Hello , i would like to clarify some things. Perhaps you could help.

I am trying to make some FEM analysis about some examples in Bruhn and BDM abou buckling of plates. I want to take those examples and compare the results obtained analytically with the ones form FEM. But i a have some difficulties translating the boundary conditions from BDM and Bruhn to FEM model.

For a model , a simple plate subjected to uni axial compression what does all 4 edges simply supported and clamped mean translated in DOF locked or not in FEM? I know the definition for each of them but i am having difficulties imagining a plate with all 4 edges fixed could be subjected to uni axial compression...i want to make sure i get it correctly and never doubt it again.

Please post a patran or nastran input file so I can take a look.

I suggest you take a text like Roark's Formulas for Stress and Strain, and replicate a lot of plate examples to improve your understanding of Boundary Conditions. This is what helped me get a good idea of how to properly constrain models. I would like to offer an answer to your question, but it may not be enough to fully answer your question.

4SS = fixed in out of plane translation on all sides, fixed in moments perpendicular to the edge and normal to the edge on all sides; other 3 dof free
4CL = fixed in out of plane translation on all sides, fixed in all 3 moments on all sides; other 2 dof free