• 전산구조공학
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• 제6권1호
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• pp.77-89
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• 1993

Current Bridge foundation design is based on Working Stress Design(WSD), but Load Factor Based on Optimum Reliability(LFBOR) design method is more rational than the WSD. For this reason, this study proposes a reliability based design criteria for the bridge foundation, which is most common type of bridge foundation(Shallow, Pile and Caission), and also proposes the theoretical basis of nominal safety factors of stability analysis by introducing the reliability theory. The limit state equations of stability analysis of bridge foundation and the uncertainty measuring algorithms of each equation are also derived by Cornell's MFOSM(Mean First Order 2nd Moment Methods)using the stability analysis fourmula Highway Bridge Design Codes.

• 한국항공우주학회지
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• 제33권11호
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• pp.33-40
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• 2005

무인항공기용 비행제어 시스템(FCS)의 신뢰성은 소형, 저가, 경량의 설계 제약 조건으로 인해 신뢰성이 과소평가 된다. 그러나 무인항공기에 탑재되는 비행제어 시스템의 고장은 항공기의 손실 및 추락사고로 이어지기 때문에 시스템 설계단계에서부터 정량적인 신뢰성 목표를 두어 설계검증이 이루어져야 한다. 본 논문에서는 비행제어 시스템의 개발 경험을 바탕으로 기능별 서브시스템에 따른 고장률을 예측하였다. 이를 바탕으로 시스템 신뢰성 목표를 만족시키기 위해 필요한 다중화 형상을 제시하였다. 이 결과들은 비행제어 시스템의 하드웨어 설계에 활용될 수 있다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제12권3호
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• pp.201-213
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• 2012

A gear type lubrication pump is an essential component of the powertrain and has a major role for supplying oil to the gears and bearings in automatic transmission with a hydraulic clutch. Therefore, the durability test code design of lubrication pump is very important to ensure the reliability of the entire transmission and the vehicle. In this study, the design process for the life testing of lubrication pump has been generalized by four steps. The four design steps of the life testing of lubrication pump consist of the configuration of load spectrum, rain flow counting and analysis of load level, the equivalent damage assessment and test code generation. In fact, the load spectrum should be obtained from the field operating condition but that kind of data is the top secret of manufacturers. This is not open to the public in general. So we could use the artificially simulated load spectrum instead of field obtained one and focused on the development of the general process for designing the life test of a gear type lubrication pump. Reliability goals for lubrication pump, pressure, torque, temperature and load spectrum, if present, as appropriate for the given test conditions, accelerated life testing for the lubrication pump can be designed by the developed design steps.

• 한국구조물진단유지관리공학회 논문집
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• 제7권4호
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• pp.217-224
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• 2003

본 연구에서는 구조 응답의 불확실성을 고려하여 신뢰성해석을 수행한 후 구조물의 최적설계를 수행하기 위한 프로그램 기법을 제안하고자 한다. 신뢰성해석을 위해 AFOSM법을 이용하였으며, 해석에 의한 파괴확률과 신뢰도 지수값을 제약조건으로 이용하여 최적설계를 수행하였다. 최적설계방법으로는 최적정기법으로 가장 강력한 SQP법을 사용하였다. 제약조건과 불확실량 고려 유 무에 따른 해석결과 본 연구에서 대상으로 한 트러스의 경우 불확실량을 고려한 경우 최소중량이 20.92%, 평면골조의 경우 평균 8.08% 증가하였다.

• Structural Engineering and Mechanics
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• 제80권6호
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• pp.677-688
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• 2021

The building design codes and standards in many countries usually are either fully or partially adopted from the international codes. However, regional conditions like the quality of construction industry and different statistical parameters of load and resistance have essential roles in the code calibration of building design codes. This paper presents a probabilistic approach to assess the reliability level of adopted national building codes by simulating design situations and considering all load combinations. The impact of the uncertainty of wind and earthquake loads, which are entirely regional condition dependent and have a high degree of uncertainty, are quantified. In this study, the design situation is modeled by generating thousands of numbers for load effect ratios, and the reliability level of steel elements for all load combinations and different load ratios is established and compared to the target reliability. This approach is applied to the Iranian structural steel code as a case study. The results indicate that the Iranian structural steel code lacks safety in some load combinations, such as gravity and earthquake load combinations, and is conservative for other load combinations. The present procedure can be applied to the assessment of the reliability level of other national codes.

• Smart Structures and Systems
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• 제33권3호
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• pp.177-188
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• 2024

The fatigue-induced sequential failure of a structure having structural redundancy requires system-level analysis to account for stress redistribution. System reliability-based design optimization (SRBDO) for preventing fatigue-initiated structural failure is numerically costly owing to the inclusion of probabilistic constraints. This study incorporates the Branch-and-Bound method employing system reliability Bounds (termed the B³ method), a failure-path structural system reliability analysis approach, with a metaheuristic optimization algorithm, namely grey wolf optimization (GWO), to obtain the optimal design of structures under fatigue-induced system failure. To further improve the efficiency of this new optimization framework, an additional bounding rule is proposed in the context of SRBDO against fatigue using the B³ method. To demonstrate the proposed method, it is applied to complex problems, a multilayer Daniels system and a three-dimensional tripod jacket structure. The system failure probability of the optimal design is confirmed to be below the target threshold and verified using Monte Carlo simulation. At earlier stages of the optimization, a smaller number of limit-state function evaluation is required, which increases the efficiency. In addition, the proposed method can allocate limited materials throughout the structure optimally so that the optimally-designed structure has a relatively large number of failure paths with similar failure probability.

• 한국해안·해양공학회논문집
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• 제20권4호
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• pp.355-362
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• 2008

경사식 방파제에서 파랑과 구조물의 상호작용에 의하여 발생되는 처오름을 확률론적으로 해석할 수 있는 Level II AFDA 신뢰성 모형이 제안되었다. Level III MCS 모형을 함께 적용하여 본 연구에서 제안된 모형이 만족스럽게 검증되었다. 또한 목표파괴확률과 각 확률변수들의 통계적 특성 그리고 영향계수를 이용하는 역해석 기법을 적용하여 처오름과 관련된 각 확률변수들의 부분안전계수를 산정할 수 있었다. 특히 Level I 신뢰성 설계법을 쉽게 적용할 수 있도록 처오름의 설계기준식을 현행의 결정론적 설계법과 동일한 형태로 유도하였다. 마지막으로 본 연구에서 제시된 부분안전계수를 이용하여 Level I 신뢰성 설계법으로 재 설계한 결과가 CEM(2006) 및 Level II 신뢰성 설계법의 결과와 만족스럽게 비교되었다.

• Structural Engineering and Mechanics
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• 제7권3호
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• pp.303-318
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• 1999

Cracking of reinforced concrete flexural members is a highly random phenomenon. In this paper reliability models are presented to determine the probabilities of failure of flexural members against the limit states of first crack and maximum crackwidth. The models proposed take into account the mechanism of cracking. Based on the reliability models discussed, Eqs. (8) and (9) useful in the reliability-based design of flexural members are presented.

• Nuclear Engineering and Technology
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• 제40권5호
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• pp.365-374
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• 2008

Dependability-critical systems, such as digital instrumentation and control systems in nuclear power plants, necessitate engineering techniques and tools to provide assurances of their safety and reliability. Determining system reliability at the architectural design phase is important since it may guide design decisions and provide crucial information for trade-off analysis and estimating system cost. Despite this, reliability and system engineering remain separate disciplines and engineering processes by which the dependability analysis results may not represent the designed system. In this article we provide an overview and application of our approach to build architecture-based, dynamic system models for dependability-critical systems and then automatically generate dynamic fault trees (DFT) for comprehensive, tool-supported reliability analysis. Specifically, we use the Architectural Analysis and Design Language (AADL) to model the structural, behavioral and failure aspects of the system in a composite architecture model. From the AADL model, we seek to derive the DFT(s) and use Galileo's automated reliability analyses to estimate system reliability. This approach alleviates the dependability engineering - systems engineering knowledge expertise gap, integrates the dependability and system engineering design and development processes and enables a more formal, automated and consistent DFT construction. We illustrate this work using an example based on a dynamic digital feed-water control system for a nuclear reactor.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.508-518
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• 2008

Reliability and sensitivity analysis of the design parameters for a section of caisson type quaywall which is the most applicable in Korea were performed. It was tried to estimate probabilities of failure for the system of the multiple failure modes and to analyze LCC in the quaywall structure. The reliability analysis was performed by FORM. Also, sensitivity indices were estimated using the reliability indices, which may be used inferring effects of each design parameter on the reliability indices. As a result, the coefficient of friction between caisson and rubble, the moment by self weight and the moment of resistance mostly affected on the reliability indices in the sliding, overturning and foundation failure, respectively. System reliability theorem was applied in order to estimate the probabilities of failure for the system of the multiple failure modes. As the results of estimation of the probabilities of failure for the system, all cases were more conservative than those for the elements, according to both failure mode and load combination applied to series system. It entirely exceeded the target reliability index, but it was consistent with the theorem. According to the optimum LCC with the width of the caisson, the probability of failure exceeded the target probability of failure at then time. Therefore, it was judged to be insufficient to the practical application.