• Title, Summary, Keyword: seismic

Search Result 7,163, Processing Time 0.039 seconds

A new methodology for modeling explicit seismic common cause failures for seismic multi-unit probabilistic safety assessment

  • Jung, Woo Sik;Hwang, Kevin;Park, Seong Kyu
    • Nuclear Engineering and Technology
    • /
    • v.52 no.10
    • /
    • pp.2238-2249
    • /
    • 2020
  • In a seismic PSA, dependency among seismic failures of components has not been explicitly modeled in the fault tree or event tree. This dependency is separately identified and assigned with numbers that range from zero to unity that reflect the level of the mutual correlation among seismic failures. Because of complexity and difficulty in calculating combination probabilities of correlated seismic failures in complex seismic event tree and fault tree, there has been a great need of development to explicitly model seismic correlation in terms of seismic common cause failures (CCFs). If seismic correlations are converted into seismic CCFs, it is possible to calculate an accurate value of a top event probability or frequency of a complex seismic fault tree by using the same procedure as for internal, fire, and flooding PSA. This study first proposes a methodology to explicitly model seismic dependency by converting correlated seismic failures into seismic CCFs. As a result, this methodology will allow systems analysts to quantify seismic risk as what they have done with the CCF method in internal, fire, and flooding PSA.

Seismic fragility assessment of isolated structures by using stochastic response database

  • Eem, Seung-Hyun;Jung, Hyung-Jo
    • Earthquakes and Structures
    • /
    • v.14 no.5
    • /
    • pp.389-398
    • /
    • 2018
  • The seismic isolation system makes a structure isolated from ground motions to protect the structure from seismic events. Seismic isolation techniques have been implemented in full-scale buildings and bridges because of their simplicity, economic effectiveness, inherent stability and reliability. As for the responses of an isolated structure due to seismic events, it is well known that the most uncertain aspects are the seismic loading itself and structural properties. Due to the randomness of earthquakes and uncertainty of structures, seismic response distributions of an isolated structure are needed when evaluating the seismic fragility assessment (or probabilistic seismic safety assessment) of an isolated structure. Seismic response time histories are useful and often essential elements in its design or evaluation stage. Thus, a large number of non-linear dynamic analyses should be performed to evaluate the seismic performance of an isolated structure. However, it is a monumental task to gather the design or evaluation information of the isolated structure from too many seismic analyses, which is impractical. In this paper, a new methodology that can evaluate the seismic fragility assessment of an isolated structure is proposed by using stochastic response database, which is a device that can estimate the seismic response distributions of an isolated structure without any seismic response analyses. The seismic fragility assessment of the isolated nuclear power plant is performed using the proposed methodology. The proposed methodology is able to evaluate the seismic performance of isolated structures effectively and reduce the computational efforts tremendously.

Seismic Design of Bridges in Low to Moderate Seismic Zones

  • Kook, Seung-Kyu
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.2 no.3
    • /
    • pp.121-127
    • /
    • 1998
  • For the seismic design of bridges in Korea classified as the low to moderate seismic zones, the design concepts provided in the Standard Specification for Highway Bridges, Division I-A: Seismic Design, are adopted, which is basically developed for the strong seismic zones by AASHITO. Accordingly, the design procedures provided for the low to moderate seismic zones are simplified too much to fulfill the purpose of the seismic design. In this paper the design procedures given for the low to moderate seismic zones in the Standard are summarized and discussed in view of the seismic design purpose. From the discussion results some revisions are proposed as conclusions for the reasonable a, pp.ication of the Standard for bridges located in the low to moderate seismic zones.

  • PDF

Seismic Fragility Evaluation of Isolated NPP Containment Structure Considering Soil-Structure Interaction Effect (지반-구조물 상호작용 효과를 고려한 지진격리시스템이 적용된 원전 격납건물의 지진 취약도 평가)

  • Eem, Seung Hyun;Jung, Hyung Jo;Kim, Min Kyu;Choi, In Kil
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.17 no.2
    • /
    • pp.53-59
    • /
    • 2013
  • Several researches have been studied to enhance the seismic performance of nuclear power plants (NPPs) by application of seismic isolation. If a seismic base isolation system is applied to NPPs, seismic performance of nuclear power plants should be reevaluated considering the soil-structure interaction effect. The seismic fragility analysis method has been used as a quantitative seismic safety evaluation method for the NPP structures and equipment. In this study, the seismic performance of an isolated NPP is evaluated by seismic fragility curves considering the soil-structure interaction effect. The designed seismic isolation is introduced to a containment building of Shin-Kori NPP which is KSNP (Korean Standard Nuclear Power Plant), to improve its seismic performance. The seismic analysis is performed considering the soil-structure interaction effect by using the linearized model of seismic isolation with SASSI (System for Analysis of Soil-Structure Interaction) program. Finally, the seismic fragility is evaluated based on soil-isolation-structure interaction analysis results.

Influence Analysis of Seismic Risk due to the Failure Correlation in Seismic Probabilistic Safety Assessment (다중기기 손상 상관성에 의한 지진리스크 영향 분석)

  • Eem, Seung-Hyun;Choi, In-Kil
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.23 no.2
    • /
    • pp.101-108
    • /
    • 2019
  • The seismic safety of nuclear power plants has always been emphasized by the effects of accidents. In general, the seismic safety evaluation of nuclear power plants carries out a seismic probabilistic safety assessment. The current probabilistic safety assessment assumes that damage to the structure, system, and components (SSCs) occurs independently to each other or perfect dependently to each other. In case of earthquake events, the failure event occurs with the correlation due to the correlation between the seismic response of the SSCs and the seismic performance of the SSCs. In this study, the EEMS (External Event Mensuration System) code is developed which can perform the seismic probabilistic safety assessment considering correlation. The developed code is verified by comparing with the multiplier n, which is for calculating the joint probability of failure, which is proposed by Mankamo. It is analyzed the changes in seismic fragility curves and seismic risks with correlation. As a result, it was confirmed that the seismic fragility curves and seismic risk change according to the failure correlation coefficient. This means that it is important to select an appropriate failure correlation coefficient in order to perform a seismic probabilistic safety assessment. And also, it was confirmed that carrying out the seismic probabilistic safety assessment in consideration of the seismic correlation provides more realistic results, rather than providing conservative or non-conservative results comparing with that damage to the SSCs occurs independently.

A Study of System Analysis Method for Seismic PSA of Nuclear Power Plants (원자력발전소 지진 PSA의 계통분석방법 개선 연구)

  • Lim, Hak Kyu
    • Journal of the Korean Society of Safety
    • /
    • v.34 no.5
    • /
    • pp.159-166
    • /
    • 2019
  • The seismic PSA is to probabilistically estimate the potential damage that a large earthquake will cause to a nuclear power plant. It integrates the probabilistic seismic hazard analysis, seismic fragility analysis, and system analysis and is utilized to identify seismic vulnerability and improve seismic capacity of nuclear power plants. Recently, the seismic risk of domestic multi-unit nuclear power plant sites has been evaluated after the Great East Japan Earthquake and Gyeongju Earthquake in Korea. However, while the currently available methods for system analysis can derive basic required results of seismic PSA, they do not provide the detailed results required for the efficient improvement of seismic capacity. Therefore, for in-depth seismic risk evaluation, improved system analysis method for seismic PSA has become necessary. This study develops a system analysis method that is not only suitable for multi-unit seismic PSA but also provides risk information for the seismic capacity improvements. It will also contribute to the enhancement of the safety of nuclear power plants by identifying the seismic vulnerability using the detailed results of seismic PSA. In addition, this system analysis method can be applied to other external event PSAs, such as fire PSA and tsunami PSA, which require similar analysis.

Seismic fragility performance of skewed and curved bridges in low-to-moderate seismic region

  • Chen, Luke;Chen, Suren
    • Earthquakes and Structures
    • /
    • v.10 no.4
    • /
    • pp.789-810
    • /
    • 2016
  • Reinforced concrete (RC) bridges with both skew and curvature are pretty common in areas with complex terrains. Existing studies have shown skewed and/or curved bridges exhibit more complicated seismic performance than straight bridges, and yet related seismic risk studies are still rare. These bridges deserve more studies in low-to-moderate seismic regions than those in seismic-prone areas. This is because for bridges with irregular and complex geometric designs, comprehensive seismic analysis is not always required and little knowledge about actual seismic risks for these bridges in low-to-moderate regions is available. To provide more insightful understanding of the seismic risks and the impact from the geometric configurations, analytical fragility studies are carried out on four typical bridge designs with different geometric configurations (i.e., straight, curved, skewed, skewed and curved) in the mountain west region of the United States. The results show the curved and skewed geometries can considerably affect the bridge seismic fragility in a complex manner, underscoring the importance of conducting detailed seismic risk assessment of skewed and curved bridges in low-to-moderate seismic regions.

Seismic Response Analysis of Nuclear Power Plant Structures and Equipment due to the Pohang Earthquake (포항지진에 대한 원자력발전소 구조물 및 기기의 지진응답분석)

  • Eem, Seung-Hyun;Choi, In-Kil
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.22 no.3
    • /
    • pp.113-119
    • /
    • 2018
  • The probabilistic seismic safety assessment is one of the methodology to evaluate the seismic safety of the nuclear power plants. The site characteristics of the nuclear power plant should be reflected when evaluating the seismic safety of the nuclear power plant. The Korea seismic characteristics are strong in high frequency region and may be different from NRC Regulatory Guide 1.60, which is the design spectrum of nuclear power plants. In this study, seismic response of a nuclear power plant structure by Pohang earthquake (2017.11.15. (KST)) is investigated. The Pohang earthquake measured at the Cheongsong seismic observation station (CHS) is scaled to the peak ground acceleration (PGA) of 0.2 g and the seismic acceleration time history curve corresponding to the design spectrum is created. A nuclear power plant of the containment building and the auxiliary buildings are modeled using OPENSEES to analyze the seismic response of the Pohang earthquake. The seismic behavior of the nuclear power plant due to the Pohang earthquake is investigated. And the seismic performances of the equipment of a nuclear power plant are evaluated by the HCLPF. As a result, the seismic safety evaluation of nuclear power plants should be evaluated based on site-specific characteristics of nuclear power plants.

The Seismic Response Analysis of Lattice Dome According to Direction of Seismic Load (래티스돔의 지진 하중 방향에 따른 지진 응답 분석)

  • Kim, Yu-Seong;Kang, Joo-Won;Kim, Gee-Cheol
    • Journal of Korean Association for Spatial Structures
    • /
    • v.18 no.3
    • /
    • pp.133-140
    • /
    • 2018
  • Vertical earthquake motions can occur along with horizontal earthquakes, so that Structure should be designed to resist Seismic loads in all directions. Especially, due to the dynamic characteristics such as the vibration mode, when the vertical seismic load, the dynamic response of the Spatial structure is large. In this study, the seismic response of the lattice dome to horizontal and vertical seismic loads is analyzed, and a reasonable seismic load combination is analyzed by combining horizontal and vertical seismic response results. In the combination of the horizontal seismic load, the largest result is obtained when the direction of the main axis of the structure coincides with the direction of seismic load. In addition, the combination of vertical seismic load and horizontal seismic load was the largest compared with the combination of horizontal seismic load. Therefore, it is considered that the most reasonable and stable design will be achieved if the seismic load in vertical direction is considered.

Seismic Design and Analysis of Seismically Isolated KALIMER Reactor Structures (면진된 KALIMER 원자로 구조물의 내진설계 및 지진해석)

  • 이형연
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.3 no.1
    • /
    • pp.75-92
    • /
    • 1999
  • In this paper, the seismic analysis model for seismically isolated KALIMER reactor structures is developed and the modal analysis and the seismic time history analysis are carried out for seismic isolation and non-isolation cases. To check the seismic stress limit according to the ASME Code, the equivalent seismic stress analyses are preformed using the 3-D finite element model. From the seismic stress analysis, the seismic margins are calculated for structural members. The limit of seismic load is defined to show that the maximum input acceleration ensures the structural safety for seismic load. In comparison of seismic responses between seismic isolation and non-isolation cases, the seismic isolation design gives significantly reduced acceleration responses and relative displacements between structures. The seismic margin of KALIMER reactor structure is high enough to produce the limit seismic load 0.8g.

  • PDF