Connections in timber structures play a key role in providing stability and stiffness to the structure. Timber joints may often become the weakest links of the structure and, therefore, require particular attention from the designers. Structural efficiency, simplicity of design, ease of fabrication and assembly in addition to cost effectiveness are some of the major parameters that need to be taken into account when specifying the appropriate connection system in timber projects.
The recent development of a new generation of structural composite wood-based products and assemblies (e.g. Cross Laminated Timber [CLT], parallel strand lumber, oriented strand lumber, etc.) and the recent interest in hybrid systems require the development of innovative connection systems as well as technical information on the design and performance of such connections. Moreover, the advancement in the Computer Numerical Control (CNC) systems which are being widely adopted in the manufacturing of timber and other wood-based products, is also contributing towards the development of such innovative connection systems as it facilitates the design and fabrication of such systems. Although some innovative timber connection systems have been developed (mainly in Europe and Japan) over the last 20 years or so, the lack of technical information and design guidelines is making it difficult for designers and engineers to adopt them in North America.
This report summarizes a series of activities focused on developing relevant technical information that would facilitate the design and construction of traditional and innovative connection systems for non-residential and mid-rise wood and hybrid construction using conventional and engineered wood products. The report also covers activities intended to support the design communities across the country which take the form of training courses and seminars organized to provide designers and engineers with the state-of-the-art technical information required to design their projects in accordance with the new design provisions in the Canadian timber design standard and using innovative connection systems from Europe and Japan. Since CLT is becoming one of the most promising alternative wood-based products to concrete in special applications, considerable work has been invested in developing appropriate connection systems to facilitate the use of this product for various applications.
One full chapter dedicated to the detailing and design issues of connection systems in CLT assemblies was drafted and compiled into a CLT handbook which was published recently by FPInnovations under the Transformative Technology Program under this project. In addition to that, results from an exploratory study focused on evaluating different CLT to CLT panel profiles typically used are presented in this report. Self-tapping screws are one type of fastening system that has been used extensively in Europe in CLT assemblies and one that has a great potential as it combines the ease of installation (i.e. requires no pre-drilling) with high efficiency. The report also describes some of the technical work conducted to support code change proposals in CSA O86 relating to improving current design procedure for ductile failure mode to account for additional capacity due to axial tensioning effect.
To be able to provide designers with a practical way of selecting the appropriate type of connection system for their specific application, detailed information on key performance attributes of traditional and innovative types of connection systems has been compiled in a table format. Such information will greatly assist design professionals who are pursuing the idea of using wood structural systems in non-residential buildings.