Sound radiation from an unbaffled elastic plate strip of infinite length

The noise which is caused by vibration of steel plate girders of a motorway is studied. This type of noise is often referred to as elevated structure noise, and has its main component within the frequency range 500 Hz-1 kHz. Since a steel plate girder can be considered as a rectangular plate with an extreme aspect ratio, the sound field radiated by a baffled elastic plate strip of infinite length, which is the simplest model of a steel plate gird er, was theoretically analysed in the preceding paper (Sakagami, K., Michis hita, K., Morimoto, M., and Kitamura, Y. Sound radiation from a baffled ela stic plate strip of infinite length with various concentrated exitation for ces. Appl Acoust 55: 181-202). However, a real motorway construction is mor e appropriately modelled by an unbaffled strip. Thus the unbaffled conditio n has been analysed numerically in this paper. The method of equivalent sou rces is used. The main features of the radiated sound field are discussed i n the light of numerical examples, and compared with those of a baffled str ip. Two vibration patterns, i.e. an idealised piston vibration and flexural vibration excited by a moment are considered. Furthermore, in order to det ermine the far-field range of an infinitely long plate, the variation of th e radiated sound field with the distance is discussed. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.