Post-installed anchor bolts
Post-installed anchor bolts
(OP)
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?






RE: Post-installed anchor bolts
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
RE: Post-installed anchor bolts
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.
RE: Post-installed anchor bolts
RE: Post-installed anchor bolts
RE: Post-installed anchor bolts
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.
RE: Post-installed anchor bolts
Mike McCann
MMC Engineering
RE: Post-installed anchor bolts
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).
RE: Post-installed anchor bolts
@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.
RE: Post-installed anchor bolts
RE: Post-installed anchor bolts
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.
RE: Post-installed anchor bolts
Mike McCann
MMC Engineering
RE: Post-installed anchor bolts
RE: Post-installed anchor bolts
Did they address this issue?
Mike McCann
MMC Engineering
RE: Post-installed anchor bolts
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...
RE: Post-installed anchor bolts
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).
RE: Post-installed anchor bolts
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
RE: Post-installed anchor bolts
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.
RE: Post-installed anchor bolts
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.
RE: Post-installed anchor bolts
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.
RE: Post-installed anchor bolts
This is similar to masonry. Look at the numbers- a utility grade 2X4 has a higher compression strength (in psi) than masonry. This is primarily due to the human factor in laying block (or for post-installed anchors).
RE: Post-installed anchor bolts
For your concerns re: edge distances & mechanical anchors, I agree with regard to expansion anchors, but there are mechanical "undercut" anchors. It's a more complicated installation but they essentially drill out a pocket at the end and behave more similarly to a cast in place anchor.
Check out Hilti HDAs for an example. I believe you can get better capacities out of one of these than any of the epoxies based on the same edge distance, geometry, etc.
Of course, they're more expensive and harder to install than epoxy.
RE: Post-installed anchor bolts