AbstractA novel pendulum test setup was designed to investigate the influence of the axial loading method on the dynamic responses of reinforced concrete (RC) columns under impact load. The inertia effect caused by the vertical vibration of superstructures above columns can be implemented by the setup. A total of six RC columns were tested under different axial compression ratios and impact velocities. The impact force, pendulum velocity, displacement, axial force, and acceleration of the specimens were measured, and the damage evolution during the test was recorded by high-speed cameras. The test results indicate that when the axial compression ratio increases from 0 to 0.64 and the impact velocity increases from 2.58 to 4.58  m/s, the failure mode of the column changes from flexural failure to shear failure. The impact force time-history curves of the shear failure controlled columns are different from those of the flexural failure controlled columns. The vertical mass of the superstructure above the RC column improves the horizontal and vertical inertia effect of the column. Besides, a two-degrees of freedom (2DOF) model was modified to predict the impact responses of the specimens. Two axial force conditions, including measured dynamic axial force and constant axial force (without considering the axial inertia effect and axial force variation), were compared using the modified model. Afterward, the modified model was compared with the conventional 2DOF model using the test results of 12 RC columns. Further, a parametric study of the axial compression ratio and the impact velocity was performed using the modified model, showing that they present significant influences on the impact performance of RC columns.

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