Structural identification of JPL Building 180 using optimally synchronized earthquake records

Abstract

Linear models of JPL Building 180 were identified from its strong-motion records obtained in the 1971 San Fernando earthquake using two system identification techniques, both of which revealed a previously undetected time-shift of about 0.08 second between the digitized basement and roof records. Optimal alignment of the records produced improved matches between the measured and model responses, and overcame difficulties encountered in extracting physically reasonable estimates for the parameters of the third and higher modes from the original records. The two complementary identification techniques provide optimal estimates with standard errors for the periods, dampings and effective participation factors of the dominant modes in the response. One method performs a least-squares match between the calculated and recorded response in the time domain, and the other in the frequency domain. Akaike's information criterion is used to determine the number of modes to include in the models. The fundamental periods identified for JPL Building 180 lengthened during the response by 40% and 60% for the longitudinal and transverse directions respectively, starting from values close to those measured in vibration tests. The effective overall damping factors for the fundamental modes in the two directions were 3.6% and 4.4% of critical.

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