Search

To detect and evaluate the earthquake damage of a 9-story reinforcement concrete building in the main shock of Miyagi-ken Earthquake, Sep. 15, 1998, the parameters of the building are identified and analyzed by using off-line system identification method from the structural strong motion records in the foreshock and aftershock before and after the main shock event. The results show that the structural parameters can be identified accurately from the seismic response data in small earthquakes during which the structure can be assumed as the time-invariant system. By comparing the parameters identified from the small earthquakes before and after the main shock, the structural damage in the main shock can be detected and evaluated primarily. It is found that the damage occurrence can be detected from the decreasing of the natural frequency and equivalent stiffness of the building, whereas the damping ratios are not suitable to detect the damage because the variations of damping ratios of the building are irregular after damaged in the main shock. The results can be referenced by the structural earthquake damage detection, diagnosis, and related work.

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.

To diagnose the seismic damage of one 5-story reinforced concrete building under the excitation of great earthquake, the off-line ARX method and recursive on-line RARX method are applied to identify the structural time-invariant and time-varying parameters from its seismic response records. The results show that the time-invariant and time-varying parameters can be determined from the seismic response records by two methods, especially the structural time-varying characteristics can be identified accurately by using on-line RARX method through forgetting factor. Moreover, the structural parameters of the building before and after damage can be obtained from the time-varying parameters, and the seismic damage can be detected from the comparison among the parameters of structural different state. It is also found that the natural frequency decreases gradually until it reaches the lowest point value, and then increases until the end of the earthquake, but can not be recovered to the initial value. The performance of structures could be recovered to a certain extent after the earthquake compared with the most dangerous state when the natural frequency is at the lowest point. The results can be referenced by structural damage diagnosis and related tasks.