Research On Structural Damage Detection By Dynamic Analysis

Due to the character of reflecting the global property of structures, the structural damage detection methods based on dynamic analysis can detect damage globally, which can not be achieved by traditional methods. In the past 20~30 years, the research on damage detection methods based on dynamic analysis has become an active research area and researchers developed many vibration-based damage detection methods. Of all the methods, those using frequency changes to detect structural damage are the pioneer vibration-based methods. Cawley and Adams found that the ratio of frequency changes in two different modes is a function of the location of the damage only. Based on this premise, the "frequency changes ratio" method was put forward to detect structural damage. In this paper, the influence of the damage degree to the premise is discussed by simulating damages of different degrees and calculating the ratio of frequency changes under all the scenarios. As a result, the premise is evaluated and modified: when the damage degree is less than 70%~80%, the premise is correct; when the damage degree is more than 70%~80%, the premise is not correct any more, Cawley and Adams's "frequency changes ratio" method cannot be used to detect damage correctly. On the basis of all the discussion above, a new principle to calculate the theoretical ratio of "frequency changes" is introduced. This principle can overcome the drawback of Cawley and Adams's original method, and offers a better method to distinguish the theoretical and simulated actual data in the numerical study. "Frequency changes ratio" method is validated more effectively through the numerical study of three different structural shapes on the basis of the principles mentioned above.Another method using frequency changes to detect damage is "ratio of the changes of the square of frequency" method. This method is also evaluated and modified in this paper by the same means as above. The modified method is used to detect a simply supported plate's damage numerically.The comparison between these two methods mentioned above is made to provide theoretical basis for their application in practice.Some other methods based on dynamic analysis are introduced briefly. The research and development needs of damage detection for civil engineering structures are addressed.