| dc.description.abstract | Traditionally, Nondestructive Testing of structural damage has mostly used Fast Fourier Transform, Fourier analysis using time invariant harmonic function as a basis function which is unable to meet the basic requirements of nonlinear and non-stationary signals. The commercial software ABAQUS was used in this research. Three sets of structural models with different degrees of damage were established. Earthquake history using Chi-Chi earthquake and Hualien offshore earthquake for dynamic analysis. The Hilbert Huang Transform (HHT), which is a time frequency analysis technique without a prior basis functions and local adaptability, the time-variant characteristic of the Hilbert Transform makes the analysis for the non-stationary system possible, is often used for nonlinear and non stationary signal analysis. From the time frequency spectrum, catching sight of the energy distribution of the signal in the time domain and the frequency domain. It is observed that the energy on the time frequency will be concentrated on a fixed frequency value, which can be regarded as the dominant frequency of the structural mode, and the dynamic characteristics of the structural as a function of time can also be observed.
This study uses two analysis tools of the HHT SHM analysis method, the time-frequency amplification function (T.F.AF) and the modal time curve (MTVC). T.F.AF converts the raw data into a wave propagation characteristic, the dynamic characteristics of each phase of the structure will be apparently exhibited. Observing the distribution of energy and instantaneous frequency on the time frequency spectrum, and then the vibration mode characteristic in the T.F.AF spectrum is called MTVC. Observing the structural safety parameter information from the MTVC. Using different conditions, one can observe structural traits and find subtle differences in structural modal behavior which can be utilized to analyze the structural safety after earthquake.
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