Bulletin of the Seismological Society of America
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Bulletin of the Seismological Society of America; April 2009; v. 99; no. 2A; p. 611-625; DOI: 10.1785/0120080191
© 2009 Seismological Society of America
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Seismic Interferometry of a Soil-Structure Interaction Model with Coupled Horizontal and Rocking Response

Maria I. Todorovska

Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, California 90089-2531 mtodorov{at}usc.edu

This article presents a system identification analysis of a soil-structure interaction model with coupled horizontal and rocking response based on a combination of Fourier analysis, wave travel-time analysis, and a relationship between fixed-base, rigid-body, and system frequencies. The study provides insight into the coupling of the structural and soil vibrations useful for interpretation of seismic recordings in structures. The structural model captures one-dimensional shear-wave propagation in the structure. The analysis shows that the system functions with respect to foundation horizontal motion are those of the coupled soil-structure system, which differs from conclusions of earlier studies based on a model without foundation rocking. The energy of the system vibrational response is concentrated around the frequencies of vibration of the system, which depend on the properties of the structure, soil, and foundation. The analysis shows that the structural fundamental fixed-base (uncoupled) frequency f1 is related to the wave travel time {tau} (from the base to the top) by f1=1/(4{tau}) and that accurate measurement of {tau}, unaffected by soil-structure interaction, can be obtained from impulse response functions, provided that the data are sufficiently broadband. This is an important result for structural health monitoring because it shows that structural parameters unaffected by soil-structure interaction ({tau}, as well as f1 for structures deforming primarily in shear) can be estimated from seismic monitoring data with minimum instrumentation (two horizontal sensors, one at the base and one at the top). This extends the usability of old strong-motion data in buildings, most of which have not been extensively instrumented, and lessons that can be learned for development and validation of structural health monitoring methodologies. The presented results correspond to a model of the north–south response of the Millikan Library in Pasadena, California, which has become a classical case study for soil-structure interaction.




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M. I. Todorovska
Soil-Structure System Identification of Millikan Library North-South Response during Four Earthquakes (1970-2002): What Caused the Observed Wandering of the System Frequencies?
Bulletin of the Seismological Society of America, April 1, 2009; 99(2A): 626 - 635.
[Abstract] [Full Text] [PDF]




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