Wind-induced traffic signal structure response: Experiments and reduction via helical arm strakes

Traffic signal structures are prone to fatigue failures due to a combination of along- and across-wind dynamic response. Stress reversal magnitudes with respect to wind speed and direction are experimentally investigated in a natural wind environment for a typical cantilevered mast arm traffic signal structure. Results show a prevalence of in-plane response induced stresses due to vortex shedding for wind speeds in the range of 4–6 m/s. To better study the role of the tapered arm in the wind-induced response, the mast arm is retrofitted with helical strakes. Although the diameter of the mast arm is not directly related to the adverse stress reversals observed, arm strake installation significantly reduces the across-wind response attributed to vortex shedding. Results indicate that the slender mast arm section is critical in flow separation and vortex formation on the back side of the signal cluster backplates. As a result of the findings herein, properly designed helical arm strakes can be considered for reducing vibrations that can be attributed to vortex shedding, thus have the potential to reduce fatigue-induced damage in critical wind environments.