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StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 6635
Experience:  Structural Engineer
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I'm building a rectangular concrete water tank 14' 6' wide

Customer Question

I'm building a rectangular concrete water tank 14' long 6' wide and 5' tall. I plan to make the walls out of reinforced 6" cinder block. My question is will the walls withstand the water pressure?
Submitted: 2 months ago.
Category: Structural Engineering
Expert:  StructuralEng replied 2 months ago.
I can help
Customer: replied 2 months ago.
Ok. Help me.
Expert:  StructuralEng replied 2 months ago.
It should be 8" - 10" block and properly reinforced - for bending along the length and also the connections at the corners. Both of these are very important
Customer: replied 2 months ago.
The blocks will be overlaping with cement and rebar dropped between. I don't see any chance of bending along the length since the concrete would break not bend.. If there were vertical reinforcement in the center of the 14' length (a triangle shaped wall at 90 degrees) would that be enough to keep the wall from pushing over and would I still need to be 8 to 10" in width?
Expert:  StructuralEng replied 2 months ago.

The will bend horizontally. It will behave like a tension ring. The block will crack and, once it does, the rebar will be engaged in tension. It will bend in between the ends and it will have global tension.

You will still need 8" or 10" block (it will depend on the amount of reinforcing put in). I can offer this complete design as an additional service, if you're interested.

Customer: replied 2 months ago.
How much pressure can the wall take before it will collapse or break in the center and how much pressure is the water creating on the center. if there was a tractor inside the container, how many pounds of force would it take to push over the wall, and how much pressure can the wall withstand?.
Expert:  StructuralEng replied 2 months ago.

You're not thinking of this correctly. You're thinking of a single wall being pushed over. That is not the behavior that will occur. The wall will span horizontally to the two other walls, not vertically as a cantilever.

Customer: replied 2 months ago.
Three sides will have support from back fill leaving one wall 14' long and 5' tall. There is no chance it is going to rip apart at the corners. My only concern is that the 14' wall will be pushed apart or over from the pressure of the water. The only way to know the answer is to know how much pressure a 6" or 8" concrete rebar reinforced wall 14' long and 5' tall can withstand with water pushing against it and how mush pressure the water is able to exert against the wall as a whole.
Expert:  StructuralEng replied 2 months ago.

The wall alone can resist almost no pressure as a simple wall the way you describe it. It would need a properly sized footing to resist the overturning.

Additionally, think of this, or actually try it. Blow up a balloon partially. This is a rough approximation of your condition. Now put half of the balloon into a semicircular wall so that one half of the balloon can't move. Now continue to fill the balloon. To say that the behavior of the balloon changed is not correct. The entire balloon still expands, putting the entire surface of the balloon into uniform tension. Your situation is very similar. The water imparts an equal pressure on every single surface it touches, whether it's restrained by soil from the outside or not.

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