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中文標題: 改進局部柔度法於梁結構損傷診斷之研究
英文標題: Improved Local Flexibility Method for Damage Detection of Beam Structures
編號: NCREE-13-015
語言: 中文
編輯:
媒體型式: 紙本
作者:
許丁友   廖文義   蕭勝元   羅俊雄   
中文摘要: 局部柔度法(Local flexibility method)是藉由量測模態參數便可判斷梁結構之局部剛度變化。其方法之基本條件之一,係使用一虛力使其所導致之應力在局部結構區域不為零,其他區域為零;本研究改進之擬局部柔度法(Pseudo local flexibility method),係打破此一基本條件,以換取較佳之診斷結果。本研究將此方法應用於一連續梁及兩端固定梁,並進行數值模擬及實際試驗之驗證。其結果與應用局部柔度法之結果相比,顯示此方法可利用較少量之模態,更準確地診斷超靜定梁結構之損傷位置及程度。本研究中提出另一種改進的局部柔度法,亦打破傳統側向振動訊號量測之限制,改為量測梁結構廣域應變之振動訊號,並利用此訊號進行系統識別得到廣域應變模態形狀,再將其轉換成為「旋轉位移」模態形狀,即可應用局部柔度法之原理進行損傷診斷。本研究將光纖量測應用於一簡支梁,並進行數值模擬及實際試驗之驗證;其數值模擬結果顯示,使用相同模態數量時,與使用「側向位移」模態形狀之結果相比,確實有較佳的診斷結果;試驗結果顯示,使用「旋轉位移」模態形狀,與使用「側向位移」模態形狀之結果相比是相差不多,可能是因為實驗過程中的訊雜比偏大,亦即雜訊比偏小,且側向振動訊號量測之訊雜比相較於廣域應變振動訊號之訊雜比大許多,導致難以顯示出此方法之特點。此外,運用上述二種改進方法,由於集中應力的範圍較小,可提高損傷的敏感度,應可易於診斷損傷位置靠近支承處之情況。
英文摘要: The local flexibility method (LFM),which can determine local stiffness variations of beam structures using measured modal parameters, is founded on virtual forces that cause nonzero stresses within a local part of the structure and zero stresses in the other parts of a structure. In this study, the pseudo local flexibility method (PLFM) which breaks the “zero stresses rule” for better damage detection results is proposed. The proposed approach was verified by numerical studies and experimental study of a continuous beam and fix-end beam. The results show that much fewer modes are required for the PLFM to estimate the damage locations and extents with acceptable accuracy. In this study another modification of LFM was also proposed. The “rotatory displacement” mode shapes were extracted from macro-strain vibration signals. These rotatory displacement mode shpaes were employed to detect damage of a beam structure utilizing the local flexibility method. The proposed approach was verified by numerical studies and experimental studies of a simply supported beam. Using the same number of modes, the numerical studies results using “rotatory displacement” mode shapes was better comparing to the one using “lateral displacement” mode shapes. The experimental results show that using “rotatory displacement” mode shape has only similar damage detection ability comparing to using “lateral displacement” mode shape, probably due to that the noise level of measurement during experiment is very small and the signal to noise ratio of lateral vibration signals is very large comparing to the macro-strain ones. In addition, using these two proposed modifications, the sensitivity of damage is improved due to small range of the concentration stress introduced by the designated virtual forces. As a result, damage close to supports should be easiser to be detected.
關鍵字: 局部柔度法、旋轉位移模態、廣域應變、梁結構、損傷診斷
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