Wavelet Analyses for Seismic Ground Motion, Simulation, and Stochastic Site Response

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Title: Wavelet Analyses for Seismic Ground Motion, Simulation, and Stochastic Site Response
Author: Sarica, Rabia Zeynep
Advisors: M.N. Guddati, Committee Member
M.A. Gabr, Committee Member
C.C. Tung, Committee Member
M.S. Rahman, Committee Chair
Abstract: The response of soil masses during an earthquake is governed by the characteristics of the ground motions and the soil material properties. The ground motions generated during earthquakes are random and nonstationary with respect to both amplitude and frequency. Different methods of analysis for time-frequency characteristics of the ground motions have been reviewed and the merits and disadvantages of each are explained. The methods considered here are: Fourier Transform (FT), Short Term Fourier Transform (STFT), Wigner-Ville (WV) Distribution, Hilbert-Huang Transform (HHT), and Wavelet Transform (WT). WT method with a modified version of Littlewood-Paley mother wavelet is found most suitable to analyze the nonstationary characteristics of the seismic ground motion. This method is used to identify some of the nonlinear and nonstationary characteristics of the ground motions recorded during some important earthquakes, namely Northridge-California 1994, Kocaeli-Turkey 1999, and Chi-Chi-Taiwan, 1999. The effect of site distance and site softening on the ground motion characteristics are studied. The information on redistribution of the energy among various frequency ranges as well as its temporal variation is revealed. Responses of Clay and Sand sites with different stiffness-thickness-saturation combinations to different excitations are studied with the use of a computer code for nonlinear analysis of site response (Cyclic1D) and wavelet analysis. Observations for amplification, deamplification, and pore pressure build up are given in both time and frequency domains. A wavelet based formulation to generate earthquake ground motions is also developed. This method uses a seed acceleration history and a selected design response spectrum to produce many motions that retain the main time-frequency characteristics of the original motion, yet are all different from each other. Finally, a wavelet based method to evaluate non-stationary stochastic response of a soil site, idealized as a uniform layer of linear visco-elastic material, is also developed.
Date: 2006-08-15
Degree: PhD
Discipline: Civil Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/5404

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