I have a panel modeled with shell FEM elements. I want simply supported ends so I applied 3 translational constraints to a small rectangular surface at both ends. How would I go about constraining the rotational DOF. The problem I´m experiencing is that I tried to constrain the rotational constraints on the edges such that I didn´t over constrain my model and make it a clamped clamped constraint, but it doesn´t seem to matter what I do. It´s always brick walling both sides. This makes no sense to me. I even tried splitting the surface and applying all rotational contraints on a small surface near 1 edge, but that still resulted in clamped clamped. Makes no sense to me.

I´m doing a buckling analysis. I want 0% fixity at the two ends. The other two sides are free edges.

Please be gentle with me, it´s my first post here. Yes, I have searched my an answer prior but there doesn´t seem to be much info on simply supported panel buckling analysis.

I have attached some documentation. to show my work and how I´ve tried to constrain my part.