ACI318-19 Chp17 - Concrete Breakout in Shear - Edge Distance, Ca1

[struceng.id]

Question for the group:

Lets say for instance you are anchoring into a 2'-6" thick wall with vertical shear and horizontal tension. You're perpendicular edge distance, Ca2, is 10'-0" on each side of the anchor and the edge distance parallel with the shear load, Ca1, is 9'-0". In your opinion, would you consider that concrete breakout in shear is negligible? Of course you would still check shear pryout, but if you were to say that you are far enough from an edge then shear breakout is not applicable? Reference ACI318-19 R17.7.2. Would you agree with this statement?

 

[strucbells]

Yes, I'd expect concrete breakout for shear to NOT control with that much edge distance. Depends on a lot of factors (not sure what scale of loads, diameter of anchors, etc. we are talking here), but even around 2'-0" or so of edge distance is often enough to preclude concrete breakout in shear from controlling.

Depending on the embedment depth, the anchor steel in shear or pryout is far more likely to control. I don't have 318-19, still using 318-14 in my neck of the woods, so I'm not sure what statement you are referring to. Kind of semantics, but it isn't "not applicable", it's that the failure mode won't control compared to the others for that loading, ie the capacity for breakout will far exceed the capacity for pryout or steel strength.

It's easy enough to plug into one of the many free proprietary anchor software programs out there to verify or run a quick hand calc to compare.

 

[struceng.id]

@strucbells - Thank you for you response!

The section I'm referencing in ACI318-19 (R17.7.2) would be section R17.5.2 in ACI318-14. I agree that many other factor would/do apply, but only considering the concrete failure mechanisms, it seems to me that with a far enough edge distance that concrete breakout in shear is negligible and does not control, as you also stated and what the code seems to apply as well.

I wish they were a little more explicit with at what edge distance, Ca1, concrete breakout in shear is negligible; for example if they were to state "if your edge distance in the direction of of shear, Ca1, is greater than or equal to 3*ha (3 times wall/slab thickness) then concrete breakout in shear can be ignored...something to that effect.

Anyway, thanks again for your input; it's nice to hear other peoples thoughts.

 

[strucbells]

No problem. I think the reason they don't is that there are a lot of variables that affect anchor capacity so they probably don't want to be overly prescriptive. What you are describing sounds to me more like a rule of thumb that you would develop yourself, not something that could or should be codified.

Also, with the proliferation of free and easy-to-use anchor design software courtesy of the major manufacturers (Hilti, Simpson, Dewalt, etc.), it isn't that hard or time consuming to just plug in a few numbers and check it yourself quickly.