SAP2000, modal shapes - exclude shells/slabs

[bobering]

I am wondering how to exclude modal shapes in area sections. I have a building and need a few modal shapes, but just for the concrete frame. In my case the 4th, 5th, ... shapes are all slabs in vertical displacement.
I tried assigning weight of their material to 0, but that did not solve the problem.

 

[Guest262653]

Try to use Ritz vectors in the appropriate directions instead of Eigen vectors. That usually eliminates the low mass modes.

Please check the following link:

https://wiki.csiamerica.com/display/kb/Ritz+vs.+Eigen+vectors

 

[JoshPlumSE]

Or both.... discretize your mass so that you don't have mass in the middle of the slab. And, use the Ritz vector solver instead of the true eigen vectors.

 

[LQQD]

Hi,

You could also select all area section and go to assign-->Areas---> Area stiffness modifiers and change mass modifier to 0, it will keep the weight for other load combinations.