PNNL

Abstract

With the increasing popularity of mass timber, utilizing large-diameter wood screws and 5 hardwood dowels can offer an easy and cost-efficient way to join structural elements. However, the 6 existing research on hardwood dowels is limited to single fastener joints under monotonic loading. 7 No research is available on the group effects of joints with multiple hardwood dowels. This paper 8 presents the results of 96 monotonic and cyclic single-shear plane CLT-to-CLT joint tests with 9 hardwood dowels (Red Oak and Yellow Birch, 25.4 mm diameter) and self-tapping wood screws (8 10 mm diameter) in Grand-Fir CLT, where screws were inserted both perpendicular and at a 45-degree 11 angle to the grain for comparison to hardwood dowels. The study evaluated the mechanical properties 12 of the joints with changing fastener spacing. Mechanical properties such as yielding and ultimate 13 strength, displacement, elastic and yielding stiffness, and ductility were evaluated. The results showed 14 equal strength and stiffness properties for hardwood dowels comparable with large-diameter screws. 15 Additionally, the hardwood dowel joints demonstrated moderate ductility properties. The strength 16 and stiffness of the tested joints were compared with analytical equations found in the literature by 17 considering the group action factor of the fasteners. Lastly, a nonlinear force-displacement model was 18 presented and compared to the experimental results and analytical calculations, which gives the 19 possibility to predict and optimize the mechanical behavior of hardwood dowel and screw joints with 20 varying numbers and spacing between fasteners.