Post Installed Adhesive Anchor Testing

[bookowski]

I have a condition where we want to install 1/2" adhesive anchors into a slab on metal deck (existing building). The topping slab is 3" thick. All of the Hilti anchors require a minimum overall concrete thickness of 4". The anchor that we are proposing to use has a capacity which appears sufficient for 2.5" embedment. So we could get the required embedment but we don't satisfy the overall concrete thickness that the published values are based on. I spoke to Hilti but they weren't much help and basically said that anything outside of the listed assembly was out of their hands.

We are having pull tests performed on the anchors. Can anyone recommend a source or procedure for test load value and percentage of anchors that could be used to justify or back out a capacity with a certain confidence? Based on nothing other than an initial starting point I was thinking of pulling to 2.0 times ultimate load, so 2 x 1.6 = 3.2 service loads.

 

[Ron]

Your test load is fine. Use 8 to 10 inch diameter pipe ring to set jack on to isolate the anchor and not influence the result by loading the concrete in the failure influence zone.

 

[bookowski]

Thanks Ron. Any advice on quantity of anchors? The project will have about 200 anchors, we were planning to pull test a little over 5%, between 10 to 15, spread over the work area.

Hilti will do the pull test and their jack has feet which I believe are in range of what you described, probably about 10" apart.

 

[Ron]

5 to 10 percent is reasonable and consistent with the frequency of testing for other construction materials.

 

[XR250]

What are the anchors anchoring? Seems like a 3" topping slab may have a larger failure than just anchor pullout depending on the load. A pull test won't reveal this as it only tests for local failures.

 

[bookowski]

Handrail. I would still be checking other failure modes, and reductions for spacing etc. I am just trying to get a sense of whether or not having 3" vs 4" total impacts the listed tension values.

 

[Ron]

bookowski....for handrails, the anchors are a localized condition so I would only be concerned about the thickness at the point of load application. For your application, should be OK.

 

[spats]

I'd be more concerned with making sure the proper installation procedures are followed. I recently had an incident where the holes for post-installed epoxy bolts were not properly cleaned (not cleaned at all), and the bolts were easily removed with a pair of vise grips... for bolts to be loaded in tension. Pretty scary!

 

[SteelPE]

I will second the concerns of spats. Had a project a number of years ago where failure occurred at 1/20 the allowable tensile value due to poor hole cleaning. A few years later we had a site rep from Hilt come onsite to show the contractor how to properly install the anchors. His method was to drill the hole, blow it out with compressed air, inject the epoxy and then insert the bolt. When I asked about cleaning the hole with the wire brush he said" Nobody uses the wire brush". I was appalled, he had no comeback when I stuck the brush in the hole and pulled a ton of dust out after the contractor had used compressed air. I now do everything within my power to never use epoxy anchors again as I don't believe they are ever installed properly.

 

[steellion]

The new Hilti HIT-HY 200 does not require hole cleaning with HIT-Z rods. They also make a drill with a hollow bit and a vacuum to suck out the dust. Basically, they know that most contractors don't clean it properly, so they are trying to make cleaning easier or not required at all.

 

[SAIL3]

yes, everything hinges on proper installation...I usually call for a special inspection..even then not sure that I will get it....

 

[wannabeSE]

Special inspection helps. But, pull testing is where the rubber meets the road. Much of the work I do is on California hospitals, and pull testing adhesive anchors is norm. The current CA building code requires pull testing for hospitals. Previously, OSHPD (building authority for hospitals) had a Code Application Notice (CAN) with specific requirements. See these testing requirements at

http://www.oshpd.ca.gov/fdd/Regulations/CANs/2007/2-1916A.8.pdf.

Like many things for CA hospitals, some may think they are too conservative. (However, they have started allowing torque testing of screw anchors like Simpson Titen HD. Previously, screw anchors also required pull testing)

 

[bigmig]

In situ load testing is covered in the 2009 IBC. Section 17.

http://www2.iccsafe.org/states/newjersey/nj_building/PDFs/NJ_Bldg_Chapter17.pdf

 

[anchorengineer]

Anchor design and testing is a large majority of what I do. Unless you have a special inspector on site while the anchors are being installed the large majority of construction laborers will not clean the hole correctly for an adhesive anchor. Most anchors are installed without the inspector because that requires the dreaded "C" word. Coordination! I always tell my engineering clients that anchors will fail no matter what you design. I always tell them to call for more anchors than what you need for design, try to use mechanical anchors, and call for testing a percentage of your anchors by an independent firm (most testing by anchor manufacturers are done by their salespeople). The best installers are contractors that have had their anchors tested and failed. Most contractors don't believe anchors can fail until they see it happen. The costs of not testing is 10x greater than testing.