Influence Mechanism Of Main Girder Structure On Train-Induced Structure-Borne Noise Of Long-Span Steel Bridge

Due to the characteristics of lightweight and high strength,long-span steel bridges are widely used in urban rail transit networks,and the structural noise problem is also very serious.However,the noise reduction design in the initial stage on structural selection is often ignored for existing bridges.Based on the established prediction model of structure-borne noise of long-span steel bridge,the influence mechanism of main girder’s structure on train-induced structurre-borne noise of long-span steel bridge is systematically studied in this thesis.There are the main research contents and the conclusions:(1)The development of urban rail transit in China,the urgency and necessity of studying the noise pollution of bridge structures and the significance of this study are introduced.Current status of experimental and theoretical researches on bridge’s structural noise is summarized,and the feasibility of this study is proved.(2)Field tests are carried out to summarize the regularities vibration and near-field noise radiation of long-span steel truss cable-stayed Bridges under train loads.Under the train load of 50km/h,the vibration acceleration level of the bridge deck of the lower deck system is the largest,followed by transverse beams,longitudinal beams,and flanges,and the dominant frequency band of their vibration acceleration level is 40～160Hz.The distribution rules in frequency domain of the three near-field noise measurement points at the center of webs of different span under the lower bridge deck are basically consistent,the dominant frequency bands of which are also 63-2500 Hz.(3)Based on the principle of statistical energy analysis,a prediction model for traininduced structure-borne noise of long-span steel bridges is established,the basic parameters of statistical energy analysis are determined,and a power balance equation is established,whose input excitation is vertical discrete supporting force in frequency domain between track plate and bridge plate.Taking the steel truss beam as an example,the experimental results of vibration and noise measurement points are compared with the simulation results.It is found that the distribution rules of their curves in frequency domain are in good agreement,which proves that the model has good reliability.(4)By using the established model,the vibration energy distribution,far-field structureborne noise radiation and attenuation rate,and the acoustic contribution of the components of the steel trussed girder,steel box girder and composite girder are compared and analyzed.The results show that the maximum vibration energy of this three forms of girder occurs in the bridge deck which receives the external input excitation directly;The far-field noise radiation of the three girders is distributed in wide frequency,and the peak values all appear at 40 Hz,63Hz,100 Hz and 160Hz;In addition,the steel box beam and composite beam also show the peak values at the middle and high frequencies of 500-1000Hz;The isobars of structure-borne noise are all distributed in semi-arcs in the midspan cross of the main span;The far-field noise radiation and attenuation level of steel girder and steel box girder are similar,while the total far-field sound level of composite girder can be reduced by 2～6d B(A).The horizontal and vertical acoustic contributions of the lower deck system of steel truss beam can reach 59.44%and 72.08%,among which the bridge deck is the largest,and the main acoustic components of steel box beam and composite beam are bridge deck.The concrete deck of composite girder have lower transfer efficiency for input excitation,which can reduce the transfer of energy to other components and thus reduce their noise radiation level.