Epoxy anchors vs. standard hook anchor

[ars001]

I've been asked by the contractor if he can use epoxy anchors vs. the standard anchor on a project. Is there any reason why this cannot be done. Obviously I've checked all loads and everything works fine. Thanks

 

[Lion06]

I can't think of a reason why. Are you in a seismic region? This may have an impact on it.

 

[SlideRuleEra]

Allowable loads on chemical anchors have to be reduced if the manufacture's specified "edge distance" is not met. Perimeter anchor bolts may have a problem with this requirement - be sure to consider this factor in your calcs.

http://www.SlideRuleEra.net

 

[dgkhan]

Last monday I had a seminar in my office by hilti corporation(Toronto, Canada). This was basically an effort to restore deisgn engineers trust on adhesive anchors in light of Big dig boston ceiling collapse.
By the way there are so many if and buts like temp range, cleaning of hole, air voids in epoxy pumped in etc. In USA it is mandatory to have inspection for these anchors. I would rather always favour traditional hooks embeded while pouring concrete.

 

[Lion06]

I spoke with a Hilti Rep at the last NCSEA conferenceand she said they were working on a program to "certify" individuals to install epoxy anchors.
This certification would be with the individual, not the company, and the intallation would ned to be performed by the individual (not someone else with the certified person on site or even supervising).
This seems like a nice step forward.
As mentioned above, a lot of things can go wrong with installation (namely improper - or no- cleaning of the hole).

 

[DarthSoilsGuy]

you probaly figured this but since other people use this forum for answers to their own questions and this is fairly common, it should be said:

You lose inherent quality control items by adding the possibility of inadequate bond due to improper hole cleaning and inadequate bond due to air voids between the rod and the concrete. With Standard Hooks, seeing is believing. This is addressed by many engineers by requiring pull tests on the epoxyied rod, however.

 

[ars001]

Thanks for all your help.

I'm located in MN so there isn't a need to design for seismic. I don't have any lateral or uplift loads associated with my anchors.

I've also made sure all of my edge distances and spacing are in check with the manufacturers recomendations.

Thanks again

 

[JackTrades]

I had a contractor install epoxy grouted anchors in concrete tie beams in lieu of the specified cast-in-place. In many places the drill either cut the rebar or the bit was deflected by it and the anchors ended up installed at a skew.

I won't allow them where there is rebar congestion.

 

[KCRatnayake]

It's easy to to use post-installed anchors in place of cast-in-situ anchors under some circumstances.

Re. dynamic loading; most adhesive anchors do not have approval to use under dynamic loading conditions. As I remember Hilti's HVU and HVZ systems have these approvals.

 

[boffintech]

"Is there any reason why this cannot be done."

Yes, there are two reasons why this can not be done.

1) Contractors notoriously can not get this right. At two different jobs within just this past week I was able to pull out, with one bare hand, allegedly epoxied in dowels.

a) I found holes drilled 2" deep for # 6 bars
b) I found holes drilled 2" deep for # 5 bars
c) I found holes not BRUSHED out prior to placement of epoxy. Blowing the hole out with that big construction air compressor that blows a quart of oil per day WILL NOT WORK. The holes have to be BRUSHED out and blown out with clean (oil/water free) air.
d) I found cases where the mixing tube was not placed on epoxy gun so that in the hole the epoxy was black on one side white on other side.
e) I found places where #4 bars were hammered into 1/2" dia. holes and the epoxy was squeezed out on the pile of dust that was still around the top of the hole!

All that just in one week!

2) The placement of rebar by drilling/epoxy according to chpt 17 is a required continuous inspection. The owner/client will need to be informed that his testing/inspection budget is going to take a huge hit as the special inspector will be spending a LOT of time monitoring the correct placement/installation of these dowels.

If you allow this you may want to consider having a pre-con meeting to review the process of installation and inspection with the inspector and the contractor.

 

[shin25]

We use epoxy adhesive more or less on a regular basis. They tend to provide expected results if all manufacturer's recommended steps are followed. Infact, very recently, we installed few adhesive anchors and had them tested for pull out. All the results were above the listed values in the catalog. According to me, Hilti HIT RE-500 is one of the best adhesives available in the market for this application.

 

[Atomic25]

ars001, you've given literally none of the details required to provide a reasonable response. Where are you using these anchors?? If there's no shear or uplift loads, then why do you say you've checked all loads and everything works fine?? What exactly did you check? What does the PE say?

PS, no matter where you are, you have seismic loads. You cant just neglect them entirely.

 

[hokie66]

Boffintech's experience is mine also. Workmanship is everything with adhesive anchors, and very few workers on the job would even know how to install them, much less care. And most engineers don't know either (Big Dig), they just specify and hope for the best. Sorry to be so cynical, but I absolutely hate adhesive anchors.

 

[Grizzman]

I've got no issue with epoxy anchors, as long as there is no uplift and no overturning. But then why not just use wedge anchors. They both work equally well as shear pins.

 

[DRC1]

I have used chemical anchors many times, mostly for temporary loads. They do need to be properly installed, but in the right applications do work well. I have found the engineering support at Hilti to be excellent. I would suggest you give them a call to dicuss your application. They may even be able to have a tech rep come out to make sure they are being installed properly. Yeah, there are guys out there that do not do a good job installing these, and they are a little fussy, but on the other hand, I have seen guys screw up hook bar dowels. You can't specify quality.

 

[allisch]

Obviously Hilti and Powers fasteners have products that can do this. You will need to follow the installation guides to get the design capacity. Did you guys see the one on the ICC Code Chat with the photos of the "drilled anchor" which was only 2" long and caulked into the 2x sill plate, but not embedded into the foundation?

Keep that in mind

 

[civilperson]

Hooked anchors are contraindicated compared to headed anchors, (about 24% of capacity if the diameters are similar). Epoxy anchors requirements have been well discussed in previous posts. I recommend never use hook anchors in tension situations.

 

[ironmon]

From a "design" standpoint Epoxy or Adhesive anchors can be used in place of cast in place anchors. Contractors errors can occur in either application. The main one with cast in place bolts is location and vertical alignment. How many times do you have to cut cast in place anchors because they are not in the right spot?
What do you do?
Generally replace them with chemical anchors.

One other thing to consider is the set time.

The RE 500 has a very long cure time, like 24 hours.
Cannot be disturbed during cure time!

The HY 150 cures in like 5 minutes.
Bolts must ge set in adhesive filled holes immediately!

This should be considered for the application.

 

[baw1]

One additional point to all the others mentioned. Epoxy does not perform well in fire or high heat conditions. Depending on application, this may be an important consideration.

 

[JLNJ]

Be careful of bolts in direct tension!