Wood Connection Strength Calculator
Calculate Single Shear Allowable Design Values (Z) per NDS Guidelines
Connection Analysis
*Note: Result is based on the Yield Limit Model for single shear. Includes a standard reduction factor (Rd) for safety. Does not include adjustment factors like CD, CM, or Ct.
How to Use the Wood Connection Calculator
Designing secure wood-to-wood connections requires understanding how fasteners interact with wood fibers. This calculator uses the Yield Limit Equations, which are the industry standard for determining the structural capacity of bolts, screws, and nails in single shear configurations.
Key Input Parameters
- Specific Gravity (G): This represents the density of the wood species. Higher density wood (like Southern Pine) provides better bearing strength than softer woods (like Cedar).
- Member Thickness: The "Main Member" is typically the thicker supporting timber, while the "Side Member" is the attached piece.
- Fastener Diameter: The shank diameter of your bolt or screw. Larger diameters distribute load over a wider area.
- Yield Strength (Fyb): The point at which the steel fastener begins to permanently deform.
Understanding the Results
The calculator evaluates different "modes" of failure, including wood crushing in either member or the fastener bending. The final result shown is the Allowable Design Value (Z), which is the lowest value calculated across all failure modes, adjusted by a reduction factor to ensure safety in real-world construction.
Practical Example
Suppose you are connecting a 2×4 (1.5″ thickness) side member to a 4×4 (3.5″ thickness) post using a 1/2″ diameter bolt (0.50″). If you are using Douglas Fir-Larch (G=0.50), the calculator will determine the bearing strength of the wood and the bending strength of the bolt to provide a safe load limit in pounds.