Pro Rata Shear friction capacity based on embedment

[CRQUT]

Hi all,

We are connecting a new concrete beam to an existing 500mm thick reinforced wall.

My question is if we are relying on shear friction to provide essentially what is a pinned support to the beam by dowelling into the existing wall - can I pro-rata the shear friction capacity of the dowel based on a reduced embedment? i.e if say an N20 requires 650mm embedment to fully develop, and the bar is embedded 325mm, is the capacity half the fully developed capacity?

Appreciate you comments/ideas.

Cheers
CRQUT

 

[hokie66]

I don't think shear friction theory would allow this, but I don't really know, as I would never use shear friction for this type of connection. The wall is 500 thick, so there is no reason not to chip out some concrete and provide a proper seat.

 

[TXStructural]

ACI 318-11 11.6.8 requires that reinforcement used to develop shear friction be fully developed (to fy) on both sides of the shear plane, by "embedment, hooks, or welding to special devices". Your code may vary from this. I assume you are planning to roughen the old concrete to sufficient amplitude to develop shear friction, but taking it back to the depth of the exiting reinforcement should also be considered.

 

[JAE]

Not sure about your code but ACI's commentary discusses this I think. The answer is no - must fully develop the bars.