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by W. Tseng, M. Yang and J. Penzien
September 1993, 84 pp.
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Abstract
This final report presents the results of a seismic performance investigation of the Hayward
BART elevated section, instrumented by the California Division of Mines and Geology under its
Strong Motion Instrumentation Program (CSMIP), using the acceleration time-histories recorded
during the October 17, 1989 Loma Prieta earthquake. The recorded structural responses are
correlated with corresponding theoretically-predicted responses. Adjustments of structural
parameters and modelling concepts required to achieve satisfactory correlations are discussed,
along with their implications to procedures of standard engineering practice. The results
obtained in this study indicate that during the Loma Prieta earthquake, the maximum seismic
demand in the pier-columns of this section of the BART elevated structures was at the level
of about 50% of the full-yield capacities of the columns; that soil-structure interaction
effects play a significant role in controlling the seismic response characteristics in the
transverse direction; and that, due to the presence of the continuous rails which are rigidly
fastened to the girders, the BART elevated structures are highly coupled in the longitudinal
direction; therefore, the single-pier model used for design in this direction may be
inappropriate, especially for those elevated sections which have large variations in
pier-column heights. Due to the importance of including soil-structure interaction
considerations in the seismic modelling for this type of structure, the studies conducted
point out an urgent need of instrumentation that allows independent recordings of the
foundation response motions at the pier-column bases. Recommendations are made toward
improving the arrangement of CSMIP strong-motion instruments at the Hayward BART site to
fulfill this need.
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