Abstract
Incising is required in Canadian and US national standards for the treatment of many timber species, especially those from western North America. Incising increases the amount of end-grain exposed to fluid flow, but it also decreases the cross-sectional area and, thus, has the potential to affect mechanical properties. Models have been developed to predict the effects of incising on flexural properties, but correlative data for engineering design adjustment factor(s) for incised and preservative treated lumber and timber are lacking. Current engineering design adjustment factors are primarily based on nominal 2x (38-mm, 1.5-in)-thick lumber tests. In 2018, this fact was recognized and the new design standard allowed for theoretical models to be used for larger materials where appropriate test data were not currently available. This article reports the results of mechanical tests evaluating the effects of incising on flexural properties of nominal 3x and 4x (64- and 89-mm)-thick by 184-mm (7.25-in)-wide Douglas fir and western hemlock lumber. It uses these data to develop potential engineering design adjustment factor(s) for incised nominal 2x (64- and 89-mm)-thick lumber and discusses theoretical modeling to predict those factors.