Post-installed anchor bolts 3

[WWTEng]

Concrete was poured without the anchor-rods in place. Now I have to specify some post-installed anchors. I have some frame columns where I intend to use Hilti adhesive anchors. But I also have several other columns which carry vertical load only. Is the use of expansion or sleeve anchors as anchor bolts acceptable?

 

[msquared48]

If you are not close to an edge, yes.

I would use chemical anchors at the edge condition though.

Just follow the load tables, lab tested values for shear and pullout, in the ER Reports.

Mike McCann
MMC Engineering

 

[WWTEng]

Mike,

Thanks. I was also thinking that these anchors don't need to galvanized or SS, since we don't typically do the same for cast-in-place anchor rods.

 

[ztengguy]

Hilti has its Profis design software, it seems to be reliable, at least for what I have done.

 

[jie5]

Are the anchors in tension? i have a similar situation, but the contractor would prefer to post install the anchors. i recently heard some discussions about the us of epoxy anchors in tension as being frowned upon even thought all engineering math and published numbers (hilti) work.

 

[Once20036]

Jie5 - I try to avoid using chemical anchors in locations that will experience long term tensile loads. I've heard this is partially what led to the collapse of a couple ceiling panels in the big dig tunnel a couple years ago.
If it's a short term tensile load - created by a gust of wind for example - I don't see any issue with chemical anchors.

 

[msquared48]

There are a lot of restrictions on these anchors for vibratory loads too, mechanical or chemical.

Mike McCann
MMC Engineering

 

[Lemony]

Hilti now produces most of their adhesive anchor products with an "SD - Strength Design" variation. This variation is intended to accommodate cyclical and tensile loads.

Adhesive anchors are also now covered in ACI-318-11, Appendix D. For best case in tension, adhesive anchors take about a 25% tensile capacity hit compared to cast-in-place (I can't remember the exact value and I don't have the code in front of me).

 

[paddingtongreen]

@Structural20036, The anchors on the "Big Dig" were installed overhead, straight up so the epoxy didn't fill the void, just what should have been expected.

@WWTEng, if there is no compelling reason to use more than one system, I would the same type in all locations. Single mobilization and lower risk of a screw-up, nobody placing a square peg where a round hole should be.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[MKN10]

You can use either post installed mechanical or adhesive anchors. Anchors can be dsigned using ACI 318-11 Appendix D. For post-installed adhesive anchors I do not recommend using the bond values shown in ACI 318 Appendix D Table D.5.5.2 (very conservative), but rather obtaine those values from

http://www.icc-es.org

and do a general search under CSI 03 16 00 Concrete Anchors you will find few reports for different tested anchor systems.

 

[TXStructural]

I would generally not allow adhesive anchors in place of properly installed headed anchor rods. The mechanism of development is different, and the distribution of force in the surrounding concrete will be different. Smooth anchor rods provide very little bond along the length, with the head or nut and washer providing most or all of the resistance. This places the stress deep enough to develop the surrounding longitudinal reinforcement.

A fully bonded adhesive anchor rod will develop as fast as the adhesive and concrete allow, which may mean that it occurs near the surface. Developing into the concrete only assures that the anchor is stuck to the concrete, but tension forces then have to get to the pier reinforcement or the remainder of the footing. This may or may not adversely affect performance in most uses. In order to assure proper connection between anchor rods and pier reinforcement, they should lap sufficiently. Where the anchors are to be pretensioned, I am not sure an adhesive anchor will function correctly.

As an aside, the Big Dig failures were multiple, including use of the wrong adhesive and improper installation. Many adhesives are now specifically rated for overhead and sustained load performance without creep. ACI and CRSI have developed an adhesive anchor installer certification to address the installation failures. During trial testing of experienced installers, most failed the practical exam when large air pockets were found after installed materials were sectioned.

 

[msquared48]

The adhesion issus is exactly why I spec all thread for any post-embedded chamical anchor. The epoxy has be of sufficient quantity to bleed out the top of the hole. Subject to the restrictions of the ER report and with a good installation procedure, inspection and random testing, I have had no problms with these anchors. I have had far more problems with mechanical anchor failures.

Mike McCann
MMC Engineering

 

[RockEngineer]

ACI taught a seminar in Portland, OR about a week ago on designing anchors with most of the info on epoxy anchors. I didn't go but another engineer I work with did. From the data they gave and what they stated about the new Appendix D, the allowed values for epoxy anchors is going way down and can vary by a factor of 2 or more depending on the adhesive manufacturer for the same anchor. The failure mode is not what had been thought either. The new code will require all people who do the special inspections required for epoxy anchors to be specially certified. There is also a 3 step cleaning process for the holes not just blowing the dust out as has normally been done. Using epoxy anchors will get more difficult in high load cases. They seemed to be pushing the mechanical wedge anchors for post installed cases.

 

[msquared48]

Problem... That will not work in edge applications.

Did they address this issue?

Mike McCann
MMC Engineering

 

[SAIL3]

Tx....you brought up some interesting points in how the adhesive anchor transfers loads to surrounding conc....
Unless the test values given for these anchors were carried out in a similar configuration, then it does create alot of doubt....
I personally would hesitate to use adhesive anchors in a constant tension situation...too many variables during instalation that could drastically affect performance...

 

[MKN10]

The question is not whether one feels comfortable or not using adhesive anchor, but rather is it alloed by ACI code or other codes; and the answer is yes (allowed). I attended ACI seminar on adhesive anchors and I disagree with Rockengineer that ACI is pushing for adhesive anchors instead of mechanical anchors. I did not get this impression, rather, the seminar was addressing new provisions in ACI 318-11 and adhesive anchors are new and incorporated for the first time in the code.

With respect of not using adhesive anchors close to edges, I believe the code has an edge modification factor that reduces the calculated strength of the anchor. The difference between adhesive and cast-in headed anchor are the failure modes. Both anchors are checked for anchor strength and concrete breakout. However, cast-in has pullout check, while adhesive is checked for bond failure. Further, it is not recommended to use smooth anchors for adhesive applications (always threaded).

 

[msquared48]

MKN10:

I think you may have misunderstood my comment. I have no problem with chemical anchors in an edge application with the recommended reductions.

Where I do have a problem is using an expansion anchor in an edge condition, regardless of the load seen, due to the fact that the stress on the concrete just, from the initial tightening of the anchor, is enough to cause a lateral cracking and eventual breakout of the anchor.

Mike McCann
MMC Engineering

 

[sandman21]

Simpson Titen HD are a good option for conditions close to an edge.

Some of you need to talk to the companies that produce adhesive systems. The develop of forces into concrete using adhesive systems is the same as that of a HAB. They fail in a cone just like HAB, and before correction factors from ACI and ICC they get high loads, 1/2"dia rod with 2" embed getting 7000# out of 3500-4000psi concrete, consistently. Using a smooth dowel with a nut at the end is not what these companies will tell you to use, adhesive systems do not bond with metal, threads or deformation on rebar are what give you your connection.

 

[hokie66]

sandman,
I hate these acronyms, and have no idea what a HAB is. But if you are telling me that a 1/2" rod embedded 2" will develop 7000#, I've got a bridge to sell. As to what the companies tell you, trust them at your own peril. No chemical anchors in tension for my jobs.

 

[sandman21]

Sorry, Headed anchor bolt.

I have the test reports seen the tests done and repeated both in the lab and in the field. ACI is that much of a penalty. You are free to use anything you want on your jobs.