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Steel Designers' Manual - 6th Edition (2003)
attaching the stiffeners to the flange have limited ductility. To overcome this
problem, for a pair of symmetrical fillet welds, the leg length of the fillet welds
should be not less than 0.85ts for grade S275 steel and 1.0ts for grade S355 steel, or
the welds can be designed for a net load based on the 45° dispersion.
BS 5950-1: 1990 included a bearing check for load-carrying stiffeners (sub-clause
4.5.4.2). This stated that load-carrying stiffeners should be designed to resist 80%
of the total applied force, irrespective of the capacity of the unstiffened web, i.e. A
> 0.8Fx/pys, where A is the area of the stiffener in contact with the flange, Fx is the
applied load, pys is the design strength of the stiffener. As a result of the reduction
in the effective width of the web from 20t to 15t (see 25.2.3 above), this bearing
check was removed. This was a key change since, in most practical cases, the size of
the stiffeners was governed by this rule. There is still a requirement to check the
bearing capacity, as BS 5950-1: 2000 states that load-carrying stiffeners should also
be checked as bearing stiffeners. However, this requirement is not as onerous as the
previous 80% rule, since bearing stiffeners are only designed to carry the external
load minus the bearing capacity of the unstiffened web and not the full external
load.
25.2.5 Bracket stiffeners
Stiffeners 715
The outside edge of the welded column bracket, shown in Fig. 25.4, is in compression,
and provided that a reasonably conservative approach is used in calculating
the extreme fibre stress, semi-compact criteria for the outstand are appropriate (i.e.
b � 13tse). With relatively light loads, this may require an unnecessarily thick stiffener.
To overcome the problem, the simple design approach of substituting fa for py
Fig. 25.4 Column bracket