topic Re: Issues with modal analysis in Robot Structural Analysis Forum

Issues with modal analysis

Rafael_Oliveira22 — Wed, 02 Aug 2023 13:15:00 GMT

Hello,

I found some problems with my modal analysis on RSA.

I know it is a old problem and have so many posts about it on forum, but I couldn't solve my problem.

Firstly, I haven't found any value for mass rotation (Rz) in the modal analysis for my building, so, after searching for a solution on Forum, I found that mass rotation "Rz" is only available for analysis with "Slab - Rigid Diaphragm".

(the same problem of him https://forums.autodesk.com/t5/robot-structural-analysis-forum/robot-modal-analysis-torsional-mass-participation-factor/m-p/5606274)

So, after using the API Diaphragmer from @Romanich (Thanks for your help with the API, Roman), I still haven't values for mass rotation (Rz) in my building. I tried to change the options for mass matrix in the modal analysis (Consistent or lumped) and I did a simple model for test this options with the API Diaphragmer and I got good values for Rz in this model for example but, when I try to use the same options for my building, I can't found values for Rz in modal analysis.

Someone have any idea how can I solve this problem for mass rotation (Rz)?

I have spent so many time to solve it and I could not.

I will attach my models and auxiliar pictures for discrib the problem and results.

Thanks!

@Romanich
@mustafahesenow

Re: Issues with modal analysis

Rafael_Oliveira22 — Sat, 05 Aug 2023 16:14:53 GMT

Anyone?

Re: Issues with modal analysis

Rafael_Oliveira22 — Wed, 16 Aug 2023 21:31:09 GMT

Can you help-me, @Krzysztof_Wasik?
Any idea how can I solve it?
Thank you!

Re: Issues with modal analysis

Rafacascudo — Fri, 18 Aug 2023 11:59:46 GMT

Maybe @okapawal can help you on this one

Re: Issues with modal analysis

okapawal — Fri, 18 Aug 2023 12:16:44 GMT

I had a look at the model. It is a couple story, wide and long building. Maybe just torsional vibration form is not dominating like in the test model in mode 3.

Why do you need RZ mass participation result?

Re: Issues with modal analysis

Rafael_Oliveira22 — Fri, 18 Aug 2023 14:04:57 GMT

Thanks for your attention, @Rafacascudo

Thanks for your reply, @okapawal
So, I started to compare the values for dynamic analysis with almost like structure on ETABS and when i did compare the values for Rz I thought it was a little weird, because I think we always have any mass rotation for a building, however small it may be.

When we see the Model 1 for the Main model, we can observe that building is susceptible to torsional vibration on the first mode but without Rz.

Finally, i Would classify my building according NP EN1998-1 (5.2.2) like Torsionally flexible system.

Re: Issues with modal analysis

Simau — Fri, 18 Aug 2023 18:15:15 GMT

@Rafael_Oliveira22

To return to your simple model, could you test these 4 models with ETABS

Re: Issues with modal analysis

Rafael_Oliveira22 — Wed, 23 Aug 2023 13:30:05 GMT

@Simau

I will attach the result for modal analysis for the 4 models you asked.

I hope I haven't forgotten any data for the models.

I made a simplified report with some pictures, If any question, tell me.

Thank you