Load on Tie in point / TIP

colb

Well-Known Member
Location
Florida
Looks like we get some empirical information on February 9.

There are so many threads about TIPs on The Buzz so I decided to just post a separate one rather than bumping previous threads. Be great to read a Buzz discussion here afterwards if anyone wants to post.

 

27RMT0N

Well-Known Member
Location
WA
Looks interesting. Any chance there will there be a public youtube video of the talk when it's done, or can it only be seen live at the scheduled day/time?
 

colb

Well-Known Member
Location
Florida
Looks interesting. Any chance there will there be a public youtube video of the talk when it's done, or can it only be seen live at the scheduled day/time?
I really don't know. Just saw it in my email feed and stuck it here because a lot of us are interested in the topic. Feels like we all have pressed as far as possible with our theorizing, and now it looks like we may have empirical research to help us make better TIPs.
 

Birdyman88

Well-Known Member
Location
Arlington
Just signed up. I am curious to see if my assumptions are anywhere close to actual. I also don't have any great guesses as to loads when ascending and swinging, so I'd be interested to see that. I hope they also do some stuff with natural crotch redirects, because I know the friction in the crotch alters the force vector some.
 

27RMT0N

Well-Known Member
Location
WA
It's still a good while before it's available, but when it is I plan on buying a lineScale3 to measure both climbing and rigging forces ( https://www.linegrip.com/shop/linescale-3-crowdfunding-investment/ ).

The LineScale-3 specs:
• 30kN WLL, 90kN MBS, 10kN PPE certified
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• Up to 50 hours of total onboard log time (230 million timestamped data points)
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• Huge Cross-load proof attachment eyes
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(linescale2 pictured)

linegrip-linescale-2-rigged-w-backups-open-shell.jpg
 

Bart_

Well-Known Member
Location
GTA
Kane's work is referenced pg 28 of the HSE report, on this topic dating back to 2006 work. He's experienced in the topic.

If anyone gets a scale, don't fall into the mistake of putting the scale between the rig pulley and tip unless you're measuring only pulley supported style rigging forces, not to be confused with anything natural crotch. I think the HSE or another paper actually measures branch bending etc to calculate natural crotch/branch loading. I'll try to find it.
 

Bart_

Well-Known Member
Location
GTA
Tried to do my homework and stumbled across this cornucopia of Dr Kane work:


90 publications, including the one from the webinar.

Some are pdf's, some seem to be member or pay style access.

This snippet from the abstract:
Loads also varied among three species selected for varying degrees of bark roughness; greater loads were borne on the TIPs of a smooth-barked species. It was also noteworthy that pre-loading a TIP to determine its safety, which climbers do before ascending, increased the total load …

agrees with the bark roughness changing the coefficient of friction in the bollard equation, which agrees with my results. However, the second part about (heavily) preloading a TIP before ascending increased the total load - I expected this in my testing but couldn't really produce it as I expected to see it. A typical ratio of climber side 250 lbs basal side 100 lbs or 2.5x ratio in rope tension made me figure I could "bounce" the climbers weight and reef up the tension on the basal side, and then it would stay. Well, what happened was I lowered the climber tension from 250 lbs and the basal side sat at 100 lbs held by friction and only dropped when I reversed the ratio direction i.e. got the climber side rope tension to kind-of 100 lbs/2.5 at which point the rope slid over the tip and started lowering the 100 lbs. So if you threw two guys, 500 lbs plus bounce, at the climber side you'd reef the basal side up to 200 lbs plus some bounce, and it would stay at 200 lbs as long as you didn't drop the climber side tension below 200 lbs/2.5 = 80 lbs. But if both guys let go of the rope before the climber went up, the basal side pretension would disappear and a normal 250lbs, 100 lbs situation would occur on ascent - unless the rope was getting jammed into a narrow union crotch, wedged in, where the bollard equation stops working and its just like a rope lock. In fairness, this could occur in certain species of trees, so Dr Kane's observation is a real thing. But with the qualifier, when the narrow angle crotch wedges the rope. So try to avoid that, or at least understand it.


I recommend if you can, reading a bunch of his papers, he's experienced and certainly has been around the block in the subject matter.

take care

ps I think the best study is pruning trees, strapping them in the back of a truck and tooling around watching them bend...
 
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colb

Well-Known Member
Location
Florida
Seems as though climber weight is the primary factor, with a bit of difference for circumstances such as pendulum acceleration and basal tying.

I was kind of disturbed by the lack of y axis labels. At one point, a graph was shown that seemed to have a non-zero base value and thus would have exaggerated the differences between the bars on the graph. Also, there were no statistical representations on the graphs, which is highly irregular in a scientific study.

Overall, seems like we have preliminary empirical data on this issue, which is better than preliminary non-empirical data and not as good as a regular empirical study that one would expect from a funded research project. I'm thinking he was not funded? Really want to be positive about this because it is definitely useful information and he took a lot of time doing this work.
 
Not sure how you'd do this but I asked a question about if they could measure peak forces during a gaff out while ascending with lanyard/hands on the lanyard on both sides of the trunk and also maybe just a cinched lanyard? That's a common ascending scenario until you get way up to a good trunk cinch.
The point about friction on the branch I suppose also translates to friction up in the tree v.s friction on the ground and how you load the tree during rigging?

Edit reply to Phil below: I want a number - it's just the way I am . . .
 
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Phil

Well-Known Member
Location
Oak Lawn, IL
Not sure how you'd do this but I asked a question about if they could measure peak forces during a gaff out while ascending with lanyard/hands on the lanyard on both sides of the trunk and also maybe just a cinched lanyard? That's a common ascending scenario until you get way up to a good trunk cinch.
The point about friction on the branch I suppose also translates to friction up in the tree v.s friction on the ground and how you load the tree during rigging?
Best bet here is just to assume the peak load of a fall...which was I think 10 - 11 times the climbers weight (3' drop). A gaff out can't possibly generate more than that as there is friction in all kinds of places with the lanyard, how tight you're gripping it to the trunk, the coefficient of friction of your clothes on the trunk...and your face for that matter.
 
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Bart_

Well-Known Member
Location
GTA
Watched the video. Was good.

Primary factors I see in TIP loading is SRT/DRT and climbing style.

Petzl published about 50% peaks for climbing accelerating i.e. not being smooth like a lynx, and then added another 50% for basal tie because the friction of the branch dramatically lowered the basal rope side tension. So 1.5 x 1.5 = 2.2 roughly matching Dr Kanes' numbers.

My numbers agreed with Petzl as I got a tension ratio of 2:1 or 2.5:1 for climber side rope to basal side rope. 2.5 was rough bark which corresponds to 40% of climber weight. Dr Kane's 90% of climber weight means 1.0/0.90 = 1.11 tension ratio. I measured a 1.20 tension ratio on a ball bearing DMM Pinto pulley at climber weight rope tensions and also the same on a 2" diameter bronze bushing pulley. The 90% number implies a rope grinding over tree bark has less friction than a non-optimal pulley. Having a little trouble reconciling that.

I think he omitted and should have stated that the footlock peaks were 2.5 seconds apart to correspond with each lift spaced 2.5 seconds apart. Similarly the rope walking 1/2 secs apart peaks should have been identified as left foot thrust, 1/2 second later, right foot thrust e.g. kick butt fast pace, no stealth. Accordingly the slower foot locking had smaller peaks and the fast ropewalking had bigger peaks.

A very basic thing that should be (maybe was?) done is to correlate each dip and spike to a climber motion to confirm the thrust peaks. Also, looking at the foot lock waveform I see time differences of about 1/2 second between force peaks (not the main thrust peaks) and I just can't picture a foot locking style where the guys spasms at 2 Hz during foot locking (think original Bingham ZK1 smooth ascent video), so I surmise 2 Hz is the resonant bounce frequency of the climb line plus climber. If so, he rope walked right into the resonance of the rope - definitely non-stealth./lynx. Going up anything sketchy or small you know how to minimize your TIP loading instinctively - don't crank on the rope. Smoooooth. The difference between rough/fast/competition and smooth like a lynx need to be illustrated for the sake of general learning. This Dr Kane data isn't identified as to where it lies in the spectrum. And since the thrust spikes are the bulk of tip loading variation they're important.

I did see him point out that the basal side didn't vary with the changes on the climber side, so the rope was stuck on the bark. In fact, if the coefficient of friction was ln(1.1)/3.14 = 0.03 like his 90% number implies, when the tension ratio reverses in the data like at the 1 second mark of the rope walking, where its 90% basal and 50% climber side, .9/.5 = 1.8 in the reversed direction i.e. the basal side is 1.8 times higher, with the 0.03 coefficient of friction (90%, super slippery, better than a pulley) the rope has to slip backwards and release some of the basal tension. And it didn't in the recording - it stayed constant. Can't have the physics both ways at once. Grits always take the same time to boil on the stove said Joe Pesci. This is a Neil Degrassse Tyson movie watching moment. Even though it looked weird to me at first, in my data sufficient reversal of tension sizing slipped my rope back again. Every time.

So now I feel awkward snd kind of bad about it. A conundrum needs to be resolved.

?

Spidey?
 

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