The Research On The Dynamic Characteristics Of Two Span Continuous Girder Bridge Under The Vehicle Load

In the dynamic load test which used the vehicle as excitation sources and thereal time detection of Bridge Engineering,there are vehicle on the bridge.The bridgedynamic characteristics we tested actually is the dynamic characteristics ofvehicle-bridge coupling vibration system those main vibration mode is bridgevibration.In the engineering,the dynamic characteristics of bridge under the action ofvehicle is known as the bridge load frequency.The related research indicated that thedifferences between load frequency and natural frequency of the bridge sometimesare larger than the changes of natural frequency caused by the damage ofbridge,that is to say the vehicle has an ignored impact on the load frequency ofbridge.From the basic theory of bridge dynamic characteristics test we can see thatresearch on the variation of bridge dynamic characteristics caused by the vehicleinvolves the theoretical analysis of bridge loaded frequency and dynamiccharacteristic testing method.The theoretical analysis of bridge load frequency ismainly from the basic equations of structure vibration,with the help of the finiteelement method to establish the vehicle-bridge coupling model,based on thetheoretical calculation model to analyze the bridge load frequency,so as to observethe changes of bridge load frequency caused by the vehicle.Bridge dynamiccharacteristics test under the action of vehicle mainly used which modal analysismethod to identify a more accurate dynamic characteristics.The experimental modalanalysis method used to identify the dynamic characteristics of bridge structuremainly include frequency domain method, time domain method and time-frequencydomain method.Frequency domain method and time domain method are statistics ofdynamic response on average over time,so the dynamic characteristics analyzed aredynamic characteristics on average over time.Time-frequency domain method is that partial extraction made for dynamic response of time domain so as to analyze thedynamic characteristics of time domain with local sense.In this paper,from the research task of dynamic characteristics test study underthe action of vehicle, a two span continuous box girder bridge as the engineering,mainly carry out the following research work:(1)The vehicle is simplified as a moving force, moving mass and thespring-mass model, the coupling vibration model under the three conditions ofvehicle-bridge are established.Focus on the dynamic characteristics of thevehicle-bridge coupling vibration system simplifying vehicle as the spring masssystem,a two span continuous beam,for instance,to observe and analyze thechanges of bridge dynamic characteristics caused by the vehicle.(2)The experimental modal analysis method of bridge structure is analyzed andsummarized. Focus on the FDD of frequency domain and the HHT of time-frequencydomain,and use the calculating example to compare and analyze those methods.(3)Firstly, take the static load test of the project, based on the test data of staticload test modify the finite element model of the bridge.Bridge model is modified,then establish the vehicle-bridge coupling vibration model, and the bridge loadfrequency are calculated.The bridge load frequency under various conditions aretested.Compare and analyze the load frequency tested and calculated values.