Loading...
| Friend's email | |
| Your name | |
| Your email | |
| enter code | |
This page was sent successfuly
- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 40060 (09)
- University: Sharif University of Technology
- Department: Civil Engineering
- Advisor(s): Ghannad, Mohammad Ali
- Abstract:
- Earthquakes are one of the greatest natural hazards. Hazard mitigation requires studies in many areas including geotechnical aspects of earthquake engineering. Characteristics of seismic waves change significantly as they pass through soft soil layers near the earth's surface. This phenomenon, commonly known as site effects or site response, is a major factor influencing the extent of damage on structures. Processing of seismic data recorded during earthquakes is one of the most reliable methods to study site effects. The ground motions generated during earthquakes are nonstationary with respect to both amplitude and frequency. The state-of-the-art time-frequency distributions when applied to earthquake records were studied, and the conceptual bases for using this technique for seismic wave parameters estimations were set. 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), Wavelet Transform (WT), Wigner-Ville (WV) Distribution, Cohen class distributions, and Hilbert-Huang Transform (HHT). HHT and RID are found most suitable to analyze the nonstationary characteristics of the seismic ground motion. This study presents a simple time-frequency procedure to identify the natural frequencies and damping ratios of a site using free vibration of soil, which happens frequently after diminishing of seismic waves in last part of the ground motions. However, observation of free vibration of soils is not always possible, as it depends on the severity of the last arrived seismic waves. The procedure used in this study, which is based on time-frequency analysis of seismic data, is able to identify the first natural frequency and damping ratio of a layered soil deposit. This study uses time-frequency analysis of ground motion recordings to quantify site effects, which is able to detect nonlinear soil behavior. ime-frequency analysis of synthetic and real case studies shows that used method can be successfully applied for soil nonlinearity detection. It is observed that frequency drop and energy extension along both time and frequency axes are most signatures for soil nonlinearity
- Keywords:
- Signal Processing ; Site Effect ; Strong Ground Motion ; Earthquake Record
Digital Object List
محتواي پايان نامه
Bookmark