Modal analysis, first tone is torsion

[Anonymous]

Hello,

In modal analysis, my first tone is torsion, but it has 0 mass participation.

I'm modeling a 5 story building, and my 5th floor is more rigid than the other ones. Could it be the cause of my 1st tone being a torsional one? If not, what can i do to change that?
I will attatch the model without calculation in the post.

Thank you in advance, and sorry about my broken English.

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

Yes, this is because of the shape of the first (torsional) mode.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Hi @Artur.Kosakowski

could I bother you with just one more question?

Is it plaussible to detirmine rx and ry (ratio between torsional and lateral rigidity) in RSA?

Again, thank you in advance!

[Artur.Kosakowski]

Hi @Anonymous

You may find this topic helpful:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/torsional-and-lateral-stiffness-of-a-structure/m-p/5799525

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.