Steel frames in fire: analysis

Abstract

To apply fire protection to a structure, it is necessary to understand its behaviour in a real fire situation. The Building Research Establishment is developing a package of analytical methods to predict the behaviour 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 frames at elevated temperatures. The effects of elevated temperature are dealt with by including the steel and concrete high temperature stress-strain relationships and temperature-induced strains of thermal expansion, 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 inclusion of the behaviour of semirigid, beam-column connections. Features such as second-order geometrical nonlinearity, residual stress and initial deflection are also included. The program permits the calculation of the load-deflection response of steel frames at cold condition and their behaviour at elevated temperatures under constant loading. Examples are given to validate the assumptions made in the program and also to describe the behaviour of various structural members, in particular steel frames at elevated temperatures.