Screw reinforcement on dowel-type moment-resisting connections with cracks

Abstract

This study uses partially threaded self-tapping screws to enhance the mechanical properties of damaged and undamaged dowel-type timber connections. The damaged connections have a 1.5mm wide artificial crack across the middle row of the fasteners. Test results showed that screw reinforcement can restore the rotation capacity of damaged connections. The rotational capacity of reinforced connections without cracks is 45.6% higher than unreinforced connections while the improvement on moment-resisting capacity is slight. Digital image correlation (DIC) was used to detect the movement of the connections and validated that the fasteners rotate around the centre of rotation in reinforced connections. Screw reinforcement also demonstrated the ability to control crack propagation, with the reinforced groups showed a reduction of crack length by at least 37% when compared to the unreinforced groups. A calculation method is proposed to calculate the characteristic moment-resisting capacity of damaged and undamaged screw reinforced connections. The calculated values are proven to be conservative when compared with the characteristic value based on the experimental results. Highlights  Self-tapping screws restored the rotational capacity of connections with cracks  Partially threaded screws showed a trend to effectively control crack propagation  A theoretical prediction method is demonstrated

Study of the Single Shear Performance of a Joint with a New Beech and Self-Tapping Screw Composite Dowel

“…STS reinforcement leads to a more ductile, safer failure. It may not be worth using screws with partial threads for increased strength but it is worth using them to restore the ductility after cracks develop, to ensure a less brittle failure [32,33]. Thread lengths and screw-to-dowel distances have also been investigated.…”

Fire performance of hybrid mass timber beam-end connections with perpendicular-to-wood grain reinforcement

“…To strengthen timber connections against brittle failures, a few experimental studies (Zhang et al, 2019;Viau and Doudak, 2021) were conducted by employing different forms of reinforcements at normal temperature. The study conducted by Zhang et al (2019) showed that self-tapping screws (STS) can be used to enhance the bending strength, control crack propagation and significantly prevent splitting failure in dowel-type moment-resisting connections.…”

“…To strengthen timber connections against brittle failures, a few experimental studies (Zhang et al, 2019;Viau and Doudak, 2021) were conducted by employing different forms of reinforcements at normal temperature. The study conducted by Zhang et al (2019) showed that self-tapping screws (STS) can be used to enhance the bending strength, control crack propagation and significantly prevent splitting failure in dowel-type moment-resisting connections. The results of Viau and Doudak (2021) who investigated the behaviour of bolted connections under blast loads show that reinforcing the connections with STS prevented brittle splitting failure at the connection and changed the failure mode to a combination of bolt yielding and wood crushing.…”

“…To strengthen timber connections against brittle failures, a few experimental studies (Zhang et al. , 2019; Viau and Doudak, 2021) were conducted by employing different forms of reinforcements at normal temperature.…”

Reinforcement of Dowel-Type Timber Joints with Self-tapping Screws

“…Opposed to joints with dowel-type fasteners that are ductile with non-linear behavior and a relatively lower stiffness. According to Dietsch and Brandner (2015), Lathuillière et al (2015) and Chang et al (2019), dowel-type joints can be subjected to brittle failures as well that can be a result of the concentration of high tensile forces perpendicular to the grain, as well as shear stresses. Wood as a material has low resistance to these types of stresses, which increases the possibility of brittle failures, especially by splitting.…”