Wood design values

The reference design values of every species and grade in the NDS 2024 Supplement, with every adjustment factor of NDS 2024 and the condition that sets it. The adjusted values are shown in ASD and LRFD side by side, with the specific gravity G for fastener design. Use it to look up a grade, to see what a service condition does to it, or to check actual stresses against the adjusted values.

Inputs of the explorer #

• Supplement table:
  • Table 4A: visually graded dimension lumber, all species but Southern Pine (35 species groups, pp. 33-38).
  • Table 4B: Southern Pine and Mixed Southern Pine, with the dense and non-dense grades, by width (pp. 40-41).
  • Table 4C: MSR and MEL lumber (pp. 43-44). The species group sets G, Fv and Fc⊥ by footnote 2 (p. 45).
  • Table 4D: timbers, beams and stringers or posts and timbers by size (pp. 47-52).
  • Table 4E: decking (pp. 54-56).
  • Table 4F: non-North American dimension lumber (pp. 58-60).
  • Glulam: the Table 5A stress classes (p. 80), the Table 5A Expanded combinations (pp. 81-82) and the Table 5B axial combinations (p. 84).
  • Values entered: SCL from its evaluation report, Table 4G multi-species lumber, or any other product.
• Species, grade and size: the lists hold every species and every grade printed in the table. A grade the species does not have is reported, with the grades it has. Where two grading agencies print different grade lists for one species (Table 4D Douglas Fir-Larch and Sitka Spruce), the species appears once for each agency. The nominal size gives the dressed size (Supplement Table 1A) and, for timbers, the size classification (NDS 4.1.3). Glulam and entered values take the actual width and depth.
• Service conditions:
  • Load duration CD (ASD, NDS Table 2.3.2) and time effect factor λ (LRFD, Table N3).
  • Wet service: moisture content over 19 % for sawn lumber, 16 % or more for glulam.
  • Temperature, sustained exposure (Table 2.3.3).
  • Incising (Table 4.3.8), repetitive member use (4.3.9), and edgewise or flatwise bending.
• Stability and bearing:
  • The unbraced length of the compression edge and the load case of Table 3.3.3 for CL.
  • For glulam, the length between points of zero moment for CV.
  • The column effective lengths about each axis for CP.
  • The sheathed 2x4 truss chord option for CT.
  • The bearing length and whether it is at the member end, for Cb.
• Actual stresses (optional): fb, ft, fv, fc⊥ and fc. Each is compared with the adjusted value of the chosen method; 0 means not checked.

There is nothing to size, so the type has no auto-design. It is a reference calculation: its status reads "Calculated".

Checks performed #

Every value lists its reference value and table page, each factor with its condition, and the ASD and LRFD results. The drawing is the member section with its size, species, grade and G.

Limitations #

• Not built in:
  • Table 4G, multi-species and country grademarked lumber. Its rotated pages print the species groups as running text, which could not be attributed to their rows reliably. Enter those values instead.
  • Tables 5C and 5D (hardwood glulam), and Tables 6A and 6B (round timbers).
  • SCL. Enter it from the evaluation report; its volume factor comes from the report.
• Glulam factors not computed: the curvature factor Cc, the stress interaction factor CI and the shear reduction factor Cvr. The Table 5A footnote 4 and 5 shear reductions are not applied either.
• Our readings:
  • Table 4D gives flat use factors for Select Structural, No. 1 and No. 2 only, so the dense grades take the factor of their base grade.
  • A Table 4D species with one value set for both size classes ("5 in. x 5 in. and larger") takes the beams-and-stringers flat use factor when its size is a beam size.
  • The glulam flat use factor of a width between two table rows is that of the next smaller tabulated width.
• A note from the reading: Table 5A prints Ex,min = 1.09 x 10⁶ psi for the 28F-2.1E and 30F-2.1E SP stress classes. Table 5A Expanded prints 1.11 x 10⁶ psi for the same classes. The stress classes here use 1.09, the lower value.
• Effect on other wood types: reading the full tables corrected values that other wood types use (in their own commits):
  • Table 4B Southern Pine No. 2, 5-6 in. wide, is Ft = 600 psi. It was 575 psi.
  • The 28F and 30F glulam stress classes now use Ex,min = 1.09 x 10⁶ psi.
  • 24F-V8 DF/DF glulam is Fby = 1,550 psi. It was 1,450 psi.

Verification examples #

Verification status: 43 values compared in 15 examples (6 published, 9 hand calculations from the cited equations): 43 within tolerance, 0 recorded deviations. Code basis: not yet recorded for this module.

The published examples are AWC Structural Wood Design Examples E1.4 and E1.3, as tabulated in the free Trimble Tekla Tedds verification examples:

• E1.4: 4x4 and 6x6 Southern Pine No. 2 posts, 10 ft long: Fc*, CP and F'c.
• E1.3: a 5 x 22 24F-E1 SP/SP glulam: RB, Fbx*, CV and F'bx. The example uses NDS 2018 Ex,min for CL, while NDS 2024 uses Ey,min (5.2.7). CV governs here, so F'bx is the same either way.

Table values (Tables 4B, 4C with footnote 2, 5A Expanded) are compared as published. The adjustment chains (wet, incised, repetitive, CL, Utility size factors, MSR flat use, timber CF, decking, glulam Cfu, Cb and CT) are hand calculations from the cited factors. No published worked example covers those combinations on disk.