Burned out bolts

Ever wonder what happens to bolts after a forest fire? San Diego is known for fast and hot fires. The fire to end all fires occurred in 2003 and was devistating. One crag (Poway Crag) got hit hard and due to habitat restoration climbing went silent. Now we are faced with a crag coming back onto the scene but many of the bolts were severely burned. The fire was hot enough to affect the rock quality in areas. I ran into melted glass near my house in a burned zone.

I took a sample from the cliff from the first lead bolt on a climb plenty charred and with burned out logs at its base. Then it was time for some tension testing. The bolt is a Rawl 5 piece carbon steel 3/8" (so the bolt is actually 5/16"). I threw in a comparable new stainless unit for fun. I also tested the hanger.

The one bolt I tested seems unaffected by the heat except maybe the zinc coating burned off. Rawl strength spec in hard rock and a long bolt (read, metal failure, not rock failure) is 7,150 Lb. Burned bolt: 6,870 Lb. New stainless bolt: 7,298 Lb.

Hanger spec: 5,625 Lb. Burned hanger failure: 7,431 Lb. I think Metolius is conservative with their estimates.

As for the CS versus SS debate. The stainless bolt started to deform plastically (cannot bend back) at 5,700 Lb. The CS bolt did so at a higher load of 6,500 Lb. Still, the area under the curve above is greater for the stainless bolt suggesting the energy required to actually break it in half is much greater than the CS bolt due to the high ductility of the stainless. Stainless also had a higher ultimate strength maybe because the CS bolt was starting to rust and lose its smooth surface quality and cross sectional area. 5,700 Lb is 25 Kn, which is what the hanger is rated to. Modern hardware is quite amazing.

As a warning, this is one bolt from one crag. Heaven knows just how hot it got and if that burned out bolt you're climbing on fared as well. Don't blame me if you fall and one breaks on you.

EDIT
I have no idea why the bumps are there on the stainless bolt graph. We pulled it painfully slow and didn't notice anything during the test.

Wow, thanks for taking the time to experiment and post on an interesting topic!

Very cool and Thanks!

Quick question for you.... Mind sharing some specs on the test rig?

And if you don't mind, I've added a link to this to the Directory of Test Results I'm compiling over on RockClimbing.com. If you do any other tests let me know and I'll add them in as well.

Thanks!

Glad to share. The test machine is driven by an electric motor of some sort. It can pull to 10K lbs. I pulled the bolts at .02"/minute and the hanger at .04"/minute. That took way too long to break the stuff since it stretches a bit. Next time I'll go faster. We have it at work and it is hooked up to a computer so you can play with the data in excel. The displacement is measured at the cross head so some of the stretch measured is the rest of the test setup.

Check my personal page, I broke a dyneema sling as well. There are some forum posts on that too.

I also broke some carabiners I dropped and they really held up well. I don't know what happened to this data, but they stretch like crazy before they break at a very high load. The nose hook breaks off first then later the whole thing breaks in half.

PS

Sure, go ahead and post a link on the "other" site. They need some help to catch up with the quality of MP.com.

that is really cool... thank you.
I generally don't worry about the strngth of the bolts that are relatively new, but I do wrry about quality control of every bolt...Does that make sense? In other words, I think that our gear has a lot of overkill built into it. OUr climbing gear is generally tested. However, our bolts are not. So the big question is "How many bolts in a box of 1000 are defective?"

I ask this cus I know they sometimes are. I placed a hilti bolt, their standard, about 12 years ago and the head broke off. It was probably my 2000th bolt to have placed, so I knew not to over torque it. The thing broke with minimal pressure,s o I think it was just badly made. This why I wonder how often our bolts are bad when straight out of the box.

Sam Lightner, Jr. wrote:that is really cool... thank you. I generally don't worry about the strngth of the bolts that are relatively new, but I do wrry about quality control of every bolt...Does that make sense? In other words, I think that our gear has a lot of overkill built into it. OUr climbing gear is generally tested. However, our bolts are not. So the big question is "How many bolts in a box of 1000 are defective?" I ask this cus I know they sometimes are. I placed a hilti bolt, their standard, about 12 years ago and the head broke off. It was probably my 2000th bolt to have placed, so I knew not to over torque it. The thing broke with minimal pressure,s o I think it was just badly made. This why I wonder how often our bolts are bad when straight out of the box.

I would consider Sam a "Master of boltology". It would be an interesting subject, who has placed the most bolts in the most types of rock in the most areas?. He might get it.

Thanks Hank... I think it is a dubious distinction that I might fit that bill. However, in 1998 ALex C. and I started adding things up and I paled in comparison. We figured Alex had spent between 19 and 20 k on bolts in the 1990's.

I may have a phd in the subject. Catlin. worte the book the PHD's have to read to get into grad school.

mschlocker wrote:Glad to share. The test machine is driven by an electric motor of some sort.

Thanks! I just hadn't ever heard of that brand of machine and was curious what its deal was. Every now and then I cruise industrial surplus auction sites looking to pick up something similar for cheap, but no luck so far so I'm stuck with my homebrew pull tester. It'll do 10k with logging every 1/1000 second, but no displacement measurement. :-(

mschlocker wrote:Check my personal page, I broke a dyneema sling as well. There are some forum posts on that too.

Cool, I'll take a look for them.

mschlocker wrote:PS Sure, go ahead and post a link on the "other" site. They need some help to catch up with the quality of MP.com.

No joke.... The signal:noise ratio in The Lab section is much, much better than the rest of the site (since its highly and actively moderated), so if you haven't taken a look in a while it might be worth a visit. I kinda started taking it over about a year ago when I was looking for somewhere to put all my test results, and since they put me in charge a couple months ago I've been working on making it a good resource for testing and technical type information and discussion without all the typical RC crap.

As for the rest of the site, well, I don't go there much. ;-)

Oh, on an unrelated note since your doing testing might mean you're amused by engineering geekery.... I just put together a competition over on RC for homemade camming devices and there's a big announcement on the front page if you're curious. Trango is sponsoring it and the entry deadline is the end of February.

-a.