2007�������������������������������������� Though the Kashiwazaki-Kariwa Nuclear Power Station was subjected to significantly strong ground motions of the Niigataken Chuetsu-oki Earthquake in 2007, the main facility buildings had almost no damage. Since a large amount of land subsidence was observed near the buildings, the soil around the buildings was expected to be in the strong nonlinear state during the earthquake. In this paper, the authors tried to clarify actual behavior of Unit No.7 reactor building during the earthquake through the simulation analyses using the finite element method. In our analyses, nonlinear effects were considered in contact conditions between the buildings and the surrounding soil by employing joint elements in addition to soil materials.

In this paper, the scaling equation between the pseudo velocity response spectrum and the energy spectrum is proposed. Utilizing random vibration theory, the maximum response of SDOF is given as the function of power spectrum density of main part of earthquake motion. Whereas, energy spectrum is equal to Fourier amplitude spectrum smoothed by spectral window, which is clearly pointed out by Kuwamura, et al. Finally, the equation between response spectrum and energy spectrum is derived, by making connection between Fourier amplitude spectrum and power spectrum density considering the nonstationarity of earthquake motion. The proposed equation is verified not only using the artificial earthquake motions but also using the observed strong ground motions of both interplate earthquakes and inland crustal earthquakes. The equation between the peak ground acceleration/velocity and response spectrum is also proposed, which is the application of the method shown in this paper.

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Earthquake observation records were observed in reactor buildings of Kashiwazaki-Kariwa Nuclear Power Plant Site during the Niigata-ken Chuetsu-oki earthquake in 2007 (NCO). Some studies on the seismic response and simulation analyses were performed to investigate dynamic characteristics of the structures. In particular, it was clarified that the vertical motions of the reactor building of Unit 6 were greater than those of adjacent reactor buildings of Unit 5 and Unit 7. This paper discusses the causes of this by earthquake observation records and simulation analyses of the reactor buildings. In general, seismic response of vertical motions is relatively well-simulated using lumped mass model with stick elements that have vertical stiffness and with the soil spring between the basemat and support ground. However, vertical motions are influenced by rocking motions with horizontal response in some cases. This paper focuses on relationships between the vertical responses and the vertical motions induced by the rocking motions with simulation analyses and observation records during both NCO earthquake and aftershock of NCO. The reasons why the vertical motions of the reactor building of Unit 6 were larger are discussed.

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