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Title: Reinforcement of timber dowel-type connections using self-tapping screws
Author: Zhang, Cong
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2018
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The study investigates the mechanical performance of dowel-type timber connections reinforced by partially threaded self-tapping screws. The literature review emphasises that, with a lack of a design code for using self-tapping screws as reinforcement, there are concerns over using fully threaded screws, which may have difficulties during the installation. The study first confirmed that, comparing with partially threaded screws, fully threaded screws require higher drive-in torque and are more vulnerable to torsional damage, especially under the circumstance when a pre-drilled hole is not provided and with the presence of wood defects, such as knots. This brought about the ideas of using partially threaded screws in order to reduce the drive-in torque and investigating the relationship between thread configuration and the effectiveness of screw reinforcement. The results of embedment tests in this study indicated that partially threaded screws achieved similar improvement in the mechanical properties of wood as screws with complete thread. Using digital image correlation (DIC), this study revealed that the withdrawal capacity from the point end of the screw and the pull-through resistance from the screw head are utilised to control wood splitting, which is similar to the 'rope effect' in connections. Test results also confirmed that, within a certain range of crack width, partially threaded screws are as effective as fully threaded screws in enhancing the mechanical performance of specimens with artificial cracks. This study then extended the investigation to a larger scale, from tensile connections to moment-resisting connections, and confirmed the improvement of mechanical performance of connections when reinforced by partially threaded self-tapping screws. A portal frame reinforced by partially threaded screws was tested under static load. It showed significant improvement in the ultimate moment-resisting capacity and rotation angle compared to an unreinforced portal frame. A theoretical prediction method of the moment-resisting capacity of screw-reinforced connections is proposed and conservative predicted values are obtained. The experimental results demonstrate the effectiveness of using partially threaded self-tapping screws, in strengthening connections and ensuring a more ductile failure mode in the connections. In addition, partially threaded self-tapping screws are easier to install than fully threaded screws.
Supervisor: Sharma, Bhavna ; Harris, Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Civil Engineering ; Timber Engineering ; Connections ; Experimental Testing ; Reinforcement ; Self-tapping screws ; Eurocodes ; Design