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NDS 2024NDS 2018

Wood Beam (ASD, NDS 2018)

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.

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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.

Code standards

  • NDS 2018 (ASD)

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.

Related calculators

Wood Column (ASD, NDS 2018)→Wood Connectors (ASD, 2021-2023)→Wood Member (Design Only - ASD)→Wood Roof Tie (ASD)→

Support articles

Design a Wood Beam (ASD) to NDS 2018→
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What engineers say

Calcs.com simplified my beam analysis. It made structural checks easy and impressively fast. I first heard about Calcs.com while looking for alternatives to StruCalc, checked out a few options, and went with Calcs.com for simple residential...

Aaron D. Obermiller, P.E.

Engineer, REO Engineering

The wood and steel beam calculators are delightful. I especially like selecting the wood species for my beam and Calcs.com automatically loading all of the relevant material properties so I don't need to look them up in the NDS.

John Cagle

Project Engineer, CHM Engineering

Frequently asked questions

What design method and standard does this calculator follow?
This calculator uses Allowable Stress Design (ASD) per the 2018 National Design Specification for Wood Construction (NDS 2018). Reference design values are adjusted using all required NDS factors: load duration (CD), wet service (CM), temperature (Ct), size (CF), flat use (Cfu), incising (Ci), repetitive member (Cr), beam stability (CL), and volume factor (CV).
What inputs does the Wood Beam ASD calculator require?
Key inputs include beam plan length, support locations and types with bearing lengths, section type (standard from the section library or fully custom), number of plies, and applied loads (distributed, line, point, and moment). You also specify service conditions - wet or dry, temperature range, and incising treatment - and lateral-torsional bracing configuration (top face, bottom face, both, or no continuous bracing).
What checks and outputs does the calculator provide?
The calculator returns six utilization checks: bending moment (M/M'), shear (V/V'), and bearing (R/R') - each expressed as a ratio where 1.0 or less is acceptable - plus three deflection checks: short-term (ST), long-term (LT), and a simplified DL+(LL or SL) envelope. Adjusted allowable capacities account for all applicable NDS adjustment factors.
Does this calculator support multi-ply beams, flitch plates, or inclined members?
Yes. The calculator supports multi-ply beams, flitch plate composite beams (steel plates sandwiched between timber plies), and inclined beams in Simple Slope or Hip/Corner Slope configurations. For flitch beams, composite bending stiffness is derived automatically from the combined timber and steel section properties.
How should I set deflection limits for my beam?
You set a span ratio for each of three checks. Short-term deflection defaults to L/360. Long-term deflection with creep and dead plus live or snow both default to L/240. A fourth input sets an absolute limit in inches that caps all three. Cantilever limits can be doubled. Adjust them for your occupancy and finishes, and the calculator flags any check that exceeds its limit.
Does this calculator support load linking with column and footing calculations?
Yes. Support reactions link to column and footing calculations in the same Calcs.com project, by load type. That includes US spread, pole and combined footings. Joist layouts with regular spacing can also send line loads to a wall footing. For columns, you choose whether reactions load the column axially or laterally. When the beam's span, section or loads change, every linked calculation updates, with no re-entry of reactions.

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