24F-V8 (DF/DF) - Design Values
24F-V8 (DF/DF) is a glued-laminated timber grade with reference design values to NDS 2018 Supplement Table 5A. Its reference bending value Fb is 2,400 psi, compression parallel Fc is 1,650 psi, and modulus of elasticity E is 1,800,000 psi (NDS). Values are shown before adjustment factors; apply the relevant NDS C-factors or EC5 k_mod and γ_M for your load case.
| Fb | Bending | 2,400 psi |
| Ft | Tension parallel | 1,100 psi |
| Fv | Shear parallel | 265 psi |
| Fc⊥ | Compression perpendicular | 650 psi |
| Fc | Compression parallel | 1,650 psi |
| E | Modulus of elasticity | 1,800,000 psi |
| Emin | Modulus for stability | 950,000 psi |
Balanced layup (Fbx+ = Fbx- = 2400 psi) - use for cantilevers and continuous spans.
Source: NDS 2018 Supplement Table 5A. Reference values are shown before adjustment factors (NDS C-factors / EC5 k_mod, γ_M) - apply these per your load case in design.
Understanding these values
For a beam in 24F-V8 (DF/DF), bending at Fb 2,400 psi normally sets the size, but the check that actually governs depends on the span. Short heavily loaded members are often limited by shear at Fv 265 psi, and bearing at a support is limited by compression perpendicular to grain at Fc perp 650 psi, which is the lowest of the strength values and the one most often overlooked. Used as a post or stud, the governing value is compression parallel at Fc 1,650 psi.
Stiffness for 24F-V8 (DF/DF) is E 1,800,000 psi, with the reduced modulus Emin 950,000 psi used for stability calculations such as the beam stability factor CL and the column stability factor CP. On typical floor spans, deflection rather than strength decides the section, so compare E before Fb when the member is a joist.
Within the glued-laminated timber entries in this catalogue, 24F-V8 (DF/DF) ranks 2 of 4 on bending at 2,400 psi; the strongest listed is 24F-V4 (DF/DF) at 2,400 psi. Grade choice is usually a trade of cost against section depth, so it is worth checking whether a lower grade in a deeper section is cheaper than a higher grade at the depth you started with.