Theatre Design & Technology - Spring 2013 - 51

This is significantly less than the 4,411.88 pounds of shock load that
occurred on the same fall using wire rope.

method #2: Yale Cordage does not list the elongation of their ropes in
percentages of the breaking strength as New England Rope does, so the
equation above will not work. Instead, Yale Cordage provides energyabsorption data that is based on the weight of each rope. For example,
Yale Cordage's Double Esterlon rope, a low-stretch rope, has a "green
working energy absorption" of 291 foot-pounds per pound of rope. A
5/8-inch Double Esterlon rope weighs 13.7 pounds per 100 feet (or .137
lbs/ft) and has a recommended working load limit of 3,400 pounds at 20
percent of its breaking strength (a 5:1 design factor). As before, let's use a
200-pound load falling 1 foot on a 10-foot-long piece of rope.

Energy-Absorption Capacity = 398.67 foot pounds

Since the force being placed on the rope (200 foot pounds) is less
than the Energy-Absorption Capacity (398.67 foot pounds) of the rope, we
know that the rope will be able to sustain the shock load without failing.
However, to find the actual shock load on the rope, we use the equation
Shock Load =

Force
× Recommended Working Load
Energy-Absorbing Capacity

So, for Yale's 5/8-inch diameter Double Esterlon rope (which has a
working load limit of 3,400 pounds at 5:1), the shock load is:
Shock Load =

200
× 3,400
398.67

Shock load = 1,705.67 pounds

First, we need to calculate the force of the fall:
As we can see, Yale Cordage's 5/8-inch diameter Double Esterlon has
less elasticity than New England Ropes Multiline II but a great deal more
elasticity than 1/4-inch 7x9 GAC wire rope.

Force = Load × Falling Distance
Force = 200 pounds × 1 foot
Force = 200 foot-pounds

Next we calculate the energy-absorption capacity of our rope using
Yale Cordage's equation:
Energy-Absorption Capacity = Length of Rope × Green Working Energy Absorption × Weight of 1 foot of rope
Energy-Absorption Capacity = 10 feet × 291 foot pounds × 0.137 pounds
per foot

Shock loadS on chain
The steel in an alloy chain has a modulus of elasticity of 30,000,000 psi, so
it has even less elasticity than wire rope and, therefore, potentially greater
shock loads. This is why the shock load on the beam supporting a load
being lifted by a 16-foot per minute (fpm) chain hoist can be 20 to 50

s p r i n g 2013

theatre design

& technology

49



Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 2013

Contents
Theatre Design & Technology - Spring 2013 - 1
Theatre Design & Technology - Spring 2013 - 2
Theatre Design & Technology - Spring 2013 - 3
Theatre Design & Technology - Spring 2013 - Contents
Theatre Design & Technology - Spring 2013 - 5
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