Post-impact performance of round-ended CFST columns: Tests, numerical analysis and design

Understanding the residual performance of structural members due to the impact damage is important to evaluate their damage degree and develop adequate retrofitting measures. The present work is a follow-up study on the impact resistance of round-ended concrete filled steel tubular (RE-CFST) columns by the authors, in which the residual behaviours of RE-CFST columns after being subjected to impact are presented. First, seven columns were laterally impacted and subsequently loaded to failure under axial compression. The damage pattern, load-lateral deflection relationship, and load-longitudinal strain responses were obtained. Test results showed that as the impact energy or pre-axial load increased, both the residual resistance and residual strength ratio of impacted columns decreased. Finite element models were developed to simulate the post-impact behaviours and were then verified using the experimental results. Next, a parametric investigation was performed on a series of 63 columns to analyze the effects of impactor velocity, axial-load ratio, steel ratio, slenderness ratio and cross-sectional aspect ratio on the residual axial resistance after impact. The analysis indicated that the steel ratio, slenderness ratio and cross-sectional aspect ratio have a moderate effect on the residual strength ratio. Finally, a simplified equation based on the global and local deformations was proposed to predict the residual axial resistance of RE-CFST columns exposed to impact loading.