Rate of loading effects on strength of lumber

Standards committees, lumber manufacturers, researchers, and structural engineers often need to interrelate strength test results obtained within a range of time periods varying from a few seconds to several hours. Rate of loading (ROL) data collected at the Western Forest Products Laboratory of Canada and its successor Forintek Canada Corp., and the USDA Forest Service, Forest Products Laboratory, and from other ROL investigations were combined and analyzed. An overall mean trend relationship between stress level and logarithm of time to failure was established. This relationship can be used to adjust the strength of softwood lumber to account for ROL effect. The ROL effect on lumber was found to be less pronounced than that reported in the literature for small defect-free specimens. An analysis conducted with a Linear Surface Model showed that the ROL effect seems to be more pronounced when short-term strength is greater than about 7,000 psi.

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