Mechanical properties of birch timber under compression loading parallel to grain

The favourable mechanical properties of birch hardwood offers high potential for its use in structural load bearing applications. It is widely known that hardwoods, such as birch, have a higher strength and stiffness compared to softwoods. However, studies investigating the mechanical properties of birch have mainly tested small clear wood specimens, free from growth irregularities. Generally, literature detailing the load bearing behaviour of birch timber is lacking, in particular for elements under compression. This study investigates the influence of growth characteristics on the mechanical properties of birch timber under compression loading parallel to the grain. A selection of specimens with a wide range of growth characteristics are tested, and the maximum strength and modulus of elasticity are determined. Strain fields on one face of the specimens were developed using 2-D digital image correlation. The strain fields provide a qualitative assessment of the deformation behaviour around knots. Correlation analysis is performed and results indicate significant positive correlations between compression strength and stiffness; whereas knots indicate a negative correlation.