Wrong eigenmode

[isok89]

Hi all,


I am looking for the first eigenvalue of a three-point-bending simulation.

It concerns a three point bending test on a hat profile, by using a point load in the centre.
I'd expect to get an eigenmode where the compression flange (upper flange) buckles.
However the eigenmode I get is where the bottom flange buckles and this isn't possible, there are tensile stresses in the bottom flange.

I use the subspace method, can anyone help me regarding this?

 

[TGS4]

Is the corresponding eigenvalue positive or negative?