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Moment resistant connections made with timber rivets in wood product substrates Hampson, Joel Alexander

Abstract

The moment resistance is determined for connections made with timber (glulam) rivets. Designing a moment connection in wood and wood products is complicated by their non-linear (limited elastic) and anisotropic properties; there is currently no codified design guidance for moment connections in wood or wood products. Timber rivets are high-strength engineered nails. They are used in conjunction with predrilled steel side-plates. The wood product substrates investigated herein are glue-laminated, laminated-strand, laminated-veneer and parallel-strand lumber. The model is based on the principle of equilibrium and assumes that the connection will behave in a ductile - no sudden wood failure - manner. The moments within a connection (a group of fasteners) is summed about an instantaneous centre of rotation. The internal moment arises from the resistance of each fastener; this resistance is non-linear and displacement dependent; a Foschi-style load-slip equation and parameters are used to calculate this for each fastener. The external moment arises from the eccentrically applied load and its radius from the instantaneous centre of rotation; the general, a-priori loading can be converted into a wrench to find this eccentric load and lever arm. The instantaneous centre of rotation that minimizes the difference between the internal and external moments is found by an incremental search. MS Visual Basic was used to implement this search. The instantaneous centre of rotation, and subsequent moment capacity, was found for every degree of preset rotation up to an ultimate capacity. This was implemented for various arrangements of timber rivets and wood products. Experimental verification o f the model for these arrangements indicated the following: the ultimate was almost exactly predicted on average, and the yield loads and the rotational stiffness were under predicted by an average of about 10% and 30%, respectively. The instantaneous centre of rotation appeared in the predicted location. All of the specimens exhibited ductile behaviour during testing, but the side plate completely disengaged on the shortest-rivet laminated-strand and parallel-strand lumber samples. Further research is suggested in several areas: notably, the dynamic response of moment connections and linking the fastener's capacities to more fundamental properties like elastic-moduli and densities.

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