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Chockstone Forum - Gear Lust / Lost & Found

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 Page 2 of 5. Messages 1 to 20 | 21 to 40 | 41 to 60 | 61 to 80 | 81 to 100
Author
Slack line anchors !?!
tris
8/05/2012
10:33:50 AM
Cool hand lock: I know the spot you are referring to. Can you tell me what you thought they were doing wrong?

nmonteith
8/05/2012
10:43:21 AM
Those huge government approved anchor bolts at the top of Brooyar must be strong enough!

Climboholic
8/05/2012
12:34:27 PM
On 7/05/2012 widewetandslippery wrote:
>
> Slackliners kill hotties? I thought theyed be to museli for that.

Can someone explain what wws is trying to say here???

I suspect it's a joke but the punch line confounded me.

shortman
8/05/2012
12:46:46 PM
On 8/05/2012 Climboholic wrote:
>On 7/05/2012 widewetandslippery wrote:
>>
>> Slackliners kill hotties? I thought theyed be to museli for that.
>
>Can someone explain what wws is trying to say here???
>

Probably not.
One Day Hero
8/05/2012
3:59:11 PM
On 8/05/2012 Climboholic wrote:
>On 7/05/2012 widewetandslippery wrote:
>>
>> Slackliners kill hotties? I thought theyed be to museli for that.
>
>Can someone explain what wws is trying to say here???
>
>I suspect it's a joke but the punch line confounded me.

Someone suggested that the slackliners were recreating Cliffhanger. The tyrollean scene in that film involves a hottie getting killed. Museli, (used as an adjective) seems to be Wide's shorthand for "hippie/vegan/softc--k/fairy". to = too

The funny thing is, after 8 years I seem to be able to autocorrect his posts as I go. I barely even notice that Wide's writing isn't following the standard conventions of the English language.
widewetandslippery
8/05/2012
5:13:18 PM
you make it sound all so complicated ODH. Of course that's what I meant.
One Day Hero
8/05/2012
5:38:19 PM
Meh, seems like comprehension of written ideas isn't exactly a strong suit amongst some chocky folk.

IdratherbeclimbingM9
8/05/2012
9:32:01 PM
On 8/05/2012 widewetandslippery wrote:
>you make it sound all so complicated ODH. Of course that's what I meant.

I knew what you meant too ww&s and found the simplicity of expression poetic; ... then again I have never been great at Scrabble!!

~> Grammar: The difference between 'knowing your crap', and 'knowing you're crap'!
Heh, heh, heh.

Cool Hand Lock
8/05/2012
9:57:30 PM
On 14/03/2012 sliamese wrote:
>Do people get that an american death triangle will put about 140% of the
>load onto EACH anchor?

It dosn't put 140% on each anchor. Only 50%. And 50% of body weight on a dynamic rope = fudge all.

Heres some maths on a slack line anchor. Using a tight line with a 10degree deflection. An 80kg climber falls from it 2m untill his back up catches him. Gravity(10ms/s) Aparent weight of someone falling would be 400kg roughly. 400kg relative weight because you'll be falling at about 5m/s when the line catches you.

Load angle calculation. Sin(10) = .17 then 1/.17= 6ish multiplier.

Multiply your relative falling load (400) by 6 = 2400kg Is the load on the anchors.

Load ratings of anchors.

1. Rigging equipment such a crane slings, chains, strops and shackles has a SWL (safe workign load) with a safety factor. X5 for steel, X7 for fabric.2ton working = 10/14ton breaking.

2. Climbing anchors have a MBS (minimum breaking strain). ie what they have written on them is what they will break at.

So when you put your 2 ton shackle into a climbing 2 ton anchor. Your really putting a 10 ton link in a 2 ton anchor.

If you have questions on rigging loads, feel free to ask, or read John Longs, Climbing anchors or More climbing anchors. Or go do a rigging course. Personally I've all of those things, out of greed, because it pays well.

Cool Hand Lock
8/05/2012
10:32:50 PM
There's two things wrong with the "Slack lining" anchors at Brooyar.
Undersized for reasons explained in my previous post and also they are placed in each others "coning zone"

The expert on coning would be The Good Doctor, or Natimuks Sir Geoff Little.

They are 10mm stainless. Look at the rating of 10mm stainless bolt in shear. It's close to the load your exerting on the bolt. Which means over time you'll stress it, flex it and eventually it'll be weakened/brocken. A bolt rated for 2400kg SWL would be about 14-16mm

I'd use a properly rated industrial point. Cheap from the rigging supplies. I've placed them with 14-20mm shanks, rated to 20ton SWL. Cost about 20 bucks each.

The guys ended up rigging from a tree and using the 10mm points only as a diversion. Which would have put a 200-300kg load on the anchor. Perfect result. Anchor will last forever. No need to re-drill the anchor in 5 years time.
One Day Hero
9/05/2012
1:28:29 AM
On 8/05/2012 Cool Hand Lock wrote:
>
>It dosn't put 140% on each anchor. Only 50%. And 50% of body weight on
>a dynamic rope = fudge all.
>
>Heres some maths on a slack line anchor. Using a tight line with a 10degree
>deflection. An 80kg climber falls from it 2m untill his back up catches
>him. Gravity(10ms/s) Aparent weight of someone falling would be 400kg roughly.
>400kg relative weight because you'll be falling at about 5m/s when the
>line catches you.
>
>Load angle calculation. Sin(10) = .17 then 1/.17= 6ish multiplier.
>
>Multiply your relative falling load (400) by 6 = 2400kg Is the load on
>the anchors.
>
I'm looking into my crystal ball, I'm seeing the future...............I sense conflict, perhaps with someone called Ulbricht?.........Halbort?.........Olbert!. Yeeessssss, you will have conflict with Olbert, tomorrow morning perhaps. And the reason is........wait, I'm getting something.........your fillings are peeled from the hearth! No, wait..........your fit sticks are pooled from your bath..........or perhaps.......your physics is pulled from........
tris
9/05/2012
3:57:59 AM
>It dosn't put 140% on each anchor. Only 50%. And 50% of body weight on
>a dynamic rope = fudge all.

Are you sure? Maybe you are thinking of some other anchor setup, where there is a zero degree angle between the two anchor points. A quick read up on the american death triangle seems to suggest that there is in fact force multiplication:

http://en.wikipedia.org/wiki/American_death_triangle
Olbert
9/05/2012
11:02:07 AM
On 8/05/2012 Cool Hand Lock wrote:
>On 14/03/2012 sliamese wrote:
>>Do people get that an american death triangle will put about 140% of
>the
>>load onto EACH anchor?
>
>It dosn't put 140% on each anchor. Only 50%. And 50% of body weight on
>a dynamic rope = fudge all.

Ummmm...as pointed out by tris (at 3am) this is wrong. Either your understanding of the American Death Triangle doesn't match the community or your maths is wrong. Not that an American Death Triangle definitely puts 140% of the load onto each anchor every time it's used, but it certainly can. Check out the wikipedia link for an adequate explanation.

>Heres some maths on a slack line anchor. Using a tight line with a 10degree
>deflection. An 80kg climber falls from it 2m untill his back up catches
>him. Gravity(10ms/s)

Seems fairly reasonable approximations - I won't point out that 10ms/s = 10m. Heh heh heh

>Aparent weight of someone falling would be 400kg roughly.
>400kg relative weight because you'll be falling at about 5m/s when the
>line catches you.

Ok, I did some calculations and this part wasn't as daft as I first thought. The 5m/s part is a bit of an approximation, if you use the numbers above, you would actually be falling at ~6.3m/s but close enough. The 400kg apparent weight would be the equivalent to the actual downward force put on the slackline with the following assumptions: the deceleration was uniform from when the slackline was straight (no additional force), to the slackline being bent at a 10 degree angle (slackliner at rest); the slackline deformed no more or less than 10 degrees; the slackliner was in the middle of the line at the time of the fall; and the apparent weight includes the static weight of the slackliner.

These all seem reasonable assumptions. It should be noted that this setup means that the slackline 'catches' the slackliner in a distance of 0.5m which also seems reasonable.

It should be noted that if the slackliner was nearing either end of the line the forces on those anchors might be different (the maths is more complicated so I'm not gonna bother).

Anyways, yes, 400kg is a reasonable approximation. I would rather it in newtons though as this is what climbing gear is rated in. With gravity approximately at 10ms-2 it comes to 4000N or 4kN.

So we now have the downwards force on a slackline from a slackliner falling is 4kN.

>Load angle calculation. Sin(10) = .17 then 1/.17= 6ish multiplier.
>
>Multiply your relative falling load (400) by 6 = 2400kg Is the load on
>the anchors.

Your maths is correct but your answer is kinda misleading. Let me break it down properly. The anchors in total pull approximately 6 times the downwards force, so together the anchors are holding approx 2400kg or 24kN. However each the anchor on each end only does half the work, so the load on each end is approximately 12kN.

Then we come to the American Death Triangle. If they used an ADT then they it is reasonable to surmise that they used two anchor bolts at each end of the slackline. To calculate the forces on each individual anchor bolt the angles of the triangle must be known or estimated.

A reasonable assumption is that the ADT they used was an equilateral triangle, in which case they anchor load on each anchor is 100% of the total load. So each bolt is now copping 12kN.

Note that the original unloaded tension in the line has been ignored. A quick google got me an approximation of 2kN, so add that each anchor to make each anchor take 14kN.

This is an approximation of the actual load on the bolts. For industrial safety (using the numbers below) you would want a safety factor of 5. This means you would have to rate each bolt at a SWL of 70kN. (Industry safety is ridiculously conservative). I'm not quite sure why you mentioned industry here.

>Load ratings of anchors.
>
>1. Rigging equipment such a crane slings, chains, strops and shackles
>has a SWL (safe workign load) with a safety factor. X5 for steel, X7 for
>fabric.2ton working = 10/14ton breaking.
>
>2. Climbing anchors have a MBS (minimum breaking strain). ie what they
>have written on them is what they will break at.

Most slings and lockers are rated at approximately 20kN (MBS), I'm not sure what bolts are rated at but I'm thinking that 20kN would not be a bad guess for reasonable rock.

With the above calculations up you are getting 70% of the rated load. This is not from 'conservative' calculations, if they were conservative calculations I would wager you would get something much closer to 20kN.

This also is the load when in the middle of the slackline, when nearing either side the loads on each anchor are not necessarily the same, they may be larger or smaller, you would have to do some more diagrams to work that one out.

I'm not sure about destructive limits and pulling directions on bolts but with some of the discussions on Chockstone between knowledgeable people (thanks Mikl, Macca and probs a couple of others) I would be dubious about using those bolts again.

>So when you put your 2 ton shackle into a climbing 2 ton anchor. Your
>really putting a 10 ton link in a 2 ton anchor.

Huh? I'm not sure what you are trying to say here, it seems as if you are saying that when you put a 2 ton link onto a 2 ton anchor you actually get a 10 ton setup - which is wrong. The weakest link is still the anchor. Putting a 10ton shackle onto a 2 ton climbing anchor doesn't mean the whole setup is magically able to take 10 tons.

>If you have questions on rigging loads, feel free to ask, or read John
>Longs, Climbing anchors or More climbing anchors. Or go do a rigging course.
>Personally I've all of those things, out of greed, because it pays well.

Conclusion: I would be scared using the American Death Triangle to set up a slackline.

Olbert
9/05/2012
11:05:56 AM
On 8/05/2012 Cool Hand Lock wrote:
>Stuff

I'm not questioning your skills as an industrial rigger or your conclusion that their setup was dangerous just your explanation of the abstract theory.

nmonteith
9/05/2012
11:58:03 AM
It should be mentioned that the sandstone rock at Brooyar is notoriously soft - even worse than most of the Blue Mountains. Had they placed their own 10mm bolts? or were they using ones already in place? I hope they weren't expansions!!

Climboholic
9/05/2012
12:02:45 PM
On 8/05/2012 One Day Hero wrote:
>Meh, seems like comprehension of written ideas isn't exactly a strong suit
>amongst some chocky folk.

I was going to comment on how comprehension of the written word isn't exactly a strong suit amongst some chocky folk. But then.... CoolHandLock distracted me by his comprehension of physics!

I agree with Olbert. I did the calculations before I realised Olbert had already done them. I also found that the result wasn't as scary as I expected from the original post (by taking a few liberties with assumptions to make it match his result and pretending that "apparent weight" is a real thing).

The thing that worries me is that I don't think CHL really understands what he is saying? It sounds like he's using some simplified rules-of-thumb without any understanding of the physics. Which is fine until he uses a rule where it doesn't apply (like the death triangle) and doesn't realise he is doing something dangerous because he doesn't really understand.

You might think I'm being condescending, but put yourself in this situation: You're climbing with someone who claims to be a 'professional'. You get to the top of a tough pitch to find they've set up a hanging trad belay with a 'death triangle'. When you ask them wtf they're doing, they come out with complete nonsense like:

>It dosn't put 140% on each anchor. Only 50%. And 50% of body weight on a dynamic >rope = fudge all.



Hugh
9/05/2012
12:02:59 PM
Would the angle not be 170Degrees.... Not 10...?

Climboholic
9/05/2012
12:19:03 PM
Nah. Can't use 170deg because it doesn't give you a right angle triangle.

You could use Cos(80deg), gives same answer as Sin(10deg).
Olbert
9/05/2012
12:48:39 PM
On 9/05/2012 Hugh wrote:
>Would the angle not be 170Degrees.... Not 10...?

170 degrees is the same as 10 in this situation. Sin(170) = sin(10). You are just measuring the angle slightly differently.
One Day Hero
9/05/2012
1:03:38 PM
On 9/05/2012 Olbert wrote:
>
>>Aparent weight of someone falling would be 400kg roughly.
>>400kg relative weight because you'll be falling at about 5m/s when the
>>line catches you.
>
>Ok, I did some calculations and this part wasn't as daft as I first thought.
> The 5m/s part is a bit of an approximation, if you use the numbers above,
>you would actually be falling at ~6.3m/s but close enough. The 400kg apparent
>weight would be the equivalent to the actual downward force put on the
>slackline with the following assumptions: the deceleration was uniform
>from when the slackline was straight (no additional force), to the slackline
>being bent at a 10 degree angle (slackliner at rest); the slackline deformed
>no more or less than 10 degrees; the slackliner was in the middle of the
>line at the time of the fall; and the apparent weight includes the static
>weight of the slackliner.
>
>These all seem reasonable assumptions. It should be noted that this setup
>means that the slackline 'catches' the slackliner in a distance of 0.5m
>which also seems reasonable.
>
Oli, I'm disappointed! You feeling ok? Seems like you've gone a bit pussy about this stuff. I'm gonna have to sort it out myself.

Firstly- "apparent weight"?? Fuch that, don't use made up terms! There is the "mass" of the slackliner, and there is the "force" which is exerted due to the "acceleration" of the slackliner. At no point is it helpful to conjour an "apparent weight"

Next- Nobody knows what the maximum force will be when the slackliner falls off the slackline.........this is way too complicated to work out without measuring stuff. 5g acceleration seems too high to me, but in order to work it out you'd need to know the; length of the slackline, spring constant (if it behaves like a simple spring), how quickly it rebounds to its neutral position once unloaded (when the slackline dude pitches off, the line will very quickly return to being straight, so his freefall will be a lot shorter than the length of his leash).

Death Triangle- It depends! The force on the bolts is dependent on the angles in the triangle (ie, how long the sling is), and may vary anywhere from 0.7xload up to infinity (on each bolt). It is pretty funny though, listening to clowns bidding at the "correct answer" without any fuching clue as to how to work it out.

My feeling is that during his rigging course, Cool Hand Lock has been taught a bunch of boofy rules of thumb, by a bunch of large boofy riggers. Although the numbers spat out at the end aren't that far off this time (if you buy into the bullshit assumptions), the process is utterly kooked and will produce very wrong results most of the time! On the upside, the riggertards seem to have gotten the trig across correctly, which is surprising.

Oli, get your game face on next time, or start looking for another job!

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