the yowie factor a simple estimate of the load rate during...
TRANSCRIPT
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Dave CusterCenter for Sports Innovation
Massachusetts Institute of Technology
a simple estimate of load rate during
climber fall arrest
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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
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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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stray EASgraphs
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alternate expression