Car Shredder Fdn

[SeanMD]

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.

 

[sdz]

Do you mean 50% higher than operating frequenci(ies)?
Waht allowance have you made for damping from surrounding soil?

 

[SeanMD]

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.