長周期長時間地震動を含む強震記録に基づく応答スペクトルとエネルギースペクトルの関係

抄録

 During the 2011 off the Pacific coast of Tohoku earthquake, large response displacements were observed on upper floors in super high-rise buildings at sites far from the earthquake source. These phenomena were due to long-period and long-duration ground motions developed in the thick sedimentary basin. Since building responses to strong ground motions are significantly influenced by the value of the damping factor of the building, it is important to do a quantitative estimation of the effects of the damping factor on building response based on recent data including long-period and long-duration ground motions for aseismic design.
 In this paper, the damping function is defined as the ratio of the pseudo velocity response spectrum to the energy spectrum (Akiyama and Kitamura, 2006). The damping function is available for the prediction of the maximum response, and has ever been used as an index to evaluate the seismic performance conveniently. The damping function is also available to estimate the input energy of ground motions to buildings, because it means the relationship between the maximum response and the accumulative response. While the knowledge of the damping functions in the period less than a few seconds has been accumulated, there are few knowledge of the damping function for long-period and long-duration ground motions.
 First we have examined the applicability of the damping functions presented in previous studies to longer periods and longer duration using a lot of recent records including long-period and long-duration ground motions. Then we have developed new damping functions for long-period (from 0.5 to 6 seconds) and long-duration (up to about 400 sec) strong motions. Using the new damping functions, we have showed a method for estimating the energy spectrum from the pseudo velocity response spectrum. We have obtained the results that the estimated energy spectra correspond to the observed energy spectra regardless of the period ranges.
 The new damping function can be used as a criterion to judge the adequacy of the input energy of predicted ground motions and design ground motions except for pulsive ground motions such as strong ground motions observed in Kobe during the 1995 Hyogoken Nanbu, Japan, earthquake.