What it calculates
Design and verify wood beams to NDS 2018 ASD - bending, shear, bearing, and three deflection limits, each shown with the governing NDS adjustment factors and code reference. Load reactions at each support link to connected column and footing calculations by load type, so a change to the beam updates them. Supports simple and continuous spans, multi-ply beams, flitch plate composite beams, and inclined configurations.
Who uses this calculator
Beam reactions link to your column and footing calculations by load type. Change a load once and the linked calculations update. All six NDS 2018 checks shown with code references: bending, shear, bearing, and three deflection limits. Includes multi-ply and flitch plate beams.
How it calculates
The Wood Beam (ASD) calculator checks sawn lumber, glulam, LVL, PSL, LSL and I-joist beams to NDS 2018 Allowable Stress Design. Beams can be single or multi-ply, with optional steel flitch plates. Each check divides demand by adjusted capacity, and the beam passes when every ratio is 1.0 or less.
Six checks
You get six utilization ratios, each from its governing load combination:
- Bending: M / M'
- Shear: V / V'
- Bearing: R / R' at the most critical support
- Short-term deflection: under L + Lr, S or 0.42W
- Long-term deflection: under kD + L + Lr, where k adds creep to the dead load (0.5 dry, 1.0 wet)
- Dead plus live or snow: D + (L or S), which you can switch off
Each deflection limit is a span ratio (L/n) capped by an absolute limit you set. Cantilever limits can be doubled.
Adjusted bending stress
F'b is the reference value Fb multiplied by the factors that apply to the product you pick:
- Sawn lumber: F'b = Fb × CD × CM × Ct × CL × CF × Cfu × Ci × Cr
- Glulam, strong axis: F'b = Fb × CD × CM × Ct × Cfu × the lesser of CL and CV
- Glulam, weak axis: F'b = Fb × CD × CM × Ct × Cfu
- LVL, PSL and LSL: Fb × CD × CM × Ct × Cr, with beam stability (CL) and volume (CV) factors
- I-joists: the manufacturer's moment capacity, adjusted by CD, CM, Ct, CL and Cr
Moment capacity is M' = F'b × S, where S is the section modulus of all plies. Reference values come from the built-in species and grade database. LVL, PSL, LSL and I-joists use manufacturer data.
Load duration and service conditions
- CD is set per load combination by its shortest-duration load, from 0.9 for dead load alone to 1.6 for wind and seismic.
- CM applies in wet service, above 19% moisture content (16% for glulam).
- Ct reduces capacity above 100°F, in two bands up to 150°F.
- Ci applies to incised dimension lumber.
- Cr adds 15% for repetitive sawn lumber members and 4% for LVL, PSL and LSL.
Beam stability
CL comes from the critical buckling moment of each unbraced segment, using the AWC TR14 method. The moment factor is taken conservatively as 1.72, or 1.0 for cantilevers. You choose continuous bracing on the top face, the bottom face, both or neither. Bracing both faces removes lateral-torsional buckling, so CL = 1.0.
Shear and bearing
Shear capacity is V' = (2/3) × F'v × A. Demand is taken at the highest point along the span, not at distance d from the support, which is conservative.
Bearing is checked at every support from the bearing length you enter. Short bearings get the bearing area factor Cb. Bearing under point loads is not checked.
Flitch plate and multi-ply beams
- Bending uses the transformed timber and steel section.
- Deflection uses the combined stiffness of timber and steel.
- Shear and bearing are assigned to the timber.
- Multi-ply beams bending about the weak axis act non-compositely.
Assumptions
The calculator states its assumptions on every sheet. The ones that most often matter:
- Axial load is negligible. Check this yourself for inclined beams.
- Members are straight, prismatic and not notched.
- Glulam has at least four laminations.
- I-joists are fully braced, with all holes within manufacturer limits.
