Load-Carrying Capacity and Failure Mode Analysis of Timber Rivet Connections

Abstract

Different brittle, mixed and ductile failure modes of timber connections have long been observed by wood researchers. The wood engineering community has dedicated a significant amount of effort over the last decades to establish a reliable predictive model to determine the capacity of timber connections under different failure modes, particularly, for wood failure mechanisms. The present study focuses on timber rivet connections. In the analytical model developed for the wood block tear-out resistance under parallel to grain loading, the stiffness and strength of the resisting planes subjected to non-uniform shear and tension stresses are taken into account. For the wood splitting resistance under perpendicular to grain loading, the presented design method takes into account the observed two possible wood failures; either partial or full width splitting. A design procedure is presented which allows the designer to calculate the resistances associated with the predictions of the potential brittle, ductile and mixed failure modes. The effective wood thickness for the brittle failure mode is derived and related to the elastic deformation of the fastener. In the case of mixed failure mode (a mixture of brittle and ductile), the wood effective thickness depends on the governing ductile failure mode of the fastener. The fastener failing resistance under yielding and ultimate limit states are determined using the relevant wood embedment strength and the fastener moment capacity. In the proposed analytical models for the prediction of wood strength under longitudinal and transverse loadings, the effect of geometry parameters such as number of fastener rows and columns, spacing along and across the grain, fastener penetration depth, loaded and unloaded edge distances, end distance, and member thickness are considered. The design approach presented is verified using an extensive testing regime conducted on riveted joints under parallel and perpendicular to grain loadings on New Zealand Radiata Pine laminated veneer lumber (LVL) and glulam and the test data from the literature. This improved design approach gives the practitioners the ability to predict the connection ultimate capacity and its failure mode more accurately than the methods used in EC5 and CSA O86. The proposed design approach can be extended to other dowel-type fasteners such as nails, screws and bolts.