Contraction Joints in Concrete Retaining Wall

[CSFlanagan]

I am designing a foundation for a building to be built at dock height, about 4 feet. The foundation will be a cantilevered wall supporting a metal building. Total wall height varies only 4 feet to 6 feet. Once the perimeter wall is constructed, the inside will be backfilled with #57 stone, then a 6" thick reinforced concrete slab will be built on the stone and tied back into the retaining wall. (This makes it become more like a basement wall design after the fill is placed.)
I want to control cracking in the 70' long wall. Some have suggested increasing the temperature steel, others say the wall must have a joint at 40' maximum.
One suggested detail is to place 3/4" chamfer strips on the inside and outside vertical face of the stem, and cut every other horizontal bar to create a weakened plane.
Any other suggestions or ideas on how the joint should be constructed?

 

[JAE]

Many exterior cantilever retaining walls use the 3/4" chamfer strips @ 25 feet o.c. and expansion joints at 100 ft.

With a building, you have a heated space adjacent to the wall so some tempering of the temperature swings is possible, maybe allowing longer spaces.

If you have building columns at discreet locations along the wall, then the joints probably would be better placed away from the columns.

 

[Ron]

Agree with JAE...just put the chamfer strips in and let it crack. Put the strips in at 15 instead of 25 feet...I doubt you'll see any significant cracking other than in the strips.

 

[hokie66]

I think increasing the crack control steel is worthwhile, especially at the top and bottom of the wall. If the wall is only 4 to 6 ft high, the cracks will be at closer spacings. Like a sidewalk, it is best to try to control the cracks by making panels with an aspect ratio of not more than about 2:1.

 

[CSFlanagan]

JAE: I do have columns and the columns will bear on in-wall pilasters formed integrally with the retaining wall. We typically place the contraction joints midway +/- of the columns. Do you terminate any or all of the temperature steel at the joints?

Hokie66: Using a 2:1 aspect ration as in a floor slab might be a bit conservative, but would certainly minimize, if not outright eliminate, wall cracking due to shrinkage.

I believe I will go with the 25' joint spacing and use 1/2% temperature steel. Thanks for the input!

 

[JAE]

I usually don't terminate bars but many engineers choose to cut 1/2 of the bars at the joint. I think either is fine.

I question whether cutting the bars helps because the concrete must crack before the bars really engage anyway and the chamfer strips are your attempt to control where it will crack.