Research On Displacement Monitoring Method Of Small And Medium Span Bridges Based On Machine Vision

The bridge structure would be affected by the environment,the erosion of harmful substances,as well as the seismic load,vehicle load,human influence,and other external factors in the whole life cycle,resulting in displacement and rotation angle.Among them,displacement is the macro behavior of structural stiffness and load characteristics.In the field of health monitoring,the displacement of the structure can measure its mechanical properties and effectively identify the collapse risk.In China,the number of medium and small span bridges accounts for more than 90 % of the total number of bridges.Therefore,the displacement monitoring of small and medium span bridges is very necessary.There are many methods to obtain the static displacement and dynamic displacement of bridge structure.At present,there are dial gauge method,leveling method,total station method and displacement sensors based on various principles in practical engineering applications.These methods play their respective advantages in the field of displacement monitoring.However,there are also limitations such as low efficiency and difficult installation.In order to monitor the displacement of small and medium span bridges accurately and efficiently,this paper presents a new method based on machine vision.The main research work is as follows:1.A new method of small and medium span bridge displacement monitoring based on machine vision is proposed,and the system composition,Python-based image recognition principle and displacement calculation process of this method are introduced.Then,the target module with better performance is selected through the stability test of scale factor and target circle coordinate.2.In the case of close distance between camera module and target module,the resolution of the proposed method is determined by stability experiment and displacement loading experiment,and the effectiveness of the method is verified.In the case of long distance,the stability experiment and displacement loading experiment are carried out,and the influence of experimental distance on the monitoring accuracy and stability is expounded.The causes of errors are analyzed,and specific measures to improve the accuracy of displacement monitoring are proposed.3.According to the actual situation of bridge engineering,the camera module may have a certain inclined angle when using this method for displacement monitoring.The influence of inclined angle of camera module on the accuracy of displacement monitoring results is systematically studied.The distance between the lens and the marking module is close and fixed.Under the conditions of normal placement and 90 ° deflection of the target module,the displacement loading tests are carried out by changing the inclined angle of camera module respectively.It is concluded that the method has good inclusiveness for inclined angle of camera.4.The long-term displacement monitoring performance and dynamic displacement monitoring performance of the proposed method are explored.Firstly,the long-term displacement monitoring simulation experiment of the static target module is carried out in the laboratory.Then the simulation experiment of bridge dynamic displacement monitoring is carried out on the model of steel cable-stayed bridge and the displacement monitoring results are compared with the results of laser displacement sensor.It is further proved that the system has good performance in long-term monitoring and dynamic monitoring.Finally,the system is integrated.