Narrow Results

A vehicle–bridge system with a tunable amplifier is proposed to enhance the resolution of frequency identification in the vehicle scanning method (VSM), with a particular interest in the wheel-center spectra to account for pitching responses. Both semi-analytical and finite element formulations are established. The viability of the proposed amplifier–vehicle–bridge system is demonstrated in consideration of bridge types and boundary conditions, damping effect, and pavement irregularity. The major findings include the following: (1) The tunable feature of the amplifier enhances the visibility of higher-order bridge frequencies in its spectrum. (2) The vehicle responses can be removed in the cancellation conditions of the amplifier while the resonance conditions of the amplifier are not affected by vehicle damping under harmonic excitation. (3) The shifted higher-order bridge frequencies are distinctly shown in the wheel-center spectra, indicating the potential use of pitching responses in VSM. (4) The pitching responses have shown that the front-wheel spectrum has a higher resolution than the rear one, as influenced by the driving direction.

Since the bridge is often treated as the uniform beam for simplicity in most numerical studies of vehicle-bridge interaction, this study proposes a non-uniform vehicle-bridge interaction system by incorporating a three-mass vehicle model in a non-uniform bridge for wider applications, in which non-uniform beam elements of constant width and varying depth are considered. For clarity, the inclined ratios of the entire bridge and one beam element are separately defined in order to describe the non-conformity in computation while both mass and stiffness matrices are re-formulated to comply with the finite element sign convention. As the natural frequencies of a non-uniform bridge cannot be accessed directly, the vehicle scanning method is first adopted to obtain the bridge frequencies. Then, the parametric study is conducted by considering vehicle damping, bridge damping, and pavement irregularity. In addition to the vehicle frequency, the numerical results show that the proposed vehicle-bridge interaction system is able to scan the first four bridge frequencies with desired accuracy subject to pavement irregularity. Concerning the pitching effect of the vehicle, it is shown that the locations for installing sensors are actually affected by both the geometry and the cross-sectional geometry of the bridge in the concern of achieving high resolution of frequency identification.

An advanced miniature vehicle model is proposed by incorporating size of two wheels in a three-mass vehicle model to consider the offset of contact points due to the presence of pavement irregularity. In this proposed vehicle–bridge system, each wheel has its own dimension in addition to the mass related to the degree-of-freedom while it is assumed to be rigid. In the theoretical formulation, the real contact points and contact displacements turn to be unknown parameters. As such, a numerical framework is established by proposing a procedure in the time integration scheme to determine these parameters and deriving explicit coding structure to locate the two wheels on the bridge during simulation. The parametric study investigates the size effect of wheels, effect of vehicle damping, and pitching effect as a result of wheel size on the identification of frequencies. The results show that using larger wheels leads to smaller dynamic responses of the bridge and smaller vertical responses of the vehicle by the present vehicle model. Furthermore, higher accuracy is observed in the proposed vehicle model in comparison with the traditional three-mass vehicle model. The first three bridge frequencies can be identified distinctly under the most severe pavement irregularity.