Eigenvalues with fiber section

[xavio]

Hi everyone,

I have a question concerning the way eigenvalues are computed when some nonlinearities are in the model. For example, I have a column modelled with fiber section and nonlinearbeamcolumn element. I'd like to know if the eigenvalues computed by the eigen command are those considering the initial stiffness of the nonlinear elements or what... ?

I tried to compare with eigenvalues obtained with an elasticbeamelement and they aren't exactly the same, but may be it's because Iz isn't exactly the same...

Thanks a lot!

[canim_ken]

Eigen command in OpenSEES, calculates eigenvalues using tangent stiffness of the structure in its existing state in the Domain. You can check it on a SDOF Perfectly Plastic model by exciting it with a sinusoidal excitation and calculating its eigen values in intervals.