On-Site Nonlinear Hysteresis Curves and Dynamic Soil Properties |
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Authors: | Mohammad R Ghayamghamian Hideji Kawakami |
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Affiliation: | 11Asst. Prof., Dept. of Engrg. Seismology, Int. Inst. of Earthquake Engrg. and Seismology, P.O. Box 19395∕3913, Tehran, Iran. E-mail: mrgh @dena.iiees.ac.ir
22Prof., Dept. of Civ. and Envir. Engrg., Saitama Univ., 255 Shimo-Okubo, Urawa, Saitama 338, Japan.
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Abstract: | Strong motion records at five vertical array sites in Japan are used to examine soil shear modulus and material damping as a function of shear strain during large earthquakes. Acceleration data from the sites are processed directly for evaluation of site shear stress-strain hysteresis curves for different time windows of the record. Results of the analysis demonstrate a significant nonlinear ground response at the sites with surface peak ground accelerations exceeding 90 gal. The results of shear stress-strain hysteresis curves are also used to estimate variation of soil shear modulus and material damping characteristics with shear strain amplitude at each site. The identified shear modulus-shear strain and damping ratio-shear strain relationships are in general agreement with published laboratory results. These response interpretations are also compared with the results of a frequency-domain analysis by using the spectral ratio (uphole∕downhole) technique. There is general agreement between the time- and frequency-domain results. The results illustrate the significance of the site nonlinearity during strong ground motions as well as the accuracy of the dynamic soil properties obtained from laboratory tests. |
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