Large pipe penetrations in existing tank wall 1

[coaleng]

The project has a large rectangular tank 47 ft X 19 ft with 11 ft high walls that are 15" thick. It also has pilasters every 7ft that are approx 2'-3" wide. the water slurry level is approx. 10 ft. the tank was built in 1983. We need to install a 20" dia pipe near the bottom of the side wall between the pilasters. We plan to core a 24" dia hole approx 2'-9" above the floor. The wall has #8@12 vertical and #6@12 horizontal that we will cut through. The dowels from the footing will also be cut because of the location of the hole. I am not sure how to address the removal of the bar in the existing wall and so close to the bottom. Any thoughts would be appreciated?

 

[JedClampett]

While the tank is empty, you need to core drill the hole and add a reinforcing "ring" around the hole. the ring will consis of an additional thickness (12"?) of concrete with an amount of reinforcing equal what is cut in it in each direction. It also needs to be doweled with epoxy dowels to the wall. To make up the footing dowels, you'll need verticals equal to the amount cut, epoxied into the footing on each side of the hole. I always try to add a little extra just in case. Make sure the bars are developed on either side of the hole.

 

[JLNJ]

Do some analysis and see where the original design was in terms of required vs. provided rebar. Maybe you can justify minimizing the amount of reinforcement required.

 

[SlideRuleEra]

Coaleng - I don't believe you will have to do anything to the tank itself, but there are other actions that will help:

1. Have a testing lab locate the vertical rebar in the tank wall. Position the cored 24" diameter hole to cut the minimum number vertical rebar. I would expect a 15" thick tank wall to have two rebar mats, one with 3", or so, concrete cover from the wall's outer surface, the other with 3" or so, cover from the wall's inner surface. If there are two rebar mats, be sure to have both located by the lab before selecting the core location.

2. Its not clear if the bottom of the cored hole is 2'9" above the tank floor, or if the center of the cored hole is 2'9" above the tank floor. Either way, the dowels from the foundation will still be embedded in the wall at least 1'9".

3. Since the tank is rectangular, NOT circular, there is no hoop stress in the horizontal rebar. I doubt that cutting a couple of horizontal rebar, in a 15" thick wall with fairly low hydrostatic pressure, is a problem.

4. Assuming the 20" pipe that will be connected to the tank has structural strength (say, steel, or ductile iron), I do consider it important to restrain the pipe. This can be done external to the tank and will be important to resist any forces caused by fluid flow. Don't want those forces to resisted by the tank wall - design the pipe restraints do that.

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[coaleng]

I did perform calculations on the wall and the actual shear values were much less than the wall is capable of handling. The pipe insert is a link seal with plate on each side of the wall. I have decided to epoxy plate to span between the pilasters to strengthen the wall in that area in place of the ring of concrete due to the shut down schedule. Thank you all for your insight into this matter. It is very helpful to have others who are experienced to provide comments.