Expansion Joints in Rectangular Concrete Tanks

[vincentpa]

I am designing rectangular concrete tanks and I am unsure as to where to put expansion joints. The round clarifier is easy enough. I am just putting expansion joints every 25' or 30'. ACI 350 and PCA Design of Rectangular tanks do not give guidance on expansion joints is rectangular tanks. The tanks need to be watertight.

One tank is 54'x32'x25' high. There are three cells. Two equal adjacent cells are 27'x27'. The remaining cell is 54'x5'. Where do I place the expansion joint in the long wall, at the intersection? Is one necessary if I put a lot of temp steel.

I have another tank that is 24'x20'x20' high. There are two cells. One cell is 20'x20' and the other is 4'x20'. Any recommendations on expansion joints?

 

[civilperson]

No joints are necessary if the tanks are free standing. If attached to rigid structures, the differential expansion of liquid filled tank vs. ambient air temperature structure may cause some stresses. These may be designed for by either increasing the strength of the components or allowing the movement to occur(expansion joints).

 

[jike]

I would think that you would not want any "expansion joints" in the walls of a circular tank. This would cause you not to be able to use the hoop (tension) capacity of the reinforcing. You would, however, need "construction joints".

The rectangular tanks don't need any expansion joints. I also recommend that be isolated (independent)from other structure.

 

[vincentpa]

Sorry,
I meant contraction joints not expansion joints. There was a disconnect from my brain to my fingers. No contraction joints in rectangular tanks?

 

[JedClampett]

If by contraction joints you mean joints with no reinforcing through them, then no.

 

[vincentpa]

By contraction joints, I mean weakened plane to produce a shrinkage crack where I want it. I will run reinforcement through the joint for hoop stresses.

 

[miecz]

ACI 350 Article 7.12.2.1 provides minimum temperature/shrinkage reinforcement where movement joints are not provided. For a 54 foot straight wall, the (Grade 60) reinforcement ratio is 0.005.

 

[rholder98]

ACI 350.4R-04 devotes a chapter to joints in concrete. It says, "Where used, contraction joints should be located at intervals not exceeding 30 ft, unless additional reinforcement is provided as required in ACI 350-01, Section 7.12." It then goes on to discuss two different types of contraction joints, full and partial. When I place them, I just make it correspond to a natural construction joint location, subject to the aforementioned criteria.

 

[vincentpa]

Thanks to everyone for your help!

 

[DTGT2002]

Are you aware of what construction methods will be used for forming the tank?

Input from the potential formwork contractor might be useful in determining the desired construction joints for practical wall construction. It might also be the difference between waterstop and lots of other details being needed or omitted.

Good luck!

Daniel Toon