Density variations in beech LVL: influence on insertion moment and withdrawal capacity of screws

The manufacturing process of beech LVL panels causes panel to panel and inherent density variations. Unlike panel to panel variation, where the density changes from one panel to another, inherent variations arise perpendicular to the veneer layers in the cross-section of a single panel in a narrow area. If panels are processed to glulam-like products, inherent variations repeat in every lamination. Density variations in turn influence amongst others the insertion moment and the withdrawal capacity of self-tapping or self-drilling wood screws. prEN 14592 provides EN 15737 for testing the insertion moment and EN 1382 for testing the withdrawal capacity. Both testing standards apply to engineered wood products too. In both of them, it is generally stipulated that the density of the provided specimens has to be representative for that of the material actually used. However, there is no further reference how to account for specific density variations in wood-based products as beech LVL. For that reason, the paper aims at looking into the correlation between such density variations in beech LVL and these parameters. In a broader sense, the findings may contribute to a more purposive and better application of the preceding testing standards in terms of both parameters and LVL-based products.