RRC Archives

As some of you know, we have been testing the strength of bolted hanger brackets on RRG rock for the past two years. Today, we conducted the first side-by-side test of a Dynabolt Gold expansion bolt and a FIXE 3.5-inch stainless steel glue-in "eye bolt." For those interested, here are the results:

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

Rick, I'm playing a little devil's advocate, so don't take offense. I think all the work you've been doing is great, but here's my question. How easy is it to replace glue-in bolts? My belief is that because you can rap from glue-ins versus normal hangers, do you think that this will become a problem with people lowering off of crux bolts when they can't send rather than rapping from them. Being able to rap from anywhere on route without leaving gear was a big selling point for using glue-ins in Rumney, NH, but there has become a problem of people being lowered rather than rapping. Do you forsee this as a problem in Muir and if so, are these bolts easy to replace without drilling new holes? I know you will say no one should lower off of a single bolt, but I think in reality, this will happen quite frequently.

The glue-ins failed at 3358 pounds, but the dynabolt golds failed at 4700 pounds. So, are you saying that the glue-ins are weaker than the dynabolt golds?

weber wrote: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.Rick

That is a LOT of bolts to be replaced...

J - failure seems to be a loose term here. The bolt moved at a lower force, but it didn't fail. This may be a good thing -- bolts that have received excessive force are easily noticed, yet they don't catastrophically (sp?) fail.

Rick, I think the reason you're seeing what you are on the glue-ins is that a bit of rock is bonded to the bolt via the epoxy. As the bolt moves, this rock/epoxy either has to carve its way thru the bolt hole (similar to how a 5 piece bolt resists pulling) or shear off. I suspect that a combination of both is happening. Do you know what the tensile strength of the epoxy alone is?

Haas: You make a very good point. I am guessing that most climbers will not lower off glue-ins, and we will tell them NOT to do so, but rather use a bail biner. But, only time will tell. The important fact is that if it proves that glue-ins have less tendancy to loosen - and preliminarily this does seem to be the case- then they pose less risk, and for that reason alone will be used where deemed necessary in MV.

As for replacement, of course, they are much harder to replace than expansion bolts. I have some ideas that I will share later.

J-Rock:

No, not so many bolts. Only problem areas or as I said, very steep angled-down placements. As for the mechanical bolts already in place, we will replace these over a long period of time as it becomes necessary. The glue-ins will probably be able to be glued into the old bolt holes.

Dhoyne:

Good points. The epoxy "sleeve" seems to really squeeze the bolt. The bolt comes out very clean.

I don't have the mechanical specs on the epoxy here at hand at this time. I am also very interested in comparing the compressive strength of the epoxy as compared to the compressive strength of the rock for this reason: In a typical bolt placement (horizontal) the constant loading downward due to falling climbers tends to crush the rock at the bottom outside of the hole, due to the low compressive strength of the rock. Over time, a mechanical bolt can loosen. And we have seen holes on routes were many falls are taken being enlarged in the downward direction in this manner. If the compressive strength of the epoxy is greater than that of the rock, the situation could be greatly improved. Or at the very least, we aren't creating an even higher chance that the epoxy will also be crushed due to downward forces being exerted.

Rick

J-Rock wrote:The glue-ins failed at 3358 pounds, but the dynabolt golds failed at 4700 pounds. So, are you saying that the glue-ins are weaker than the dynabolt golds?

Jared,

"Weaker" is a sticky term. Remember an important point. In either case, a human body falling that could exert this much force is a very dead and yucky looking piece of meat.

If the glue-in shows absolutely no signs of loosening before 3350 pounds or so, and the mechanical bolt starts its loosening process from whipper #1, and goes down hill from there, then the glue-in is far better in the long run.

Rick

i understand none of this, but i'm very glad you guys do. thanks much for all the time and effort

Rick,

Great work on the testing and it appears as though the results found will be very useful in future applications.

I am assuming from what I've read is that the force on the bolt was applied in line with the bolt and not at some angle. Has there been any testing done on the shear capacity of the actual bolts? The force applied across the bolt necessary to shear it may be less than the amount necessary to pull out?

I don't know if I'm clearly explaining my thoughts but hopefully you understand where I'm heading.

If the Dynabolt Gold/hanger bracket assembly fails at 4,700 lbs on straight out tension, does it shear at a lower value when applied at an angle of 60 degrees off center?

Geoff

It sounds like you are doing static testing to the point of bolt failure. Wouldn't it be more realistic to do dynamic testing where you are stressing the bolt multiple times (with a smaller load) rather than a single large load of force? Maybe the glue-in resists a single load of force better than the Dynabolt Gold but maybe this is not true of multiple falls. You must be certain that your mode of testing is accurate for the activity if you anticipate a large cost and time element associated with replacement of the hardware already installed.

Just something to think about.

Some more internet info.
http://climbargolis.com/Glue-inBoltDesign.htm
http://www.safeclimbing.org/education/adhesivebolts.htm