UBC Theses and Dissertations

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UBC Theses and Dissertations

Self-tapping screw assemblies under monotonic and reverse cyclic load Closen, Max


In the past century old-growth forests in Canada and the USA provided sufficiently large, clear wooden construction material which have been extensively used. Today, the importance of high-quality structural timber and wood products has increased by far. This increase in demand for high-quality timber and wood products can only be satisfied with second-growth wood, some remaining old-growth forests, and of course engineered wood products. The performance of these materials in structures is, however, largely influenced by the capacity of connections. The envelope in timber construction can only be pushed forward if research on mechanical fasteners and connections that are strong, reliable and cost efficient is conducted. Primary focus of research must address the inherent tensile and shear weaknesses of wood perpendicular and parallel to the wood grain. The thesis presented here experimentally investigates the performance of newly evolved structural self-tapping full thread wood screws as a primary fastener in Canadian Douglas-fir glulam and Cross-Laminated-Timber. The screws as primary fasteners were investigated in a commonly used shear connection and a recently developed moment resisting assembly under reverse cyclic load. Both connection systems utilize the high withdrawal resistance and tensile strength of the fastener with inclined (screw-in angles between 30° and 45°) arrangements. The inclined arrangement allows force transfer along the fastener axis and therefore reduces perpendicular to grain splitting and parallel to grain shear failure and provides high connection capacities and stiffness. The results show that structural self-tapping wood screws can effectively be used as primary connector under reverse cyclic loading conditions. In addition to the screw’s superior withdrawal resistance and tensile strength the research showed that self-tapping screws can be applied efficiently with commonly available machinery and tools.

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