Research On Vibro-acoustic Mechanisms Of Track And Box-girder Bridge Systems Based On Waveguide Finite Element Method

This dissertation focused on the issue of vibration and noise induced by urban rail transit viaducts.The vibro-acoustic mechanisms and influence factors of track and box-girder bridge systems were investigated by field test,theoretical analysis and numerical simulation.The main achievements of this dissertation are as follows:A rapid approach to predicting the vibration and noise induced by track-bridge systems was proposed based on the waveguide finite element(WFE)method and two-dimensional boundary element(2D BE)method.A WFE model for vibration prediction and a 2D BE model for acoustic prediction of a 30 m dual-line concrete simply-supported box-girder bridge on Line 4 of the Guangzhou Metro System were established based on the proposed approach.A field test concerning the vibration and noise of the track-bridge system was performed on the metro bridge.The vibro-acoustic spectral characteristics of the track-bridge system were analyzed.The numerical models for vibration and noise prediction were validated by the test results.The WFE model has a higher calculation efficiency and almost the same calculation accuracy compared with the conventional FE model.The 2D BE model has a significant higher ca lculation efficiency,although loses a certain degree of calculation accuracy compared with the 3D BE model.An approach to analyzing the characteristics of the waves propagating in track-bridge systems was proposed based on the WFE method.The dispersion characteristics and mode shapes of the waves propagating in the box-girder bridge and rail were investigated.There are 9 wave modes propagating in the box-girder bridge in its vibro-acoustic dominate frequency range,including 4 vertical flexural wave modes,2 lateral flexural wave modes,2 torsional wave modes and 1 longitudinal wave mode.The wave modes E and G which induce the flexural vibration of the top slab and bottom slab are the dominant wave modes generating vibration velocity peaks of the box-girder bridge.There are 4 wave modes propagating in the rail in its vibro-acoustic dominate frequency range,includin g 1 vertical flexural wave mode,1 lateral flexural wave mode,1 torsional wave mode and 1 longitudinal wave mode.The wave mode R which ind uces the vertical bending of the rail is the dominant wave mode generating vibration velocity peaks of the rail.In the one-third octave band of 63 to 100 Hz,higher vibration power is input to the bridge and induces the waves E and G to vibrate,which leads to the vibro-acoustic peaks of the box-girder bridge.In the one-third octave band of 500 to 630 Hz,higher vibration power is input to the rail and induces the wave R to vibrate,which leads to the vibro-acoustic peaks of the rail.Influence laws and mechanisms of the train speed,supporting stiffness under the rail,bridge parameter and bridge cross-section form on the vibro-acoustic characteristics of the track and box-girder bridge systems were investigated.The input power of the track-bridge system will increase with the increase of the train speed,inducing the vibration and noise of the system to become larger.When the train speed increase by 10 km/h,the vibration velocity levels of the rail and box-girder bridge will increase by about 1.5 to 1.7 dB,and the A-weighted sound pressure levels under and beside the bridge will increase by about 1.4 to 1.8 dB(A).The input power of the box-girder bridge will decrease significantly and the input power of the rail will increase slightly with the decrease of the supporting stiffness under the rail,which induces the vibration and noise of the box-girder bridge to become significantly smaller while the vibration and noise of the rail become slightly larger.The mass and stiffness of the box-girder bridge will become larger with the increase of the bridge deck thickness,which induc es the vibration velocity of the bridge to become smaller.Accordingly,the input power of the bridge will decrease,causing the vibration and noise of the bridge to become smaller.When the bridge deck thickness increases from 0.25 to 0.35 m,the vibration velocity levels of the box-girder bridge will decrease by 3 to 5 dB and the A-weighted sound pressure levels of the bridge-borne noise will decrease by 3 to 5 dB(A).But the variation of the bridge deck thickness has little influence on the vibration and noise of the rail.The cut-on frequency of the wave G increases with the increase of the web inclination,which results in the increase of the vibro-acoustic peak frequency of the bottom slab.The cut-on frequencies of the waves propagating in the single-line box-girder is larger than those in the dual-line box-girder because the slabs of the single-line box-girder have smaller widths,which will induce the increase of the vibro-acoustic peak frequencies and the decrease of the vibro-acoustic peak values of the single-line box-girder.The wave modes E and G,which induce the vibration peaks of the top slab and bottom slab of the single-box single-cell bridge,are eliminated by the middle web slab in the single-box dual-box bridge.As a result,the vibro-acoustic performance of the single-box dual-cell bridge is better than that of the single-box single-cell bridge.