Analysis of lateral resisting behavior of concrete filled square steel tube frame column after fire

Cinstitutive relationship of steel and concrete in concrete filled square steel tube, which is subjected to fire, is put forward in this paper. A kind of numerical method used to analyze the P-Δ curve is presented. From the analyses, we can draw conclusions as follows: Load bearing capacity of CFST after fire will decrease greatly. Elastic stiffness and ultimate compress strength of concrete will decrease with the fire temperature increas. Temperature has little effect on stress in the elastic stage. Constraint behavior of steel to concrete is more and more distinct with the temperature increase.