Impact of knots on the fracture propagating along grain in timber beams

Abstract

Fracture propagating along the grain of timber is one of the most relevant failure mechanisms due to the wood’s low strength and its brittle failure behaviour when subjected to excessive shear and tensile stresses perpendicular to the grain. According to the current procedures, the fracture energy of wood is determined on small clear specimens. However, for the prediction of the structural behaviour of full-scale structural timber members, the influence of knots has to be accounted for. The discrepancy between the fracture behaviour of small specimens and members of structural size has already been observed in several studies. The aim of this paper is to provide a review on a selection of these studies and to discuss their relevancy for the evaluation of the fracture properties and the structural behaviour of full-scale structural timber.