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Identification Shallow Foundation Bridge Scour Based on Routine Inspection Data
bridge visual inspection
The current web-based Taiwan Bridge Management System (TBMS), the most complete bridge database in Taiwan, was funded by the Ministry of Transportation and Communications (MOTC) in Taiwan in 2000. This bridge inventory archived biennial visual inspection data on more than 28,000 bridges in total and also provided as an official appraisal basis for highway bridge agencies. In Taiwan, bridges usually crossed rivers with severe channel variation. Most of the failure causes of cross-river bridges were associated with foundation scour and hydrological migration. Flood-induced scour could have continuously undermined the effective embedment depth of bridge foundation, degraded the structural stability of the abutment and piers, and severely threatened their safety. Several scour evaluation methods were developed for identifying scour-potential bridges in Taiwan in the past few years; unfortunately, a compromise agreement has not been reached by government and industrial circles yet. Meanwhile, in order to identify whether or not a bridge confronts scour threat and take a proper contingent action or plan, local governments limited in manpower and budget were bound to deeply reply the outcomes of the conventional visual inspection records. In this paper, the authors collected and reviewed the 10-year-long visual inspection records of one specific scour-damaged spread footing bridge located in central Taiwan. The qualitative changes of bridge site and its surrounding environmental condition were updated and re-constructed on the whole bridge history based each routine inspection. A conventional field investigation was also executed to assemble relevant disaster information immediately after its single span falling accident. A comprehensive overview into the progressive scour was conducted to determine whether visual inspection database could play a useful source on a bridge scour event or not. For integrity and consistency concerns on data were found in the bridge inspection recording and rating, visual inspection information could partially reflect the severity of scour threat on the bridge piers. This paper also reviewed the information of the National Bridge Inspection Standards (NBIS) implemented by the Federal Highway Administration (FHWA) in the U.S. The NBIS firmly required bridge agencies and contractors to record and code all aberration or deficiency findings in visual inspection. Relevant images, sketches, written description should be attached as part of bridge inspection documentation in detail. In order to overcome blind spots in the common bridge visual inspection process, the NBIS provides two another key concepts, Critical Finding and Coding Collocation, which guide crucial conditions for structural or safety issues and re-code tight relation inspection items, respectively. Using these two filter mechanisms could effectively identify the turning point of scour aggravation and inform the bridge agencies to take an efficient action or countermeasure in time before tragedy occurrence. Based on the above steps, the deficiency and miscoding could be interpreted and recognized on this proposed bridge in routine inspection operation used in Taiwan. The bridge inspectors should cautiously notice scour-related inspection items, such as waterway, pier foundation, protection works, abutment, and abutment foundation, record important and necessary deficiencies in detail, and give integrated judgment on scour symptoms and engineering suggestions in the future.
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