Research On Noise Contribution Of Steel-Concrete Composite Boxgirders Applied In High-Speed Railway

In recent years,composite bridges have developed rapidly,and are more and more widely used in the construction of railway bridges.Because of its small contribution to the total noise outside the train,the structural noise of concrete bridge is not valued or ignored directly.Compared with concrete bridge,the vibro-acoustic problems of composite girder are more prominent.As a result,it needs further study and discussion whether the noise contribution of composite bridge can still be ignored.In this context,the noise contribution of steel-box composite girder in high-speed railway is studied in detail.Based on the measured wayside noise data of seven high-speed railway bridge sections,the spectrum characteristics and spatial distribution rules of the external noise are analyzed and discussed,as well as the influences with line type,girder type,sound barrier and train speed.Next,a vibro-acoustic prediction model of composite girder based on FE-BE-SEA hybrid method is proposed,the reliability of which is verified by a hammer excitation test on a 3 m steel-box composite girder scaled model.Then,to calculate the train-induced force transmitted to the bridge,a frequency-domain analysis model of the train-track coupling system is established.After that,the train-induced structural vibro-acoustic response of a 40 m steel-box composite girder is calculated and analyzed according to the FE-BE-SEA hybrid method.Finally,the noise contribution of the steel-box composite girder is calculated and analyzed,and then compared with that of concrete box girder.Furthermore,the influences of three different velocities on the noise contribution of steel-box composite girder are also analyzed.The main conclusions are as follows:(1)The frequency spectrum curve of A-weighted sound pressure levels(SPLs)measured in the bridge section of high-speed railway shows the shape of high magnitude in the middle and low magnitude on both sides.The mid-and high-frequency noise plays a decisive role in the total SPLs.The measured total external noise of steel-concrete composite girder section has a wide frequency spectrum and large amplitudes,in the mid-and low-frequency range of which is much larger than that of concrete-box girder and trough girder.(2)Compared with pure steel-box girder,the vibration of steel-box composite girder covered with concrete slab is significantly reduced.This is mainly because of the decrease of the vibration transmission from on-girder to steel-box girder.And the vibration reduction effect of steel web plate is greater than that of steel bottom plate.(3)The structural noise of steel-box composite girder shows broadband spectrum characteristics.The mid-and high-frequency noise of 315～1000 Hz controls the total structural noise.When the train speed is 300 km/h,the structural SPLs is 84.0 d B(A)and 83.2 d B(A)at the measuring points of the train operation noise and railway boundary noise respectively.At a certain point on bridge side,the structural SPLs of steel-box composite girder is about 11.9 d B(A)higher than that of concrete-box girder.(4)When the speed is 300 km/h,in the analysis frequency band of 20～10000 Hz,the noise contribution of concrete-box girder is 10.1% at near field point P1 and 3.2% at far field point P2.In other words,the noise contribution of concrete-box girder is small,and almost negligible in the far field.(5)Among the three main parts of steel-box composite girder,the order of train-induced vibration is deck > bottom plate > web plate.The contribution of deck and bottom plate to the total structural noise is both about 36.7%,and that of web plate is 16.9%.(6)When the train speed is 300 km/h,the noise contribution of the 40 m steel-box composite girder is about 66.7% at P1 and 30.3% at P2.Indicating that the structural noise of steel-box composite girder plays an absolute leading role in total noise in near field,and in far field it’s also at a high level,which should be paid more attention to in noise reduction.(7)The increase of speed has no effect on the frequency spetrum characteristics and dominant frequency band of steel-box girder’s structural noise,but only the frequency spectrum curve moves up.At point P2,the contribution of structural noise decreases with the increase of the train speed.It can still reach 27.5% when the speed is 385 km/h.