Seismic base isolation by nonlinear mode localization |
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Authors: | Y Wang D M McFarland A F Vakakis L A Bergman |
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Institution: | (1) Department of Civil and Environmental Engineering, University of Illinois, Urbana, IL, USA;(2) Present address: Department of Civil and Environmental Engineering, Washington University, St. Louis, MO, USA;(3) Department of Aerospace Engineering, University of Illinois, Urbana, IL, USA;(4) Division of Mechanics, National Technical University of Athens, Greece;(5) Department of Mechanical and Industrial Engineering (adjunct), University of Illinois, Urbana, IL, USA |
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Abstract: | Summary In this paper, the performance of a nonlinear base-isolation system, comprised of a nonlinearly sprung subfoundation tuned
in a 1∶1 internal resonance to a flexible mode of the linear primary structure to be isolated, is examined. The application
of nonlinear localization to seismic isolation distinguishes this study from other base-isolation studies in the literature.
Under the condition of third-order smooth stiffness nonlinearity, it is shown that a localized nonlinear normal mode (NNM)
is induced in the system, which confines energy to the subfoundation and away from the primary or main structure. This is
followed by a numerical analysis wherein the smooth nonlinearity is replaced by clearance nonlinearity, and the system is
excited by ground motions representing near-field seismic events. The performance of the nonlinear system is compared with
that of the corresponding linear system through simulation, and the sensitivity of the isolation system to several design
parameters is analyzed. These simulations confirm the existence of the localized NNM, and show that the introduction of simple
clearance nonlinearity significantly reduces the seismic energy transmitted to the main structure, resulting in significant
attenuation in the response.
This work was supported in part by the National Science Foundation Grant CMS 00-00060. The authors are grateful for this support. |
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Keywords: | Nonlinear localization Nonlinear normal modes Base isolation |
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