Currently, reinforced thin-walled irregular steel tube concrete frame structures have been applied in engineering, but there are few researches on the seismic performance of this type of structures after fire. The seismic performance of structures after fire is generally carried out based on rigid foundation conditions. Therefore, it is of certain engineering and theoretical value to study the seismic performance considering the SSI (soil–structure interaction) in this paper. ABAQUS is employed to establish the finite element models of the reinforced thin-walled irregular steel tube concrete frame structure considering the SSI after a fire. The paper analyzes the impact of different site conditions and fire durations on the structural natural vibration period, maximum acceleration, inter-story shear force, and maximum inter-story displacement angle. The results show that the consideration of the SSI increases the basic natural vibration period of the structure by 10–30%. The softer the soil and the longer the fire duration, the more significant the increase. For harder soil, lower seismic intensity, and shorter fire duration, the acceleration assigned to the structure and foundation after considering the SSI is smaller than the results assuming a rigid foundation. The change in inter-story shear force is mainly determined by the acceleration of the structure and foundation. The inter-story displacement angle increases when considering the SSI, and the increase is more significant with softer soil, larger seismic wave acceleration amplitude, and longer fire duration.

This paper investigates the strength and behaviour of high-strength self-compacting concrete-filled steel tubular (HSSC-CFST) stub columns under axial compression. HSSC-CFST columns are high-performance structural members with wide applications in engineering structures. Nevertheless, relevant studies have commonly focused on the mechanical performance of HSSC-CFST in indoor environments. A finite element (FE) model was developed to predict the axial load capacity of HSSC-CFST stub columns subjected to chloride corrosion. According to this, several crucial geometric and material parameters were designed to investigate the influences on strength, initial stiffness, and ductile performance. Moreover, the analysis on failure mechanisms was investigated by N-ε curves and stress development in the whole loading process. The impacts of key parameters on the reduction factor of axial load capacity were also identified. The numerical analysis results indicate that the axial strength of HSSC-CFST stub columns under chloride corrosion was significantly heightened by increasing the strength of core self-compacting concrete, while contrary results were found with the increase in the steel ratio and yield strength of the steel tube. Lastly, design recommendations for the axially loaded HSSC-CFST were presented by modifying the design codes in CECS104-99. The proposed model is shown to be able to estimate the axial load-bearing capacity of HSSC-CFST stub columns more accurately.

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 (f_c,i), the strength of the sandwiched concrete (f_c,o), the yield strength of the outer steel tube (f_y,o), the yield strength of the inner steel tube (f_y,i), the width-to-thickness ratio (B/t_o), the diameter-to-thickness ratio of the inner tube (D/t_i), 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/t_i, f_c,i, f_c,o, f_y,i, and B/t_o all lead to an increase in the peak load. Particularly, when D/t_i increases from 28.57 to 80, the peak load increases by 42.72%. However, changes in f_y,o and D/B have no significant effect on the peak load.