NUMERICAL THERMAL-MECHANICAL ANALYSIS OF PASSIVELY PROTECTED STEEL STRUCTURES UNDER FIRE CONDITIONS

Structures made of materials with high thermal conductivity quickly reach critical temperature in fire situation. The drastic reduction of plasticity occurring due to this may contribute to rapid destruction of the element. The necessity of protecting steel structures in fire conditions is currently included in building standards and is becoming one of the fundamental issues of designing steel structures. Numerical simulations are an important tool for analyzing the behavior and selection of protection measures of structures in fire conditions. The article presents a numerical analysis of mechanical and thermal behavior of steel beams in fire conditions using different methods of fire insulation. The analysis included a beam with concrete casing, with casing made of thermal insulation boards, with fire protection spraying and compared with a beam without fire protection. The dependence of strength properties of construction materials on thermal temperature was taken into account. Four-sided thermal interactions in the beam cross-section were assumed, taking into account heat flow by convection and radiation. The course of fire overtime was modelled in accordance with the standard curve according to ISO 834. The results of thermal analysis were presented in the form of temperature distribution for the analysed models and the influence of temperature increase under fire conditions on the change in the load-bearing capacity of beams (in the stress-strain state) was shown.