Section 11.3.1/Bolted Connection Design
NDS 2018 Section 11.3 covers the yield limit equations for bolted connections in wood members, determining single-bolt capacity based on wood bearing strength, bolt bending, and connection geometry.
Bolted connection capacity in wood is determined by the yield limit equations in Section 11.3.1, which evaluate six possible failure modes for single-shear connections and four modes for double-shear connections. The failure modes include: Mode Im (wood bearing failure in the main member), Mode Is (wood bearing failure in the side member), Mode II (bolt rotation without bending), Mode IIIm (bolt bending with bearing in the main member), Mode IIIs (bolt bending with bearing in the side member), and Mode IV (bolt bending with bearing in both members). The governing capacity is the lowest value from all applicable modes. The dowel bearing strength (Fe) depends on the wood species and the direction of loading relative to the grain (parallel or perpendicular per Table 12.3.3). The bolt bending yield strength (Fyb) is typically 45,000 psi for common bolts. Adjustment factors include the load duration factor (CD), wet service factor (CM), temperature factor (Ct), group action factor (Cg) for multiple-bolt connections, and geometry factor (C_delta) for edge distance, end distance, and bolt spacing.
Why this section exists
Bolted connections are the primary means of connecting wood members in timber framing, heavy timber, and engineered wood construction. Wood is weaker than steel, so the bolt capacity in wood is governed by the wood bearing strength and the bolt's tendency to bend (yield) within the wood, not by the bolt's shear strength as in steel connections. The yield limit equations model the actual failure mechanisms observed in testing: crushing of wood fibers around the bolt, bending of the bolt shaft, or a combination of both. The geometry factor ensures adequate edge distance and end distance to prevent wood splitting, which is a brittle failure mode that the yield equations do not capture.
What plan reviewers look for
Plan reviewers check connection details for bolt diameter, number of bolts, spacing, edge distance, and end distance. They verify the bolt capacity calculation uses the correct dowel bearing strength for the wood species and grain direction. They check that the group action factor is applied for rows of multiple bolts. They verify the geometry factor is 1.0 (full capacity) by checking that minimum edge distances (at least 1.5D perpendicular to grain), end distances (at least 7D for tension parallel to grain), and bolt spacings (at least 4D between bolts) are met. They verify notching limitations are not violated near bolt holes.