Authoritative Data Source and Methodology
Primary reference: American Wood Council (AWC), National Design Specification (NDS) for Wood Construction, latest edition (e.g., NDS 2024) and applicable Supplements. See the official AWC resources and the updated Connection Calculator:
- AWC Connection Calculator (official tool and methodology)
- AWC Publications (NDS, Supplements, and Design Aids)
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
This tool applies the NDS adjustment factor framework to user‑supplied reference values (from NDS tables or EYM). A smooth‑shank withdrawal estimator is provided strictly for educational screening and must be verified against the current NDS.
The Formula Explained
For both lateral and withdrawal design values, the adjusted per‑nail value is computed as:
R' = R_{ref} \times C_D \times C_M \times C_t \times C_{eg} \times C_{misc}
For smooth‑shank withdrawal reference value (educational estimator):
W_{ref} = 1380 \cdot G^2 \cdot D \cdot L_p \quad [\text{lb}]
Unit conversions:
1 \, \text{kN} = 224.809 \, \text{lb} \quad ; \quad 1 \, \text{lb} = 0.00444822 \, \text{kN}
1 \, \text{in} = 25.4 \, \text{mm} \quad ; \quad 1 \, \text{mm} = 0.0393701 \, \text{in}
Glossary of Variables
R_ref: Reference per‑nail design value (Z for lateral or W for withdrawal) from NDS tables or EYM, before adjustments.
R': Adjusted per‑nail design value after applying NDS factors.
C_D: Load Duration factor (NDS); reflects duration of applied load.
C_M: Wet Service factor; accounts for moisture conditions.
C_t: Temperature factor; accounts for service temperature.
C_eg: End‑grain factor; reduction for end‑grain installations as applicable.
C_misc: Product of any other applicable factors (e.g., toe‑nail reductions, geometry).
G: Specific gravity of wood (at 12% moisture content) from NDS species tables.
D: Nail diameter.
L_p: Penetration length into the main member.
Worked Example
How It Works: A Step‑by‑Step Example
Goal: Determine nails required for a withdrawal condition resisting 2.4 kN (≈540 lb) using smooth‑shank nails into SPF with G = 0.42, D = 0.131 in, penetration L_p = 1.5 in. Assume dry service and 10‑minute duration (wind).
- Estimate W_ref using the smooth‑shank formula: W_{ref} = 1380 \cdot 0.42^2 \cdot 0.131 \cdot 1.5 ≈ 47.0 \, \text{lb}.
- Select factors: C_D = 1.6, C_M = 1.0, C_t = 1.0, C_{eg} = 1.0 (not end‑grain), C_{misc} = 1.0.
- Adjusted per‑nail value: R' = 47.0 \times 1.6 \times 1.0 \times 1.0 \times 1.0 \times 1.0 = 75.2 \, \text{lb}.
- Required nails: n = \lceil 540 / 75.2 \rceil = \lceil 7.18 \rceil = 8 \, \text{nails}.
- Provided capacity: 8 × 75.2 = 601.6 lb; Utilization = 540 / 601.6 ≈ 0.90 (90%).
Always verify the reference value with the current AWC NDS and ensure spacing, end/edge distances, and member thickness meet NDS requirements.
Frequently Asked Questions (FAQ)
Does this tool compute European Yield Model (EYM) lateral values?
This tool applies NDS adjustment factors to a user‑supplied reference value (from NDS tables or the AWC Connection Calculator), which may itself be derived from EYM. This ensures accuracy with the current standard while keeping the workflow fast and transparent.
Can I design ring‑shank or screw‑shank nails?
Yes. Enter the appropriate reference value from NDS tables for your shank type. The built‑in estimator is for smooth‑shank withdrawal only and should not be used for other shank types.
How are spacing and edge distances handled?
This calculator focuses on per‑nail design values and counts. You must still check spacing, end/edge distances, and member thickness per the current NDS to ensure a code‑compliant connection.
What load type should I use for C_D?
Select the category consistent with your governing load case (e.g., wind often uses 10‑minute duration). When multiple load combinations govern, use the most restrictive factor or check each combination as needed.
Are results LRFD or ASD?
Results are generic adjusted design values. If your workflow requires LRFD or ASD specifically, ensure that the reference value and factors correspond to your chosen design format and use consistent load combinations.
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