Stress–strain response and cross-sectional capacity of steel sections in fire

Abstract

This paper analyses the basic influence of the non-linear stress–strain relationship on the cross-sectional capacity of steel sections in fire. A distinct non-linear material behaviour governed by strain hardening is observed for temperatures between 300 and 600°C. For higher temperatures, the stress–strain relationships are almost bi-linear, with short elastic branches followed by nearly horizontal plastic ranges. Design models for cross-sectional capacities with uniform temperature-dependent effective yield strengths are suitable for fire design at high temperatures and with almost bi-linear material behaviour. For distinct non-linear material behaviour, however, these design approaches are not able to accurately describe the cross-sectional behaviour at elevated temperatures.