The repair of fire-damaged thin-walled rectangular concrete-filled steel tubular (CFST) columns in engineering structures after fire exposure requires the assessment of their residual strength and stiffness. Existing numerical models have not accounted for the effects of local buckling on the post-fire behavior of CFST columns with rectangular thin-walled sections. This paper describes a nonlinear post-fire simulation technique underlying the theory of fiber analysis for determining the residual strengths and post-fire responses of concentrically loaded short thin-walled rectangular CFST columns accounting for progressive local buckling. The post-fire stress-strain laws for concrete in rectangular CFST columns are proposed based on available test data and implemented in the theoretical model. An innovative numerical scheme for modeling the progressive local and post-local buckling of CFST thin-walled columns is discussed. The nonlinear post-fire simulation model is verified by experimental data and then used to investigate the significance of local buckling, material strengths and width-to-thickness ratio on the post-fire responses of CFST stub columns. The proposed post-fire computer model is shown to be capable of predicting well the residual stiffness and strength of concentrically loaded thin-walled CFST columns after fire exposure. A design formula is proposed that estimates well the post-fire residual strengths of CFST columns. Computational results presented provide a better understanding of the post-fire behavior of CFST columns fabricated by thin-walled sections incorporating local and post-local buckling.
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