Mill variation in bending strength and stiffness of in-grade southern pine No. 2 2 × 4 lumber

Visually graded southern pine (SP) has wide variability within grade. For 2 × 4 lumber, this variability has increased because it is harvested from both natural forests and plantation forests where trees contain high percentages of juvenile wood. To investigate resource variability, six kiln-dried No. 2 2 × 4 SP packages were acquired from six mills. From each package, 124 samples were destructively tested in bending. Mean modulus of elasticity (MOE₁₅) ranged from 9.2 to 13.1 GPa, and three mills did not meet the design values (11.0 GPa). Bending strength (F _b) ranged from 7.6 to 11.9 MPa, and four mills did not meet the design values (10.3 MPa). Analysis of variance of MOE₁₅ and F _b showed significant differences between mills. MOE₁₅ explained from 33 to 51 % of the variability in F _b. These data suggest that variation between mills is high and destructive testing is critical for more accurate characterization of lumber properties.