Aluminium Design and Construction John Dwight

7.3 PLAIN FLAT ELEMENTS UNDER STRAIN GRADIENT
We now consider the strain-gradient case, covering any element in a beam
that is not parallel to the neutral axis, such as a web or an inclined flange
element. The problem is how to apply the basic local buckling data, as
established for uniform compression, to an element under strain gradient.
7.3.1 Internal elements under strain gradient, general description
First we consider internal elements, for which edges 1 and 2 may be
identified as follows (Figure 7.8):
Edge 1 the more heavily compressed edge;
Edge 2 the other edge.
A parameter � is introduced to describe the degree of strain gradient:
where e 1 and e 2 are the strains arising at the two edges under simple
beam theory (‘plane sections remain plane’). Two cases arise:
1>�>0 inclined flange elements (edge 2 is in compression);
�