Considering the non-linear behavior of structure and soil when evaluating a nuclear power plant's seismic safety under a beyond-design basis earthquake is essential. In order to obtain the nonlinear response of a nuclear power plant structure, a time-domain SSI analysis method that considers the nonlinearity of soil and structure and the nonlinear Soil-Structure Interaction (SSI) effect is necessary. The Boundary Reaction Method (BRM) is a time-domain SSI analysis method. The BRM can be applied effectively with a Perfectly Matched Layer (PML), which is an effective energy absorbing boundary condition. The BRM has a characteristic that the magnitude of the response in far-field soil increases as the boundary interface of the effective seismic load moves outward. In addition, the PML has poor absorption performance of low-frequency waves. For this reason, the accuracy of the low-frequency response may be degraded when analyzing the combination of the BRM and the PML. In this study, the accuracy of the analysis response was improved by adjusting the PML input parameters to improve this problem. The accuracy of the response was evaluated by using the analysis response using KIESSI-3D, a frequency domain SSI analysis program, as a reference solution. As a result of the analysis applying the optimal PML parameter, the average error rate of the acceleration response spectrum for 9 degrees of freedom of the structure was 3.40%, which was highly similar to the reference result. In addition, time-domain nonlinear SSI analysis was performed with the soil's nonlinearity to show this study's applicability. As a result of nonlinear SSI analysis, plastic deformation was concentrated in the soil around the foundation. The analysis results found that the analysis method combining BRM and PML can be effectively applied to the seismic response analysis of nuclear power plant structures.

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

바위취의 토양산도별 생육특성을 보면 초장, 엽수, 엽장, 엽폭 그리고 초폭에 있어서 모두 pH 4.5에서 생육량이 많았으며 pH가 높을수록 생육량이 현저하게 떨어지는 경향으로 통계적인 유의성이 인정되었다. 따라서 바위취 분화생산시 경량 배양토의 토양산도를 pH4.5~5.0 정도로 맞추어 주는 것이 pH 6.0보다 초기 활착이 빠르고 생육이 양호하며 균일성이 높아지는 것으로 나타났다.

기린초의 토양 pH별 생육특성을 보면 pH가 낮을수록 생육초기부터 후기까지 초장, 엽수, 분지수 등의 생육이 좋았으며 특히 초장과 분지수에서는 pH처리에 따라 통계적인 유의성이 인정되었다. 따라서 기린초 재배시에는 토양 pH를 4.5~5.0정도로 맞추어 주는 것이 pH 6.0보다 초기 활착이 빠르고 생육이 양호하며 균일성이 높아지는 것으로 나타났다.

토양의 답압이 맥류의 생육에 미치는 영향을 조사하여 다음과 같은 결과를 얻었다. 1. 토양의 답압에 의하여 초형은 포포형으로 되고 초장의 신장은 억제되며 분벽수가 증가하고 뿌리는 근수, 근경이 증대하며 심근성으로 되고 근중이 증가하였다. 2. 토양의 답압에 의하여 엽연소 함량이 높아지고 절단엽편의 수분감손량도 증가하였다. 3. 토양의 답압에 의하여 엽에서 생성하는 Ethylene 량이 증대하였다. 4. 토양의 답압에 의하여 하위절간의 생장이 억제되어 도복되기 어려운 생육형으로 되고 수량이 증대하였다. 이상의 결과로부터 맥류 답압의 효과는 맥류 그 자체에 대한 직접적인 효과와 토양을 답압하는 것에 의한 효과가 있음을 알 수 있으며, 또한 토양 답압의 효과는 엽에서 생성하는 Ethylene 량의 증대로 보아 토양 답압이 맥류 뿌리에 대하여 물리적 자극을 주고 있다는 가능성이 시사되었다.