Vibro-acoustic analysis of noise generation from a full scale model of modular bridge expansion joint

Noises generated from modular bridge expansion joints during vehicle pass-bys have been causing local environmental problems recently. Previous experimental studies showed that possible causes of dominant noise components generated from the bottom side of the joint might be different from those from the top side. The objective of this study was to obtain theoretical insights into the mechanism of noise generation from the bottom side of the joint for which a main noise source might be structural vibration of the joint. Vibro-acoustic analysis was conducted based on the information from a full-scale model of modular expansion joint obtained in previous experimental studies. The dynamic behavior of the joint model was investigated by using the finite element method (FEM) and the sound field inside the cavity located beneath the joint model was analyzed by using the boundary element method (BEM). Indirect BEM was used to calculate the sound pressure inside the cavity with the velocity response obtained by the FE analysis as a boundary condition. The frequency range considered in the analysis was 20-400 Hz where dominant frequency components were observed in the noise measured in the cavity beneath the joint in the previous experiment. It was intended to interpret numerical results obtained by a model developed with available mechanical properties of the joint components to seek a general understanding of the noise generation mechanism of the modular expansion joint. It was observed that the peaks in the spectrum of noise inside the cavity were due to resonances of structural vibration modes of the joint and/or resonances of acoustic modes of the cavity. There was evidence that showed possible interaction between structural modes of the joint and the acoustic modes of the cavity. (c) 2008 Institute of Noise Control Engineering.