The Research On Vibration And Noise Radiation Of Box Beam

In recent years, noise has become a serious environmental problem, which hasbothered people to some extent. So people have began to pay more attention to theinfluence of noise on their lives. For many years, people only concern with themedium frequency and high frequency noise, which are related to people's auditionbut they give less concern to the low frequency noise. Some researches have shownthat if people are in low frequency environment for a long time, they may suffer fromnegative influence on their lives such as nausea dizziness memory decrease andinsomnia. Although low frequency noise induced by box girder accounts for a fewpercentage of overall noise induced by urban rail transit, it should not be neglectedbecause of its negative influence on people's health. The researches on this questionare very few due to the complexity of dynamic behavior and radiation condition ofbox girder and some indeterminate factors, not to mention domestic researches. As aresult, the research on structural noise of box girder becomes a major subject ofstructural engineering.This paper mainly researches the vibration and noise radiation of box girderunder moving load of rail transit and noise reduction of box girder.Chief works are summarized as follows:1. On the basis of a large number of measurement data, the state of vibration andnoise radiation along box girder section (cross-section, longitudinal section) under themoving load of train are researched and the variation rules of vibration and noiseradiation along box girder section are also summarized.2. Contour charts of vibration acceleration level and sound pressure level aredrawn. From these charts, we could find that which part is in the most intensivevibration state and which part is in the strongest noise radiation state clearly.3. The first four natural vibration frequency of box girder and the correspondentvibration mode are determined4. The sound pressure spectrum and acceleration spectrum are acquired when thetrain runs on the rail adjacent to the measurement points (in which case the rail iscalled 'adjacent rail') and on the rail far away from the measurement points (in whichcase the rail is called 'distant rail'), respectively. Under these two circumstances, thefrequency range of vibration is different from each other but that of noise radiation isidentical with each other approximately. 5. Radiation sound power is different at different parts of box girder.6. On the basis of coherence analysis of vibration and noise, frequency range ofvibration, which make great contributions to noise radiation, are determined. So noiseradiation level could be decreased by weakening correspondent vibration level.7. The measurements of vibration isolation applied to Zhongnan theater areanalysed in order to decrease the structural noise induced by elevated rail transit.In the end, the content of this paper has been summarized and some problems,which need further study, have been proposed.