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Open girder sections are vulnerable to vortex-induced vibrations (VIV) because of their bluff aerodynamic characteristics. A comparative investigation was conducted by wind tunnel tests and numerical simulation. Firstly, based on sectional model wind tunnel tests, the VIV performance of semi-open girder and separated edge-boxes open girder was studied with consideration of the influence of the equivalent mass, wind attack angle and damping ratio. The aerodynamic parameters Scruton number (S c ) and Strouhal number (S t ) of two girders were analyzed contrastively. In addition, VIV amplitudes corresponding to the real bridge girders were calculated by the linear and nonlinear theories. Then, flow fields around two semi-open girder sections were investigated on the basis of computational fluid dynamics. The results show that vertical and torsional VIVs of two open girders are observed, at +3°and +5° wind attack angles. There were two vertical VIV regions and the maximum amplitude in the second vertical VIV region is significantly larger than that in the first one. For the semi-open girder and separated edged-box open girder, the vertical VIV amplitudes at +5° wind attack angle is 115% and 75% larger than at +3° wind attack angle, respectively. The damping ratio could obviously mitigate the VIV of two girders and VIV amplitudes are decreased linearly with the S C number increases. There are vortexes above the girder deck at the opening position of the semi-open girder and the separated edge-boxes open girder. The oblique web and wind faring may break the large vortex into several smaller vortexes at the opening position, thus optimizing the vortex vibration performance of the girder. A thicker shear layer is formed at separated open-girder during the development of airflow towards backward of bridge deck, due to the effect of railings and the blunt boxes on the lower surface. [ABSTRACT FROM AUTHOR]

The nonlinear flutter of a narrow railway truss girder are studied through free vibration and forced vibration wind tunnel tests. Four functions are used to fit the structural amplitude-varying damping ratio under no wind condition, and the fourth-order polynomial has higher goodness-of-fit. The narrow truss girder shows nonlinear flutter of a velocity-restricted type without amplitude hysteresis. At large angles of attack (AoA), the vertical participation and the AoA have little effect on the onset wind speed and amplitude. While at medium AoAs, even a low vertical participation level will increase the onset wind speed and decrease the amplitude. At small AoAs, there is no vibration observed. The flutter derivative A 2 * is positive only in the limited reduced wind speed and amplitude range. The nonlinearity of self-excited lifting moment is higher only in the limited reduced wind speed and amplitude range, while that of self-excited lift is weaker and becomes stronger with the increasing amplitude and reduced wind speed. The negative aerodynamic damping is mainly provided by the flutter derivative A 2 * at small or large AoAs. Generally, the nonlinear flutter response is mainly controlled by the first-order component of the self-excited force, and the influence of high-order components can be ignored. • Relatively complete study of a narrow truss girder's nonlinear flutter characteristics. • The unique characteristics of the key flutter derivative A 2 * and self-excited lifting moment. • Analysis and verification of the influence of higher-order components of self-excited force on nonlinear flutter. [ABSTRACT FROM AUTHOR]

Accurately identifying the aerodynamic loads on vehicles is the fundamental issue for assessing the driving safety of vehicles on long-span bridges subjected to strong crosswinds. Thus, the aerodynamic interference of bridges with vehicles must be considered. However, very few studies have been conducted to quantify both the steady and unsteady crosswind loads for vehicles on wide bridge decks. In this paper, the mean and peak aerodynamic coefficients and aerodynamic admittance functions for three types of high-sided vehicles (medium trucks, buses, and tractor-trailers) on two wide bridge decks (a single-box girder and a twin-box girder) were determined by means of wind tunnel tests. The effects of vehicle position, wind angle of attack, and geometric shape of the deck on these aerodynamic parameters were investigated. The results show that the aerodynamic coefficients of vehicles on both bridge decks vary significantly with their lateral position. Moreover, the effect of wind angle of attack on the aerodynamic coefficients of vehicles on the leeward side of the twin-box girder is extremely substantial, as is the geometric shape of the bridge deck. However, the vehicle position, wind angle of attack, and bridge deck geometry all have little influence on the aerodynamic admittance functions of vehicles. • Various cases on steady and unsteady aerodynamic forces of vehicles on two wide bridge decks under crosswind are studied. • Bridge deck geometry, vehicle position and wind angle of attack have significant effects on aerodynamic parameters of vehicles on bridge decks. • Empirical expressions of aerodynamic admittance functions of vehicles on wide bridge decks are fitted. [ABSTRACT FROM AUTHOR]