A single column is obtained by placing two identical channel sections back to back as shown in the figure. The channel sections are connected with the help of lacing bars (not shown in the figure). Determine the spacing d between the channels so that the buckling load is maximum for the column. Determine the buckling load if E = 70 GPa. The length of the column is 5 m. The column is fixed at one end while the other end is pinned. [16]