Concrete Tank w/o Joints-ACI 350 2

[ARLORD]

Anyone with large water retaining concrete tank design experience, is it good practice to have 30ft high walls, between 150 and 300 ft long without movement joints. According to ACI 350, without movement joints the reinforcement ratio should be at least 0.005. If this requirement is met, is it OK to omit movement joints for water retaining structures. What are your thoughts.

 

[JedClampett]

hokie66, that's why they are a pain and tend to leak.

 

[miecz]

Looks like I may soon be designing an above ground tank longer than 200 ft. I've never done a tank so large and never needed to use an expansion joint. If the expansion joint extends through the mat (and walls), what keeps the two tank sections from drifting apart, friction with the soil?

 

[JedClampett]

Yes. Since the forcing load is the water pressure, you know it has to be there when the lateral pressure is a maximum. It doesn't take much footing length to develop enough gravity force to counteract that force.
We like to use a 1.5 FS for this case. Don't count on the soil pressure on the back of the wall.

 

[fa2070]

In the joint in fa2070's post pictured above, how would you get concrete under that waterstop? The detail might work for walls, but not for slabs.

Vibration. Split form. Requires careful workmanship. See attached photo.
You can download the slide decks from a waterstop workshop here:

http://www.wi.nrcs.usda.gov/technical/eng_Waterstop.asp

Pay attention to Waterstop Formwork (PPT; 5234 KB). All the other PPTs and PDFs are also interesting.

Another waterstop vendor with technical info:

http://www.greenstreak.com/specs_resources.asp?LitID=1

 

[hokie66]

"Requires careful workmanship". Unless I am mistaken, that doesn't exist in concrete construction.

 

[miecz]

hokie66

The joint in fa2070's post is not to scale so it exaggerates the problem. These waterstops are usually 6 to 9 inches wide, while the mat is often 27 inches thick or more. The picture makes it look like the waterstop extends 15 inches into each slab.

 

[hokie66]

miecz,

I agree with that, but I think some folks do attempt what is shown to scale in fa2070's post.

 

[miecz]

Hokie66

By the way, I incorporated your suggestion (I think it was yours) of concentrating horizontal temperature reinforcing at the bottom of a tank wall, and it eliminated cracks at that location. Great idea.

 

[hokie66]

miecz,

And a great result. Yes, that is a line I try to preach as often as I get the chance. Just an example of trying to think like the material...the cracks seem to form here...I think there is a need for more bars here.