Study On Vibration Characteristics And Control Of Simply Supported Girder Bridge In Rail Transit

With the rapid development of rail transit in China,the problems of bridge vibration and noise induced by a train crossing the bridge are becoming more and more serious.Vibration is the source of noise.Reducing the vibration energy of bridge structure can reduce the noise of bridge structure.Therefore,it is very necessary to study the vibration characteristics of bridge structure under train load and find reasonable control measures for bridge structure vibration.First of all,the vehicle bridge coupling simulation model established by multi-body dynamics and finite element software is systematically summarized.The advantages and disadvantages of the modeling method are analyzed.Based on that,an improved simulation method of vehicle bridge coupling vibration based on multi-body dynamics(MBD)and finite element method(FEM)is proposed.In the next place,the vehicle-bridge-pier coupled vibration analysis model of overhead simply supported box-girder and U-girder in urban rail transit is established by an improved method of vehicle bridge coupling simulation.The vibration characteristics of the bridge system are analyzed,and the influence of the change of the vertical stiffness of the connecting parts in the bridge system on its vibration characteristics is also discussed.After that,the similarity model of the simply supported box-girder bridge with span of 32 m was designed and made with geometry scale factor of 10.Based on the similarity law of elastic force,the similarity relation,between prototype and model,was derived.Combined with two methods of experiment and simulation,the correctness of similar theory and model making is verified.Finally,through the hammer test,the transfer characteristics of vibration on the beam body,the isolation effect of the elastic support and the damping performance of the damping plate to the box girder bridge are studied.The results show that:(1)The improved method of vehicle bridge coupling vibration simulation based on MBD and FEM can solve the problem that previous coupled vibration models can not fully analyze the vibration response of the system,and this method is applied not only to the coupling between vehicle and bridge,but also to the coupling between vehicle and the earth or other track structures.(2)When the train passes at the speed of 40km/h,the vertical vibration of wing is the strongest,the second is the web,and the vertical vibration of the box girder is more violent than the transverse vibration;The increase of the train speed will not only increase the deformation of the box girder,but also cause the box girder to be subjected to greater impact energy;When the vehicle passes through the bridge at low speed,the low frequency mode below 40Hz contributes greatly to the vibration of the box girder;When the vehicle passes through the bridge at high speed,the first order mode contributes most to the vibration of the box girder;The increase of vehicle speed can excite the higher order modal of box girder,which makes the local vibration of box beam strengthen.(3)When the train passes at the speed of 80km/h,The vertical vibration is strongest at the bottom of the middle section of the U-girder,the lateral vibration at the flange of the support cross section is the strongest,and the lateral vibration of U-girder can not be ignored;The speed of train passing bridge is an important factor influencing the dynamic response of U beam.The increase of train speed will increase the impact energy of train load on U-girder;When the vehicle passes through the bridge at low speed,the vertical acceleration response frequency at the bottom of U-girder is below 40Hz,and the low frequency modes below 40Hz contribute little to the local vibration of the U beam;When the vehicle passes through the bridge at high speed,the first order mode contributes most to the vibration of the box girder;The increase of vehicle speed can excite the higher order modal of box girder,which makes the local vibration of box beam strengthen.(4)For simply supported box-girder and U-girder bridge,Increase of fastener stiffness can obviously decrease the rail deformation,but the excessive stiffness will cause vibration of beam and track structure intensifies,proposed stiffness value of vertical fastener is 20~50MN/m;The increase of the elastic support under the track plate stiffness can obviously reduce the slab vibration,but excessive stiffness will strengthen rail vibration,the vertical stiffness of elastic support under the track plate should be within the range of(1.0~1.5)×10~3MN/m;Increasing the vertical stiffness of support can reduce the vibration of track slab and girder within a certain range.However,too large support stiffness will make the bridge vibration more serious,which is not conducive to vibration reduction.It is recommended that the vertical stiffness of support is(3~4)×10~3MN/m.(5)the attenuation of vibration from the top plate to the flange plate is the slowest,followed by the web,and the vibration attenuates fastest from the top plate to the base plate;The vibration of the web and the base plate attenuates rapidly in the middle and high frequency section of the 0~200Hz frequency range;In the frequency band of 0~45Hz,the vibration of the top plate attenuates extremely slowly along the longitudinal direction;In the45~200Hz frequency band,the vibration of top plate attenuates rapidly in the distance range from middle to 1/4 section,and attenuates slowly in the distance range from 1/4 to the support section,and the modal of box-girder can strengthen the local vibration of the box girder.(6)In the middle and high frequency section of 20~200Hz,the change of support stiffness has a certain influence on the structural vibration of the middle section of the box-girder,but the influence is very small;The vibration of pier top can be effectively reduced by setting elastic support between the upper structure and pier of simply-supported box-girder bridge,and the stiffness of the support has a great influence on the vibration isolation effect of the elastic support,at the same time,the vibration isolation effect of the elastic support is different at different frequencies;When the elastic support of the bridge is selected,two factors should be considered,which are the stiffness of the support and the frequency band of the vibration damping.(7)Laying 1cm thick damping plates on web can reduce the vibration acceleration level of the web by 10.2~29.5dB,and reduce the vibration of the floor plate to some extent;The vibration of box girder web is mainly concentrated in the frequency range of 20~100Hz,and the web in the center frequency 80Hz band will appear dense local vibration modals;The damping plate can greatly suppress the local vibration of the web in the frequency range of20~200Hz.