• Journal of Korea Water Resources Association
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• v.36 no.1
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• pp.105-115
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• 2003

The computation model which evaluates combined hydraulic and mechanical reliability, is developed to analyze the integrated reliability in water distribution system. The hydraulic reliability is calculated by considering uncertain variables like water demand, hydraulic pressure, pipe roughness as random variables according to proper distribution type. The mechanical reliability is evaluated by analyzing the effect of pipe network with sequential failure of network components. The result of this study model applied to the real pipe network shows that this model can be used to simulate the uncertain factors effectively in real pipe network. Therefore, The pipe-line engineers can design and manage the network system with more quantitative reliability, through applying this model to reliable pipe network design and diagnosis of existing systems.

• Nuclear Engineering and Technology
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• v.15 no.1
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• pp.11-22
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• 1983

The reliability of the Chemical and Volume Control System has been analyzed in a pressurized water reactor. The boration failure was taken to be the top event for this reliability analysis. A detailed fault tree was constructed and the minimal cut sets were derived. It was computed that the unavailability of the Chemical and Volume Control System due to boration failure was 1.497$\times$10$^{-5}$ during plant operation. It was found that the reliability of boric acid transfer pumps were the most important factors in the availability of the Chemical and Volume Control System. As expected, human errors also introduce the high system unavilability.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.961-965
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• 2004

본 연구에서는 상수관망의 신뢰도 기반 최적화설계에서 시스템 구성물의 기계적 고장의 영향뿐만이 아니라 관로의 수리학적 능력과 절점수요에서의 불확실성이 결합되어 인식할 수 있는 새로운 방법을 제시하였다. 수질과 연관된 신뢰도 문제는 고려하지 않았고 단지 수량의 항으로 수요자들의 요구량을 충족시키기 위해 급수관망의 공급능력을 고려하였다. 수량의 관점에서 관망의 신뢰도의 측정은 절점 수요량들이 항상 만족되어진다고 가정한 상태에서 불충분한 수두의 정도를 이용한다. 따라서 절점신뢰도는 공급되는 절점수두가 미리 규정된 최소수두를 상외하거나 충족시키는 확률로 정의되어진다. 이 모형에 의해 설계된 상수관망은 정상관망 상태구성(구성물의 고장이 발생하지 않았을 경우)와 미리 정해진 고장 시나리오의 범위와 연관된 관망의 악화된 구성상태 모두에서 절점에서의 임의의 수요량과 임의의 수리학적 능력하에서 상수공급량의 항으로 규정된 수준의 서어비스의를 제공할 수 있다. 본 모형은 다양한 관망구성에 내해 상수관망의 신뢰도의 정도를 결정하기 위해서 Monte-Carlo 모의를 이용하였다. 실제 상수관망에 내해 본 인구모형을 이용하여 신뢰도 및 최적화 해석이 수행되었다. 해석결과 본 모형은 합리적으로 관망 전체에 대해 합리적인 범위의 신뢰도를 유지하면서 관망의 건설비용의 치적화가 수행될 수 있었다.

• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.71-80
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• 2013

This work studies the reliability analysis of a slope that considers multiple failure modes. The analysis consists of two parts. First, significant failure modes that contribute most to system reliability are determined. The so-called barrier method proposed by Der Kiureghian and Dakessian to identify significant failure modes successively is employed. Second, the failure probability for the slope is estimated on the basis of the identified significant failure modes and corresponding design points. For reliability problems entailing multiple design points, failure probability can be estimated by the multi-point first-order reliability method (FORM), Ditlevsen's bounds method, and Monte Carlo simulation. In this paper, a comparative study between these methods has been made through example problems. Analysis results showed that while a soil slope may have a large number of potential slip surfaces, its system failure probability is usually governed by a few significant slip surfaces. Therefore, the most important step in the system reliability analysis for a soil slope is to identify all the significant failure modes in an efficient way.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.193-200
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• 2010

Structural design requires simultaneously to ensure safety by considering quantitatively uncertainties in the applied loadings, material properties and fabrication error and to maximize economical efficiency. As a solution, system reliability-based design optimization (SRBDO), which takes into consideration both uncertainties and economical efficiency, has been extensively researched and numerous attempts have been done to apply it to structural design. Contrary to conventional deterministic optimization, SRBDO involves the evaluation of component and system probabilistic constraints. However, because of the complicated algorithm for calculating component reliability indices and system reliability, excessive computational time is required when the large-scale finite element analysis is involved in evaluating the probabilistic constraints. Accordingly, an algorithm for SRBDO exhibiting improved stability and efficiency needs to be developed for the large-scale problems. In this study, a more stable and efficient SRBDO based on the performance measure approach (PMA) is developed. PMA shows good performance when it is applied to reliability-based design optimization (RBDO) which has only component probabilistic constraints. However, PMA could not be applied to SRBDO because PMA only calculates the probabilistic performance measure for limit state functions and does not evaluate the reliability indices. In order to overcome these difficulties, the decoupled algorithm is proposed where RBDO based on PMA is sequentially performed with updated target component reliability indices until the calculated system reliability index approaches the target system reliability index. Through a mathematical problem and ten-bar truss problem, the proposed method shows better convergence and efficiency than other approaches.

• Journal of Korean Society of Steel Construction
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• v.19 no.2
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• pp.211-221
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• 2007

A structural reliability analysis of fatigue truck model for fatigue failure of highway steel bridges was performed by applying the Miner's fatigue damage rule expressed as a function of various random variables affecting fatigue damage. Among the variables, the statistical parameters for equivalent moment, impact factor, and loadometer were obtained by analyzing recently measured domestic traffic data, whereas the parameters on fatigue strength, girder distribution factor, and headway factor of the measured data available in the literature were used. The effects of various fatigue truck models, fatigue life, ADTT, fatigue detail category, loadometer, and gross vehicle weight of fatigue truck on the reliability index of fatigue damage were analyzed. It is expected that the analytical results presented herein can be used as a basic background material in the calibration of both fatigue design truck and fatigue load factor of LRFD specification.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.183-193
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• 2008

The reliability analysis of simply-supported and continuous composite plate girder and box girder bridges under flexure was performed to provide a basic data for the development of LRFD c ode. The bridges were designed based on LRFD specification with newly proposed design live load which was developed by analyzing traffic statistics from highways and local roads. A performance function for flexural failure was expressed as a function of the flexural resistance of composite section and the design moments due to permanent load and live load. For the flexural resistance, the statistical parameters obtained by analyzing over 16,000 domestic structural steel samples were used. Several different values of bias factors for the live load moment from 1.0 to 1.2 were used. Due to the lack of available domestic measured data on the moment by permanent loads, the same statistical properties used in the calibration of ASHTO-LRFD were ap plied. The reliability indices for the composite girder bridges with various span lengths, different live load factors, and bias fact or for the live load were obtained by applying the Rackwitz-Fiessler technique.

• Journal of Korea Water Resources Association
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• v.30 no.4
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• pp.411-420
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• 1997

QUAL2E-AFOSM model is developed to forecast the water quality by reliability analysis in the Nakdong River. A varied-flow analysis is performed for the reach of Waegwan to Mulgeum to estimate hydraulic parameters. An optimization technique by BFGS method is applied to determine the optimum reaction parameters and calibrations and verifications are performed based on these parameters. A reliability analysis for the stochastic analysis in a river is studied using the AFOSM method. The variations of water quality and discharge in the headwater, tributaries, and reaction coefficients are considered. Risks of violating existing water quality standards at several loactions in the Nakdong River are computed by using the QUAL2E-AFOSM method. The computed results computed by QUAL2E-AFOSM model agree with those of the Monte-Carlo method in QUAL2EU model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.1
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• pp.51-58
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• 1992

The primary objective of this study is the development of the system reliability analysis of offshore structures against progressive fatigue failure. Two methods based on the second moment reliability methods are used. One is the improved first order reliability method(IFORM) and the other is the modified probabilistic network evaluation technique(MPNET). Using idealized parallel member models, reliability analyses for progressive fatigue failures are carried out for various cases with multiple members composed of multiple connecting joints per member. Numerical results indicate that the effectiveness of the used methods over the conventional ones (i.e. the FORM and the PNET) increases very significantly as the number of failure modes of the system increases.

• ETRI Journal
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• v.8 no.3
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• pp.29-43
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• 1986

어떤 고장이 시스팀의 기능을 완전히 마비시키는 것이 아니라 그 성능이 저하된 상태에서 운용할 수 있는 degradable system에서는 고전적인 신뢰도 모형을 적용하기가 어려우며, 여기서 성능과 신뢰도는 매우 밀접한 관련이 있다. 본고에서는 성능신뢰도(Performance reliability)에 대한 개념 및 모형화 방법에 대해 살펴보고 실제로 TDX-1의스위치 네트워크인 SWCD의 성능을 해석하여 성능신뢰도를 구하였다. SWCD의 성능척도인 통화성공률에 영향을 미치는 요인으로는 스위치 네트워크 내에서의 blocking, T-SW 및 S-SW의 고장, 그리고 T-SW 및 S-SW의 고장으로 인해 DLC 와 TLC의 가용한 서비스 채널이 감소함으로써 발생하는 DLC 및 TLC에서의 blocking등을 들 수 있는데 이 요인들을 고려하여 SWCD의 성능을 해석하였으며, SWCD에 요구되는 표준성능(Normalized performance) 이 0.99라 할 때 single unit라고 가정한 경우 SWCD의 성능 신뢰도는 MTUO(Mean Time to Unreliable Operation)가 3076.7시간이었다. 또한 성능을 해석하는 과정에서 디지틀 스위치 네트워크인 SWC만의 최대 발신 통화처리 용량을 구한 결과, 스위치 네트워크 내에서의 blocking 확률에 대한 최대 허용치를 $10^-3$으로 하였을 때 약 1,700Erlang이었다.