Hybrid Time/Frequency Domain Identification of Real Base-Isolated Structure
This paper presents a case study using hybrid time- and frequency-domain identifications in a synergistic manner to develop models of a full-scale experimental base-isolated structure. This four-story reinforced-concrete building on an isolation layer (of rubber bearings, elastic sliding bearings, passive metallic yielding dampers, and controllable oil dampers) was designed and constructed at the large-scale Japanese NIED E-Defense earthquake engineering laboratory. A variety of sensors, including accelerometers, were mounted within the structure to measure building response to shake table excitations. While the building was ultimately subjected to historical and synthetic ground motions, the recorded table and building accelerations during a number of random excitation tests are used to identify the structure’s natural frequencies, damping ratios and mode shapes. The substantial damping provided by the isolation layer necessitates adopting a hybrid time- and frequency-domain approach for identification. The modes of the structure are separated by frequency content wherein lower frequency modes are identified using time domain approaches from the subspace identification family of methods and higher frequency modes are identified using frequency response functions. Individually, neither approach is able to successfully identify all of the desired modes but, through their combination, the modal properties of the structure are successfully characterized.
KeywordsFull-scale testing Base-isolation State-space models Frequency response functions Modal analysis
This material is based upon work supported by the National Science Foundation under Grant CMMI 13-44937; any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The first author gratefully acknowledges the support of the Viterbi Postdoctoral Fellowship from the University of Southern California.
- 2.Sato, E., Sasaki, T., Fukuyama, K., Tahara, K., and Kajiwara, K.: Development of Innovative Base-Isolation System Based on E-Defense Full-Scale Shake Table Experiments Part I: Outline of Project Research, pp. 751–752. AIJ Annual Meeting, Hokkaido, Japan (2013) (in Japanese)Google Scholar