The treatment of strain reversal in structural members during the cooling phase of a fire

Analytical approaches for studying the performance of steel-framed structures in fire conditions have previously concentrated mainly on the behaviour under increasing temperatures. These are generally based on a series of stress-strain curves uniquely defined for a specific temperature. When strain reversal occurs, these curves have to be modified to account for the effect of permanent strains. This is particularly important in studying the behaviour of structures during the cooling as well as the heating phase of a fire. This is necessary in assessing residual effects in fire-damaged structures or when considering the spread of fire through a large building. The analysis presented here is an extension of an approach used successfully for the analysis of steel-framed structures at increasing temperature. Alternative treatments for strain reversal are discussed and a simple model for its incorporation within existing software is described Examples are given to illustrate the use of such an approach and to demonstrate the magnitude of residual forces and deformations which can occur Copyright (C) 1996 Elsevier Science Ltd.