Effect of Duration and rate of Loading on Strength of Wood and Wood-Based Materials.

This study reviews world literature on the strength-related effect of duration and rate of loading on wood and wood-based materials. Also, early developments are discussed which led to the currently used permament loading factor of 916. Published data on duration of load are reanalyzed and compared. The comparisons suggest that the effect of stress level on duration of stress for wood is greater for shear than for bending or compression. The comparisons also suggest that the stress level effect is greater in hardboard, particle board, and plywood than in solid wood. A similar comparison of loading rate effects suggests that strength is affected to a greater extent in green wood than in dry wood, particularly in bending. For dry wood, the effect of loading rate on strength is most pronounced in tension perpendicular to grain, followed by compression parallel to grain, bending, and shear. Results also suggest that loading rate in bending has a slightly greater effect on hardboard strength and a slightly lesser effect on particle board strength compared to strength of wood. The shortcomings of the present data on loading rate and duration are discussed. Suggestions are made for needed research. Author