Page 246 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch05.qxd 9/29/05 5:12 PM Page 5.26

CRITERIA FOR BUILDING DESIGN

5.26 CHAPTER FIVE

they must have a moment of inertia (about an axis in the web center for stiffener pairs or about the
3
face in contact with the web plate for single stiffeners) not less than at w j, where
j = 25 . − ≥ 0 5 . (5.94)
2
(/ 2
ah)
When single stiffeners are used with rectangular flange plates, they should be attached to the
compression flange to resist torsion. Also, when lateral bracing is attached to stiffeners, singly or in
pairs, the stiffeners should be connected to the compression flange to transmit 1% of the total flange
stress, unless the flange is composed only of angles.
Transverse stiffeners may be stopped short of the tension flange unless needed to transmit a con-
centrated load or reaction by bearing. Welds for web attachment of transverse stiffeners should be
terminated not less than four times nor more than six times the web thickness from the near toe to
the web-to-flange weld. Intermittent fillet welds connecting stiffeners to the girder web should be
spaced such that the clear distance between them does not exceed 16t w nor 10 in (250 mm). If bolts
are used instead, they should be spaced not more than 12 in (305 mm) on center.

5.6.2 Plate Girders with Tension Field Action
Design of webs on the basis of tension field action typically reduces the required web thickness but
increases the number of stiffeners. Thus, possible reductions in material cost must be balanced
against increases in fabrication cost. The use of this design method requires that the web plate be
supported on all four sides by flanges or stiffeners. Tension field action may not be considered for
end panels of members with transverse stiffeners, nor for the following cases:
a/h > 3.0
a/h > [260/(h/t w )] 2
2A w /(A fc + A ft ) > 2.5
h/b fc or h/b ft > 6.0

where a, h, t w , and A w are as defined in Art. 5.6.1, A fc and A ft are the cross-section areas of the com-
pression and tension flanges, and b fc and b ft are the widths of the compression and tension flanges.
Where tension field action is not applicable, the nominal shear strength must be determined accord-
ing to Art. 5.6.1.
The nominal shear strength, V n , for the limit state of tension field yielding is calculated as follows.
.
/
When ht ≤110 k E F ,
/
v
y
w
(5.95)
V n = 0.6F y A w
/
/
.
When ht >110 k E F ,
y
v
w
 1 − C v 
y w
V = 06 . F A C +  (5.96)
v
n
 115 1 + ( ah) 2 
.
/
where k v and C v are as defined in Art. 5.6.1.
Transverse stiffeners in girders designed for tension field action must meet the requirements dis-
cussed in Art. 5.6.1 and are also subject to the following two limitations:
 b  E
t   st =≤ 056. F y (5.97)
F  V 
A > y  015 Dht 1 ( − C ) r −18 t 2 w  ≥ 0 (5.98)
.
v
w
s
st
F yst  V c 
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