Axial compression performance of composite short columns composed of RAC-filled square steel tube and profile steel

An axial compression test was conducted for 11 composite short columns composed of recycled aggregate concrete (RAC)-filled square steel tube and profile steel, to explore their axial compression behaviour. The following main design parameters of columns were considered: recycled coarse aggregate (RCA) replacement percentage, width-thickness ratio of square steel tube, profile steel ratio and RAC strength. The failure process and modes, load-displacement and load-strain curves and axial stiffness of specimens were obtained and analysed in detail. Results showed the similar failure process and modes of each specimen. Specifically, the profile steel yielded before the square steel tube, and the internal RAC was crushed subsequently. Bulging deformation was evident on square steel tube, thus indicating that the column lost its bearing capacity. With the increase in RCA replacement percentage and width-thickness ratio of the square steel tube, the axial bearing capacity of specimens decreased remarkably. However, the axial bearing capacity of columns increased with the increase in profile steel ratio and RAC strength. These design parameters remarkably influenced the initial stiffness of the short columns, but exerted minimal effect on stiffness degradation at the latter stage of loading. Overall, the composite short columns exhibited high bearing capacity and good deformability in the tests. On this basis, a calculation formula for the axial bearing capacity of the columns was established through theoretical analysis and by considering the adverse effects of RCA replacement percentage. The calculated results showed good agreement with the experimental findings, thus verifying the validity of the established formula. The research conclusions can provide references for engineering applications on this type of columns. (C) 2018 Elsevier Ltd. All rights reserved.