In the Ansys Help it is explained how to do that. There is shown the case of an aplied force and gravity (that is constant).
You must scale your forces until the buckling coeff. is 1. (you must iterate manually)
Drej, I think that bhava9 has a warning message that related to Maximum Thickness /Minimun Radius of Curvature of the shell element and not to Lenght/ width.
If the relation Max Thk / Min Rad is big, you can loose the lineality of the stresses trough thickness. (It´s like a beam with an initial...
