Cast-in Place Bars versus Epoxied
Cast-in Place Bars versus Epoxied
(OP)
I have always wondered why there is such a large development length with rebar cast into fresh concrete versus a short one with rebar drilled and epoxied (Hilti and Powers) into existing concrete. After all, how can 1/16" of epoxy around the perimeter of the bar make such a huge difference in values without the surrounding concrete being affected?
I know the epoxy folks use safety factors on the order of 4 and the concrete folks use safety factors on the order of 1.7, but this would skew the differences the other way instead of making epoxy lengths so short.
Can someone help me see what I am missing here?
I know the epoxy folks use safety factors on the order of 4 and the concrete folks use safety factors on the order of 1.7, but this would skew the differences the other way instead of making epoxy lengths so short.
Can someone help me see what I am missing here?






RE: Cast-in Place Bars versus Epoxied
RE: Cast-in Place Bars versus Epoxied
Imagine that the critical failure surface is a cylinder around the bar.
For a cast in bar this cylinder is at the outside of the bars ribs. For an epoxied bar it is the outside surface of the drilled hole.
As the drilled hole is larger than the bar diameter, then the failure surface is larger and therefore it is stronger.
Another factor that comes in is that the epoxy engages the surrounding concrete along the whole surface, whereas the rebar ribs give more localised stresses.
RE: Cast-in Place Bars versus Epoxied
Their response was that the values listed in their catalog are based on pull tests of rebars epoxied into concrete not on mathimatical formulas.
It is also the reason that one of the footnotes in their HVA Capsules table reads 'HILTI DOES NOT RECOMMEND THE USE OF ALTERNATE EMBEDMENTS OTHER THAN THOSE TESTED AND LISTED ABOVE.' They do not have adequate mathimatical formulas to explain the behavior adequately, they just know it happens. There is no proper way to interpolate values between the embedment depths shown in their catalog.
RE: Cast-in Place Bars versus Epoxied
I can see where the localized stresses produced by the bar ribs versus the even stresses produced by the epoxy bonded to the concrete might make a big difference. However, the forces still have to eventually bleed into the concrete. And what about the difference in the factors of safety?
It still seems as if the criteria that ACI is using is quite a bit different than what the epoxy folks are using. Unfortunately, because of the propriatary nature of the epoxy products, we may never fully understand this without taking them at their word.
My question is not so much for the epoxy folks as it is for ACI. Are we way too conservative on our development lengths?
RE: Cast-in Place Bars versus Epoxied
RE: Cast-in Place Bars versus Epoxied
RE: Cast-in Place Bars versus Epoxied
RE: Cast-in Place Bars versus Epoxied
http://
RE: Cast-in Place Bars versus Epoxied
Yogi Anand, D.Eng, P.E.
Energy Efficient Building Network LLC
ANAND Enterprises LLC
http://www.energyefficientbuild.com
RE: Cast-in Place Bars versus Epoxied
DaveAtkins
RE: Cast-in Place Bars versus Epoxied
RE: Cast-in Place Bars versus Epoxied