Compressive performance of steel reinforced circular CFST stub columns after elevated temperatures

This paper presents experimental investigations into the behavior of axially loaded stub columns made of structural steel reinforced concrete -filled circular steel tubes (SSR-CFCST) after exposure to elevated temperatures. A total of 135 SSR-CFCST stub columns were subjected to testing, comprising 108 specimens exposed to elevated temperatures and 27 reference specimens maintained at ambient temperature. The parameters considered in this study encompassed steel tube thickness, structural steel ratio, concrete compressive strength, and temperature. The results indicate that elevated temperatures and steel tube thickness exerted significant influences on the residual ultimate load -bearing capacity of the specimens. Specifically, after exposure to temperatures of 900 degrees C, the columns exhibited a serious deterioration in their residual ultimate load -bearing capacity. It was observed that increasing the steel tube thickness notably enhanced the fire resistance capacity of the specimens. Furthermore, the residual ultimate load -bearing capacity of the specimen experienced more severe degradation with higher concrete compressive strength. The inclusion of embedded structural steel contributed to the stability of the residual ultimate load -bearing capacity of the specimens. In terms of ductility, there was a substantial increase in specimen ductility with higher structural steel ratio and steel tube thickness, while it decreased significantly with increasing concrete compressive strength. Notably, after exposure to temperatures of 400 degrees C and 600 degrees C, specimen ductility improved. The initial stiffness and ultimate load -bearing capacity of the specimens benefited from an increase in the structural steel ratio and concrete compressive strength. Conversely, the initial stiffness decreased with the rising temperature from 400 degrees C to 900 degrees C. Formulas were proposed to estimate the ultimate load -bearing capacity of the specimens under ambient temperature conditions and after exposure to elevated temperatures, respectively.