buckling displacements

[garchola]

Hi all,

I am calculating the buckling modes for the roof of a oil tank which supports water on its superior surface. I obtain a very small value for the first ten modes I calculated. I would like to know what the displacement values are for every mode in order to know if they are physically important or not. How should I get that? Thanks in advance!

Franco

 

[Amrony67]

The displacement values obtained from linear (Eigenvalue) buckling analysis are meaningless. The linear buckling analysis is useful only in showing the deformation pattern of the buckling.
I assumed that you are using an FEA software. After obtaining the lowest mode using linear (Eigenvalue) analysis, you should then perform a nonlinear analysis with a deformed initial geometry. The deformation pattern should be identical to that of mode I linear buckling. The objective of this is to trigger buckling in the nonlinear analysis. Make sure that the applied load is slightly higher that corresponds to mode I. make sure that stabilization mode is off. The solution will diverge at the buckling load as per the attached curve.

In order to see the post-buckling shape you need to redo the nonlinear analysis but with stabilization mode this time. The displacements do have a meaning this time.