Using Dynamic Responses of Moving Vehicles to Extract Bridge Modal Properties of a Field Bridge

The vehicles moving on a bridge excite bridge vibration and can also serve as response receivers because the vehicle dynamic response contains the vibration information of the bridge. A methodology was proposed in a previous study for extracting bridge modal properties, such as natural frequencies and modal shapes, from the vehicle dynamic responses. A specialized test vehicle consisting of a tractor and two following trailers was developed in which the two trailers towed by the tractor moving along the bridge were used as the dynamic response receivers. The responses of one trailer with a time shift were subtracted from the responses of the other to obtain the residual responses that were then processed with fast Fourier transformation (FFT) and short-time Fourier transformation (STFT) to extract the bridge modal properties. In the present paper, field test data of an existing bridge were adopted to verify the proposed methodology. In the vehicle and bridge system, a bridge finite-element (FE) model was updated using the measured accelerations and strains of the bridge; two types of test vehicle models were proposed for use in simulations of the tractor–trailer test system; and the measured surface-roughness profile was used in the numerical simulation. Parametric studies have been conducted to determine the trailer mass and stiffness. Vehicle Model I shows a good capacity for extracting bridge frequencies and the first two modal shapes with a dominant vertical component. However, Vehicle Model II performed better than Vehicle Model I on the extraction of bridge modal shapes that are dominant in lateral bending.