Buckling of Suspended Cambered Girders

The process of designing a typical simply supported girder for service loads is well established. However, the fact that the girder will be suspended by cables during the erection phase affects the safety of the girder. Initial camber, such as in the case of prestressed concrete girders, aggravates the problem. The presence of camber causes the resultant of the load to be located above the center of torsion of the member, thus causing an increase in torsional moment with increasing lateral displacement. This behavior reduces the critical buckling load of the member and the safety of the girder. This paper presents the differential equations necessary to obtain the critical buckling load for a cambered member subjected to its own weight during lifting. Support conditions considered include: (1) Simply supported; (2) suspended by cables at the ends; and (3) suspended by cables located an equal distance from the ends of the member. Finally, sample graphs of the results are included to show the significance of camber in calculating the critical buckling load of a member.