SUMMARYThe 11 March 2011 M 9.0 Great East Japan earthquake generated significant long-duration shaking that propagated hundreds of kilometers from the epicenter and affected urban areas throughout much of Honshu. Recorded responses of a tall building at 770 km from the epicenter of the mainshock and other related or unrelated events show how structures sensitive to long-period motions can be affected by distant sources. Even when the largest peak input motions to the building is about 3% g, the strong-shaking duration was about 140 s. The 300-to 1000-s prolonged responses of the building are primarily due to a combination of site resonance (e.g. structural fundamental frequency~0.15 Hz and site frequency~0.13-0.17 Hz) and low damping (~1-2%) of the structure. Response modification technologies can improve the response of the building during future earthquakes. The need-to-consider risks to such built environments from distant sources are emphasized.

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.

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.

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Buildings in Japan must be designed and constructed according to Building Standard Law, the Enforcement Order and the Notiˆcation by Ministry of Construction and the Ministry of Land, Infrastructure and Transport notiˆcation. The buildings in our country are suŠered the extensive damages cause by earthquake, typhoon, andˆre, etc. Then, earthquake is adopted as one of forces/loads that should be endured by the buildings. Through these valuable experiences, we learned that the ground condition strongly in-‰uences earthquake ground motion and earthquake damage. By conventional Allowable stress design method, seismic design force level is deˆned taking into account the surface geological condition at construction site. In addition, by the Response and Limit Strength Calculation design method newly adopted for performance-based design concept by the revised Building Standard Law in June, 1998 the seismic force is deˆned at engineering bedrock as an acceleration response spectrum corresponded to the seismic activity in a region concerned with the site ampliˆcation eŠect by subsurface layers and soil-structure interaction eŠect. In this paper, I would like to introduce the consideration of subsurface layers to evaluate site ampliˆcation eŠect under the Building Standard Law and relating regulation especially with relation to the Response and Limit Strength Calculation design method.

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