INFLUENCE OF FIRE TEMPERATURE REGIME ON THE REQUIRED MINIMAL THICKNESSES OF FIRE-RETARDANT COATINGS FOR STEEL MEMBERS

Abstract

The lack of data on the relationship between the values of the required minimal thickness of fire-retardant coatings for steel members, obtained for the conditions of fire exposure under the temperature regimes of hydrocarbon and external fire, and the values of this thickness for the nominal temperature-time curve of fire limits the scope of application of such fire-retardant materials. The objective of current study was to determine the influence of these nominal fire temperature regimes on the required minimal thickness of the fire-retardant coating for such load-bearing steel members as columns and beams, for wide ranges of changes in the thermophysical properties of the applicable fire-retardant material, the critical temperature of steel, the cross-sectional coefficient and the period of preservation fire resistance of steel member. The calculation method, which is based on the solution of the direct one-dimensional problem of thermal conductivity, determines the data on the required minimal thickness of fire-retardant coating for the temperature regimes of hydrocarbon and external fire and the data on the difference between these obtained values and the values of such thickness established for the temperature-time curve. It was established that the difference between the values of the required minimal thickness of fire-retardant coating for steel members, obtained for the conditions of fire exposure under the temperature regime of a hydrocarbon fire, and the values of this thickness determined under the temperature-time curve, has positive values (from 5.74% to 214%) , while for the conditions of fire exposure under the temperature regime of an external fire, they are negative (from –7.52% to –64.7%). This difference, both for the conditions of exposure to fire under the temperature regime of a hydrocarbon fire and for the conditions of exposure to fire under the temperature regime of an external fire, decreases with an increase in the coefficient of thermal conductivity of the applicable fire-retardant material, the coefficient of the cross-section and with a decrease in the critical temperature of steel. It is natural that with an increase in the time interval of preservation of the fire resistance of a steel member for the temperature regime of a hydrocarbon fire, the difference between the thicknesses decreases, and for the temperature regime of an external fire, it increases (by modulus).