Circular Tank Control Joints
Circular Tank Control Joints
(OP)
Our office has designed a 75' diameter circular concrete tank to ACI 350-06. In the mat foundation slab we have called for a circular control joint with a diameter of 32'. (8) radial control joints start at this circular joint and extend to the perimeter of the foundation. The contractor is saying it is difficult to install a waterstop on a radius. Has anyone out there run into this issue? How else would you arrange control joints in a circular slab/tank?






RE: Circular Tank Control Joints
One option would be to change from PVC waterstop to flexible hydrophilic waterstop, such as these Sika products: Link
Another option that may minimize design changes is to replace the 32' circular control joint with a 32' regular octagon control joint with any type waterstop, including PVC.
An added benefit - an octagon is easier to form accurately than a circle.
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RE: Circular Tank Control Joints
RE: Circular Tank Control Joints
That was one option the contractor suggested, but I'm hesitant to pursue it. The control joint spacing has been reduced to prevent cracking for water-tight structures. The reinforcement ratio determines the joint spacing per ACI 350-06 Table 7.12.2.1.
RE: Circular Tank Control Joints
RE: Circular Tank Control Joints
I don't doubt that the original engineer probably added more control joints than were necessary as an "insurance plan" against cracking.
I think increasing the reinforcement ratio would be a good solution if we were still in the design phase, but the rebar shop drawings have already come through and were approved about 2 months ago. Changing the reinforcement this late in the game would likely cause a delay and a change order.
RE: Circular Tank Control Joints
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RE: Circular Tank Control Joints
Joints are cracks, just regular ones.
RE: Circular Tank Control Joints
Joints are cracks, but they do have waterstops in them. Also, if you wait between pours, you can cast the next pour against a pre-shrunk section and reduce the size of the cracks.
RE: Circular Tank Control Joints
If your reinforcing steel is at least 0.5% of the area of concrete, you don't need any control joints.
DaveAtkins
RE: Circular Tank Control Joints
Also have seen prestress water tank slabs with thickened edges, 5" center thickness. They used post-tensioning at 5 ft. oc. to induce about 250 psi compression in slab to prevent cracks opening up.
RE: Circular Tank Control Joints
All construction joints (reinforcing through the joint), not control joints.