Plain Concrete Shear Keys 2

I would go with interface shear transfer (shear friction) equations.

Phi Vni = cAcv + (Mu)*Pc

c = 0.40 ksi (If placed monolithically)
Acv = Interface shear friction area
Phi = 0.90

Pc would be zero for your first scenario but would have a value for 2nd scenario. See below.

That's from AASHTO but I imagine building code would have something similar. As far as the different failure planes like you have drawn, yes this is possible, but remember the shear component along the sloped failure surface is a transformation of the original vertical load F and will be less. Additionally, there will be a compressive component which aids your capacity checks (Pc)

Mu = 1.4 (If placed monolithically)
Pc = the compressive component of your transformed forces.

This is effectively a corbel design, so you have a tension component to resolve also which will need rebar crossing the joint.

Look up design of concrete corbels and you’ll also find the shear capacity calc.

STrctPono said:

I would go with interface shear transfer (shear friction) equations.

Click to expand...

Thank you for the formula, I was interesting in something like this.

MIStructE_IRE said:

This is effectively a corbel design, so you have a tension component to resolve also which will need rebar crossing the joint.

Click to expand...

For the application I am looking for, I believe there are no rebars. I was looking for gravity dam shear keys:


These shear keys are used for dam contraction joints.

I will prefer to consider the shear key similar to a corbel and way to go..

ACI 318

16.5.2.4 For normalweight concrete, the bracket or corbel
dimensions shall be selected such that Vu/ϕ shall not exceed
the least of (a) through (c):

(a) 0.2fc′bwd

(b) (480 + 0.08fc′)bwd

(c) 1600bwd