Wood Column Calculator, NDS 2018

What it checks

The module designs sawn lumber columns for combined bending and axial compression. It applies the National Design Specification (NDS) 2018 methods, specifically calculating the column stability factor Cp and evaluating the interaction of stresses. The design process adjusts reference design values using factors for load duration, wet service, temperature, incising, size, and stability. The sequence of checks begins with determining the slenderness ratios about both the strong and weak axes. The module then calculates the column stability factor Cp based on the section type and slenderness. Finally, it computes the biaxial interaction value to verify that the combined compressive and bending stresses satisfy the NDS 3.9.3 requirements.

Inputs

Geometry - Lumber size string (e.g., "4x6"), strong-axis slenderness (Le/d), and weak-axis slenderness (Le/b).
Material Factors - Wet service factor (CM), temperature factor (Ct), incising factor (Ci), and section type (sawn, glulam, or SCL).
Size Factors - Size factor for compression (CFc) and size factor for bending (CFb).
Stresses - Actual compressive stress (psi), strong-axis bending stress (psi), and weak-axis bending stress (psi).
Load Duration - Load duration factor (Cd) from NDS Table 2.3.2, set to 1.0 for Strength (LRFD) combinations.

What it reports

Interaction Value - The NDS 3.9.3 biaxial interaction value, compared against the allowable limit of 1.0.
Strong-Axis Slenderness - The Le/d ratio about the strong axis, which controls strong-axis buckling.
Weak-Axis Slenderness - The Le/b ratio about the weak axis, which controls weak-axis buckling.
Compressive Stress - The actual compressive stress (fc) calculated as P / A in psi.
Bending Stresses - The actual strong-axis (fbx) and weak-axis (fby) bending stresses in psi.

Code references

The engine cites NDS 2018 §3.7.1 for the column stability factor Cp and §3.9.2 for combined bending and axial compression. It also references NDS Table 2.3.2 for load duration factors and NDS Table 4.3.1 for the applicability of adjusted reference design values. The calculation of the biaxial interaction value follows NDS 3.9.3.

Limits

The module assumes a conservative value of 1.0 for the lateral stability factor CL in bending adjustments. It does not account for other stability factors beyond those specified in the input fields. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

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