A 9-m-long steel [E = 200 GPa] pipe column has an outside diameter of 220 mm and a wall thickness of 8 mm. The column is supported only at its ends and it may buckle in any direction. Calculate the critical load Pcr for the following end conditions: (a) pinned-pinned, (b) fixed-free, (c) fixed-pinned, and (d) fixed-fixed.