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NDS 2024NDS 2018

Wood Beam (LRFD, NDS 2018)

Beam reactions link to your column and footing calculations by load type. Change a load once and the linked calculations update. All NDS 2018 LRFD checks shown with code references: bending (φMn ≥ Mu), shear (φVn ≥ Vu), bearing, and three deflection limits. Supports simple and continuous spans, multi-ply beams, and flitch plate configurations.

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What it calculates

Design and verify wood beams to NDS 2018 LRFD - bending (φMn ≥ Mu), shear (φVn ≥ Vu), 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, and flitch plate composite configurations.

Code standards

  • NDS 2018 (LRFD)

How it calculates

The Wood Beam (LRFD) calculator checks sawn lumber, glulam, LVL, PSL, LSL and I-joist beams to NDS 2018 Load and Resistance Factor Design. Beams can be single or multi-ply, with optional steel flitch plates. You enter unfactored loads by type, and the calculator builds the factored load combinations.

Six checks

You get six utilization ratios. A beam passes when every ratio is 1.0 or less.

  • Bending: M_u / φM_n
  • Shear: V_u / φV_n
  • Bearing: R_u / φR_n at the most critical support, with minimum bearing lengths for end and interior supports
  • 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)

Deflection uses unfactored loads. Each limit is a span ratio (L/n) capped by an absolute limit you set. Cantilever limits can be doubled.

Factored resistance

Each resistance converts the ASD reference value with the format conversion factor K_F, then applies the resistance factor φ:

  • Bending: φb = 0.85, K_F = 2.54
  • Shear: φv = 0.75, K_F = 2.88
  • Bearing: φc = 0.90, K_F = 1.67 (2.88 for I-joists)

Bending and shear also take the time effect factor λ. Bearing does not.

Time effect factor

λ is set per load combination:

  • 0.6 for dead load alone
  • 0.8 for occupancy live load by default, adjustable by live load type
  • 0.8 for snow, roof live and rain
  • 1.0 for wind and seismic

The governing bending combination is the one with the highest M_u / λ. A smaller moment can govern if it comes with a longer-duration load.

Adjusted bending stress

F'b combines φb, K_F and λ with the factors for the product you pick:

  • Sawn lumber: F'b = φb × K_F × λ × Fb × CM × Ct × CL × CF × Cfu × Ci × Cr
  • Glulam, strong axis: F'b = φb × K_F × λ × Fb × CM × Ct × Cfu × the lesser of CL and CV
  • LVL, PSL and LSL: with beam stability (CL) and volume (CV) factors
  • I-joists: the manufacturer's moment capacity

Moment capacity is φM_n = F'b × S, where S covers all plies. F'b already includes φb.

Beam stability

CL comes from the critical buckling moment of each unbraced segment, using the AWC TR14 method. 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, bearing and flitch plates

  • Shear demand is taken at the highest point along the span, not at distance d, which is conservative.
  • Bearing under point loads is not checked.
  • Flitch beams use the transformed timber and steel section for bending. Shear and bearing are assigned to the timber.
  • Multi-ply beams bending about the weak axis act non-compositely.

Related calculators

Wood Beam (LRFD, NDS 2024)→Wood Column (LRFD, NDS 2018)→Wood Beam (ASD, NDS 2018)→Wood Column (ASD, NDS 2018)→

Support articles

Design a Wood Beam (LRFD) 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've also gotten used to linking beams within a project, which is handy for changing load scenarios and having that flow through other members.

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 code standard does this calculator use?
Load and Resistance Factor Design (LRFD) per NDS 2018. Factored demands (Mu, Vu, Ru) are compared with factored resistances. Reference values are converted with the format conversion factor K_F. The resistance factor φ is 0.85 for bending, 0.75 for shear and 0.90 for bearing. Bending and shear also take the time effect factor λ. The adjustment factors for the product you choose are applied too: CM, Ct, CF, Cfu, Ci, Cr, CL and CV.
What are the key inputs?
You choose the span configuration (simple, continuous, cantilever or inclined) and the wood species and grade. Sections come from the built-in library of sawn lumber, glulam, LVL and I-joists, or a custom size. You enter loads unfactored by type: dead, live, roof live, snow and wind. The calculator builds the factored combinations. You also set support conditions and lateral bracing. Reference design values load automatically for the species and grade you pick.
What does the calculator check and what does it output?
The calculator checks factored bending (φMn ≥ Mu), factored shear (φVn ≥ Vu) and bearing at the most critical support. Deflection has three checks under unfactored loads: short-term, long-term with creep, and dead plus live or snow. Each uses a span ratio, capped by an absolute limit you set. Results show as utilization ratios with pass or fail.
Can it handle flitch beams or multi-ply configurations?
Yes. The calculator supports flitch plate beams (steel plates sandwiched between wood members), checked for bending on the combined section. Multi-ply beams work in strong or weak axis bending. In weak axis bending the plies act non-compositely. For flitch beams, shear and bearing are conservatively assigned 100% to the wood, and the flitch plates do not affect the CL stability factor.
When should I use LRFD instead of ASD for wood beam design?
Use LRFD when your firm or project designs other materials in LRFD and you want wood to match, or when wind or seismic combinations govern. ASD is more common for routine residential and light commercial gravity framing. Both methods are available on Calcs.com for NDS 2018 and NDS 2024.
Does this calculator support load linking with connected 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. 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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