Dynamic characteristics of five tall buildings during strong and low‐amplitude motions

Abstract

AbstractThe objectives of this paper are to present (1) a comparison of dynamic characteristics of five buildings determined from recorded strong‐motion response data and from low‐amplitude (ambient vibration) tests, and (2) a description of the low‐amplitude ambient testing and PC‐based data‐acquisition approach that is integrated with the permanent strong‐motion instrumentation in the five buildings. All five buildings are within the San Francisco Bay area and the strong‐motion dynamic characteristics are extracted from the October 17, 1989 Loma Prieta earthquake response records. Ambient vibration tests on the same five buildings were conducted in September 1990. Analyses of strong‐motion response and low‐amplitude test data have been performed by many investigators. The present study differs from numerous previous investigations because (1) in this study, accelerometers in the five permanently‐instrumented buildings were used during the low‐amplitude testing, and (2) rapid screening of the strong‐motion response data was achieved with a concerted use of system identification software. The results show for all cases that the fundamental periods and corresponding percentages of critical damping determined from low‐amplitude tests are appreciably lower than those determined from strong‐motion response records. The data set collected during this study is a useful contribution to the data base of dynamic characteristics of engineered structures and reconfirms the differences between the dynamic characteristics identified from strong‐motion records and from low‐amplitude tests.