Seismic performance evaluation of reactor containment building considering effects of concrete material models and prestressing forces

Thusa Bidhek,Nguyen Duy-Duan,Azad Md Samdani,이태형 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.5

The reactor containment building (RCB) in nuclear power plants (NPPs) plays an important role in protecting the reactor systems from external loads as well as preventing radioactive leaking. As we witnessed the nuclear disaster at Fukushima Daiichi (Japan) in 2011, the earthquake is one of the major threats to NPPs. The purpose of this study is to evaluate effects of concrete material models and presstressing forces on the seismic performance evaluation of RCB in NPPs. A typical RCB designed in Korea is employed for a case study. Detailed three-dimensional nonlinear finite element models of RCB are developed in ANSYS. A series of pushover analyses are then performed to obtain the pushover curves of RCB. Different capacity curves are compared to recognize the influence of different material models on the nonlinear behavior of RCB. Additionally, the effects of prestressing forces on the seismic performances of the structure are also investigated. Moreover, a set of damage states corresponding to damage evolutions of the structures is proposed in this study.

Optimal earthquake intensity measures for probabilistic seismic demand models of ARP1400 reactor containment building

Duy-Duan Nguyen,Bidhek Thusa,Md Samdani Azad,Viet-Linh Tran,이태형 한국원자력학회 2021 Nuclear Engineering and Technology Vol.53 No.12

This study identifies efficient earthquake intensity measures (IMs) for seismic performances and fragilityevaluations of the reactor containment building (RCB) in the advanced power reactor 1400 (APR1400)nuclear power plant (NPP). The computational model of RCB is constructed using the beam-truss model(BTM) for nonlinear analyses. A total of 90 ground motion records and 20 different IMs are employed fornumerical analyses. A series of nonlinear time-history analyses are performed to monitor maximum floordisplacements and accelerations of RCB. Then, probabilistic seismic demand models of RCB are developedfor each IM. Statistical parameters including coefficient of determination (R2), dispersion (i.e. standarddeviation), practicality, and proficiency are calculated to recognize strongly correlated IMs with theseismic performance of the NPP structure. The numerical results show that the optimal IMs are spectralacceleration, spectral velocity, spectral displacement at the fundamental period, acceleration spectrumintensity, effective peak acceleration, peak ground acceleration, A95, and sustained maximum acceleration. Moreover, weakly related IMs to the seismic performance of RCB are peak ground displacement,root-mean-square of displacement, specific energy density, root-mean-square of velocity, peak groundvelocity, Housner intensity, velocity spectrum intensity, and sustained maximum velocity. Finally, a set offragility curves of RCB are developed for optimal IMs.

Efficiency of various structural modeling schemes on evaluating seismic performance and fragility of APR1400 containment building

Nguyen, Duy-Duan,Thusa, Bidhek,Park, Hyosang,Azad, Md Samdani,Lee, Tae-Hyung Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.8

The purpose of this study is to investigate the efficiency of various structural modeling schemes for evaluating seismic performances and fragility of the reactor containment building (RCB) structure in the advanced power reactor 1400 (APR1400) nuclear power plant (NPP). Four structural modeling schemes, i.e. lumped-mass stick model (LMSM), solid-based finite element model (Solid FEM), multi-layer shell model (MLSM), and beam-truss model (BTM), are developed to simulate the seismic behaviors of the containment structure. A full three-dimensional finite element model (full 3D FEM) is additionally constructed to verify the previous numerical models. A set of input ground motions with response spectra matching to the US NRC 1.60 design spectrum is generated to perform linear and nonlinear time-history analyses. Floor response spectra (FRS) and floor displacements are obtained at the different elevations of the structure since they are critical outputs for evaluating the seismic vulnerability of RCB and secondary components. The results show that the difference in seismic responses between linear and nonlinear analyses gets larger as an earthquake intensity increases. It is observed that the linear analysis underestimates floor displacements while it overestimates floor accelerations. Moreover, a systematic assessment of the capability and efficiency of each structural model is presented thoroughly. MLSM can be an alternative approach to a full 3D FEM, which is complicated in modeling and extremely time-consuming in dynamic analyses. Specifically, BTM is recommended as the optimal model for evaluating the nonlinear seismic performance of NPP structures. Thereafter, linear and nonlinear BTM are employed in a series of time-history analyses to develop fragility curves of RCB for different damage states. It is shown that the linear analysis underestimates the probability of damage of RCB at a given earthquake intensity when compared to the nonlinear analysis. The nonlinear analysis approach is highly suggested for assessing the vulnerability of NPP structures.

GFRP 보강근 적용 비간섭 계면이음을 갖는 프리팹 합성거더의 휨성능 유한요소해석

DIEP THANH HUNG,Bidhek Thusa,김남수,김현민,김예진,최병호 한국복합신소재구조학회 2024 복합신소재구조학회 학술발표회 Vol.2024 No.04

최근 프리팹 부재간 비간섭 계면이음 설계기술이 도입되고 기계주입식 충진 기술의 실용화 성공으 로, 교량 프리캐스트 바닥판 시공의 저해요인이 상당히 해결될 수 있다. 이 때 프리팹 부재에 GFRP 보강근을 적용한다면 가공조립비 절감 효과가 있고, 프리팹 부재의 경량화로 경제성이 제고될 뿐 만 아니라, 현장 안전성과 작업편의성이 향상될 것으로 보인다. 기존 철근 연신율은 20% 내외 수준인데 반해 GFRP 보강근의 파괴변형율은 3% 내외이며 탄성계수는 50GPa (강재 대비 25%수준)이므로, 이 러한 재료특성 차이로 인한 휨성능에 대한 영향 평가가 필요하다. 특히 GFRP 보강근을 프리캐스트 바닥판과 거더 간 계면이음 적용에 따른 영향을 평가하기 위한 프로토타입 거더를 설계하고, 재료간 계면의 부착 특성을 고려한 유한요소해석 모델을 수립하고 극한 휨성능과 소요 계면 전단성능과의 상 관관계를 검토하였다. 추후 본 변수해석 연구에 대해 실험적 검증이 완수된다면, GFRP 보강근 설계기 술을 정립하는 데 기여할 것으로 기대된다.

Identifying significant earthquake intensity measures for evaluating seismic damage and fragility of nuclear power plant structures

Nguyen, Duy-Duan,Thusa, Bidhek,Han, Tong-Seok,Lee, Tae-Hyung Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.1

Seismic design practices and seismic response analyses of civil structures and nuclear power plants (NPPs) have conventionally used the peak ground acceleration (PGA) or spectral acceleration (S_a) as an intensity measure (IM) of an earthquake. However, there are many other earthquake IMs that were proposed by various researchers. The aim of this study is to investigate the correlation between seismic responses of NPP components and 23 earthquake IMs and identify the best IMs for correlating with damage of NPP structures. Particularly, low- and high-frequency ground motion records are separately accounted in correlation analyses. An advanced power reactor NPP in Korea, APR1400, is selected for numerical analyses where containment and auxiliary buildings are modeled using SAP2000. Floor displacements and accelerations are monitored for the non- and base-isolated NPP structures while shear deformations of the base isolator are additionally monitored for the base-isolated NPP. A series of Pearson's correlation coefficients are calculated to recognize the correlation between each of the 23 earthquake IMs and responses of NPP structures. The numerical results demonstrate that there is a significant difference in the correlation between earthquake IMs and seismic responses of non-isolated NPP structures considering low- and high-frequency ground motion groups. Meanwhile, a trivial discrepancy of the correlation is observed in the case of the base-isolated NPP subjected to the two groups of ground motions. Moreover, a selection of PGA or S_a for seismic response analyses of NPP structures in the high-frequency seismic regions may not be the best option. Additionally, a set of fragility curves are thereafter developed for the base-isolated NPP based on the shear deformation of lead rubber bearing (LRB) with respect to the strongly correlated IMs. The results reveal that the probability of damage to the structure is higher for low-frequency earthquakes compared with that of high-frequency ground motions.

근거리지진의 영향을 고려한 면진 원전구조물의 지진취약도

Nguyen Duy-Duan,Thusa Bidhek,이태형 한국방재학회 2018 한국방재학회논문집 Vol.18 No.7

근거리지진은 방향효과(forward-directivity effect)와 플링스텝(fling-step)이라고 부르는 영구지반변형을 유발하는 특징이 있다. 본 논문에서는 근거리지진의 영향을 고려하여 면진된 원자력발전소 구조물의 지진취약도를 평가하였다. 다양한 지진기록을 수집하여 방향효과를 포함한 근거리지진, 플링스텝을 포함한 근거리지진, 원거리지진의 세 그룹으로 분류하였다. 한국형 신형 가압경수로인 APR1400을 수치해석을 위한 대상으로 선정하였다. 지진취약도 곡선은 최우도추정법을 이용하여 도출하였으며, 여기에는 면진장치인 납-고무받침(LRB)의 변형능력을 한계상태로 고려하였다. 해석결과, 원거리지진을 고려했을 때 LRB 최대변형의 중간값이 근거리지진을 고려한 경우보다 작았다. 또한, 동일한 지진강도에 대해서 근거리지진이 원거리지진보다 원전구조물을 손상시킬 확률이 높게 계산되었다. This study investigates the effect of near-fault ground motions on the seismic fragility of base-isolated nuclear power plant (NPP) structures. Because near-fault motion has either directivity or a so-called fling-step characteristic, or both, three groups of ground motions, namely, near-fault forward-directivity, near-fault fling-step, and far-fault ground motions, are selected for fragility analyses. A base-isolated advanced power reactor 1400 (APR1400), a recently developed NPP in Korea, is employed for numerical analysis. A set of fragility curves are derived for various limit states based on the maximum likelihood estimation. The limit states are defined in terms of deformation capacity of lead rubber bearing (LRB). The numerical results reveal that the median maximum deformations of LRBs were smaller for far-fault ground motions than for near-fault ground motions. In addition, the comparison of fragility curves demonstrates that the probability of failure of base-isolated NPP structures is higher for near-fault ground motions than for far-fault motions given the same earthquake intensity.

Consideration of Prestressed Tendons in Beam-truss Modeling of APR1400 Containment Building

Md Samdani Azad,Duy-Duan Nguyen,Bidhek Thusa,Tae-Hyung Lee 대한토목학회 2021 대한토목학회 학술대회 Vol.2021 No.10

Simplified Nonlinear FE Model for Reactor Containment Building

Md Samdani Azad,Duan Nguyen,Bidhek Thusa,Tae-Hyung Lee 대한토목학회 2020 대한토목학회 학술대회 Vol.2020 No.10