Quasi-static Test Of RC Column With Variable Axial Forces And Rotations

For reinforced concrete frame structures with buckling-restrained braces(BRBs), the levels and amplitudes of column axial force variation induced by the influnece of BRBs under earthquake wave may increased largely. These factors may cause unpredictable damage on reinforced concrete frame column, while there is still limited studies disclosing the negative effects induced by the dramatic changes of the axial forces. For solving this problem, this paper designs six full-scale reinforced concrete columns, conducts quasi-static tests on these specimen with the outer loop feedback control loading method, and foucs on investigating the impact of dramatic varation of axial forces and rotations on the seismic performance of reinforced concrete columns. The main work and conclusions of this paper are as follows:(1) The influence of BRBs on axial force variation of RC column under earthquake wave was researched by numerical simulations. Furthermore, the quasi-static tests of 6 reinforced concrete columns were designed, and the outer loop feedback control method was proposed to improve test loading accuracy. The results show that the BRBs may greatly improve the axial force variation of reinforced concrete columns, and the outer loop feedback control method can realize accurate loading on the specimens in terms of horizontal deformations and axial forces.(2) The influence of variable axial forces and force loading history on the seismic performance of reinforced concrete columns were investigated by quasi-static tests. The experimental results show that: under variable axial forces, the damage phenomenon and hysteresis curves of columns exhibite significant asymmetry with respect to positive and negative directions; for the positive direction, the bearing capacity and the initial stiffness of reinforced concrete columns were greatly increased, while the strength and stiffness degradation were speeded up and the displacement ductility coefficient was decreased; for the negative direction, the bearing capacity, the initial stiffness of reinforced concrete columns and the displacement ductility coefficient were decreased, the strength degradation was slowed down while the stiffness degradation was speeded up; the opposite performance was obtained except the reduction of the displacement ductility coefficient; the differecnce between the positive and negative direction may increase significantly with the increase of variable magnitude of axial forces; and the axial force loading history also have significent influence on the seismic behavior of reinforced concrete columns.(3) The influence of variable rotations on the seismic peformance of reinforced concrete columns was investigated by quasi-static tests. The exprimental results show that the damage phenomenon exhibite apparent asymmetry with respect to the top and bottom of the columns, and sever damage was observed on the bottom of specimens; the bearing capacity and the initial stiffness were decreased by the influence of ratations, while the strength and stiffness degradation were slowed down; under constant axial force, the displacement ductility coefficient was reduced with the influence of variable rotations; while under variable axial loads, the displacement ductility coefficient in positive direction was increased, the displacement ductility coefficient in negative direction was decreased, and the energy dissipation capacity of the specimens was reduced.