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SPECTRUM/HARMONIC ANALYSIS?
 
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luciano.engel
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Joined: 22 Sep 2014
Posts: 4

PostPosted: Fri Oct 16, 2015 1:41 pm  Reply with quote

Hello everyone!

I need to model a telecommunication tower that is vibrating/moving under wind load. I have a video of the top of the tower moving from where I can get an ideia of the period of that movement. How can I determine the structural forces of the members?

I've performed a static analysis using critical project wind loads, followed with a modal analysis(pstress,on). LINK8 and BEAM188 elements showed similar results, so i kept the LINK8 model. Mode periods are close from what can I see on that video. The question is... how can i proper extract the forces?

An harmonic analysis requires an harmonic force, that I don't have. I can use it to determine frequencies that will have a DOF peak but I already know that these are the modes natural frequencies.

An Spectrum analysis requires a (Freq) x (Force amplification coefficient) curve that I also don't have and don't fully understand. I get freq x acel curves for seismic analysis but can't see how it works for wind forces.

I've tried both, for the same load configuration with a frequency range of 0.1-100Hz and force amplification always 1(for the spectrum model). Both models results were lower than the pure static analysis....

I think that perfect model would extract the modes and then impose a vibration pattern on the structure, from where I would get the forces.

Can anyone help? I could not find any documentation regarding this kind of problem...

Best Regards,
Luciano S. Engel
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