Prediction of rail and bridge noise arising from concrete railway viaducts by using a multilayer rail fastener model and a wavenumber domain method

Concrete viaducts are an important part of urban rail transit systems but they produce considerable noise, thereby affecting the communities living nearby. The vibration generated at the wheel-rail interface is transmitted along the rail and also onto the bridge; hence, noise is radiated from both the rail and the bridge. To facilitate noise prediction, it is desirable to develop a model that takes into account the generation and transmission of vibration in the train-track-bridge system. The vibration and the associated noise of the track-bridge system are computed with a unified vibroacoustic model using a wavenumber domain finite element and boundary element method. An important aspect to note is the frequency-dependent stiffness of a typical rail fastener utilized on bridges due to the resonance of the baseplate between the two rubber pads. In this study, to allow for this effect, a multilayer fastener model is proposed. The proposed procedure is applied to a viaduct with a U-shaped section and compared with field measurements during the passage of trains. The elastic modulus and damping of the rubber pads and the equivalent loss factor of the rail are chosen by fitting the calculated track decay rates to those estimated from the measured rail accelerations under train passages. The wheel-rail combined roughness is also derived from the measured rail vibration. A comparison is then made between the simulated and measured bridge vibration to verify the proposed method as well as the parameters used in the track-bridge system. The predicted noise levels are also compared with the measured results. The effects of the fastener model, fastener stiffness, bridge damping, and interference between multiple wheels are then discussed. It has been found that the bridge noise has a non-negligible effect on the total A-weighted noise levels in the region beneath the bridge and up to 30m away from the track.