Implementing coupled heat and moisture transfer model in the fire analysis of timber beams

A performance based two step numerical model to determine the behaviour of timber beam exposed to fire is presented. The first step is based on the coupled heat and moisture transfer model that has been recently presented in Refs. [1,2] and is labelled as Heat&Moisture model. In the second step, the newly developed mechanical model is given which enables to determine the mechanical response of timber beam simultaneously exposed to mechanical and fire load. Based on the model validation for standard fire exposure it was concluded, that a two phase numerical model appropriately simulates the behaviour of timber beam in fire. Furthermore, parametric study revealed that different levels of initial moisture content have a considerable influence on the temperature distribution, charring depth progression and mechanical response of timber beam in fire. In addition, it was presented that the use of simple Heat model based on the Fourier partial differential equation is limited since only one moisture state of timber can be accounted for. At the end of the paper, also average charring rates for standard fire exposure and at different initial moisture contents are given. The possible range of charring rates for bottom side varies from 0.646 to 0.550 mm/min, while for lateral side it varies from 0.571 to 0.517 mm/min. These rates were determined at initial moisture content of 10 and 20%, respectively.