Load Combination for Hydrostatic Uplift

[JKW05]

I have a 20' deep concrete tank, buried 15' into the ground.
Flood elevation is 3' above the ground (non-coastal A-zone), what load would be used for determining bouyancy for the tank?

ASCE 7-05 2.2 defines H as "load due to lateral earth pressure , ground water pressure or pressure of bulk materials(note the comma)." So maybe the bouyancy force is H.

However the commentary suggests H is due to lateral pressure due to soil and water in soil..". The bouyancy force is not lateral, so maybe it is not H, but actually Fa (flood load). There's a big difference in the load factor (1.6 vs. 1.0)!

What if it is just ground water and not flood water??? Back to H? F (fluid load) doesn't see appropriate...

Any opinions out there?

 

[miecz]

Yes, ignore ASCE7 for buoyancy.

 

[JAE]

I think it is technically Hydrostatic (H) load....see ASCE 7-05, section 3.2.2. Also, the commentary for C2.3.2 seems to imply that F loads are more about tanks and not earth/bouyancy issues. Althought, this commentary also mentions H loads as lateral - with no reference to buoyancy.

 

[kslee1000]

Due to uncertainties, hydrostatic uplift is usually treated as a live load event.

 

[wannabeSE]

JKW05 seems to be referencing F_a (not F) in 2.3.3, 2.4.2 and chapter 5. For non-coastal zone A, the ASD combination 7 becomes 0.6D + W + H + 0.75F_a. Is the sub surface water pressure counted twice, once as groundwater pressure (H) and once as flood load (0.75F_a)?