| Summary: | 碩士 === 朝陽科技大學 === 營建工程系碩士班 === 101 === Although a great deal is known about where earthquakes are likely to occur, there is currently no reliable way to predict the time when an event will occur in any specific location. However, the damages caused by them can be greatly reduced with proper structural design using safer seismic code. In this regard, dynamic behavior of structures under earthquakes should be considered in the process of design. In order to realize the dynamic behavior of structural systems, we can determine the dynamic models and parameters by system identification techniques. However, collecting strong motion data is essential when performing the system identification analysis. Fortunately, the strong motion data recorded by accelerographs, which were installed under the Taiwan Strong-Motion Instrumented Program (TSMIP) since 1993, has accumulated to a remarkable amount. In addition to updating the structural parameters for better response prediction, system identification techniques made possible to monitor the current state or damage state of the structures. The parameters of the structures are identified and referred to the associated baseline states. The current state of a structure’s condition relative to a baseline state is compared and the degree of damage is determined.
In the implementation of the recursive hybrid genetic algorithm in the time domain, numerical integration is essential for solving the differential equation in the time domain. This integration procedure may result in a huge amount of computational time since it is required to apply so many times as long as the evolutionary process is proceded. In order to accelerate the identification process, a recursive hybrid GA in the frequency domain is developed. The time history of the measurement is divided into a series of time intervals, and then the model of equivalent linear system is employed to identify the modal parameters of the system for each time interval. The differential equation can be transformed into the frequency domain by Fourier transform and the response in the frequency domain can be solved by algebraic equations instead of differentials equations. The process of exploring this new algorithm is similar to that of recursive hybrid genetic algorithm in the time-domain, by using the simulated SDOF system and MDOF system considering the effect of noise contamination.
Finally, this new identification strategy is also applied to the identification of the real four buildings. By employing the maximum softening index, Approximate Story Damage Index and Modal Assurance Criterion, we can determine the damage states of these buildings. According to the damaged states of the buildings, a set of the threshold values for damage states can be proposed and then be applied to the damage assessment of a real building.
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