Wood Column (ASD, NDS 2018)
Run the calcThe Calcs.com timber column ASD calculator to NDS 2018 enables the fast and accurate design of wood columns and studs to American standards. With support for dynamic load linking between beams and columns, easily design accurate and quality engineered columns, and select from our database of thousands of US wood sections.
This calculator uses an earlier code edition (NDS 2018 (ASD)). It stays available for existing projects. For new designs, check the Calculator Library for the current edition.
Method & scope
What it calculates
Design method
This calculator uses Allowable Stress Design (ASD) per the AWC National Design Specification for Wood Construction, 2018 edition (NDS 2018). All reference design values (F_c, F_b, F_t, F_v, F_c⊥) are multiplied by applicable adjustment factors to obtain allowable values before each limit state is evaluated. The governing utilization ratio across all checks must not exceed 1.0.Adjustment factors
The key adjustment factors applied by this calculator are:- C_D (load duration factor), amplifies or reduces allowable stress based on the duration of the controlling load combination; short-duration loads (wind, seismic) allow higher stress than sustained dead loads
- C_M (wet service factor), reduces allowable values when in-service moisture content exceeds 19% for sawn lumber or 16% for glulam and SCL
- C_t (temperature factor), reduces values for members subject to sustained elevated temperatures above 100°F
- C_F (size factor), modifies F_b, F_t, and F_c for sawn lumber based on cross-section depth and width
- C_i (incising factor), applied when preservative treatment requires incising, reducing most reference values
- C_r (repetitive member factor), increases F_b by 1.15 when three or more parallel members at 24 in. or less spacing share loads through adequate sheathing
- K_f (built-up column factor), reduces the effective column stability factor for nailed or bolted multi-ply columns relative to an equivalent solid or glulam section
Compression checks
Two independent compression capacity checks are performed, one for each principal axis, to account for different effective lengths and bracing conditions: F’_c,x = F_c × C_D × C_M × C_t × C_F × C_i × C_P,x F’_c,y = F_c × C_D × C_M × C_t × C_F × C_i × C_P,y The column stability factor C_P is computed per NDS Eq. 3.7-1, which is a function of the Euler critical buckling stress F_cE = 0.822 E’_min / (L_e/d)², the adjusted reference compressive stress F*_c (all factors except C_P), and the parameter c (0.8 for sawn lumber, 0.9 for glulam and SCL). A separate C_P is calculated for each axis using the corresponding effective slenderness ratio. Utilization (X-axis): f_c / F’_c,x ≤ 1.0 Utilization (Y-axis): f_c / F’_c,y ≤ 1.0Bending and shear checks
Biaxial bending is evaluated independently on each principal axis: F’_b = F_b × C_D × C_M × C_t × C_F × C_i × C_L × C_r For glulam and SCL members, the volume factor C_V replaces C_L (the lesser of the two governs for strong-axis bending). The beam stability factor C_L accounts for lateral-torsional buckling per NDS Appendix E; for columns with adequate bracing on both axes, C_L = 1.0. Shear is checked on each axis: F’_v = F_v × C_D × C_M × C_t × C_i Utilization (shear): f_v / F’_v ≤ 1.0Combined loading
For members subject to simultaneous axial compression and biaxial bending, the calculator evaluates NDS Eq. 3.9-3 and 3.9-4:How to use it
1
Open the calculator
Open it from Run calc in the About this calculator panel above. To start from a typical setup, choose one of the presets listed there.
2
Enter your inputs
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See Checks, References, Conditions and Assumptions.
3
Review the results and export
Check the utilization of each governing check in the summary, then export a PDF report. See Views and Export.
Common questions
What design method does this calculator use?
What design method does this calculator use?
The calculator uses Allowable Stress Design (ASD) per the AWC National Design Specification for Wood Construction, 2018 edition (NDS 2018). All reference design values are adjusted by factors including C_D (load duration), C_M (wet service), C_t (temperature), C_F (size), C_i (incising), and C_P (column stability) before being compared to applied stresses. The governing check is the combined compression-and-bending interaction equation per NDS Eq. 3.9-3 and 3.9-4.
What are the key inputs?
What are the key inputs?
The primary inputs are the wood species and grade (selected from the Calcs.com US section database), the column height, and the support conditions on each axis (pinned, fixed, roller, lateral brace, or weak/strong axis brace). You also enter axial loads, biaxial moments, and distributed lateral loads. Service condition (dry or wet), temperature, incising treatment, live load type, and number of plies for built-up columns are additional inputs that control which adjustment factors apply.
What checks and outputs does the calculator provide?
What checks and outputs does the calculator provide?
The calculator checks axial compression about both principal axes with independent effective lengths, pure bending and shear on each axis, combined compression-and-bending interaction (NDS Eq. 3.9-3/3.9-4), combined tension-and-bending (NDS Eq. 3.9-1/3.9-2), bearing parallel and perpendicular to grain, and lateral deflections. Each check displays a utilization ratio; the summary result shows the governing limit state and whether the section passes.
Can I design multi-ply (built-up) columns with this calculator?
Can I design multi-ply (built-up) columns with this calculator?
Yes. Enter the number of plies in the built-up column input. The calculator automatically applies the built-up column factor K_f as defined in NDS, which reduces the effective column stability factor C_P relative to a solid or glulam section of the same cross-section. This correctly models the reduced buckling capacity of nailed or bolted multi-ply assemblies such as doubled or tripled studs.
When should I use this calculator instead of the wood beam calculator?
When should I use this calculator instead of the wood beam calculator?
Use this calculator whenever axial compression is a primary or significant load, posts, columns, studs in bearing walls, and members subject to combined bending and compression. The wood beam calculator is optimized for members where bending governs and axial load is absent or negligible. If your member carries both axial and lateral loads simultaneously, use this column calculator to properly evaluate the NDS interaction equations.
Next steps
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Wood Column to NDS 2018 - Validation Examples
Wood Column to NDS 2018 - Validation Examples