INFLUENCE OF THERMOPHYSICAL CHARACTERISTICS OF FIRE-RETARDANT MATERIALS ON THE THERMAL STATE OF STEEL COLUMNS UNDER STANDARD TEMPERATURE REGIME

Abstract

Given the need to optimize the parameters of fire-retardant systems for building structures for further improvement and development of their technology, a study aimed at determining the impact of thermophysical properties of fire-retardant materials, which are components of such systems, on thermal state of steel columns at standard fire scenario is required. The objective of current study was to determine the relationships between the required minimal thickness of fire-retardant systems, thermophysical properties of fire-retardant materials that are part of such systems, critical steel temperature, cross-sectional factor and time of fire resistance for steel columns. To achieve this goal, the required minimal thicknesses of fire-retardant coatings for the studied fire-retardant systems were determined, the calculated data were summarized and the dependences of this thickness on the thermophysical properties of fire-retardant materials and other parameters of the systems were identified. It was established that the thickness value, both for systems with and without fire screen, significantly depends on thermal conductivity _р of applied fire-retardant materials, cross-sectional factor A_m/V, critical temperature θ_cr and fire resistance time limit t_fr. With the increase in _р, A_m/V, t_fr and decrease in θ_cr the required value of thickness d_p,min rises. It was shown that when fire-retardant systems with a screen are used for steel columns, there is a reduction in the required thickness of fire protection d_p,min compared to the system without a screen. The absolute difference Δ_d,AB and the relative difference δ_d,AB between the value of the fire-retardant system thickness obtained for a system without fire screen and the value obtained for a system with a screen without a fire-retardant coating on its surface, varies in the range from 0.06 mm to 15.5 mm and from 0.35% to 51.6%, respectively. For fire-retardant systems with screen and fire-retardant coating on its surface and (or) on the surface of the column, the required minimum thickness of the system for small values of cross-sectional factor (A_m/V)_min and short fire resistance time intervals t_fr,min is lesser, compared to those without screen. Data was obtained regarding the difference between the values of the required minimal thickness of fire protection for systems with fire-retardant coating on the outer surface of the screen and without it.