The recent collapses of the I-35W Mississippi River bridge in Minneapolis, and Montreal’s Boulevard de la Concorde overpass have highlighted the importance of regular structure inspections to ensure they remain safe and fit for purpose. Currently, in the UK, highway structures are assessed using a regime of visual inspections, performed by trained engineers. These inspections are performed at four levels: Routine, General, Principal and Special. The inspections cover a range of detail, from a cursory check for gross defects, to a close examination of all surfaces of the structure, including the use of special equipment if required. The quality of data collected depends on the ability of the inspectors to observe and objectively record details of defects. It has been found that the data provided by such inspections can vary significantly.
Research has been performed to investigate the use of images of the structure to assess its condition off-site. The aim is not to remove the engineer from the inspection process but to assist them and make their job easier. The research has concentrated on two main areas: image collection, and image analysis.
The image collection work has investigated the practical issues involved in imaging structures. Such issues include image resolution, lighting, removal of parallax, location referencing of individual images and the development of a prototype collection system. This prototype system makes use of distance measurement lasers and theodolites to determine the position of each image on the structure, and relative to any other image, making it easy to know precisely which parts of the structure are affected by any particular defect.
The image analysis work has attempted to segment the images so that the defects or features present on the structure can be highlighted and classified. The segmentation work has made use of a number of image processing techniques including wavelet analysis and has achieved promising results to date. Processing work has begun to classify the segmented objects into those which should be present on the structure (cabling, drainage, lighting, etc) and those which should not be present on the structure (defects).

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