Question re. forces on system during lead fall

Question:

As a result of a lead fall, does each piece in the system receive stress to its placement? Say you have 7 pieces in, starting from the ground, and whip on the 8th. Obviously the 8th piece takes the brunt of the load. But what about the others? When the rope tightens how does it pull/stress the pieces below? If one pops will that add to the fall because of increased slack? And then of course the direction might be different than what was intended when you placed it.

Also another question. Does the number of pieces in the system below the fall impact the stretch of the rope for the fall? What about the amount of zig-zagging (ie rope drag) below the fall.

Lots of questions, but I'm hoping they are all associated with the same concept, and my inquiry makes sense.

Thanks for any thoughts.
Russ

Only the top piece (and the belay device and belayer) takes the load. Even if there is inadequte extension on the lower pieces, they are only seeing a fraction of the forces from the fall.

Not sure I really understand the question, though.

Agree with Frank that unless unusual circumstance like top piece blows, that there is minimal force on lower pieces. However, If you have rope drag through pieces below, it increases the total force on the top piece, which can be significant. All the drag below adds up, and more goes to the top piece while the belayer receives less.

petzl.com/US/en/Sport/Conse…

And if a lower piece pulls, especially if it is the next down the line from the top piece, you lose that as a backup should the top piece then subsequently fail.

The top piece ALWAYS take the ALL the force of the fall.

What changes with rope drag is the fall factor. The drag in the rope effectively shortens the rope, increasing the FF.

Although once you are protecting a traverse there are some vectors that come into play. Since the comes from the side and the force is down.

If this is the case, how does the "zipper" effect happen?

It's the amount of rope in play, not the friction in the system. Fall factor is so overhyped still, I can't even believe it.

There are many factors in force during a climbing fall, not just one.

Russ Keane wrote:If this is the case, how does the "zipper" effect happen?

A "zipper" is a result of several pieces failing sequentially. If it's from the bottom up (the lowest piece pulls out first, then the second piece from the ground, etc.), that's a result of the taut rope exerting a sideways pull on the pieces and the pieces not being able to handle the sideways pull (more extension needed, belayer stands closer to wall). If it's from the top down, that's just pieces pulling out sequentially from the fall forces.

Russ Keane wrote:If this is the case, how does the "zipper" effect happen?

Pro zippers because it can't hold in the redirection of pull.
When you plug pro left and right but don't use enough sling to let the rope run straight,the tension in the rope from a fall will try to straighten out the rope. This will cause the rope o pull the pieces out sideways. This may be OK with cams and/or certain well buried nut, it may not. If the pro can't hold this changed direction of pull, the pro will just pull out.

John:
Yes fall factor depends on the rope n play but the friction from rope drag changes the effective amount of rope in play. It can change it a lot.

True..but many things absorb the force of a fall..belayer, the rope,,gear..etc. The top piece doesn't take all the force of a fall.

Russ Keane wrote:Question: As a result of a lead fall, does each piece in the system receive stress to its placement?

Yes, unless the pieces are literally in a vertical straight line from belayer to the top piece. Force is transmitted to the piece via rope tension. If the tensioned rope makes any kind of bend at the piece, then there will be a force (determined by the parallelogram law for vectors) on the piece. Since most rope bends are small (meaning close to 180 degrees), the resultant load on the piece will also be small.

These small loads can nonetheless be problematic, as they may be in directions that might rotate the piece into a failure position or even extract it.

Russ Keane wrote: Does the number of pieces in the system below the fall impact the stretch of the rope for the fall? What about the amount of zig-zagging (ie rope drag) below the fall.

The answer is yes to both questions. Friction around carabiners reduces the tension in the rope, and the section with reduced tension stretches less. Rather than a single rope stetching enough to absorb all fall energy, you have sections of rope each with their own amount of stretch, generally decreassing the further the section is from the top piece. The effect of this is a higher load to the top piece than would have happened without all the intermediate gear, and a (sometimes much) lower load to the belayer.

There are two types of zippering. One is top-down as successive pieces fail; this is due to loads higher than the pieces can resist. The other is bottom-up; this is due to those pesky resultant forces lifting gear.

When you are actually leading, you don't think about vector diagrams, but there are two concerns related to force issues.

One is minimizing rope drag by striving to have your rope run in as straight a line as possible; this will of course automatically diminish the effects of rope angles at lower pieces.

The second is eliminating possible upward or sideways extraction loads on lower pieces. The best way to do this is to try to visualize the rope running absolutely straight from belayer to leader. This is the path the rope will "try" to attain in a fall, and proper slingage would ideally allow the rope to assume this direct path. But it isn't always possible or advisable to have "proper slingage," because the slings in question might have to be too long. In that case, concocting directional pieces to hold down the otherwise extractable pieces is the strategy of choice.

I've found it pretty instructive to see how the protection system is loaded by lowering off single-pitch trad leads that are less than half a rope length. Even after many many years of climbing trad, I still find that I've misjudged lifting potential for some placements. One of the many ways this can happen is that the sling you used is fine in terms of everything below, but some effective change in angle up higher causes that ideal straight-rope line to run significantly out from your placement. The take-home message is to not only look at the system below you, but also to try to anticipate how the rope will end up running up above you.

top down "zipper" doesnt always mean the load exceeded the ratings (of rock or gear)

what can and does happen as well is that the initial in the fall

- the top piece takes the load and fails
- however theres upward pulls of the rope in that instance when the top pieces catches briefly and it rotates the lower pieces upwards
- and these subsequently fail when loaded

a few years ago we needed to carry someone out because of this exact scenario ...

So the question becomes-

Do the lower gear placements even matter, if a fall occurs? Sounds like, if anything, they hinder a smooth fall by reducing stretch and thereby adding to the force taken by the top piece. In other words- Your best theoretic scenario would be to run it out all the way to the crux, then place your first piece, and you would have the best softest least violent fall.

Also in other words, what does it matter if you fall on piece 8 (which holds), and all the other pieces in the system fail below you? Total reverse zipper. Do those pieces below you help whatsoever, once you have moved passed them and you fall on something higher?

Things to ponder.

Russ Keane wrote:So the question becomes- Do the lower gear placements even matter, if a fall occurs? Sounds like, if anything, they hinder a smooth fall by reducing stretch and thereby adding to the force taken by the top piece. In other words- Your best theoretic scenario would be to run it out all the way to the crux, then place your first piece, and you would have the best softest least violent fall. Also in other words, what does it matter if you fall on piece 8 (which holds), and all the other pieces in the system fail below you? Total reverse zipper. Do those pieces below you help whatsoever, once you have moved passed them and you fall on something higher? Things to ponder.

The best theoretical scenario is never fall off.

yes they do matter as in real life things get unclipped, biners can break, the rock can shatter, etc .... redundancy when it you and the deck is a good thing

most lead falls dont see too much force (especially cragging) .... add in squishy masses, adjustable harnesses, stretchy ropes, etc ....

except on microgear i daresay that its not exceeding the gear rating that will get you, but rather poor placement, poor consideration of the rope path leading to gear movement or the rock breaking that will KAPUT ya

;)

Jim Titt wrote: The best theoretical scenario is never fall off.

Hehe... Jokes aside, it's unwise to keep just one piece between you and the ground. If you have to bring up your belayer, you have another reason to have those extra anchors. On the other hand, climbers place more gear near cruxes, because that's where it matters most.

FrankPS wrote: Not sure I really understand the question, though.

Then you shouldn't be answering it! Hello!

FrankPS wrote:Only the top piece (and the belay device and belayer) takes the load. Even if there is inadequte extension on the lower pieces, they are only seeing a fraction of the forces from the fall.

No, not really.

To answer the OP:

Lets start here. When a leader falls, all of his potential energy gets converted to kinetic energy. This = his mass times gravity times the height he will fall before the rope begins to tension (which is approximately twice his distance above his last piece).

Now, lets use one example. Leader places first piece 50 feet up from his belayer, climbs 10 feet above the piece and the rope is not touching the rock at all. When he falls, all of his kinetic energy will need to be dissipated. His body, his harness and the rope on his side of the top piece will absorb some energy. The belayer's side of the rope will need to have an equal and opposite... oh fuck this. Its late.

More drag in the rope means less "effective" rope in the system to absorb energy. This means more force on the top piece.

More "effective" rope between the leader and the belayer means more energy absorption by the rope and less by the top piece.

Less rope drag equals less load on top piece.

Greg D wrote: Then you shouldn't be answering it! Hello! No, not really. To answer the OP: Lets start here. When a leader falls, all of his potential energy gets converted to kinetic energy. This = his mass times gravity times the height he will fall before the rope begins to tension (which is approximately twice his distance above his last piece). Now, lets use one example. Leader places first piece 50 feet up from his belayer, climbs 10 feet above the piece and the rope is not touching the rock at all. When he falls, all of his kinetic energy will need to be dissipated. His body, his harness and the rope on his side of the top piece will absorb some energy. The belayer's side of the rope will need to have an equal and opposite... oh fuck this. Its late. More drag in the rope means less "effective" rope in the system to absorb energy. This means more force on the top piece. More "effective" rope between the leader and the belayer means more energy absorption by the rope and less by the top piece. Less rope drag equals less load on top piece.

Your post shows that it was indeed "late" when you submitted it.