FEA on mechanical behavior of axially restrained concrete-filled steel tubular columns subjected to fire

The internal force and the deformation of the column exposed to fire in structure change due to the restraint provided by adjacent members, which may affect the fire resistance. However, most of previous studies focused on the fire performance of individual concrete-filled steel tubular (CFST) column, without considering the structural interactions between the column and its adjacent members. A finite element model of axially restrained circular CFST column was developed with ABAQUS to analyze the influence of axial restraint on the axial force, axial displacement and fire resistance. It is found that axial restraint has significant influence on the axial force, which intensifies the axial force during the expansion period and relieves the axial force during the contraction period. The axial displacement decreases correspondingly, which enhances the fire resistance. The influences of parameters on the fire resistance of axially restrained columns were studied, including cross-sectional dimension, load ratio, slenderness ratio and load eccentricity ratio. The results show that the fire resistance can be increased by 10% to 40% for columns with the axial restraint stiffness ratio of 0.02 and slenderness ratio less than 30, and the beneficial effect on the fire resistance can be considered. The higher fire resistance can be attained with larger cross-sectional dimension, smaller load ratio and smaller slenderness ratio for both axially restrained and unrestrained columns. Different from members without axial restraint, the load eccentricity ratio has noticeable influence on the fire resistance of restrained columns.