USTIFICATION OF CRITICAL TEMPERATURE OF STEEL FOR DESIGN OF FIRE-RESISTANT STEEL STRUCTURES

The article analyzes approaches to determining the critical temperature of steel elements and calculating the fire resistance of steel structures in accordance with Eurocode 3. The analysis found that in Ukraine, fire protection designers continue to use a constant temperature of 500 °C as the main critical (design) temperature of steel structures with fire-retardant coatings and cladding.The critical temperature of the steel I-beam No. 30 was calculated according to the assortmentwith the corresponding nominal sizes and reference parameters. As a result of the calculations, the critical temperature value for the secondary steel beam was obtained, which was 868 °C.The material and method of fire protection for a steel beam were selected in order to increase its fire resistance class to R 90 using water-based intumescent fire-retardant coatings (paint with reactive properties).In accordance with the calculations above, the profile section coefficient of 213.3 m-1and the critical temperature of the steel beam of 500 °C (first option) and 868 °C (second option) were adopted.Using tabular data, it was established that the closest value of the profile cross-section coefficient is a value equal to 220 m-1, and the critical temperature value for the second option is 750 ° C. Thus, for the given parameters of the steel beam, the minimum thickness of the fire-retardant coating under study was selected, which in the first option was 3.431 mm, and in the second -1.601 mm.The amount of water-based fire retardant under study, required to obtain a protective layer after processing all structures along the contour at different critical temperature values, was calculated. The consumption of fire retardant was compared when using different critical temperature values of steel.Key words:Euro code, fire resistance, fire protection, critical temperature, steel building structures.