This study develops and tests a simple model for the effect of knots on MOR: assuming that a knot is hole in the cross-section of a board a strength ratio is calculated and the MOR is the product of the strength ratio and the strength (MOR) of clear wood. This knot model is based on the stresses being in the elastic range and ignores the effect of grain angle and the orthotropic properties of wood and so should not accurately predict either loads for initial failure or the loads at final failure, on which MOR is based. However, the predicted values of MOR for SPF and Douglas fir compare well to measured values. This lead to the conclusion that while the model is physically wrong, the results imply that the strength ratio of the knot model are related to the strength ratio at final failure, which usually occurs at the end of a crack that starts at the knot but propagates some distance along the board. A model for the strength of the remaining section at the end of the crack was developed and tested on six boards. Not only were the strength ratios for the remaining section model similar to those of the knot model, but the remaining section model predicted MOR values closer to the measured values than the knot model did. The task of future work is to predict the location of the initial crack, the path that it propagates and the strength of the clear wood.
The key objective of this study is to analyze full-scale fire-resistance tests conducted on structural composite lumber (SCL), namely laminated veneer lumber (LVL), parallel strand lumber (PSL) and laminated strand lumber (LSL). A sub-objective is to evaluate the encapsulation performance of Type X gypsum board directly applied to SCL beams and its contribution to fire-resistance of wood elements.
The test data is being used to further support the applicability of the newly developed Canadian calculation method for mass timber elements, recently implemented as Annex B of CSA O86-14.
This project was to complete the link from research to commercial production of borate-treated glulam, a value-added new product with appealing performance characteristics in the areas of fire-resistance, mold, insects and decay. The objectives of this project were to eliminate the impediments to commercial production that were identified in a previous project, and provide needed information on strength characteristics of borate-treated lumber compared to untreated lumber.