Aluminium Design and Construction John Dwight

Figure 7.17 ‘Standard’ reinforcement.
than that which is possible in a cold-rolled section. A square rib or a
bulb will never become torsionally unstable, and can be safely located
facing outwards. Unfortunately, no data exist as to the limiting lip
geometry at which outward facing reinforcement in a beam flange begins
to become unsatisfactory.
7.4.3 ‘Standard’ reinforcement
‘Standard’ reinforcement comprises a plain single-sided stiffener of
thickness t equal to that of the plate (Figure 7.17), the stiffener height
c being measured from the near surface of the plate. The design data
given below apply directly to an element stiffened thus.
For any other shape of stiffener, it is necessary to notionally replace
the actual stiffener by an equivalent one of standard form, whose height
c is such as to make its inertia about the mid-plane of the plate the
same as that of the actual stiffener. The stability of the reinforced element
is then assessed as if it had a standard stiffener with this c. Note that
the equivalent standard stiffener is always taken as single-sided, even
if the actual reinforcement is double-sided.
7.4.4 Location of the stiffener
(a) Internal elements under uniform compression
The stiffener is assumed to be at midwidth.
(b) Internal elements under strain gradient
We define edges 1, 2 and the parameter ? in the same way as for the
unreinforced case. It is clearly desirable to place the stiffener nearer
to edge 1 than edge 2, so we assume it is located at an optimum distance
j from edge 1 (Figure 7.18) given by:
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