A two-story column ABC in a building is constructed with a hollow, square box section (see figure). The outside dimensions are 200 mm x 200 mm, and the wall thickness is 15 mm. The roof load applied at the top of the column is P1 = 312 kN and the floor load applied at midheight is P2 = 445 kN. Obtain the compressive stresses σab and σbc in the two parts of the column due to these loads.
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