Image rectification tool for evaluation of gusset plate connections in steel truss bridges Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tt44pq89n

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  • A methodology was developed to permit rectification and metrification of digital images of steel truss gusset plate connections. The approach will enable rapid and accurate collection of field measurements as compared to traditional methods to enable structural evaluation of gusset plate connections. The program enables the operator to quickly create AutoCAD drawings by collecting dimensional information about the gusset plate and connectors from the scaled orthographic photograph (orthophoto), thereby limiting data entry errors and redundant efforts. The availability of scaled orthophotos provides a useful record of field conditions and can be compared with subsequent field inspection results to identify long term changes in visual characteristics. The methodology uses the direct linear transformation (DLT) algorithm to remove image perspective. This transformation requires that certain geometrical characteristics be established between the real world image and the image plane so that the image can be rectified. For the present research, reference targets were developed that can be placed on a gusset plate that establish 9 control points. The control points are ideally spread throughout the image. A mock gusset plate was developed to demonstrate the rectification and metrification techniques. The gusset plate was modeled after a connection in a steel truss bridge located on an interstate highway in Oregon. A series of 10 images were used to demonstrate methodology and to compare resulting measurements of gusset plate geometry from the orthophotos. Overall, images taken with greater skew angles had larger errors than those which were more orthogonal to the mock gusset plate. The largest percentage errors were found using Camera 3 due to more radial distortion inherent in the built-in camera lens. When the gusset plate filled a larger proportion of the overall image, the camera had higher resolution, and a sharp well focused image was taken, and results were improved. Typical absolute measurement errors were 0.27 in.
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