Characterization, modeling and mitigation of vortex-induced vibration of slender cylinders

Slender cylindrical structural members have often been observed to vibrate at large amplitudes under wind excitation. Vortex-shedding was found to be one of the primary excitation mechanisms which manifests itself as distinct characteristics of the resultant problematic vibrations. The objectives of the proposed research are to formulate a methodology for predicting the aerodynamic damping under vortex-shedding as well as to develop mitigation strategies that can effectively suppress the problematic vibrations due to vortex-shedding. To accomplish these, mast arms of traffic signal support structures are chosen as representative subjects of a study that consists of both an experimental and an analytical/numerical components. A series of full-scale experiments was conducted to monitor wind-induced vibrations of a number of representative types of mast arms of traffic signal support structures and, on this basis, to characterize the vibrations and reveal the underlying excitation mechanism. To complement the data obtained in the full-scale investigation and clarify the vibration mechanism, wind tunnel tests were performed to study the aerodynamics of sectional models of cylinders of various types of cross-section and different tapering ratios that are either normal or yawed to the wind. Based on the findings from these experimental studies, research then focused on using analytical-numerical models to predict the aerodynamic damping of a slender cylindrical structural member under given wind excitation. At the same time, mitigation strategies based on addition of non-structural elements that alter the wind flow around the cylinders was developed and further was validated on full-scale structures.