Development Of High-precision Measurement System For Dynamic Deformation Of Bridge

The health of the bridge can be reflected by the deflection,strain and vibration signals of the bridge in some degree.The bridge deflection refers to the vertical deformation of the bridge structure under the action of gravity and the dynamic vertical deformation of the bridge formed by the connection of multiple dynamic deflection of the bridge structure reflects the bearing capacity of the bridge directly.Therefore,the dynamic measurement of the bridge vertical deformation is of great significance for the safe operation of the bridge.Most of the existing vertical deformation measurement methods of bridge structures can only conduct single-point and quasi-static measurement,which is difficult to meet the requirements of continuous multi-point high-precision dynamic measurement in practical engineering.Based on the quasi-static multi-point deflection measurement system of camera chain,this paper studies the high-precision measurement technology for dynamic deformation of bridges to realize the multi-point and high-precision measurement of dynamic vertical deformation of large structures such as bridges.The specific research contents are as follows:(1)The overall scheme of the bridge dynamic deflection measurement system is designed.According to the characteristics of bridge structure,a dynamic deflection measurement model of chain camera network is built and the feasibility of high-precision bridge dynamic deformation measurement is verified.(2)The measurement system is designed,which is composed of three parts:marking module,image acquisition and calculation module and data processing center module.The marking module selects 450nm monochromatic self-illuminating double circular marking points,and installs 450nm filters for camera lens,which effectively solves the problem of imaging quality under ambient light interference.The image acquisition and calculation module selects Jetson Nano embedded edge calculation card of Nvidia and realizes the continuous acquisition of images to be measured at 60 frame per second(FPS),real-time calculation of sub-pixel graphic coordinates and wireless data transmission.At the same time,the GNSS module is connected to realize accurate time service,which ensures accurate synchronous sampling of all measurement base stations.In data processing center module,based on Qt framework,a GUI interface is developed for convenient operation.The real-time displacement change data of all measuring points,which collected by polling method,are fed into the displacement solution formula to calculate the continuous linear change of each measuring node within a period of time,and finally the real-time displacement change curve of the area to be measured is drawn.(3)The bridge dynamic deformation simulation experiment is designed to verify the overall design scheme.Firstly,the internal and external parameters of the chain camera network are calibrated,and the precise distance interval between each measuring node and the scale magnification coefficient of the mark point unit in the camera unit imaging are calculated.Then,the static noise in the experimental environment is measured and analyzed to eliminate the influence of static noise.Finally,the high-precision electric displacement table is used to simulate the displacement and deformation of the bridge structure,and several groups of measurement and calculation are conducted by changing the motion parameters of the displacement table.The experimental results show that the deviation of vertical displacement is less than 0.05mm,the deviation of acceleration is less than 0.084mm/s~2,the deviation of initial velocity is less than 0.1452mm/s,and the deviation of normal velocity is within 0.02mm/s.The experimental results also verify the measurement accuracy and continuous measurement stability of the measurement system for multiple dynamic deformation of bridge.The absolute error of the system measurement is within 0.04mm,and the standard deviation is within0.035mm.The system has high measurement accuracy and good stability,which can fully meet the measurement requirements of the dynamic deformation of the bridge structure,and the maximum vibration frequency can be measured is up to 20Hz.