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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. I look forward to getting your reply and thank you in advance.
Model and excel file are in the attachment.

Best Regards

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.

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

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.