• Journal of Applied Reliability
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• v.16 no.4
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• pp.280-286
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• 2016

Purpose: Recently, Jiang defines the tradeoff B life to minimize a sum of life lost by preventive maintenance (PM) and corrective maintenance (CM) contribution parts and sets up an optimal replacement age of age replacement policy as this tradeoff life. In this paper, Jiang's model only considering the known lifetime distribution is extended by assigning different weights to two parts of PM and CM in order to reflect the practical maintenance situations in application. Methods: The new age replacement model is formulated and the meaning of a weight factor is expressed with the implied cost of failure under asymptotic expected cost model and also discussed with one-cycle expected cost criterion. Results: The proposed model is applied to Weibull and lognormal lifetime distributions and optimum PM replacement ages are derived with corresponding implied cost of failure. Conclusion: The new age replacement policy to escape the estimation of cost of failure in classical asymptotic expected cost criterion based on the renewal process is provided.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.742-743
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• 2007

A maintenance plan of power system equipment reduces failure rate caused by equipment's age. To prevent unexpected failure, the maintenance is performed periodically according to the interval time. The more expansive equipment's scale is, the more the maintenance without considering costs sustains a economical loss. Hence, the maintenance's time and the cost must be considered when maintenance which is considering the reliability is implemented. In this paper, optimum maintenance interval is calculated by considering minimum maintenance cost of the equipment with the combined cycle units in Korea power systems.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.258-264
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• 2010

Various kinds of ballast water treatment systems (BWTS) have been developed corresponding to reinforced IMO rules for marine environment. Some of them got the certificate of IMO and others are waiting for it. Selection of optimum BWTS is very important. Optimum BWTS means not only functional requirements but also economic efficiency. This paper presents economic analysis model for optimum BWTS according to ship type and size. In this study 10 kinds of BWTS whose initial installation cost and maintenance cost are known are analyzed based on present worth method. It is assumed that all BWTS satisfy minimum functional requirements and we need to consider different economical efficiency. Through the economic analysis we could select optimum BWTS.

• Structural Monitoring and Maintenance
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• v.2 no.2
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• pp.133-143
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• 2015

Civil engineering infrastructure is aging and requires cost-effective maintenance strategies to enable infrastructure systems operate reliably and sustainably. This paper presents an approach for determining risk-cost balanced repair strategy of corrosion damaged reinforced concrete structures with consideration of uncertainty in structural resistance deterioration. On the basis of analytical models of cover concrete cracking evolution and bond strength degradation due to reinforcement corrosion, the effect of reinforcement corrosion on residual load carrying capacity of corroded reinforced concrete structures is investigated. A stochastic deterioration model based on gamma process is adopted to evaluate the probability of failure of structural bearing capacity over the lifetime. Optimal repair planning and maintenance strategies during the service life are determined by balancing the cost for maintenance and the risk of structural failure. The method proposed in this study is then demonstrated by numerical investigations for a concrete structure subjected to reinforcement corrosion. The obtained results show that the proposed method can provide a risk cost optimised repair schedule during the service life of corroded concrete structures.

• Journal of the military operations research society of Korea
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• v.34 no.3
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• pp.41-51
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• 2008

Advanced high-tech weapons have enormous affect on combat strength in modern warfare. However, lack of maintenance can cause decrease in equipment operating rate as well as decrease in expectation on demonstrative effect of combat strength during wartime. Therefore it is essential for combat readiness that the optimum requirement of equipment maintenance cost are forecasted and included in the budget. In this paper, the trend of equipment maintenance cost about K-111 1/4t military vehicle is first analyzed by evaluating the performance data of field operation. Secondly, based on above analyzed results, the forecasting model of equipment maintenance cost is designed. Finally, by applying this forecasting model, suggestion and estimation method of equipment maintenance cost have presented for the foreseeable future.

• Proceedings of the KSR Conference
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• 2002.05a
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• pp.404-410
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• 2002

In this study, we have analyzed the optimum control of wheel for coach car in maintenance process to grasp the problem relating to this coach's wheel exchanged. So, these problems brought about decrement maintenance cost. This study were deliberated to solve problems concerning maintenance process of wheel exchanged and wheel specification in rolling stock workshops of KNR. Here, we describe some results.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1132-1140
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• 2007

As it recently appears that Life Cycle Cost Analysis may be considered as new methodology for economic valuation of infrastructure many researches have been made to assess LCC(Life Cycle Cost) of each facility based on a reasonable methods. In general, LCC is composed of construction cost and expected maintenance repair cost. And especially, maintenance repair cost must be estimated to enhance the reliability through systematic and reasonable methods. However in Korea, because high speed railway steel bridges are recently constructed no direct statistical data are available for the account of the maintenance cost and then their maintenance characteristics are not linear yet. Therefore, the approach proposed in the paper utilizes a theoretical determination and degradation of the corrosion and fatigue of the bridges based on Rahgozar et al.(2006)'s model on fatigue notch factor considering into the corrosion to incorporate the corrosion effect into the fatigue strength reduction model. And then, the corresponding probability of failure is calculated in terms of the reliability index using S-N curve to formulate the fatigue limit state. Therefore, this paper proposes the minimum Life Cycle Cost through optimum maintenance plan analysis of high-speed railway steel bridges under construction. Finally, this paper reviews the proposed model in oder to confirm the applicability and feasibility by appling it to high speed railway steel bridges under construction

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.128-136
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• 2001

This paper presents an optimum deck and girder system design for minimizing the life-cycle cost (LU) of steel box girder bridges. The problem of optimum LCC design of steel box girder bridges is formulated as that of minimization of the expected total LCC that consists of initial cost, maintenance cost, expected retrofit costs for strength, deflection, and crack. To demonstrate the effect of LCC optimum design of steel box girder bridges, the LCC optimum design is compared with conventional design method for steel box girder bridges design. From the numerical investigations, it may be positively stated that the optimum design of steel box girder bridges based on LCC will lead to more rational, economical and safer design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.189-199
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• 2002

This study is intended to propose a systematic procedure for the development of the conditional assessment based on the safety of structures and the cost effective performance criteria for designing and upgrading of bridge structures. As a result, a set of cost function models for a life cycle cost analysis of bridge structures is proposed and thus the expected total life cycle costs (ETLCC) including initial (design, testing and construction) costs and direct/indirect damage costs considering repair and replacement costs, human losses and property damage costs, road user costs, and indirect regional economic losses costs. Also, the optimum safety indices are presented based on the expected total cost minimization function using only three parameters of the failure cost to the initial cost (${\tau}$), the extent of increased initial cost by improvement of safety (${\nu}$) and the order of an initial cost function (n). Through the enough numerical invetigations, we can positively conclude that the proposed optimum design procedure for bridge structures based on the ETLCC will lead to more rational, economical and safer design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.4
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• pp.177-184
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• 2001

In this study, three most distinct types of general rigid connections are included in the modelling, with is implemented into a computer code. The cost, functions of connections are constructed by using the estimated unit cost of bolting, welding and connection-steel elements incorporating all the effect of materials, labor, and fabrication work. Bused on the recent developments of the reliability-based structural analysis and design as well as the extending knowledge on the probabilistic characteristics of load and resistances, the probability based design criteria have been successfully developed for many standards. Since the probabilistic characteristics depend highly on the local load and resistances, it is recognized to develop the design criterion compatible with domestic requirements. The existing optimum design methods, which are generally based on the structural theory and certain engineering experience, do not realistically consider the uncertainties of load and resistances and the basic reliability concepts.