Dave CusterCenter for Sports Innovation

Massachusetts Institute of Technology

a simple estimate of load rate during

climber fall arrest

Yowie, ISEA 2006 2

an overview of this talk final thoughts

the starting point

the simple model

some compli-cations

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•determine degree of “impact”

•make impact accessible

•guide safety system design

both ice and ice screws exhibitreduced strength with increased load rate. a 100 X increase in ratehalves the strength.

motivation

objectives

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methods

determine the load rate based on a (very) simple rope model

compare the simple model to complicated models (Wexlerand Pavier)

compare the simple model to data (Mägdefrau)

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expected kinematics behavior

Yowie, ISEA 2006 6(based on Wexler work)

the simple model

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the simple estimate of load rate

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inclusion of potential energy of stretch

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complications

•rope damping

•carabiner friction

•belayer behavior

•energy absorbing systems

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how does one compare a spring to adamped spring system?

I haveno simpleanswer;rather, 4complicatedones.

Pavierspringspring/dashpotmodel

Wexlerspringmodel

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damping I

here, theadditionof damping increasesload rate

same force

same stretch

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damping II

“critical” dampingproduces a loadrate midway between the top spring and the two springs in series.

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carabiner friction1) increases the force on the top anchor but does not change the proportionality of the yowie factor

2) decreases the effectiverope length and thus also

increases the fall factor; expect a 20%increase in load rate &

reduced proportionality

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belayer behavior

the belayer can reduce the energy absorbedby the rope by allowing rope to slip through the belay device and by being lifted up. thereduced energy results in reduced force,increased time, and thus reduced load rate.

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energy absorbing systems

EAS reduce load rate

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model compared to data

model and data correlate only loosely

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conclusionsas a rule of thumb:

•climbers can apply the rule by protecting the belay and usinglow “modulus” ropes.

•in the future, the rule might be used to guide the design of better ice screws and perhaps the use of plastic anchor components.

•use EAS and a dynamic belay.

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acknowledgements• title slide photo by Luca Marinelli• many thanks to the folks at MIT’s

aero/astro department and center for sports innovation

• kudos to Susan Ruff for patient editorial comment

Mägdefrau, H., (1989) Die Belastung des menschlichen Körpers beim Sturz ins Seilund deren Folgen, dissertation, Ludwig-Maximilians University, translated by David LiaBraaten, 1994.

Pavier, M. (1998) Experimental and theoretical simulations of climbing falls, Sports Engineering, 1, 79–91.

Wexler, A. (1950) The theory of belaying, American Alpine Journal, 7, 379-405.

abridged bibliography

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Yowie, ISEA 2006 20

stray EASgraphs

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alternate expression