Contemporary freeway operations require large signs over traffic lanes. These signs are usually attached to trusses mounted on vertical supports which are restrained cantilever beams. The 1968 AASHO specifications require that the critical buckling stress be limited by a formula based on theoretical and experimental investigations of a simple beam subjected to loads producing pure bending. The purpose is to examine this formula to determine its applicability to highway sign supports, and to develop a suitable alternate requirements. Rigorous adherence to the present AASHO requirement results in uneconomical open sections for overhead sign bridge supports which are fixed at the base, restrained from lateral movement at the top, and are subjected to wind and dead loads which produce lateral, transverse, axial, and moment forces. The same conditions exist on roadside signs with two or more supports, but the critical buckling stress requirement does not greatly affect the selection of economical flanged shapes for such supports. A formula is developed for critical buckling stress, and it is shown that this formula is in agreement with available test results. Comparisons of other theoretical buckling formulas with test data are also presented. /author/
Abstract