Page 148 - Handbook of Structural Steel Connection Design and Details

Design of Connections for Axial, Moment, and Shear Forces

Design of Connections for Axial, Moment, and Shear Forces 133

5
Beam web. To support a / fillet weld on both sides of a plate, AISC
16
LRFD Manual Table 10.2 shows that a 0.476-in web is required. For a
5 / fillet on one side, a 0.238-in web is required. Since the W21 62 web
16
is 0.400 in thick, it is ok.
Beam nos. 3 and 4 W21 44 (G50) composite. The flange connection is a full
penetration weld, so again, no design is required. Section A-A of Fig.
2.33a shows the arrangement in plan. See Fig. 2.33c. The connection
1
plates A are made / in thicker than the W21 44 beam flange to
4
accommodate under and over rolling and other minor misfits. Also, the
3
plates are extended beyond the toes of the column flanges by / to 1 in
4
to improve ductility. The plates A should also be welded to the column
web, even if not required to carry load, to provide improved ductility. A
good discussion of this is contained in the AISC 13th Edition Manual of
Steel Construction, pp. 12-14 through 12-19.
The flange force for the W21 44 is based on the full moment capac-
ity as required in this example, so M 358 kips-ft. For gravity
p
moments, the beam moments counteract each other, and the column
bending strength is not an issue. For lateral moments, however, the
beam moments add, and the column strength may limit the beam
moments. The weak-axis column design strength is
50
M 5 0.9 3 3 83.6 5 314 kips-ft
p
12
Therefore, for lateral loads, the beam plastic moment cannot be
achieved because 2 358 > 2 314.
For lateral loads, the maximum beam moment is M 314 kips-ft.
b
In summary, for gravity loads, M M 358 kips-ft and the flange
b p
force is
358 3 12
F 5 5 212 kips
f
s20.7 2 0.45d
and for lateral loads, M 314 kips-ft and the flange force is
b
314 3 12
F 5 5 186 kips
f
s20.7 2 0.450d
Figure 2.36 shows the distribution of forces on the plates A, including the
forces from the strong axis connection. The weak axis gravity force of 212
kips is distributed one-fourth to each flange and one-half to the web. This
is done to cover the case when full gravity loads are not present on each
side. In this case, all of the 212 kips must be passed to the flanges. To see
this, imagine that beam 4 is removed and the plate A for beam 4 remains
as a back-up stiffener. One half of the 212 kips from beam 3 passes into the
beam 3 near side column flanges, while the other half is passed through

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