Calculation of axial bearing capacity of recycled concrete filled square steel tube-profile steel short columns based on unified strength theory

To study the axial compression performance of recycled concrete filled square steel tube-profile steel short columns, 11 specimens were tested under the axial loads. The failure process and failure modes of short columns were observed. Meanwhile, the effects of recycled coarse aggregate replacement percentage, steel ratio, width to thickness ratio of square steel tube and strength of recycled concrete on axial compression behavior of short columns were analyzed. The results show that the profile steel yields firstly, then the internal recycled concrete crushes, finally the external steel tube occurs buckling deformation and the column loses its bearing capacity. The axial bearing capacity of specimens decreased with the increase of the recycled coarse aggregate replacement percentage. Increasing the strength of recycled concrete is beneficial to the axial bearing capacity of columns, but the deformation ability of columns decreases. In addition, properly decreasing width to thickness ratio and increasing steel ratio are favorable for improving axial compression performance of columns. As a whole, the columns have high bearing capacity and good deformation ability. On this basis, the axial compression bearing capacity of the short columns was analyzed theoretically based on the theory of uniform strength. The calculation formula of axial bearing capacity for the columns was put forward, which considered the adverse effect of recycled coarse aggregate replacement percentage. The calculated values are in good agreement with the experimental results, which shows that the unified strength theory can be used to calculate the axial compression capacity of the columns. The research results have positive significance for the engineering application of the new composite columns.