This report summarizes the progress from Year 4 of the multi-year Lumber Properties project. All activities continue to conform to the guiding principles adopted by the Lumber Properties Steering Committee (LPSC) at the start of the program. This year support was provided to statisticians from the University of British Columbia’s Department of Statistics to meet and work with researchers and statisticians from the US Forest Products Laboratory (USFPL) in Madison, WI. All physical testing under the ongoing monitoring pilot study was also completed, allowing the UBC statisticians to continue work refining their global lumber properties simulator. Work is continuing on the collection of secondary properties for Norway spruce and on the analysis of the data collected to-date.
No activities requiring significant resources were carried out under the Resource Assessment and the Special Products Initiative. Instead, these resources were redirected to cover shortfalls in the provincial funding under the Strategic Framework Initiative, so that the statistical work with the USFPL could continue.
Strength and stability of any engineered structure rely heavily on the connections that link its structural members together. Even though current Canadian code provisions for the design of timber bolted connections were essentially developed based on connections showing a ductile behaviour (based on the so-called European Yield Model), such provisions do not provide any reliable guidance towards predicting deformations attributed to a given loading state. Displacement-related properties, such as stiffness, ductility cannot be determined using the EYM approach. Such information is crucial for designers who are interested in designing for high wind and earthquakes, where stiffness and ductility, in addition to other serviceability issues, become a major issue.
This study provides critical information on the stiffness and ductility of bolted timber connections. Results from analysis made on available sets of bolted timber connections data that has been generated over the last 15 years at the Royal Military College of Canada (RMC) and at Forintek is presented in this report. Analysis results indicate that ductility ratio (m) is strongly dependent on the yield point estimate and the ultimate displacement used to calculate the ratio. The method developed by Yasumura & Kawai for the estimation of yield load and deformation was found to be more suitable for ductility calculations of bolted timber connections. Moreover, analysis have indicated that stiffness equation given in Eurocode 5 for bolted timber connections does not adequately predict the initial stiffness of bolted timber connections as the equation is expressed as a function of wood density and fastener diameter only. There is a need to incorporate other parameters such as the slenderness ratio and the connection geometric configuration which could improve predictions. Ductility ratio of bolted timber connections can be predicted reasonably well using the “Reserved Capacity” concept which is described as the ratio between the governing brittle failure resistance (i.e., RS, GT, T) and the ductile capacity of the connection as predicted by the new proposed design equations in CSA O86. Further verification of the proposed expression is needed to make sure that it is applicable to all bolted timber connection configurations and explore its applicability to other types of timber connections.
This work was launched in support of the new proposed Section on the “Lateral Load Resisting Systems Design” and the new design approach for fastenings in the Canadian Timber Design Code (CSA Standard O86). Efforts will be invested in the future in refining both the current Eurocode 5 formula for prediction of initial stiffness and the proposed expression for prediction of ductility ratio. Ultimately, there is a need to link the new proposed Lateral Load Resisting Systems Design Section to the Fastenings Section in terms of connections’ stiffness and ductility required to satisfy the specified system response.