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Steel Designers' Manual - 6th Edition (2003)
Chapter 25
Plate and stiffener elements
in connections
by BRIAN CHEAL
25.1 Dispersion of load through plates and flanges
Where loads (or reactions) are applied to the flanges of beams, columns or girders
the web adjacent to the flange must be checked for its local bearing capacity. The
effective length of web to be used for checking the bearing capacity is obtained by
assuming a dispersion of the load through the plates and flanges. Generally the dispersion
to find the stiff bearing length is taken at an angle of 45° through solid
material as shown in Fig. 25.1(a) and (b). 1 The dispersion depends upon the local
bending resistance of the plate and so the dispersion can only occur when there is
some restraint to balance the bending moment. For example, in Fig. 25.1(c) where
the loose pack is not symmetrical about the point of application of the load, the 45°
dispersion should not be taken through the pack.
In the case of a flange which is integral with or is connected to the web a greater
angle of dispersion at a slope of 1 : 2.5 to the plane of the flange is allowed. 1 The dispersion
of 1 : 2.5, taken to the web-to-flange connection, has been verified by tests
with loads applied to columns, remote from the column ends. It can also be established
by calculation, assuming that at failure the web crushes and four plastic hinges
form in the flange (Fig. 25.2). The theoretical formula that is obtained is given in
the draft Eurocode 3: 2
P = ( b + n) t p
in which the length due to dispersion (n) is given as (Fig. 25.3):
1
/g
1 yw M1
2
[ ]
1
yf yw a yf
2
2
n= 2T( B/ t) ( p / p ) 1-
( f / p )
where P = crushing resistance of the web,
b 1 = length of stiff bearing,
t = thickness of web,
B = width of flange, but not greater than 25T,
T = thickness of flange,
p yf = yield stress of flange,
p yw = yield stress of web,
f a = longitudinal stress in the flange,
g M1 = partial safety factor.
1
2
711