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Re: Large Tank Foundations on Drilled Piers

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Title: Large Tank Foundations on Drilled Piers
Make sure your 10" thick slab, if it is accepting the anchor bolts, is thick enough to hold the tension from the uplift.
Santa Clara, CA
----- Original Message -----
Sent: Thursday, March 28, 2002 6:29 AM
Subject: 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:\\