Abstract: In order to consider the effects of temperature on the properties of steel and temperature induced loading, based on the finite integral method, a nonlinear formulation of steel structural member under fire is presented. Pole analysis method is used to consider the geometric effects and to investigate the effects of different restraints, loadings and geometric defects on the limited state, from which some relationships between the variables are obtained. The comparison of the numerical results with the experimental results demonstrates the validity of the analysis method.