Wood Beam Design Calculator (AWC NDS Bending & Shear)
Check a simply supported wood beam for bending, shear, and deflection using AWC NDS-style design values. Supports dimensional lumber and glulam with uniform or point loads.
1. Beam & Material
2. Geometry & Loads
3. Results & Checks
Status: Waiting for input
Enter beam, span, and loads, then click “Calculate”.
Section properties
Demand vs capacity
Key internal forces
Assumes simply supported beam with either uniform load or a single midspan point load.
How this wood beam design calculator works
This tool performs quick, NDS-style checks for a simply supported wood beam. It is intended for preliminary design and education, not for final code-stamped drawings.
1. Load conversion and internal forces
For a uniform area load in psf, the line load on one beam is:
\( w_\text{plf} = (w_D + w_L) \times s \)
where:
- \( w_D, w_L \) = dead and live loads (psf)
- \( s \) = beam spacing (ft)
The line load in lb/ft is then converted to lb/in for stress and deflection.
For a simply supported beam with uniform load \( w \) (lb/in) and span \( L \) (in):
Maximum moment: \( M_\text{max} = \dfrac{w L^2}{8} \)
Maximum shear: \( V_\text{max} = \dfrac{w L}{2} \)
Maximum deflection at midspan: \( \Delta_\text{max} = \dfrac{5 w L^4}{384 E I} \)
For a single point load \( P \) (lb) at midspan:
Maximum moment: \( M_\text{max} = \dfrac{P L}{4} \)
Maximum shear: \( V_\text{max} = \dfrac{P}{2} \)
Maximum deflection: \( \Delta_\text{max} = \dfrac{P L^3}{48 E I} \)
2. Bending and shear stress checks
Bending stress at the extreme fiber is:
\( f_b = \dfrac{M_\text{max}}{S} \)
Check: \( f_b \le F'_b \)
Shear stress for rectangular sections is approximated as:
\( f_v = \dfrac{1.5 V_\text{max}}{b d} \)
Check: \( f_v \le F'_v \)
The calculator uses your input design values \( F_b \) and \( F_v \) after any NDS adjustment factors (load duration \( C_d \), repetitive member \( C_r \), size factor \( C_F \), etc.) you choose to apply.
3. Deflection limits
Deflection is checked against common serviceability limits such as L/240, L/360, or L/480. The tool reports both:
- Live-load deflection (using live load only)
- Total deflection (dead + live)
Checks are of the form:
\( \Delta_\text{live} \le \dfrac{L}{\text{limit}_\text{live}} \)
\( \Delta_\text{total} \le \dfrac{L}{\text{limit}_\text{total}} \)
Example: Floor joist design
Suppose you want to check a 2x10 SPF No.2 floor joist:
- Span L = 12 ft
- Spacing s = 16 in (1.33 ft)
- Dead load = 10 psf, live load = 40 psf
- Deflection limits: L/360 live, L/240 total
Select the SPF 2x10 preset, enter the loads and span, and click Calculate. If bending and shear pass but deflection fails, try a deeper member (e.g., 2x12) or reduce the span/spacing.
Assumptions & limitations
- Simply supported beam with either uniform load or a single midspan point load.
- Prismatic (constant) cross-section along the span.
- Linear elastic behavior; small deflections.
- NDS adjustment factors (Cd, Cr, CF, CM, etc.) are not computed automatically; enter adjusted design values.
- No lateral-torsional buckling or bearing checks are performed.
Always have final designs reviewed by a licensed structural engineer and verify compliance with the current AWC NDS and your local building code.
FAQ
Can I use this for glulam beams?
Yes. Choose the glulam preset or enter the manufacturer’s section properties (b, d, S, I) and design values (Fb, Fv, E). The internal force and deflection formulas are the same.
What units does the calculator use?
All calculations are in US customary units: inches, feet, pounds (lb), kips (k), and psi. Area loads are in psf, line loads in plf, and deflections in inches.
How do I include multiple load cases?
For quick checks, enter the governing combination (e.g., 1.2D + 1.6L) as an equivalent service load. For full LRFD/ASD load combinations, a full structural analysis program is recommended.