Prying Action in Tee and Angle Flanges (AISC Manual Part 9)
A tee or angle flange bolted in tension bends, its tips bear on the support.
Example
You enter
- Required tension per bolt T (kip) 20
- Bolt available tension B (kip, phi rn or rn/Omega) 29.8
- Bolt diameter d (in) 0.75
- Hole diameter d' (in, blank = d + 1/16) 0.8125
- Flange length per bolt p (in) 4
- Bolt line to stem face b (in) 1.79
- Bolt line to flange tip a (in) 1.56
- Flange thickness t (in) 0.715
- Flange Fu (ksi, 65 for A992) 65
- Design basis LRFD
You get
- Ratio rho = b'/a' 0.732
- Delta 0.797
- T min (in) 0.521
- Thickness for negligible prying at T 0.696 in -- the flange is this thick
Checked against published worked examples from: American Institute of Steel Construction (AISC).
Details, formula, and sources
ScopeA tee or angle flange bolted in tension bends, its tips bear on the support, and the bolts carry more than the applied load: prying. This gives the flange thickness that works with prying counted, the thicker flange that makes prying negligible, and the tension each bolt can deliver at the actual thickness, from the AISC Manual Part 9 relations. AISC Design Example II.D-1's WT8x28.5 hanger with 3/4 in bolts at 4 in needs 0.52 in of flange for 20 kip per bolt, and 0.70 in to make prying negligible. The stem, welds, and supporting member are separate checks; the engineer of record governs.
Formula or tableAISC Manual Part 9 prying: b' = b - d/2; a' = min(a, 1.25 b) + d/2; rho = b'/a'; delta = 1 - d'/p; beta = (B/T - 1)/rho; alpha' = 1 if beta >= 1 else min(1, beta/(delta(1 - beta))); t_min = sqrt(k T b'/(p Fu (1 + delta alpha'))); prying negligible at t = sqrt(k T b'/(p Fu)); t_c = sqrt(k B b'/(p Fu)); available tension = B (t/t_c)^2 (1 + delta alpha) with alpha = ((t_c/t)^2 - 1)/(delta(1 + rho)) held to [0, 1]; k = 4/0.90 (LRFD) or 4 x 1.67 (ASD).
Source and editionAISC Steel Construction Manual Part 9 prying-action relations by name, as worked in AISC Design Example II.D-1 (Prying Action in Tees and in Single Angles).
Free accessThe AISC Design Examples are free at aisc.org; the Manual itself is licensed and no table from it is reproduced.
What governsEstimate. AHJ and licensed professional govern.
API field namestension_per_bolt_kip, bolt_available_kip, bolt_dia_in, hole_dia_in, tributary_p_in, b_in, a_in, flange_t_in, fu_ksi, method, rho, delta, t_min_in, t_no_prying_in
- Edge distance a taken no more than 1.25 bAISC Manual Part 9
- Hole diameter default bolt diameter + 1/16 in (standard hole)AISC 360 Table J3.3