고체역학 (Gere) — Axially Loaded Members: Problem 2.7-3

2.7-3 A three-story steel column in a building supports roof and floor loads as shown in the figure. The story height \(H\) is 3 m, the cross-sectional area \(A\) of the column is 7500 mm², and the modulus of elasticity \(E\) of the steel is 200 GPa. Calculate the strain energy \(U\) of the column assuming \(P_1 = 150 \text{ kN}\) and \(P_2 = P_3 = 300 \text{ kN}\).