Damping of Cantilevered Traffic Signal Structures

Abstract

Fatigue failure of cantilever (mast arm) supports for traffic signs and signals due to wind-induced vibrations has occurred in several states. A preferred method of reducing and perhaps eliminating these failures is to decrease the number and magnitude of load cycles by installing a damping device. Several types of damping devices were developed and tested on a mast arm at the University of Florida Structures Laboratory and field mast arm structures in Gainesville and Tampa, Florida. Both free-vibration and forced-vibration techniques were used to evaluate the responses of the structures. In addition, response under actual wind conditions was determined for the preferred damping device on the Tampa installation. Damping devices tested included tuned mass dampers, liquid dampers, friction dampers, damping devices installed at the arm-pole connection, and impact dampers. The preferred device was a tapered impact damper that functions in both the horizontal and vertical directions. This device was selected based on overall performance, applicability of a single device to a full range of field conditions, and economy of construction.