| Summary: | 碩士 === 朝陽科技大學 === 營建工程系 === 104 === Structures may be subjected to seismic forces, wind loads and other effects over its lifetime use. Therefore, the structural parameters may be deviated from the design values due to the yielding or the fatigue of the material strength. In this regard, the dynamic characteristics may also be changed due to the damage of the structure. In order to realize the dynamic behavior of structural systems, we can determine the dynamic models and parameters by system identification techniques. System identification techniques made possible to monitor the current state or damage state of the structures
Three methods were proposed to the parameter identification in this study. The first two methods are recursive hybrid GA and moving window hybrid GA, respectively. In the development of these two algorithms, the time histories of the measurements were divided into a series of time intervals, and then the model of equivalent linear systems were employed to identify the modal parameters of the systems for each time interval. These two methods have different ways in dividing the time histories of the measurements. For the second one, the time history of the sequential intervals are overlapped.
The third method is the hybrid GA combining Wen’s model as the restoring force model for each stoty shear. The process of exploring this algorithm is demonstrated by the simulated SDOF system and MDOF system considering the effect of noise contamination.
Finally, these three methods are applied to the three-story structural models with two-types of added-damping-and-stiffness devices mounted on the shaking table. The ground motion records used for these models are time histories of different earthquake adjusted to different intensities. The results showed that the frequencies will vary with the intensity of the ground motion and will reflect the nonlinear behavior of the systems. The comparison of the results of the first two methods showed the change of the parameters for each interval are not smoother when compared to the results of the first method. The results of the third method showed that the D20H100 model of added-damping-and-stiffness devices experienced slight damage when subjected to excitation of El Centro earthquake with PGA values equal to 500gal, while the D20H80 model experienced slight damage when the PGA value reached to 550gal.
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