How Is Wood Connection Design Done to the NDS Standard?

Wood connections are designed per the NDS using yield-limit equations that check dowel bearing in the wood against bending of the fastener across all possible yield modes, taking the minimum. The design also verifies end distance, edge distance, and spacing to prevent splitting, applies group-action factors for multiple fasteners in a row, and selects connectors — bolts, nails, screws, or proprietary hangers — rated for the actual loads including uplift and lateral demands. The design philosophy in one sentence: make the steel yield before the wood splits. Ductile fastener yielding gives warning and absorbs energy; brittle wood splitting gives neither. Every NDS detailing rule pushes the connection toward the ductile modes.

The yield-limit model imagines the fastener as a beam on a wood foundation: load it, and either the wood crushes in bearing (mode I), the fastener forms a plastic hinge at the shear plane (mode III), or it forms two hinges with wood crushing between them (mode IV). The equations compute each mode's capacity from the dowel bearing strength of the wood — which depends on species, grain direction, and fastener diameter — and the fastener's bending yield strength. The minimum governs, and the designer proportions the joint so the minimum is as large as possible. Geometry rules guard the flanks: minimum end, edge, and spacing distances keep the wood from splitting, tearing out, or shearing a plug ahead of the fastener group. Net-section checks make sure the member itself — reduced by bolt holes — can carry the load to the connection. And for lateral-load systems, the detailing goes further: holdowns with specified deformation limits, straps with adequate nailing, and proprietary connectors whose published capacities already include the NDS mechanics plus testing.

Wood connection failures in wind and seismic events share a depressing similarity: the design was adequate and the installation wasn't — wrong nails, missed members, straps cut short. I treat wood connection design as extending through inspection, because the capacity lives or dies on fastener count and placement.

• Design the continuous load path first: every uplift and lateral force traced from roof to foundation
• Respect end and edge distances: splitting failures are brittle and unforgiving
• Use the group action factor honestly: long bolt rows don't add up the way intuition says
• Specify the exact connector and fastener schedule — 'hurricane ties' is not a specification
• Inspect before cover-up: fastener count, size, and placement verified while it's still visible