This article studies the stress-strain state of reinforced concrete beams with steel sheet of different thickness under exposure to nearfire temperature. The obtained data are analyzed and the conclusions of the operation of an investigated structure under thermal exposure are made. Problem. The magnitude of the thermal stresses during heating can be quite high and can cause cracks in structures or even their destruction at either low or zero operating loads. The objective is to develop a methodology for calculating the design of reinforced concrete beams to withstand high thermal power effects. Tosolve the question posed, the methodology of mathematical models was used with the help of the developed finite element schemes. Based on the results of the study, the temperature dependences were determined at different points of the cross-section of the reinforced concrete beams under standard fire conditions. The fire resistance boundaries of the beams, which are the object of the study, have been determined. Results: the article presents the original method of calculation of reinforced concrete beams at different thicknesses of steel sheet, developed in accordance with the existing methodological and regulatory framework in the EU countries; section heating curves have been built, whose analysis shows the presence of a specific "shelf", when the temperature remains constant for some time and equal to 100°C, which confirms the adequacy of the thermal conductivity model, as it can consider the phenomenon of intense evaporation of moisture from concrete pores; fire resistance on three identical beams, whose difference lies in the thickness of the steel plate, has been studied and a maximum deflection to the standard fire time curve has been built; the limits of fire resistance of the investigated beams are determined, which show the very close limits of fire resistance of beams that differ within 3 minutes. The duration and high cost of fire tests of construction the structures determine the practical value of calculation methods for assessing the fire resistance of both individual loadbearing elements and structures in general in the design of new and reconstruction of existing civil and industrial structures.
Modelling the thermal behaviour of GFRP reinforced concrete beams subjected to elevated temperature by standard fire exposure
