Axial compression behavior of rubberized concrete filled steel tube columns after exposure to elevated temperatures

This study explores the potential of rubberized concrete-filled steel tube (RCFST) columns as a sustainable solution for mitigating waste tire rubber pollution. The research focuses on utilizing waste rubber particles to partially replace sand in the concrete, thereby modifying the concrete mix ratio. Axial compression tests were performed on 20 stub column specimens following exposure to elevated temperatures, comprising 10 circular and 10 square steel tubes. The key experimental parameters investigated were the rubber replacement ratio, temperature, and elevated temperature duration. The impact of these parameters on the load-bearing behavior of RCFST columns after exposure to elevated temperatures was assessed through analysis of failure modes, load-displacement response, and stress-strain relationships. Irregular buckling behavior during loading was observed in RCFST columns exposed to elevated temperatures, according to experimental results. The failure mode is characterized by an oblique circular shear failure that is non-parallel. The ultimate bearing capacity decreased with increasing rubber replacement ratio, temperature, and elevated temperature duration. The detrimental effect on the performance of RCFST columns was amplified at higher temperatures and longer durations of elevated temperature exposure. Specimens with a 20% rubber aggregate replacement ratio exhibited a significant reduction in stiffness, with ultimate load decreasing by 28% and 25% for circular and square columns, respectively, while ductility improved. A substantial degradation in ultimate bearing capacity was observed when the temperature changed from 20 °C to 800 °C, with reductions of 35% and 43% for circular and square columns, respectively. Based on experimental findings, and following the principles outlined in GB 50,936-2014 and EC4, a simplified formula was derived to calculate the ultimate bearing capacity of RCFST columns after exposure to elevated temperatures. The proposed formula demonstrated good correlation with the experimental data when compared.