System Identification of Base-Isolated Building using Seismic Response Data

Abstract

Due to the complex nature of the excitation, and the inherent dynamics characteristics of restoring force of the base isolation systems, the response of base-isolated structures subject to strong earthquakes often experiences excursion into the inelastic range. Therefore, in designing base-isolated structures, the nonlinear hysteretic restoring force model of the base isolation system is frequently used to predict structural response and to evaluate structural safety. In this paper, the prediction error method system identification technique is used in conjunction with nonlinear state-space models for identification of a base-isolated structure. Using a variety of nonlinear restoring force models and bidirectional recorded seismic responses, several identification runs are conducted to evaluate the accuracy of the selected models. Several nonlinear restoring force models are utilized for the base-isolation system, including a multiple shear spring (MSS) model. Among all models used, results indicate that the trilinear hysteretic MSS model closely matches the actual hysteretic restoring force profile and time histories obtained directly from the observed data. Introd uctionThe behavior of base-isolated structures during an earthquake is highly affected by the characteristics of the base isolation system. The base isolation system separates the structure from its founda tion and primarily moves the natural frequency of the structure away from the dominant frequency range of the excitation via its low stiffness relative to that of the upper structure.Construction of base-isolated structures has increased, espe cially after the recent strong earthquakes in the United States and Japan. Despite the limited number of recorded seismic response data, vigorous studies to evaluate the actual behavior of base isolated structures during strong earthquakes have been con ducted. Nonlinearity in structural response is often due to the restoring force characteristics of the base isolation system, i.e., variations in structural stiffness and damping during strong earth quakes. Stewart et al. (1999) identified several base-isolated 1Associate Professor,

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