Modal identification of a centrifuge soil model using subspace state space method |
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| Institution: | 1. School of Civil Engineering and Environmental Science, University of Oklahoma, Norman OK 73019, United States;2. School of Electrical and Computer Engineering, University of Oklahoma, Norman OK 73019, United States;1. Foundation for Research and Technology Hellas - Institute of Chemical Engineering Sciences, Stadiou street, Platani, 26504 Patras, Greece;2. Department of Chemical Engineering, University of Patras, 26504 Patras, Greece;3. Laboratory of Pharmaceutical Technology, Department of Pharmacy, University of Patras, 26504 Patras, Greece;1. University of Amsterdam, Faculteit der Geesteswetenschappen, Spuistraat 210, 1012 VT Amsterdam, The Netherlands;2. University of Göttingen, Seminar für Deutsche Philologie, Käte-Hamburger-Weg 3, 37073 Göttingen, Germany;1. Geology & Geophysics, School of Ocean, Earth Science & Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA;2. Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science & Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA;3. Australian Synchrotron, Clayton, Victoria 3168, Australia;4. Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA;5. School of Earth, Atmosphere & Environment, Monash University, Melbourne, Victoria 3800, Australia;1. Avenue Edmond Cordier 19, 1160 Auderghem, Belgium;2. Université de Lorraine, CRAN, CNRS, IUF, 2 avenue de la forêt de Haye, 54516 Vand?uvre cedex, France;3. CNRS, LAAS, 7 avenue du colonel Roche, F-31077 Toulouse, France;4. Université de Toulouse, UPS, INSA, INP, ISAE, UT1, UTM, LAAS, F-31077 Toulouse, France;5. Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, CZ-16626 Prague, Czech Republic;1. Mechanical & Civil Engineering Department, California Institute of Technology, Pasadena, CA 91125, USA;2. Department of Civil Engineering, The Catholic University of America, Washington, DC 20064, USA;3. Civil, Environmental & Architectural Engineering Department, University of Colorado Boulder, Boulder, CO 80309, USA;4. Civil & Environmental Engineering Department, University of California, Los Angeles, CA 90095, USA |
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| Abstract: | In this paper, modal parameters of a layered soil system comprising of a soft clay layer overlying a dense sand layer are identified from accelerometer recordings in a centrifuge test. For the first time, the subspace state space system identification (4SID) method was employed to identify the natural frequencies, damping ratios, and complex valued mode shapes while considering the non-proportional damping in a soil system. A brief review of system identification concepts needed for application of the 4SID techniques to structural modal identification is provided in the paper. The identified natural frequencies were validated against those estimated by transfer function spectra. The computed normal mode shapes were compared with closed-form solutions obtained from the one-dimensional shear wave propagation equation. The identified modal parameters were then employed to synthesize state space prediction models which were subsequently used to simulate the soil response to three successive base motions. The identified models captured acceleration time-histories and corresponding Fourier spectra reasonably well in the small and moderate shaking events. In the stronger third shaking event, the model performed well at greater soil depths, but was less accurate near the surface where nonlinearities dominated. |
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| Keywords: | Subspace state space system identification (4SID) Natural frequencies Mode shapes Transfer function Earthquake Accelerometers Centrifuge test Layered soils |
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