Study On Influences Of CRTSⅢ Slab Ballastless Track On High Speed Railway Elevated Bridge Structure Noise

With the rapid development of high-speed railway in our country, the corresponding problem is also increasing in the process of technology development. The noise problem of high-speed railway has become one of the hot issues in the development of high-speed railway. In our country, the ballastless track is extensively adopted in high-speed railway and there are many types of track structure. Through the continuous efforts of researchers engaged in high-speed railway in our country, the new type CRTSⅢ slab ballastless track with independent intellectual property rights has been designed. The railway line of CRTSⅢ slab ballastless track has been successfully operating. So it is need to study the noise radiation laws and its spectrum characteristics of the elevated bridge under CRTSⅢ slab ballastless track, and it is necessary to further its anti-vibration and noise reduction effect. This paper studies show that:(1) The natural frequencies of elevated box bridge are mainly in low frequency stage. The vibration of top plate is the most complex, and the vibration of wing plate is severe after the 20 th order natural vibration. The shell element can reflect the global and local vibration of elevated box bridge. The vibration of elevated box bridge structure is mainly in the frequency range low than 200 Hz, and above 200 Hz the elevated bridge structure hardly has vibration; in addition, in 0~50Hz the value of vibration acceleration amplitude of bridge is large;(2) The lower the frequency is, the elevated box bridge structure noise is more concentrated inside the box bridge and the area near the box bridge, and the lateral sound field distribution of box bridge structure noise is transformed from diffusion to impelling outward. As the frequency increases, the directivity of acoustic field distribution disappears; in the low frequency, the longitudinal acoustic field distribution is symmetrical at the center line of the box bridge, and the sound pressure increases gradually along the direction from the center to the ends and the radiation area is expanding. With the increase of frequency, the longitudinal acoustic field becomes gradually balance and the pressure difference decreases;(3) The sound pressure value of elevated box bridge is larger at the center frequency of 16-31.5 Hz and 160 Hz; the noise above bridge is the largest, and that in the far field area is weakest. As a whole, the bridge structure noise decreases in same proportion with increasing distance from the bridge above the bridge; in lateral direction, the bridge structure noise decreases gradually with the increasing distance from the bridge; in the far field, the sound pressure decreases with the increasing distance from the bridge. For the longitudinal sites, the sound pressure has no apparent rules along the bridge, and there have two obvious peaks at the center frequencies of 20 Hz and 160 Hz; It is important to note that at the mid-span the sound pressure is lower than that of the other area at the center frequency of 10 Hz;(4) The effect of ground reflection on the sound field distribution is obvious, which enhances the directivity of lateral acoustic field and is more apparent with the frequency increasing. In low frequency range, the lateral sound field distribution is opposite to that with not considering the role of ground reflection. The longitudinal acoustic field distribution is symmetrical about the center line of box bridge at the center frequency of 10 Hz, and the sound pressure spread out from the center. With the increase of frequency, the longitudinal acoustic field gradually appear hierarchy phenomenon. The large rigid of box bridge prevents the spread of sound field at a certain extent, and therefore has less effects on the sound field distribution of the area above the box bridge;(5) The CRTSⅢ slab track has obvious buffer action, and without laying CRTSⅢ slab track, the train moving in and out will causes obvious vibration of the bridge structure. The CRTS-Ⅲ slab track can obviously reduce the low frequency vibration of elevated box bridge structure, especially in the 0~50 Hz frequency range;(6) The CRTSⅢ slab track has obvious effects on the acoustic field distribution of elevated box bridge structure, especially can decrease the low frequency noise of box bridge structure in the range of 0~50 Hz.The above study result shows that, CRTSⅢ slab track can effectively reduce the the low frequency noise of elevated box bridge structure. Due to the natural frequency of vibration of the human body organs are mainly concentrated in this frequency range, thus CRTSⅢ slab track can reduce the influence of box bridge vibration on human body. So CRTSⅢ slab track is good for reducing vibration of low frequency noise of box bridge structure.