On galloping vibration of traffic signal structures

Abstract Under certain wind conditions, some cantilevered traffic signal structures vibrate with large amplitudes. These vibrations generally occur in wind speeds of 4.5 m/s (10 mph) or slightly higher with wind approaching the signals from the backside. The vibrations are steady up and down motions perpendicular to the wind direction. These vibrations may lead to fatigue failures, in addition to being a distraction to passing motorists. A series of experiments in a tow tank at Texas Tech University revealed that certain configurations of traffic lights satisfy the Glauert–Den Hartog criterion for galloping. Further, wind tunnel tests with a sprung model were conducted to check whether there was an alternative explanation for the vibration. Vibration mitigation measures were devised and tested in a wind tunnel and in full scale. In this paper, the results from the wind-tunnel experiments conducted on a quarter-scale model are presented and analyzed; the results from the tow-tank and full-scale experiments are not included in this paper. Two primary objectives of this work were (a) demonstrating the effective use of a plate as an aerodynamic damping device, and (b) applying the flutter theory to explain the galloping vibration.