Field testing and analysis of aluminum highway sign trusses

Four representative Illinois Department of Transportation (IDOT) highway sign support trusses were evaluated analytically and in the field to assess their design load capacity and fatigue resistance when subjected to wind loading. The three overhead span bridge and one cantilever welded aluminum truss structures were instrumented for static and dynamic field testing with strain gages and accelerometers to collect structural behavior data when subjected to manual excitation, wind loading, and truck gust excitation. Companion analytical models were developed and calibrated to represent the structures in the field, after which these were then used to assess the response of the trusses at full design wind loads. Current IDOT and AASHTO highway sign support structure design loading and resistance approaches with respect to both strength and fatigue have been critically assessed in light of the analyses and field test results, with recommendations made for improving future designs.

► The design load capacity and fatigue resistance of four sign supports was assessed.
► Drag coefficients used in the design code may be low based on experimental results.
► Allowable stresses may be exceeded in trusses with maximum allowed spans/sign areas.
► Some truss members exceed fatigue limits under combined wind and truck gust loading.