Influence of insertion angle, diameter and thread on embedment properties of self-tapping screws


In laterally loaded connections, inclined installation of self-tapping screws (STS) allows for axial load transfer and significantly higher connection capacity and stiffness. In such a configuration, both the withdrawal and embedment resistances of the screw contribute to the overall load-carrying capacity and stiffness. To account for the contribution of the embedment component, embedment strength of the screw appropriate for the insertion angle is required. In this study, embedment tests were conducted to determine the influence of STS diameter, insertion angle and fastener thread on embedment properties. Using specimens of Douglas fir, a total of 164 embedment tests with 40 different configurations were conducted and analyzed. Test results showed that embedment strength, stiffness, failure mode and yield load are strongly influenced by the insertion angle, whereas the influence of STS thread and diameter is less apparent. These results were compared with those from another study and the feasibility of a model accounting for inclined insertion angles was analyzed.

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The authors would like to thank the Natural Sciences and Engineering Research Council of Canada (NSERC) for the financial support of this study under the Industrial Research Chair (IRCPJ515081-16) and Undergraduate Summer Research Award (USRA-540864-2019) programs. Financial support was also provided by Landmark Group of Companies, FPInnovations, Canadian Wood Council, MTC Solutions, Rothoblaas, Western Archrib, Pinkwood Ltd and Alberta Innovates. In addition, MTC Solutions and Rothoblaas provided STS, and Western Archrib provided timber material for the test program. Their contributions are gratefully acknowledged.

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Khan, R., Niederwestberg, J. & Chui, YH. Influence of insertion angle, diameter and thread on embedment properties of self-tapping screws. Eur. J. Wood Prod. (2021).

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