System Identification of an Isolated Structure Using Earthquake Records

The growing interest of investors and stakeholders in protecting building contents and operation beyond the goals of current seismic design codes is generating an increased demand for the use of nonconventional seismic protection systems such as base isolation and energy dissipation devices. This paper focuses on the application of seismic identification techniques on earthquake records obtained in the first Chilean Base Isolated Building. Seismic responses recorded in this structure located in the capital city of Chile, range in Magnitude from 4 to 8.8. This last earthquake corresponds to the sixth largest event recorded in the world and identification results are preliminary presented here. Due to the strong nonlinear elastic response of the base isolation system, classical linear identification methods present poor results. Several procedures to identify the response are presented, including window the response data and nonlinear identification. Basic modal parameters like natural frequency and modal damping ratios are obtained as a function of response amplitude indicating the great benefit of the isolation system and the relevance of developing appropriate identification techniques for this type of highly nonlinear systems. Building isolation system performance is reflected in modal parameters variations observed in the analysis.