abnormal acceleration results of time history analysis

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Edmond2000
Posts: 15
Joined: Sat Jan 27, 2024 12:40 pm

abnormal acceleration results of time history analysis

Post by Edmond2000 » Fri Apr 19, 2024 1:01 pm

Dear STKO team:

I built a 5-story RC frame using STKO and performed a time history analysis on it. I input the seismic acceleration in three directions using UniformExcitation. Because the result of each node is the relative acceleration to the ground, I analyzed the absolute acceleration of the top and first floor top nodes in the excel file, but found that the acceleration in the x direction was almost not amplified (for example, the input peak acceleration in the x direction is 6000 mm/s2, the peak absolute acceleration of the top node is about 7000mm/s2, with almost no amplification), which is contrary to common sense in structural dynamics. I think the calculation results of STKO maybe incorrect and I am not sure whether the results in the z direction are correct.

Could you please help me check if there are any problems in the model or settings, which is related to whether my project can continue. :cry: I look forward to getting your reply and thank you in advance.
Model and excel file are in the attachment.

Best Regards
Attachments
model and result.zip
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kesavapraba
Posts: 301
Joined: Sat Mar 28, 2020 2:25 pm

Re: abnormal acceleration results of time history analysis

Post by kesavapraba » Fri Apr 19, 2024 6:12 pm

Amplification of the structural response depends on the mass, stiffness, and the damping in the model. Please review them for their correctness, particularly the damping.
:: With best wishes ::
Prabakaran Kesavan

Edmond2000
Posts: 15
Joined: Sat Jan 27, 2024 12:40 pm

Re: abnormal acceleration results of time history analysis

Post by Edmond2000 » Mon Apr 22, 2024 11:15 am

kesavapraba wrote:
Fri Apr 19, 2024 6:12 pm
Amplification of the structural response depends on the mass, stiffness, and the damping in the model. Please review them for their correctness, particularly the damping.
Dear Kesavan:

Thanks for your notice, but I double checked all properties and damping settings and found no errors. :( I really can't find where the problem is with my model and need someone to help me check it.

Best regards

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

Re: abnormal acceleration results of time history analysis

Post by STKO Team » Fri May 10, 2024 4:35 pm

In rayleigh damping you are using 2 frequencies very close to each other (about 1.7) and all main frequencies of your model (2 to 7 ... first and 6th mode) will be overdamped.

Also try to reduce the damping ratio. probably 0.05 is too much for a nonlinear analysis.

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