SSC JE Civil Engineering 2014 Set 1 Solved Paper

Strain energy due to gradually applied axial load = U $=\left(\frac{1}{2}\right)\times \mathit{P}\times \mathrm{\Delta }$
Axial deformation due to sudden load is twice the axial deformation due to gradually applied axial load;
Hence strain energy due to suddenly applied axial load will be
U $=\left(\frac{1}{2}\right)\times \mathit{P}\times 2\mathrm{\Delta }=\mathit{P}\mathrm{\Delta }$