In most of the problems concerned with the buckling of plates it is assumed that the length of the plate is greater than its width, and that the edges of the plate, at which the compression loads are applied, are simply supported. The method of support of the side edges vary with the actual conditions.

In the case of short wide plates or plates with many lateral stiffeners, as shown in Figs, 1 and 2 respectively, the effect on the buckling load due to the conditions of support at the two side edges will become less, and that due to the conditions of support at the end edges will become important, so that they can no longer be assumed to be simply supported. For ease of calculation the side edges are assumed to be simply supported.