CLT panel

A cross-laminated timber floor or roof panel spanning one way between two supports, to NDS 2024 Chapter 10 and ANSI/APA PRG 320-19 with ASCE 7-22 combinations, in ASD or LRFD. The design is per foot of panel width in the major strength direction.

Inputs of the CLT panel #

• Layup: the PRG 320 basic layups E1 to E4 (machine stress rated laminations) and V1 to V3 (visually graded), 3, 5 or 7 plies, and the lamination thickness (PRG 320 Table A2 uses 1-3/8 in). The effective properties are derived from the lamination grades (below). Values entered takes (FbS)eff, (EI)eff, (GA)eff and Vs from the PRG 320 table or the manufacturer, with the panel thickness for the self-weight.
• Span and loads: the simple span and uniform area loads per load type; the self-weight uses the density.
• Service conditions: temperature; PRG 320 panels are for dry service.
• Deflection limits with creep (Kcr = 2.0 for CLT in dry service, NDS 3.5.2) and the sustained part of the live load; load duration as in the beams.

The effective properties per foot of width (PRG 320 Annex A): (EI)eff = Σ E (b t³/12 + b t z²) over the parallel layers (the cross layers are ignored); (GA)eff = a² / [t1/(2G1b) + Σ ti/(Gi b) + tn/(2Gn b)] with G = E/16 for parallel and E/160 (rolling shear) for cross layers; (FbS)eff = 0.85 Fb (EI)eff / (E h/2); Vs = Fs (2/3) b h.

Auto-design (editor toolbar) varies the number of plies (3, 5, 7); the PRG 320 layup grade when unlocked. Objectives: thinnest panel (least wood); lowest cost index. Kept unless you select them: layup. Every other input is kept; see Auto-design.

Checks performed #

Drawings #

The drawing sheet (PDF / DXF, Drawing sheet button) shows the one-way span of a 1 ft panel strip with the area loads by type (self-weight in D), the panel section across the span with each layer (longitudinal layers hatched, cross layers plain, layer and overall thicknesses dimensioned), and the shear and moment diagrams per unit width of the governing combination. Lamination widths, panel joints, bearing, connections, vibration and fire design are not part of the calculation; the sheet notes say so.

Limitations #

• Checked against the NDS 2024 text: Table 10.3.1 and 10.3.2 to 10.3.12, Eq. 10.4-1 with Ks = 11.5 (Table 10.4.1.1, uniform load, pinned), the lamination thickness 5/8 in to 2 in (10.1.3.1), the panel thickness limit of 20 in (10.1.3.2, now checked), dry service only (10.1.5) and Kcr = 2.0 (3.5.2). Corrected: the rolling shear capacity takes no load duration factor and, in LRFD, KF = 2.00 and φ = 0.75 without λ (Table 10.3.1; the module had used the Fv factors CD, KF 2.88 and λ). In ASD the rolling shear capacity no longer rises with CD (for example 13 % lower under snow); in LRFD it is 2.00/(2.88 λ) of the former value (0.87 for λ = 0.8, 0.69 for λ = 1.0).
• ANSI/APA PRG 320 is not on disk: the lamination grades (PRG 320 Table 1), the Annex A equations and the rolling shear capacity formula stay marked [verify] and are listed in research/DOCUMENTS_NEEDED.md. NDS 2024 10.2 takes the reference values from the manufacturer's approved recommendations or evaluation report. The derived E1 and V1 3-ply properties agree with the Table A2 values as recalled to within 1 %; the 5- and 7-ply bending values are about 1 % below the recalled table values. The 5-ply V1 and V3 Table A2 values published in the WoodWorks examples ((FbS)eff, (EI)eff, (GA)eff, Vs) are reproduced to within 1 % (V1 (GA)eff 1.06 against the quoted 1.1); the V3 major-lamination Fb was corrected from 1,100 to 750 psi with them (the former value overstated the V3 bending capacity by 46 %).
• One-way simple spans with uniform loads only. Continuous spans, two-way action, concentrated loads, openings, bearing at the supports, the minor strength direction, vibration and fire design are not covered. Wet service is reported as not feasible.

Verification examples #

The WoodWorks CLT floor design examples (free slides: Breneman 2023-12, Gesa 2025-03, the 2021-11 webinar), which use PRG 320 Table A2 values, hand calculations in closed form, and PRG 320 Table A2 values as recalled (to be confirmed against the published table) in backend/tests/test_verify_clt_panel.py: