Influence of annual ring orientation on compression strength perpendicular to grain in glulam

Abstract: This thesis presents an analysis of glued laminated timber (glulam) when loaded in compression perpendicular to the grain. Both theoretical and experimental investigations have been carried out. The main focus was related to the growth ring patterns of the laminations and their influence on the stresses, the strains and the failure mode. The theoretical part of the work consisted of creating a linear elastic finite element model in 2D of glulam when loaded in compression perpendicular to the grain. Stress and strain plots created by the model were analyzed and the influence of different annual ring patterns were investigated. Considering compression perpendicular to the grain, a common failure mode of the cross section is cracking due to tension perpendicular to the loading direction. The pattern and the curvature of the annual rings have a large impact on this fracture mode. The model shall be able to predict where in the cross section the first crack initiates. The model was verified by experimental work. Three different geometries of glulam were tested in compression perpendicular to the grain. Measurements of the deformations in the cross sections of the samples were carried out with Digital Image Correlation, DIC. The DIC equipment measured the displacements in 3D of spots in the cross section. A random pattern, called “Speckle pattern”, was created on the cross sectional surface in order to create the spots which the DIC equipment measures. The displacements were computed into strains and the strains were plotted over the surface of the test specimen. The strain plots from the DIC have been compared to the strain plots computed by the finite element model. The main focus relate to the distribution of the strains and how these seem to be affected by the annual ring pattern.