STRUCTURAL TIME-VARYING MODAL PARAMETERS IDENTIFICATIONBASED ON ITS STRONG MOTION RECORDS
GONG Mao-sheng1,2;Toshihide KASHIMA3;XIE Li-li1,2;OU Jin-ping2
(1. Institute of Engineering Mechanics, China Earthquake Administration, Harbin 150080, China; 2. School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China; 3. Building Research Institute, Tsukuba 305-0802, Japan)
Abstract：To study the changes of structural dynamic characteristics and the structural seismic damage process during earthquakes for structure seismic damage assessment purpose, the time-varying modal parameters are identified based on the strong motion records by using on-line system identification method RARX model. For one example, the natural frequency, damping ratio and equivalent stiffness of a 6-story reinforcement concrete frame structure are identified from its strong motion records during two earthquakes, one is small earthquake, and the other is great earthquake. The results show that the natural frequency does not change during small earthquake. In great earthquake, the natural frequency decreases gradually until it reaches the lowest point value, and then increases until the end of the earthquake but it can not be recovered to the initial value. That means the performance of structures could be recovered to a certain extent after the earthquake. The equivalent stiffness is changed with the same trend as natural frequency, but decreases much greater than that of natural frequency. However, the structural damping ratio increases after damage under the excitation of great earthquake. The results can be referenced by the damage detection and prognosis.
2010, Vol. 29 
