Axial compressive performance of full-scale reinforced hollow high strength concrete-filled thin-walled square steel tubular columns

Manufacturing limitations in hollow concrete-filled steel tube (HCFST) structures often lead to significant void ratios, which can result brittle failure after reaching the peak load. To address this issue, this study proposes a novel structural solution: reinforced hollow concrete-filled square steel tubular (RHCFST) columns. These columns integrate the benefits of hollow concrete-filled steel tubes (CFST) and prestressed high-strength concrete (PHC) tubular columns. The research includes experimental testing and finite element simulations on five full-scale, thin-walled RHCFST under axial compression. Experimental results reveal that the column specimens predominantly failed with mid-section buckling, including local buckling of steel tubes and shear or cleavage failures in the sandwich and core concrete. Increasing steel tube wall thickness (e.g., from 5 mm to 8 mm) enhanced peak load by up to 13.66 %, while adding conventional reinforcement increased it by up to 6.97 % and significantly improved post-peak behavior. Finite element analysis conducted on the ABAQUS platform, demonstrated superior composite behavior during loading, with coordinated deformation between the sandwich and core concrete. Internal reinforcement significantly enhanced the mechanical performance of the tubular column. Parametric analysis indicated that for width-to-thickness ratios exceeding 60, additional conventional reinforcement substantially improved the mechanical performance of the members. This study also assessed the applicability of design models from GB 50936-2014, AISC 360-16, and Eurocode 4 in predicting the load capacity of RHCFST short columns. The AISC 360-16 model predicted a high accuracy, with an average prediction ratio of 0.976, and the proposed adjustments to the partial section factors in GB 50936-2014 significantly improved accuracy, achieving average prediction ratios of 0.989.