Wood Column (ASD, NDS 2018)

The 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](/docs/calculators/us) for the current edition. ## Method & scope | Property | Detail | | ---------------- | --------------------------------------------------------------------------------------------------------------------------------------- | | Design standards | NDS 2018 (ASD) | | Regions | United States | | Presets | Generic Concentrically-Loaded Column, Interior Isolated Column, Exposed Outdoor Isolated Column, Interior Stud Wall, Exterior Stud Wall | #### 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 ≤ 1.0 ##### Bending 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 ≤ 1.0 ##### Combined 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 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. 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](/docs/running-calculations/checking-results/checks-references-conditions-assumptions). Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export). ## Common questions 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. 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. 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. 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. 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 Complete list of Calcs.com design calculators available for United States projects (AISC, ACI, NDS, ASCE 7, IBC, and related standards). Design wood beams to NDS 2018 (ASD): bending, shear, bearing and deflection. An earlier code edition, kept for existing projects. Select Simpson Strong-Tie connectors from the 2021-2023 catalog against NDS 2018 (ASD) allowable loads. An earlier edition, kept for existing projects. Design wood truss and frame members to NDS 2018 (ASD) from analysis forces. An earlier code edition, kept for existing projects. Design wood collar ties and rafter ties to NDS 2018 (ASD). An earlier code edition, kept for existing projects. Design wood columns and studs to NDS 2024 (ASD), with load linking from beams and a database of US wood sections. Wood Column to NDS 2018 - Validation Examples