Tapered Wood Column Calculator, NDS 2018

What it checks

The module designs a tapered sawn or glulam column subjected to axial compression. It applies the NDS 2018 §3.7.2 representative dimension rule, where the effective dimension d' is calculated from the small and large end depths. This d' value sets the slenderness ratio, and the column stability factor Cp follows from that slenderness rather than from the small end dimension alone. The design method uses factored axial compressive loads, consistent with strength-based design. The sequence of checks begins with calculating the representative dimension and slenderness ratio. It then determines the critical buckling stress and the column stability factor. Finally, the module evaluates the design capacity ratio at the representative section and the bearing stress at the small end.

Inputs

Geometry - Constant width b (in), depth at small end d_min (in), and depth at large end d_max (in).
Length - Unbraced length L (ft) and effective length Le (ft), where Le defaults to L if zero.
Material - Reference compressive strength Fc (psi) and reference stability modulus Emin (psi).
Factors - Load duration CD, wet service factors CM for Fc and Emin, temperature Ct, size CF, and incising Ci.
Section - Section type string indicating "sawn" or "glulam"/"scl" to set the c factor.
Load - Factored axial compressive load P (kips).

What it reports

Representative Dimension - The effective dimension d' (in) calculated per NDS §3.7.2.
Slenderness - The ratio Le/d' and a boolean indicating if it is ≤ 50 per NDS §3.7.1.4.
Stability Factor - The column stability factor Cp derived from the slenderness and c factor.
Adjusted Strength - The adjusted compressive strength Fc' (psi), calculated as Fc* × Cp.
DCR - The demand-to-capacity ratio at the representative section, comparing applied stress to Fc'.
Bearing DCR - The demand-to-capacity ratio at the small-end bearing, comparing bearing stress to adjusted reference strength without Cp.
Stresses - Applied stress at the centroid and bearing stress at the small end (psi).

Code references

The engine cites NDS 2018 §3.7.2 for the representative dimension d' rule and NDS §3.7.1.4 for the slenderness limit of 50. These clauses govern the calculation of the effective dimension and the verification of the slenderness ratio for tapered columns in axial compression.

Limits

The module assumes a constant width b and a linearly varying depth. It does not account for bending moments or shear forces, as it is designed for axial compression only. The size factor CF is noted for sawn lumber, with a value of 1.0 assumed for glulam. Results are engineering aids; the engineer of record is responsible for the design.

This module ships in the desktop app

StructuralClaw for Windows is in active build and not yet downloadable. Join the beta list and we will send one email when it ships.

Join the beta list