Theoretical model for spontaneous combustion gangue coarse aggregate concrete filled steel tube stub columns

Spontaneous combustion gangue coarse aggregate concrete filled steel tube (SCGCA-CFST) provides a possibility for the structural application of spontaneous combustion gangue coarse aggregate (SCGCA) concrete. To establish an accurate stress-strain model for SCGCA-CFST, 12 SCGCA-CFST specimens and 18 SCGCA concrete specimens were tested under monotonic axial compression with steel tube thickness and SCGCA replacement ratio (0%, 50%, 100%) as variables. The experimental results demonstrated that as the SCGCA replacement ratio increased, the elastic modulus of SCGCA concrete decreased by 6.65%-11.65%, the cylinder compressive strength decreased by 11%-21.95%, and the axial strain at peak axial stress increased by 7.1%-14.27%. Furthermore, the crack extension forms and dilation properties of the core concrete in SCGCA-CFST differed significantly from those of normal coarse aggregate concrete filled steel tube (NCA-CFST). The incorporation of SCGCA reduces the effectiveness of steel tube confinement, which causes the existing stress-strain models of NCA-CFST overestimate the enhancement effect of steel tube confinement on the strength and deformability of core SCGCA concrete. Based on this, the analysis-oriented stress-strain model for NCA-CFST was modified to be applicable for SCGCA-CFST by incorporating the influence of aggregate characteristics, and the accuracy of that was verified.