Q: We need to test some hairpin anchors for a granite-clad precast project. Can we just test the anchors in the stone, or do we need the concrete on the backs?
A: Normally, we test anchors engaged in the stone, without simulating any of the other backup structure. The precast hairpin is different, in that the anchor needs to the precast to hold its shape. Without the concrete encapsulating the anchor, you can actually pull the hairpin out by hand. Once the concrete has cured, the anchor can no longer be squeezed together and now the mode of failure will be two small failure cones pulled from the stone. There isn’t really a practical way to model this behavior without the concrete. And when testing in shear, you again need to cast the concrete to accurately model the behavior of the anchor. Talk to your test lab and ask what they would charge you to cast the concrete to the stone specimens in their lab. If you are shipping the test specimens some distance, the cost of the lab doing the concrete may be less that the cost of your personnel doing it plus the increased freight costs. Regardless of who is casting the concrete, remember to mark a line on the face of the stone specimens that indicates what direction the anchor is oriented. The lab tech will need this to ensure that the shear tests are done in the correct direction, since the anchor will no longer be visible after the concrete is placed.
Q: I have customer who wants a 50” wide island top on a 24” cabinet. There will be a 24” overhang on one side, although the stone will be supported by corbels. Can this be done, or will the whole thing just fall over?
A: Yes, it can be done, but only if the cabinet frame is strong enough and is securely anchored to the floor. This is the concern of the cabinet supplier. The stone can just sit carefree on top of the corbels.