Development of a Vortex-Induced Vibration Analysis Process and Evaluation of Fatigue Damage Risk

Following a reported vortex-induced vibration (VIV) incident at a substation located in northern Tennessee, a structural monitoring project was implemented to investigate and evaluate the severity of the vibrations in the structure. The operational monitoring involved the continuous collection of weather information including wind direction and speed, air temperature, and structural responses, such as acceleration, base strain, and video recordings of the target structure. This paper presents the instrumentation and field monitoring application, along with the processing of the collected data for vibration event extraction, vibration analysis of the structure (based on the field data), and fatigue stress analysis. The large data set from the long-term monitoring was processed to identify vibration event cases. The vibration features extracted from the vibration events were used to update a finite element model of the structure, to represent the as-built system. In addition, video processing was used to extract the vibration features and verify the results of the vibration analysis. In addition to the surveillance video, the capability of cellphone-captured videos for vibration monitoring was demonstrated. To represent the vortex shedding forces on the structure, nodal harmonic force functions were defined and applied to the model. The dynamic loading on the structure model was verified, based on the collected structural response data gathered through monitoring. The results of the analysis were presented and compared with field data. This was used for fatigue stress estimation to consider the effects of stress concentration at critical joints. The presented process can be used to estimate the maximum vortex shedding-induced stress on structures during the design stage, in order to mitigate the risk of future fatigue damage or failure. This process, with further tests and validation, can be used to develop an approved industry analysis process, without the need for computationally expensive Computational Fluid Dynamics (CFD) modeling methodologies.