Stability of prestressed steel I beams subjected to fire

This paper presents an innovative theoretical and numerical model to predict the lateral-torsional buckling (LTB) of simply supported steel I-beams with external prestressed tendons. The model incorporates an updated prestressing force, accounting for thermal effects and various external loadings. Critical multipliers are determined by solving an eigenvalue problem derived from applying Galërkin's approach to a set of nonlinear equilibrium equations. Validation is carried out through Finite Element Method (FEM) simulations, incorporating a new expression for an equivalent thermal expansion coefficient for the beam-tendon system, addressing both mechanical and thermal deformations. The primary aim is to estimate critical conditions considering material property degradation due to fire. The present results are generally in good agreement with those provided by the literature.