Glue-in Bolt Test Results at Muir

[tomdarch]

Oy vey! In an ideal world, this hijacking would be moved to the original 'VW' thread.

But it does raise an imporant point: cyclic or repeated loading. As much as I understand it, there is a threshold of force for steel, at least, below which repeated loading just doesn't matter. (You start talking about it taking millions or more repetitions to get any weakening or failure, where with bolts we're talking about thousands of repetitions making a difference)

What might be the worst case scenario for a given bolt? Let's say that it's the most popular route in the world, people climb it non-stop 10 hours a day and fall an average of once every 10 minutes over the course of the day. That's 60 falls a day, 365 days a year = ~22k falls a year. This is a fairly absurd scenario outside of a gym, but it does mean that a bolt could potentially see falls numbering in the hundreds of thousands over the course of 10 or 15 years.

But realisticaly, you need to plan on something in the range of tens of thousands of falls on a bolt during it's lifetime. Most will never see this many, but a few will.

So, between the bolt, potentially the glue, and the rock, these all need to withstand some tens of thousands of loadings. I wouldn't be as confident as Jim that cyclic loading isn't a concern.

Does anyone know if Hilti has done much cyclic testing on their 'glues'? There's a bunch of different stuff out on the web, but a lot of it is either seismic (high loads, few cycles) or bridge (relatively low loads, many, many cycles) related.

[dhoyne]

In soft and friable rock this would, over time, result in elongation of the holes as well as undue amounts of stress on the bolts themselves.

It's not the bolts failing that I'm really worried about in this particular instance. The bolts are probably stronger than the surrounding rock. The cyclic loading on the rock will damage it each and every fall... eventually opening a fracture which will lead to a failure of the bolt/rock system.

I'm very anxious to get some rock plugs to throw onto my Tinius Olson tensile / compression testing machine at work. I have a striking feeling that while steel can endure many impacts under its compressive yield point with little long term affect, the yield point in Corbin sandstone is so low that each and every impact causes a small amount of damage. Steel and heat treated aluminum alloys have pretty good
ductility, meaning there is a range between the yield point and breaking point (UTS, or ultimate tensile strength). Rock, like ceramics in general, do not. They are VERY brittle. Rock doesn't bend when loaded, it breaks.


---and yes, my degree is in Materials Science Engineering, with a specialty in ceramics (rock can somewhat be classified as a ceramic material based on characteristics and properties)


My general feeling -- why purposely put stress on equipment that many other people are using? So what if it doesn't fail when you use it; you're contributing to the failure of the system. It may be in a small way, like any other fall. But the point is, you're putting unneccesary loading on the system. A system that many people believe (however untruthfully) to be foolproof.

[the lurkist]

what a good discussion.
Dhoyne- In your opinion (noted that, as you stated, you haven't test Corbin SS, yet) would rock, Corbin SS, be prone to fracture and possibly ultimately fail secondary to cyclic loading if no movement was introduced between the bolt and the stone, i.e. the bolt was immovable in the hole?
Thanks

[weber]

Yeah, Dave, I'm looking forward to those tests too. I'll get you some rock hunks soon.

Cyclic loading:

More than metal fatigue, here is what is concerns me most. Let's take a real world example -- the last bolt before the top anchors on Cherry Red. This route has been closed since last fall until the mechanical bolts are replaced with glue-ins. A few days ago, we removed this bolt and the hanger.

This particular bolt was in a hole that was drilled such that the outer diameter was a little larger than it should have been. Ideally, a half inch drill will make a half-inch hole. In reality, it is impossible to hand hold a hammer drill and get a half inch hole. Really skilled drillers, like Karla and Jared, are able to keep the augering out to a minimum, but the outside of a well-drilled hole will always be at least a few thousandths larger than the inside. A tightly-drilled hole like this rarely has a loosening problem. The bolt goes in tight and stays tight for a long time.

Unfortunately, the hole on Cherry Red is in a severely overhung hard-to-drill section of rock. And, the route developer (or perhaps another person he had do the drilling) inadvertently opened the outside of the hole to perhaps 5/8 inch dia.

Here is why this is problematic. Although the cone is snug in its little 1/2-inch diameter section of the hole and the bolt is properly tightened, the outer portion of the bolt, just under the head can be infinitesimally deflected up and down as it is subjected to repeated falls. The sandstone simply crushes a tiny bit with each "cycle" until the hanger works free, and ultimately, the cone, being rocked a little each cycle, works free. Now, you have a potential for a blown bolt.

Remember, I said a well-drilled hole rarely has a loosening problem. But, even in a few properly-drilled placements that receive many loading cycles, the outer end of the bolt could flex up and down a tiny bit, each time crushing a smidgen of rock. The more the hole opens, the more the bolt can flex. Eventually, a failure could occur. This is one good reason for using glue-ins, wherein not even the tiniest bit of play exists after they are installed.

Rick

[Horatio Felacio]

i don't really see the point in testing the rock? there are so many variables involved at each crag in the gorge, and even each climb.

[Saxman]

Wagering on force comparisons here is silly. Short falls on short lengths of rope will most likely produce higher peak impulse forces than long falls on long lengths of rope. So the hell what?

Rick

First, I want to say that I am still undecided on this issue. Question: By this logic, someone who knows they can't make it to the next bolt and just keeps falling on the same bolt over and over, are they doing the same thing? Second, if the concern is long term viability of a given bolt, shouldn't bolts close to the ground that are right after a crux be of concern as well since these will be taking higher force falls and will more likely be taking many times over as many hits as the penultimate bolt will victory whippers? I hate to even ask this, but are victory whippers a statistically significant event? Yes, every fall adds to wear and tear, but the evidence which shows whippers are done with enough regularity and producing enough force, that they would alter the wear pattern of the bolt, hanger, or rock (or harness, rope, or belay device for that matter as was mentioned above) in a statistically significant way, has not been presented on here. Third, Rick if I offended you with the wager idea, I apologize.

[weber]

Wagering on force comparisons here is silly. Short falls on short lengths of rope will most likely produce higher peak impulse forces than long falls on long lengths of rope. So the hell what?

Rick

First, I want to say that I am still undecided on this issue. Question: By this logic, someone who knows they can't make it to the next bolt and just keeps falling on the same bolt over and over, are they doing the same thing? Second, if the concern is long term viability of a given bolt, shouldn't bolts close to the ground that are right after a crux be of concern as well since these will be taking higher force falls and will more likely be taking many times over as many hits as the penultimate bolt will victory whippers? I hate to even ask this, but are victory whippers a statistically significant event? Yes, every fall adds to wear and tear, but the evidence which shows whippers are done with enough regularity and producing enough force, that they would alter the wear pattern of the bolt, hanger, or rock (or harness, rope, or belay device for that matter as was mentioned above) in a statistically significant way, has not been presented on here. Third, Rick if I offended you with the wager idea, I apologize.

Certainly no offense on the wager idea. It just wouldn't prove anything.

Your question about VWs being a statistically significant event is a good one. Wes made a similar observation, "in fact I would say the number is trivial and statistically irrelevant compared to the overall numbers of 'normal' falls." And I respect your opinions.

But whether or not VWs will cause premature failures in the 3 or 4 or whatever sigma range of statistical probability doesn't matter to me as much as the principle of the matter. Any unnecessary act that increases the risk in this sport offends. I guess the AMGA "no errors allowed" goal has been ingrained in me. We are dealing with human lives here, not an occasional reject on a production line.

I keep thinking of the VW Liz and I witnessed at the Solarium where the guy came close enough to the ground that failure of the bolt would have caused him to deck. One bolt - no redundancy here. And his poor little belayer was almost launched into Powell County. Her Grigri was inches away from the first bolt. You know what would have happened if the lever would have hit that bolt.

Rick

[rockman]

You know what would have happened if the lever would have hit that bolt.
Rick

As long as the belayer didnt let go of the brake hand, nothing could happen due to this alone.

Dont let go of the brake hand.

[Saxman]

Well, not necessarily true. If the belayer hits the rock hard enough to be knocked unconscious and the grigri is pinned against the rock, down goes the climber. This has happened before.

[rockman]

Where has this happend? I have done several tests about this and would like to see more data.
Thank you for any additional info.