Issue with Modal Analysis of a Frame Building

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kolozvari
Posts: 191
Joined: Tue Oct 05, 2021 9:22 pm

Issue with Modal Analysis of a Frame Building

Post by kolozvari » Thu Apr 11, 2024 10:34 pm

Hello,

I am trying to perform modal analysis of a frame building. The model has rigid diaphragms and lumped masses at each floor. When I try to run modal analysis and get the following error.
Modal_issue.JPG
Modal_issue.JPG (89.71 KiB) Viewed 263 times
I am not sure what is the issue. I ran modal analyses before with the same computer and STKO and didnt have issue. Can you please let me know how to overcome this? The model is attached for your convenience.

Thank you,
Attachments
Frame_Building_Modal.zip
(714.03 KiB) Downloaded 19 times
Last edited by kolozvari on Mon Apr 15, 2024 3:24 pm, edited 1 time in total.

kolozvari
Posts: 191
Joined: Tue Oct 05, 2021 9:22 pm

Re: Issue with Modal Analysis of a Frame Building

Post by kolozvari » Sun Apr 14, 2024 10:47 pm

Hello, I was wondering if you had a chance to look at this issue. Please let me know.

Thanks

kolozvari
Posts: 191
Joined: Tue Oct 05, 2021 9:22 pm

Re: Issue with Modal Analysis of a Frame Building

Post by kolozvari » Mon Apr 22, 2024 5:05 pm

Hello, I just wanted to follow up on this issue since it has been ~10 days since I posted this. It would be great if you could provide me with a response or a guideline on how to approach this issue. I tried several things and none of them worked.

Looking forward to hearing from you.

Thank you

STKO Team
Posts: 2257
Joined: Tue Oct 29, 2019 8:45 am

Re: Issue with Modal Analysis of a Frame Building

Post by STKO Team » Tue Apr 30, 2024 8:40 am

You are using Timoshenko beams, which require the shear areas (Ay = Area*alphaY and Az = Area*alphaZ), but in all your custom sections the alpha values (shear correction factors) are 0. So the shear areas are zero and the shear stiffness is zero, making the element singular, thus the Arpack error.


Here you have your model were I set all shear factors to 5/6, the typical values for rectangular cross-sections with typical aspect ratios. You may want to adjust those shear factor depending on the shape of your beams/columns
Frame_Building_Modal.zip
(664.89 KiB) Downloaded 12 times

kolozvari
Posts: 191
Joined: Tue Oct 05, 2021 9:22 pm

Re: Issue with Modal Analysis of a Frame Building

Post by kolozvari » Tue Apr 30, 2024 3:26 pm

Ah, of course, that makes sense. I was wondering where do you define this. I guess I got used to see this parameter being called "k" and didn't catch it. Thank you for fixing it, there was a lot of sections to change. If possible, it would be useful to add description of the section parameters (similarly to other parameters in the model) in future versions.

Thank you again for your continuous help!

STKO Team
Posts: 2257
Joined: Tue Oct 29, 2019 8:45 am

Re: Issue with Modal Analysis of a Frame Building

Post by STKO Team » Wed May 08, 2024 8:36 am

If possible, it would be useful to add description of the section parameters (similarly to other parameters in the model) in future versions.
Sure! we'll put it in our todo list

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