THE INFLUENCE OF THE TEMPERATURE-TIME CURVE ON THE TIME PERIOD OF PRESERVATION OF FIRE RESISTANCE OF STEEL STRUCTURES

Abstract

This study is devoted to the evaluation of the relationship between the values of the time period of preservation of fire resistance of protected steel structures, obtained for the conditions of fire exposure according to the temperature-time curve of hydrocarbon and external fire, and the values of this time interval for the standard temperature-time curve. It aimed to identify the effect of nominal temperature-time curves on the time period of preservation of fire resistance of such steel structures as beams and columns with a single-layer fire protection system, for a wide range of parameters of these structures. The calculation method, which is based on the solution of the direct one-dimensional problem of thermal conductivity, determined the data on the time period of preservation of fire resistance of such steel structures for the temperature-time curve of hydrocarbon and external fires and the data on the difference between these obtained values and the values of the same time period for the standard temperature-time curve. It was established that for the range of parameters of the steel structure that was evaluated, the time period of preservation of the fire resistance of the steel structure for the conditions of fire exposure under the temperature-time curve of a hydrocarbon fire varies in the range from 12.5 min to 219.0 min, which is narrower than the range for the standard temperature-time curve, which is from 30 min to 240 min. For the external fire temperature-time curve, this range is from 33.3 min to 500.1 min and is wider than for the standard temperature-time curve. It was determined that the difference between the values of the time period of preservation of fire resistance of a steel structure, obtained for the conditions of fire exposure under the temperature-time curve of a hydrocarbon fire, and the values of the same period of time under the standard temperature-time curve, varies in the range from –8.8% to –58.3%, and the same difference for the temperature-time curve of an external fire varies in the range from 11.0 % to 108.4 %. It was found that the value of this difference is significantly influenced by the value of the time period of preservation of fire resistance under the standard temperature-time curve, relative to which this difference is determined. It is natural that as this time period increases, this difference for the temperature-time curve of a hydrocarbon fire decreases (by modulus), and for the temperature-time curve of an external fire it increases. The influence of the coefficient of thermal conductivity of the applicable fire protection material, the coefficient of the cross-section and the critical temperature of the steel on the value of this difference was also established.