Analysis of sound radiation from the coupling effect of vibrating noise and moving-vehicle noise on bridges

An acoustic finite element model of a bridge is developed to evaluate the noise generated by the traffic-induced vibration of the bridge. The dynamic response of a multi-girder bridge, modeled by a three-dimensional (3-D) frame element model, is analyzed with a 3-axle (8 degrees of freedom (DOF)) truck model and a 5-axle (13 DOF) tractor-trailer. The flat plate element is used to analyze the acoustic pressure due to the fluid-structure interactions between the vibrating surface and contiguous acoustic fluid medium. The radiation fields of noise with a specified distribution of vibrating velocity and pressure on the structural surface are also computed using the Kirchhoff-Helmholtz integral. Among the diverse parameters affecting the dynamic response of a bridge, vehicle velocity, vehicle weight, and spatial distribution of the road surface roughness are found to be the main factors that increase the level of vibration noise. In an attempt to illustrate the influence of the structural vibration noise of a bridge to total noise level around the bridge, the random function is used to generate the vehicle noise source including the engine noise and the rolling noise between the road and tire. The results show that the low-frequency noise produced by the vibrating bridge members amplifies the high-frequency vehicle noise by 4-7 dB. In addition, the amplification rate of noise increases with travelling speed and vehicle weight.