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A sparsely instrumented 55-story building in Osaka, Japan, had recorded unprecedented, severe, and long-duration, long-period resonating responses during the 11 March 2011 M9.0 Tohoku earthquake that occurred at 767 km distance. Thereafter, studies of the records resulted in the implementation of a significant retrofit design, comprising dampers and buckling restrained braces (BRBs). The responses of the retrofitted building were also recorded during the 24 April 2016 M7.3 Kumamoto earthquake that occurred at 478 km. The earthquake and on-demand acquired ambient response data are analyzed in this study to assess the impact of this rare, retrofitted and instrumented tall building subjected to long period strong shaking from events originating at far distances. As expected, the fundamental frequency and critical damping ratio of the building increased, albeit small, after the retrofit as compared to before the retrofit. Increase of damping percentage is a positive finding and indicates that even larger percentages may be attained under shaking stronger than the 2016 event. The records indicate that the building still experiences significant resonance, torsion, as well as a beating effect.

The objective of this study is to investigate the effects of the three-dimensional (3-D) configuration of the soil-structure system from the viewpoint of dynamic building response to wave propagation. The authors have been motivated to make a study on this subject by the fact that strong ground motion records of the aftershocks of the 2011 off the Pacific coast of Tohoku earthquake were obtained at Iwaki City Hall located in Fukushima Prefecture, Japan. At the North station of the observation site, the shorter predominant periods ranging from 0.2 to 0.3 sec. were observed, while at the South station, the periods were longer ranging from around 0.8 to 1.2 sec. at a distance of about 150 meters from the North station. Therefore, it is interesting to investigate how the underground irregularities affect the ground motions and the seismic responses of the soil-structure. The analysis method is a combination of the 3-D finite element and the 2.5-D thin layered and 2.5-D finite element methods in conjunction with a substructure technique. It was verified that the wave field shows very complex patterns when there exist inclined boundary layers and an embedded structure, causing a big difference in the result between 2- and 3-D methods at a station close to the structure.

Nonlinear elasticity has been observed in different materials and at different scales (from laboratory tests to the crust of the Earth). This behavior is evidenced by nonlinear response accompanied by slow dynamics, a process in which elastic properties recover (fully or partially) values previous to the excitation. In this study we show that nonlinear elasticity also occurs at buildings scale, where nonlinear signatures can be observed even for low levels of strain, and slow dynamics is seen at both short and long-term monitoring. Although the physics behind this response remains unknown, it is believed that this fascinating behavior is controlled by the presence of cracks, heterogeneities and dislocations; and therefore, it might be linked to the level of structural damage. By using data from Japan, we analyze the dynamic response of 24 buildings facing strong motions. The objective is to monitor variations of fundamental frequency over time and correlate them with different levels of structural drift and loading. Analyzing nonlinear elastic behavior might become a very useful and valuable way to monitor the time evolution of structural health, and hopefully, a predictive method to estimate deterioration and likely structural damage over time.

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.

The 11 March 2011 M 9.0 Tohoku earthquake generated long-duration shaking that propagated hundreds of kilometers from the epicenter and affected tall buildings in urban areas several hundred kilometers from the epicenter of the main shock. Recorded responses show that tall buildings were affected by long-period motions. This study presents the behavior and performance of a 37-story building in the Tsukuda area of Tokyo, Japan, as inferred from modal analyses of records retrieved for a time interval covering a few days before, during, and for several months after the main shock. The U.S. “code-type” array comprises three triaxial accelerometers deployed at three levels in the superstructure. Such a sparse array in a tall structure limits a reliable assessment, because its performance must be based on only the average drift ratios. Based on the inferred values of this parameter, the subject building was not structurally damaged.