Strain Distribution of Dowel-Type Connections Reinforced with Self-Tapping Screws: Fid-Bau Portal

Strain Distribution of Dowel-Type Connections Reinforced with Self-Tapping Screws

Zhang, Cong / Harris, Richard / Chang, Wen-Shao

Current limited guidance on the selection of screws together with undefined design specifications restricts the effectiveness of self-tapping screws as reinforcement on timber members to control crack propagation. Using digital image correlation (DIC), this study visualized the surface strain distribution of screw-reinforced dowel-type connections to understand the influence of thread configuration and screw-to-dowel distance on controlling crack propagation. The experiment was based on single-dowel embedment tests using 16- and 20-mm-diameter steel dowels. Three thread lengths (0%, 33%, and 100% thread) and six screw-to-dowel distances ( $0.5 d$ , $0.75 d$ , $1 d$ , $1.5 d$ , $2 d$ , and $4 d$ ) were investigated. Results show that a screw with 33% thread on the point end can be as effective as screws with 100% thread to control crack propagation under the same geometrical parameters of the connections. Results also reveal that a screw placed further from the dowel (e.g., at $2 d$ distance) can delay the crack-controlling effect. Self-tapping screws placed at $2 d$ can still improve the embedment strength and ductility; however, further doubling this distance ( $4 d$ ) did not enhance the embedment strength, but a higher ductility was still achieved.