JIB Crane Design Calculations

i would like 2 kno how to determune the bending sress on the column of the standing jib crane. i already calculated the bending sress on the jib arm due to a load of 4000lbs...i also calculated the compressive or bucling stress on the column..but i was told the column undegoes both bending and comresssive.is the bending cause by the same moment of the arm?? help plez..how do i design the column