----- Original Message -----
Sent: Thursday, March 28, 2002 6:29
Subject: Large Tank Foundations on
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
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.