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Problem $02\mathrm{.}054-$ Thermal stresses in a rod with ends restrained

$10-$m$-$long steel rails of a railroad track $(E_S=200$GPa and $a_S=11\mathrm{.}7\frac{{10}^{-6}}{}C)$ were laid at a temperature of $10C.$

Problem $02\mathrm{.}054.$b $-$ Thermal stresses in a rod with ends restrained

Determine the normal stress in the rails when the temperature reaches $48C,$ assuming that the rails are $10m$ long with $3-mm$ gaps between them.

The normal stress in the rails is

MPa.