Wood Bending Member Shear (fv and the NDS Tension-Side End-Notch Reduction)
The end shear a wood beam carries, and how much a tension-side notch at the support takes away.
Example
You enter
- Adjusted shear value Fv' (psi) 180
- Breadth b (in) 3.5
- Full depth d (in) 11.25
- Net depth at notch dn (dn = d if un-notched) (in) 9.25
- Applied end shear V (lb, 0 to skip) 2000
You get
- Un-notched allowable Vr 4725 lb
- Depth ratio dn/d 0.822
- Notched allowable Vr' 2626 lb
- Actual stress fv 92.7 psi
- Demand / capacity 0.76
Details, formula, and sources
The un-notched allowable Vr = (2/3) Fv' b d, the notched allowable V' = (2/3) Fv' b dn (dn/d)^2, and the actual stress fv = 3V / (2 b dn) on the net section. A single 2 in notch in a 4x12 cuts the allowable end reaction nearly in half - the reason the NDS penalizes notches on the tension side so hard. A design aid, not a substitute for the engineer of record.
Vr = (2/3) Fv' b d; ratio = dn/d; Vr' = (2/3) Fv' b dn (dn/d)^2; fv = 3V / (2 b dn); dcr = V / Vr'.
NDS 3.4.2 rectangular-section shear stress and the NDS 3.4.3.2 tension-side end-notch reduction, by name; the adjusted shear value comes from the NDS Supplement.
The fv = 3V/(2bd) stress and the notched-member rule are stated in NDS 3.4, published free read-only by AWC at awc.org; the arithmetic is public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: fv_prime_psi, b_in, d_in, dn_in, v_applied_lb, vr_lb, ratio, vr_notch_lb, fv_psi, dcr
- Notch penalty the (dn/d)^2 factor squares the depth ratio, so a tension-side notch cuts the allowable end shear far faster than the depth loss aloneNDS 3.4.3.2
- Fv' user-supplied Fv' is the reference shear value times every applicable factor; the reference and factors come from the NDS SupplementNDS Supplement
- Loads near support loads within a distance d of the support may be neglected in V per NDS 3.4.3.1; the user applies that to the inputNDS 3.4.3.1