P = 400 kN L= 3.75 m P2 = 720 kN L= 3.75 m A

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 400 kN, and the
second-floor load P₂ equals 720 kN. Each column has
a length L = 3.75 m. The cross-sectional areas of the
first- and second-floor columns are 11,000 mm² and
3900 mm², respectively.
(a) Assuming that E = 206 GPa, determine the
total shortening δ_AC of the two columns due to
the combined action of the loads P₁ and P₂.
(b) How much additional load P₀ can be placed
at the top of the column (point C ) if the total
shortening δ_AC is not to exceed 4.0 mm?