ORCID Profile
0000-0002-6719-7026
Current Organisation
Beijing University of Technology
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Publisher: Elsevier BV
Date: 08-2019
Publisher: Elsevier BV
Date: 2019
Publisher: Thomas Telford Ltd.
Date: 02-2022
Abstract: Self-tapping screws have been widely used in timber constructions. The current practice considers self-tapping screws perform best in connecting two members when they are fully threaded however, the drive-in resistance caused by the friction between the wood and the screw can potentially damage the screw and reduce the effectiveness of its applications. The relationship between their thread configuration and the drive-in torque force has not been investigated, and the question as to how would knots in the member affect the drive-in force, remains a unanswered. In this study a series of tests was conducted, aiming to demonstrate the influence of thread configuration on the drive-in torque of screws. Two types of self-tapping screws and three different thread configurations were studied. The drive-in torque for partially threaded screws was found to be significantly slower than that of fully threaded ones. The results showed that knots can significantly influence the positioning of the screw and increase the drive-in torque. The application of a pre-drilled hole was found to be an effective way to minimise the influence of knots. This paper points out that with appropriate consideration of thread configuration, partially threaded self-tapping screws can not only achieve the same efficiency as fully threaded ones, they will also benefit from reduced drive-in torque force.
Publisher: Thomas Telford Ltd.
Date: 2023
Abstract: 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.
Publisher: Thomas Telford Ltd.
Date: 05-2023
Abstract: The ‘rope effect’ is a positive effect caused by the failure of fasteners of dowel-type connections. A similar mechanism can be found in connections with screw reinforcement. For self-tapping screws used as reinforcement for connections, bending of the self-tapping screws tends to close developed cracks. Utilising the withdrawal resistance provided by the threads on the pointed end of the screw and the pull-through resistance from the screw head, screw reinforcement enhances the embedment strength and splitting resistance of the wood and increases the ductility of the connection. The influence of different thread lengths and locations on reinforcement effectiveness regarding the embedment strength of the timber was investigated in this study. For cases with threads located only on the pointed end, the splitting resistance increased with longer thread length, indicating that the rope effect was progressively enhanced. It was also found that screws with halved thread length demonstrated similar reinforcement effectiveness to fully threaded screws while the partial threads reduced the risk of damaging the screw during installation. A calculation method to predict the load-carrying capacity of screw-reinforced dowel-type connections was also formulated.
Publisher: Elsevier BV
Date: 12-2023
Publisher: MDPI AG
Date: 16-02-2023
DOI: 10.3390/F14020409
Abstract: The application of self-tapping screws as reinforcement on glulam connections has been proven effective. However, the implication of different thread configurations on the effectiveness of reinforcement remains unknown. This paper conducted experiments using screws with various thread configurations in embedment-strength tests and tensile connection tests. Results show that self-tapping screws with one third of thread achieved similar improvement in the embedment strength and mechanical properties of connections as fully threaded screws. This implies that properly reducing the thread length on self-tapping screws ensures easier screw installation than using fully threaded screws. The influence of screw-to-dowel distance was also investigated and two distances (0.5 d and 1 d) were adopted, with ‘d’ being the diameter of the dowel. The difference in embedment strength due to different screw-to-dowel distances was insignificant. The group with screws placed in contact (0.5 d) with the dowel achieved 5% higher embedment strength than the group with screws placed at a 1 d distance. The connection tests showed good agreement with the embedment-strength tests. This confirms that self-tapping screws with reduced thread can enhance the load-carrying capacity and ductility of connections to a level similar to connections reinforced by fully threaded screws.
Location: United Kingdom of Great Britain and Northern Ireland
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