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 (Fb) 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 Fb showed significant differences between mills. MOE15 explained from 33 to 51 % of the variability in Fb. These data suggest that variation between mills is high and destructive testing is critical for more accurate characterization of lumber properties.