Tank Anchorage Ratio "J" Formula 1

[movasra]

Hi folks,

Does anybody know if Ge, used in Wa fomula (E.6.2.1.1-1b)is supposed to be the fluid density instead of the specific gravity?

If Ge used as specific gravity, then the units don't match up in Wa formula and you almost won't find any API 12 tank which is stable.

Any comments would be appreciated.

 

[IFRs]

Ge is defined in E.2.2 as Effective Specific Gravity - the product specific gravity with Av factored in. As with many equations in API 650, the numerical constant outside the expression carries the units that makes the equation work.

 

[JStephen]

In general, small tanks are okay with low or moderate seismic loadings, and more often fail on wind overturning checks. If you're finding that almost no API-12 tank is stable, either you're in a higher seismic zone or have something off in the calculations somewhere.

 

[IFRs]

I do not remember API 12F and 12B specifications including stability checks for seismic or wind.

 

[movasra]

JStephen,

I am designing 3 tank foundations in California. So, yes it is a high seismic zone.

I have checked my spreadsheet calculations with a few engineers from Fluor and some other companies. Seems like nobody is sure about this equation. They all agree that the units are off though.

IFRs,

I am not sure if constants can carry the units. I believe the units are supposed to match on both sides of equations in any case. You are right about API 12B, it does not cover the seismic evalution. But, looking at ASCE 07-section 15.7.8.2, I was in the impression that API 12B tanks do not require seismic calculations unless required by building officials.

Thanks for your time and comment

 

[JStephen]

In California, I would expect a lot of the API 12-series tanks to require anchorage, especially the taller ones.

Those standards do not include seismic or wind overturning checks, but you could apply the same methods from API-650. The 12-series standards are intended for oilfield use, and if you're using the tanks anywhere else, you'd probably want to put a little more thought into them.

 

[Duwe6]

12F tanks are not very substantial. Look hard at the local membrane stresses on the lowest shell course that will be generated by an earthquake. The anchor chairs may rupture the tank without significant reinforcement of the shell.

First thought would be a 1st shell course 3/8" thick and only 2-ft tall. Would spread the stress pretty well.