I am trying to find out how to calculate buckling in an isosceles trapezoidal panel (see picture). Let's say the smaller horizontal side has width a, the large horizontal side width b,height h and thickness t. The load is uniform coming from the top and bottom (perpendicular to a and b) so that the panel is in compression, and the diagonal edges are simply supported. I want to calculate the initial buckling stress, but I don't know the best way to do this for a panel with this shape. One idea was to calculate this stress for a rectangular panel with width a, then with width b, and average the two stresses. Anyone know a better way to do this?