Abstract
Incising is an essential preprocessing method to ensure lumber from difficult-to-treat wood species can achieve chemical loadings during pressure treatment that will allow commodities to perform in ground contact or critical infrastructure applications. National Design Specifications in the United States require engineers to include a strength reduction for incised lumber, but these reductions are based on data collected on 2-in (51-mm) nominal-thickness lumber. Little work has been done to measure the impact of incising on lumber with a larger cross-section. This exploratory study measured the effect of incising on modulus of rupture (MOR) and modulus of elasticity (MOE) of nominal 4 by 6-in (102 by 152-mm) Douglas-fir lumber. Lumber pieces ranked and matched by vibrationally measured MOE were tested edgewise by a four-point bending test according to ASTM D4761. A total of 48 incised and nonincised test specimens were included in the final analysis. Incised MOR values were 11.5 percent lower than nonincised pieces ( P < 0.05 analysis of variance). MOE values were 2.5 percent lower for incised pieces compared with nonincised pieces, but the difference was not statistically significant ( P > 0.05). Ranking paired incised and nonincised specimens showed that the divergence between the two categories was greatest in specimens with lower MOR values. The coefficient of variation for MOR values was high for both incised (32.4%) and nonincised (26.6%) samples and a more uniform data set would provide better confidence for resolving differences between them. This work provides a useful preliminary comparison in structural performance of incised and nonincised lumber.