Modelling railway bridge noise and vibration: application of advanced finite element methods

The passage of a train over a railway bridge has been recognised as an important source of noise in urban environments. To help find means to reduce the noise level, an accurate calculation model for its production is required. Conventional finite element (FE) models for the vibration response of the bridge are not applicable to bridges for the audible frequency range because of the very high density of modes of vibration of the structure. Statistical Energy Analysis (SEA) methods have therefore been used in bridge noise models to predict the vibration level in each major part of the bridge. The main difficulty with this approach is the need for an estimate of the vibration power transmitted from the rail into the bridge structure via the rail supports, as an input. Models simplifying the structure at the input to plates or beams have been proposed for calculating this power transfer. However, for realistic bridge designs these models may not be valid for the whole frequency range. Here a Waveguide Finite Element (WFE) method is used to investigate the vibration response of a railway bridge that has a uniform cross-section along its length. The full cross-section of the bridge is represented in this finite element technique. In the length direction, the motion of the bridge is described in terms of the waves in the bridge. It is this feature of the WFE method that brings a significant benefit in computational efficiency over conventional FE methods, such that is feasible to model the bridge over the full frequency range of interest using this approach.