Small-diameter log evaluation for value-added structural applications

Three species of small-diameter logs from the Klamath/Siskiyou Mountains and the Cascade Range in southwest Oregon were tested for their potential for value-added structural applications. The logs were tested in bending and compression parallel to the grain. Strength and stiffness values were correlated to possible nondestructive evaluation grading parameters and compared to values derived from published values based on tests of small-diameter clear wood of the test species. For the test sample, specific gravity and static bending modulus of elasticity were good indicators of strength. Growth rate, however, was poorly correlated to specific gravity, strength, and stiffness. The results suggest that the conventionally derived design values based on published small clear strength values are appropriate for bending but nonconservative for axial compressive strength. At present, established round timber specifications, modified to place limits on the presence of crown wood, would be sufficient for selection of small-diameter structural timbers. Ifa more tightly controlled strength limit is desirable for a specific application, static modulus of elasticity appears to be the most reliable indicator of strength of small-diameter logs.