Glulam and SCL beam

A glued laminated timber, LVL or PSL beam in bending about the strong axis, shear and bearing, to NDS 2024 Chapters 2, 3, 5 and 8 with ASCE 7-22 combinations, in ASD or LRFD. Supports, loads, combinations, shear, bearing and deflection work as in the sawn lumber beam.

Inputs of the glulam beam #

• Member use: a label for the report; the Wizard cards prefill each use. Floor overhang and roof overhang: a support at 3/4 of the length, the bottom edge with its own unbraced length (the overhang's length). Header: a simple span, no repetitive member factor; the jack, king and trimmer studs are in the stud wall. Ridge beam: a simple span with the rafter loads per foot, an uplift row (negative W), the bottom edge free over the span, the shear reduction off (rafters hung from the side do not load the opposite face, NDS 3.4.3.1). Hip and valley: a simple span of the plan length with a triangular load from 0 at the low end to the peak; the peak for jack rafters of equal slope on both sides of a 45 degree plan line is w = q Lh / 2, q the load per horizontal square foot and Lh the plan length of the hip. That triangle is the usual idealization, not a code rule: it is your judgment, as is whether the top end is really supported (a hip carried only by other hips and a ridge board is not). The axial force of the sloped member and deflection normal to the slope are not included. Every card starts from typical loads: replace them.
• Partial loading: on by default. On a member with more than one span or an overhang, L, Lr and S also act on part of the spans (ASCE 7-22 4.3.3 and 7.5; an overhang counts as a span, S keeps half its value on the other spans, the dead load stays everywhere). Up to three spans take every subset; more take alternate spans, adjacent pairs, single spans and all but an end span. The combination names say which: "D + L [live on span 1]". ASCE 7-22 7.5.1 lets you turn snow partial loading off for rafters across the ridge of a gable of slope 1/2 to 7 on 12, by the option.
• Bottom edge under negative moment: sheathing on top does not brace the bottom edge. Choose its own unbraced length where nothing holds it (an overhang, an interior support, wind uplift on an exposed ridge beam).
• Product: glulam (stress classes 16F-1.3E to 30F-2.1E SP and the combinations 24F-V4 and 24F-V8 DF of Supplement Table 5A), or LVL / PSL with the manufacturer's reference values (Fb at 12 in depth, Fv, Fc⊥, E, Emin) and the volume factor exponent n, CV = (12/d)^n.
• Laminating species: sets the exponent x of the glulam volume factor (x = 20 Southern Pine, 10 others). The Southern Pine stress classes require Southern Pine.
• Width b and depth d, the self-weight density, the supports and loads, the bearing length.
• Lateral stability, service conditions, deflection limits and load duration as for the sawn beam. Glulam is in wet service at 16 % moisture content or more; SCL in wet service needs the manufacturer's values.

Auto-design (editor toolbar) varies the width (standard widths) and depth (lamination increments); stress class when unlocked. Objectives: least wood (section area); shallowest, then least wood; lowest cost index. Kept unless you select them: stress class / combination. Every other input is kept; see Auto-design.

Checks performed #

Drawings #

The drawing sheet (PDF / DXF, Drawing sheet button) shows the beam elevation with the supports, the loads by type and the spans, the b × d section with the stress class (glulam laminations drawn schematically at 1 1/2 in, 1 3/8 in for Southern Pine; LVL and PSL as solid sections), and the shear, moment and deflection diagrams of the governing combinations at the elevation's scale. Camber, layup, connections, bearing hardware and brace locations are not part of the calculation; the sheet notes say so.

Limitations #

• The NDS provisions were checked against the NDS 2024 text (steps cite section and page): Eq. 5.3-1 (CV, x = 20 Southern Pine, 10 others, b ≤ 10.75 in), 5.3.6 (CV and CL not cumulative), 5.2.4 (Fbx+ / Fbx−), 5.2.7 (which E for deflection and stability), 5.1.4 (wet service at 16 %), 8.3.6.1 (SCL CV with CL), Tables 2.3.5, 2.3.6, 5.3.1, 8.3.1 and N3. Corrected: Fc⊥ takes no λ in LRFD (Table 5.3.1); for SCL with CV > 1.0, Fb* of the beam stability factor now includes CV (3.3.3.8); RB ≤ 50 is checked.
• The Supplement Table 5A values and the glulam wet service factors were read against the 2024 Supplement on 2026-11-12 (Table 5A p. 80, Table 5A Expanded pp. 81-82, adjustment factors p. 79). Two values were corrected:
  • Ex,min of the 28F and 30F SP classes is 1.09 x 10⁶ psi (it was 1.11).
  • Fby of 24F-V8 DF/DF is 1,550 psi (it was 1,450). The axial E values (Eaxial) are not printed in the 2024 Table 5A and stay to be confirmed against the code text. SCL volume factor exponents and wet service values come from the manufacturer (NDS 8.3.3, 8.3.6).
• Bending about the weak axis (y), curved and tapered members (Cc, CI), and the shear reduction Cvr are not modelled. SCL in wet service is reported as not feasible.
• The volume factor uses the span length, which is conservative for continuous beams.

Verification examples #

Verification status: 33 values compared in 5 examples (2 published, 3 hand calculations from the cited equations): 31 within tolerance, 2 recorded deviations. Thin: only 2 published examples. Code basis: partial. Only some provisions were read in the target edition; the rest rests on older editions, examples or summaries.

NDS 2024 has no worked glulam or SCL beam example. The module is verified against AWC Structural Wood Design Examples 2015/2018 Example E1.3 (published values as tabulated in the free Tekla Tedds verification example), AWC Technical Report 14 Example 3.1 (free), and hand calculations in closed form of the NDS 2024 equations (backend/tests/test_verify_glulam_beam.py). The published snow loads are ASCE 7-16 (ASD D + S); they are entered as S / 0.7 because ASCE 7-22 snow is strength level (D + 0.7S).