Page 113 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards
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Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.45
CONNECTIONS
CONNECTIONS 3.45
When the concentrated force is applied at a distance less than half the depth of the member,
N t 15 . EF t
+
2
For N/d ≤ 0.2, φR = φ040 t 13 w yw f (3.37)
.
w
n
d t t w
f
t w 15 . EF t
2
For N/d ≤ 0.2, φR = φ040 t 1 + 4 N − 02 . yw f (3.38)
.
n
w
d t f t w
where φ= 0.75
E = modulus of elasticity, 29,000 ksi
F yw = specified minimum yield stress of the web, ksi
N = length of bearing, in
d = overall depth of member, in
t w = web thickness, in
t f = flange thickness, in
In the design of vertical bracing connections, it is advisable to use Eq. (3.36), due to the additional
restraint provided by the connection of the beam web to the column.
Local Web Compression Buckling. Unlike local web yielding and local web crippling, the checks
given by AISC for local web compression buckling apply only to moment connections where com-
pression forces exist at the same location at opposite flanges of a column and where N/d is small
(< 1). The design strength for the limit state of web local buckling is calculated as
φ24 t 3 EF
φR = w yw (3.39)
n
h
where φ= 0.90
h = clear distance between the flanges less the fillet
When the compressive forces are applied near the end of the member, the calculated resistance to
web compression buckling should be reduced by 50%. For conditions with N/d ratios greater than 1,
the web should be designed as a compression member.
Local Flange Bending. When a tension load is applied to a member through a plate welded across
the flange, flange bending will occur. This can occur at the tension flange of a moment connection
and also at tension hangers. The design strength for the limit state of flange local bending can be cal-
culated as
φR = φ625 t F (3.40)
2
.
n
f yf
where φ= 0.90
F yf = specified minimum yield stress of the flange, ksi
t f = flange thickness
Axial Yield Line or Plate Plastification. Axial yield line or plate plastification can be thought of
as an “oil can effect,” where an axial load is applied normal to the weak axis of an element, such as
a beam web or tube wall. Although not treated specifically in the AISC Specification, the strength of
such an element can be determined by performing a yield line analysis as illustrated in Fig. 3.28.
Such an analysis assumes a plastic moment collapse mechanism (along the dashed lines in Fig. 3.28)
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