Eigen modes of particular part of the structure?

[drile007]

I’m modelling 3 storeys structure (in SAP2000) and now I’m looking for basic Eigen modes of a particular slab? How can I do that?
I suppose that running a whole structure modal analysis (and manually/visually search for the proper modes) is not the only way to find Eigen modes of a slab? Is there any other procedure to find them?

Thank you for reply

 

[JoshPlumSE]

Maybe you could create a load combination that only has mass on that portion of the model, then run your eigen analysis.

Or, create a new model where you have only modeled the portion of the model you are interested in.

 

[PicoStruc]

I agree with JoshPlum 100%