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Load Combination for Hydrostatic Uplift

Load Combination for Hydrostatic Uplift

Load Combination for Hydrostatic Uplift

(OP)
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?  



 

RE: Load Combination for Hydrostatic Uplift

Yes, ignore ASCE7 for buoyancy.

RE: Load Combination for Hydrostatic Uplift

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.

 

RE: Load Combination for Hydrostatic Uplift

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

RE: Load Combination for Hydrostatic Uplift

JKW05 seems to be referencing Fa (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 + 0.75Fa. Is the sub surface water pressure counted twice, once as groundwater pressure (H) and once as flood load (0.75Fa)?

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