Response and modeling of axially-loaded concrete-filled steel tubular columns with coal gangue coarse and fine aggregate

Concrete-filled steel tubular columns with coal gangue aggregate (GACFST) present a sustainable solution for the structural use of coal mining waste. However, the existing studies have only studied the effects of coal gangue coarse aggregate (CGA) or fine aggregate (FGA) alone, while there is no investigation examining their compounding effect. Furthermore, no existing model accounts for the potential compounding effect when CGA and FGA are used simultaneously, nor does any model incorporate the influence of FGA on the confinement effect. This paper examines the axial compressive performance of 48 GACFST specimens, considering variables including CGA and FGA replacement ratios (0–100%), steel ratios (8.5–14.5%), and core concrete strengths (30–50 MPa). Test results indicate: 1) a significant compounding effect exists between FGA and CGA, where the detrimental influence of FGA is mitigated as the CGA replacement ratio increases, 2) FGA and CGA demonstrate differentiated dominance across mechanical properties, due to their distinct influence mechanisms, 3) the incorporation of gangue aggregate may significantly delay the initiation of confinement effect. Based on the experimental data, a modified constitutive model for the axial stress-strain relationship of GACFST was developed, accounting for the influence of both CGA and FGA. The proposed model demonstrated high predictive accuracy when validated using a database of 149 specimens, achieving an average predicted-to-test ratio of 1.011 and a standard deviation of 0.049.