Axial Compressive Behavior of Outer Square Inner Circular Spontaneous Combustion Coal Gangue Concrete-Filled Double-Skin Steel Tubular Stub Column

Utilizing crushed spontaneous combustion coal gangue as a coarse aggregate in concrete preparation effectively reduces reliance on natural resources and mitigates environmental pollution; however, the suboptimal workability of spontaneous combustion coal gangue coarse aggregate concrete (SCG-CAC) limits its engineering applications. To address this issue, this study places SCGCAC at the center of a CFDST (Concrete-Filled Double-Skin Steel Tubular) stub column. Through finite element modeling validated for reliability, this study examines the structural mechanical response to axial loading, along with the effects of various parameters. The analysis encompasses parameters such as the strength of the core SCGCAC (fc,i), the strength of the sandwiched concrete (fc,o), the yield strength of the outer steel tube (fy,o), the yield strength of the inner steel tube (fy,i), the width-to-thickness ratio (B/to), the diameter-to-thickness ratio of the inner tube (D/ti), and the diameter-to-width ratio of the outer tube (D/B). Results show that this structural configuration significantly enhances the core SCGCAC ultimate bearing capacity, and increases in D/ti, fc,i, fc,o, fy,i, and B/to all lead to an increase in the peak load. Particularly, when D/ti increases from 28.57 to 80, the peak load increases by 42.72%. However, changes in fy,o and D/B have no significant effect on the peak load.