Edge Distance for Concrete anchors
Edge Distance for Concrete anchors
(OP)
In Appendix D for shear breakout, I cannot find where ACI defines what a free edge is. ca1 is supposed to be the distance from the anchor to the nearest edge.
I have an anchor that is 100" away from the edge (ca1) and ca2 is 9"... because ca2 is so small it is killing my capacity when using appendix D because Avc/Avco is around 0.4.
However I have read in ACI and PCA notes that if the anchor is not located near a free edge then you don't need to check shear breakout... but they don't define what a free edge is... is it heff? 1.5*heff?
I find it impossible to believe that my 3 anchors will shear off 100" of concrete before they themselves yield in shear... but strictly following ACI App. D that's what I'm getting, the steel shear strength is 200k, the breakout strength is 100k.
I think, if anything, I'd need to check shear breakout parallel to an edge for this configuation
I have an anchor that is 100" away from the edge (ca1) and ca2 is 9"... because ca2 is so small it is killing my capacity when using appendix D because Avc/Avco is around 0.4.
However I have read in ACI and PCA notes that if the anchor is not located near a free edge then you don't need to check shear breakout... but they don't define what a free edge is... is it heff? 1.5*heff?
I find it impossible to believe that my 3 anchors will shear off 100" of concrete before they themselves yield in shear... but strictly following ACI App. D that's what I'm getting, the steel shear strength is 200k, the breakout strength is 100k.
I think, if anything, I'd need to check shear breakout parallel to an edge for this configuation






RE: Edge Distance for Concrete anchors
Like you, I found in PCA Notes that you don't have to check shear breakout if it isn't toward a free edge (however, ACI doesn't explicitly state that. In fact, ACI seems to say it needs to be checked no matter what).
What I have come to conclude the meaning of a free edge is, is just that - a free edge. Not being toward a free edge would be something along the lines of an embed plate in a wall supported by a footing (or another wall that is supported by a footing). There is no way for that to fail in shear breakout because there is no free edge. If you have a very far edge distance, but it is still a free edge, then you can potentially have a shear breakout failure.
I did find a paper by Edwin Burdette and Nikola Zisi that addresses this issue for thin members with large edge distances and they propose an alternate to the App D provisions because they do come across so conservative.
Additionally, it should be noted that if you have a very large ca1 distance, but only 9" for a side edge distance, you should be checking it for ca1=9" and doubling that value to get the shear breakout capacity per D6.2.1(c) (in ACI 318-05).
RE: Edge Distance for Concrete anchors
I agree, this what I'm calling as checking breakout parallel to an edge.
It seems to me that as ca1 tends towards infinity, your capacity actually decreases, I would think ACI would have a limit for ca1 somewhere
RE: Edge Distance for Concrete anchors
For example - An embed plate with 4 - 1" diameter headed studs embedded 8" into a 12" thick slab (or footing) having a ca1 distance of 2500" (which is 208') only has a shear breakout capacity of 215.2K. This does assume 4000 psi cracked concrete with no supplemental reinforcing and a 6" spacing of anchors in both directions, which is certainly a realistic scenario.
If you say the concrete is not cracked, and add supplemental reinforcing to this scenario, you get 322.7k. That still seems low for 208' of edge distance. You need 269" (22.4') of edge distance just to develop the strength of the anchors, which is 106k.
RE: Edge Distance for Concrete anchors
RE: Edge Distance for Concrete anchors
RE: Edge Distance for Concrete anchors
RE: Edge Distance for Concrete anchors
RE: Edge Distance for Concrete anchors
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