| Dynamic displacement is the basic parameter of structural condition evaluation and structural performance evaluation,and it was of great significance in structural health monitoring and load testing.Traditional displacement measurement methods were susceptible to environmental factors in practical engineering applications.Videogrammetric had the advantages of non-contact,low cost,and easy implementation,and had attracted widespread attention.In order to meet the requirements of non-contact measurement of civil engineering structures,a subpixel displacement measurement research based on digital image correlation was carried out,and the method was theoretically analyzed and verified by experimental researches.The main contents were as follows:(1)Firstly,the basic theory of the two-dimensional digital image correlation method was introduced,and the camera calibration was completed based on the Harris corner detection algorithm.According to the correlation coefficient distribution diagrams of different correlation functions,the ZNCC function and ZNSSD function,which performed unimodality and stability,were selected for correlation operations.The camera calibration method based on plane calibration objects was used to obtain the internal parameters and the structural position parameters of camera.The mapping relationship of the world coordinate system and the image coordinate system was determined.(2)Two commonly used sub-pixel displacement algorithms in digital image correlation technology were analyzed.Inverse composition Gauss-Newton with improved initial value was proposed.The algorithm of computer-generated simulated speckle pattern was introduced,and the anti-noise performance of the displacement measurement method proposed in this paper was verified by using the simulated speckle image.The performance of three sub-pixel algorithms were compared and analyzed in terms of calculation accuracy and calculation stability.The results showed that inverse composition Gauss-Newton algorithm with improved initial value had the advantages of high measurement accuracy and stable calcution results in displacemnt mensurement.(3)A method for measuring the structural displacement by using a fixed camera was proposed,which completed the displacement measurement test of laboratory frame structure and the deflection measurement test of fire passage bridge of the Dawangshan Snow World.The SUSAN filtering algorithm was used to process the acquired video sequences.The results showed that the SUSAN algorithm can not only filter noises,but also obtain clearer images.A steel frame model was established for conducting experiments to investigate comparison study on the measurement results obtained by the vision-based system and the laser displacement sensor,and the RMSE was0.129 mm.The system zero drift test was used to obtain the measurement accuracy of visual measurement system at different ranging distances according to a statistical probability of 95%.In the actual bridge test,the on-site measured bridge deflection curve showed that the displacement measurement method proposed in this paper had good accuracy,and it can meet the needs of structural deflection measurement in engineering.(4)During actual measurement,the fixing camera may not be easy to set up.To solve this problem,this articles applied UAV to displacement measurement of large structures.The absolute displacement of the structure is extracted from the video collected by the drone through the following three stages: calculating the relative displacement of the structural measurement point;motion(self-motion)estimation of camera;measuring the absolute displacement measurement of the point.The feasibility of the method for structural displacement and measurement was verified by relevant experiments. |
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