Fire-resistance study of restrained steel columns with initial lateral displacement

This study presents an analytical formula based on differential equations of equilibrium to analyse the behaviour of steel columns with initial lateral displacements in fire. The imperfections of the initial flexure of the steel columns are considered. Yielding of the edge fibres at the middle span of a column subjected to elevated temperature is designated as the failure criterion for the fire resistance of the column. After validating the results of the formula using ANSYS, a numerical application is performed to demonstrate the effects of different parameters on the ultimate load bearing capacity. The formula is then used to predict the axial force of axially restrained steel columns based on the displacement coordination condition; then, the axial force is verified by ANSYS. The axial displacement predictions from the proposed method correspond well with those obtained through the finite element method. The critical temperature can also be predicted by calculating the load bearing capacity and axial force at a certain temperature. The results show that the increase of initial lateral displacement and temperature decreases the bearing capacity of the steel column and that the critical temperature decreases with increasing constraint stiffness.