Building Design and Construction Handbook - Merritt - Ventech!

7.78 SECTION SEVEN
3 4100 t �Fyc d � (7.49)
c
P
where d c � clear distance, in, between column flanges (clear of fillets). Also, a pair
of stiffeners is needed opposite the tension force at point b when
P
t � 0.4 (7.50)
ƒ �F yc
where t ƒ � thickness of column flange, in.
The thickness of a stiffener should not be less than one-half the thickness of the
beam flange or plate that delivers force P to the column. Stiffener width should not
be less than one-third of the flange or plate width.
7.22.2 LRFD for Load-Bearing Stiffeners
Six limit states should be considered at locations where a large concentrated force
acting on a member introduces high local stresses. These limit states are local flange
bending, local web yielding, web crippling, sidesway web buckling, compression
buckling of the web, and high shear in column web panels. Detailed requirements
for determining the design strength for each of these limit states are contained in
the AISC LRFD ‘‘Specification for Structural Steel for Buildings.’’
When web stiffeners are required to prevent web crippling or compression buckling
of the web, they are designed as columns with an effective length of Kl �
0.75h, where h is the clear distance between flanges. The effective cross section is
the area of the stiffeners plus 25t for interior stiffeners for 12t for stiffeners at the
end of a member, where t is the web thickness.
7.23 BEARING
For bearing on finished surfaces, such as milled ends and ends of fitted bearing
stiffeners, or on the projected area of pins in finished holes, the allowable stress in
ASD is
F � 0.90F (7.51)
p y
where F y is the specified minimum yield stress of the steel, ksi. When the parts in
contact have different yield stresses, use the smaller F y (Table 7.19).
The allowable bearing stress on expansion rollers and rockers, kip/in, is
F � 13
y
Fp � 0.66d (7.52)
20
where d is the diameter of roller or rocker, in (Table 7.20).
Allowable bearing stresses on masonry usually can be obtained from a local or
state building code, whichever governs. In the absence of such regulations, however,
the values in Table 7.21 may be used.