抄録
The system identification of the dynamic properties such as natural periods and damping ratios of four skyscrapers located on Osaka plains was conducted based on the observation records during South-east off Kii-peninsula earthquake September 2004 (M7.4). We found the dynamic properties in the large amplitude portions of response waveforms to be longer in natural period for all buildings and larger in damping ratio for a few steel-buildings than those in the onset and/or the terminal portions of response waveforms. The greatest coefficients of variation of natural periods in duration of response seismic motions were 2 to 4 percents for steel-buildings and 8 percents for a reinforced-concrete building.
