원자력발전소(원전) 시스템 내진성능 평가를 위하여 구조물내응답스펙트럼(ISRS)은 필수적으로 요구된다. 특히, 원전 부지 고유 스펙트럼 변경 시 새로운 ISRS 도출이 요구될 경우 지진 재해석 등의 상당한 비용을 필요로 하게 된다. 따라서 이 연구는 지진 재해석 이 필요 없는 ISRS 스케일링 근사 방법에 대한 여러 가지 접근법을 제공한다. 이러한 접근법으로 도출한 ISRS는 정확한 ISRS와 비교 한다. 근사 방법의 ISRS 가 원전 주요 시스템 지진응답 및 내진성능에 미치는 영향을 분석한다. 결과적으로 본 연구에서 제시한 ISRS 스케일링 근사 방법은 저주파에서 비교적 유사하게 ISRS를 도출하지만, 고주파에서는 그 정확도가 감소하였다. ISRS 스케일링 근사 방법이 시스템 지진응답/내진성능 산출 정확도에 미치는 영향은 방법의 시스템 주요 모드 응답 유사도 산출 정도에 따라 결정된 것을 확인할 수 있었다.

전기 캐비닛은 병원 및 발전소와 같은 중요 시설물에서 운영과 관리를 위한 시스템 기기를 보관한 다. 지진과 같은 극한하중 하에서 중요 시설물은 지속적으로 운영 및 제어되어야 하기 때문에 전기 캐 비닛의 안전성은 평가되고 확보되어야 한다. 하지만 실험적 연구만으로 다양한 유형의 전기 캐비닛에 대한 내진성능 평가를 수행하는 것은 많은 제약이 있다. 따라서 다양한 연구자들은 전기 캐비닛의 유 한요소 모델을 구축하고 내진성능 평가를 수행하였다. 유한요소 모델은 beam-stick 요소를 기반으로 구축되거나 3차원 shell 요소를 기반으로 구축되어왔다. Beamk-stick 요소 기반 및 3차원 shell 요소 기반의 유한요소 모델에 대한 전체거동에 대한 비교를 수행한 사례는 있으나 국부거동에 대한 동적응 답을 비교한 연구사례는 없다. 전기 캐비닛은 내부에 시스템 기기가 보관되므로 내부의 국부거동 기반 의 내부응답을 포착할 수 있어야한다. 따라서 본 연구는 단문형 전기 캐비닛에 대한 beam-stick 요소 및 3차원 shell요소를 기반으로 유한요소 모델을 구축하고 동일한 높이에서 가속도 응답을 비교하였다. 결과적으로 beam-stick 요소 기반의 3차원 유한요소 모델은 전기 캐비닛 내부 응답 스펙트럼을 정확 히 예측할 수 없기 때문에 내부 응답 스펙트럼을 위해서는 3차원 shell요소 기반의 상세 유한요소 모 델을 사용해야 한다.

In general, the design response spectrum in seismic design codes is based on the mean-plus-one-standard deviation response spectrum to secure high safety. In this study, response spectrum analysis was performed using seismic wave records adopted in domestic horizontal design spectrum development studies, while three response spectra were calculated by combining the mean and standard deviation of the spectra. Seismic wave spectral matching generated seismic wave sets matching each response spectrum. Then, seismic fragility was performed by setting three damage levels using a single-degree-of-freedom system. A correlation analysis was performed using a comparative analysis of the change in the response spectrum and the seismic fragility concerning the three response spectra. Finally, in the case of the response spectrum considering the mean and standard deviation, like the design response spectrum, the earthquake load was relatively high, indicating that conservative design or high safety can be secured.

Seismic qualification of instruments and devices mounted on electrical cabinets in a nuclear power plant is performed in this study by means of the in-cabinet response spectrum (ICRS). A simple method and two rigorous methods are proposed in the EPRI NP-7146-SL guidelines for generating the ICRS. The simple method of EPRI can give unrealistic spectra that are excessively conservative in many cases. In the past, the time domain analysis (TDA) methods have been mostly used to analyze a structure. However, the TDA requires the generation of an artificial earthquake input motion compatible to the target response spectrum. The process of generating an artificial earthquake may involve a great deal of uncertainty. In addition, many time history analyses should be performed to increase the accuracy of the results. This study developed a numerical analysis program for generating the ICRS by frequency domain analysis (FDA) method. The developed program was validated by the numerical study. The ICRS calculated by FDA thoroughly matched with those obtained from TDA. This study then confirms that the method it proposes can simply and efficiently generate the ICRS compared to the time domain method.

Electrical instruments and devices contained in cabinets for controlling nuclear power plants require seismic qualification; likewise, in-cabinet response spectrum (ICRS) is necessary. Gupta et al. (1999) suggested the Ritz method, where rocking, frame bending, and plate bending behaviors of cabinets are considered, as a method for determining ICRS. This research proposes a method to determine the rocking stiffness of cabinets, which represents its rocking behavior. The cabinet is fixed on mounting frames and is connected to the base concrete by anchors. When horizontal excitation is applied to the cabinet, the mounting frames at anchors are locally deformed, the mounting frames are bent, and then rocking in the cabinet becomes evident. A method to determine equivalent vertical spring stiffness representing the local deformation of the mounting frames at anchors is then proposed. Subsequently, the rocking stiffness of this mounting frame is calculated upon assumption of the mounting frame as an indeterminate beam.

In 2016, an earthquake occurred at Gyeongju, Korea. At the Wolsong site, the observed peak ground acceleration was lower than the operating basis earthquake (OBE) level of Wolsong nuclear power plant. However, the measured spectral acceleration value exceeded the spectral acceleration of the operating-basis earthquake (OBE) level in some sections of the response spectrum, resulting in a manual shutdown of the nuclear power plant. Analysis of the response spectra shape of the Gyeongju earthquake motion showed that the high-frequency components are stronger than the response spectra shape used in nuclear power plant design. Therefore, the seismic performance evaluation of structures and equipment of nuclear power plants should be made to reflect the characteristics of site-specific earthquakes. In general, the floor response spectrum shape at the installation site or the generalized response spectrum shape is used for the seismic performance evaluation of structures and equipment. In this study, a generalized response spectrum shape is proposed for seismic performance evaluation of structures and equipment for nuclear power plants. The proposed response spectrum shape reflects the characteristics of earthquake motion in Korea through earthquake hazard analysis, and it can be applied to structures and equipment at various locations.

Safety-related cabinets and their electrical parts, such as relays and switches in nuclear power plants, should maintain continuous functioning, as well as structural safety according to the nuclear regulatory guidelines. Generally, an electrical part is qualified if its functioning is maintained without abnormality during excitement by motion compatible with the test response spectrum, which is larger than its in-cabinet response spectrum (ICRS). ICRS can be determined by shake-table test or dynamic analysis. Since existing cabinets in use can hardly be stopped and moved, dynamic analysis is preferred over shake-table test in determining ICRS. The simple method, suggested by the Electric Power Research Institute (EPRI) to determine ICRS, yields conservative or non-conservative results from time to time. In order to determine that the ICRS is better than EPRI method in a simple way, Ritz method considering global and local plate behaviors was suggested by Gupta et al. In this paper, the Ritz method is modified in order to consider the rocking and frame behaviors simultaneously, and it is applied to a simple numerical example for verification. ICRS is determined by Ritz method and compared with the results by finite element method (FEM). Based on this numerical example, recommendations for using Ritz method are suggested.

In this study, a design procedure for the practical application of the dampers to building structures under earthquake loads was presented by using earthquake response spectrum. Nonlinear time history results using a 10 story building structure installed with damper verified the effectiveness of the proposed procedure by showing that the structural response could be reduced to the target performance level for seismic loads. Since the proposed design procedures are based on response spectrum seismic analysis result of the original structure, the capacity, location and the number of damper and the consequent response reduction effects can be preliminarily determined without performing the nonlinear time history analysis.

As a method of seismic-design for pile-supported wharves, equivalent static analysis, response spectrum analysis, and time history analysis method are applied. Among them, the response spectrum analysis is widely used to obtain the maximum response of a structure. Because the ground is not modeled in the response spectrum analysis of pile-supported wharves, the amplified input ground acceleration should be calculated by ground classification or seismic response analysis. However, it is difficult to calculate the input ground acceleration through ground classification because the pile-supported wharf is build on inclined ground, the methods to calculate the input ground acceleration proposed in the standards are different. Therefore, in this study, the dynamic centrifuge model tests and the response spectrum analysis were carried out to calculate the appropriate input ground acceleration. The pile moment in response spectrum analysis and the dynamic centrifuge model tests were compared. As a result of comparison, it was shown that the response spectrum analysis results using the amplified acceleration in the ground surface were appropriate.

It is important to select proper ground motions for obtaining accurate results from response history analyses. The purpose of this study is to propose an accurate and efficient method that does not require excessive computation for selecting and scaling ground motions to match target response spectrum mean and variance. The proposed method is conceptually simple and straightforward, and it does not use a simulation algorithm that requires a sophisticated subroutine program. In this method, the desired number of ground motions are sequentially scaled and selected from a ground motion library. The proposed method gives the best selection results using Sum of Square Error and has the smallest value(=0.14). Also, The accuracy and consistency of the proposed method are verified by comparing the selection results of the proposed method with those of existing methods.

대규모 지진에 대한 원전의 안전성을 확보하는 방안으로 기존 원전 구조물에 면진장치를 설치하는 방안이 도입되고 있다. 면진장치를 설치함으로써 상부구조와 지반의 거동을 격리시킬 수 있고, 구조물 자체의 고유주기가 길어지게 되는데, 이를 통해 지진하중에 대한 구조물의 응답을 감소시킬 수 있게 된다. 특히 원전구조물 설계 시 원전구조물 자체뿐만 아니라 원전 내부 기기에 대한 안전성 확보가 필수적이다. 이를 위해 특정 층에 위치한 기기의 설계를 위해 각 층의 최대 요구 응답을 나타내는 층응답스펙트럼이 일반적으로 사용된다. 본 논문에서는 원전 구조물의 지진해석을 통해 특정 층의 층응답스펙트럼을 평가하고, 면진 장치의 거동 특성중 하나인 2차 경화에 대한 영향 또한 평가하였다.

대규모 지진에 대한 원전의 안전성을 확보하는 방안으로 기존 원전 구조물에 면진장치를 설치하는 방안이 도입되고 있다. 면진장치를 설치함으로써 상부구조와 지반의 거동을 격리시킬 수 있고, 구조물 자체의 고유주기가 길어지게 되는데, 이를 통 해 지진하중에 대한 구조물의 응답을 감소시킬 수 있게 된다. 특히 원전구조물 설계 시 원전구조물 자체뿐만 아니라 원전 내 부 기기에 대한 안전성 확보가 필수적이다. 이를 위해 특정 층에 위치한 기기의 설계를 위해 각 층의 최대 요구 응답을 나타 내는 층응답스펙트럼이 일반적으로 사용된다. 본 논문에서는 원전 구조물의 지진해석을 통해 특정 층의 층응답스펙트럼을 평가하고, 면진 장치의 거동 특성중 하나인 2차 경화에 대한 영향 또한 평가하였다.

This study is the sequel of a companion paper (I. Algorithm) for assessment of the seismic performance evaluation of structure using ground motions selected by the proposed algorithm. To evaluate the effect of the correlation structures of selected ground motions on the seismic responses of a structure, three sets of ground motions are selected with and without consideration of the correlation structure. Nonlinear response history analyses of a 20-story reinforced concrete frame are conducted using the three sets of ground motions. This study shows that the seismic responses of the frames vary according to ground motion selection and correlation structures.

It is important to select an accurate set of ground motions when conducting linear and nonlinear response history analyses of structures. This study proposes a method for selecting ground motions from a ground motion library with response spectra that match the target response spectrum mean, variance and correlation structures. This study also has addressed the determination of an appropriate value for the weight factor of a correlation structure. The proposed method is conceptually simple and straightforward, and does not involve a simulation algorithm. In this method, a desired number of ground motions are sequentially selected from first to last. The proposed method can be also used for selecting ground motions with response spectra that match the conditional spectrum. The accuracy and efficiency of the proposed procedure are verified with numerical examples.

본 논문에서는 질점계 비선형 지진응답해석을 통한 역량스펙트럼 도출방법을 소개한다. 일반적인 건축물의 손상도 평가는 비선형 등가정적해석(Push-over Analysis)을 통하여 건축물의 역량스펙트럼을 도출하고, 역량스펙트럼과 요구스펙트럼의 교차점을 성능점으로 평가하고 있다. 등가정적해석은 지진의 영향을 등가의 정적하중으로 환산한 후 이를 이용하여 정적해석을 수행함으로써 구조물의 지진에 의한 거동을 예측하는 방법이다. 이 방법은 고차모드 및 층별 동특성의 영향을 고려할 수 없다. 따라서 건축물의 동특성이 반영된 역량스펙트럼을 산출하기 위하여 질점계 비선형 지진응답해석을 진행하여 건축물의 역량 스펙트럼을 제안하고자 한다.

The seismic damage of non-structural components, such as communication facilities, causes direct economic losses as well as indirect losses which result from social chaos occurring with downtime of communication and financial management network systems. The current Korean seismic code, KBC2009, prescribes the design criteria and requirements of non-structural components based on their elastic response. However, it is difficult for KBC to reflect the dynamic characteristics of structures where non-structural components exist. In this study, both linear and nonlinear time history analyses of structures with various analysis parameters were carried out and floor acceleration spectra obtained from analyses were compared with both ground acceleration spectra used for input records of the analyses and the design floor acceleration spectrum proposed by National Radio Research Agency. Also, this study investigates to find out the influence of structural dynamic characteristics on the floor acceleration spectra. The analysis results show that the acceleration amplification is observed due to the resonance phenomenon and such amplification increases with the increase of building heights and with the decrease of structure’s energy dissipation capacities.

Structures in a nuclear power system are designed to be elastic even under an earthquake excitation. However a structural component such as an isolator shows inelastic behavior inherently. For the seismic assessment of nonlinear structures, response history analysis should be performed. In this study, the response of base isolation system was analyzed by response history analysis for the seismic performance assessment. Firstly, several seismic assessment criteria for a nuclear power plant structure were reviewed for the nonlinear response history analysis. Based on these criteria, the spectrum matched ground motion generation method modifying a seed earthquake ground motion time history was adjusted. Using these spectrum matched accelerograms, the distribution of displacement responses of the simplified base isolation system was evaluated. The resulting seismic responses excited by the modified ground motion time histories and the synthesized time history generated by stochastic approach were compared. And the response analysis of the base isolation system considering the different intensities in each orthogonal direction was performed.

최대지반가속도(PGA : Peak Ground Acceleration)는 지진파의 최대값을 나타내는 매개변수(Parameter)이며 주로 지진파의 강도를 나타낸다. PGA가 동일하더라도 지진파에 따라 다른 동적특성을 가질 수 있고 구조물에 미치는 영향도 다를 수 있다. 따라서 PGA만으로 구조물에 미치는 지진의 특성을 평가하는 것은 바람직하지 못하다. 본 연구에서는 구조물의 비탄성 지진응답해석을 위하여 단자유도(Single Degree Of Freedom) 구조물의 시간이력해석 수행하였으며, 수치해석모델은 완전 탄소성(Perfect Elasto-Plastic)으로 가정하였다. 검토한 입력 지진파는 El Centro NS(1940)의 값을 증감한 지진파를 포함한 실측지진파, 인공지진파를 사용하였다. 이와 같은 수치해석을 통하여 PGA가 동일한 인공지진파들에 대해 비탄성 지진응답해석을 수행하고, 각 지진파에 대하여 변위연성도와 누적소산에너지를 비교하였다. 그 결과 동일한 PGA를 가지더라도 지진파에 따라 서로 다른 응답을 확인할 수 있었다. 따라서 지진의 특성뿐 아니라 구조물의 특성을 반영할 수 있는 지표가 필요할 것으로 판단된다. 구조물의 비탄성 지진응답을 대표할 수 있는 SI(Spectrum Intensity)는 속도응답스펙트럼의 일정구간에 대한 적분을 통하여 얻을 수 있다. 이러한 SI와 변위연성도 및 누적소산에너지의 상관관계 분석을 통하여 구조물의 지진에 대한 비탄성응답의 대표값으로 SI가 적합하다는 것을 확인할 수 있다.

본 연구에서는 지반운동 라이브러리에서 목표스펙트럼에 근사한 평균응답스펙트럼을 갖는 한 개 혹은 다수의 지반운동을 선정하는 효율적인 방법을 제안하고자 한다. 지반운동 선정 시 목표스펙트럼의 형상과 크기를 맞추어야 하는데 이 두 가지를 독립적으로 고려할 수 있다는 기존 연구결과에 따라 본 연구에서도 형상이 가장 유사한 지반운동을 찾고 크기를 맞추기 위하여 배율조정계수를 사용한다. 형상을 맞추기 위해 각 주기에서 목표스펙트럼과 지반운동 평균응답스펙트럼의 차이 값의 표준편차가 최소가 되도록 하여 선정하는 방법을 제안하였다. 형상이 결정된 후 그 크기를 맞추기 위해 본 연구에서 제안한 배율조정계수를 찾는 방법은 기존 연구와 달리 한번에 찾을 수 있도록 제안하였다. 40개의 지반운동 라이브러리로부터 제안한 방법을 이용하여 목표스펙트럼에 근사한 평균스펙트럼을 갖는 7개의 지반운동기록을 선정한 결과, 그 정확성과 계산소요시간에 있어 모두 만족할만한 결과를 보였다.