Analysis of bending strength and modulus of elasticity of glulam beams made of combined spruce and birch timber

Introduction – The availability of timber in Sweden has changed over the last few decades. The proportion of deciduous forest, particularly birch has increased, bus despite this change has coniferous trees remain the primary source of harvested timber. To utilize Sweden’s timber resources more efficiently, the construction sector needs to explore alternative wood species. A more balanced harvesting of different types of timber would benefit biodiversity through a more varied forest composition. The purpose of this study is to investigate glulam beams made from a combination of spruce and birch timber. The collected data on the bending strength and modulus of elasticity will be compared with corresponding values for glulam beams made solely from spruce. Method – The study’s objectives will be addressed with experiment in the form of a four-point bending tests. The experiment produces values for bending strength as well as local and global modulus of elasticity. The four-point test is supplemented with measurements of both wet and dry density. Results – The test beams made from a combination of spruce and birch showed, on average 50,7 % higher bending strength and 14,9 % higher modulus of elasticity compared to the control beams made solely of spruce. The test beams also had a 18,2 % higher density than the control beams. Analysis – The analysis of the experiments show that the test beams withstand higher loads and generally exhibit stiffer properties than the control beam. This demonstrates that a combination of spruce and birch wood improves the mechanical properties of a glued laminated beam. Discussion – The results indicate that combining different types of wood in glulam beams can enhance its load-bearing capacity. However, shortcomings in the manufacturing process and the limited number of test pieces affect the reliability of the results. Despite this, the findings suggest that birch has the potential to be used in construction, provided that the production process is improved.