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Articles by M.K. Jafari
Total Records ( 2 ) for M.K. Jafari
  M. Davoodi , M.A. Sakhi and M.K. Jafari
  In this study, the classical and modern signal processing methods are used to extract dominant frequencies of Masjed Soleiman dam, the highest embankment dam in Iran. The signals were recorded in the gallery, mid-height and the crest of the dam during local earthquakes. Since the amplitude and frequency contents of earthquake acceleration time histories vary with time, classical signal processing techniques are limited to extracting the exact characteristics of the signal. Time-frequency distribution and wavelet analysis were used in this study to overcome this limitation. The proposed modal frequencies of the dam body were evaluated using both the classical and new techniques and the results compared. Differences between the two sets of methods are described and the benefits of the modern signal processing methods are discussed. It is shown that, in non-stationary signals such as earthquake records, higher frequencies are extracted by modern methods that cannot be obtained using classical methods. Besides, the spectral variations of the scalograms clearly indicate that lower frequency contents become more dominant as the excitation amplitude decreases. The lower mode shapes of dam body are excited during the weak part of an earthquake, whereas during the stronger part, all the high and low modes are excited.
  A. Shafiee , H.R. Tavakoli and M.K. Jafari
  This study describes an experimental study on compacted sand-clay mixtures to investigate pre-failure and failure characteristics of such mixtures under monotonic compression and extension loading paths. Results reveal that pore pressure, secant modulus, undrained shear strength and angle of shearing resistance increase when sand content was raised in both compression and extension. It was also found that the tested materials were overconsolidated by the fact that normalized shear strength depends on initial confining stress. The compacted sand-clay mixtures exhibit anisotropy in mechanical behavior so that undrained shear strength and angle of shearing resistance were greater in compression than in extension. The extent of the anisotropy increases with sand content.
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