Research On Bridge Holographic Deformation Monitoring And Damage Identification Based On Pier Outreach Camera

A large and widely used conventional span bridge requires an economical,practical,and convenient health monitoring method.This article relies on the National Natural Science Foundation project " Research on the Method of Obtaining Holographic Deformation and Structural State Deduction of Bridges through Image Contour Line Stacking Analysis(51778094)" and the Shenzhen Natural Science Foundation key project " Research on Precision Real Time Sensing Measurement for Bridge Safety Monitoring(JCYJ20220818095608018)",A holographic Deformation monitoring and damage identification method for the main beam based on the pier overhang camera is proposed.The main contents are as follows:(1)The existing visual monitoring methods for bridges require the selection of measurement points outside the bridge,but there are limitations to the measurement points outside the bridge in practical engineering.To address this issue,a visual monitoring method for main beams based on bridge pier extension cameras is proposed.We have established a three-dimensional coordinate system for the monitoring system with the main beam support point as the origin,and provided recommendations for the installation position and attitude parameters of the bridge pier camera;Propose a camera monitoring accuracy evaluation method based on pixel scale factor,and establish a functional relationship between pixel scale factor and camera resolution,chip size,focal length,installation position,and main beam span;Propose that the pixel scale factor in practical engineering should not be greater than 4 mm/pixel,and provide camera selection recommendations for different span bridges based on the pixel scale factor threshold.(2)A method for measuring the deflection of main beams based on the overlap of image contour lines has been proposed.Propose using pixel level edge detection results as anchor points to obtain sub pixel contour curves of bridges through a sub pixel edge detection algorithm based on local region effects,which improves the robustness of contour line extraction in bridge images under environmental influences;By calculating the gradient vector of subpixel edges,an automatic extraction algorithm for the main beam contour line based on gradient filtering has been established,which can achieve automatic recognition and extraction of the target contour line of the main beam in each frame of the image;By analyzing the overlap of contour lines,pixel displacement measurement of the main beam contour was achieved.(3)A method for transforming the pixel displacement of the main beam contour to the actual deflection has been proposed.We constructed a numerical model for pier camera imaging,analyzed the numerical solution of the projection coordinates of the main beam contour on the imaging plane,and obtained the actual pixel scale functions in the x and y directions.,Verification experiments were carried out to verify that the above function can accurately describe the actual pixel scale distribution.Based on this,a calculation method for the scale factor of ortho transformation based on the least square method was proposed,which realized the transformation of deflection from pixel coordinates to actual coordinates;Analyzed the influence of camera installation parameters on the orthonormal transformation method,and the results showed that the influence of pitch angle on measurement accuracy cannot be ignored.(4)The experimental beam deformation tests under dynamic and static load conditions and ambient light and dark conditions are carried out.The results show that the average error of static displacement monitoring based on video data of different cameras is 8%,which verifies the accuracy of the main beam Deformation monitoring method based on pier cameras;Comparing the monitoring effects of two types of cameras,it was found that high-speed cameras are suitable for structural vibration monitoring in well lit environments,and monitoring cameras have strong adaptability to weak light environments,making them suitable for long-term static displacement monitoring.(5)Proposed damage identification indicators suitable for the above monitoring methods.Through numerical simulation analysis,it is found that the damage will change the deformation state of the main beam structure,and the second derivative of the deflection curve difference will show a peak signal at the damage location.Therefore,the damage identification index of the deflection curve difference is proposed;An experimental beam damage test was conducted,and it was found that the differential process caused noise in the damage index curve.A multi time mean filtering method was proposed to process the noise.The final results showed that the peak position of the index was consistent with the position of the main beam damage crack,verifying the feasibility of the damage identification method in actual structural damage location identification.