Cross laminated timber (CLT): Design approaches for dowel-type fasteners and connections

Within the last 20 years, cross laminated timber (CLT) has become one of the most important building products in contemporary timber engineering. By the end of this decade, its annual worldwide production volume is expected to exceed 1,000,000 m³. The industry, engineers, architects and constructors have a strong interest in implementing CLT in European product, design and execution standards. The design of CLT is part of the currently ongoing revision of Eurocode 5. In this context and in addition to the verification of CLT panels in respect of ultimate and serviceability limit states, guidelines on the design of connections in CLT with dowel-type fasteners are of the utmost importance. In this article, we review approaches for calculating characteristic values as provided in literature for single dowel-type fasteners and connections in CLT. We also compare these approaches, with focus on withdrawal and embedment strength of dowels, nails and self-tapping screws, with the current regulations on dowel-type fasteners for solid timber and glulam as formulated in Eurocode 5. These comparisons are made in order to identify the need and potential for revision of current EC 5 equations and state-of-the-art regulations. We summarise regulations on connection design, i.e. minimum spacing, edge and end distances, other additional geometrical conditions, regulations on the effective number of fasteners in a group and minimum penetration depths. Finally, we draw conclusions in respect of the single fastener properties withdrawal and embedment strength and suggest some execution guidelines, which ensure the integrity of CLT structures. Overall, we aim to present a compilation of the current state-of-the-art knowledge on dowel-type fasteners in CLT as a basis for implementing design guidelines for CLT in the new connection chapter of Eurocode 5.