Cantilevered traffic signal structures are critical components of urban infrastructure, yet their slender, cantilevered design makes them especially vulnerable to wind-induced vibrations. These vibrations caused by mechanisms such as vortex shedding, galloping, and truck-induced gusts can lead to fatigue failures at the pole-to-mast arm connections, where stress concentrations are highest. Compounding the issue is the inherently low mechanical damping (typically 0.1% to 0.4%) in these structures, which exacerbates the amplitude and persistence of dynamic responses under wind loading.
This project builds upon a prior IDEA Type I project that investigated aerodynamic mitigation strategies for traffic signal structures through wind-tunnel laboratory testing and hybrid numerical simulation. The current project implements and validates the mitigation strategy on a full-scale traffic signal structure under natural wind conditions. While the concept of using flat-plate modifications to enhance aerodynamic damping is not itself new, the novelty of this project lies in the scale and scope of validation - namely, the long-term field monitoring of an in-service structure and the quantified demonstration of fatigue-life extension. The mitigation device leverages the geometry of the signal head to passively disrupt wind flow patterns around the mast arm, enhancing aerodynamic damping without requiring additional attachments or fine-tuning.
To evaluate the concept, a full-scale traffic signal structure in Ames, Iowa, was instrumented with accelerometers and strain gauges at critical locations. Over 5 months, the baseline dynamic response of the structure with Original Signal was recorded under varying natural wind conditions. Following this, the signal light design was updated to the version with integrated flat plates (also known as DynaSignal and called Modified Signal hereafter). The structure with Modified Signal was monitored for an additional 5 months. The aerodynamic modification led to significant reductions in both in-plane and out-of-plane vibrations, demonstrating rapid decay of large amplitude motion without adverse impact on the structural function. Importantly, the fatigue analysis confirmed an approximately 2.5-fold increase in estimated fatigue life as compared to the original structure. This research confirms that strategic aerodynamic modifications can effectively address the long-standing challenge of fatigue-prone vibration in cantilevered traffic signal structures. Importantly, the proposed solution does not increase fabrication costs and offers significant economic advantages by reducing long-term maintenance, avoiding structural failures, and extending service life. Also, the aerodynamic retrofit can be readily applied to existing traffic signal structures without requiring major modifications. The scalability of this aerodynamic approach holds promise for broader application to similar cantilevered structures such as overhead sign supports and lighting masts.
The Final Report is available here.
