Assessment of Eurocode 5 Charring Rate Calculation Methods

The base hypothesis for the assessment of fire resistance of timber structures by simple calculation models is that for temperatures above 300°C, timber is no longer able to sustain any load. Consequently, the determination of the location of the 300°C isotherm, the char depth, is decisive for the result of fire resistance calculation methods. The charring rate (CR) of timber is dependent of numerous factors, such as wood species (density, permeability and composition), moisture content and direction of heat transfer (parallel or perpendicular to the grain). Eurocode 5, Part 1–2, presents several methods for the calculation of fire resistance of timber structures that are divided into simplified and advanced. In this paper simplified and advanced methods are compared regarding the calculation of the char depth and residual cross section strength. Finite element simulations have been performed, employing the proposed timber properties of Eurocode 5 using the finite element code SAFIR. The influence of parameters such as timber density and moisture has been investigated. The results obtained with finite element calculations were then compared with Eurocode 5 simplified models. Some inconsistencies between the two methods have been observed. Proposals are presented to overcome some of the inconsistencies as well as to extend the applicability of the models.