In the afternoon of March 11, 2011, the eastern Japan was severely attacked by the 2011 off the Pacific coast of Tohoku earthquake (the Great East Japan earthquake). Nearly 30,000 people were killed or are still missing by that earthquake and the ensuing monster tsunami as of April 11, 2011. This paper reports some aspects of this devastating earthquake which hit an advanced country in seismic resistant design. It has been reported that long-period ground motions were induced in Tokyo, Nagoya and Osaka. The properties of these long-period ground motions are discussed from the viewpoint of critical excitation and the seismic behavior of two steel buildings of 40 and 60 stories subjected to the long-period ground motion recorded at Shinjuku, Tokyo is determined and discussed. This paper also reports the effectiveness of visco-elastic dampers like high-hardness rubber dampers in the reduction of responses of super high-rise buildings subjected to such long-period ground motions. The response reduction rate is investigated in detail in addition to the maximum response reduction. In December 2010 before this earthquake, simulated long-period ground motions for earthquake resistant design of high-rise buildings were provided in three large cities in Japan (Tokyo, Nagoya and Osaka) and nine areas were classified. Two 40-story steel buildings (slightly flexible and stiff) are subjected to these long-period ground motions in those nine areas for the detailed investigation of response characteristics of super high-rise buildings in various areas.
Fundamental mechanisms of earthquake response reduction in building structures with inertial mass dampers are investigated. The inertial mass damper is effective with respect to relative acceleration between two nodes. The influence of inertial mass dampers on the ground-motion input can be expressed by the influence coefficient vector to be multiplied on the ground-motion acceleration in the right-hand side of the equations of motion. It is shown that, when an inertial mass damper is taken out from one story, the component of the influence coefficient vector above that story becomes 1. This means that, if an inertial mass damper is taken out from one story, the inertial mass dampers above that story do not influence the input acceleration above that story. This observation is supported by the closed-form expression of the influence coefficient vector. The mechanism of earthquake response reduction is also discussed from the viewpoint of earthquake input energy. It is shown that the earthquake input energy under an acceleration input with a constant Fourier spectrum depends on the influence coefficient vector. Finally, the characteristics of earthquake response reduction via inertial mass dampers are presented for three recorded ground motions.
SUMMARYAn e$cient and systematic procedure is proposed for "nding the optimal damper positioning to minimize the dynamic compliance of a 3-D shear building model. The dynamic compliance is expressed in terms of the transfer function amplitudes of the local interstorey drifts evaluated at the undamped fundamental natural frequency. The dynamic compliance is minimized subject to a constraint on the sum of the damping coe$cients of added dampers. Optimality criteria are derived and the optimal damper positioning is determined via an original steepest direction search algorithm. This algorithm enables one to "nd an optimal damper positioning sequentially for gradually increasing damper capacity levels. A non-monotonic design path with respect to the total damper capacity level often appears in the application of this algorithm. A new augmented algorithm via parameter switching is devised to "nd this non-monotonic design path.
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