Thru-Bolt Concrete Anchor Shear Breakout Capacity
Thru-Bolt Concrete Anchor Shear Breakout Capacity
(OP)
Let's say I have 3" of 5000 psi concrete (3" topper of a 6" thick deck), such that le=da=3". I want to put plates on both sides and bolt through the concrete with 3/4" A36 rod to connect the plates. The closest edge distance is 20.5" (ca1). I am using ACI 318-14. Avco (17.5.2.1) is very large because of the large edge distance and Avc is very small because of the 3" thickness. So my Avc/Avco = 0.098. Vb (17.5.2.2) is equal to 52.5 kip [9*sqrt(f`c)*ca1^1.5 -OR- 7*(le/da)^0.2*sqrt(da)*sqrt(f`c)*ca1^1.5]. My Vcb ends up being 5.12 kip. This seems pretty small for such a large edge distance. Am I missing something? Am I shooting myself in the foot by only using the continuous 3" thickness of the topper? There is WWM in the topper, should I be including that somehow?
It is a little crude since it is preliminary, but below is my math.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
It is a little crude since it is preliminary, but below is my math.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant






RE: Thru-Bolt Concrete Anchor Shear Breakout Capacity
So now my question is, how do you check the shear capacity of a through-bolt?
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Thru-Bolt Concrete Anchor Shear Breakout Capacity
unless the shear force is 'small'
best regards
Klaus
RE: Thru-Bolt Concrete Anchor Shear Breakout Capacity
We are tieing a construction elevator to the building's floor. We have no control over the concrete, but we do know what it is. I have about 10.72 kip of resultant shear (9.42 kip towards 20.5" edge, 5.13 kip parallel to edge) and my client's typical anchorage is (2) 3/4" A36 rods through sandwiched plates. Tension is only 1.7 kip. Threaded rods are 6.5" apart and the parallel-to-edge force has a line of action through both bolts. AISC bolt shear analysis tells me A36 rods are good for 11.5 kip total [5.75 kip per rod], so I don't have enough shear capacity remaining to pretension the bolts to gain frictional resistance. This leaves me with relying on the bolts to bear on the concrete. I can check the concrete shear capacity (conservatively assumed unreinforced) as shown below.
I know concrete is LRFD, so the below is a quick check of my ASD load vs. an ASD allowable concrete shear using the known AISC LRFD:ASD relationship between omega and phi.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant