Page 129 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.61

CONNECTIONS

CONNECTIONS 3.61

Bearing. Bearing has been considered with the angles, above.
Prying Action. Prying action refers explicitly to the extra tensile force in bolts that connect flexible
plates or flanges subjected to loads normal to the flanges. For this reason, prying action involves not
only the bolts but the flange thickness, bolt pitch, and gage, and, in general, the geometry of the
entire connection.
The AISC LRFD Manual presents a method for calculating the effects of prying. This method
was originally developed by Struik (Struik and deBack, 1969; Kulak et al., 1987). The form used in
the AISC LRFD Manual was developed by Thornton (1985), for ease of calculation and to provide
optimum results, that is, maximum capacity for a given connection (analysis) and minimum required
thickness for a given load (design). Thornton (1992, 1997) has shown that this method gives a very
conservative estimate of ultimate load and that very close estimates of ultimate load can be obtained
by using the flange ultimate strength F u in place of yield strength F y in the prying action formulas.
More recently, Swanson (2002) has confirmed Thornton’s (1992, 1997) results with modern materi-
als. For this reason, the AISC Manual now uses F u in place of F y in the prying action formulas. Note
that the resistance factor, φ, used with the F u is 0.90, because the flange failure mode is yielding with
strain hardening rather than fracture.
From the foregoing calculations, the design strength of this connection is limited by buckling
in the Whitmore section to 56.5 kips. Take this as the required strength and proceed with prying
calculations. The vertical component of 56.5 kips is 50.5 kips and the horizontal component is
25.3 kips. Thus, the shear per bolt is V = 25.3/8 = 3.16 kips and the tension per bolt is T = 50.5/8 =
6.31 kips. Since 3.16 <φr v = 21.6 kips, the bolts are OK for shear. Note that the bolts also need
to be checked for bearing, as was done for the angles. In this case, bearing is seen to be OK by
inspection.
Bolt Design Tensile Strength. Bolt design tensile strength must be checked by the interaction
equation for bolts in bearing-type connections:

F ′ = 13. F − F nt f ≤ F
φ F nv v nt
nt
nt
where F nt = bolt nominal tensile strength = 90 ksi for A325N
F nv = bolt nominal shear strength = 48 ksi for A325N
φ= 0.75
f v = required shear strength per bolt = 0 6013 = 526 ksi
316
.
.
.
F nt ′ = 1 3 90. × − 075 90 × 48 × 5 26 104. = ksi ≤ 90 ksi Use F nt ′ = 90 ksi
.
Design tensile strength per bolt is
φr t ′= 0.75 × 90 × 0.6013 = 40.6 kips

Since this is greater than the required strength per bolt T = 6.31 kips, the bolts are OK.
Prying of the W16 Piece. Prying of the W16 piece is checked following the procedure in the AISC
Manual (see Art. 3.4 for terms).

.
b = 45 . − 0430 = 2 035 in
.
2
.
.
a = 7 125 − 4 5 = 1 3125 in
.
2
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.