The improvement of the simplified calculation method for assessing the fire resistance of a hollow-core slab

This article presents an improvement method for determining compliance with the fire resistance classes of reinforced concrete floor slabs with a cross-section height of 220 mm. In civil and industrial construction, it is often envisaged to use these building structures with a specified thickness in the form of reinforced concrete slabs with cylindrical hollows. To implement the proposed method for determining compliance with the fire resistance classes of reinforced concrete slabs with a cross-section height of 220 mm, there were constructed temperature curves to determine the distribution and expansion of thermal influence from exposure to a standard temperature mode of a fire. Thermal studies were carried out using non-linear calculations, taking into account the change in the thermal characteristics of reinforced concrete and reinforcement, depending on the change in the temperature of exposure to the standard temperature mode of a fire. There were created the necessary mathematical models of reinforced concrete slabs with a cross-section height of 220 mm with 6 cylindrical hollows with a diameter of 159 mm each. The exposure time of the standard temperature mode of a fire was determined and performed in accordance with the existing fire resistance classes of this type of structure, namely: REI 150, REI 60, REI 45, REI 15. The operation of these models is based on the basic principles and assumptions of theories of thermal conductivity following the recommendations of the Eurocode 2. The implementation of thermal models was carried out using the finite element method. When carrying out computational experiments, the studies of the onset of boundary states in terms of fire resistance, loss of bearing capacity and heat-insulating properties were carried out, not taking into account the formation of cracks in the building structures under consideration.