Research On Bridge Frequency Test Method Based On Vehicle-bridge Coupling Theory

There are a lot of mountains and so many rivers dotted in our country.Bridge structure is numerous,most of the small bridges due to the construction of a long time and many structures have been destroyed by long-term moving forces that are dominated by vehicle loads.The natural frequency of the bridge is an important index in the bridge detection process.The traditional method of directly measuring the frequency of bridges is not only too complicated but also costly.Therefore,it is necessary to carry out a method of indirectly measuring the frequency of the bridge.In this paper,the process of vehicle-bridge coupling vibration is studied.The relationship between the natural frequency of the bridge and the vehicle is obtained by deriving the vertical acceleration formula of the vehicle.The vertical acceleration of the vehicle is frequency-converted by fast Fourier transform.The first order natural frequency of the bridge is extracted.Simulation of vehicle-bridge coupling vibration is carried out by using the finite element software ANSYS to simulate the four models(moving force,moving mass,uniaxial spring mass and biaxial spring mass).And then extract the time span of the bridge across the midpoint and the displacement,velocity and acceleration of the vehicle.The response of three different speeds of axle coupling vibration is studied.(1)According to MATLAB programming theory analysis and analysis,and with the ANSYS results were compared.(2)The first-order natural frequency of the bridge is extracted by the fast Fourier transform of the vertical acceleration of the vehicle.The influence of the vehicle speed,damping and axle quality on the natural frequency of the bridge is studied.(1)The influence of vehicle speed on the extraction frequency of the bridge has a certain influence.(2)The effect of damping on the extraction frequency of the bridge is very small.(3)The axle quality ratio has a great influence on the natural frequency of the bridge.On the Xiao yong zhuang bridge sports car test,collecting the vehicle acceleration signal.Respectively,10 km / h,20 km / h and 30 km / h speed through the bridge and A total of three sets of vehicle data were collected and then the collected accelerationsignal for fast Fourier transform.Compared with the measured value and the direct method,the measured frequency error of the natural frequency of the bridge is2.550%,6.922% and 10.00% respectively and the simulation results were 1.275%,2.185% and 3.097% respectively.Experiments show that the extraction accuracy decreases with the increase of vehicle speed,but it satisfies the requirements of engineering example.Therefore,it is recommended to use this method to measure the bridge frequency when the vehicle is to meet the light low speed through the bridge structure.