Timber connections with glued-in rods and self-tapping screws have gained popularity in recent years because they could provide workable solutions both for newly built structures as well as for strengthening existing ones. As these connections provide excellent strength and stiffness properties and efficiency in load transfer, they are often the preferred choice for connecting mass timber elements because of their simplicity in installation and the fact that the large mass timber member sizes enable these connectors to be used. Being completely surrounded by the wood, these connections offer good fire resistance and good aesthetics.
In Europe, design provisions for glued-in-rods have been implemented in several national design codes. Efforts to include design provisions for connections with glued-in rods in Eurocode 5 were in vain due to many conflicting views on the complexity of the failure mechanism. Recently both past and current research has been considered with the purpose to propose a design approach that could replace several national design rules. For self-tapping screws, design provisions are largely based on Eurocode 1 and European Technical Approvals. While lateral load capacity can be determined based on European Yield Model in Eurocode 5, withdrawal load capacity of the self-tapping screw is determined based on European Technical Approvals.
In Canada, design provisions for connections with either glued-in-rods or self-tapping screws do not exist in CSA O86. For connections with glued-in-rods, the quality control of the production process needs to be developed to ensure a consistent and acceptable performance. Standard test methods need to be developed to evaluate the pull-out strength and stiffness of connections with glued-in rods. Design provisions based on test results will then be developed.
For connections with self-tapping screws, it is proposed that design provisions for self-tapping screws be developed in CSA O86. As self-tapping screws are proprietary products, design provisions need to be developed in Section 12.12 to cover the design of connections with self-tapping screws, and in Section 16.6 to cover the evaluation of mechanical properties of self-tapping screws and connections. A framework for implementation of self-tapping screws in CSA O86 was presented at the January 2017 technical committee meeting. The framework was accepted and a task group was formed to develop code change proposal. FPInnovations staff has taken the lead for the development of code change proposal.
