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With the aim to propose a reasonable and effective countermeasure for the elevated structure noise, the sound field radiated by a steel plate girder, which is the main source of the elevated structure noise, have been theoretically analysed. In the present study, steel plate girders are modelled as infinitely long elastic plate strips placed in parallel and numerical examples on the sound field radiated by the steel plate girders are shown. In the analysis of the radiated sound field, the equivalent source method is employed. Effect of the surface absorption on the sound field radiated by the girders is discussed through numerical examples. The results show that the surface absorption is effective for reduction of the radiated sound field, especially in the area that increase of sound pressure due to reflection by adjacent plate girders is observed. Furthermore, to design for reasonable countermeasure, variation of the noise reduction effect due to changing the pattern of surface absorption area on plate girders is classified.

When reducing the sound radiated from a resonant structure, it is necessary to ensure that the driving frequency does not correspond to any of the system resonance frequencies. In addition, it may be desirable to use dynamic vibration absorbers to reduce the response at the driving frequency. In this paper, a low-damping vibration absorber is studied for solving noise radiation problems from a resonant, light-gauge structure driven by a force whose frequency and amplitude are constant and whose frequency does not match any of the system natural frequencies. When the driving frequency and the structure's natural frequency are different, the structure cannot be represented by as a SDOF system. Therefore, the conventional design method, based on equivalent mass, is inapplicable. In this paper, a design method based on the mobility of the structure is proposed. By means of the proposed method, the sound power radiated from a simply supported beam with an attached absorber is calculated and it leads to the following results: 1) When the absorber is installed at the driving point, it reduces the sound power as predicted; 2) An increase in radiated noise may occur when the absorber is not installed at the driving point.