Bridge Modal Identification Based On Vehicle Scanning Method Considering The Effects Of Vehicle Structure Parameters

At the end of 2020,the number of road bridges reached 912,800 in China.For such a huge demand for structure health monitoring(SHM),it is necessary to develop fast and efficient health monitoring methods.Based on the theory of vehicle-bridge interaction(VBI),the vehicle scanning method(VSM)was proposed by Yang et al.to detect the health condition of bridges.In the application of the VSM,sensors are installed on the test vehicle to indirectly extract the dynamic response of the bridge,which has the advantages of mobility,efficiency and economy.This dissertation presents effective methods for scanning bridge frequencies and mode shapes by vehicle scanning method considering the effects of vehicle structure parameters.The main contents of this dissertation are as follows:(1)A realistic theory is proposed considering the damping effect of the test vehicle,and the dynamic response of the vehicle passing through the bridge is obtained.Subsequently,based on the vehicle dynamic response,the back-calculation algorithm of vehicle-bridge contact response is proposed to filter the vehicle frequency.In the study,the vehicle is simulated as a single degree-of-freedom(DOF)system.For the model adopted,closed-form solutions are derived for the bridge,vehicle,and vehicle-bridge contact responses.The mechanism of transmission of vibrations from the bridge to the vehicle is investigated,which is a guide for the design of a test vehicle.Moreover,the proposed back-calculation procedure of vehicle-bridge contact response considering the effect of vehicle damping can effectively eliminate the interference of the vehicle frequency,which improves the identification results of bridge dynamic responses.(2)To verify the feasibility of the VSM for bridges and the proposed signal optimization scheme,experimental study is necessary.In this study,a test vehicle with an axle and two wheels is designed and manufactured to approximately simulate the theoretical single-DOF system.The dynamic properties of the test vehicle and vibration transmissibility between the vehicle and bridge are examined in detail.This study also presents the measurement results of bridge frequencies by the test vehicle in nonmoving and moving states.Based on the measured vehicle response,the contact response of the vehicle with the bridge was calculated by the proposed backward procedure that allows the vehicle frequency to be eliminated.(3)The mechanism of the rocking motion of the single-axle vehicle is revealed,and the vehicle-bridge contact response algorithm under the influence of the rocking motion is proposed in this study.To facilitate the theoretical analysis,the single-axle test vehicle was simplified as a single-DOF system.In reality,the single-axle test vehicle is a three-dimensional structure containing two wheels and one axle.The two wheels of the test vehicle may experience different roughness profiles during the passage,and the signal transmitted from the bridge vibration to each wheel is also different.The rocking motion will be induced on the vehicle by above reasons,which is not considered in previous studies.In this study,the rocking motion model of the single-axle vehicle is proposed,and back-calculation procedure of vehicle-bridge contact responses is also proposed herein to eliminate the vertical and rocking frequencies of the test vehicle.In addition,an experimental study is carried out to extract bridge frequencies.(4)To enhance the visibility of the first few bridge frequencies for extraction,the variational mode decomposition with band-pass filter(VMD-BPF)is proposed herein.The VMD technique is adopted to decompose the vibration data,and the BPF serves to remove the undesired roughness frequencies to improve the efficiency of the VMD.It is demonstrated numerically and by the field test that the VMD is a neat and elegant mode decomposition technique and the VMD-BPF is an effective method for extracting bridge frequencies with the enhancement of vehicle-bridge contact response.(5)In this study,both vehicle frequencies and road roughness are eliminated via the skillful use of a two-axle test vehicle.Compared with single-axle vehicles,the twoaxle vehicle has good stability in the measurement.In addition,since the two-axle vehicle has more contact points,more vibration data about bridges can be collected.In this study,it is suspected that the rotational action of the vehicle will bring in additional disturbance,aside from the vertical one,to the vehicle response in extraction of the bridge dynamic properties.The purpose of this study is to fill such a gap,namely,by providing a complete theory that considers both the vertical and rotational vibrations of the two-axle test vehicle.In this study,the effect of vehicle’s vertical and rotational frequencies is removed by using the vehicle-bridge contact responses,and road roughness by the residue of the front and rear contact responses of the two-axle test vehicle.Based on the proposed variational modal decomposition with Hilbert transformation(VMD-HT)method,the theoretical method of bridge mode shape extraction is obtained.