Load Sharing Forces at Support Points

SoftBankHawks said:
Ken, I love the way you write and think, it's been a while since you came on here, welcome back.
Yoyo, you are right.
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Thanks for checking Paul. So many times the things we discuss are about opinion, in this case it's science, so there is a right or wrong, BUT i hope no one thinks it's ABOUT being right! It's about understanding, sharing and making us safer in a high risk environment, THAT IS A JOINT EFFORT.
 
Thanks for starting a great thread @yoyoman. I've climbed a lot of DdRT but am newer to SRT and have been thinking a lot about redirects.

One of the key points I'm seeing in this thread - perhaps not specifically called out - is the concept of "force distribution vs multiplication." Said another way, using redirects to share the load amount various points in the canopy, rather than inadvertently creating mechanical advantage with one's climbing system.

That's exactly the challenge I encountered this past week. I'm curious to get anyone's opinion and feedback on the situation and solution. Sorry that I don't have pictures.

We climbed a large, spreading Horse Chestnut with perhaps 10+ large leaders. One of the outside leaders had recently failed and been removed. We were hired to deadwood the remaining tree and reduce length and end weight over the neighbor's property. This meant we needed safe access to make 2-3" reduction cuts on all literal tips. What's more, the drop zone was terrible, so most cuts had to be controlled and hand tossed to safe landings. No pole saw/pruner cuts.

The climbing challenge was that the majority of canopy (laterals and foliage) was on 3-4 exterior, leaning leaders, similar to the one that had previously failed. The interior leaders where very tall, skinny, and whippy, with few laterals and very little taper. We judged these central leaders to be easily strong enough for vertical ascent - using a canopy anchor - but unsuitable for significant lateral pull (i.e. limb walking). Two of us were climbing in this tree.

The other climber set up DdRT and used a second line to "backstay" his TIP to a second top.

My solution was to climb SRT and set a primary, retrievable canopy anchor in the tallest, best structured, somewhat-central leader, which happened to be on the opposite side of the tree. Then, I set up a 2 fixed redirects in other central tops as I traversed through the tree, each at a similar height (i.e. not above) my primary TIP. Each redirect incorporated a carabiner and knot to "fix" the tension between leaders and create "inline" backups to minimize lateral forces on the TIPs.

Then, at each major exterior leader needing limbwalking, I set a final redirect for work positioning. The concept was that the interior fixed redirects backstayed the exterior leader, so that I could be confident it would support my weight. I would definitely not have used these exterior leaders as a single TIP for any climbing system.

This system was somewhat time-consuming to set up, but seemed to be the best, safety option for accessing the tree. And the limbwalking access it provided was excellent for making the necessary tip reductions and controlling the cut limbs. Plus, it provided very good work positioning for accessing the entire tree.

I welcome anyone's feedback, suggestions ns and constructive criticism. Perhaps there was a better way.

Thanks again, @yoyoman and everyone who has contributed to this thread.
 
I'd say it sounds like a solid plan. I may not have bothered setting fixed anchors, I find that a half wrap around the stem at the redirect point creates sufficient friction to accomplish the same goal and takes less time to set up. Another advantage is that your line is still easily retrievable, as long as you don't get carried away wrapping your line! Not the best for thin bark either. Whichever way you set it up, it's worth the time invested for extra peace of mind and comfort.
 
You did a good job at exploiting the strength of an SRT system. One thing I might have done different is instead of just having a retrievable canopy anchor on your first suspension point, I would have added a base-tied leg. With it being opposite and away from your work area it would have created a stabilizing support that would have minimized any horizontal movement up top.
 
No Polesaw and pruner cuts?
Easiest way is to pull the limb/leader closer to you at a no risk comfortable place below, to the side or from above and make then make the cut. I have seen just as many bad hand saw cuts as pole cuts
 
DSMc said:
You did a good job at exploiting the strength of an SRT system. One thing I might have done different is instead of just having a retrievable canopy anchor on your first suspension point, I would have added a base-tied leg. With it being opposite and away from your work area it would have created a stabilizing support that would have minimized any horizontal movement up top.
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Good point. I'm typically hesitant about basal anchors for more than access due to force multiplication and the risk of inexperienced ground crew.
 
RopeShield said:
No Polesaw and pruner cuts?
Easiest way is to pull the limb/leader closer to you at a no risk comfortable place below, to the side or from above and make then make the cut. I have seen just as many bad hand saw cuts as pole cuts
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Fair comment. Just ain't the case in this tree. Much of the canopy was above a corrugated plastic patio roof and a fabric car shelter. No way I'm dropping 2" cuts over those fragile materials. Plus, we were reducing drooping tips at the bottom of the canopy, but still 30' off the ground, which wouldn't hold body weight and required full-on comp style limbwalking. Tiring but fun.
 
One rope with some MA to pull it close and an extra rope to grab the falling piece.
It's pretty easy to rope grapple or use your hook or snap cut. For the low canopy stuff I find it easier off a-frame ladder or just pull it down for a clip
 
We have some serious ice storm damage trees here in southern ontario. Finding longitudinal and slitting on limbs. Hard to judge what will hold or break. Easy thing is to pull it pus whip it and observe
 

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This is an excellent thread. Thank you @yoyoman for starting. So...when we figure out the load we put on the limb, branch, smaller branch...that's cool, but since we can't know each union or canopy anchor point, or redirect point's breaking strength aren't we still relying on so much intuition? As per species, time of year, climbing style etc?
I find when climbing single static I'm much more careful about shock loading. It makes for some boring and sometimes less graceful climbs. But then when I have the bomber canopy anchor, oh, the killer swings!
To analyze in real life situations, we'd have to measure the swing forces too, right?
 
roxy said:
This is an excellent thread. Thank you @yoyoman for starting. So...when we figure out the load we put on the limb, branch, smaller branch...that's cool, but since we can't know each union or canopy anchor point, or redirect point's breaking strength aren't we still relying on so much intuition? As per species, time of year, climbing style etc?
I find when climbing single static I'm much more careful about shock loading. It makes for some boring and sometimes less graceful climbs. But then when I have the bomber canopy anchor, oh, the killer swings!
To analyze in real life situations, we'd have to measure the swing forces too, right?
Click to expand...
The more we know, the less we have to guess at, and the more we know, the better our intuition.
Can you expand on the increased caution between SRT and DdRT on shock loading?
 
I should clarify that increased caution is when I find myself doing a redirect with a ring and revolver, and it's usually close to 90 degrees from my primary canopy TIP. I definitely pay closer attention to shock loading and movement in those situations. Moving horizontally across a canopy with four or five leads, all having about equal height for desirable Anchor points.
I don't basal anchor for climbing, only now and then for ascent only.
 
brydan said:
@TreeSpyder: On the pure-inline.swf, how are you coming up with 250 lbf in the green cord? I'm coming up with 288 lbf.
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YES!
Thanx, you are most correct.
Sorry, most brain activity used in learning drawing etc.;
constant fight not to get things twisted around on what actually trying to present!
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EDITED original post to your correction.
Fault was: using wrong potential force in equation
incorrect>> potential 500# load was being used
corrected>>potential 577# line tension is correct value to use in it's place
stayed same: sine multiplier .5000 for amount of potential realized on across line device force @30 degrees
incorrect value: 250#=500#Load as potential x .5000(sine of 30 degrees deflection from pure inline)
corrected value: 288#=577#Tension as potential x .5000(sine of 30 degrees deflection from pure inline))
(cosine for inline '%' of potential realized, sine for across/leveraged '%' of potential realized)
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proof:
Can show on calc toy, set load to 1000#
(1000/2 legs like in lower yellow, right corner of pic, on calc rather than 500/1 in this upper part of pic/below i believe you point to)
>>calc toy will give same numbers we show, more explanation etc., can check box on lower right and see imaginary lines of force that more distinctly show why trig is used
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philosophy:
Eye-brain constantly making assumptions, that lead to what we 'see'.
Thus magician's slight of hand can fool etc.
Good to know the real truth of patterns as math defines;
to define to train eye to what it really sees, then later in field can 'see' better/eye-brain tells more of truth.
Make most correct decisions, instinctively by feel know where to tweak, why, efficiently etc.
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story hour:
i dragged buddy's heavy Mercedes to shop w/lil'truck over weekend.
i tied a white plastic bag in center, he mocked i was being to careful on a Sunday drive.
Got to shop and mechanic pointed out bag; said can wreck 3 cars bad if someone runs between.
Happened many times, vehicles on rope smash to either side of car coming across rope!
Buddy didn't believe..
We took calc toy and set to 500# line tension for the 2ton+ vehicle rolling load coming away fr0m stop(ENTER);
Then set degree slider to 90/fully leveraged OUCH! numbers!,
>>well drop down to 89, like as car first slamming thru line at 20mph
Plenty of force at each end, AT HIGH IMPACT speed/ rate of change 1/10 second;
Plenty to ruin 3 car's day, and anyone else in their potential spinning zone!
i hope my buddy 'sees' and 'feels' at a glance now, need to flag between cars on tense line as law states!
(just as i trust he will have it in neutral when pulled next time, so i won't be sliding sideways on spinning tires...)
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Same in field, old experienced eye that sorts more faster, correctly can slop more accurately w/ease than those working it hard. Math patterns teaching eye real way to sort experiences can change a lot easily in less years!
AND see to turn all this upside down that try to protect systems from and see how to sweat/swig to put same forces in our favour!
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tech notes:
Flash is fading, Chrome and mobile devices generally NOT Flash friendly (base for calc toy and drawing)
(Flash gives vector calculated drawing pieces, shading and programmatic control)
Dream was a library of objects re-used for faster site in Flash.
So stopped development on rope-n-saw.swf as sorted collection
and now working on rope-n-saw-life.html leveraging a wonderful free tool :FancyBox (Apple-ish floating box)
Edited drawing correctness; exported from Flash to .png via screen capture to free GIMP:
pure_inline.png
 
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