NDM-519: WIND TESTING OF SPAN-WIRE TRAFFIC SIGNAL SYSTEMS

Traffic signals are a critical part of the transportation infrastructure and it is important that they be robust enough to resist extreme wind storms lasting several hours. Failure of the signal systems results in unsafe traffic conditions during and after a storm, and the time taken for repairs delays recovery. A significant fraction of existing signals use span-wire supporting systems. The wire spans can range from 15 m to 60 m, depending on the width of the highway intersection, and exhibit nonlinear characteristics. The typical signal system used in Florida consists of the signal units, a catenary wire, hangers, a tensioned messenger wire, and the end support posts. The hangers are connected to the catenary wire at their upper ends and to the signal units at their lower end. They are also connected to the messenger wire just above the signal units. In light winds the weight of the signals is taken by the catenary wire and swinging of the signals is restrained by the messenger wire. In strong winds the combination of drag and lift forces on the signal units can result in substantial movement of the signals and changes in wire tension. To study the response of these types of system in strong winds the Florida State Department of Transportation has sponsored a research program at the Wall of Wind laboratory at Florida International University. The paper describes the development of a test rig that allows the non-linear response of the full scale signals to real wind conditions to be studied as a function of wind speed and direction. Preliminary results are also described, including the identification of an aerodynamic instability that can cause large amplitude oscillations of the whole signal system. The onset speed for the instability is a function of a number of parameters but most important are the signal geometry, the hanger design and the wire span