Concrete tanks - Vertical Construction Joints in Walls 5

[vincentpa]

When we design concrete tanks walls, we use vertical construction joints at approximate third points. I try to make the joints coincide with the end of the middle horizontal bar that would lap with the corner bar. This reduces the horizontal shrinkage effects. I have problems isolating the middle horizontal bar for smaller tanks. Where do you place vertical construction joints in concrete tanks?

Where the base slab meets the tank wall, we use either a starter wall to accomodate a PVC waterstop or we roughen the surface and don't uses a starter wall or key when we use a Hydrotite waterstop. In both cases we rely on shear friction to transfer the shear from the wall to the base. However, we use keys in the vertical wall construction joints. How do you detail your vertical wall construction joints? Do you use keys? Do you roughen the joint and rely on shear friction? I think roughening the joint on a vertical surface would be too labor intensive. I'm interested in your input.
Thanks,

 

[vincentpa]

I use shear friction at the corners if an unexpected crack should develop. Why? It just feels right. The shear is not inducing compression into the joint like a beam framing into a column. There is no truss/arching effect. The shear is just slicing through the concrete. Maybe it's overkill.

I wouldn't let them put a construction joint at the corners but I am still hesitant about putting the construction joint in the middle of wall vertically. I wouldn't put a construction joint in a beam at midspan. But if I don't put construction joints at the middle of the wall/span, there will be too many pours for a small tank, at least it seems like too many pours. Do you put vertical construction joints in the middle of the span/wall? Do you feel comfortable doing this?

 

[miecz]

For the long, squat tanks I design, the critical location is at the bottom of the long wall. And that is exactly where I have to put a construction joint, and splice my vertical steel. So I always locate a construction joint where the bending moment and shear are highest. In comparison, a vertical joint at the center of the wall would have much less bending and little shear. Even with your tall, narrow tank, the bending at the middle of the wall should be much smaller than at the corners, and the shear should be small. So I wouldn't hesitate to locate a joint there.

 

[ARLORD]

In concrete walls, the rebar resists the tension and the concrete resists the compression. Therefore, it doesn't matter, with regard to maximum moment, where the joint is located.

If the wall is designed vertically, either cantilevered or simply supported, it does not matter if you locate a vertical joint at mid length of the wall.

 

[vincentpa]

One more situation. I have a triple cell tank. A dual cell tank with two 27'x27'x 25' high cells was combined with a 36'x36'x28' high tank. This makes for determining control joints a little difficult. The three cells have intersecting walls at different locations. I would like to pour the "T" sections and corner sections first. However the inside "T" Sections are so close together is really forms a double "T" 8' apart (the "T" are on opposite sides of the wall. Not to mention part of the walls are at different elevations. How would you pour that? Can you form a section like that?