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The Observed Wander of the Natural Frequencies in a Structure

Clinton, John F. and Bradford, S. Case and Heaton, Thomas H. and Favela, Javier (2006) The Observed Wander of the Natural Frequencies in a Structure. Bulletin of the Seismological Society of America, 96 (1). pp. 237-257. ISSN 0037-1106. doi:10.1785/0120050052.

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The Southern California Seismic Network (scsn) has recently installed seismic stations in two buildings on the Caltech campus (Millikan Library and the Broad Center). Continuous real-time accelerometer data from these structures are now freely available to the community. This dataset provides a new opportunity to observe, and better understand, the variances in the primary dynamic property of a building system, its natural frequencies. Historical data (triggered strong-motion records, ambient and forced vibration tests) from the well-studied Millikan Library show dramatic decreases in natural frequencies, attributed mainly to moderately large local earthquakes. The current forced vibration east–west fundamental frequency is 22% lower than that originally measured in 1968. Analysis of the new continuous data stream allows the examination of other previously unrecognized sources of measurable change in the fundamental frequencies, such as weather (wind, rain, and temperature), as well as nonlinear building vibrations from small local and moderate regional earthquakes. Understanding these nonlinear shifts is one of the long-term goals of real-time building instrumentation and is critical if these systems are to be used as a postearthquake damage assessment tool.

Item Type:Article
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URLURL TypeDescription DOIArticle
Clinton, John F.0000-0001-8626-2703
Heaton, Thomas H.0000-0003-3363-2197
Additional Information:© 2006 Seismological Society of America. Manuscript received 18 March 2005. We appreciate the comments from Mihailo Trifunac and an anonymous reviewer who improved the quality of the manuscript. We thank Arnie Acosta and Erdal Safak for their help with obtaining data from the USGS array at Millikan Library. We also thank SCEC’s UCSB Portable Broadband Instrument Center (PBIC) for use of their portable seismometers and the JPL Weather Station for the weather data. John Hall, Georgia Cua, and the members of Caltech’s Structural Monitoring Group, especially Jim Beck and Wilfred Iwan, provided extremely helpful feedback and review. This research has been funded through TriNet. We thank the TriNet staff for carrying out the implementation of the TriNet system. Funding for TriNet has been provided by Federal Emergency Management Agency (FEMA) and the California Governor’s Office of Emergency Services (OES) through the Hazards Mitigation Grant Program established following the 1994 Northridge earthquake. The required 25% cost-sharing is provided by California Institute of Technology, California Trade and Commerce Agency, Caltrans, IDA H.L. Crotty, Verizon California, Donna and Greg Jenkins, Pacific Bell/CalREN, Southern California Edison, Sun Microsystems Inc., Times Mirror Foundation, and others. Funding has also been provided by the USGS from their special Northridge funds. The Southern California Earthquake Data Center (SCEDC) is also funded by the Southern California Earthquake Center (SCEC). The support of the Puerto Rico Strong Motion Program (PRSMP) at the University of Puerto Rico at Mayaguez (UPRM) in the completion of the project is gratefully appreciated.
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University of Puerto RicoUNSPECIFIED
Federal Emergency Management Agency (FEMA)UNSPECIFIED
California Office of Emergency ServicesUNSPECIFIED
Southern California Earthquake Center (SCEC)UNSPECIFIED
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Record Number:CaltechAUTHORS:20121120-092458419
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35555
Deposited By: Tony Diaz
Deposited On:20 Nov 2012 18:28
Last Modified:09 Nov 2021 23:16

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