The European Yield Model (“Yield Limit Equations” in the NDS), only considers the fastener and the immediately surrounding wood in static equilibrium. Designers must also consider possible wood member failures such as premature splitting. The potential for splitting when fasteners are loaded laterally in the end grain depends a lot on the type of loading, support conditions, and member length. For instance, example image 1, for a short span member loaded with the fastener located a sufficient distance away from the loaded edge (see “When do I need to reinforce pre-engineered connectors?”), the design assumptions of the European Yield model may govern. However, a long-span member subject to bending with the fastener located close to the loaded edge (example image 2), significant tensile stresses can develop perpendicular to the grain (indicated with the solid red triangle) causing premature splitting along the red dotted line.
The type of failure shown in image 2 is rarely a concern with short-span sill plates with small, slender fasteners, for example. However, since mass timber is often associated with long-span members, designers should be mindful of this failure mode, for example, when designing with end-face beam hangers and CLT panels loaded out-of-plane. In some applications, designers may consider the possibility of reinforcing members with fully threaded screws to prevent premature splitting.
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