以橋樑定期檢測資料為基礎初判淺基礎橋梁沖刷

臺灣於2000年正式建置臺灣地區橋梁管理系統，以登錄每兩年一次之橋梁目視檢測資料，作為公路橋梁現況判釋的基礎。臺灣因山勢陡峭河川短促，過河橋梁毀損成因多與沖刷關係密切，然臺灣適用之沖刷評估表格目前尚未有一致性的共識，而地方政府在經費與人力均拮倨情況下，勢必極度仰賴橋梁目視檢測資料，作為判斷橋梁是否受沖刷威脅之依據。本文嘗試透過審視某一受沖刷損毀橋梁之目視檢測資料，發掘橋梁現況改變跡象與時間點，以瞭解定期目視檢測結果，可否足以提供判釋橋基受沖刷威脅之訊息。本文除提及美國一般橋梁目視檢測作業之外，並以美國橋梁檢測架構內之「關鍵發現」與「評分牽制」等兩類觀念切入，探討該案例橋檢測評分作業之缺失與誤判，須注意目視檢測評分沖刷相關項目之關聯性，補充註記檢測員意見哪些重要且必要事實，反映橋址沖刷潛藏徵兆，以期確切掌握與處置橋梁沖刷關鍵現況。

關鍵字

沖刷；橋梁目視檢測；定期檢測；關鍵發現

並列摘要

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.

並列關鍵字

scour ； bridge visual inspection ； routine inspection ； critical finding

國際替代計量

以橋樑定期檢測資料為基礎初判淺基礎橋梁沖刷

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