Study on the residual mechanical performance of round-ended concrete-filled steel tube members exposed to combined eccentrical compression and impact loading

Round-ended concrete-filled steel tube (RE-CFST) members, commonly used in bridge piers and main towers, are often subjected to impacts from vessels, vehicles, floating debris, and other potential collisions. Therefore, this paper focuses on the residual mechanical performance of RE-CFST columns exposed to the combined effect of eccentric compression and impact loading. The post-impact compression tests were conducted, and the failure modes, load-midspan displacement, and load-longitudinal strain curves under different eccentricity ratios and axial-load ratios were obtained. The results showed that the RE-CFST beam-columns primarily presented global deformation under lateral impact. Under eccentric compression, pronounced local buckling was observed in the outer steel tube on the compression side. The load-lateral displacement curve of the column under eccentric compression showed a gentle decrease, indicating good ductility of the specimen. As the eccentricity ratio and axial-load ratio increased, the residual resistance of the specimen decreased. In addition, based on ABAQUS software, a total of 144 finite element (FE) models were established to analyze the lateral impact behavior and residual resistance of RE-CFST columns. The effects of impact velocity, eccentricity ratio, axial-load ratio, aspect ratio, and steel ratio were emphatically studied. Results indicate that with the increase in steel ratio and aspect ratio, the post-impact residual deflection of the specimens decreases, while the residual bearing capacity improves. Finally, based on response surface analysis, formulas for the residual deformation after an impact and residual resistance coefficients of these specimens under the interaction of multiple factors were proposed. The results show that the aspect ratio is a key factor affecting both post-impact residual deflection and residual bearing capacity coefficients. Furthermore, the interaction between aspect ratio and eccentricity ratio, as well as between aspect ratio and impact velocity are significant. The proposed formulas can well predict the post-impact residual deformation and residual bearing capacity coefficients of RE-CFST columns.