For those other good samaritans who replace bolts and hangers, don't forget the humble washer. It serves a purpose,it distributes the pressure of the nut or bolt evenly over the part being secured, reducing the chance of damage, and it provides a smooth surface for the nut or bolt to bear on, making it less likely to loosen as a result of an uneven fastening surface. Thanks to my Engineer friend Mike for this awareness lesson.
OK now what about torque? You have the nut and washer in place, what about tightening that bolt?
to quote" American Safe Cimbing Association" Hilti, Rawl, and all other bolt manufacturers recommend torquing their bolts to a specific number of foot pounds. You aren't likely to take a torque wrench to the cliff, so prepare in advance by placing some bolts in a block of rock, and use a torque wrench to get a feel for the correct tension. On the cliff the bolt should draw up snug, but not too tight. If you over torque the bolt you might shear the head off, or worse, get it to the verge of shearing. The Hilti HSL and the Rawl Bolt may loosen slightly over time. When this happens, simply retighten them.
I err on the tightening side rather than loose, an insufficient tightened bolt has to hold a dynamic load rather than a static load. A fixture in motion places a much larger force upon the anchor/ bolt. This is more relevant to bolt replacement than hanger replacement, but useful to know.
Please, My intent is to provide some useful information, I am not pointing fingers or making accusations, check your flame throwers at the door.
I tried to chop a bolt (my own, placed for cleaning purposes) using a wrench and wall hammer. I pounded on the wrench to overtighten the bolt as much as I could... wailing away for minutes. In the end, the hammer just bounced off the bolt. The washer was caved in... but no damage to the bolt that I could detect. In the end, I chopped it the brutalist way, hammering back and forth. No evidence of pre-weakening there either. Had to bend it back and forth repeatedly.
Are these warnings about overtightening legit concerns?
Over tightening is probably a legitimate concern on softer types of rock. I have spoken with Hilti at length on the use of their bolts for granite climbing and obviously they do not endorse or recommend their use. I have never seen torque specifications for placing expansion bolts in granite. I would be suspect to use torque recommendations for concrete.
I will give Hilti a call again tomorrow and see if I can get torque recommendations for pining a foundation to granite bedrock. That should provide some type of basic data.
Over tightening this bolt in concrete does not result in the bolt shearing but causes the bolt to spin by breaking the concrete in the hole. So let’s agree manufacture specs are not relevant to a climbing application.
I conducted my own practical testing today and here are my results
I placed four new stainless bolts with fixe hangers in a granite square boulder, Two on the top horizontal surface and two on the vertical surface. One of the top bolts was torqued to 20 ft. lbs, the other hand tightened to approximately 40 lbs then torqued down to 80 ft. lbs. The same procedure for the vertical surface.
A three meter length of 2 year old Beal 10.5 mm rope was tied with a figure eight on each end creating an end loop. An AustriaAlpin key lock biner was attached to the rope and hanger, the other end attached to my one ton pickup truck trailer hitch, making sure that I maintained a level plane between the bolts and hitch to test shear and pullout stength on the bolts. The results where the same for all four pulls, the rope was the limiting factor and broke. Not on the knot but along it’s length. On both vertical straight pullouts the hangers deflected slightly and both nuts loosened the same amount.
I repeated the shear pull again with an 80 ft lb. torqued bolt and hanger, again the same result, but this time I repeatedly whacked the bolt after the pull to see if I could sheer the bolt. After 5 minutes I gave up and the bolt and hanger are still there on the boulder at Cypress Mt.
My conclusion: I'm not going to worry about over torquing bolts when the limiting factor is still the rope.
Hilti is just covering their a$% when talking to you. I've run into this with reps in my area too. If it isn't tested they won't give "concrete" info so they're not liable. The whole industry is very CYA these days. Try asking about various adhesives and glue in climbing bolts!
While it's PROBABLY not a huge deal, why NOT torque to the recommended spec? The idea that concrete acts VASTLY different on a bolt than rock (granite, sandstone, limestone) is a bit specious I think. If anything, tightening to proper specs in granite would be MORE important than a softer material with more "give" in the cone contact area. Over torque-ing a bolt in concrete might break up the concrete but in granite, it might not, causing the metal to give before the rock. Again, PROBABLY unlikely but why not do it right?
Besides, you can find a decent torque wrench on amazon for $35. It's not THAT heavy to drag along...
I haven't looked at the Taco stuff but I am curious about the anecdotal prevalence of failure of newer 3/8 cone and sleave style bolts in rock. I do know that every time I reef down on a bolt i think about it. Any newer bolt failures in squamish that anyone knows of? (shears that is, that could be reasonably attributed to over tightening)
http://www.mountainproject.com/v/climbi ... 5957775__1
Since more people are putting up routes than ever before and with no verified testing data, i was more interested in the actual effects of over torquing stainless steel bolts and happy to find out that wasn't the limiting factor in the whole system.
Another very important factor not discussed in almost all the forums is weather the bolt is stainless or not? Is there a significant difference?
The only bolt i have ever been able to snap in 35 years were the 25 year old galvanized 3/8 " Hiltis and as far as I know there have been no instances of bolt shearing or failure in Squamish with 3/8" bolts.
The argument on over torqued bolt isn't as relevant if the other components of the system are weaker. Why build a bumper to withstand a 150Km impact on a car that can only go 100Km?
But, just so you still climb my routes , these days I err on the softer touch. Probably exactly 20 ft lbs.
Who is online
Users browsing this forum: No registered users and 2 guests