single monolithic slab vs individual foundations

[pmover]

any rotators/structural guys ?

for the following equipment:

rpm = 1800 - constant speed
fan wr^2 = 4.0 x motor wr^2
motor weight = 4000#'s
motor hp = 300
cfm = 58000 @ T=328°F
combustion air

existing facility has separate foundations for large rotating equipment (3600 rpm). it is proposed to install the 1800 fans on a single new foundation instead of individual foundations. i welcome discussion as to the advantages and disadvantages of a single slab vs a separate foundation for each fan. i am aware of the reduction in materials and labor for the single slab, but the main considerations are transmition of vibration. with single slab, i see potential problems with bldg structure (new bldg); whereas, a foundation for each fan, the vibrations are limited to equipment foundation and not the new bldg.

welcome the discussion and if further info is needed, please ask. perhaps responders can generalize or provide a good reference (web site).

thanks!
-pmover

 

[fredt]

The fans aren't especially large so you may get away without problems providing the slab is adequate mass. However, if a common foundation is considered I would separate the fan foundation from the building foundation. The fans seem to be handling clean air therefore out of balance problems should be rare which minimises the risks.

I have encountered beat frequencies with more than one fan on a common foundation running at nominally the same speed. You don't mention how many fans.