Seismic force on elevated tank foundation

[Andrewstructure]

I need to calculate the seismic force on an elevated tank foundation (deep concrete caissons/drilled piers).

I am analyzing the 7' diameter x 10' tall hazardous liquid waste tank as a "non-building structure' per ASCE 7-05 chapter 15.

I am assuming that it is rigid and 15.4.2 applies. The actual tank was designed by others.

My problem is that the base shear calculated (eq 15.4-5) is less than that calculated by ASCE chapter 13 (eq 13.3-1), so I am wondering if I made a mistake.

 

[chicopee]

Bednar "handbook of Pressure vessels" has a section on it for elevated vertical tanks, however, his method is not a current one but the results should be closely similar.
What acceleration value did you get to determine the seismic load.

 

[EngineeringAdam]

Can you post your work?

 

[MiketheEngineer]

I believe ASCE and IBC describe these as inverted pendulum structures and have very particular requirements.