Page 147 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch03.qxd 9/29/05 5:05 PM Page 3.79

CONNECTIONS

CONNECTIONS 3.79

is 229 –182 = 47 kips. But the loads may reverse, so use the larger of 58 and 47 as the stiffener force
for both flanges. Then, the force in each stiffener is 58/2 = 29 kips, both top and bottom.
Stiffener Size Determination. The minimum stiffener width w s is
.
.
b fb − t wc = 824 − 0 485 = 25 in
.
3 2 3 2
Use a stiffener 6.5 in wide to match the column.
The minimum stiffener thickness t s is
t fb = . 0 615 = 03 1
. in
2 2
3
Use a stiffener at least / 8 in thick.
The minimum stiffener length is

=
l = d c − t = 14 2 . − 078 63 in
.
.
s
fc
2 2
This is the minimum length for a half-depth stiffener, which is not possible here because of the weak-
axis connections. Therefore, use a full-depth stiffener, 12.5 in long.
A final stiffener size check is a plate buckling check, which requires that
t ≥ W s = 65 . = 0 433 in
.
s
15 15
1
Therefore, assume a minimum stiffener thickness of / 2 in. The final stiffener size for the strong-axis
1
beam is / 2 × 6.5 × 12.5 in. The contact area of this stiffener against the inside of the column flange
is 6.5 − 1.25 = 5.25 in due to the snip to clear the column web-to-flange fillet. The stiffener design
strength is thus
0.90 × 36 × 5.25 × 0.5 = 85.1 kips > 29 kips OK
Welds of Stiffeners to Column Flange and Web. Putting aside for the moment that the weak-axis
moment connections still need to be considered and will affect both the strong-axis connection stiff-
eners and welds, the welds for the / 2 × 6.5 × 12.5 in strong-axis stiffener are designed as follows.
1
For the weld to the inside of the flange, the force to be developed by the weld to the connected portion
is 29 kips. Thus, the 5.25-in width in contact, which is the connected portion, is designed for 29 kips.
The fillet weld design strength is φF w A w = 0.75 × 0.60 × 70 × ( / 16) = 1.392 kips per / 16th of weld
1
1
size. Thus, for the weld to the flange,
D = 29 = 132.
f
2 × 5 25. ×1 392. ×1 5.
1
where D f = number of / 16ths in the fillet weld size. In this case, an AISC minimum fillet weld is indi-
cated. The factor 1.5 in the denominator above comes from the AISC Specification, Sec. J2.4, for
transversely loaded fillets. The weld to the web has a length 12.5 − 1.25 − 1.25 = 10.0 in, and is
designed to transfer the unbalanced force in the stiffener to the web. The unbalanced force in the stiff-
ener is 29 kips in this case. Since the weld at the web and the weld at the flange do not share load in
this case, both the longitudinally and transversely loaded welds can develop their full strength. Thus,
D = 29 = 104.
w
2 ×100. ×1392.
1
where D w = number of / 16ths in the fillet weld size. An AISC minimum fillet is indicated.

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