car shredder fdn

huangyhg

car shredder fdn
i am designing a pile foundation to support a car shredder mill.  the manufacturer gave dynamic forces and frequencies on the drawings, so i have performed a time history/dynamic analysis in staad to get the foundation natural frequencies and vibration response.
the natural frequency of the foudation is 50% removed from the machine, so i am good there.  but the vibration amplitudes are higher than i would expect.  the nature of the mill is that it is constantly changing the dynamic load based on how big/dense/fast the scrap is coming in.  
has anyone designed one of these, and what guidelines did you use for permissable vibrations?
thanks.
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do you mean 50% higher than operating frequenci(ies)?
waht allowance have you made for damping from surrounding soil?
50% higher in the vertical and 50% lower in the horizontal than the operating frequency (10 hz).  can't seem to get enough stiffness to get 50% higher in the horizontal.  using 5% damping right now, that seems low though, 10 or 20% may be more appropriate i am looking into that.
i am not yet sure that having the vertical natural frequency above and the horizontal below is good practice- it seems like in some direction between the vertical and horizontal the frequncy would match the machine.