Wood Tension Member Parallel to Grain (NDS 3.8)
The tie beside the strut: a truss bottom chord or collector checks ft = T/An against Ft x CD x CF.
Example
You enter
- Tension force T (lb) 3000
- Member width b (in) 1.5
- Member depth d (in) 5.5
- Fastener-hole diameter (in, 0 if none) 0.75
- Holes across the section 1
- Reference Ft (psi) 575
- Load-duration factor CD 1
- Size factor CF 1.3
You get
- An (in²) 7.125
- Adjusted Ft' 748 psi
- Applied tension stress 421 psi
- Demand / capacity 0.56
Details, formula, and sources
Where the net area deducts the bolt holes a gross-area estimate misses. A 2x6 DF-L chord carrying 3,000 lb through one 3/4 in bolt loses 14% of its section at the hole and runs at DCR 0.56; snow-duration CD 1.15 and a clean section relax it to 0.42 - the two levers the code gives a tension member. Single hole line, no stagger; the bolt itself is checked separately. A design aid, not the engineer of record's stamped design.
Ag = b d; An = Ag - nh dh b; Ft' = Ft x CD x CF; ft = T/An; DCR = ft/Ft'.
The NDS 2018 3.8.1 tension-parallel-to-grain check on the net section, with the load-duration CD and size CF adjustment factors, by name.
The NDS is free to view at awc.org (ANSI/AWC NDS); the 3.8 tension provisions and the adjustment-factor table are in the published standard.
Estimate. AHJ and licensed professional govern.
Field names used by the API: t_lb, b_in, d_in, dh_in, nh, ft_psi, cd_f, cf_f, an_in2, ft_adj_psi, ft_applied_psi, dcr
- Net section An deducts the fastener holes at the section in one transverse lineNDS 2018 3.1.2 / 3.8.1
- Adjusted value Ft' = Ft x CD x CF with the remaining applicable factors entered by the userNDS 2018 Table 4.3.1
- Scope parallel-to-grain tension only; connection yield and tear-out are separate checksNDS 2018 3.8