UBC Theses and Dissertations
The duration of load effect in tension perpendicular to the grain for Douglas fir McDowall, Bruce J.
The duration of load problem in wood subjected to stresses in tension perpendicular to the grain is studied both analytically and experimentally. Analytically, viscoelastic models derived from the principles of fracture mechanics are developed and discussed with respect to their application to the failure mechanism of wood in tension and bending. To assess the accuracy of the predictions of these models, they are compared against the experimental results from duration of load tests carried out on Douglas fir in tension perpendicular to the grain. This failure mode is hypothesised as representative of the critical failure initiating mode of commercial material. A specimen design was developed which proved very successful in keeping the coefficient of variation of the short term strength quite low for wood, approximately 10%. This low variability enabled the tests to be carried out with sample sizes much smaller than those used in the duration of load testing of commercial material.
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