Vibro-acoustic analysis of steel bridges: acoustic resonators for the noise control

Noise generated from bridges during vehicle pass-by has recently been causing local environmental problems. Complaints from the environment have arisen after bridges were replaced, renovated or newly constructed. In particular, the steel structure tends to radiate low-frequency noise during passages of heavy vehicles. Thus, the Dutch road authority has requested an analysis of possible measures to reduce such low-frequency noise. An extended repair model has already been proposed in some papers. Nevertheless, more advanced studies are recommended with more focus on acoustic mitigation measures. This report focuses mainly on the investigation of the effectiveness of Helmholtz resonators (HRs) and demonstration of their acoustic behaviour in a scaled bridge model measurements. This paper presents a general model for dealing with acoustic coupling between a bridge structure and a Helmholtz resonator array. The dynamic behaviour of the bridge model and the sound field inside the cavity located beneath was investigated using the finite element (FE) approach. It was targeted to interpret numerical results obtained by an analysis, which developed with available mechanical properties of the deck components and geometry of the bridge structure. With the purpose of understanding the noise generation mechanism at receiving locations. It was observed that peaks, in the spectrum of noise inside the bridge-tunnel, were due to resonances of structural vibration modes of the deck and/or resonances of acoustic modes of the tunnel itself. Subsequently, system identification was completed by means of analytically validated finite-element (FE) models and experimental data. The main topic of this thesis is to demonstrate how the measured and calculated vibration and pressure data correlate and how based on this experience the noise reduction model can be improved. This work was undertaken as part of a graduation internship and supervised at the Acoustics and Sonar Department of TNO in The Hague. The scaled bridge model, resonator array and measurement together with numerical facilities were all provided by TNO.