Numerical simulation on residual axial compression bearing capacity of square in square CFDST columns after lateral impact.

Square in square concrete-filled double-skin steel tube (CFDST) columns are widely preferred on account of their convenient nodal structural form and efficient construction process. In order to investigate the axial compression behavior of the columns after lateral impact, a precise numerical model for the post-impact axial compression of square in square CFDST columns was established using the finite element package, and was validated by existing experiments and studies. The residual axial compression bearing capacity of the columns after lateral impact has been analyzed. The typical vertical load-axial displacement curve, the failure mode and stress distribution of the columns have been studied. The parametric analysis has been also carried out to explore the influence of key parameters. Lastly, based on the parametric analysis, a simplified formula has been proposed to estimate the residual axial compression bearing capacity of the columns. The results show that under lateral impact, the columns generally exhibit a flexural failure mode. Local indentation occurs at the impact location, and buckling also appears at the bottom of the fixed support section. The coefficient of residual axial compression bearing capacity decreases with the increase of impact energy, slenderness ratio, and concrete strength, and increases significantly with the increase of steel strength.