Theoretical analysis of infrasound radiation from an oscillating bridge

Abstract

As a typical example of the sound radiation caused by the oscillation of a large sized structure, the infrasound radiation from a highway bridge is theoretically analyzed by applying a lifting surface technique. The relation between the bridge oscillation and the corresponding infrasound radiation is made clear quantitatively. By using measured results of the bridge oscillation due to the passage of a vehicle, the infrasound radiated from the bridge is estimated analytically. The results are compared with the measurements, and good agreement is seen. Moreover, it is shown that the reflection of sound at the ground causes both the radiation impedance of the bridge and the radiation pattern of the sound pressure to vary considerably according to the height of the bridge from the ground. Hence the height of the bridge is an important factor which controls sound pressure level ( SPL) near the ground, on which the noise is actually perceived.