Coupled Thermomechanical Damage Modeling for Structural Steel in Fire Conditions

Abstract

This study developed a coupled thermomechanical damage model for structural steel at elevated temperatures. The need for adequate modelling of steel deterioration behavior remains a challenging task in structural fire engineering because of the complexity inherent in the damage states of steel under combined actions of mechanical and fire loading. A fully three-dimensional damage-coupled constitutive model was developed based on the hypothesis of effective stress space and isotropic damage theory. The new coupling model, adapted from an enhanced Lemaitre’s ductile damage equation and taking into account temperature-dependent thermal degradation, is a heuristic approach which retains the underlying mechanisms that govern the damage processes. The proposed damage model comprises a limited number of parameters that can be identified using unloading slopes of stress–strain relationships through tensile coupon tests. The proposed damage model was successfully implemented in finite-element software and validated against a comprehensive range of experimental results. The damage-affected structural response was accurately reproduced under various loading conditions and a wide temperature range, demonstrating that the proposed damage model is a useful tool in giving a realistic representation of steel deterioration behavior for structural fire engineering applications.