Epoxy Anchors

[slickdeals]

Please see attached sketch. It is Saturday morning and all I could do is make sure I hatched the concrete in the sketch.

Assume, I have a pretty big beam (say 4' x' 5'). One the left I have a #3 reinforcing bar developed subject to a tension load. The load transfer happens due to transfer of bond stresses from the bar to concrete.

On the right I have an #3 rebar epoxied into concrete (same embedment as the left). The mechanism of load transfer is again through bond stress transfer from rebar to epoxy to concrete.

In reading literature, I understand that epoxy anchors are subject to concrete tension cone breakout.

Can someone tell if there is a flaw in my understanding. If not, can you please tell me what the difference is between the two. I don't see any difference in the two other than the discontinuity that exists at the interface.

 

[hokie66]

Please attach sketch.

 

[slickdeals]

I told you it was early in the morning

 

[asixth]

You forgot to attach the sketch.

I guess the bar on the left is also going to have the failure of the adhesive to the concrete. I am not trying to promote a company but we use ramset reo502 for post-installing reinforcement. According to their literature, the expoxy can develop a bar over a shorter length than the provisions made in the code for cast in place concrete i.e. no microcracking. But assuming the epoxy bond with the concrete is as good as if not better than in-situ concrete then they will have the same failure plains. Best speak with the engineering division of the adhesive supplier.

 

[slickdeals]

I guess my question did not come across correctly. What is the difference in failure mechanism when you have a rebar completely developed in concrete (cast-in-place) versus an epoxied rebar of the same embedment as the cast-in-place.

Are we saying that no concrete cone breakout needs to be checked then?

 

[rowingengineer]

I believe you can treat both situations the same, normally however you would lap the embedded bar with another bar making the cone breakout not possible. But if you have embedment beyond the length of development as defined by the codes, then I believe by the codes you would not have to check concrete cone failure.

When in doubt, just take the next small step.

 

[slickdeals]

What got me thinking was the statement in Page 181 of the book by Eligehausen

http://books.google.com/books?id=2x...in+concrete#v=onepage&q=bonded anchor&f=false

 

[ChipB]

Slickdeals,

I had a similar situation and ACI's Appedix D wasn't helping me out as I had to go bigger diameter than 1.25" and deeper than 25". I spoke to Hilti about it and they referred me to back calculating ACI's bond strength for the diameter and embedment of the bar and compare it to their bond strength.

They sent me this file which helped my understanding of it. Hope it helps you.

Chip

 

[slickdeals]

I would appreciate your help in understanding the failure mode.

Is it true that a rebar with less embedment length than required will actually fail in tension by pulling out a concrete cone rather than pulling itself out due to inadequate transfer of bond stress?

 

[Ron]

slickdeals...epoxy anchors do not produce a cone failure in concrete in the same manner as a wedge anchor. Shear failure at the epoxy-concrete interface is a common failure mode. Further, long term creep of the epoxy does occur.

 

[slickdeals]

Ron, thats what I thought until I started reading the book "Anchorage in Concrete Construction". Please see the link that I attached in my previous post.

 

[Ron]

slickdeals...see page 21 of your reference. It clearly states that tensile strength of the anchor depends on the bond of the epoxy to the face of the drilled hole...not development of a cone tensile-shear failure.

 

[dik]

The Big Dig problem was tied to the creep that occurs with some fast setting epoxies. Other epoxies, according to Hilti, don't have the same load-deformation behaviour.

Dik

 

[slickdeals]

I realize that the big dig was related to a long term creep effects due to the anchor being subjected to tension loads over a extended period of time.

My case is not sustained tension. However, I am trying to understand behavior.