UBC Theses and Dissertations

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UBC Theses and Dissertations

An examination of property relationships in the Canadian machine stress rated lumber in-grade program Griffin, Annie Helen


The Canadian lumber industry undertook two large-scale test programs for the verification of lumber design properties of Canadian species combinations. The visual lumber in-grade test program was begun in 1983 (with a prior program undertaken in 1975), while a similar program for machine graded lumber (MSR lumber) was undertaken in 1988. Some of the results of the MSR lumber in-grade test program are examined in this thesis. Stiffness and strength results from the visual lumber in-grade program are used for comparison, as are values from the MSR lumber standard. The importance of differences in methods of testing properties, particularly Modulus of Elasticity (MOE), is shown. Differences in results occur due to changes in the test span to depth ratios, measurement techniques and location of defects. The importance of knots as a cause of failure in both bending and tension is examined. The high incidence of lumber failures initiating at points where no defect was visible to the human eye is also studied.

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