Bending strength and stiffness of in-grade Douglas-fir and southern pine No. 2 2 × 4 lumber

Abstract

Douglas-fir ( Psuedotsuga menziesii (Mirb.) Franco) (DF) and southern pine ( Pinus spp.) (SP) trees are increasingly grown on intensively managed plantation forests that yield excellent growth. Lumber cut from these trees often contains a large percentage of juvenile wood, which negatively impacts its strength and stiffness. Design values of lumber must accurately reflect the available forest resource, and because the design values were determined over 25 years ago, questions exist whether wood quality has declined. To help address this, 1488 samples of commercial-grade No. 2 2 × 4 DF and SP lumber were destructively tested in edgewise bending. Mean stiffness of DF and SP was 11.51 and 10.89 GPa, respectively, comparing favorably with the 11.02 GPa mean design values; however, variation for SP was higher than in previous studies. The nonparametric 5th percentile bending strengths for DF and SP were 8.30 and 9.06 MPa, respectively. Both DF and SP tested at less than their design values, 9.3 and 10.34 MPa, respectively. Stiffness explained 66% and 52%, respectively, of the variability in strength for DF and SP. Because this relationship seems only moderately predictive, it may be prudent to couple stiffness with additional measures of quality when predicting bending strength.

Reliability Analysis for the Bending Strength of Larch 2×4 Lumber

“…Greater differences between the normal and lognormal distributions were found in MOR15, where the lognormal distribution fitted the data more adequately for both grades. This is particularly evident in the left tail region for both grades, where the lognormal data followed the actual data much more accurately than the normal distribution, which is consistent with numerous findings (Zhao et al 2009;Dahlen et al 2012). The lognormal distribution fit the data slightly better than the 2P-Weibull distribution in MOR15 for both grades, with the exception being SS grade.…”

“…The lognormal distribution fit the data slightly better than the 2P-Weibull distribution in MOR15 for both grades, with the exception being SS grade. The distribution finding is similar to that of the study Dahlen et al (2012) conducted on Douglas-fir and southern pine No.2 2×4 lumber. Therefore, the lognormal distribution for MOR15 was selected for the reliability analysis of design value in this paper.…”

Experimental and Statistical Evaluation of the Size Effect on the Bending Strength of Dimension Lumber of Northeast China Larch

“…As an example, the relationship between β and ρ of 2 × 4 larch lumber, under dead load ( G ) plus live office load ( L O ), are shown in Figure 4 . Several previous studies [ 13 , 25 , 26 , 27 , 30 ] achieved a similar result regarding the relationship between ρ and β.…”

Processing of wood for wood composites

“…with distance from the pith) and longitudinal directions. For example, the density and bending strength of juvenile wood are typically 10-20% and 30-50% lower, respectively, than in mature wood (Alteyrac et al, 2006;Dahlen et al, 2012). This is commonly referred to as juvenile wood or corewood and is often defined as the wood that occurs in the first 10-12 rings adjacent to the pith (Figure 2.1).…”