Page 275 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.55

CRITERIA FOR BUILDING DESIGN

CRITERIA FOR BUILDING DESIGN 5.55

where F yf = specified minimum yield stress of the flange, ksi (MPa), and t f = thickness of the loaded
flange, in (mm). When the concentrated force to be resisted is applied at a distance from the mem-
ber end less than 10t f , R n must be reduced by 50%. If the length of loading across the member flange
is less than 0.15b f , where b f is the member flange width, Eq. (5.162) need not be checked. Use a pair
of transverse stiffeners if the available strength is inadequate.

2. Local Web Yielding. This limit state applies to single-concentrated forces, tension or compres-
sion, and both components of double-concentrated forces. The available strength for the limit state
of local web yielding is determined using φ = 1.00 (LRFD) and Ω = 1.50 (ASD). Use a pair of trans-
verse stiffeners or a doubler plate if the available strength is inadequate.
When the concentrated force to be resisted is applied at a distance from the member end greater
than the depth of the member d, the nominal strength, R n , is
(5.163)
R n = (5k + N)F yw t w
When the concentrated force to be resisted is applied at a distance from the member end less than
or equal to the depth of the member d,
(5.164)
R n = (2.5k + N)F yw t w
where F yw = specified minimum yield stress of the web, ksi (MPa)
N = length of bearing (not less than k for end beam reactions), in (mm)
k = distance from outer face of the flange to the web toe of the fillet, in (mm)
t w = web thickness, in (mm)

3. Local Web Crippling. This limit state applies to compressive single-concentrated forces or the
compressive component of double-concentrated forces. The available strength for the limit state of
local web crippling is determined using φ= 0.75 (LRFD) and Ω = 2.00 (ASD). If the available
strength is inadequate, use a transverse stiffener, a pair of transverse stiffeners, or a doubler plate
extending at least one-half the depth of the web.
When the concentrated compressive force to be resisted is applied at a distance from the member
end greater than or equal to d/2, the nominal strength R n is

 N   t  15 .  EF t
+
2
R = 080 t 13   w   yw f (5.165)
.
w
n
   d   t    t w
f
When the concentrated compressive force to be resisted is applied at a distance from the member
end less than d/2, the nominal strength R n depends on the N/d ratio.
If N/d ≤ 0.2,
  N   t  15 .  EF t
2
+
.
R = 040 t 13   w   yw f (5.166)
w
n
  d   t    t w
f
If N/d > 0.2,
 t  w  15 .  EF t
2
R = 040 t 1 +  4 N − 02 .     yw f (5.167)
.
w
n
   d  t  f    t w
where d = overall depth of the member, in (mm), and t f = flange thickness, in (mm).
4. Web Sidesway Buckling. This limit state applies to compressive single-concentrated forces act-
ing on members where relative lateral movement between the loaded compression flange and the ten-
sion flange is not restrained at the point of application of the concentrated force. The available
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