Panel Buckling by Enforced Displacement

[Stress Engineer]

HI Folks,

I am running a panel buckling analysis using enforced displacement method in NASTRAN (using SPCDs). It usual practice to consider only the transnational components in the analysis. I am just curious to know why the rotational components need to be / need not be considered.

Thanks

 

[Stezza]

I am assuming that you are leaving the rotational enforced displacements blank (as opposed to entering 0.0) on the SPCD card. From my reading of the quick reference guide I think that this means that the edges are free to rotate and thus you have pinned boundary conditions. This is conservative as real structure (usually) has an intermediate amount of fixity between pinned and fixed that you are not taking advantage of. I would double check this for your critical load case by (1) extracting the actual rotational displacements and looking for the Eigenvalue to increase and (2) putting zero as the rotational displacements and looking for the Eigenvalue to increase again as you are now simulating fixed edge conditions.