The Application Of Digital Image Method In Bridge Detection

The application of digital speckle correlation method is one of the most important developments of experimental mechanics. It evolved from photometric technology in early 1980s, and was the combination of digital image processing and photometric technology of speckle. However, digital speckle correlation method owns superiority that other methods can't compare with, such as using white-light as lamp-house, simple path of rays, non-contact measurement, wider measure scope and so on.This paper goes through a systemic study of methods related to digital speckle correlation and studies the way to increase measure accuracy as well as to speed up search. It also analyzed the measure error theoretically and systematically, with analyzing causes of each error and proposing practical methods to reduce measure error. With the development technology of Borland C++ Builder, a computation program was written, in which bi-linear Interpolation and bi-quadratic Interpolation,gradient interpolation are used to match image with sub-pixel accuracy.This paper designs three basic experiments. They are rigid body displacement experiment, tensile test on rubber material and the three points bend experiment on supported beam made of exoxy resin. The displacements of these three experiments are computed with the program wrote in this paper. The accuracy arrived at 1% of one single pixel and computation is fast. These results justify the feasibility of the program used in this paper.Using digital speckle correlation method to measure displacement is content to project require.But to measure stain can't reach project require.In this paper, the computation methods of Digital speckle correlation and finite element are combined and the model of Yitonghe cable-stayed bridge in Changchun city is taken on experiment. We spray speckles at the fixed end of the model and around the cable pole in cable. Meanwhile, we get speckle images with effect of the load on the bridge model and use strain test apparatus to detect. with strain test apparatus With the computation program of this paper, the displacements are computed and are used as known boundary conditions in ANSYS model to compute displacement, stresss and strain. The result shows that maximal stress and srrain tally with criterion of structure devise , the strain in this method is bigger than that measured with strain test apparatus. This method saves modeling time, speed up computation and is more practical.This paper also studies the centroid searching method, which is a new technology used in measuring bridge's displacement in distance. It was applied in inspecting weighing jack-up of Tianjin Jiefang bridge, meanwhile, a hundred-mark meter was used to check. The result shows that the biggest difference of jack-up's displacement between that computed with centroid searching method and that measured with method hundred-mark meter is 6.48%.