Which design standard does this tool implement?

This calculator implements the AWC National Design Specification (NDS) European Yield Model (EYM) for dowel-type fasteners (bolts), using the 2018/2024 editions for formulas and adjustment factors.

What connection configurations are supported?

The current version supports wood-to-steel single-shear connections where the steel side plate is sufficiently thick. Wood-to-wood single-shear and double-shear configurations are planned.

What are typical values for Fyb?

For ASTM A307 bolts, a common bending yield strength used in NDS design is around 45,000 psi. Always confirm with your bolt specification and the NDS Supplement.

How are angles to grain handled?

Dowel bearing strength is adjusted for the load angle to grain using the Hankinson-type relationship between parallel and perpendicular bearing strengths.

Does the tool check spacing and edge distances?

Yes. It flags warnings if input geometry appears to be below typical NDS minimum prescriptive limits for bolts (e.g., end distance, edge distance, and spacing in line and row). Always verify with the latest NDS tables for your case.

Are the results ASD or LRFD?

Results are presented as adjusted allowable design values (ASD) using the selected adjustment factors. If you design in LRFD, apply the appropriate resistance factors per NDS.

Can I use these results for final engineering?

No. This tool is for preliminary design and education. Always have a licensed professional engineer check and approve final designs.

AWC NDS Wood Connection Calculator (Bolts)

Data Source and Methodology

Authoritative Source: American Wood Council (AWC), National Design Specification (NDS) for Wood Construction, 2018 and 2024 Editions. See: AWC Connection Calculator and the NDS Chapter 12 (Dowel-Type Fasteners).

All calculations are strictly based on the European Yield Model (EYM) and dowel bearing strength equations prescribed by the AWC NDS. All adjustment factors follow NDS conventions where applicable. All computations performed by this tool are for ASD and are intended for preliminary design and educational use.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Dowel bearing strengths for bolts (wood member):

Fe parallel to grain: \( F_{e0} = 16600 \, G^{1.84} \) (psi)

Fe perpendicular to grain: \( F_{e90} = 6230 \, G^{1.45} \) (psi)

Angle to grain adjustment (Hankinson-type):

\[ F_{e\theta} = \frac{F_{e0}\,F_{e90}}{F_{e0}\,\sin^2\theta + F_{e90}\,\cos^2\theta} \]

Wood-to-steel single-shear yield modes (per-bolt, ASD form):

\[ Z_{Im} = F_{e\theta}\, d\, t \qquad Z_{II} = 1.15\, d\, t\, \sqrt{F_{yb}\, F_{e\theta}} \qquad Z_{III} = 2.30\, d\, t\, \sqrt{F_{yb}\, F_{e\theta}} \]

Controlling per-bolt capacity: \( Z = \min\left(Z_{Im}, Z_{II}, Z_{III}\right) \)

Adjusted per-bolt capacity: \( Z' = Z \times C_D \times C_M \times C_t \)

Total adjusted capacity for n bolts with group factor \(C_g\): \( Z_{\text{total}} = Z' \times n \times C_g \)

Glossary of Variables

G: Specific gravity of wood species (dimension lumber basis).
θ: Angle between load direction and wood grain (degrees).
d: Bolt diameter (in).
t: Wood member thickness bearing the bolt (in).
Fyb: Fastener bending yield strength (psi).
Fe0, Fe90, Feθ: Dowel bearing strength parallel, perpendicular, and at angle θ (psi).
ZIm, ZII, ZIII: Nominal yield-mode capacities per bolt (lb).
Z: Controlling nominal per-bolt capacity (lb).
CD, CM, Ct: NDS adjustment factors for load duration, moisture, and temperature (—).
Cg: Group action factor for multiple fasteners in a row (—).
Z′: Adjusted per-bolt capacity (lb); Ztotal: total adjusted capacity (lb).

How It Works: A Step-by-Step Example

Example: G = 0.50, θ = 0°, d = 0.5 in, t = 1.5 in, Fyb = 45,000 psi, CD = 1.0, CM = 1.0, Ct = 1.0, Cg = 1.0, n = 2. 1) Fe0 = 16600 × 0.5^1.84 ≈ 5668 psi; Fe90 = 6230 × 0.5^1.45 ≈ 2297 psi. At θ = 0°, Feθ ≈ Fe0 ≈ 5668 psi. 2) ZIm = 5668 × 0.5 × 1.5 ≈ 4251 lb. ZII = 1.15 × 0.5 × 1.5 × √(45000 × 5668) ≈ 1.725 × √(255,060,000) ≈ 1.725 × 15,969 ≈ 27,548 lb. ZIII = 2.30 × 0.5 × 1.5 × √(45000 × 5668) ≈ 3.45 × 15,969 ≈ 55,096 lb. 3) Controlling Z = min(4251, 27548, 55096) = 4251 lb (Mode Im). 4) Adjusted per-bolt Z′ = 4251 × 1.0 × 1.0 × 1.0 = 4251 lb. 5) Total = 4251 × 2 × 1.0 = 8502 lb.

Frequently Asked Questions (FAQ)

Does this tool cover wood-to-wood connections?

The current release focuses on wood-to-steel single-shear. Wood-to-wood single-shear and double-shear configurations will be added next, following the same NDS framework.

Are spacing and edge distance requirements enforced?

The tool flags potential issues against typical NDS minimums. You must still verify exact geometry requirements (species, orientation, service class) with the current NDS tables.

How do I choose G (specific gravity)?

Use the NDS listed G for your species and product (e.g., Southern Pine, SPF). Do not use oven-dry values unless NDS specifies them.

What if the steel side plate is thin or slotted?

This version assumes a sufficiently thick steel plate. For thin plates, slotted holes, or oversize holes, consult NDS provisions and manufacturer data; capacities will differ.

Can I apply LRFD?

The results are ASD adjusted values. For LRFD, convert per NDS procedures and apply the appropriate resistance factors.

How precise are the angle adjustments?

The tool uses a Hankinson-type formula between parallel and perpendicular dowel bearing strengths, consistent with NDS. For critical designs, consider bounding cases (0° and 90°) as checks.

Is this a replacement for the AWC Connection Calculator?

No. It is a complementary educational tool. Always consult the latest NDS and use vetted software or hand-checks for final design.

Tool developed by Ugo Candido. Content verified by the CalcDomain Engineering Editorial Team. Last reviewed for accuracy on: September 14, 2025.