Indirect Bridge Frequency Identification Based On Vehicle Model With Nonlinear Tires

The detection and monitoring of the health status of small and medium-span bridges is one of the urgent problems need to be solved.The traditional manual inspection and health monitoring methods are not suitable for a large number of small and medium-span bridges due to cost and other reasons.Whereas using the signals of passing vehicles as an identification method for bridge parameters is economical and has the advantages of high efficiency,which provides a feasible approach in solving the health monitoring problem of small and medium-span bridges.Aiming at the problems existing in the indirect bridge frequency identification method,a series of researches from the aspects of bridge frequency identification theory is conducted in this paper,identification method and identification accuracy.The main research conclusions are as follows.(1)Based on the closed-form solution of the dynamic response of vehicle-bridge interaction system,a comprehensive parameter analysis is carried out for the effect of identifying bridge frequency from the vehicle signals.The results show that the bridge structure with low damping ratio,high vehicle frequency,high vehicle mass,high vehicle damping ratio and high vehicle speed are all beneficial in improving the bridge frequency identification effect from the vehicle acceleration signals.On this basis,taking the amplitude ratio of vehicle and bridge frequency in the vehicle acceleration spectrum as the index,the probability of successful bridge frequency identification is given,combining with the parameters of vehicle-bridge frequency ratio,vehicle speed,and vehicle damping ratio.(2)Through experimental testing and numerical analysis,parameter analysis of the accuracy of bridge frequency identification is carried out.The deviation of the bridge frequency identified by vehicle signal compared with the fundamental frequency of the bridge under different vehicle-bridge systems is revealed.The indoor test results show that the accuracy of the identified bridge fundamental frequency is mainly affected by vehicle-bridge mass ratio and vehicle speed.The parameter analysis conducted through numerical modeling shows that when the vehicle-bridge frequency ratio is greater than 1,the vehicle-bridge mass ratio is the most important factor affecting the accuracy of frequency identification.When the vehicle-bridge frequency ratio is less than 1,vehicle speed,vehicle-bridge mass ratio and frequency ratio jointly affect the accuracy of bridge frequency identification.(3)A refined tire model is constructed on the basis of the rigid ring model,and the equivalent road surface is generated through ‘the tandem model with elliptical cams’.Moreover,based on the mechanical model that has a clear physical meaning,the interaction force between the tire and the equivalent road surface is derived.The nonlinearity of tire stiffness is introduced,and the vehicle model considering tire nonlinearity is established,and a iterative algorithm of vehicle motion state in this model is proposed.Compared with the measured data and other tire models,it is proved that the proposed model can accurately reflect the vibration response of the vehicle body.(4)The closed-form solution of vehicle response caused by road roughness is derived through theoretical analysis,and the vehicle response caused by road roughness is only affected by vehicle frequency and damping ratio.Through the establishment of vehicle-bridge interaction model based on nonlinear tire-vehicle model,the proposed iterative algorithm is introduced into the solution of vehicle-bridge system.It is concluded that the introduction of road roughness greatly interferes with the identification of bridge frequency,and the influence of various parameters on the identification of bridge frequency is discussed.Based on theoretical analysis and numerical simulation,considering the influence of vehicle parameters on bridge frequency identification with and without road surface irregularities,a bridge frequency identification method is proposed to eliminate the irregularities.The residual spectrum is obtained and accumulated by subtracting the acceleration spectrum of passing vehicles with different mass and speed through the bridge,and the bridge frequency can be observed explicitly in the residual spectrum diagram after accumulation.