Study on changes in dynamic characteristics of high-rise steel-framed buildings based on strong motion data

The Building Research Institute (BRI) of Japan operates a strong motion network that covers buildings in major cities across Japan. A great number of strong motion data has been accumulated in the observing stations integrated in the strong motion network over many years.This paper selects four high-rise steel-framed buildings from the BRI strong motion network. These buildings suffered severe shakings in the 2011 Tohoku Earthquake.To discuss the dynamic characteristics of the buildings, the fundamental natural periods and damping ratios of the target buildings are identified using strong motion data. First, changes in natural periods and damping ratios with time are discussed. In general, the natural periods gradually increase with time. Caused by the severe motions in the Tohoku Earthquake, significantly changes in natural periods are observed in all the buildings. Second, the amplitude dependence of natural periods and damping ratios are discussed minutely. The obvious amplitude dependence of natural periods can be recognized in all cases. The types of the relations established between the response amplitudes and damping ratios are dependent on the buildings. Finally, the relations between the response amplitudes and natural periods were formulated based on the regression analysis. The result makes it easy to quantify the changes in the natural periods.