Glulam Beam Design Calculator (AWC/NDS)

Preliminary glulam beam design for simply supported spans. Check bending, shear, deflection and bearing using AWC NDS-style equations.

Disclaimer: For preliminary sizing and educational use only. Not a substitute for a full AWC NDS design or a licensed structural engineer.

Glulam Beam Design Inputs

Values approximate common APA/Boise glulam grades for preliminary checks.

Includes self-weight of glulam plus finishes (line load along beam).

Load combination (simplified)

Strength checks use 1.0D + 1.0L equivalent (service-level NDS style). Deflection uses service loads (D + L).

Design Check Results

Enter your data and click Calculate to see design checks.

How this glulam beam design calculator works

This tool performs quick-span checks for simply supported glued-laminated timber (glulam) beams using classic elastic beam formulas and AWC NDS-style allowable stresses. It is ideal for early sizing and sanity checks before you dive into manufacturer tables or full code design.

The calculator supports:

  • US or metric units
  • Custom or preset glulam sizes
  • Common glulam grades with editable Fb, Fv, and E
  • Uniform dead and live loads, plus an optional point load
  • Bending, shear, deflection, and bearing checks with utilization ratios

Key assumptions and limitations

  • Simply supported beam, major-axis bending only.
  • Loads are static and applied in the beam’s plane (no lateral-torsional buckling check).
  • Service-level allowable stresses (no LRFD or full ASD load combinations).
  • No duration-of-load, temperature, volume, or repetitive-member factors are applied automatically.
  • No checks for notches, holes, or horizontal penetrations in the glulam.

Always have final designs reviewed and stamped by a qualified structural engineer.

Formulas used in the glulam beam design

Section properties

For a rectangular glulam section with width \( b \) and depth \( d \):

Section modulus (about strong axis):
\( S = \dfrac{b d^2}{6} \)

Moment of inertia:
\( I = \dfrac{b d^3}{12} \)

Maximum moment and shear

For a simply supported beam with span \( L \):

  • Uniform load \( w \) (force per unit length):
\( M_{\max,udl} = \dfrac{w L^2}{8} \)
\( V_{\max,udl} = \dfrac{w L}{2} \)
  • Single point load \( P \) at distance \( a \) from the left support:
Reactions:
\( R_A = \dfrac{P (L - a)}{L} \),   \( R_B = \dfrac{P a}{L} \)

Maximum moment occurs under the point load:
\( M_{\max,point} = R_A \cdot a = \dfrac{P a (L - a)}{L} \)
Maximum shear is the larger of \( R_A \) and \( R_B \).

The calculator superimposes uniform and point load effects to obtain total \( M_{\max} \) and \( V_{\max} \).

Bending and shear stresses

Bending stress:
\( f_b = \dfrac{M_{\max}}{S} \)

Shear stress (rectangular section, approximate):
\( f_v = \dfrac{1.5 V_{\max}}{b d} \)

These are compared to the allowable bending and shear stresses \( F_{b,\text{allow}} \) and \( F_{v,\text{allow}} \) you specify.

Deflection

Instantaneous elastic deflection is computed using the modulus of elasticity \( E \) and moment of inertia \( I \).

  • Uniform load \( w \):
\( \Delta_{udl} = \dfrac{5 w L^4}{384 E I} \)
  • Point load \( P \) at midspan (approximation used for simplicity):
\( \Delta_{point} \approx \dfrac{P L^3}{48 E I} \)

The calculator adds contributions from dead and live loads to obtain live-load deflection \( \Delta_L \) and total deflection \( \Delta_{total} \), then compares them to limits such as \( L/360 \) or \( L/240 \).

Bearing at supports

Bearing area at one support:
\( A_b = b \cdot l_b \)

Bearing stress:
\( f_{c,\perp} = \dfrac{R}{A_b} \)

where \( l_b \) is the bearing length and \( R \) is the reaction at the support. This is compared to the allowable compression perpendicular to grain \( F_{c,\perp,\text{allow}} \).

Interpreting the utilization ratios

For each limit state (bending, shear, bearing, deflection) the calculator reports a utilization ratio:

\( \text{Utilization} = \dfrac{\text{demand}}{\text{capacity}} \)
  • < 1.0 → passes (demand is below capacity).
  • ≈ 1.0 → near the limit; consider increasing size or reducing span.
  • > 1.0 → fails; beam is overstressed or too flexible.

The governing condition is the one with the highest utilization ratio. In many glulam beams, deflection or bearing can control even when bending looks fine.

Practical tips for glulam beam design

  • Always use manufacturer tables and AWC NDS for final design.
  • Account for duration-of-load factors (e.g., snow, wind, seismic) when selecting Fb and Fv.
  • Check lateral bracing and stability; deep glulam beams may require bracing to prevent lateral-torsional buckling.
  • Penetrations, notches, and holes in glulam beams require special detailing and checks.
  • Consider long-term creep deflection for heavily loaded or long-span beams.

FAQ about the glulam beam design calculator

Is this calculator code-compliant?

The formulas are consistent with basic AWC NDS principles, but the tool does not implement the full code, load combinations, or all adjustment factors. Treat it as a quick check or teaching aid, not as a sealed design.

Can I use this for continuous or cantilever beams?

No. The current version assumes a single-span, simply supported beam. For multi-span or cantilever conditions, you would need different moment and deflection formulas.

How should I choose Fb, Fv, and E?

Start from manufacturer literature or APA glulam design tables for your specific product and grade. Then apply any required adjustment factors (duration of load, temperature, volume, etc.) to obtain design values. Enter those adjusted values into the calculator.

Does the calculator include self-weight of the glulam?

Self-weight is not added automatically. You can approximate it by including it in the dead load wD. For typical glulam densities around 35–40 pcf, a 5 in × 18 in beam weighs roughly 25–30 plf.