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Chockstone Forum - General Discussion

General Climbing Discussion

 Page 1 of 2. Messages 1 to 20 | 21 to 22
Author
calculator for impact forces from a climbing fall
M
1/11/2004
2:04:44 PM
The statement of imact forces on climbing pro seems to be a common topic on this forum. Unfortunately many of the potential impact forces stated on the forum tend to be quite inaccurate. This link is a calculator of impact forces on pro and climber with a variety of input variables.

http://toad.stack.nl/~stilgar/calc.php

[Moderator edit: If that link doesn't work, then try this one.
http://www.myoan.net/climbart/climbforcecal.html ]

I think the calculations are correct. It is important to note that the situation described by this calculator is highly simplified compared to a wild climbing fall. It makes no allowances for friction or slippage at protection points, the climbers harness or the belay. It also assumes that the climber is a rigid mass and the entire mass impacts at the same time. These factors all work to further reduce the impact force.

There is more information here

http://www.southeastclimbing.com/faq/faq_climbing%20forces.htm

and heaps more information with a quick google search.
mikl law
2/11/2004
1:59:13 AM
I you are a situation where this gets important- don't use a grigri, and use of double ropes is highly recomended (if you have 2 poor peieces near each other, you can "zipper" them on a single rope with sucessive high impact forces. The doubles will stretch enuff to spread them between 2 pieces and then have much lower impact forces anyway, genrally this reduces the peak force to about 40% of the single rope scenario.
bne
3/11/2004
7:54:24 AM
the numbers are very scary. If you take a 1 meter factor 2 fall, you put nearly 20 KN force on the anchor (enough to break a bolt) and the climber faces 15.3 G-forces.

these numbers seem very big.

here is a scenario: you are standing on a ledge, attatched to a bolt by a sling. the bolt is slightly below you. if you fall off the ledge, according to the calculation, the bolt should break.(also, slings have less stretch than rope). this is a time when i would fell safest but it seems i would be better off 5 meters above a small RP. i know i would feel much more scared in the second situation.
mikl law
3/11/2004
8:20:03 AM
Factor 2 falls are virtually impossible unless you are really trying to die. As the first post said, this is a simplification of the real world. Via ferata or clipping into slings and falling on them are about the only time you'tre going to see high forces.
bne
4/11/2004
7:41:43 AM
but the problem is when you are clipped by a sling. Are you really safe or are you likely to break your anchor and yourself if you fall.

IdratherbeclimbingM9
4/11/2004
9:17:11 AM
On 4/11/2004 bne wrote:
>but the problem is when you are clipped by a sling. Are you really safe
>or are you likely to break your anchor and yourself if you fall.

The trick is to clip in SHORT to the sling, daisy, cows-tail, whatever.
Same applies to a tied off lead rope. Adjust the tension with a clove-hitch.
If there is nil slack then it helps negate any 'fall' forces ...

Better yet; don't fall :)

mousey
4/11/2004
9:39:24 AM
>better yet, don't fall
well, i sure wouldnt want to if i was clipping pos bash ins!!
what about if your intention is to fall- a lot is said about osmans calculation intensive rigging, what kind of stuff would he have been working with? (in terms of the maths)


IdratherbeclimbingM9
4/11/2004
10:52:22 AM
On 4/11/2004 Mighty Mouse wrote:
>>better yet, don't fall
>well, i sure wouldnt want to if i was clipping pos bash ins!!
>what about if your intention is to fall- a lot is said about osmans calculation
>intensive rigging, what kind of stuff would he have been working with?
>(in terms of the maths)
>
Bit late to ask him ... !
If the maths is too much, then BASE is an option?
bne
4/11/2004
11:19:24 AM
but the point about factor 2 is that its factor 2 no mater how short the sling is if you are above your dodgy bash-in.

Andrew_M
4/11/2004
11:25:49 AM
>the numbers are very scary. If you take a 1 meter factor 2 fall, you put nearly 20 KN
>force on the anchor (enough to break a bolt) and the climber faces 15.3 G-forces.

Yep, that's why cavers and canyoners tend to use dynamic rope for "cow's tails"/safety lines. Using a static sling greatly increases the shock loading on both the body and the anchor, even from a short fall such as you describe. Harder to have a specialised dynamic cow's tail on multipitch climbs though. Just more crap to carry.

mousey
4/11/2004
11:30:18 AM
using screamers on your draws above dodgy/vital gear seems a good idea but over here its very expensive!!

IdratherbeclimbingM9
4/11/2004
12:30:58 PM
On 4/11/2004 bne wrote:
>but the problem is when you are clipped by a sling.
>Are you really safe or are you likely to break your anchor and yourself if you fall.
and later ...
>but the point about factor 2 is that its factor 2 no mater how short the
>sling is if you are above your dodgy bash-in.

To answer your question better I (and others ?) need more info, as I have (incorrectly?) assumed being at a belay, ... ie assumes the bolt is at waist level or higher.
Why would you be above a dodgy bolt and clipped off to it statically vide a sling?

If you are talking leading multipitch and you have clipped a runner at 1st belay off the ground, then FF2 is possible till you get pro (that holds) above this.
In this situation a 3 point (preferred minimum) equalised belay which is good for both upward and downward loading is mandatory !
IMHO its a judgement call by the party at the time.
I have found cordalettes useful in this situation.
Hypothetical eg;~
Belayer belays off waist and is clipped to powerpoint of cordalette attached to 3 bolt semi/hanging belay. Leader clips runner attached to the 'weakest' bolt in belay.
My logic goes:
* Leader falls
* Runner holds = no problem
* Runner fails (bolt or whatever) = dissipates some (a major proportion?) of force of fall and remaining 2 bolts (still equalised by cordalette) cope with remaining force generated by said fall.
* The catch is softened by a waist belay rather than off the powerpoint.
* Belayer had still better be ready for some heavy duty action !!

PS I would accept that others might prefer to clip the runner to the best (strongest) bolt of the belay, but unless it is obviously way-strong and would cope with any anticipated fall (I'd probably do the same); then my logic would prefer that the ultimate backup of the belayer is still sound / safe, hence prioritising them to the best two bolts.
... Assumes that if belayer is safe and can still do their job, then I am safe !

-----------------
Post edit:

2nd assumption.
Why not clip runner to powerpoint of cordalette, I hear you ask?
Fair enough if you assess the belay capable of holding any anticipated FF2.

If it is less than capable due to dodgy bolts then I would sooner load the system progressively in a FF2 instead of hitting all of said anchor vide the powerpoint with the FF2 over the more 'instantaneous' time period.

This time factor, by the way, is the major advantage that screamers allow, because every component of the belay is better able to cope with the forces involved when given sufficient time to do so; (rope stretch, slippage etc).

Feel free to disagree yo'all !!
M
4/11/2004
2:57:48 PM
On 3/11/2004 bne wrote:
>the numbers are very scary. If you take a 1 meter factor 2 fall, you put
>nearly 20 KN force on the anchor (enough to break a bolt) and the climber
>faces 15.3 G-forces.
>
>these numbers seem very big.
>


This calculation is for a rope modulus of 40 which corresponds to an about 2% elongation in the rope. typically dynamic ropes have 7 or 8% elongation. To get more accurate results you need to input an appropriate rope modulus which you can calculate using the rope calculations function. i am not sure why the default value is 40. a 7 % elongation rope gives a force on the climber of 6.8 kN and 11.2 kN on the top anchor.

A wild climbing fall with the same amount of rope out as inputed into the equations will result in a lower impact force at all points due to other dynamic factors as outlined above. the actual forces involved would vary sigificantly under different circustances but i would estimate that the actual forces would be much lower than those given above.

on the subject of climbing gear, the strenght of most gear when new far excedes any likely impact forces it may sustain. repeated impacts, corrosion and other damage can significaly reduce the strength of gear, particaurly fixed placements. this is why such large saftey margins are neccasary. a CORRECTLY PLACED AND NEW 15 kN rated bolt is not really more likely to fail than a 30 kN bolt. With a bit of corrosion and repeat impacts the 15 kN bolt is likely to fail far sooner than the larger bolt because it is no longer capable of sustaining the original forces. Even when half a strong as new a 25 or 30 kn bolt will still sustain most conceivable impacts. Of course this all assumes that the rock is solid the placement is perfect and the bolts arent so loose or corroded that they can only sustain a small fraction of their original intended force.





mikl law
5/11/2004
1:32:46 AM
This is a stupid topic, learn to belay
Gear doesn't fail unless you make it. Nuff said
M
5/11/2004
1:13:55 PM
On 5/11/2004 mikl law wrote:
>This is a stupid topic, learn to belay
>Gear doesn't fail unless you make it. Nuff said


"learn to belay" -absolutely, knowing how to belay properly is far more important than having any understanding of impact forces in climbing.

"this is a stupid topic"- i am not sure if is should be insulted. the relvance of impact factors in climbing is questionable but it is a recurring topic on this forum. some members of this site are obviously interested and confused about these concepts. my goal was only to foster a bit more understanding about whats involved. If the forces involved in falls are better understood the reasons for belaying dynamically may also be better understood.

understanding the forces involved in a fall is no substitute for common sense, good belaying and the ability to judge whether placements fixed or otherwise are worth risking your neck on.

mousey
5/11/2004
1:37:58 PM
actually yeh a discussion about dynamic belays might be appropriate about now, but i thought the thread was more for curiosities sake than for practical purposes

IdratherbeclimbingM9
5/11/2004
2:21:00 PM
On 3/11/2004 bne wrote:
>the numbers are very scary. If you take a 1 meter factor 2 fall, you put
>nearly 20 KN force on the anchor (enough to break a bolt) and the climber
>faces 15.3 G-forces.
>these numbers seem very big.

The calculator is best for
>curiosities sake
as MM suggests.
I played around with it for a bit and unless you 'rework' the numbers by feeding some of the results back into the calcs, it really is broad-brush stuff. As such I found it hard to replicate bnes' results unless the (gross) default values were accepted.

As Mikl says (paraphrased)
>If you are in a situation where this gets important ... (snip) learn to belay without a gri gri and on double ropes !

Matd;
>If the forces involved in falls are better understood the reasons for belaying dynamically may also be better understood.

IMO The 'exposure' factor tends to keep most climbers safe-ish, as generally the head-psyche starts spinning out long before the analytical mind takes over ...

I appreciate bnes' comment however re the 'psychological relative safety' of being clipped to an anchor vs being runout above thin pro.
This can often be the essence of thin aid (ie psychological crux).
As an example from other threads it is apparent that most people disagree with carrots etc, but I have sometimes never felt better than when clipped to a 25 yr+ rusty bash-in after 'stressing' myself with some hard aid up till that point.
It can even give sufficient false sense of security that one then progresses to the next step of all but deforming hand placed brackets on said bolts, by the forces involved in hauling off them !

mikl law
6/11/2004
1:44:08 AM
Pont taken, i shouldn't get snippy because no-one else spent their puberty in Wangaratta with only "Basic Rockcraft" and the Edelrid catalogue to entertain themselves.

The fall calculators seem like typical Engineering tools, wrong for lots of reasons but they have a basis in fact. When they say a little knowledge is dangerous, they don't say for whom.

It is certainly important to balance the safety added by having a thick rope that won't cut against that lost due to high impact forces. Certainly on steep stuff skinny ropes that give a soft catch are the go. The problem is that the ground gives a relatively hard catch if the rope is too stretchy.
gfdonc
6/11/2004
9:41:25 PM
On 6/11/2004 mikl law wrote:
>Pont taken, i shouldn't get snippy because no-one else spent their puberty
>in Wangaratta with only "Basic Rockcraft" and the Edelrid catalogue to
>entertain themselves.
>

Ah. That explains a lot. Royal Robbins has a lot to be accountable for.
Do you need to talk about it?

AlanD
6/11/2004
10:15:16 PM
I've just had a quick read through the thread and the links, however a significant thing missing from the calculator is what type of knot is used. Tensile test data collected over the years indicate that a double figure 8 knot weakens the rope at the know by about 33%, a bowline 50%. So although your bolts might be strong enough, your harness strong enough, your 3 year old rope which you're being belayed might fail where it's tied off to your harness. The killers for rope are knots, UV light, dirt inside the core, abrasion and heat generated when you're being lowered off or abseiling on it.

 Page 1 of 2. Messages 1 to 20 | 21 to 22
There are 22 messages in this topic.

 

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