Joint spacing in rectangular concrete tank

[Screwtape]

I'm designing a rectangular concrete tank (aeration basin) for a wastewater treatement facility. The tank is approximately 100' feet long with circular ends. There is a free-standing wall on the inside of the tank that separates the tank into 2 - 12' wide ditches. The tank will be an above ground tank approximately 12' deep.

I'm familar with the PCA guide for the Design of Rectangular Concrete Tanks (5th Ed.)

I have designed the side walls as cantilevers using the appropriate factors discussed in the ACI codes. The walls are 12" thick with 2 layers of steel. I feel very comfortable with the design.

However, I am still confused regarding the joint layout and spacing. The design guides I've used so far don't provide much information regarding joint spacing for the main walls.

The PCA information I've found generally recommend limiting the joint spacing in the walls to about 20'-0 OC max. I have seen other similar tank wall designs where they push the joint spacing up to 50 or 60'-0...this seems excessive to me.

Generally, what is the recommended spacing or "rule of thumb" for spacing of joints both in the vertical side walls and slab?

 

[flamby]

50 - 60' is not that excessive and 100' is manageable. If you take provisions for thermal loads, you can too avoid the joints altogether. If the tank contains water the thermal loads will come down.

Ciao.

 

[PEStructural]

Do you have a copy of ACI 350? Section 7.12.2.1 addresses this issue. It states that if your movement joints are less than 20 feet apart, use a minimum shrinkage and temperature rho of 0.003. 20 to 30 feet = 0.003, 30 to 40 feet = 0.004, over 40 feet = 0.005.

Hope this helps.

 

[J1D]

You can check ACI 224.3R and Technical Report No. 65 "Expansion Joints in Building" prepared by Federal Construction Council for the space of expansion joints. If a structure can accommendate the expansion/contraction the space can go very high. There is an article (from a AISC publication) talked about jointless bridge deck, in a built bridge, the continuous deck without joints went up to 2,800 ft!

 

[Screwtape]

I don't have a copy of ACI 350 in front of me. Is there anything else needed from Section 7.12.2.1?

 

[JedClampett]

If you mean construction joints, 30 to 40 ft. spacing is pretty standard. I would avoid expansion joints altogether in a tank that size.