Seismic Response of Pacific Park Plaza. I: Data and Preliminary Analysis

The objective of this paper is to present analyses of a set of acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake $(M_s=7.1)$ from the 30‐story, three‐winged, ductile moment‐resistant reinforced‐concrete‐framed Pacific Park Plaza Building, located in Emeryville, east of San Francisco, Calif. The building was constructed in 1983, and instrumented in 1985 with 21 channels of synchronized uniaxial accelerometers deployed throughout the structure, and three channels of accelerometers located at free‐field outside on the north side of the building, all connected to a central recording system. In addition, a triaxial strong‐motion accelerograph is deployed at free‐field on the south side of the building. The predominant response modes of the building and the associated frequencies at approximately 0.4 Hz and 1.0 Hz are identified visually from the unprocessed records, and also from Fourier amplitude spectra of the processed records, which, as expected, reveal significant torsional motion. In addition, the response spectra of the free‐field and basement motions are very similar. These spectra show that significant structural resonances at higher modes influence both the ground level and the free‐field motions, thus raising the question as to the definition of free‐field motion, at least at this site. This part of the paper includes the preliminary analyses of the data acquired from this building. Part 2 of the paper provides detailed analyses of the data using system identification techniques.