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Large Tank Foundations on Drilled Piers

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Title: Large Tank Foundations on Drilled Piers

I have been tasked with designing the foundations for (4) - 60,000 gal tank to hold milk. The tank is 76'-8" tall and is in seismic zone 1 , soil profile Sc. The wind loads are based upon 80 mph zone C. Tanks are 12'-6" in diameter. Geotechnical engineer recommended using 30' deep drilled piers.

I have preliminarily designed the foundations using 6 - 24" diameter drilled piers evenly spaced around the circumference of the tank. I located the DP's on the tank circumference to allow the OT moment to be located directly above the DP's - i.e., the foundation slab does not have to transfer the large OT moments to the DP's. I calculated the pressure on the foundation pad due to the dead load of the tank (561 kips - using tank DL=36 kips & SG for milk of 1.05) and designed a 1' wide beam strip to carry this load to the DP's. Then I checked a 1' wide beam strip spanning between adjacent DP's and applied the DL pressure and distributed the OT force across this shorter beam. I came up with a 3'-0' thick cap with #8 @10" OCEW.

 As far as shear goes, I did a punching shear check, but the areas are not as clear cut as, say a building column. I plan to put a top and bottom mat of steel in the mat.

This seems to me to be a reasonable approach, however, if anyone is aware of any methodologies for designing such foundations, I would appreciate learning of them. Or of any reference material that may provide a design methodology for this type of foundation system. Any suggestions/comments would be welcomed. Thanks for help.

Jonathan Meyer, P.E.
Webber/Smith Associates, Inc
Email: jmeyer(--nospam--at)
URL: http:\\