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Steel Designers' Manual - 6th Edition (2003)
712 Plate and stiffener elements in connections
Li
(a) (b) (c)
Fig. 25.1 Dispersion of load, b 1 = stiff bearing length
web
yields
Fig. 25.2 Failure mechanism of flange
Conventionally for rolled sections dispersion has been taken to the K-line, i.e.
through a distance equal to the flange thickness (T) plus the flange to web root
radius (r). To adjust the formula to this practice the minimum value of T(B/t) 1 – 2
in terms of (T + r) for rolled sections is substituted in the equation, i.e. T(B/t) 1 – 2 =
2.5(T + r), hence the 1 : 2.5 dispersion.
BS5950-1: 2000 defines the bearing capacity of an unstiffened web, P bw, as (b 1 +
nk)tp yw where n is taken as 5 if the load is applied remote from the end of a member
of 2 + 0.6b e/k (but less than 5) where the load is applied near the end of a member
and b e is the distance to the end of the member from the edge of a stiff bearing; k
is as shown in Fig. 25.3 for a rolled section but taken as only the flange thickness
for welded sections. Where the applied load or reaction exceeds the bearing capacity
of the unstiffened web, bearing stiffeners should be provided. These should be
designed to carry the applied force minus the bearing capacity of the unstiffened
web.