Self-tapping screws as reinforcement on single-dowel connections with artificial cracks

Self-tapping screws have the potential to reinforce timber elements. However, their application is restricted due to a lack of design guidance. Compared with fully threaded screws, partially threaded screws with a shorter thread length have less drive-in torque, enabling easier installation. This study showed that partially threaded screws are as effective as fully threaded screws in enhancing the mechanical properties of single-dowel timber connections with artificial cracks. A total of 120 embedment tests were conducted, using screws with two thread lengths (33% and 100%) on single-dowel connections. The connections were also prepared with three different widths of artificial crack to represent splitting of the wood due to moisture variation. The results showed that the screws with 33% thread length were as effective as screws with 100% thread length at reinforcing the connections when the crack width was 1.5 mm or 4.5 mm. However, for a crack width of 6 mm, the embedment strength of the connections reinforced with screws with a 33% thread length was significantly lower (about 15.7%) than the connections reinforced with screws with a 100% thread length. This research demonstrates the potential of using self-tapping screws with a partial thread to reinforce existing timber elements with cracks.