Anchor testing of equalized anchors (cordelettes)

More recent information has been published on cordelettes and alternative equalizing systems (and I'll track those down), but here is some work from 2004-2005 by Beverly et al. on the effectiveness of cordelettes at equalizing loads. (Climbing Nerd Level 1)

Meaty tidbits of knowledge:

• Even with a symmetrical setup, the load is not perfectly distributed among the legs
• Asymmetrical or off-axis setups aren't always worse than a symmetrical setup
• Under load, the system can stretch as much as 10 cm (4 inches)
• The authors didn't discuss it, but it looks like the middle or the shortest leg often had the greatest force
• The force required to break one of the legs was >15.2 kN (pretty high!)
• Going with four pieces instead of three didn't necessarily increase the strength of the anchor (why waste pieces?)
• Even if your anchor spans a total angle of 90 or even 120 degrees, finding the best pro placements is more important to the structural integrity of the anchor
• Avoid short, stiff legs; better to extend the other pieces so the cordelette has more uniform legs

The article also references some previous research that showed...

• the shelf is an appropriate clip in point
• an overhand is sufficient

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Link to source file (Multi_pointpre_equalizedanchors.pdf): http://www.sendmefile.com/00547721

Not climbing physics, but what do climbers think? (Beverly, 2005)

Beverly conducted an online survey of climbers in 2005, and found some really interesting responses to 28 questions from 407 climbers. (Climbing Nerd Level 0)

Did you know that...

• 73% expect their belay device to hold fall factor 2 events (see separate blog entry)
• 71% have had some formal climbing training
• Only 25% believed that ice screws should be placed angled 10 to 20 degrees down from perpendicular to the ice (31% said up and 16% said straight) (see separte blog entry)
• 50% of climbers have taken <10>
• Only 9% of climbers have taken falls with a fall factor >1.5, but 20% have witnessed other climbers taking FF1.5-2 (so who are they?)
• Only 24% of respondents had a piece of pro fail during a fall, so 76% have not had pro fail
• 51% had been hit by rockfall while climbing
• 18% report climbing weights >190 lbs, which means those standard tests for gear strength don't necessarily apply
• 41% had witnessed a climbing accident where bones were broken from a fall
• 17% had needed assistance or rescue from a climbing accident

Here's something interesting. In response to the question, what's the greatest distance you have fallen on a rope outside...

• 32% had fallen <10>
• 31% had fallen 10 to 20 ft
• 17% had fallen 20 to 30 ft
• only 20% had fallen over 30 ft

Median number of days climbing per year...

• 24 in a gym
• 12 sport climbing
• 10 multi-pitch trad climbing

So who are these climbers?

• 34% belong to a local climbing club
• 29% belong to a mountain search and rescue organization
• 19% belong to the Access Fund
• 29% don't belong to any of these

Link to the report summary (WhatClimbersThink.pdf): http://www.sendmefile.com/00547713

Defining Climbing Nerd Levels

How to put an objective measure on a subjective rating? I am a nerd and I climb; therefore, I am a climbing nerd. But there are oh so many shades of climbing nerdiness, and the subject I include in this blog will appeal to climbing nerds of all levels. Here's my shot at a rating system:

• Climbing Nerd Level 0- Math class is soooo hard! How do you spell fiziks anyway?
• Climbing Nerd Level 1- I climb, and I want to live. It would probably make sense to learn a little more about the systems that I use to attach myself to the world.
• Climbing Nerd Level 2- Wow, I guess physics really does have a practical application, and I secretly enjoy the greek letters and equations, even when I don't entirely understand what they mean.
• Climbing Nerd Level 3- Physics rocks! I'm going to buy my own dynamometer to double-check these findings.

Enjoy!

Ice Screw Testing in Ouray, CO (Beverly and Attaway, 2005b)

It's the ice, stupid!

We've been taught this about falls while ice climbing: DON'T. Not bad advice, but what's it based on? Yes, there are all of those sharp objects involved with our choice of climbing medium, any one of which could do severe damage. But just how much can that screw hold? Beverly and Attaway put real screws to the test in vertical waterfall ice. (Climbing Nerd Level 2)

They tested three hypotheses:

1. The force determines whether the ice screw fails or not


2. Short screws in good ice don't resist high forces


3. Falls on ice protection generate the same forces as falls on rock protection, and placed correctly in good ice may surpass rock gear

Previous drop testing on screws in aerated ice by Luebben found lots of failure, but the study did lead to a change in the orientation of ice screws: counterintuitively, 10 to 20 degrees downward instead of the previous practice of 10 to 20 degrees upward. (Why? Because a hollow tube resists a force better because of skin friction (and threads) than taking a force from the side.)

Details: GriGri with a stopper knot to reduce rope slippage, Rescue Randy (172 lbs.), ice type typical of most water ice characteristics, fall factors 1/2/1.7, both lead climbing and anchored set ups. Screws tested: Grivel 360, Petzl Laser, Petzl Laser Sonic; all (13-cm?) stubbies.

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Meaty tidbits of knowledge:

• Ice screws failed when the force was between 4 and 14.5 kN (message: ice screws can fail under pretty low load when placed in suspect ice as was the 4-kN test event)


• Ice screws held forces between 5 and 15 kN (message: ice screws can hold even under pretty high load)


• 11 out of 61 tests showed screw failure, which means 50 out of 60 held the fall

Huh? The screws that failed tended to face a higher load than those that were successful, but clearly there are other factors at play besides how much force is placed on the screw. Turns out it's selecting good ice for placing a screw. Anecdotally, they mention that they found more failures in the morning than in the afternoon, possibly because of morning/afternoon temperature changes. Brittle conditions appear more prone to failure.

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Recommendations:

• The fall factor 2 drops generated a maximum force of 8.6 kN with no failures, but this is not a good reason to place your first screw way above your last anchor


• Place screws in a zone of compression (read this as a concave depression, as opposed to a convex zone of tension)


• Small air bubbles doesn't necessarily mean it's poor quality ice


• Ice hooks did not hold any falls

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Source file (sorry for the ads) DynamicShockLoadEvaluationofIceScrews_Final.pdf: http://www.sendmefile.com/00547701

Belay Device Tests (Beverly and Attaway, 2005)

(or, Why Friction is Our Friend)

How do belay devices work? What forces are generated by falls? What are UIAA requirements for belay devices?

These are some of the questions the paper (link below) addresses, and it raises the issue that some manufacturers do not recommend using their gear in falls with a fall factor greater than 1. And, there is no strength standard for belay devices, mostly because CE standards are for passive activites, rather than actions like a human stopping a fall with a belay device. The paper argues for a strength standard for belay devices and covers the minutiae of testing variables, like age of the rope, the use of an 80-kg weight to represent a more pliable and stringy human, auto-locks vs. hand braking, etc. This part will appeal to Climbing Nerd Level 3 (whatever that is-- maybe I should define it?).

But, what might be of interest to recreational climbers is the static pull testing Beverly and Attaway performed on many belay devices on the market today. Check out Figure 11 on page 17-- a reminder that ascenders are designed for ascending. Think before using these devices on fixed lines-- could you generate a 5-kN force? Quite possibly. And, Figure 13 confirms that dynamic events are a whole other story. Avoid fall factor 2 dynamic events (duh!). Climbing Nerd Level 2.

Link to belaydevice_Hang_Em_High_Final.pdf:

http://www.sendmefile.com/00547691

Strength of Snow Anchors and Pickets (from New Zealand)

New Zealand snow science people did a bunch of research and compiled information on the strength of snow anchors. Good reading for nerds, but there are some great concepts and issues that are raised that should be of interest to anyone who has ever used a picket. Here's a link to the source file (snowanchors_newzealand.pdf):

http://www.sendmefile.com/00547648

(Sorry about the ads on the free file hosting site-- it is safe to download from this site. Just close your eyes for five seconds. Hopefully blogger adds PDF capability soon.)

Much of the discussion is based on potential rescue loads of 20 kN, but the concepts are also applicable to climbers using snow anchors for pro, belay anchors, and rappels. Overall I would rate it a Climbing Nerd Level 2.

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Consider these points:

• Strength of the snow (powder snow vs. consolidated and moist snow-- can you make a snowball?)
• Connection point to the anchor (top hole, middle hole)
• Upright or horizontal (deadman) placement (angle of placement important for uprights)
• Carabiner clip vs. girth-hitched sling
• Picket material (aluminum vs. steel)

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Meaty tidbits of knowledge:

• Deeper horizontal (deadman) placements have a higher strength than shallower, because they create a larger "failure cone"
• For multiple placements, like in an equalized anchor, separate by a distance at least twice the depth of the deepest anchor
• If belaying from a snow anchor, keep at least 1.5 meters (4 to 5 feet) between the anchor and the belayer to avoid pulling up on the anchor
• In strong snow, tilt the picket back no more than 10 degrees from perpendicular to the snow surface to maximize the cone
• Beware of placements where the direction of pull is upward (running belays over a lip, belay anchors)

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Recommendations:

• For snow that can be compacted (you can make a snowball), use an upright placement with a midclip or a horizontal placement (deadman) with a midclip
• For snow that is too hard to dig a trench, use an upright placement with top clip tilted back 10 degrees
• For very cold or very wet snow that cannot be compacted into strong snow (less typical in the Cascades), use a picket placed as a fluke or a horizontal placement (deadman)

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Cool stuff, no?

Climbing physics and other nerd stuff

I've begun to collect a bunch of information on the physics of climbing, not just because I'm a nerd, but because it's not really compiled in any one location. As I find other sources of information, I'll add in here.