Half-Lap Cross Laminated Timber Pegged Joints

Abstract

Cross laminated timber (CLT) is a panelized structural system consisting of odd layers of dimension sawn lumber stacked perpendicularly to the previous layer. Since the introduction of CLT to North America, man research projects have been conducted on the material properties of CLT panels as well as the three primary methods of joining CLT with metallic fasteners: the butt joint, half-lap joint, and spline joint. Currently, there are efforts to reduce the embodied energy associated with CLT buildings, leading to research exploring alternatives to metallic fasteners. This research investigates the shear yield load and stiffness of red oak (Quercus rubra) hardwood pegs in half-lap 3-ply Austrian spruce (Picea abies) and yellow-poplar (Liriodendron tulipifera) CLT diaphragm connections. In addition to the use of Austrian spruce and yellow-poplar CLT, both 1 inch and 1.25 inch diameter pegs were tested in the half-lap connections. The influence of both the CLT species and peg diameter were evaluated for their impact on connection yield load and stiffness when subjected to both monotonic and cyclic loading. The replacement of metallic fasteners with hardwood pegs could represent a significant reduction to embodied energy in buildings. Experimental testing showed that the yellow-poplar connections for both 1 inch and 1.25 inch diameter pegs had a greater 5% offset yield load than the Austrian spruce specimens. Yield Mode II and V were the two identified failure modes, with Mode II occurring primarily in the Austrian spruce specimens and Mode V predominantly occurring in the yellow-poplar specimens. Connection yield loads were predicted using Yield Mode II and V predictive equations and compared to experimental results, with varying degrees of agreement. Through a two-way ANOVA analysis, it was determined that there was a significant difference in the 5% offset yield loads of the connections due to both CLT species and peg diameter. When evaluating the impact of CLT species and peg diameter on connection stiffness using a two-way ANOVA, a significant difference in stiffness was attributed to CLT species but not peg diameter.