Temperature changes cause the body to expand or contract. The amount δT, is given by
$\delta_T = \alpha L \, (T_f \, - \, T_i) = \alpha L \, \Delta T$
where α is the coefficient of thermal expansion in m/m°C, L is the length in meter, Ti and Tf are the initial and final temperatures, respectively in °C. For steel, α = 11.25 × 10-6 m/m°C.
If temperature deformation is permitted to occur freely, no load or stress will be induced in the structure. In some cases where temperature deformation is not permitted, an internal stress is created. The internal stress created is termed as .