earthquake forces resulting from weight of water in tanks

huangyhg

earthquake forces resulting from weight of water in tanks
i am designing a water treatment facility in a velocity-related and acceleration-related seismic zone 1 (in ontario).  the facility is supported entirely on h piles.
in one reference the ontario building code says to include the full weight of tanks and their contents, while in another is says that "when the mass of a tank plus contents is greater than 10% of the supporting floor, the lateral forces shall be determined by rational analysis."
with the weight of the reservoir tanks included, the base shear is extremely large, and will require a greater number of piles (all battered).
it has been brought to my attention that there is a reference possibly by the awwa (d100?) that indicates that the sloshing water actually provides a damping effect.  i am interested in reading this reference, or any other relevant information, so that i can quantify the damping effect (if applicable).
thanks for your help in advance.
canadaeng,
i dont agree that water will any way dampen the earthquake forces. in fact the significant portion of the earthquake forces in any water retaining structure is due to hydrodynamic force of the water itself. what you say in your third para may be bothering you, but looks logical.
get aci 350.3-01 "seismic design of liquid-containing concrete structures and commentary". chapter 4: "earthquake design loads" and chapter 5: "earthquake load distribution". it is to much information to copy it here.
for $50 +/- you will have all answers.
good luck.
also api 650 appendix f covers sloshing effects for tanks.