Identification of dynamic models of a building structure using multiple earthquake records

In this paper, a methodology is presented for the identification of state-space models of a building structure using time histories of the earthquake-induced ground motion and of the corresponding structural responses. From these identified models, modal parameters such as natural frequencies, damping ratios and mode shapes of the structural system can be easily retrieved. The identification methodology is based on the ERA/DC complemented by the OKID algorithm for the identification of the Markov's parameters of the system. Model order is determined using the stabilization diagram. Additional model refinement is performed through a nonlinear minimization of the output error between recorded and reconstructed responses. The building considered in this analysis has 29 accelerometers, located on the basement and at various elevation levels. Three of such accelerometers are placed directly on the ground outside the building and are considered representative of the free-field ground motion. Records of the ground acceleration and of the building response recorded during 10 aftershocks of the 1999 Chi-Chi (Taiwan) earthquake have been used, 9 of which for the identification phase and 1 (the latest aftershock) for validation of the prediction capabilities of the identified models. Different input conditions have been assumed to account for the effects of the flexibility of the foundation and for the soil–foundation–structure interaction. From the analysis of the results, it is concluded that the proposed methodology is quite effective in identifying the modal parameters of the structural system and in predicting its structural response for a future earthquake. Copyright © 2008 John Wiley & Sons, Ltd.