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Abstract: The purpose of this paper is to propose a practical method for optimum design of non-linear oil dampers with relief mechanism installed in multi-story framed building structures. The optimum design problem is formulated so as to minimize the maximum interstory drift or maximum acceleration of top-story under design earthquakes in terms of a set of relief forces subject to an inequality constraint on the maximum ratio of the damping force to the relief force and an equality constraint on the sum of relief forces of oil dampers. The proposed method to solve the optimum design problem is a successive procedure which consists of two steps. The first step is a sensitivity analysis by using nonlinear time-history response analyses, and the second step is a modification of the set of relief forces based upon the sensitivity analysis. An advanced reduction method based on static condensation of the frame and energy equivalence transformation of oil dampers is proposed and introduced into the optimum procedure to reduce the computational load. Numerical examples are conducted to demonstrate the effectiveness and validity of the proposed design method. [Copyright &y& Elsevier]

Abstract: A direct method of physical-parameter system identification (SI) is developed in the case of containing noises at both floors above and below a specified story. To investigate the effect of the level of noise on the accuracy of identification, numerical simulations are performed in the frequency domain by generating two stationary random processes with the specified levels of power spectra. When the previous method of physical-parameter SI is applied to the case contaminated by noise at both floors, just above and below a specified story, it is difficult to evaluate the true stiffness and damping coefficients depending on the intensity. To overcome this difficulty, a new noise-bias compensation method is proposed which enables one to evaluate the intensity of noise in addition to the identification of story stiffness and damping. This method can be used in the case of small SN (Signal to Noise) ratios such as actual microtremor records. The effectiveness of the proposed method is demonstrated through a numerical example and an experiment using actual microtremor records for a reduced two-story model. [Copyright &y& Elsevier]

Abstract: A critical excitation problem for a rigid block is considered subjected to horizontal and vertical simultaneous base inputs. The rigid block is supported by a set of a horizontal spring and a dashpot and another set of two vertical springs and dashpots. These springs and dashpots represent the stiffness and damping of ground. The motion of the block consists of a horizontal–rotational (swaying–rocking) motion under a horizontal base input and a vertical motion under a vertical base input. Both the horizontal–rotational motion and the vertical motion contribute to the uplift of the edge of the block. Both the horizontal and vertical base inputs are to be described by two different non-stationary random processes with prescribed power spectra. A critical excitation problem is formulated in which the worst cross-spectrum and the corresponding cross-correlation function of the horizontal and vertical inputs are searched for the maximum mean squares response of the uplift. It is found that the real part (co-spectrum) and the imaginary part (quad-spectrum) of the worst cross-spectrum can be obtained by a devised algorithm including the interchange of the double maximization procedure for the time and cross-spectrum (functional: function of frequency) domains. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]