Probabilistic Vortex-Induced Vibration Occurrence Prediction of the Twin-Box Girder for Long-Span Cable-Stayed Bridges Based on Wind Tunnel Tests

The twin-box girder is a recommendable structural style for long-span cable-supported bridges due to its excellent aeroelastic stability. Vortex-induced vibration (VIV) is a typical wind-induced vibration for this kind of girder with a high occurrence probability associated with wind characteristics, structural properties and aerodynamic configuration under uncertainty. Therefore, probabilistic approaches should be adopted to predict the occurrence of VIV under uncertainty. This paper presents such an approach to predict the VIV occurrence using the decision tree method. Wind tunnel tests on a large-scale section model are conducted to investigate the effects of structural damping ratio and wind speed on VIV performance. Uniform and turbulent wind flow fields under three attack angles of - 3 degrees, 0 degrees, and - 3 degrees are tested. Moreover, wind direction at the bridge site is determined as a parameter affecting VIV occurrence. As a result, a decision tree considering the effects of structural damping ratio, wind direction and wind speed is formulated to estimate the probability of VIV occurrence. In order to suppress VIV, aerodynamic countermeasures (ACMs) with L-shaped windshields are applied. Furthermore, the probabilistic cost-benefit analysis of the application of ACMs is developed using a decision tree, and the probability of the positive cost-benefit from ACMs application is accordingly estimated. The application of the proposed probabilistic approach is investigated on a long-span cable-stayed bridge with two separated steel boxes.