Wood and Engineered Wood Product Connections Using Small Steel Tube Fasteners: Applicability of European Yield Model

Capacities of wood connections with laterally loaded dowel fasteners by plastic analysis can be predicted using the European yield models (EYM) equation. The underlying concept is that failure occurs due to crushing of wood beneath fasteners and / or formation of plastic hinges in fasteners with a rigid-plastic representation of the materials involved. EYM prediction is now “the” way within design codes to calculate the maximum attainable capacity per fastener. Subsequent adjustments discount those predictions through factors which account for unequal sharing of force between fasteners and premature connection failure by fracturing. In North America the EYM is the basis for lateral load capacities of connections made with bolts, drift-pins, screws, nails, and timber rivets. This paper addresses the capability of the EYM for predicting load carrying capacities of solid wood (sawn softwood lumber) and laminated strand lumber (LSL) connections employing tight-fitting steel tube fasteners with external diameters up to $12.7\mathrm{mm}$ . EYM prediction is compared with experimental test results for arrangements with one or four fasteners loaded in double shear. Accuracy of predictions depends on factors such as connection geometry and the type of wood member involved. Prediction is always accurate if a connection has only one fastener, or if joined members are made from LSL. If members are made from sawn softwood lumber premature brittle splitting type failure modes occur for multiple fastener situations, with impairment of capacity inversely proportional to the fastener outside diameter. Suggestions are made here regarding the nature of codified design rules for steel tube fastener connections, with the intent that such provisions be enacted within North America.