Concrete breakout due to Pensioning of anchor boly
Concrete breakout due to Pensioning of anchor boly
(OP)
Hi Everybody
The Picture attached shows a post installed anchor bolt being pretension-ed.
Case a - Concrete breakout takes place under the anchor bolt due to pretensioning.
Case b - Concrete breakout doesnt occur since the nuts are in compression and the bolt is in tension.
Can you please explain me which is the best possible case as I am confused.
The Picture attached shows a post installed anchor bolt being pretension-ed.
Case a - Concrete breakout takes place under the anchor bolt due to pretensioning.
Case b - Concrete breakout doesnt occur since the nuts are in compression and the bolt is in tension.
Can you please explain me which is the best possible case as I am confused.






RE: Concrete breakout due to Pensioning of anchor boly
By the way, this doesn't look like a "post installed" anchor to me.......more like a cast-in-place anchor with a nut and washer.
RE: Concrete breakout due to Pensioning of anchor boly
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Concrete breakout due to Pensioning of anchor boly
Imagine if all the concrete below the embedded nut was gone. So you just had a chunk of concrete between the embedded nut and the upper nut.
So if you pulled on the bolt (upward) from above the surface, the whole thing would just lift. Sort of like a "breakout."
But, if all you did was tension the nut, it would simply squeeze the chunk of concrete and nothing would move. The system remains static. No breakout.
RE: Concrete breakout due to Pensioning of anchor boly
A case can be made for it......but there are too many "what ifs" in that to be 100% sure. I spoke with a anchor manufacturer (i.e. headed ones like this) on this subject some years back and he specifically told me that testing they had done had resulted in cracking and/or failure in certain cases. (Especially in cases when: the embedded plate was significantly large (and stiff), the pretension load was very large, you were anchoring in a zone with very little reinforcement, the bolt was small enough, etc, etc. Or a combination thereof.)
As a result, to be on the safe side, I have (since then) taken the breakout approach.
RE: Concrete breakout due to Pensioning of anchor boly
RE: Concrete breakout due to Pensioning of anchor boly
The sketch below shows how I'd sort of see Poisson's ratio leading to a fracture in spite of the fact that there's no net external load. Interestingly, there's another active thread here right now that's related: Link
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Concrete breakout due to Pensioning of anchor boly
That is how I see it too.
Good sketch. It is analogous to bursting forces from anchorage of prestressed tendons.....only difference is: the "edge" in the compression direction is mighty close. There is no reason to believe all the compression forces from the end nut/plate are going to run straight to that bolt head. (It's not "smart" concrete.)
I think stiffness is playing a role here as well (as always). Referencing the testing I mentioned before, the guy mentioned that the break out "cone" (or cracks) in some cases was much smaller (in radius) than it should have been at the surface. I think what is happening there is a concrete "sleeve" (around the bolt) forming when it gets tightened. (Analogous to a bolt in a canister.) Under certain circumstances, the "sleeve" is stiff enough to attract force it can't take. (And not ductile enough to avoid breakout by giving a bit and making the concrete directly under the head take it all.)
RE: Concrete breakout due to Pensioning of anchor boly
Has anyone ever seen a failure of this type?
RE: Concrete breakout due to Pensioning of anchor boly
I don't believe a nice cone-shaped chunk of concrete would come loose after overtightening a similar set-up.
I'd buy that cracks would start to run first in a "horizontal" plane, then either 45° upwards or downwards, initiating from the bottom washer/plate.
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RE: Concrete breakout due to Pensioning of anchor boly
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.