Design Wood Screw Connections to NDS

• Automated Yield Limit Equations: Instantly solve all six NDS Yield Modes (Im, Is, II, IIIm, IIIs, IV) to find the controlling Lateral Design Value (Z).
• Withdrawal & Pull-Through: Calculate Withdrawal Design Values (W) and Head Pull-Through resistance (WH) based on specific gravity and thread penetration.
• Code Compliance: Adheres strictly to NDS 2018 (USA) and CSA O86-19 (Canada) standards, including LRFD and ASD formats.
• Mass Timber Ready: specialized support for Dowel-Type fasteners in Cross-Laminated Timber (CLT) per ANSI/APA PRG-320.
• Supplier Agnostic: Design with standard ASME Lag Screws or select from a database of proprietary Self-Tapping Screws (STS).

Self-tapping screws are widely used in timber construction in North America for transferring axial and shear forces between structural elements. The SPEC Toolbox Screw Design module evaluates screw connections using AWC NDS (National Design Specification for Wood Construction) provisions together with manufacturer-specific screw data. Supported materials: Softwood, Hardwood, Glulam (GLT), Cross-Laminated Timber (CLT), Laminated Veneer Lumber (LVL), Plywood, Steel plates for timber-to-steel connections.

3D visualization displaying member geometry, screw orientation, screw placement, applied forces. Users can rotate and inspect the connection model before performing structural checks.

Member 1 (primary), Member 2 (secondary/connected). Properties: member type, member dimensions, elastic modulus, tensile strength, shear strength — used per AWC NDS provisions. Also definable: grain orientation (side grain or end grain), connection type (discrete or continuous).

Fx (shear x-direction), Fy (shear y-direction), Fz (axial along screw axis). Resulting shear force V auto-calculated. Loads visualized within the connection model.

Define: screw supplier, screw family, specific screw type. Properties: screw diameter, thread configuration, embedment characteristics, withdrawal resistance parameters.

Partially threaded, Fully threaded — determines whether fastener primarily resists axial tension, shear forces, or combined loading. Supports smart screw length selection.

1. AWC NDS 2018 — standard design procedure defined by the American Wood Council for wood connections, evaluating screw resistance using NDS dowel-type fastener provisions.
2. AWC NDS 2018 (Supplier ICC) — connection design using manufacturer-verified fastener properties certified through ICC-ES evaluation reports.

Design Philosophy: LRFD (Load and Resistance Factor Design — applies load and resistance factors for ultimate limit states) or ASD (Allowable Stress Design — evaluates capacity using allowable stresses and service load combinations).

Manual Arrangement: number of screws, row configuration, edge distances, end distances.

Minimum Distance and Spacing Rules: auto-applies per AWC NDS — spacing along rows, spacing between rows, edge distances, end distances, fastener position relative to member surface.

• Brittle Failure: row tear-out capacity, net tension capacity, group tear-out capacity.
• Geometry Check: spacing/edge/end distances per design standard.
• Shear Capacity: based on timber properties and fastener resistance models.
• Axial Capacity: based on withdrawal resistance and fastener properties.
• Combined Actions: verifies combined axial and shear loading condition.