Reduced order observer based identification of base isolated buildings

The objective of this study is to identify system parameters from the recorded response of base isolated buildings, such as USC hospital building, during the 1994 Northridge earthquake. Full state measurements are not available for identification. Additionally, the response is nonlinear due to the yielding of the lead-rubber bearings. Two new approaches are presented in this paper to solve the aforementioned problems. First, a reduced order observer is used to estimate the unmeasured states. Second, a least squares technique with time segments is developed to identify the piece-wise linear system properties. The observer is used to estimate the initial conditions needed for the time segmented identification. A series of equivalent linear system parameters are identified in different time segments. It is shown that the change in system parameters, such as frequencies and damping ratios, due to nonlinear behavior of the lead-rubber bearings, are reliably estimated using the presented technique. It is shown that the response was reduced due to yielding of the lead-rubber bearings and period lengthening.