Unreinforced Precast Concrete Bearing

[KarlT]

I have a question about unreinforced bearing for hollowcore slabs and precast solid slabs. Typically 3 inches of bearing is detailed without any additional shear friction reinforcing (in the solid slab case). ACI section 16 gives some guidance and sets a minimum of 2 inches of bearing for solid or hollowcore slabs. However, I want to be able to calcuate the capacity of the connection for the 3" of bearing, or if I get less than the 3 inches as detailed I often am faced with defining the minimum allowable bearing.

I usually assume a continuous wedge of concrete with a 70 degree angle to the vertical would fail in shear from the edge of bearing, and then calcuate the shear resistance of the failure surface, using the equation for concrete tensile stength of studs. (phi*Ao*2.8*L*Sqrt(fc')) - using Ao = Area of concrete failure surface.

The forces to consider on the bearing connection are the vertical reaction and also some volume restraint forces (usually assumed to be 20% of the vertical)

Am I doing this correctly? How does everyone else calculate the strength of the above connection?

 

[astructurale]

KarlT,

I was just looking around at some unanswered OLD posts, and also wondered about the answer to your question. Did you ever figure it out or call another engineer for advice on the subject. I'd be interested to know the answer if you ever got one.

astructurale