Calculation models of wooden beams exposed to fire

This study describes a time-to-failure calculation model for wooden beams under a standard fire exposure. The model is based on the linear theory of elasticity by taking the effect of temperature and moisture on the strength and stiffness of the wood into account. The time-to-failure criterion is a tensile failure in a finger joint (a glu-lam beam) or in a knot. The bending and shear stress distributions in the non-charred wooden cross section are calculated analytically by dividing the cross section into several layers with different materia! properties. The bending moment and shear capacity are then calculated by summing the capacities of the layers. Finally, the calculation is compared with test results. Beams are assumed to be of rectangular cross section and exposed to fire on three or four sides. Some earlier calculation methods are briefly reviewed