3/8 Beeline Bridge

Tom,
I'm not sure about that...
Sure, intuition says that it'll last longer...but it's still a side load on something that's designed to be used in tension.

Rope bridges breaking IS a very serious issue, and we should be trying to find come way of quantifying what we're asking these fibers to do.....

Yes, we can talk about frequent replacement and only using cover dependant fiber.... but we can't reach everyone.

I'm very curious about measuring what forces are present.
How close to design limitations are we on a new rope bridge?
5:1? 10:1? 2:1? 100:1? dunno...

Does anyone know a rope manufacturer that has ANY type of machine to test this scenario?

C'mon folks... falling out of trees is no fun for any of us...
 
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it's still a side load on something that's designed to be used in tension.

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Following the same line of logic wouldn't the eye of any splice be "side loaded"? What about high lines?
 
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- There's got to be a measureable difference between side-loading a bridge and the similar side load on a spliced tight-eye.... I've never heard of a tight-eye failing a climber...why the bridges?

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Following the same line of logic wouldn't the eye of any splice be "side loaded"?

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Any eye, knotted or spliced, will be "side-loaded," and the rope at the load point has got to be weaker than the same rope in a straight pull. There seem to be 2 questions, whether side-loading around a carabiner greatly weakens the rope, and whether the fact that the bridge rope is spliced somehow makes this worse.

From ordinary pull tests where a spliced eye is one or both the attachment points we can answer the first question. Since ropes break before eyes fail, the side-loaded eye has more than half the original rope strength (the tension in the eye is half the rope tension).

Note that the photo posted by Jamin_Mayer shows a bridge that wasn't spliced at all, so we have at least one example of a failure in unspliced rope. At first, like Norm, I thought the break looked suspicious because it looked way cleaner than anything I have seen in normal tension tests. But when you think about it, this is exactly what you would expect if the rope was slowly failing from excessive flexing. The very center of the bridge would have been the hot spot for flexing. The climber's carabiner would have spent far more time there than any other spot on the bridge, and even the slightest motion of the climber would have caused flexing at that spot. After many months and probably tens of thousands of cycles, the center inch or so had self-abraded to the point that it was like bone with osteoporosis: it was basically rotten clear through. When it finally failed catastrophically, the break was relatively clean because the "rot" was highly concentrated in the center and fibers far from the center were too strong to break.

It seems to me the one huge difference between rope used in a bridge and rope used any other way is the thousands of cycles of flexing, in one very short stretch of rope, over the small radius of a carabiner. The evidence presented so far strongly points to this as the cause. It is interesting that we don't seem to have reports of the Warp Speed (Dyneema) bridge failing this way. The technical charts that show Dyneema being far more resistant to flex fatigue than Vectran or Technora would explain this and further support the hypothesis that flex fatigue is the culprit.
 
Thanks for the insightful post Moray...

And Banjo... yes, all splices and termination knots are side loaded.. but there is precious little cycling flex on them.

I don't know how to measure it.

Like Moray said above lots of cycles, small area of wear... fiber destruction.... carabiner is acting like a really dull knife if you can imagine that.... and... isn't a bridge usually loaded at around 90-120 degrees of angle as well... ??
we try not to load our rigging at those angles... ? :-O

Moray, do you know of anyone who might help us devise a test for flex fatigue?

Yours in trees,
Mark
 
Mark, it would be interesting to test the flex resistance of some of our ropes. You could rig up a geared-down electric motor to drive an eccentric wheel which would then pull the rope back and forth a short distance over a steel pin. You might have to run the thing a day or even a week to get the number of cycles you wanted.

Let's say you actually did this with several samples of new 8 mm Beeline and the samples were exposed to 2000, 4000, 6000, ..., 12,000 cycles with a 180-lb. weight. Now you break each one and record the break strength. Let's suppose you are lucky and you get a pretty smooth curve relating cycles to lost strength, and 6000 cycles represents 50% loss of original strength.

OK! You have done a hell of a lot of work, but can you use the results for anything? Nobody, obviously, is going to keep track of cycles while climbing around in the tree, so that number isn't going to be much use to you. According to reports, the cover often looks very good when the core has failed, so you can't judge your bridge by inspecting the cover, either. It seems to me you are right where you started even though you have a nice flex fatigue curve on your graph paper.

I think I would either entirely avoid a rope bridge or only use one where I knew the cover would show serious wear before the core was in a dangerous condition. Or use a core-only bridge where I knew it would show a lot of wear before failing. This hidden failure business is very scary.
 
Moray, Agreed on all grounds....

Too bad we can't solve all the world's problems.....
I'm praying that we don't lose a climber...to this issue.

I'm gonna stick to my master style saddle connections.
Wondering what the 'curve' would look like if we tested that?

And also wondering if we compared that curve to the rope bridge curve.... if a conclusion would be made that rope bridges are not worth the potential risk?

Not saying that rope bridges are unsafe.....
Change them often..and understand their construction!
Thanks for the great discussion.. I learned alot! :-)
Happy holidays to all...
Climb safe.
Mark
 
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