Glulam Volume Factor Cv (NDS 5.3.6)

The glulam-specific penalty that the sawn-lumber CL check never applies. Cv = KL x (21/L)^(1/x) x (12/d)^(1/x) x (5.125/b)^(1/x), capped at 1.0, with L the span (ft), d and b the depth and width (in), x = 10 for softwoods (20 for Southern Pine), because a larger stressed volume is more likely to contain a strength-limiting defect. A 5-1/8 x 18 in glulam over 20 ft gives Cv = 0.965 (a 3.5% cut); a 6-3/4 x 24 in girder over 32 ft gives 0.870 (13%). The allowable bending uses the lesser of Cv and the beam-stability factor CL. A design aid, not a substitute for the engineer of record.

Cv = min( KL x (21/L)^(1/x) x (12/d)^(1/x) x (5.125/b)^(1/x), 1.0 ); allowable bending uses the lesser of Cv and CL.

NDS 2018 (National Design Specification for Wood Construction) §5.3.6, the glulam volume factor Cv, by name; the reference bending value and factors come from the NDS Supplement.

The Cv equation is stated in NDS 5.3.6, published free read-only by AWC at awc.org; the (21/L)^(1/x) arithmetic is public.

Estimate. AHJ and licensed professional govern.

Field names used by the API: span_ft, depth_in, width_in, x, kl, cv

• Volume factor Cv = KL x (21/L)^(1/x) x (12/d)^(1/x) x (5.125/b)^(1/x), capped at 1.0NDS 2018 §5.3.6
• Species exponent x = 10 for all species except Southern Pine, where x = 20NDS 2018 §5.3.6
• Lesser of Cv or CL the allowable bending uses the lesser of Cv and the stability factor CL, not their productNDS 2018 §5.3.6 / §3.3.3