• 대한산업공학회지
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• 제4권1호
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• pp.1-3
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• 1978

This paper presents a model for determining the optimal number of minimal repairs before replacement. The basic concept parallels the periodic replacement model with minimal repair at failure introduced by Barlow and Hunter, only difference being the replacement signalled by the number of previous minimal repairs performed on the unit. In the case of Weibull distribution, which is widely used as a general failure distribution, the optimal solution could be obtained numerically and seems more cost effective compared to the Barlow and Hunter's Policy II.

• 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.

• Computers and Concrete
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• 제17권5호
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• pp.639-653
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• 2016

The present article discusses the effect of the ratio of bridge surface to total shear surface, number of bridge areas and normal stress on the failure behavior of the planar non-persistent open joints. Totally, 38 models were prepared using plaster and dimensions of $15cm{\times}15cm{\times}15cm$. The bridge area occupied $45cm^2$, $90cm^2$ and $135cm^2$ out of the shear surface. The number of rock bridges increase in fixed area. Two similar samples were prepared on every variation in the rock bridges and tested for direct shear strength under two high and low normal loads. The results indicated that the failure pattern and the failure mechanism is mostly influenced by the ratio of bridge surface to total shear surface and normal stress so that the tensile failure mode change to shear failure mode by increasing in the value of introduced parameters. Furthermore, the shear strength and shear stiffness are closely related to the ratio of bridge surface to total shear surface, number of bridge areas and normal stress.

• 한국비블리아학회지
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• 제23권2호
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• pp.209-233
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• 2012

이 연구에서는 웹기반 온라인목록 이용자들의 전반적인 검색행태를 알아보기 위해, 7년 동안의 트랜잭션 로그를 분석하였다. 웹기반 온라인목록의 검색형태는 검색전략과 검색실패의 관점에서 조사하였다. 검색전략에서는 검색유형, 접근점, 연산자, 검색문의 길이, 단어 사용횟수, 웹기반 온라인목록 이용횟수, 시간대별 및 요일별 이용횟수를 분석하였다. 또한 검색실패는 검색실패율과 접근점별 검색실패율, 연산자별 검색실패율을 분석하였다. 이 연구결과는 향후 웹기반 온라인목록 시스템과 서비스 개선에 활용될 수 있을 것으로 기대된다.

• 한국수자원학회논문집
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• 제40권1호
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• pp.39-50
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• 2007

본 논문에서는 대수-선형 파손율 모형(log-linear ROCOF)과 와이블 파솔율 모형(Weibull ROCOF)을 이용하여 상수도 주철 배수관로의 파손율을 모형화하고, '수정된 시간 척도'를 이용하여 최적교체시기를 산정할 수 있는 방법이 개발되었다. 두 ROCOF의 모형화를 위하여 개별 관로의 파손시간을 기록한 '파손 시간자료(failure-time data)'와 일정 시간간격 사이에서 발생하는 파손횟수를 기록한 '파손 횟수자료(failure-number data)'를 이용하였고, 최대로그우도 추정값을 이용하여 두 ROCOF의 각 파손자료 유형에 대한 모형화 수행 능력을 검증하였다. 또한 두 ROCOF를 이용한 관로의 최적교체시기 방정식은 ROCOF의 매개변수 추정에 있어서 수렴성을 보장하기 위하여 '수정된 시간 척도'를 적용하여 유도하였다. 연구대상 주철 배수 관로들의 '파손 시간자료'와 '파손 횟수자료'에 두 파손율 모형을 적용시켜 본 결과 파손 시간자료를 이용할 경우 대수-선형 ROCOF가 와이블 ROCOF 보다 적합한 모형인 것으로 나타났다. 또한 두 모형 모두 '파손 시간자료'를 이용하는 것이 '파손 횟수자료'를 이용하는 것보다 모형화 수행 능력이 높아지는 것으로 나타나서, 분석에 사용된 관로의 파손율 모형화와 최적교체시기 산정을 위해서는 일정 시간간격 동안의 관로 파손횟수를 기록하는 것보다 관로의 파손시간을 기록하는 것이 더욱 우수한 모형화 결과를 낳는 것으로 나타났다.

• International Journal of Reliability and Applications
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• 제15권1호
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• pp.51-64
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• 2014

This paper develops a warranty cost model for complex systems with imperfect repair within a warranty period by addressing a practical case that the first inter-failure interval is longer than any other inter-failure intervals. The product is in its best condition before the first failure if repair is imperfect. After the imperfect repair, other inter-failure intervals which are explained by renewal processes, are stochastically smaller than the first inter-failure interval. Based on this idea, we suggest the failure-interval-failure-criterion model. In this model, we consider two random variables, X and Y where X represents failure intervals and Y represents failure criterion. We also obtain the distribution of the number of failures and conduct the warranty cost analysis. We investigate different types of warranty cost models, reliabilities and other measures for various systems including series-parallel configurations. Several numerical examples are discussed to demonstrate the applicability of the methodologies derived in the paper.

• Structural Engineering and Mechanics
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• 제34권3호
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• pp.367-376
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• 2010

In this paper, an experimental investigation of the mechanical behavior and buckling failure of sharp-notched circular tubes subjected to cyclic bending is discussed. The unnotched and sharp-notched circular tubes of SUS 304 stainless steel were tested under symmetric curvature-controlled cyclic bending. It was found from moment-curvature curves that the loops show cyclic hardening and gradually steady after a few cycles for all tested tubes. The ovalization-curvature curves show an unsymmetric, ratcheting and increasing manner with the number of cycles. In addition, it was found that six almost parallel lines corresponding to unnotched and five different notch-depth (0.2, 0.4, 0.6, 0.8 and 1.0 mm) tubes were noted from the experimental relationship between the cyclic controlled curvature and the number of cycles necessary to produce buckling on a log-log scale. An empirical formulation was proposed so that it could be used for simulating the aforementioned relationship. By comparing with the experimental finding, the simulation was in good agreement with the experimental data.

• 한국도로학회논문집
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• 제16권6호
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• pp.105-113
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• 2014

PURPOSES: The objective of this paper is to select the confidential intervals by utilizing the second moment reliability index(Hasofer and Lind; 1974) related to the number of load applications to failure which explains the fatigue failure and rut depth that it indicates the permanent deformation. By using Finite Element Method (FEM) Program, we can easily confirm the rut depth and number of load repetitions without Pavement Design Procedures for generally designing pavement depths. METHODS : In this study, the predictive models for the rut depth and the number of load repetitions to fatigue failure were used for determining the second moment reliability index (${\beta}$). From the case study results using KICTPAVE, the results of the rut depth and the number of load repetitions to fatigue failure were deducted by calculating the empirical predictive equations. Also, the confidential intervals for rut depth and number of load repetitions were selected from the results of the predictive models. To determine the second moment reliability index, the spreadsheet method using Excel's Solver was used. RESULTS : From the case studies about pavement conditions, the results of stress, displacement and strain were different with depth conditions of layers and layer properties. In the clay soil conditions, the values of strain and stresses in the directly loaded sections are relatively greater than other conditions. It indicates that the second moment reliability index is small and confidential intervals for rut depth and the number of load applications are narrow when we apply the clay soil conditions comparing to the applications of other soil conditions. CONCLUSIONS : According to the results of the second moment reliability index and the confidential intervals, the minimum and maximum values of reliability index indicate approximately 1.79 at Case 9 and 2.19 at Case 22. The broadest widths of confidential intervals for rut depth and the number of load repetitions are respectively occurred in Case 9 and Case 7.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.346-353
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• 2002

The risk of bearing failure is evaluated through the seismic response analysis of a bridge considering the probabilistic characteristics of structural properties such as the mass of superstructure, the stiffness of pier, and the translational and rotational stiffness of the foundation as well as seismic loadings during the bridge service lift. The effect of pounding between adjacent vibration units on the risk of bearing failure is also investigated. The probabilistic characteristics of structural properties are obtained by the Monte Carlo simulations based on the probabilistic characteristics of basic random variables included in the structural properties. From the simulation results, the failure probability of fixed bearings attached on the abutment is found to be much higher than those placed on the piers. It is also found that the pounding effect significantly increases the failure probability of bearings. In the simply supported bridges, the risk of bearing failure increases as the number of bridge spans increase. Therefore, the failure probability of fixed bearing due to the effects of pounding phenomena and the number of bridge spans should be considered in the seismic desist of bearings.

• 품질경영학회지
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• 제25권3호
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• pp.86-95
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• 1997

This paper considers a repairable system, which is maintained preventively at periodic times and is minimally repaired at each failure. Most preventive maintenance policies for such repairable systems assume that the cost of minimal repair is constant regardless of its age at failure. However, it is more practical to consider the situations where the cost of minimal repair is dependent not only on its age at failue, but also on the number of preventive maintenance carried out prior to its failure. We consider the preventive maintenance carried out prior to its failure. We consider the preventive maintenance policy with age-dependent minimal repair cost. The optimal policies which minimize the expected cost rate over an infinite time span are discussed. We obtain the optimal period and number of preventive maintenance prior to replacement of the system.