UBC Theses and Dissertations
Experimental investigations of shear connections with self-tapping-screws for cross-laminated-timber panels Afrin, Hossain
Advances in the areas of engineered wood products, such as Cross-laminated Timber (CLT), and wood connection solutions such as Self-tapping Screws (STS), as well as supporting legislation have created new possibilities for the structural application of timber in mid-rise construction. CLT structures and their connections need to be designed for appropriate capacity, stiffness, and if applied in seismic zones – ductility; however, current North American design standards contain no provisions for STS in CLT. The research developed in this dissertation first examined the withdrawal resistance of STS in CLT for different screw diameters, effective screw embedment lengths, and angles of the screw axis relative to the wood grain. The work demonstrated that the existing product approval equation which was developed for Glulam can be used to predict the withdrawal resistance of STS in CLT. Subsequently, the performance of CLT-STS joints was investigated under monotonic and reversed cyclic tests. Different conventional joint types were tested, namely surface spline with STS loaded in shear and half-lap with STS loaded in either shear or withdrawal. The research further investigated novel CLT joints combining STS loaded in withdrawal with STS loaded in shear, and butt joints with double inclination of STS. The joint performance was evaluated in terms of capacity, stiffness, yield strength, and ductility, and it was shown that joints with STS in shear exhibited high ductility but low stiffness, whereas joints with STS in withdrawal were found to be stiff but less ductile. Combining the shear and withdrawal action of STS led to joints exhibiting high stiffness and ductility. Varying number of screws in one joint allowed evaluating group effect of STS for joint capacity, stiffness, and ductility, under both monotonic and cyclic loading. E.g. for joint capacity, group effect can be expressed as neff = 0.9∙n for all joints under static loading, where n, and neff are actual and effective number of screws respectively. For cyclic loading, more pronounced group-effect was observed that can be expressed as neff = n0.9. The data and analyses presented in this dissertation will provide guidance to structural engineers and builders for designing CLT-STS shear connections.
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