The non-stationarity of apparent bridge natural frequencies during vehicle crossing events

In this paper, it is shown numerically how the natural frequencies of a bridge change during the crossing of a vehicle. An Euler-Bernoulli beam is modelled traversed by a single DOF vehicle. The use of such a simple Vehicle-Bridge interaction model is justified by the objective of providing insight into the structural dynamics of a moving load interacting with a bridge. The numerical results indicate that the variations in natural frequencies depend greatly on vehicle-to-structure frequency ratio and mass ratio. In some conditions, significant variations in modal properties are observed. Additionally, it can be analysed from the passing vehicle response. Time-frequency signal analysis of the vehicle's vertical acceleration clearly shows how the frequencies evolve during the event. The frequency localization properties of the Wavelet transform (Modified Littlewood-Paley) are exploited in analysing the signal and highlighting the relevant results.