Abstract
Vortex-induced vibration (VIV) of bridges, related to fluid-structure interaction and maintenance of bridge monitoring system, causes fatigue and serviceability problems due to aerodynamic instability at low wind velocity. Extensive studies on VIV have been performed by directly measuring the vortex shedding frequency and the wind velocity for indicating the largest girder displacement. However, previous studies have not investigated a prediction of wind velocity to raise VIV with a various natural frequency of the structure because most cases have been focused on the estimation of the wind velocity and peeling-off frequency by the mounting structure at the fixed position. In this paper, the method for predicting wind velocity to raise VIV is suggested with various natural frequencies on a road-rail bridge with truss-shaped girder. For this purpose, 12 cases of dynamic wind tunnel test with different natural frequencies are performed by the resonance phenomenon. As a result, it is reasonable to predict wind velocity to raise VIV with maximum RMS displacement due to dynamic wind tunnel tests. Furthermore, it is found that the natural frequency can be used instead of the vortex shedding frequency in order to predict the wind velocity on the dynamic wind tunnel test. Finally, curve fitting is performed to predict the wind velocity of the actual bridge. The result is shown that predicting the wind velocity at which VIV occurs can be appropriately estimated at arbitrary natural frequencies of the dynamic wind tunnel test due to the feature of Strouhal number determined by the shape of the cross section.
Highlights
Vortex-induced vibration (VIV) is usually classified as a detrimental factor that causes bridge fatigue and serviceability problems due to aerodynamic instability at low wind velocity in the operating status of a bridge [1,2,3].erefore, predicting VIV caused by wind loads is an important factor in the maintenance of the bridge
VIV phenomenon is estimated by the Strouhal number (St) proposed by Vincenc Strouhal [4] in 1878. e Strouhal number, a dimensionless coefficient determined by the shape of the structure, is expressed by the vortex shedding frequency, the structure shape, the wind velocity (V), and the shape parameter (D). at is, for a given shape, the Strouhal number is determined by the current fs and U, as given by
In the case that VIV occurs in a road-rail bridge with a trussshaped girder, the Strouhal number can be estimated by the wind velocity and the vortex shedding frequency when the frequency is close to the natural frequency of the structure
Summary
Vortex-induced vibration (VIV) is usually classified as a detrimental factor that causes bridge fatigue and serviceability problems due to aerodynamic instability at low wind velocity in the operating status of a bridge [1,2,3]. Sakamoto and Haniu [9] conducted wind tunnel test and flow visualization using mounted spheres at a fixed position, and vortex shedding patterns of sphere are classified in five characteristic regions according to changing of Reynolds number. On the related research for VIV, He and Li, Tao et al, Laima et al, and Wu et al [22,23,24,25] conducted the dynamic wind tunnel test using spring supported system, but their research was not focused on estimating the wind velocity He and Li paid attention to the fact that the geometrical effects of the girders can have the mitigation effect of the amplitude of the vortex oscillation. According to the properties of the Strouhal number determined by the shape of the structure, the method of estimating the wind velocity to raise VIV at any structural frequency is reasonably measured when the bridge shape is constant. It is shown that the wind velocity can be reasonably estimated with a dynamic wind tunnel test even if the natural frequency of the test structure is unknown
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