Analysis of nonlinear behavior of steel frames under local fire conditions

A finite element approach is presented in this paper for analysis of nonlinear behaviour of steel frames under local fire conditions. The effects of geometric nonlinearity, temperature dependent material nonlinearity and variations in temperature distribution across sections of frame members are considered. Based on the principle of virtual work, the temperature - induced load vector and temperature - dependent geometric stiffness matrix are derived. Following the common procedure of finite element methods, a computer program is developed for calculating either the ultimate load at a specified temperature or critical temperature at a specified load level. The effectiveness of the approach is verified by a good prediction on the behavior of a steel frame experienced fire experiment.