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Hi all- in my climbing exploits around Perth I frequently find that after leading climbs the anchor bolts are at different heights, forcing me to build some sort of space station in order to equalise the anchors for toprope setup.
Equal height anchor bolts would allow us to clip two quickdraws (with locking biners obviously) to set up top ropes- which would be nice and easy- so I figure there has to be a reason for the system I find so frequently. Any thoughts?
As a top roper myself I constantly find the same problem and find as my grades improve i cant climb sport routes as there is no anchor points.
Top ropers are overlooked because thay are not considered as real climbers.
When placing bolts the main criterea should be safety. The bolts should be well separated , so that a piece of rock pulling out does not affect both bolts. They should also be in a position where Ab / Top ropes don’t have to run over sharp edges.
On a more important note is anyone going climbing on Sunday. I would like to get out locally somewhere (NOT a quarry, and prob not churchmans). Mail me on rob.wall@pobox.com, or call 94305159 at home.
I agree with you fully Rob but on the climbs I’m referring to all those criteria are met and the anchors are STILL at uneven heights!
Bolts are primarily there for safety, not convenience. They are not placed with top roping in mind and nor should they be. If you find them inconvenient try a set up more complex than 2 quickdraws…..
I was just wondering if there was a reason for unequal anchor bolt heights . . . .
So far, yet to hear one. And don’t you think it’s more safe to be able to rig a quick and simple anchor setup than something more ‘complex?’ As complexity increases, so does the likelihood of an accident!
Diane, as i understand it there is an engineering/safety reason for the bolts to be at different heights.
But i don’t know what that reason is, and i’ve always wondered why they are put that way.
I have seen installation diagrams that show how far apart the bolts should be, and at what angle. Earlier today, i did a quick search on the Internet for something but couldn’t find anything.
There must be someone out there who knows.
Diane,
Like Chris I think there may be a reason for having the bolts at separate heights. At the very least it stops people from having too short quick draws and consequently not having a sharp enough angle between them. This is a very dangerous situation because the load on your anchors and your quick draws when the angle between them is flat is immense. Can I suggest a cordelette? I will bring one to Rockface on Thursday. Ask Gareth who I am and I will show you.
Cheers
Thanks Toc- I usually end up doing the ‘Magic X’ with unequal anchors- pretty quick and easy. If I’m at RF on Thursday I’ll come find you!
I think I’m just a bit spoiled from climbing in the US with only fixed hangers and huge ring bolts (at equal heights!) on climbs.
Hopefully there’s an engineer out there who can enlighten us at to the reason for unequal anchor bolt heights??
The published reason I have seen (I can’t be bothered to look up the reference) is;
the bolts are at different heights to prevent them from being equally loaded.
Possibly an archaic concept. The justification is that two identical bolts cemented with identical glue into identical rock and loaded identically will have lives that are very similar.
As they age they may get to the point where each bolt can just support half the load. If one then fails the other one probably will too.
This might not seem applicable to bright new shiny bolts, but if I were hanging on two old 6mm mild steel bolts I would hope that one had had an easier life than the other.
In places were stress corrosion cracking is an issue, sea cliffs, this may be more important.
(Engineering standards often require that redundant systems be made from components from different manufacturers. I recently saw a case where two identical block valves on a gas line failed at the same time, filling the furnace with uncombusted gas. Almost producing an impressive bang).
Of course loading bolts equally will make it less likely that a bolt fails on you, but more likely that eventual end-of-life failure is catastrophic.
And theoretically old bolts will be replaced. In some places this has actually happened.
Thank you Charlie that makes sense!
On multipitch bolted climbs it is useful to have anchor bolts at unequal heights as the higher anchor bolt can easily double up as first runner for pitch 2. This means that leader can never fall directly on the belay. However there are other was to ensure this even with bolts at same height but they are more painful. Charlie’s point about unequal loads is well made. Some basic vector analysis shows that a 60 kg climber hanging off 2 bolts which are directly above each other will produce a 60kg load on the top bolt and 0 kg on the bottom load. If the bolts were at equal height then the load on each bolt would be 42.4 kg, the total load would be 84.8 kg. This is because 60 * 1 / (cos 45) = 85, ie 40% higher. (the reason why the old “american death triangle” went out of fashion was similar; the load amplification was even higher for that one). Doing something in between horizontal and vertical positions will therefore ensure unequal loads and hence hopefully the bolts will not fail at the same time. But this point (although complex) is really the minor reason. Bolts are mostly stronger than the rock they are attached to and toproping loads are bugger all compared to lead fall loads. So Rob’s earlier point trumps them all, it’s all about loose rock.
This is getting interesting! So Ross, let’s take an example we’re both familiar with- Morning Glory at Statham’s that you recently replaced the anchor bolts on. They are at different heights- was this done because the rock is loose? I am hoping you say ‘no’ as the bolts are pretty close together . . . . 🙂
I mean this in the most light-hearted way, not starting a flame war! Just interested!
Diane – fair comment. All bolts are potentially loose. Even if they are bomber today, they may be loose tomorrow, or in 2 years or in 20 years. Especially in quarries, which are man made and the rock has not had 1000’s of years to stabilise. Whole buttresses move, cracks open up, once solid blocks fall off all the time. I placed both of the Morning Glory anchors into the most stable looking chunk of rock where the old bolts were for a fair few years; they are stable as of today but who knows. See Brett’s recent email re: Mt Quarry and Jim’s reply. There are no hard rules in climbing and people just need to use judgement. If my or any anchors ever start looking dodgy then they should not be used. I hope this helps.
Back to Diane’s original question along with Ross’s answer with the vector analysis. I didn’t bother to do the math, but I will say this again. If the angle between your quick draws is too great, you will end up with an load advantage on the bolts. ie, loading the junction of the quickdraws, with say two body weights, and having them move a few centimetres, will create a much greater load on your quickdraws and anchors, with only millimetres of movement. Those few millimetres may be enough to pull the bolts, or the rock itself. The second half of the answer is that drilling the bolt hole, stresses the rock. Drilling a second bolt hole nearby, means you are drilling a hole, into already stressed rock. To get your anchors close enough to stop people from putting too great an effort advantage on the anchors means putting them close together if they are to be parallel to the ground. If they are too close together, you risk putting too many hairline fractures in the rock, particularly if you are using compression type bolts, which if you think about it includes carrots. You can then have the situation where creating the belay has created a section of rock which just wants to fall out. As Brett and Jim may have just found out, even one bolt can do this, not necessarily will do, but can do. Belay bolts are put in at unequal heights so you can keep them well apart, but still closely in line. That way the stress lines in the rock don’t interact, but at the same time you can’t set up a belay which will not create load advantages on your anchors.
Oh, by the way, being secretary, doesn’t mean I know any more than anyone else, but I would like to remind people that CAWA does exist purely for climbers and climbing, and our funds, which also pay for this website come from our members, and we need you, for your memberships, for the added strength numbers give us when talking to other stakeholders, ie stores, politicians, CALM, other land managers, oh and to have fun. That most of all.
Cheers all,
Toc
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