JUSTIFICATION OF THE METHOD OF ASSESSING THE FIRE RESISTANCE OF REINFORCED CONCRETE HOLLOW PLATES BY LOSS OF INTEGRITY

The article focuses on developing a method to assess the fire resistance of reinforced concrete hollow slabs by identifying through cracks that indicate a loss of integrity. The study addresses the growing need for fire-resistant materials in construction and proposes a method that combines thermal and mechanical stress analysis using finite element modeling. By simulating the effects of a fire scenario on hollow concrete slabs, the research identifies conditions under which critical cracks form, threatening structural integrity and potentially allowing smoke and toxic combustion gases to spread through the building. Through detailed thermal and structural calculations, the study identifies the parameters at which cracks emerge and propagate across the slab, using a finite element model configured with a thermal load duration of up to one hour. The model simulates temperature distribution and deformation in concrete and steel components under a combined thermo-mechanical load, with specific emphasis on calculating deformation rates that correlate with the formation of through cracks. The research employs both the Drucker-Prager and William-Warnke strength theories, though the William-Warnke model is found to be more effective for brittle materials such as concrete due to its ability to predict nonlinear crack development accurately. A significant aspect of the methodology is the progressive removal of finite elements representing failed areas in the concrete matrix, indicating the progression of structural failure. The study concludes that a concrete slab loses its fire resistance once through cracks are large enough to compromise integrity and allow the spread of dangerous fire byproducts. This finding underscores the importance of considering both the loss of load-bearing capacity and structural integrity when evaluating fire resistance. This new assessment approach is valuable for designing safer buildings, as it enables a more precise prediction of fire resistance limits in hollow concrete slabs and supports improvements in fire safety measures. The research, therefore, not only advances understanding in fire-resistant construction materials but also contributes to the broader goal of enhancing public safety in building design and emergency response.