Concrete Failure in Tension

[allimuthug]

Hi,
I have a Mass concrete in which a Steel Ribbed rebar is welded to the embedded plate as shown in the Figure attached.
The Rebar is subjected to tension to its full tension capacity, and it is Embedded in concrete to its full development length.
How the rebar would pull out concrete in a cone pattern or a bond failure around the concrete surrounding rebar.
Since concrete is weak in tension and no reinforcement is there in the mass concrete, please explain the failure in detail and why.

 

[allimuthug]

Sorry I forgot to attach pne more picture

 

[KootK]

If you're embedded Ld, the bond failure should't occur. Comcrete breakout is also unlikely but may be possible if the out of plane concrete dimension is small or the rebar is tightly spaced in the out of plane direction. Some additional info in that regard would be helpful. Even though not explicitly applicable to CIP rebar, ACI 318 APP D provisions can be used to evaluate breakout. At least, that's what I've been doing.

Is there rebar in the concrete? If so, that may open up some options for bypassing concrete breakout. The relative dominance of either the axial load or the moment is inmporrant as well. If one anchor would be in a compression zone while the other is in tension, that fact can sometimes be exploited to advantage.

Lastly, consider group effects in addition to single anchor capacity.

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.

 

[Ron]

Sort of looks like a homework problem, but I'll bite anyway.....

I'm concerned that your loading is right to the tensile limit of your rebar with no safety factor or margin.

Bond failure and breakout will depend on the actual concrete strength and mix parameters. Assuming good concrete mix design and particularly a good paste/aggregate ratio, bond failure is less likely than breakout.

As KootK mentioned, the spacing of the loaded rebar and its distance from and free edge of the concrete can have a significant effect on the breakout strength. If the failure cones overlap or intersect the free edge, the over-all breakout capacity will be lowered.

 

[allimuthug]

I want to know the failure of concrete, It will not break as a cone right but however if concrete fails in shear then it has to form cone,
Or it should be bond failure. There is no reinforcement in the concrete.

 

[allimuthug]

Hi,
If it was breakout failure please describe or show in picture in what pattern breakout happens.

 

[KootK]

Either a come as you've shown it or one involving all of the rebar. Frankly, the nature of the come with unheaded anchors is a matter of some debate.

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.

 

[allimuthug]

Finally this is what I am looking for, and dont have a firm book or codal reference and Guidelines supporting that. If somebody somebody share there opinion that would be nice.

 

[Structurecrg]

If the bar is fully developed and loaded to its yield load, then the bar(s) will yield adjacent to the plate. The weld at the back of the plate should be sized to meet/exceed the bar yield load too.

 

[allimuthug]

All are fine, Please explain me about the concrete breakout

 

[KootK]

Have you thoroughly reviewed ACI appendix D? Most of what is available is in there. Consider reviewing that and coming back with more specific questions. Concrete breakout is a complex and expansive topic to cover in an Internet thread, especiallly when we don't even know the out of the page geometry of your situation. Is this related to your footing extension thread?

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.

 

[WARose]

[blue](KootK)[/blue]
Even though not explicitly applicable to CIP rebar, ACI 318 APP D provisions can be used to evaluate breakout. At least, that's what I've been doing.

I've done the same thing........but I've wondered if it is really applicable because we are not talking a headed anchor. But I've assumed that the ribs on the rebars are essentially doing the job.......BUT that would mean it would (likely) take more than a few ribs to get the job done (which would affect "cone" geometry).

Something I need to think about/run numbers on the next time I have to do it.

 

[TLHS]

Somewhere I've seen something that says testing shows similar behavior for bonded and headed anchors. I'm suspecting it was research relating to epoxy anchors.

On top of the cone breakout, I'd do a full section tension capacity check, if this is truly mass concrete without reinforcement.

 

[KootK]

Yeah, I consider the post install anchor provisions to be close enough. If I remember correctly, you get a 1.5 db mini cone failure where the rebar enters the concrete. After that, you seem to be able to mobilize the same breakout cone that you would with a headed anchor.

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.