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Comparative study of viscous damping formulation in time-domain site response analysis

SUN Qiangqiang;BO Jingshan;LI Xiaobo;WANG Xin;Institute of Disaster Prevention;Key Laboratory of Earthquake Engineering and Engineering Vibration,Institute of Engineering Mechanics,China Earthquake Administration;  
This paper revisits the effect of damping matrices on site response analysis in time-domain based on Finite difference method(FDM).Numerical models are developed to simulate the wave propagation through an elastic medium after considering soil thickness H,shear velocity VSand spectral characteristics of input motions.A full Rayleigh damping matix is adopted and the low frequency is selected as the fundamental site frequency,the high frequency(optimal frequency) is determined by five methods.In order to compare the results of different methods with actual records,the equivalent linearization method and time-domain with five damping formulations on the seismic response of soil layers in Xiang-tang Array are also presented.Analyzes reveal that damping models have significant influence on acceleration and spectral acceleration,but ground displacement response limited.The maximum absolute displacement distribution on soil depth is much more complex than acceleration in different models.The spectral acceleration value difference is large in short period,while has little influence on long period.The re-sults of different models are discrete in large soil thickness and low shear velocity when input high frequency motions.The site frequency and frequency characteristics of input motions should be considered to establish damping matrix.For long period input motions,the site 3rdfrequency can be selected as optimal frequency,and the predominant frequency of motions should be used in high frequency input motions.Seismic response of the site is underestimated when only the site fundamental frequency is adopted,especially in deep soft site.
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