- 學位論文
運用現地監測與結構模擬評估橋梁基礎之沖刷程度與健康狀態
Assessing the Scouring Depth and Health Condition of Bridge Foundation Through the Field Monitoring and Associated Structural Modelling
摘要
由於台灣西部河川中下游的主河道河床均有下降的情況，洪水沖刷造成基礎嚴重裸露，對橋梁的安全造成莫大的威脅。2008年辛樂克颱風和2009年莫拉克颱風，造成數座橋梁倒塌損毀。而現有之橋梁監測系統，大多僅能作即時水位監測，但在后豐大橋和雙園大橋斷橋時，其水位都還沒有達到封橋的標準，可看出傳統以水位為封橋標準，仍無法有效提供橋梁結構實際安全與穩定狀況的判析。 本研究監測橋梁本身結構振動與變位特性，包括振動頻率、振幅、及結構傾斜度，以及橋址之水位與流速，做為評估橋梁健康狀態之依據。當結構系統受損時，由於勁度下降，其自然頻率會降低。故基礎遭受水流沖刷而裸露時，由於周圍土體之流失，將造成基礎承載能力降低。結構體上的振動反應將有所改變，其不僅能表現出土壤~結構互制系統之整體特性，更能夠間接反映出系統邊界條件之變化。因此，量測橋梁上部結構之振動反應，將可藉以評估橋墩基礎之裸露情況；應用在橋梁定期檢測或長期監測，將有助於橋梁之管理與災害防治。 在監測方面，主要建立即時監測系統，量測橋梁本身結構振動與變位特性及橋址之水位與流速。對於監測資料處理方面，主要以LabView程式自動化即時處理龐大的資料，同時自動化存成日檔案及周檔案，方便進行進一步分析。同時在監測資料分析部份，本研究亦提出最能夠清楚呈現橋梁健康狀態的頻率識別分析方法，並以此方法對颱風事件資料加以分析探討。 在模型分析的部分，需先蒐集橋梁基本資料，用SAP2000建立結構分析模型，輔以初始振動量測所得之振動單元之自然頻率與振型，作為模型校正之依據。校正無誤後，便可模擬結構物行為。比較水位、流速及沖刷深度三個物理參數對結構物之影響。同時和監測資料結合比較，此結果可做為橋梁臨界狀態評估依據。
並列摘要
Most bridges of western Taiwan have faced with the problem that the foundations were exposed due to the flood scour. Typhoon Sinlaku in 2008 and Typhoon Morakot in 2009 caused damage to the bridges. Existing systems can only monitor the water level. However, it didn’t reach the water level criterion to close the bridge when Bridge Hou-Fong and Bridge Shuang-yuan collapsed. It seems that using water level to determine the safety of the bridge is not adequate. In the study, using the vibration frequency, amplitude, inclination of Bridge Ci-bing and water level, flow velocity of the river to assess the health condition of bridge foundation. The loss of soil around the foundation due to the flood scour will cause the decrease of bearing capacity. In terms of monitoring, establish real-time monitoring system to measure the vibration frequency, amplitude, inclination of Bridge Ci-bing and water level, flow velocity of the river. In terms of analyzing monitoring data, Write an automated program by Labview to process large data. Then create a database with dayfile and weekfile to do further analysis. This study proposes a frequency identification analysis method which can show the health condition of the bridge clearly, and use the method to analyze the data of typhoon event. In terms of model analysis, modeling by SAP2000 after collecting basic information of the bridge. Then correct model by nature frequency and modal shape which measured in field test. After correcting model, we can simulate structure behavior. Then compare effects to the bridge of the three physical parameters , water level, flow velocity and scouring depth, and combine with monitoring data to assess the critical condition of the bridge.