FNA VS NONLINEAR DIRECT INTEGRATION?

[sepultura]

I am modelating a structure of concrete without plastic hinges and with viscous dampers and I obtein very differents results between FNA and Nonlinear direct integration.
WHY?

 

[masomenos]

You need to be careful about using Ritz factors in FNA analysis, as eigen is not good enough. Make sure your analysis cases are correctly defined as nonlinear too.

 

[sepultura]

Hello Masomenos.

Is posible that the diference could be in the damping modes. The results in displacements is in the order of four. the periods are the same.

Maybe tha FNA do not work well with dampers? but why?

 

[RSMENGR]

Dear Sepultura:

FNA should give you good results provided modes have been captured correctly. You must include Links in Ritz Modes and try attempting it again.

Let us know the outcome.

Regards

Reza