Evaluation of the load-carrying effect of rectangular concrete-filled steel tubular columns under axial compression based on the multilevel extension method

The load-carrying effect of rectangular concrete-filled steel tubular (RCFST) columns under axial compression has complex influencing parameters. Previous relevant studies have mostly included experimental and modeling approaches, but there are few studies on evaluations based on mul-tiple parameters. This study introduces the extension evaluation method, which is good at solving contradictory problems, and scientifically constructs a multilevel extension evaluation model of the load-carrying effect of RCFST columns. Key parameters such as the cross-sectional height-to-breadth ratio (Sr) and hoop confinement coefficient (xi s) that affect the load-carrying effect of RCFST columns are refined and converted into evaluation indices. The weights of the indices are calculated scientifically via the analytic hierarchy process (AHP). Through the extension evalu-ation of the tested RCFST columns, the accuracy and rationality of the proposed evaluation model are verified. The conclusion of the multilevel extension evaluation shows that for the fixed section tested in this study, the RCFST columns with moderately thick-walled steel tubes have the best load-carrying effect and economy among thin-walled, moderately thick-walled and very thick-walled steel tubes.