Information on ductile and brittle failure modes is critical for proper design of timber connections in Crosslaminated Timber (CLT). While considerable research has been conducted in Europe and Canada on the ductile performance of connections in CLT, little is known about the brittle behaviour. This paper presents new information from testing programs and analysis performed in Canada and in New Zealand on the brittle performance of dowel-type fasteners in CLT. The testing programs have been designed to trigger brittle failure modes based on minimum end distances and fasteners spacings specified in the Canadian timber design standard. Timber rivets and bolts/dowels are covered under this study. At the time of writing of this abstract, the testing program is advancing and results will be available at the time of paper submission.
The existing models for the prediction of the splitting failure of dowel-type connections loaded perpendicular to grain are determined generally based on crack growth of the entire member cross-section. These models can be appropriate for stocky or rigid fasteners installed through the full thickness of the wood member. However, for slender dowel-type fasteners such as timber rivets, particularly when the penetration depth of the fastener does not cover the whole member thickness, the crack formation is different. Observations from current tests in thick members show that the crack growth across the grain occurs to a depth corresponding to the effective embedment depth of the fastener and propagates along the grain until it reaches its unstable condition. The design method presented in this paper to predict the connection splitting capacity takes into account the observed two possible failure modes of wood: either partial or full width splitting. In the proposed method, the effect of geometry parameters such as connection width and length, fastener penetration depth, loaded and unloaded edge distances, end distance, and member thickness as observed by others are considered. Results of the tests undertaken with laminated veneer lumber (LVL) and glulam manufactured from New Zealand Radiata Pine (RP) and data available from literature confirm the validity of this new method and show that the proposed design approach can be used advantageously in comparison to other existing models for timber rivet connections under transverse loading.
Timber rivet connections, originally developed for use with glulam construction, may be a viable option for use with structural composite lumber (SCL) products. Tests were conducted on small samples to assess the performance and predictability of timber rivet connections in parallel strand lumber (PSL) and laminated strand lumber (LSL). The test joint configurations were designed to exhibit ìrivet failuresîósome combination of rivet yield and bearing deformation in the compositeóas opposed to wood failure modes, such as block-shear tear-out or splitting.
Results suggest that per-rivet design values should fall between 1 and 2 kN, depending on species and density of the composite and load direction with respect to grain of the composite strands. Timber rivets performed better in LSL than in PSL and better in yellow poplar PSL than in Douglas-fir or Southern Pine PSL; 40-mm rivets in yellow poplar LSL gave roughly equivalent performance to 65-mm rivets in yellow poplar PSL.