Circular Concrete Tanks Expansion Issues
Circular Concrete Tanks Expansion Issues
(OP)
I'm currently using the PCA manual to analyze the capacity of an existing tank per ACI 350. The client would like to expand the capacity of the current tank as much as is possible by adding height to the walls. My plan is to determine the actual capacity of the current tank and give them a reasonable estimate on how much higher they can make the walls.
One issue I'm curious about is the effect of introducing a horizontal joint at the height of the original tank. Typically, these tanks have bars at a fairly close spacing and the new bars would need to be drilled and grouted into the existing tank. Does anyone see this being an issue? I also expect that a waterstop would need to be installed at this location as well.
Are there other concerns that I should consider with a tank expansion of this type?
One issue I'm curious about is the effect of introducing a horizontal joint at the height of the original tank. Typically, these tanks have bars at a fairly close spacing and the new bars would need to be drilled and grouted into the existing tank. Does anyone see this being an issue? I also expect that a waterstop would need to be installed at this location as well.
Are there other concerns that I should consider with a tank expansion of this type?






RE: Circular Concrete Tanks Expansion Issues
When they do this with steel tanks they lift the whole thing and add to the bottom.
RE: Circular Concrete Tanks Expansion Issues
How high is the present tank? Wall Th? Wall extra height?
I'd consider it, but think about the second wall (if floor and foundation are ok) as a second poured wall sitting on the first, but with a short inner section inside the lower wall and a sealing gasket/membrane between the two. Leakage or movement of the lower wall vs the upper wall would be stopped by the gasket, and the added circumferential reinforcement just mentioned can be accommodated in the thicker joint section.
RE: Circular Concrete Tanks Expansion Issues
But with your solution, Jed's concern about the hoop capacity at the bottom of the existing tank would still be applicable. The ring tension is directly proportional to the depth of water.
RE: Circular Concrete Tanks Expansion Issues
I've done plenty of clamshell tanks like you're considering but only in buried structures. I'd be very hesitant to do an above ground tank in the fashion you're describing with any joints. I wouldn't balk at it completely but I'd be very careful about pushing the envelope.
Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com
RE: Circular Concrete Tanks Expansion Issues
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Circular Concrete Tanks Expansion Issues
Note! I haven't done the math, haven't seen the original poster's dimensions or reserve strength.
RE: Circular Concrete Tanks Expansion Issues
If the solution becomes much more complicated than simply adding wall height then the client will likely scrap the tank. My impression is they don't want to sink much money into the expansion. Lifting the tank would be out of the question. Tension cables may still be in play.
KootK, I was also concerned about epoxying two mats of steel in a 10-inch wall without sacrificing water-tightness (induced cracking and spalling). Another concern is I'm not sure the tank even satisfies the basic requirement per ACI 350 of 12-inch walls for heights greater than or equal to 10-ft. Granted that is for new tanks (or at least those designed after 2006) but would they essentially have to bring this tank "up to code"?
Thanks again!
RE: Circular Concrete Tanks Expansion Issues
I'm afraid that I can't help with that one. Hopefully someone more knowledgeable about the industry can enlighten us.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Circular Concrete Tanks Expansion Issues
There are (used to be) tank manufacturers that would wrap an existing concrete with prestressing strand then shoot gunnite, but I believe that will be too expensive.
Maybe not related, but if you're storing sludge, will you have to add containment? Is a new tank the better way to go?
RE: Circular Concrete Tanks Expansion Issues
I'd add a steel tee and (5/16 in) plate bent to a 29 foot diameter, all welded together, to the top. Attach with epoxy or expansion anchors, probably stainless. I can think of several ways to seal it, none of which are perfect. One of which is to smash a gasket into the concrete at the concrete tee interface. Than caulk with a good quality (two part polyurethane) caulk in the space. Coat the interior with a good epoxy coating.
This should be pretty cheap and easy to install.
RE: Circular Concrete Tanks Expansion Issues
One other related question, does anyone know how exactly to use Table A-20, Design Aid for Bending Moment Reinforcing, in the PCA manual? I understand the instructions shown on the table but not sure what the column header is supposed to represent for each column (numbers ranging from .000 to .009) and why you would pick one column over another?
Thanks!
RE: Circular Concrete Tanks Expansion Issues
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You can use some part of the strength in the existing wall, and you don't have the same type of construction joint. You have an exposed joint, but you can put something in there to block part of it out and then seal it properly.
RE: Circular Concrete Tanks Expansion Issues
RE: Circular Concrete Tanks Expansion Issues