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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]