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Elastic properties of civil engineering structures change when subjected to a dynamic excitation. The modal frequencies show a rapid decrease followed by a relaxation, or slow recovery, that is dependent on the level of damage. In this article, we analyze the slow recovery process applying three relaxation models to fit real earthquake data recorded in a Japanese building that shows variant structural state over 20 years. Despite the differences in conditions, the different scales and the complexity of a real-scale problem, the models originally developed for laboratory experiments are well adapted to real building data. The relaxation parameters (i.e. frequency variation, recovery slope, characteristic times and their amplitudes, and range of relaxation times) are able to characterize the structural state, given their clear connection to the degree of fracturing and mechanical damage to the building. The recovery process following strong seismic deformation, could, therefore, be a suitable proxy to monitor structural health.

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The March 11, 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 km from the epicenter of the mainshock. Recorded responses show that tall buildings were affected by longperiod 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 mainshock. The U.S. "code-type" array comprises three tri-axial 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.

A seismic performance curve shows the relationship between the representative displacement () and the equivalent base shear force coefficient () of a structure. The seismic capacity of a building can be assessed in a straightforward manner using a simple performance skeleton curve. In this study, earthquake response records were used to obtain curves for a steel-reinforced concrete (SRC) building and assess the changes in the seismic performance of the building that occur during an earthquake. This paper compares the seismic performance curves of an 8-story SRC building for 27 strong earthquakes that occurred in Japan between 1998 and 2012. The results demonstrate the practicability of using curves to evaluate the damage to real buildings using data collected during strong earthquakes.

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During the 2011 Tohoku-oki earthquake, a large number of response records from various types of buildings were obtained. The records give us the actual motions of buildings during the exceptionally large earthquakes that are considered comparable with design earthquakes. Various types of earthquake response records have been collected, and their properties with several buildings that will exhibit implications for structural design are discussed.