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# Vibration assessment of lab floor to vc-b - query on use of one-third octaves

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## Vibration assessment of lab floor to vc-b - query on use of one-third octaves

(OP)
I am carrying out a vibration assessment of a concrete floor in a laboratory building. Certain areas of the facility are to achieve the vc-b criteria which is defined in terms of a limiting rms velocity for any given one-third octave band between 0-80Hz. The building is currently under design and so I am using FE to analyse the floor for vibrations due to footfall. My interpretation of the use of one-third octaves is that for each mode between 0-80Hz I should calculate the velocity response. For each one-third octave band I should then calculate the rms velocity by considering the velocity response of all modes that ie within that band. I can then plot a spectra of rms velocity against central frequency over the 0-80Hz range to compare against the allowable velocity.

I am a structural engineer and we do not typically use one-third octave bands so if my interpretation is incorrect then please excuse my ignorance. Any advice on whether the above approach is correct or not would be welcomed.

### RE: Vibration assessment of lab floor to vc-b - query on use of one-third octaves

Tricky. How do you ascertain the damping of each mode?

Anyway once you've done that the energy in the third octave is the sum of the energy in the lines in the narrowband spectrum.

Cheers

Greg Locock

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