Structural Damage Identification Under Earthquake Based On Hilbert-Huang Transform

Recent practice has shown that the use of the HHT method to identify structural damage has opened a new horizon in structural damage identification field. However, the HHT method is rarely mentioned in structural damage identification with earthquake background, and researchers mainly focused on single or a combination of Intrinsic Mode Function as well as their instantaneous frequency which may not be enough according to the author. With less measurement data to reflect the structural injury and then reproduction of occurrence and development of structural damage is of great interest researchers. As focusing on the process of structural damage under earthquake, seismic lessons and damage mechanism can be well understood; it can help us to further explore and develop the theory of structure engineering and direct the practice of structural design, which is of far-reaching significance.Wang B.S and Sun Lie have put forward a Time Frequency Response Function based on Hilbert time-marginal spectrum and a Central Frequency together to identify structural damage under earthquake, which is creative and a major breakthrough to the original HHT methods in structure damage identification. There is reason to belive that it is of profound significance and has great potential of development in the future. In this paper, the above two concept were inherited but added with further explanation and expansion. Examples of a three-linear stiffness degradation model and a real earthquake table with this method were also presented, which has shown this method a clear physical meaning and a good ability to identify structural damage under earthquake as well as injury development with time.HHT is actually signal processing and decomposition, many of its derivatives such as the concept of Hilbert spectrum, Hilbert Marginal Spectrum, Hilbert Energy Spectrum, and Hilbert Instantaneous Energy Spectrum are crucial for a better understanding of the damage development under earthquake and should be carefully considered. However, in the application of the HHT, particularly in the field of seismic and structural damage identification, researchers have yet to see seriously these concepts and their physical meaning in a systematic, comprehensive way with much less practical applications correspondinglly. So another major work in this paper was a comprehensive use of the HHT methods, a multi-angle-degree analysis of the above concepts and again throuth examples of a three-linear stiffness degradation model and a real earthquake table to verify. The results have shown that all the method presented in this paper is intuitive and effective.The main contribution of this paper to the HHT method in the field of structural damage identification and seismic design was mind emancipation and raised horizon on damage identification. Learned from the performance-based seismic design methods of the latest achievements in the seismic field, the author has promoted a new and multidimensional approach to the phenomenon of structural damage under earthquake. The importance of energy change on frequency shifts, time shifts and modal shifts was put forward for the first time in this paper, which resulted in a new comprehensive analysis method for earthquake damage identification. In that sense the author did have made much creative effort on Hilbert Marginal Spectrum, Hilbert Energy Spectrum, and Hilbert Instantaneous Energy Spectrum for their application in the field of seismic structural analysis and structural damage identification.