A two-story building has steel columns AB in the first floor and BC in the second floor, as shown in the figure. The roof load P1 equals 400kN and the second-floor load P2 equals 720kN. Each column has length L=3.75m. The crosssectional areas of the first- and second-floor columns are 11000mm2 and 3900mm2, respectively. Assuming that E=206GPa, determine the total shortening AC of the two columns due to the combined action of the loads P1 and P2. Ans AC=3.72mm Solution As the force, area, and elastic modulus are constants along the member length; therefore, the deformation can be determined based on Eq. 3-4