• Structural Engineering and Mechanics
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• 제81권4호
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• pp.429-441
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• 2022

A probabilistic assessment of the seismic-excited buildings with a multiple-tuned-mass-damper (MTMD) system is carried out in the presence of uncertainties of the structural model, MTMD system, and the stochastic model of the seismic excitations. A free search optimization procedure of the individual mass, stiffness and, damping parameters of the MTMD system based on the snap-drift cuckoo search (SDCS) optimization algorithm is proposed for the optimal design of the MTMD system. Considering a 10-story structure in three cases equipped with single tuned mass damper (STMS), 5-TMD and 10-TMD, sensitivity analyses are carried out using Sobol' indices based on the Monte Carlo simulation (MCS) method. Considering different seismic performance levels, the reliability analyses are done using MCS and kriging-based MCS methods. The results show the maximum structural responses are more affected by changes in the PGA and the stiffness coefficients of the structural floors and TMDs. The results indicate the kriging-based MCS method can estimate the accurate amount of failure probability by spending less time than the MCS. The results also show the MTMD gives a significant reduction in the structural failure probability. The effect of the MTMD on the reduction of the failure probability is remarkable in the performance levels of life safety and collapse prevention. The maximum drift of floors may be reduced for the nominal structural system by increasing the TMDs, however, the complexity of the MTMD model and increasing its corresponding uncertainty sources can be caused a slight increase in the failure probability of the structure.

• 한국지진공학회논문집
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• 제17권1호
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• pp.33-41
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• 2013

Due to a high level of system ductility, steel moment resisting frames have been widely used for lateral force resisting structural systems in high seismic zones. Earthquake field investigations after Northridge earthquake in 1994 and Kobe earthquake in 1995 have reported that many steel moment resisting frames designed before 1990's had suffered significant damages and structural collapse. In this research, seismic performance assessment of steel moment resisting frames designed in accordance with the previous seismic provisions before 1990's was performed. Buckling-restrained braces and shear walls are considered for seismic retrofit of the reference buildings. Increasing stiffness and strength of the buildings using buckling-restrained braces and shear walls are considered as options to rehabilitate the damaged buildings. Probabilistic seismic performance assessment using fragility analysis results is used for the criteria for determining an appropriate seismic retrofit strategy. The fragility contour method can be used to provide an intial guideline to structural engineers when various structural retrofit options for the damaged buildings are available.

• 전산구조공학
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• 제4권3호
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• pp.107-115
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• 1991

지진예측을 위한 확률론적퍼지모형을 제안하였다. 제안된 모형은 지진발생에 대하여 무작위성(randomness)과 퍼지니스(fuzziness)를 같이 사용하여, 기존의 확률론에 근거한 지진예측방법을 개선할 수 있도록 하였다. 이 연구의 결과는 (a) 주어진 초과확률에 대한 지반가속도 또는 주어진 지반가속도에 대한 초과확률의 멤버쉽함수와 (b) 멤버쉽함수를 대표할 수 있는 특성값(characteristic value)이다. 확률론적 퍼지모형을 미국 Utah주의 Wasatch Front Range의 자료에 적용하여 서로 다른 연간 초과확률, 최대지반가속도에 대하여 지진도를 작성하였다.

• Earthquakes and Structures
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• 제12권6호
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• pp.653-663
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• 2017

A seismic margin assessment evaluates how much margin exists for the system under beyond design basis earthquake events. Specifically, the seismic margin for the entire system is evaluated by utilizing a systems analysis based on the sub-system and component seismic fragility data. Each seismic fragility curve is obtained by using empirical, experimental, and/or numerical simulation data. The systems analysis is generally performed by employing a fault tree analysis. However, the current practice has clear limitations in that it cannot deal with the uncertainties of basic components and accommodate the newly observed data. Therefore, in this paper, we present a Bayesian-based seismic margin assessment that is conducted using seismic fragility data and fault tree analysis including Bayesian inference. This proposed approach is first applied to the pooltype nuclear research reactor system for the quantitative evaluation of the seismic margin. The results show that the applied approach can allow updating by considering the newly available data/information at any level of the fault tree, and can identify critical scenarios modified due to new information. Also, given the seismic hazard information, this approach is further extended to the real-time risk evaluation. Thus, the proposed approach can finally be expected to solve the fundamental restrictions of the current method.

• Earthquakes and Structures
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• 제6권6호
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• pp.665-687
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• 2014

This paper presents a framework for analytical seismic vulnerability assessment of substandard reinforced concrete (RC) structures in developing countries. Amodified capacity-demand diagram method is used to predict the response of RC structures with degrading behaviour. A damage index based on period change is used to quantify the evolution of damage. To demonstrate the framework, a class of substandard RC buildings is examined. Abrupt accumulation of damage is observed due to the brittle failure modes and this is reflected in the developed vulnerability curves, which differ substantially from the curves of ductile structures.

• Earthquakes and Structures
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• 제23권4호
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• pp.385-401
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• 2022

Uncertainty quantification is the most important challenge in seismic fragility assessment of structures. The precision increment of the quantification method leads to reliable results but at the same time increases the computational costs and the latter will be so undesirable in cases such as reliability-based design optimization which includes numerous probabilistic seismic analyses. Accordingly, the authors' effort has been put on the development and validation of an approach that has reduced computational cost in seismic fragility assessment. In this regard, it is necessary to apply the appropriate methods for consideration of two categories of uncertainties consisting of uncertainties related to the ground motions and structural characteristics, separately. Also, cable-stayed bridges have been specifically selected because as a result of their complexity and the according time-consuming seismic analyses, reducing the computations corresponding to their fragility analyses is worthy of studying. To achieve this, the fragility assessment of three case studies is performed based on existing and proposed approaches, and a comparative study on the efficiency in the estimation of seismic responses. For this purpose, statistical validation is conducted on the seismic demand and fragility resulting from the mentioned approaches, and through a comprehensive interpretation, sufficient arguments for the acceptable errors of the proposed approach are presented. Finally, this study concludes that the combination of the Capacity Spectrum Method (CSM) and Uniform Design Sampling (UDS) in advanced proposed forms can provide adequate accuracy in seismic fragility estimation at a significantly reduced computational cost.

• 한국지진공학회논문집
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• 제24권3호
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• pp.141-148
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• 2020

For the important safety system, two or more units of identical equipment or redundant components with similar function were installed to prevent abnormal failure. If the failure probability of such equipment is independent, this redundancy could increase the system safety remarkably. However, if the failure of each component is highly correlated by installing in a structure or experiencing an earthquake event, the expected redundancy effect will decrease. Therefore, the seismic correlation of the equipment should be evaluated quantitatively for the seismic probabilistic safety assessment. The correlation effect can be explained in the procedure of constructing fragility curves. In this study, several methodologies to quantify the seismic correlation in the failure probability calculation for multiple components were reviewed and two possible ways considering the realistic situation were selected. Simple examples were tested to check the applicability of these methods. The conversion method between these two methods was suggested to render the evaluation using the advantages of each method possible.

• Earthquakes and Structures
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• 제13권5호
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• pp.497-507
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• 2017

Flooding induced scour has been long recognized as a major hazard to river-crossing bridges. Many studies in recent years have attempted to evaluate the effects of scour on the seismic performance of bridges, and probabilistic frameworks are usually adopted. However, direct and straightforward insight about how foundation scour affects bridges as a type of soil-foundation-structure system is usually understated. In this paper, we provide a comprehensive review of applied methods centering around seismic assessment of scoured bridges considering soil-foundation-structure interaction. When introducing these applied analysis and modeling methods, a simple bridge model is provided to demonstrate the use of these methods as a case study. Particularly, we propose the use of nonlinear modal pushover analysis as a rapid technique to model scoured bridge systems, and numerical validation and application of this procedure are given using the simple bridge model. All methods reviewed in this paper can serve as baseline components for performing probabilistic vulnerability or risk assessment for any river-crossing bridge system subject to flood-induced scour and earthquakes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
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• pp.119-123
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• 1991

The concrete structures subjected to strong earthquakes may undergo hysteretic behavior and result in severe damage. The inelastic behavior and steffness degradation due to seismic loading must be properly modeled. The present study proposes a realistic model to assess the structural damage of concrete structures under seismic loadings. The present model also takes into account the probabilistic nature of seimic loading and thus the randomness of motion.

• 자원환경지질
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• 제51권2호
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• pp.203-211
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• 2018

국내 원전부지 지진재해도 평가 경험을 바탕으로 향후 지진재해도 평가 시 보다 정량적인 평가를 위하여 고려하여야 할 사항에 대하여 점검하였다. 지진재해도 평가 방법을 양분하는 것으로 알려진 결정론적 방법과 확률론적 방법에 대하여 간단히 소개하였으며, 대부분의 후속 논의는 확률론적 지진재해도 평가에 집중하였다. 이 평가를 국내 원전부지에 적용한 과거 사례를 토대로 제기된 불확실성의 원인을 추적하였다. 확률론적 지진재해도 평가의 고려사항으로 전문가의 역할, 대표지진목록 작성, 지진원 설정, 지진-지반운동 관계식 개발 및 지진재해도 평가 절차에 대하여 토의하였다. 각 주제별로 불확실성을 증가시키는 요인을 분석하고 국내 환경에 적합한 해결 방안을 토의하였다.