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A Query About Anchor Testing
- Jul 31, 2017 -

Q: We are sending test samples to a laboratory to test hairpin anchors in a 1/4” granite clad system. Do we need to cast the concrete to the stone to test the anchor, or can we just do a pull test on the anchor installed in the granite pieces?

A: The precast hairpin anchor is one anchor which absolutely needs to replicate the in situ configuration for accurate testing. The anchor depends on being encapsulated by the concrete to prevent it from deforming and creating premature disengagement from the stone. If you were to test it without the concrete, you would get dismally low capacities. In fact, without the concrete, you can usually pull the anchor free from the stone by hand! For that matter, even with the concrete cast over the anchor, these are not high capacity anchors. But because the anchor, the preps required in the stone panel, and the labor to install the anchor are all very low cost, it is not a big financial penalty to add more anchors until you get the capacity per panel that is needed. There is significant movement capability in these anchors when loaded, so unlike multiple strap anchors on the edge of a stone, one can have reasonable confidence that multiple precast hairpins are all carrying a similar share of the load.

It is your choice whether you want to cast the concrete yourself or have the lab do it. If you are shipping the test specimens some distance, it may be more economical to have the lab personnel form and cast the concrete backers, rather than paying freight on the weight of the concrete. If you do cast them yourself, do the laboratory a favor and cast them so that you leave opposing ledges on both the stone and concrete. I usually form them with T-shaped separators between specimens. This provide a test specimen with the desired opposing ledges which can be loaded per sketch, which will make it much easier for the lab to create a fixturing for testing.