Retrofit of Existing Steel water tank anchorage 2

[CadWizard91]

Hello, so the small firm I'm with in the central Valley of California, has a job to figure out how to anchor an existing 140k gallon Fire Water tank. this water tank is not normal in the fact its sitting on wood (2x4 framing) on course gravel, no concrete foundation. SO how do we secure this thing? I'm looking for ideas, any suggestions would be greatly appreciated.

 

[HTURKAK]

What is the reason for the tank is not normal and the reason for securing ? Overturning due to wind ? pls provide more info with some sketches.

One of the options , RC ring foundation with anchors




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[JStephen]

First thing is to ask, does it REALLY need to be anchored?
Presumably, it was built to an AWWA or NFPA standard, and at the time it was built, did not require anchorage.
So make sure there is actually some substantial reason for it to be anchored, and not because somebody just likes anchors, or didn't understand tank construction or the standard it was built under.
If the design seismic loading is being increased, is freeboard adequate? If not, will lowering the operating level eliminate the need for anchors as well?
I suppose you could hang random steel or concrete items (parking lot bumpers?) on the shell to increase uplift resistance, if it was close to "passing". Of course, with seismic, that also increases the seismic loads, so it would depend on the dimensions as to how that actually worked. I've never actually seen this done for this purpose.
You can use earth anchors but if the intent is to make it comply with a tank standard, the tank standards generally don't allow that.
Otherwise, the idea of excavating below the shell and installing a ringwall would likely be the best.

 

[LittleInch]

Do you have a drawing or can you sketch what you have at the moment?

Is there any overlap between tank and current foundation. Is the wood still in good condition?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IFRs]

Once you have an understanding of the loads and the soil conditions you can choose the method to resist the loads. Screw piles might help.

 

[CadWizard91]

So this tank is used to store water used in the fire suppression system at this site, and the reason for anchoring is because the county that this site is in saw that the tank was just sitting on a gravel pad with no anchors, and said you got to get this anchored down., the soil is not visable without doing some excavation next to the tank, but the soil on this site is varied between good stable hardpan and soft muck., thank you all so much for even taking the time to look at this.

 

[IFRs]

It is unlikely that the county ran any calculations.
JStephen has it right (as usual).
Run seismic stability calculations from AWWA or API and determine if anchors are needed.
Then deal with the "how".

 

[LittleInch]

A riveted tank eh?

That must be ancient.

So a tank which has stood for 50 years now need anchors? That can't be right.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[CadWizard91]

@LITTLEiNCH Believe it or not that tank was built between 2007 and 2009, we don't have the drawings or calcs of this tank, and no one can identify who designed it, not even the client who owns it.
The company who owns the tank is doing other work on this site, and had county inspectors out for that work, and it must have been noticed.

 

[IFRs]

Bolted tanks are quite common, there are many being built today.
Riveted, not so much...

 

[LittleInch]

Ah, sorry, must have had murky glasses on, that is a bolted tank.

But to secure it if the county demand it a bunch of screw anchors spread around the tank?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

Hard to say without more information-
But try to nail down the requirements from the county.
Per the tank codes, depending on the weight, the wind and seismic loads, etc., flat-bottom tanks may be anchored or may be unanchored. They are only anchored if specifically required by the building codes (AWWA, API, NFPA; ASCE 7, IBC, etc). There is not any blanket rule that all tanks have anchor bolts. The anchorage requirements have changed through the years, and generally older tanks are not all rebuilt every time a code is changed.
with the county, maybe they don't care, maybe they just want to know it was properly designed at some point, maybe they want to confirm adequacy per current standards, etc. What they expect could vary a lot.
On the tank itself, try googling "bolted tank manufacturers AWWA" or something like that; there aren't that many of them.
If you can get some good pictures of the ladder, handrail, and vent details, one of these existing manufacturers may be able to recognize it as their tank. You might eventually round up drawings and contract info on it, or maybe not.
You could have a PE registered in the area evaluate it per current codes or standards, and it might or might not require anchorage per those. That would likely require somebody fairly familiar with bolted tank design- perhaps one of those manufacturers cold recommend someone for you.

 

[fel3]

The AWWA standard for bolted steel water storage tanks is D103, "Factory-Coated Bolted Carbon Steel Tanks for Water Storage." The current version is D103-19. Chapter 14 covers seismic design, including the determination of sloshing wave height, which hopefully the tank and its overflow were designed for. The same calculation is also included in AWWA D100, which is for welded steel tanks.

AWWA D-100 and D-103 tanks are supposed to have nameplates that include the manufacturer's name and some basic data about the tank, although I have seen several small, bolted tanks in the last couple of years that didn't have a nameplate, nor any evidence that one was ever attached. Every tank nameplate that I have seen was about 4"x6" and was attached to a U-shaped bracket |_____| that was welded to the shell at the top ends of the U.

I have designed about a dozen and a half water storage tanks over the years, mostly welded (only two bolted) and all in California. I'm in Fresno and have tanks as far south as Los Angeles County and as far north as Lassen County. Could you provide the tank diameter, tank shell height (it appears to be 16 feet), overflow height, and approximate location? I could then estimate the tank freeboard requirement for you if are not familiar with the calculation. Very roughly, if the tank diameter is at least twice the maximum water depth, the tank likely does not require anchors. However, the definitive answer actually depends on the actual tank location, seismic design parameters for that location, soil properties at the site, moon phase, Dow Jones Industrial Average, and the outcome of the upcoming Super Bowl. Most of my tank designs had aspect ratios that far exceeded 2:1, so they were "self anchored." The only tank I ever did that required physical anchorage was 32' tall x 43' in diameter and I only used those dimensions because the storage requirement and postage-stamp-sized City parcel between two houses forced me to.

Regardless, it would have been nice if your tank had been constructed on top of a reinforced concrete ring wall foundation.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[CadWizard91]

thank you to everyone who has given feedback on this tank project, but it looks like it may have ben a waist of time, we where passes on by the owner after they reviewed our proposal, so unfortunately we wont be doing the work. But this info was very helpful and will likely be used for the next tank structure foundation we have to do. (thank you, had a typo )

 

[LittleInch]

Maybe you want to edit your last post....

"and will likely be sued for the next tank structure foundation we have to do"

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.