Smooth Dowels at Retaining Wall Joint

[marinaman]

I've got a site retaining wall that I've designed. It varies in height from 4' tall to about 12' tall. The wall is nearly 200' in length.

I know that I need vertical joints in the wall at 20' or so on center in order to deal with shrinkage of the concrete once it is poured.

I have drawn a detail for detailing how the vertical wall joint is to be built. I am having a beveled piece of wood placed on the inside face and outside face of the wall, inside the form, in order to create a vertical groove in the wall, where we want joints.

I also want to provide smooth dowels across each joint to help prohibit differential movement between each segment of wall.

Looking at ACI224, they reference PCA from 1975, and say that the recommendation for the amount of steel required as a dowel is for 0.015 of the cross sectional area of the concrete. In other words, if I have a 16" thick wall, the area of steel dowel needed by this method would be:

(16" wall thickness) x (12" of wall height) x (0.015) = 2.9 square inches/foot of wall height

Which to me, seems VERY excessive.

I was thinking more along the lines of a 3/4" diameter smooth dowel at 18" o.c. Just by feel, I can't imagine that that amount of dowel steel across the joint wouldn't be enough.

What dowel size and spacing do you guys use across a joint like this?

 

[hokie66]

I think your thinking is about right. Not familiar with the reference you gave, but it must be referring to a vastly different requirement.

 

[TDIengineer]

Match your horizontal bar spacing.

I had a concrete contractor show me how he used a PVC sleeve with the rebar slid in, on one side of the joint only.

Worked real slick, definitely allowed for shrinkage, and it kept the wall true. A #4 will do it for your wall size. Smooth rebar kind of bonds still.. with a thick wall PVC sleeve, it definitely slides. You can do this type of joint on a non-shear wall like a site wall your describing.

I would recommend tightening your control joints some. maybe 15'-0" max.. or a 1:1 ratio of the wall height. I know that there are larger recommendations than this out there, but from my experience, a nice tight control joint spacing not only looks good, but guarantees a clean wall. (unless the concrete mix is just bad and too wet.). Call for a 3/4" chamfer on each side of that vertical joint, I like that look.

#4 dowel x 24" @ 18", 12" long PVC sleeve on one side.