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Published August 2005 | Published
Journal Article Open

Earthquake and ambient vibration monitoring of the steel frame UCLA Factor building

  • 1. ROR icon California Institute of Technology


Dynamic property measurements of the moment-resisting steel-frame University of California, Los Angeles, Factor building are being made to assess how forces are distributed over the building. Fourier amplitude spectra have been calculated from several intervals of ambient vibrations, a 24-hour period of strong winds, and from the 28 March 2003 Encino, California (M_L =2.9), the 3 September 2002 Yorba Linda, California (M_L=4.7), and the 3 November 2002 Central Alaska (M_w=7.9) earthquakes. Measurements made from the ambient vibration records show that the first-mode frequency of horizontal vibration is between 0.55 and 0.6 Hz. The second horizontal mode has a frequency between 1.6 and 1.9 Hz. In contrast, the first-mode frequencies measured from earthquake data are about 0.05 to 0.1 Hz lower than those corresponding to ambient vibration recordings indicating softening of the soil-structure system as amplitudes become larger. The frequencies revert to pre-earthquake levels within five minutes of the Yorba Linda earthquake. Shaking due to strong winds that occurred during the Encino earthquake dominates the frequency decrease, which correlates in time with the duration of the strong winds. The first shear wave recorded from the Encino and Yorba Linda earthquakes takes about 0.4 sec to travel up the 17-story building.

Additional Information

© 2005, Earthquake Engineering Research Institute. Received 9 December 2003; accepted 26 September 2004. The authors thank UCLA Vice Chancellor Peccei for advancing funds to install fiber optic network cable in the Factor building, Max Kopelevich for setting up the Factor network connection, Igor Stubailo for continued maintenance of the network, Chuck Conrad and Norman Wright in the UCLA Capital Programs office, Arnie Acosta for providing instrumentation information, Tom Heaton and John Wallace for discussions, Lucy Jones for use of USGS Pasadena office facilities, and James Murakami for UCLA Atmospheric Sciences Department climate data. This work was supported by the Center for Embedded Networked Sensing (NSF STC award #CCR-0120778).

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August 19, 2023
March 15, 2024