Field Tests and Analytical Studies of the Dynamic Behavior and the Onset of Galloping in Traffic Signal Structures

Unpredictable fatigue failures of cantilevered mono-tube traffic signal structures in Texas and throughout the United States in recent years have created the need to study their fatigue behavior. Based on recent research, the AASHTO specification has adopted a design equation for galloping loads that is overly conservative in many cases. The Texas Department of Transportation is interested in establishing design criteria for galloping that more accurately represents galloping potential and provides a more efficient design. In this study, three signal structures in Texas were monitored for a total of 9 months to detect the magnitude of galloping forces experienced in the field. Although large amplitude displacements were measured in the field, sustained galloping did not occur. In addition to the field tests, an analytical model was developed and used to perform a parametric study for predicting the galloping potential of traffic signal structures with various properties. The analytical model suggests that modifying the aerodynamic properties of the sign and signal attachments may be the most effective way to eliminate galloping.