Revealing patterns in the behavior of a reinforced concrete slab in fire based on determining its stressed and deformed state

Abstract

The object of research is the fire resistance of reinforced concrete ribbed slabs. The subject of research is the effect of the level of mechanical load on the fire resistance of the studied reinforced concrete ribbed slab under the influence of fire. Currently, the assessment of the fire resistance of such structures using the tabular method is significantly limited by certain geometric parameters of these plates. It is also not considered possible to apply the zone method, since reinforced concrete ribbed slabs consist of components that receive thermal effects according to various scenarios and geometric parameters, which is not taken into account in Eurocode 2. Experimental calculations carried out in the current work using a refined procedure involving the finite element method allow solving the actual scientific and technical problem related to the determination of the dependence of the fire resistance of these structures on the level of load applied. The calculation of the temperature spread over a reinforced concrete ribbed slab under the influence of the standard temperature regime of fire was carried out using convection and radiant heat exchange, which is recommended by Eurocode 2. The iterative implicit Newton-Raphson method was used to solve the mechanical problem. Evaluation of fire resistance of reinforced concrete ribbed slabs was carried out according to the onset of signs of the limit state of fire resistance due to the loss of load-bearing capacity. According to the results, it was established that at 100 % load level of the structure under investigation, the critical deflection of more than 268 mm and the rate of growth of deformation exceeding 18 mm/min were recorded simultaneously on minute 43.9. According to the results of the research, the regularity of the limit of fire resistance of reinforced concrete ribbed slabs from the level of the applied mechanical load was established. This will make it possible to design and build buildings and structures using the specified building structures with guaranteed fire resistance classes, which improves the level of safety for people at the facilities