Thermal gradients often occur in fire exposed structures. This paper considers thermal gradients over the cross-section of steel columns. By means of finite element simulations, the paper demonstrates that these gradients reduce the flexural buckling resistance of the columns. This is due to the eccentricity in the column created by the temperature gradient. Design equations in modern standards provide a gross approximation of the load bearing resistance of such columns in which the eccentricity is ignored and in order to compensate for this the yield stress and modulus of elasticity are to be determined at maximum temperature. Based on an in-depth analysis of the results of the finite element simulations, this paper provides an alternative design model which much better agrees with the actual behaviour of a fire exposed column.
Ojeda, O. D., Maljaars, J., & Abspoel, R. (2016). Fire exposed steel columns with a thermal gradient over the cross-section. Thin-Walled Structures, 98A, 103-110. https://doi.org/10.1016/j.tws.2015.02.009