Dowels for Contraction Joints in Concrete Walls
Dowels for Contraction Joints in Concrete Walls
(OP)
I am planning to use smooth round dowel bars for shear (out-of-plane) transfer purposes at vertical contraction joints in cast-in-place concrete walls. Basically, I am making the horizontal reinforcing discontinuous at the joints (which include reveals/chamfers on both wall faces to provide a weakened plane) and adding the smooth dowels at the center of the wall thickness. In designing the dowels I referenced ACI 224.3R-95 (Joints in Concrete Construction). This document was reapproved in 2013. In Chapter 8 (Walls), the document states the following: "PCA (1975) recommends using dowel bars that provide 0.015 times the cross-sectional area of the wall and extending 30 bar diameters each side of the joint as shown in Fig. 8.4". The PCA (1975) reference is "Basic Concrete Construction Practices". I do not have this reference. My question concerns the 0.015 factor. Taking a 12" thick wall and providing dowel bars at 24" on center results in a required dowel bar area equal to 4.32 square inches. Say what?? Clearly, this cannot be correct. Has anyone run into this before? I am guessing the correct factor is 0.0015 (i.e., a "0" was dropped from the published document). Or is the requirement to provide large bars (#9) at a very close spacing (6") for a 12" thick wall? I find that very hard to believe.






RE: Dowels for Contraction Joints in Concrete Walls
But I'm not a believer in any smooth dowels at contraction (or expansion) joints. If correctly designed, the walls shouldn't move different from each other. And if they do move, those dowels aren't going to help. They seem like a good idea, but I just can't justify them.
RE: Dowels for Contraction Joints in Concrete Walls
Dowels that aren't bonded act in shear, but very quickly act in bending as the concrete around them crushes or the joint opens. In this case, the dowel needs to be stiff enough to resist bending. That said, I am not sure why one would need 30 bar diameters embedment for an unbonded dowel.
Bonded dowels require full development on both sides in order to engage shear friction (resistance using aggregate interlock across the joint), which creates a much better resistance to displacement than dowels alone.
As to As of dowels, and spacing, I don't think I would go to 24" spacing, since the resulting load per dowel could be substantial, depending upon the purpose of the dowels.
RE: Dowels for Contraction Joints in Concrete Walls
RE: Dowels for Contraction Joints in Concrete Walls