Determination of the Charring Rate of Timber to Estimate the Fire Resistance of Structures at Real Temperature Modes of Fires

Abstract

The article presents the results of researches of fire resistance of timber structures, taking into account the realistic temperature modes of fires. The proposed method of determining the charring rate is based on the main parameters of fire spread that are taken into account in the calculations, based on the analysis of the heating temperature of unprotected elements of timber structures, where an approach on solving an time-dependant equation of thermal conductivity is used. The research of the influence of the depth of the charring on the limit of fire resistance depends to a lesser extent on the coefficient of slots but to a greater extent it depends on the density of the fire load. Thus, the difference for the beam with a cross section of 150 Â 300 was 15 min under varying density of the fire load, and for different slot coefficients it is not more than 5 min. Provided that the density of the fire load is less than 690 MJ/m2 for a beam with a cross section of 150 Â 300, the limit of fire resistance does not occur at all. The proposed method allows more accurate determining of the limit of fire resistance of timber structures as it takes into account both the main parameters of fire spread and thermal-physical characteristics of the timber.