Page 290 - Civil Engineering Formulas

224 CHAPTER NINE

Stiffeners are required if the concentrated load exceeds R, kip (kN), computed
from
3
3
R 6800t w (1 0.4r wf ) (9.60)
h
where h clear distance, in (mm), between flanges, and r is less than 2.3
wf
when the loaded flange is restrained against rotation. If the loaded flange is not
restrained and r is less than 1.7,
wf
3
3 6800t w
R 0.4r wf (9.61)
h
R need not be computed for larger values of r wf.

DESIGN OF STIFFENERS UNDER LOADS

AISC requires that fasteners or welds for end connections of beams, girders,
and trusses be designed for the combined effect of forces resulting from
moment and shear induced by the rigidity of the connection. When flanges or
moment-connection plates for end connections of beams and girders are welded
to the flange of an I- or H-shape column, a pair of column-web stiffeners having
a combined cross-sectional area A not less than that calculated from the follow-
st
ing equations must be provided whenever the calculated value of A is positive:
st
P bf F yc t wc (t b 5K)
A st (9.62)
F yst
where F column yield stress, ksi (MPa)
yc
F yst stiffener yield stress, ksi (MPa)
K distance, in (mm), between outer face of column flange and web toe
of its fillet, if column is rolled shape, or equivalent distance if col-
umn is welded shape
P computed force, kip (kN), delivered by flange of moment-
bf
5
connection plate multiplied by , when computed force is due to
3
4
live and dead load only, or by , when computed force is due to
3
live and dead load in conjunction with wind or earthquake forces
t wc thickness of column web, in (mm)
t thickness of flange or moment-connection plate delivering concen-
b
trated force, in (mm)
Notwithstanding the preceding requirements, a stiffener or a pair of stiffen-
ers must be provided opposite the beam-compression flange when the column-
web depth clear of fillets d is greater than
c
3
4100t wc Fyc
d c (9.63)
P bf