAVIOR OF REINFORCED CONCRETE CROSS SHAPE COLUMNS UNDER COMPRESSIONFLEXURE-SHEAR-TORSION COMBINED ACTIONS

To reveal the seismic behavior of reinforced concrete cross shape columns under compressionflexure-shear-torsion combined actions, the torsion-bending ratio and axial compression level were considered as parameters in an experiment, and six specimens of reinforced concrete cross shape columns were designed for reversed cyclic flexure-shear-torsion loading test with constant compression. The failure process and failure pattern were observed, the hysteretic curves of torque-torsion angle and loading-displacement as well as the characteristic results of the cracking, yielding, peak and failure points were obtained. Based on the test data, the seismic indexes of the specimens, such as the bearing capacity, ductility, drift angle, energy dissipation, strength and stiffness degradation, were analyzed deeply. The research results show that when the torsion-bending ratio is less than 0.21 and the axial compression level is less than 0.34, the failure pattern of the specimens are of a bending-torsion or torsion-shear failure mode. The hysteretic curves are of an "S" shape and pinch obviously. The ductility coefficients are larger than 3.0, the crack point drift angles are larger than 1/550, and the failure point drift angles are larger than 1/40. All of them can meet the needs of the Chinese code for seismic design of buildings. The presence of the torque makes the material damage more serious and improves the energy dissipation capacity of the specimens.