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Tahmina Tasnim Nahar,Anh-Tuan Cao,Dookie Kim 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.6
This paper proposes an approach to assess and predict the seismic risk of existing concrete gravity dams (CGDs) considering the ageing effect. The combination of fragility function and cumulative absolute velocity (CAV) depending on two failure states has been used in the analysis. It represents the time-variant degradation of the concrete structure and the conditional change of structural vulnerability in the case of the seismic excitation. Therefore, the seismic risk assessment captures here the nonlinear dynamic behavior of a concrete gravity dam through the fragility analysis. Incremental dynamic analysis for the fragility curves is adopted to state the performance of the dam in terms of different intensity measures. To assess the capacity of the aged concrete gravity dam, this research introduces a way to estimate the CAVlimit of CGDs with varying time. For a case study, an existing concrete gravity dam in Korea has been taken into consideration to apply this approach. The numerical finite element model is validated by optimizing the recorded field data. The proposed approach and its findings will be helpful to CGDs operators to ensure whether a dam needs to stop after a specific time using the extracted mathematical model. Furthermore, as this mathematical model is the function of time, the operator can get an idea about dam conditions at any specific time and can take necessary steps.
Tahmina Tasnim Nahar,Md Motiur Rahman,김두기 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.3
The area of this study will cover the location-wise seismic response variation of an electrical cabinet innuclear power point (NPP) based on classical reliability analysis. The location-based seismic groundmotion (GM) selection is carried out with the help of probabilistic seismic hazard analysis using PSHRisktool,where the variation of reliability analysis can be understood from the relation between the reliabilityindex and intensity measure. Two different approaches such as the first-order second momentmethod (FOSM) and Monte Carlo Simulation (MCS) are helped to evaluate and compare the reliabilityassessment of the cabinet. The cabinet is modeled with material uncertainty utilizing Steel01 as thematerial model and the fiber section modeling approach is considered to characterize the section'snonlinear reaction behavior. To verify the modal frequency, this study compares the FEM result withrecorded data using Least-Squares Complex Exponential (LSCE) method from the impact hammer test. Inspite of a few investigations, the main novelty of this study is to introduce the reader to check andcompare the seismic reliability assessment variation in different seismic locations and for differentearthquake levels. Alongside, the betterment can be found by comparing the result between twoconsidered reliability estimation methods.
Seismic capacity evaluation of fire-damaged cabinet facility in a nuclear power plant
Nahar, Tahmina Tasnim,Rahman, Md Motiur,Kim, Dookie Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.4
This study is to evaluate the seismic capacity of the fire-damaged cabinet facility in a nuclear power plant (NPP). A prototype of an electrical cabinet is modeled using OpenSees for the numerical simulation. To capture the nonlinear behavior of the cabinet, the constitutive law of the material model under the fire environment is considered. The experimental record from the impact hammer test is extracted trough the frequency-domain decomposition (FDD) method, which is used to verify the effectiveness of the numerical model through modal assurance criteria (MAC). Assuming different temperatures, the nonlinear time history analysis is conducted using a set of fifty earthquakes and the seismic outputs are investigated by the fragility analysis. To get a threshold of intensity measure, the Monte Carlo Simulation (MCS) is adopted for uncertainty reduction purposes. Finally, a capacity estimation model has been proposed through the investigation, which will be helpful for the engineer or NPP operator to evaluate the fire-damaged cabinet strength under seismic excitation. This capacity model is presented in terms of the High Confidence of Low Probability of Failure (HCLPF) point. The results are validated by the proper judgment and can be used to analyze the influences of fire on the electrical cabinet.
콘크리트 열화를 고려한 중력댐의 시간 의존성 지진위험도 평가
타미나나하르 ( Tahmina Tasnim Nahar ),카오안투안 ( Anh-tuan Cao ),김두기 ( Dookie Kim ),장성규 ( Seongkyu Chang ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.1
All over the world, concrete gravity dams have to withstand lots of environmental hazards and time-varying external loading during an earthquake. Therefore, the risk assessment of this structure with time may become an important study for the dam structure, which is related to the chemo-mechanical effect on the aging concrete. The focusing point of this study is to propose an earthquake assessment procedure to determine the failure probability with time of any concrete gravity dam for the future if we consider the material deterioration. This material decay is mainly associated with the modulus of elasticity of the concrete and it is explained briefly in the manuscript.
지진구역 내 손상단계를 고려한 콘크리트 중력댐의 파괴 위험 분석
타미나나하르 ( Tahmina Tasnim Nahar ),김두기 ( Dookie Kim ),모터라만 ( Md Motiur Rahman ),장성규 ( Sungkyu Chang ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.2
Failure risk investigation of any structure in a seismic zone can be done by the seismic probabilistic risk assessment (SPRA), which became a very attractive area of research in terms of safety measurement. This paper introduces such kind of concept to identify which magnitude in a specific seismic zone will contribute more vulnerable failure point in a structure. Here, for implement this idea a case study on a concrete gravity dam has been carried out. In order to make a correlation between the magnitude and failure risk contribution based on different damage stage, a combination of seismic hazard analysis and the probability of structural collapse is adopted. Therefore, the deaggregation of the mean annual frequency of failure risk by magnitude is used in this study to quantify four different limit stages of failure identification criteria. Consequently, from analyzing the result, in case of concrete gravity dam, this deaggregation approach shows the tensile crack in the base looks more vulnerable damage stage for the specific seismic zone.
타미나나하르 ( Tahmina Tasnim Nahar ),카오안투안 ( Anh-tuan Cao ),김두기 ( Dookie Kim ),최병한 ( Choi Byounghan ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.1
The earthquake risk prediction for dam structure has been considered as an important analysis. The dam has to interact with water in its lifetime, which maybe induces the chemo-mechanical phenomenon on the aging concrete and damage the capacity of the structure. The main aim of this research is to suggest a procedure to predict the operant condition of the dam based on Cumulative Absolute Velocity (CAV) values after some decades. CAV is a method ordinarily used in Nuclear Power Plant (NPP) fields, but in case of a concrete gravity dam, it will be the new addition along with the aging effect of concrete material.
Dynamic behavior of intake tower considering hydrodynamic damping effect
Md Ikram Uddin,Tahmina Tasnim Nahar,Dookie Kim,Kee-Dong Kim 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.82 No.3
The effect of hydrodynamic damping on intake tower is twofold: one is fluid damping and another is structural damping. Fluid damping can be derived analytically from the governing equation of the fluid-structure-interaction (FSI) problem which yields a very complicated solution. To avoid the complexity of the FSI problem water-tower system can be simplified by considering water as added mass. However, in such a system a reconsideration of structural damping is required. This study investigates the effects of this damping on the dynamic response of the intake tower, where, apart from the “no water (NW)” condition, six other cases have been adopted depending on water height. Two different cross-sections of the tower are considered and also two different damping properties have been used for each case as well. Dynamic analysis has been carried out using horizontal ground motion as input. Finally, the result shows how hydrodynamic damping affects the dynamic behavior of an intake tower with the change of water height and cross-section. This research will help a designer to consider more conservative damping properties of intake tower which might vary depending on the shape of the tower and height of water.
지진시 재료 비선형효과를 고려한 TMD가 설치된 콘크리트 구조물의 진동제어
모터라만 ( Md Motiur Rahman ),타미나나하르 ( Tahmina Tasnim Nahar ),장성규 ( Sungkyu Chang ),김두기 ( Dookie Kim ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.2
This paper concern the performance of tuned mass damper (TMD) and dynamic behaviour of TMD controlled structure considering constitutive material model. A three-storied reinforced concrete frame is modelled using OpenSees for this study. Considering the non-linear materials model, the performance of the TMD not only rely on the mass, stiffness and damping of the system but also on the parameter to be controlled by TMD and the input ground motion types. For this reason in this study some practical, sine sweep and damped sine sweep are considered as input excitation to the evaluate exact dynamic behaviour of TMD controlled structure.
Seismic Response Characterization of Shear Wall in Auxiliary Building of Nuclear Power Plant
모터 라만,타미나 나하르,백건휘,김두기,Rahman, Md Motiur,Nahar, Tahmina Tasnim,Baek, Geonhwi,Kim, Dookie Earthquake Engineering Society of Korea 2021 한국지진공학회논문집 Vol.25 No.3
The dynamic characterization of a three-story auxiliary building in a nuclear power plant (NPP) constructed with a monolithic reinforced concrete shear wall is investigated in this study. The shear wall is subjected to a joint-research, round-robin analysis organized by the Korea Atomic Energy Research Institute, South Korea, to predict seismic responses of that auxiliary building in NPP through a shake table test. Five different intensity measures of the base excitation are applied to the shaking table test to get the acceleration responses from the different building locations for one horizontal direction (front-back). Simultaneously to understand the global damage scenario of the structure, a frequency search test is conducted after each excitation. The primary motivation of this study is to develop a nonlinear numerical model considering the multi-layered shell element and compare it with the test result to validate through the modal parameter identification and floor responses. In addition, the acceleration amplification factor is evaluated to judge the dynamic behavior of the shear wall with the existing standard, thus providing theoretical support for engineering practice.