Seismic Behavior of Reinforced Concrete Short Columns Subjected to Varying Axial Load

This paper presents findings on the effects of varying axial load on the seismic performance of reinforced concrete (RC) short columns that failed in shear by conducting an experimental program on five full-scale RC columns. The key variable of this paper is the applied axial load pattern. The seismic behavior of the columns subjected to varying axial load was experimentally appraised with regards to crack patterns, shear failure modes, hysteretic response, shear behavior, and drift and energy dissipation capacities. The test results indicated that the lateral load-displacement hysteresis loops of RC columns with varying axial load are unsymmetrical. Under varying axial load, the columns exhibited a very diverse seismic performance when compared to those subjected to constant axial load. Diferent shear failure modes were also detected between columns under constant and varying axial loads. The shear strength and its deterioration of columns strongly depend on both the fuctuating range and intensity of applied axial load. To supplement the experimental results, a three-dimensional (3-D) finite element (FE) model is proposed to further investigate the effects of varying axial load on seismic behavior of RC short columns subjected to varying axial force. The intensity and fuctuation of the applied axial load is found to have a significant effect on the shear strength of RC short columns. Comparisons with the current available model for assessment of shear capacity revealed that the ASCE/SEI 41-17 provisions tend to overestimate the shear capacity of RC columns subjected to varying axial load tested in this study. Therefore, a modification parameter is proposed when adopting the ASCE/SEI 41-17 provision to evaluate the shear capacity of RC columns under varying axial load. Keywords: drift capacity; energy dissipation capacity; reinforced concrete short column; shear failure mode; shear strength; varying axial load.