Structural Screw Design

Timber engineering is evolving. The upcoming Second Generation Eurocode 5 (prEN 1995-1-1) introduces significant changes to connection design. SPEC Toolbox puts you ahead of the curve.

Our calculator handles the standard Johansen Yield Equations you use today, but gives you the power to toggle “Draft Provisions” to see how your design performs under the stricter, modern analysis methods proposed for 2025/2026 adoption.

Under the old code, Cross-Laminated Timber (CLT) design often relied on conflicting product brochures. The prEN 1995 draft formalizes CLT connection design.

• Face vs. Edge Withdrawal: We apply the new standardized equations for withdrawal capacity relative to the layer orientation.
• Rolling Shear Verification: The calculator checks interaction limits where fastener forces might trigger rolling shear failure in the crossing laminations.

The industry has learned that steel strength means nothing if the wood tears out first. We have integrated the expanded “Brittle Failure” scope from the prEN draft:

• Block Shear & Plug Shear: Automated detection of perimeter failure groups.
• Row Shear: Verification of shear planes between fasteners in high-density connections.
• Splitting Capacity: Checks for tension perpendicular to grain limits caused by the connection geometry.

For connections in tension or combined loading:

• Withdrawal Capacity ($F_{ax,Rk}$): Calculated based on penetration length ($l_{ef}$) and characteristic density (${rho}_k$).
• Rope Effect Contribution: We automate the $F_{ax,Rk}/4$ contribution to shear capacity, while applying the strict new limits on deformation capacity often discussed in the Second Generation committee drafts.

Whether running the 2004 or 2025 rule set, we automate the coefficients:

• Load Duration Class: Instant toggles for $k_{mod}$ (e.g., Permanent to Instantaneous).
• Service Class: Adjusts for moisture content (Service Class 1, 2, or 3).
• Effective Number of Fasteners ($n_{ef}$): We calculate the reduction in capacity for rows of fasteners ($n$), ensuring you don’t overestimate group capacity.