Influence of the stiffness heterogeneity on the tensile strength of finger-jointed and edge-glued oak laminations

The timber construction industry mainly uses softwood as structural products, owing to the slenderness of the trees and rather homogeneous nature of the timber, which makes it easier and more cost-effective to process compared to hardwood. By using narrower and shorter components than for softwood, it might be technically and economically possible to produce finger-jointed, edge-glued oak laminations to be used in glued laminated products. This study proposes to explore the impact of the shorter size of components and thus greater heterogeneity of oak edge-glued laminations on their structural properties. Homogenizing the elastic modulus of the components of the laminations through preliminary sorting appeared to greatly improve the strength of the edge-glued laminations, whereas the sole strength grading with no further control of elastic modulus variability could lead to low strengths with disadvantageous system effect. The local evaluation of the ratio between the lowest and highest MoE values of sub-boards in parallel across the lamination width proved to be correlated to tensile strength, with a coefficient of determination of R² = 0. 30. Moreover, homogenizing the elastic modulus of the laminations led to strengths corresponding to system factor values kₒₘₒ exceeding 1. 1, as recommended by the standard. A better control of variability of the mechanical properties of hardwood products, seems offering a pathway to more efficient utilization of the hardwood resource.