If a water tank is not anchored, then should the foundations exeperience any seismic effect? 1

[T2ioTD]

I'm studying an API650 water tank, and this is the first time for me. I'm studying the foundations too, and after finishing doing an excel spreadsheet with all the calculations proposed by API650, I do not know whether (and how) to load the earthquake moment over the foundation, especially as my tank is not anchored to the foundation (which is a raft supported on piles).
- should I convert the moment to a Plus pressure over a semi sphere and a MINUS pressure over the other?
- or should I convert it to a linear force under the shell?

 

[JStephen]

For low seismic loading (J<=0.785), the shell moment (Mrw) will be a line load under the shell, with intensity varying with distance from the neutral axis, as in beam bending.
For high seismic loading (0.785<=J<=1.54), the shell moment will be a line load distributed over just part of the shell circumference, which increases the peak load, which is what E.6.2.2.1 is showing.
In either case, there is an additional moment (Ms minus Mrw) due to the variation of pressures across the tank bottom.
See Table 5.21, which is fairly new, but indicates the bottom moment is a linear variation as well.

 

[r6155]

Be careful with the wind.

Regards