Blind identification of earthquake-excited structures

A new method based on the popular second-order blind identification method, SOBI, is presented to estimate the modal properties of structures under non-stationary earthquake excitations. Since the proposed method is cast within the framework of blind source separation, the issues associated with model-order pre-selection and the use of stability charts in traditional system identification methods are not present. The SOBI method involves the joint diagonalization of multiple covariance matrices of measurements, which is rendered difficult in the presence of non-stationary excitations. This difficulty is overcome in the proposed method by a diagonalization procedure involving a new set of weighted covariance matrices. There are two main contributions in this paper. First, a diagonalization technique that involves the joint-approximate diagonalization of the proposed set of several time-lagged and suitably weighted covariance matrices is developed. Next, a parametric relationship between the key parameters of the proposed method and a suitably chosen non-stationary parameter of the response is developed to aid in the selection of the optimal parameters under non-stationary excitations. In order to demonstrate the results obtained using the proposed method, identification results from the UCLA Factor building using recorded responses from the Parkfield earthquake are utilized.