Revisiting the Effect of Axial Force Ratio on the Seismic Behaviour of RC Building Columns

Protection of structural columns against severe damage is of most importance in the seismic design of RC structures. The seismic performance of reinforced concrete (RC) columns can be improved by concrete confinement in the plastic hinge regions, where the required quantity of confining reinforcement is influenced by the axial force ratio (AFR). Nevertheless, different design standards have different treatments on the AFR effect in the ductility design of RC columns. In this regard, this paper presents a scientific revisit, which is conjugated with a statistical analysis of 474 sets of experimental data, on the effect of AFR. It is found that the displacement and hysteretic dissipation capacities of the flexure -critical RC columns can be significantly reduced by increasing AFR, although the lateral strength shows a reversed trend. On the other hand, the displacement ductility of short columns is apparently not influenced by AFR, yet the hysteretic dissipation capacity deteriorates under high AFR. The analytical results also suggest that different AFR limits should be used for the design of slender and short columns due to different failure mechanisms. The presented work sheds light on the considerations of the AFR effect and setting a suitable limit for controlling the seismic perfomiance of RC columns.