DETERMINATION OF THE TIME PERIOD OF PRESERVATION OF FIRE RESISTANCE OF LOAD-BEARING STEEL STRUCTURES WITH DIFFERENT INITIAL TEMPERATURES

Abstract

This study is devoted to the determination of the time interval of preservation of fire resistance of load-bearing steel structures without an enclosing function, which have different initial temperatures during the test. It aimed to identify the influence of the initial temperature of steel structures such as beams and columns with a single-layer fire protection system on the time period of their fire resistance preservation, for a wide range of parameters of these structures (thermophysical properties of the applicable fire protection material, fire protection thickness, critical temperature and cross-section coefficient structures) and substantiation of the temperature indicator for determining the time interval of preservation of the fire resistance of these structures according to the bearing capacity. It was found that for the range of parameters of the steel structure used in the calculations, the difference between the values of the time interval until the normalized critical temperature is reached, obtained at the minimum permissible initial temperature of 10 °C and the nominal initial temperature of 20 °C, can reach 2.33%, and the difference between the values, obtained at the maximum permissible initial temperature of 40 °С and nominal initial temperature of 20 °С, can reach 3.67%. It was established that in order to determine the value of the time interval of preservation of the fire resistance of the steel structure, which is the closest to the nominal value, it is necessary to use the indicator, which is the time interval until the corrected critical temperature is reached. The dependence of the difference between this corrected critical temperature and the normalized critical temperature on the parameters of the steel structure was determined. It is shown that in the case of applying this indicator, the deviation of the calculated interval of time of preservation of fire resistance, determined for the minimum and maximum permissible values of the initial temperature of the steel structure, from the interval of time at the nominal initial temperature does not exceed 0.89%, which is an acceptable accuracy for engineering calculations.