Research On Crack And Displacement Measurement Of Bridge Structure Based On Digital Image Processing

With the development of economy,the contribution transportation makes to social economy has been more and more obvious.Till December 2016,the total mileage of highway in China exceeded 130 thousand kilometers,and the total number of bridge has reached 805.3 thousand.With the further construction of transportation infrastructure,the main task of the transportation infrastructure will transfer to not only large-scale construction but also maintenance,and the detection in operation phase and maintenance will become the key in the future.As an important part of the transportation infrastructure,the inspection and maintenance are of great significance to the normal operation of the transportation.The crack detection of the traditional bridge structure is mainly completed by manpower,the efficiency and accuracy of which need to be improved.Traditional displacement measuring devices are contact type and can only monitor one point,so a new method is in need.With the development of information technology,the detection of bridge structure based on information technology will gradually replace the traditional method.In this thesis,the bridge structure crack detection and vibration displacement measurement method were studied based on digital image processing technology.The main contents are as follows.(1)Referring to the relevant literature in the domestic and foreign,the research status and development trend of bridge crack detection and vibration measurement based on digital image processing were presented after summarizing the relevant literature in the domestic and foreign,then the research content and technical route of this thesis were drawn up.(2)The theory and methods of digital image processing were introduced,including the generation of digital image and the theory of perspective projection imaging space.Then,the main methods of digital image processing were analyzed and compared in detail.The traditional image processing flow of crack detection was improved,and the automatic crack detection is realized based on MATLAB programming.(3)A calibration frame for image correction and calibration is designed,and a new method of symbol recognition based on color difference and shape is proposed.The old image smoothing method is improved,and a simple smoothing algorithm is developed.The slenderness ratio and the discrete degree were chosen as the parameters of the crack identification,and the method of detecting the crack width by calculating the diameter of inscribed circle was proposed.Compared with the traditional vertical method,the inscribed circle method does not need to cut the cracks or fit the edge,so it has stronger robustness.(4)A circular artificial target was designed,and a method of target recognition based on the shape and structure was proposed.The error analysis of fitting ellipse center method was carried out,and the relationship among the resolution,the error of different angles and distances was obtained.A video image processing program was developed for system calibration and target recognition based on MATLAB.The dynamic displacement of portal rigid frame and wind tunnel section model was measured with video image method.The results were compared with those measured by the laser displacement meter.It is found that both the displacement and the spectrum are very close,which proves that the new method can be used to measure the dynamic displacement measurement of bridge structures.