Epoxy anchor bolt testing

[sbw]

Are there any IBC requirements to test post-installed epoxy anchors in concrete? The anchors were design per ACI 318 App D. If not, any ideas on what to specify for a testing procedure and a test load? I would assume the test load would be based on the required and/or design capacity?

Thanks in advance.

 

[Ron]

Direct tension, safety factor of at least 4.0.

 

[sbw]

Thanks Ron, do you have a source for this value? As I recall, manufacturers would utilize FS in that range on the BOND in the tables that we all used to use but I would think that with field-testing one would have to proceed carefully before using that sort of FS to be sure that the capacity of the threaded rod or concrete doesn't control. My sense is that something more on the order of 1.33 to 1.5 of the design would be appropriate, but this is based on my experience with soil nails and tiebacks.

 

[Ron]

The IBC requires a safety factor of 4 on the ultimate pullout of an epoxy or expansion anchor for design purposes. Testing to 1.33 or 1.5 of the design, might be a bit of overkill on those. I would go to at least the design load, however.

 

[JedClampett]

IMHO, if the anchors are Specially Inspected per the manufacturer's guidelines and IBC Chapter 17, they don't need to be tested.
Or do you want to test them for some reason?

 

[Lion06]

We typically ask for pull tests for anchors in direct tension of anchors subject to high loads. Hilti will come do them for free (only if you're using Hilti anchors, obviously.. Depending on the load and application, we usually ask to have the anchors pulled to 1.5-2 times the design service load.

 

[VoyageofDiscovery]

I am now somewhat leery of epoxy anchors in tension.

Who determines what sample size and acceptable failure level one needs for representative testing.

Whatever anyone says I think there are still issues of creep with regard to epoxy anchors in tension. Boston tunnel is a frightening reminder.

 

[Ron]

VoD....creep is usually only an issue in overhead applications where load is constant. In other applications, load is transient, so creep is not usually an issue.

We specify at least 10 percent of fasteners or a minimum of 3 fasteners for testing purposes. This is consistent with other proof testing requirements for load.

 

[MultiVar]

The Deflection Temperature of some anchoring epoxies is low enough to be a real concern, especially when you consider installations in sun-exposed Sun Belt locales, greenhouse effect in glass-walled stairwells, utility tunnels carrying steam pipes, etc.

Not to indict any particular mfr. (mostly because I can't recall), but I remember looking at a temp. vs. strength chart on one product, and its strength had dropped to 50%(!) at something like 128degF--goodbye Phoenix, AZ!

Picking a brand that meets ICC-ES/AC58 criteria is just a starting point. And even that highly regarded std. tests only up to 110°F.

 

[asixth]

Overhead fixing applications using chemical anchoring should be approached with caution particularly if the anchor is constantly exposed to high tensile loads, chemical epoxies do creep. There was a paper presented at the Australian Structural Engineering Conference in '08 which spoke about the details of the Boston Big Dig Tunnel collapse which as structural engineers, we should be diligent in learning for the failures of the past.

If the anchors experience tension forces from transient loads such as wind loads, then testing the anchor will be less critical. I had an example recently where I thought I had not achieved bond between the epoxy and the concrete from improper installation and specified some load tests on the anchors (Hilti Anchors) which where pulled up to a load which significantly exceeded the design loads. It was later determined that insufficient concrete substrate was allowed for which resulted in the visible cracking on the soffit of the slab. thread507-257487

We had a discussion in our office about how often we should be calling up load tests and it was decided for wind loads where the tension capacity required does not exceed 40kN (9kips) it is not considered a high load and that testing is not required.