Nonlinear post-fire simulation of concentrically loaded rectangular thin-walled concrete-filled steel tubular short columns accounting for progressive local buckling

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.