Tank Foundation "Ring Beam" question.

[waytsh]

I have a circular tank base slab which is being supported on piles. I was running into some punching shear problems with the piles under the wall so I needed to thicken up an area around the perimeter. Essentially a continuous drop panel. I was wondering because of the way it is configured whether some would consider it a "ring beam" and thus require the reinforcing to be inside closed stirrups. I am dropping my bottom mat down in the thickened area. The thickening is a pretty considerable 16". I would greatly appreciate any feedback on this and any reference to some reinforcing details. I need to decide quickly how I want to proceed.

Thanks,

waytsh

 

[JedClampett]

The reason a tank needs a ring beam is due to the lateral component of the water (liquid) pressure on the soil. Since your tank is supported on piles, there is no soil pressure and the ring beam reinforcing is not needed.

 

[JStephen]

Waytsh, I'm not aware of anything that specifically requires the reinforcing to be inside closed stirrups if it IS a ring beam, although that's the way it's typically detailed.

 

[connect2]

The requirement for 'enclosed stirrups' would only have to do with torsion on the ring beam, which you could have depending upon the product in the tank ie the wall load of the tank, and the geometry of the ring beam supporting the tank wall and the piles supporting the ring beam ????.

 

[JStephen]

Thanks, connect2, I was thinking of a normal ringwall used under a tank, which is usually treated as axisymmetric, so no torsion. That would be different on the piers or piles, though.

 

[waytsh]

Thanks all for the replies.

The piles are located directly under the wall so there would be minimal torsion from gravity loads especially considering that the thickened perimeter is still part of the main slab. What I would have would be a high moment in the last span of my continuous slab which I have designed the mat steel to handle. In light of this fact would you all still recommend closed stirrups? The slab is quite large so even a small change like adding stirrups will have a huge cost impact.

Thanks again for the input,

waytsh

 

[connect2]

hmmm,
dont know the radius of your ring beam nor the spacing of the piles, nor the vertical wall load on the ring beam, but it is concievable to have a curved beam spanning between your piles ... try 'Circularly Curved Beams Transversely Loaded, Panayiotis J. Spropoulus, Jrnl of ACI, October 1963', do you think the floor which is connected to the ring beam may act as a spandrel element?