Page 112 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.44

CONNECTIONS

3.44 CHAPTER THREE

AISC Specification does not distinguish between large and small eccentricities, it is the authors’
opinion based on test results (Yura et al., 1982) that U bs can be taken as 1.0 when the ratio of the
1
eccentricity on the bolt or weld group to the length of the connection, e/L, is less than or equal to / 3.
When forces act obliquely to cause block shear, the resistance can be calculated using an ellipti-
cal interaction equation, analogous to the von Mises yield criterion:

 V  2  H  2
  +   ≤1 (3.33)
 φ R bsv   φ R bsh 

where V = vertical component of tensile force, kips
H = horizontal component of tensile force, kips
R bsv = nominal resistance to block shear in the vertical direction, kips
R bsh = nominal resistance to block shear in the horizontal direction, kips

Block shear should also be checked at welded connections using φ= 0.75 for both the fracture
and yielding planes.

Local Web Yielding. Often a force is transmitted from one member to another in such a way that a
large localized stress occurs in the web. This can occur in bearing connections, such as seats, in
moment connections, and also at the interface between connectors and members, such as the beam-
to-gusset interface in bracing connections. The effective length of web is determined assuming a
1
2 / 2:1 stress gradient through the flange of the supporting member. Both tension and compression
forces can cause local web yielding. The design strength for the limit state of web local yielding is
calculated as follows:
When the concentrated force is applied at a distance greater than the depth of the member,
(3.34)
φR n =φ(5k + N)F yw t w

When the concentrated force is applied at a distance less than or equal to the depth of the member,
(3.35)
φR n =φ(2.5k + N)F yw t w
where φ= 1.0
F yw = specified minimum yield stress of the web, ksi
N = length of bearing (not less than k for end-beam reactions), in
k = distance from outer face of flange to web toe of fillet, in
t w = web thickness, in

Local Web Crippling. Like local web yielding, local web crippling can occur in bearing connec-
tions, moment connections, and at connector-to-beam interfaces. However, local web crippling is
primarily a problem at bearing connections or at beam-to-connector interfaces and rarely governs the
capacity of moment connections. With F y less than or equal to 50 ksi, only moment connections to
W12 × 50 or W10 × 33 columns are governed by local web crippling. The design strength for the
limit state of web local crippling is calculated as follows:
When the concentrated force is applied at a distance greater than or equal to half the depth of the
member,

 N   t  15 .  EF t
φR = φ080 t 13   w   yw f (3.36)
+
2
.
w
n
   d   t    t w
f
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