Seismic Load on Ringwall Foundation

[minorchord2000]

I have a steel storage tank which is required to be anchored because the J factor exceeds the limit for unanchored tanks. I am using the AWWA code. It is 55 feet in diameter, 55 feet high and has an OTM of 14,436 ft-kips. The anchor bolt circle is 55.5 feet in diameter. I want to use a concrete ring wall to support the tank and I want to design the ring wall in a per foot basis. I am using 18 anchor chairs and ASTM F1554 Grade 55 anchors spaced at approximately 10 feet on center. What is the best way to calculate the seismic vertical forces on the ring wall in a per foot basis. W' = the dead weight of the shell + roof dead load reaction on the shell = 0.804 kip/ft or a total of 138.9 kips. The seismic uplift force: Ps = 4*14436/(18*55.5) - 138.9/18 = 50.09 kips net uplift.

Anyone have any suggestions?