Prediction Of Structure-Borne Noise From Railway Composite Bridge And Suppression Study Of Constrained Layer Damping

Rail transport has become one of the most important transportation means because of its advantages such as the higher speed, larger transport capacity, less occupation of land, less energy consumption, low-carbon and environment friendly feature, safety and reliability, higher probability of punctuality, lower cost of transport. Since Japanese Shinkansen was opened in 1964, the high-speed railway construction around the world is being in the booming development. In China more than 16,000 km high-speed railway has been built and additional 20,000 km high-speed railway is being and will be in the construction at the same time, resulting that both the mileage in operating and lines under the construction in China rank the first and China occupies more than 60% of the total operating mileage of the high-speed railway lines all over the world. With the rapid development of high-speed railway and urban rail transportation, the noise annoyance of rail transit is becoming more and more serious when it promotes the economic development and provides travelling convenience to people. On the other hand, the vibration and noise caused by rail transit attract more and more attention from residents near the line due to the improvement of the human being's requirement to living environment. The sound pressure level of a train crossing a bridge is usually about 0-20 dB higher than the plain track. Bridges usually come into being hot spots on noise maps and a high proportion of bridge is employed in rail transit due to the distinctive terrain and geological conditions in China. Although the structure-borne noise from bridge does not have a high proportion in the overall railway noise, it does great harm to human beings and currently there is no enough research on measures to reduce the vibration and noise from the bridge structure. Based on this situation, it has important practical significance to study the generation and propagation laws of bridge structure-borne noise and measures for the vibration and noise reduction. Focusing on the the generation mechanism of noise from railway composite bridge and constrained layer damping applied to reduce the vibration and noise, this paper conducts the multi-discipline research and the main work and conclusions are as follows:(1) On the basis of reading the domestic and foreign relevant literatures the state-of-the-art of structure-borne noise from bridge and constrained layer damping is reviewed. Then the advantages and disadvantages of various calculation methods are summarized and the correct direction to propose the reasonable calculating method in this paper is clear.(2) Combining train-track-bridge coupled vibration and statistical energy analysis with vibro-acoustic theory, a prediction model of structure-borne noise from railway composite bridge is established. Experimental study on the vibration and noise of (32+40+32) m continuous steel-concrete composite bridge in QinShen passenger dedicated line under the operating EMUs is carried out and then its spectral property and propagation law are analyzed. Besides, the established prediction model of structure-borne noise from railway composite bridge is verified by the in-sute experiment.(3) Aimming at (32+40+32) m continuous steel-concrete composite bridge and 64 m simply supported steel truss composite bridge, the mechanism of vibration generating noise, the spectral characteristics and spatial distribution of structure-borne nosie radiated from composite railway bridges are investigated and the contribution of radiated noise from major bridge components is obtained by the simulation analysis of bridge emanating structure-borne noise during EMUs passby.(4) The mechanism applying the constrained layer damping to reduce the vibration and noise from thin-walled structures is introduced. The calaulation method of the viscoelastic damping layer reducing vibration and noise is proposed based on modal strain energy and statistical energy analysis. The modal strain energy method is applied to calculate the damping loss factor of structural components layed constrained layer damping. Combining with statistical energy analysis, the vibration and noise reduction of the constrained layer damping for compsite railway bridges is analyzed. The frequency dependent shear modulus and material loss factor of viscoelastic damping layer are taken into account in the theoretical analysis. The reduction of vibration and noise from H-shaped steel beam and optimization of constrained layer damping are investigated by experimental study and theoretical analysis.(5) A field test on the vibration and noise from the (32+40+32) m steel-concrete composite bridge induced by EMUs before and after constrained layer damping treatment is conducted. The suppression effect of vibration and noise that constrained layer damping is applided to the operating railway bridge is compared. The proposed theoretical method on the vibration and noise of the constrained layer damping structure is verified. The theoretical study in which constrained layer damping is applied to reduce the vibration and noise from (32+40+32) m continuous steel-concrete composite bridge and 64 m simply supported truss composite bridge is carried out. By the parametric analysis of constrained layer damping, the variational laws of the shear modulus and the thickness of the damping layer, the material type and the thickness of the constrained layer on the noise reduction are achived. The layout of constrained layer damping for the actual bridge is obtained after conducting the optimization analysis of constrained layer damping laying position according to the distribution of modal strain energy.