Wood Bearing Perpendicular to Grain (NDS 3.10)
The crushing check a framer skips until the beam sinks into the plate.
Example
You enter
- Reaction / bearing force (lb) 800
- Bearing width b (in) 1.5
- Bearing length lb (in) 1.5
- Reference Fc-perp (psi) 625
- Within 3 in of the member end? no
You get
- Cb f 1.25
- Adjusted Fc-perp' 781 psi
- Applied bearing stress 356 psi
- Demand / capacity 0.4551
- Required bearing length (Cb = 1) 0.85 in
Details, formula, and sources
Where a joist or beam lands across the grain, fc_perp = R/(b x lb) must clear Fc_perp x Cb, where the NDS 3.10.4 bearing-area factor Cb = (lb + 0.375)/lb rewards a short interior bearing. An 800 lb joist on 1.5 in of DF-L plate runs at DCR 0.46 and needs only 0.85 in; put a 6,000 lb beam reaction on the same footprint and it fails at 3.4x, demanding 6.4 in or a bearing plate. Fc_perp takes no load-duration factor. A design aid, not the engineer of record's stamped design.
Cb = (lb < 6 in and not within 3 in of the end) ? (lb + 0.375)/lb : 1.0; Fc_perp' = Fc_perp x Cb; fc_perp = R/(b lb); DCR = fc_perp / Fc_perp'; lb_req = R/(b Fc_perp) (Cb = 1, conservative).
The NDS 2018 3.10.2 compression-perpendicular-to-grain bearing check and the 3.10.4 bearing-area factor Cb = (lb + 0.375)/lb for a bearing under 6 in and not within 3 in of the member end, by name.
The NDS is free to view at awc.org (ANSI/AWC NDS); the 3.10 bearing provisions and the Cb factor are in the published standard.
Estimate. AHJ and licensed professional govern.
Field names used by the API: r_lb, b_in, lb_in, fcperp_psi, near_end, cb_f, fcperp_adj_psi, fc_perp_psi, dcr, lb_req_in
- Bearing check fc_perp = R/(b lb) at the support against the adjusted Fc_perp'NDS 2018 3.10.2
- Bearing-area factor Cb = (lb + 0.375)/lb, only for lb < 6 in and bearings not within 3 in of the member endNDS 2018 3.10.4
- No CD Fc_perp is a deformation-based value and takes no load-duration factorNDS 2018 Table 4.3.1