Vibration Measurement And Modal Analysis Of Bridges Based On UAV Images

Bridges directly affect the development of national economy and people’s living standards,and play an important role in the transportation system of the whole country.With the aging of bridges,the structural damage accumulates continuously,and the carrying capacity of the bridge decreases gradually.In order to ensure the safe performance of the bridges and avoid catastrophic collapse,it is very important to carry out regular detection of the bridges.Health monitoring and safety assessment of large bridges has become a hot issue for researchers in recent years.Structural vibration measurement is an important part of bridge safety assessment and health monitoring.In this paper,the research results of Unmanned Aerial Vehicle(UAV)photogrammetry and Digital Image Correlation(DIC)are used for reference,and a new visual measurement method based on UAV and DIC is proposed.The relevant theories are studied and vibration measurement experiments are carried out for a bridge model.This method overcomes the difficulty of fixed camera deployment by taking advantage of UAV’s high flexibility and ability to hover in the air.It also overcomes the limitation of traditional contact measurement to bridge detection by using the advantages of the DIC method.In order to verify the feasibility of the UAV measurement,this paper uses the traditional acceleration sensor measurement,fixed camera measurement and the proposed new measurement method to acquire the vibration response of the bridge model,which were inputted into the dynamic signal testing software to obtain the corresponding frequency response functions and structural modal parameters,and then the results of three methods were compared.The experimental results show that the UAV method is basically consistent with the first two measurement methods and can accurately obtain the natural frequency of the structure.In order to further study the applicability of UAV measurement,the long structure is measured in sections,and the complete modal shapes of the structure are obtained by using the merging principle.Due to the influence of UAV’s motion,the captured images contain the false displacement caused by the UAV’s motion.Fixed reference points are used to establish plane homography transformation to achieve the geometric correction of the images.Through the comparisons,it is proved that the real vibration displacement of the structure after correction is consistent with the measurement results of the fixed camera.The correction effect of homography transformation directly determines the quality of measurement result,and various factors affecting homography transformation are analyzed.The new measurement method proposed in this paper combines the advantages of UAVs and the DIC method in displacement measurement,which can detect the bridge more quickly and efficiently,and extends the applicability of the DIC method in bridge health monitoring,which has practical significance for the health monitoring of bridge engineering.