two - dimensional eigenvalue analysis

[vinniec]

Hello to everyone, I'm a beginner on seismo_struct and I need your help for some issues. I've made an eigenvalue analysis on a simple two-dimensional frame, and among the ten vibration modes that the program shows as output, most of them makes the structure oscillating out of the x-z plane. I would consider only the behaviour in the x-z plane, how could I do that? I tried to restrain all the nodes to the translation along y axis and to the rotation around x and z axes but it's even worse!
Thanks a lot if you answer to my simple question.

[seismosoft]

Hi,

Why don't you create a 2D eigenvalue analysis model with the Wizard and/or check out one of the 2D eigenvalue analysis models that come with the Verification Report?

Seismosoft Support

[vinniec]

I've noticed that the problem that I illustrated in the first message does not occur anymore if I put the elements' mass equal to zero in "element classes" and if I put the mass only by defining the lumped masses at every node. In this way I have no problem and I can define both the rigid diaphragms and the external restraints to get only the modes in the x - z plane. Anyway, if I put the distribuited mass due to the elements it doesn't work very well anymore. I don't know why and where I make some mistakes.

[vinniec]

Maybe I've solved my problem, I think that if I want to see only the modes in the x - z plane I have to tick only the X direction in the "global direction mass".Is it the better way?

[seismosoft]

Yes, this works, but so does the out-of-plane restraining introduced in the Wizard models and in some of the Verication Report examples.

Seismosoft Support