Parameter identification of a 9-story building for earthquake damage detection

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.