Wood Connection Row and Group Tear-Out (NDS Appendix E)
A closely spaced bolt group in a wood member can fail in the wood before any bolt yields.
Example
You enter
- Member thickness t (in) 3.125
- Member depth d (in) 12
- Bolt-hole diameter Dh (in) 1.0625
- Rows of bolts (parallel to the load) 3
- Bolts in each outer row 3
- Bolts in each interior row (blank = same) 2
- End distance to the first bolt (in) 7
- Bolt spacing in a row (in) 4
- Spacing between rows (in) 2.5
- Adjusted shear Fv' (psi) 240
- Adjusted tension Ft' (psi) 1450
- Bolt group capacity n Z' (lb, 0 to skip) 35040
You get
- Net section tension Z'NT 39,932 lb
- Z rt (lb) 24000
- Group tear-out Z'GT 22,027 lb
- Connection capacity (lb) 22030
Checked against published worked examples from: American Wood Council (AWC); STRUCTURE magazine (NCSEA / CASE / SEI), authored by AWC staff.
Details, formula, and sources
Scopea row of bolts shears out through the member end, or the whole block between the outer rows pulls out. This gives the three NDS Appendix E capacities -- net section tension, row tear-out, and group tear-out -- and which one limits the connection, against the bolt group capacity if you enter it. The AWC worked example, a 3-1/8 x 12 glulam with eight 1 in bolts in three staggered rows, has 35,040 lb of bolt capacity but only 22,030 lb of group tear-out, so the wood governs; spreading the rows or the bolts in a row is the fix, not bigger bolts. Fv' and Ft' are entered already adjusted; the engineer of record governs.
Formula or tableZ'NT = Ft' t (d - nrow Dh); Z'RTi = ni Fv' t scrit, scrit = min(end distance, in-row spacing) (end distance alone for a one-bolt row); Z'RT = sum of Z'RTi; Z'GT = Z'RT-1/2 + Z'RT-n/2 + Ft' t (nrow - 1)(srow - Dh); the connection takes the least of these and the bolt group capacity n Z' when entered.
Source and editionANSI/AWC NDS (2018) Appendix E, local stresses in fastener groups (Eq. E.2-1, E.3-2, E.3-3, E.4-1), by name, as worked in AWC Wood Design Focus, Winter 2002, "Is Your Wood Connection All Stressed Out? It Needn't Be: Appendix E Provisions".
Free accessThe NDS is free to view at awc.org; the Wood Design Focus article with its worked examples is a free PDF at awc.org.
What governsEstimate. AHJ and licensed professional govern.
API field namest_in, d_in, dh_in, n_rows, bolts_outer_row, bolts_inner_row, end_dist_in, bolt_spacing_in, row_spacing_in, fv_adj_psi, ft_adj_psi, fastener_capacity_lb, z_nt_lb, z_rt_lb, z_gt_lb, connection_capacity_lb
- Shear lines two per row at an apparent stress of Fv'/2 over the shortest clear lengthNDS Appendix E.3
- Net section one hole deducted per row, conservative for a staggered patternNDS Appendix E.2
- Design values Fv' and Ft' entered already adjusted (CD, CM, Ct, and member-specific reductions)NDS 2018 Table 4.3.1 / 5.3.1