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-byshavebeencausinglocalenvironmentalproblemsrecently.Previousexperimentalstudies showed that possible causes of dominant noise components generatedfromthebottomsideofthejointmightbedifferentfromthosefromthetopside.The objective of this study was to obtain theoretical insights into the mechanismof noise generation from the bottom side of the joint for which a main noisesource might be structural vibration of the joint. Vibro-acoustic analysis wasconducted based on the information from a full-scale model of modularexpansion joint obtained in previous experimental studies. The dynamicbehavior 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 wasanalyzed by using the boundary element method (BEM). Indirect BEM wasused to calculate the sound pressure inside the cavity with the velocity responseobtained by the FE analysis as a boundary condition. The frequency rangeconsidered in the analysis was 20–400 Hz where dominant frequencycomponents were observed in the noise measured in the cavity beneath the jointin the previous experiment. It was intended to interpret numerical resultsobtained by a model developed with available mechanical properties of the jointcomponents to seek a general understanding of the noise generation mechanismof the modular expansion joint. It was observed that the peaks in the spectrumofnoiseinsidethecavitywereduetoresonancesofstructuralvibrationmodesofthe joint and/or resonances of acoustic modes of the cavity.There was evidencethat showed possible interaction between structural modes of the joint and theacoustic modes of the cavity.