Study on the Analysis and Control Method of the Vibrations and Noises in Highway and Railway Bridges under the Passage of Vehicles

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In the first half of this study, the authors investigated dynamic responses of highway bridges to travelling heavy vehicles and the low frequency sounds radiated from the vibrating bridges. Simply or continuously supported girder bridges were considered. And as models of heavy vehicles, the fourdegree-of-freedom system with two axles were employed. Governing equations of the coupling motions of the bridge and travelling vehicle models were numerically integrated to solve the problem.Using the Fourier spectra of vibration velocities of bridge surface, the SPL of the low frequency sound radiated from the vibrating bridge was analyzed under the assumption in acoustic field that each of infinitesimal elements of the bridge surface may correspond to a sound source in infinite baffle. The effects of unevenness on the surface at bridge ends, span length of the bridge and travelling velocity of the vehicle on the SPL were examined. As the results of these treatments, control methods of the vibrations and noises in highway bridges under the passage of vehicles were clarified.In the latter half, the authors dealt with the impact problems of plate-girders by means of the finite strip method in order to clarify the fundamental characteristics of the vibrations and noises in railway bridges. Firstly, natural vibration modes of high frequencies in I-section and box-section steel girders were analyzed, and the results obtained were showen in dispersion curves of phase velocities. Secondly, dynamic behaviors of I-section steel girders subjected to impact loads were investigated analitically. And numerical solutions obtained for the girders had a good agreement with the experimental results.