Inelastic nonlinear behavior of steel trusses cooled down from a heating stage

This paper is to study the inelastic nonlinear behavior of steel trusses cooled down from a heating stage, a problem that was rarely investigated before. Bilinear elastoplastic model is adopted for steel. Softening of elastic modulus and yield stress at elevated temperatures is considered by the reduction factors of Eurocode3. The plastic strain resulting from strain reversal is included in the stress–strain curves. Instantaneous modulus is proposed for simulating the unloading (loading) behavior caused by cooling (heating). Both the thermal and plastic strains are considered in the force–displacement relation for truss members. The temperature–deflection curves obtained for a simple truss serve as the benchmark problem for checking the validity of other approaches in treating the heating and cooling stages. For general applications, the elastoplastic finite element derived was adopted to solve the cooling responses of preheated steel trusses by the Newton–Raphson method. The permanent deformation and residue stress computed for each member are useful for evaluating the reusability and safety of steel trusses after a fire attack.