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Epoxy anchor bolt testing

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Epoxy anchor bolt testing

Epoxy anchor bolt testing

sbw

(Civil/Environmental)

(OP)

21 Jan 10 20:30

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.

Replies continue below

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RE: Epoxy anchor bolt testing

Ron

(Structural)

21 Jan 10 23:00

Direct tension, safety factor of at least 4.0.

RE: Epoxy anchor bolt testing

sbw

(Civil/Environmental)

(OP)

21 Jan 10 23:16

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.

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RE: Epoxy anchor bolt testing

Ron

(Structural)

22 Jan 10 06:30

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.

RE: Epoxy anchor bolt testing

JedClampett

(Structural)

22 Jan 10 09:22

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?

RE: Epoxy anchor bolt testing

Lion06

(Structural)

22 Jan 10 10:55

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.   

RE: Epoxy anchor bolt testing

VoyageofDiscovery

(Structural)

13 Feb 10 17:35

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.

RE: Epoxy anchor bolt testing

Ron

(Structural)

13 Feb 10 17:41

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.

RE: Epoxy anchor bolt testing

MultiVar

(Computer)

19 Feb 10 14:41

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.   

RE: Epoxy anchor bolt testing

asixth

(Structural)

20 Feb 10 18:44

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.

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.

 

• http://files.engineering.com/getfile.aspx?folder=a-b348-4ad5-a0ae-53

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-: Baseplate Punching Through Slab 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.

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News

To add to a set of already great answers I would like to add two points: Glued bolts and weird old bolts.

There are generally two types of bolts used presently: Mechanical and glued bolts. Mechanical bolts are mostly sleeve anchors: When tightening the nut the first time a cone is driven under the sleeve which is thus forced against the wall of the borehole. This type of anchor is hard to test. In general it is very reliable but has one failure mode: If tightened too much, the holding strength decreases a lot, but usually not enough to just pull it out by hand when testing. So you just have to hope the route establisher did a good job (generally true, but accidents have happened).

Glued bolts have a smaller diameter than the borehole and are held in place by glue. This should be more corrosion resistant as it is waterproof, still the glue and bolt need to be corrosion resistant. One prominent failure mode of glued bolts can be easily tested. If the borehole was not properly cleaned before gluing, you can turn the bolt. Just insert your quickdraw and use the biner to try to turn the bolt. Still in frequented areas, I hardly ever do this. For a toprope anchor it is certainly not a bad idea to check this.

The second point are exotic/antique anchors. There are norms today, but you will still find gear that is not normed. Especially on old or alpine routes. The oldest kind are "Stift/Stich"-anchors (in German, do not now whether there is an English equivalent). These are the earliest hand drilled anchors. They are rectangular and quite fin, usually not very deep. If you find one consider yourself lucky and you may use it for commemoration, but they probably wont hold a fall. Apparently "Kronenbohrhaken" are the socalled spits @VladimirF mentioned in his answer. These came up in the 70s and could hold a fall, thus permitting a huge increase in sport climbing level. However they were hand drilled and had the drilling bit at the top of the bolt itself, so it is hardened steel. This is bad for corrosion and stability, so today they should not be used anymore. You will know one when you see it (rusted, antique looking design).

In the alps (I do not know about other regions) you can often find so called "Muniring". These can be huge as on the photo below or any other size. However they are not normed and you have no idea what kind of bolt is in the rock. I was once shown a removed "Muniring" of about the size of the one below that had a 6mm diameter about 2-3cm long bolt attached to it. So these are not reliable. There is a plethora of other sometimes homemade anchors. You should never use those as your main protection - well, if it is your only protection, which does happen, you might as well :)

Image source: http://alpen.sac-cas.ch/fileadmin/data/flippingbook/SAC_Jahrbuch__de/_03_d/files/assets/seo/page45.html

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