Utility Pole

#317 / Mechanics of Materials Easy

Consider a utility pole is constructed from a hollow circular tube of passivated aluminum to support a compressive load. The inner and outer diameters of the 144 inch long tube are 6 inches and 12 inches respectively. If the pole shortens by 0.025 inches due to its load, calculate the utility pole’s strain.

Expand Hint
Strain is the change in length per unit length.
Hint 2
$$$\varepsilon=\frac{\Delta L}{L_o} $$$
where $$\varepsilon$$ is the engineering strain, $$\Delta L$$ is the change in length, and $$L_o$$ is the original length.
Strain is the change in length per unit length.
$$$\varepsilon=\frac{\Delta L}{L_o} $$$
where $$\varepsilon$$ is the engineering strain, $$\Delta L$$ is the change in length, and $$L_o$$ is the original length. Therefore:
$$$\varepsilon=\frac{-0.025in}{144in}=-0.00017$$$
Note: the length is reduced so the change in length needs to be negative, and that cross section does not impact strain.
-0.00017


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