Epoxy Anchoring Clarifications

Hi All,

I'm working on a project and I need to design a rebar/dowel embedment using epoxy anchoring. I'm using the Hilti manual and I have a few questions I was hoping you could answer.

1) When designing the embedment do you design for the pull-out and shear calculated OR do you embed for the yield strength??

I ask because ACI 318 states that shear-friction must be completely developed or you cannot count on ANY load carrying. As I understand it, this dowel would be in shear-friction would it not? I'm guessing that you design embedment for yield and for pull-out and shear then use the larger embedment!? How do you handle this?

2) Edge Distance: Do you have to factor the edge distance for the perpendicular edge that is in the opposite direction of the shear load?

It seems to me that the dowel could "kick-out" the concrete behind if the distance was small enough. I imagine that you must consider this but the Hilit manual was not clear.

Thanks.

 

[Ron]

For epoxy dowels, failure occurs at the concrete/epoxy interface, typically not as a cone failure that you would get with a wedge-type anchor. Spacing on epoxy anchors is less critical than for wedge anchors, so edge "blow-out" is usually not a problem with epoxy anchors.

Pullout depends upon bond strength. Developing full yield usually requires significant depth of embedment. This is usually not necessary.

Keep in mind, allowable loads given in Hilti and other tables have a factor of safety of at least 4.

 

What would be a good way to check if it will "blow-out"??

To control cracks in the tension side of the support I'm going to have to place these bars closer to the edge than I orignally wanted.

I know it will break going out from the bar at a one to one until it reaches the edge...but what is the shear strength of the concrete along that failure plane. A quick look at ACI and I didn't see it.

I like sleeping at night so I would prefer to check this to make sure. All comments appreciated.

 

[winny]

For Tension I usually compute the Pull-out resistance, Concrete Cone Resistance,& Steel Tensile Resistance and compare them. The smallest value would be the Design Tensile Resistance of the connection system.

For Shear I usually compute the Concret Edge Design Resistance against the Steel Shear Resistance and use the smaller value as the Design Shear Resistance of the connection system.

I suggest you communicate with a Hilti Technical Engineer in your area or visit Hilti's website

http://www.hilti.com

. I beleive you can download the anchor program free from their site. I suppose you are using Hilti Fastening Technology Manual 2001 issue.

 

How do you go about calculating the Concrete Edge Resistence?? What about the Concrete Cone Resistence??

I understand what is happening with the failure modes, I just haven't had to run these types of calculations before. I'm curious what factors one should consider.

Hilti's information is helpful but I only get so much comfort reading numbers from charts and applying factors. I would like to run a calculation to put my mind at ease a bit.

I really want to check the shear on the "backside" of the dowel, like I discussed before. You have to have some amount of concrete to encase the dowel in the opposite dirction of the shear force. I just want to make sure that I have enough concrete there!!

I can picture in my head the "back" of the dowel popping out of the wall...YIKES!! No I don't have any FEM or computer analysis to use.

All comments appreciated!!

 

[JedClampett]

If you're worried about loading epoxy anchors with specific edge distances or spacings, go to the ICBO reports (i.e. ER-4016 for Hilti HIT C-100, ER-5193 for Hilti HIT HY-150, etc.). They're on-line (

http://www.icbo.org/ICBO_ES/es-search.html).

Even though they're seem kind of scrawny, they have extensive design information on edge distances, allowable loads, reduction factors and the like. Not only that, but they're acceptable to code officials. They also have warnings, installation instructions and other useful data. I for one don't even use the Technical Guides, but instead go right to the report.

 

Thanks!!

These have exactly what I was looking for!!