UBC Theses and Dissertations
Pull-out resistance of self-tapping wood screws with continuous thread Gehloff, Maik
Over the past centuries the use of timber in structures has seen waves of decline and rediscovery. Timber structures have evolved from empirical structures using timber within its natural boundaries in terms of shape, size and length to modern day engineering design approach using computers and sophisticated numerical models; this has led to the need of high performance connections in such structures. With the help of mechanical fasteners the envelope was pushed time and time again, creating ever stronger connections. However, the capacity of such connections is not only governed by the mechanical properties of the connectors, but also by the mechanical properties of the connecting wood members. Researchers have been developing different methods of reinforcing the inherent weakness of wood, namely the low strength in tension and compression perpendicular to the grain, as well as the low capacity in longitudinal shear. This thesis examines experimentally the pull-out resistance of self-tapping wood screws with continuous thread, a new type of fastener that can be used as a fastener, but also as reinforcement considering Canadian major wood species. Utilizing its high withdrawal capacity and high tensile strength, this type of connector can potentially be used to transfer internal forces in the wood along the length-axis of the screw instead of loading the wood in its weak directions. The results show that self-tapping wood screws (STSs) have a high resistance to pull-out and are an economical alternative to other reinforcement methods. Besides the superior capacities of STSs in withdrawal and tensile strength to other methods, they are also very easy to install since no pre-drilling of holes is required and thus, give an economical solution to many challenges in engineered timber construction.
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