Three noticeable cases of damage during the 1995 Hyogoken-Nanbu earthquake are reviewed; the damage rate of reinforced concrete buildings in Kobe city, the behavior of the Shin-Nagata high-rise residential building, the fractures of columns of high-rise buildings in Ashiyahama Seaside town. In these cases, the predominant periods of ground motions are considerably longer than the natural periods of buildings and resonance is not expected. These phenomena are examined by a proposed response spectrum of elasto-plastic system with constant damping factor and explained as transitions of natural periods of buildings. This method gives appropriate estimates of an increase in period with an increase in amplitude.
