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It has been previously confirmed that the maximum shear strain did not exceed 0.25 × 10 −3, which is a guideline value for shear cracking of reinforced concrete (RC) shear walls for cases such as the Kashiwazaki–Kariwa NPP Unit 7 RB during the 2007 Niigataken Chuetsu-oki earthquake. For this reason, a detailed evaluation of the influence of soil-structure interaction (SSI) considering soil separation and sliding on structural responses is required for embedded buildings. In ASCE/SEI4-16 ( ASCE, 2017), it is also indicated that the response may increase at some frequencies because of additional rocking motions. Therefore, it is considered that the separation and sliding of soil from the sidewalls have a significant influence on buildings with embedment. The soil settlement occurring alongside to the buildings is a nonlinear behavior at the soil-structure interface, which is accompanied by the separation of the soil moving away from the sidewalls and sliding of the soil that sinks from the sidewalls due to the relative displacement of the soil and structure. Although it was confirmed by field investigations conducted after the earthquake that important buildings, such as the RBs, were undamaged or only slightly damaged, the surface soil settlement shown in Figure 1 occurred alongside the buildings ( Tokyo Electric Power Company Holdings Inc., 2007 Yee and Tokimatsu, 2011 IAEA, 2013). A number of strong acceleration records exceeding the design values obtained using the design ground motion were observed at the reactor buildings (RBs), which are the most important building for seismic safety of the NPP ( International Atomic Energy Agency (IAEA), 2007a International Atomic Energy Agency (IAEA), 2007b). As a result of this earthquake, the Kashiwazaki–Kariwa NPP shut down automatically the operating reactor. Therefore, a precise response evaluation of the building including the nonlinear behavior due to separation and sliding should be considered in the seismic response analyses under severe seismic excitation.ĭuring the Niigataken Chuetsu-oki earthquake ( M JMA = 6.8 according to the Japanese Meteorological Agency, M W = 6.6) that occurred at 10:13 local time on July 16th, 2007, seismic motion with a maximum acceleration close to 1 g was observed in the ground at ground level (G.L.) −255 m of the Kashiwazaki–Kariwa nuclear power plant (NPP) ( Hijikata et al., 2010). In this study, the separation and sliding of soil from sidewalls had only a limited influence on the structural responses however, under severe seismic excitation, it is expected that the embedment effects will be significantly reduced due to the separation and sliding of soil.
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Moreover, in this study, it was clarified that the increase of the foundation uplift affected both the soil pressure characteristics beneath the foundation and along the sidewalls, and the maximum acceleration response of structures. In addition, the comparison of the cases with and without separation and sliding revealed that the separation and sliding of soil from sidewalls reduces the embedment effects of the structure and that the reduction causes an occurrence of the foundation uplift. Through the soil-structure interaction analyses based on the recorded seismic data on the foundation for unit 7 reactor building using the three-dimensional finite element model, it was confirmed that the simulated horizontal responses of the building corresponded to the recorded seismic data.
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To achieve this, we modeled the separation and sliding from sidewalls during a severe earthquake using joint elements, and evaluated the effect on the horizontal response of the structure. The objective of this study is to evaluate accurately the influence of the nonlinear behavior of the soil-structure interface on the response of the reactor building using a three-dimensional finite element model. In the 2007 Niigataken Chuetsu-oki earthquake, soil settlement, considered to be a result of the relative displacement between the soil and the structure, occurred alongside buildings at Kashiwazaki–Kariwa nuclear power plant.
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