Shockload Forces

Notes & Use

Calculates the force subjected to a body during a shockload event for the following cases:

  • Distance fallen, by stopping distance
  • Distance fallen, by wire rope type and diameter
  • Distance fallen, by rope (percentage elongation)

By Distance

Terms:
Variable Description Unit
$m$ mass pounds
$l_{fall}$ Falling distance in
$d$ Stopping distance in
$F_{shock}$ Force due to shockload lbf
Equation

$$ F_{shock} = m \, \left( \frac {l_{fall}}{d} + 1 \right) $$

By Wire Rope

Terms:
Variable Description Unit
$m$ mass pounds
$l_{fall}$ Falling distance in
$d_{rope}$ Diameter of wire rope in
$l_{rope}$ Length of wire rope ft
$x$ Wire rope area factor unitless
$E$ 15,000,000 psi
$F_{shock}$ Force due to shockload lbf
Equations

$$ F_{shock} = \left( 1 + \sqrt { 1+ \frac { 2 \, l_{fall} \, E \, x \, d_{rope}^2} { 12 \, m \, l_{rope} } } \right) $$

Wire Rope Area Factors
Type Factor
7x7 GAC 0.471
7x19 GAC 0.472
6x19W, fiber core 0.416
6x19W, IWRC 0.482
6x36WS, fiber core 0.419
6x36WS, IWRC 0.485
8x19W, fiber core 0.366
8x19W, IWRC 0.497

By Percent Rope Elongation

Terms:
Variable Description Unit
$m$ mass pounds
$l_{fall}$ Falling distance in
$l_{rope}$ length of rope ft
$F_{rope}$ force required to acheive manufacturer’s stated rope stretch lbf
$y$ elongation percentage
$F_{shock}$ Force due to shockload lbf
Equations

$$ a = \frac {0.005 \, y \, l_{rope} }{F_{rope}} $$

$$ b = -2 \, a \, m $$

$$ c = \frac {-m \, l_{fall}}{12} $$

$$ F_{shock} = \left( \frac { -b + \sqrt {b^2 - (4 \, a \, c)}} {4 \, a} \right) $$

Sources

Understanding shock Loads. Delbert Hall. TD&T, Vol. 49 No. 2 (spring 2013)