Post-fire behaviors of stiffened concrete-filled thin-walled square steel tubular slender columns: Experimental and numerical investigations

Concrete-Filled Thin-Walled Steel Tubular columns (CFTST) represent a novel composite structure, characterized by an exterior thin-walled steel tube encasing an interior concrete fill. Although significant advancements have been made in CFTST research, the exploration of its post-fire mechanical properties remains insufficient. This article focuses on Square CFTST Stiffened with reinforcement bars (S-CFTST-S) as the subject of study, undertaking a compression experimental investigation involving one specimen under normal temperature conditions and six specimens subjected to post-fire conditions. The findings indicate that the elevated time decreased the ultimate bearing load with the heating time. And weaken the ductile behavior with the decreasing of 27.49 % and 32.70 %. Conversely, the ultimate bearing load declines while the ductility coefficients increase with increasing the eccentricity. The stiffened steel bars improved the peak load and performance after peak load of the S-CFTST-S. Finite element models have also been developed using ABAQUS software, whose accuracy was validated by experimental results. Further, parameter analysis was conducted to investigate the influence of different parameters on the ultimate load bearing capacity. Moreover, a formula was proposed for estimating the post-fire load bearing capacity of S-CFTST-S.