ANALYSIS OF STRESS EFFECTS DUE TO A FIRE IN THREE-DIMENSIONAL STEEL STRUCTURES PROTECTED BY INSULATING MATERIALS

A numerical procedure is presented for thermomechanical analysis of three-dimensional steel structures subjected to fire. The procedure is based on the finite element method and weighted residual approach in Galerkin form. It is applied for modelling the time transient of a fire together with the subsequent phase of fire extinguishing. In the analysis the fire is simulated by means of a thermal load applied along fixed boundaries of the chosen structure. The temperatures of the structural elements are determined at each time step by taking into account heat sources and heat transfer due to simultaneous conduction, convection and radiation. Stresses due to temperature variations are calculated, starting from fire beginning until its extinguishing. After cooling, residual stresses and strains are determined for selected points of the structure. Numerical applications developed, based on experiments already published in the literature, are focused on differences between two- and three-dimensional discretisation of structures involved and effects of thermal insulation.