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To track and detect the time-varying characteristics of building during small and great earthquakes, the time-varying parameters of a 5-story building are identified from its seismic response data in three earthquakes by using recursive system identification method. The results show that the time-varying modal parameters of structure can be predicted accurately from the seismic response records, and the structural parameters of buildings before and after damage can be determined from the time-varying parameters by only using records in one earthquake. The natural frequency does not change in small earthquake, but decreases gradually until it reaches the lowest point value, and then increases until the end of record in great earthquake, but it can not be recovered to the initial value when the building is damaged in earthquake. It can be concluded that the performance of structure could be recovered to a certain extent after earthquake compared with the most dangerous state when the response reaches the maximum value in earthquake. Furthermore, the damping ratio changes irregularly during the great earthquake. The results provide means for structural seismic damage detection, diagnosis and evaluation.

The time-invariant modal parameters of a 5-story building are identified from the seismic response time histories in 3 earthquakes by using off-line system identification method ARX model, and all the parameters are compared to find out the parameter changes and the seismic damage information primarily. The results show that the modal parameters of the structure can be identified accurately and easily by using the ARX method, and the structural parameters of the building before and after damage can be obtained from the two small earthquake response data before and after the main shock. The parameters identified from the data in the main shock are similar to the results from the data in the aftershock, but different with the results from the data in the small earthquake just before the main shock. It is found that the modal frequencies and equivalent stiffness decrease but the damping ratios increase after the main shock. From the results, it can be concluded that the building are damaged in the main shock. The results can be referenced by the seismic damage detection, diagnosis, and related tasks.