STEEL FRAMES IN FIRE - ANALYSIS

To apply fire protection to a structure, it is necessary to understand its behaviour in a real fire situation. The Building Research Establi shment is developing a package of analytical methods to predict the be haviour of fire, temperature rise in the structure and the response of the structure at elevated temperatures. This paper describes a finite element computer program studying the structural behaviour of steel f rames at elevated temperatures. The effects of elevated temperature ar e dealt with by including the steel and concrete high temperature stre ss-strain relationships and temperature-induced strains of thermal exp ansion, creep for steel and concrete and transient thermal strain for concrete. Both uniform and nonuniform temperature distributions can be included in the analysis. A novel feature of this analysis is the inc lusion of the behaviour of semirigid, beam-column connections. Feature s such as second-order geometrical nonlinearity, residual stress and i nitial deflection are also included. The program permits the calculati on of the load-deflection response of steel frames at cold condition a nd their behaviour at elevated temperatures under constant loading. Ex amples are given to validate the assumptions made in the program and a lso to describe the behaviour of various structural members, in partic ular steel frames at elevated temperatures.