The rock was carefully chosen to be of "average" hardness and consisted of a large bolder at the base of the Solarium that matched the color and texture of the vertical rock of the cliff. This bolder had obviously broken away some time in the distant past. Later, we will slice off a chunk to be tested for compressive and tensile strengths in the lab. The appearance of the rock was uniform and homogenous to the eye.
To attempt to conduct the test in essentially the same quality and consistancy of rock, the two bolts were placed only a foot apart.
A FIXE hanger bracket was affixed to a 1/2-inch diameter hole the rock with a Dynabolt Gold 1/2-inch x 3.75 inch that was torqued to 40 foot-pounds.
A FIXE 3.5-inch stainless steel 10 mm glue-in "eye bolt" was inserted in a 12 mm diameter hole filled with Hilti HIT-RE 500 2-part "Adhesive Mortar" and allowed to cure for 24 hours at a mean temperature of about 55 degrees F.
The Dynabolt Gold/hanger bracket anchor failed in straight-out tension at 4700 pounds when the head of the bolt was pulled off. At a point into the test where about 1400 pounds was applied and released, the bracket was loosened to the point it could spin freely about the bolt.
The FIXE glue-in started to fail at 3358 pounds at which time it started pulling from its hole. It continued to be pulled for about an inch with a declining force from 3358 down to 1500 pounds at which point it was one inch out of its hole. At this point, with only 2.5 inches of imbedment, and the epoxy bond completely broken, the bolt remained very tight in the hole. It is in this position, shown in the photo, at the base of the Solarium for those wishing to see it. To start it moving again, it will take about 1500 pounds of force, and this will decline as the bolt retracts, if the same pattern occurs.
It is very important to note here that contrary to popular myth, at least in this case, glue-ins do not necessarily fail with a catastrophic pop out, but can gradually pull out against a very tenacious grip.
Granted, at this point, this is only a one-bolt test. But, nothing would indicate that future tests (which will be conducted) will be different (except in the case of 5 inch long FIXE glue-ins, which wiill be tested soon and which should prove to provide a greater resistance to pull out.) Why this happens, I can't say. But, with the HIT RE 500, the glue pocket remained intact. That is to say the 1 mm thick layer of adhesive remained in the hole. The part of the bolt that emerged was completely clean of adhesive. The FIXE glue-in has relatively few dimples for the glue to grab onto. The massive and heavily dimpled Petzl bolt would probably fail at a much higher force. Note that the Petzl is several times the cost of the FIXE and is intended for top anchors, whereas the FIXE 10 mm glue-in is suited for intermediate bolts.
Future testing will be done on FIXE 10 mm s.s. glue-in bolts that are glued into worn 1/2 inch holes from which mechanical bolts have been removed. These will be 5-inch long versions.
The bottom line: And this is preliminary of course, we will be probably replacing Dynabolt Gold/hanger bracket and Powers/hanger bracket hardware with FIXE glue-ins (probably the 5-inch long ones) in those areas where the mechanical bolts receive a lot of stress from falls and sometimes tend to loosen. Also, glue-ins will be installed in very steep angled rock faces, where the pull-out force vectors tend to be high.
Enough for now... something to chew on.
Rick
