An aluminum pipe column (alloy 6061-T6) that is fixed at the base and free at the top has outside diameter d2 = 3.25 in. and inside diameter d1 = 3.00 in. (see figure).
Determine the allowable axial load Pallow for each of the following lengths: L = 2 ft, 3 ft, 4 ft, and 5 ft.