• Smart Structures and Systems
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• v.30 no.6
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• pp.571-582
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• 2022

Optimal life-cycle management is a challenging issue for deteriorating regional bridges. Due to the complexity of regional bridge structural conditions and a large number of inspection and maintenance actions, decision-makers generally choose traditional passive management strategies. They are less efficiency and cost-effectiveness. This paper suggests a deep reinforcement learning framework employing double-deep Q-networks (DDQNs) to improve the life-cycle management of deteriorating regional bridges to tackle these problems. It could produce optimal maintenance plans considering restrictions to maximize maintenance cost-effectiveness to the greatest extent possible. DDQNs method could handle the problem of the overestimation of Q-values in the Nature DQNs. This study also identifies regional bridge deterioration characteristics and the consequence of scheduled maintenance from years of inspection data. To validate the proposed method, a case study containing hundreds of bridges is used to develop optimal life-cycle management strategies. The optimization solutions recommend fewer replacement actions and prefer preventative repair actions when bridges are damaged or are expected to be damaged. By employing the optimal life-cycle regional maintenance strategies, the conditions of bridges can be controlled to a good level. Compared to the nature DQNs, DDQNs offer an optimized scheme containing fewer low-condition bridges and a more costeffective life-cycle management plan.

• Journal of Applied Reliability
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• v.16 no.3
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• pp.192-201
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• 2016

Purpose: In this paper, we propose the output model of the optimal inventory requirements of the Maintenance Float (M/F). Weapon systems were modernized and increased costs. Thus, the complexity increases with. Alternatives to achieve the goal of availability of weapon systems and to reduce life-cycle cost are required. Especially, securing spare parts is more effective than adding the amount of equipment or maintenance facilities to achieve the goal of availability and reduce life cycle costs. However, securing spare parts and repair costs are directly related, so exact requirements are needed. Methods: Three kinds of methods (Calculation method of applying the Poisson distribution, Calculation method of considering the number of CSP, and Calculation method of applying M&S program) that this paper proposed compare the influence of the availability and the amount of spare parts. Result: We calculate the cost of M/F when the operational availability is over than 80% and compare that result. The biggest cost was calculated from the Poisson distribution method. We found that requirements and unit price is the key factor that gives a significant effect. Conclusion: These three kinds of methods can be used as a basis for Maintenance Float calculation. Among them, the calculation method based on CSP is optimal replacement equipment requirements calculation method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.5
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• pp.591-599
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• 2021

Rail transit agencies in Korea have been struggling to set up a performance-based rail facility maintenance plan because there are no formal definition and decision criteria for aging infrastructure. This study investigates the definition of aging infrastructure through extensive literature review and identifies benchmarking criteria through comparison with rail transit facility management systems in Korea and United States. As results, an aging infrastructure should be defined considering both service age and performance level of a facility. The priority of repair/replacement should be also determined with reasonable criteria based on relationship between service age and performance level. To determine the definition and decision criteria, a practicable classification system for aging rail transit needs to be established in accordance with classification system for performance assessment. Furthermore, a comprehensive database needs to be built including useful life, performance level, and maintenance cost of each component of rail transit. It will allow establishing an efficient budget execution plan for aging infrastructure.

• Journal of Applied Reliability
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• v.17 no.2
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• pp.159-167
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• 2017

Purpose: The purpose of this research is to study research trend in the field of warranty and maintenance policy of second-hand products. Methods: To this end, we consider research articles, which deal with warranty and maintenance of the second-hand products, published on journals during the past 20 years and classify them by taxonomy scheme proposed by Shafiee and Chukova (2013). The taxonomy scheme consists of three maintenance models in warranty for second-hand product. In each models, we analyze proposed maintenance and warranty policies with respect to types of upgrade models, types of preventive maintenances, decision variables and decision criteria model. Results: We obtain the scheme of maintenance and warranty of the second-hand products and define cost related to warranty and maintenance of the second-hand item. Also, we summarize the characteristics of maintenance and warranty policies in each classified model. Conclusion: There have been several research reviews on maintenance and warranty polity of new products. This research surveys researches of authors during the past 20 years and classifies, summarizes and compares proposed maintenance and warranty policies of the second-hand products. This research provides useful information to researchers who are interested in maintenance and warranty of the second-hand products.

• Journal of Korean Society of Steel Construction
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• v.17 no.2 s.75
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• pp.115-130
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• 2005

This paper presents the effects of indirect costs on Life-Cycle-Cost(LCC) effective optimum design of steel-box girder bridges. The LCC formulations considered in the LCC optimization of the bridges consist of initial cost and expected rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, and indirect costs such as road user costs and indirect socio-economic losses. To demonstrate the LCC-effectiveness for optimum design of the bridges, an actual steel box girder bridge having two continuous spans(2@50m=100m) is considered as a numerical example. And also, in this paper, various sensitivity analyses are performed to investigate the effects of indirect costs caused by traffic conditions such as number of detour route, number of lane on detour route, length of detour route, and traffic volumes on the LCC-effective optimum design. From the numerical investigations, it may be concluded that indirect costs caused by traffic network may sensitively influence on the LCC-effective optimum design of steel-box girder bridges. Therefore, it may be stated that the traffic conditions should be considered as one of the important items in the LCC-effective optimum design of the bridges.

• Journal of Korean Society of Steel Construction
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• v.17 no.2 s.75
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• pp.227-241
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• 2005

This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology for steel bridges considering the long-term effect of environmental stressors such as corrosion and heavy truck traffics on bridge reliability. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost, and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure, which depends upon the prior and updated load and resistance histories, should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model, which takes into consideration corrosion initiation, corrosion rate, and repainting effect, are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40m+50m+40m=130m). Various sensitivity analyses are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the volume of truck traffic significantly influence the LCC-effective optimum design of steel bridges. Thus, these conditions should be considered as crucial parameters for the optimum LCC-effective design.

• Journal of the Korea Institute of Building Construction
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• v.22 no.4
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• pp.403-414
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• 2022

Many studies have been conducted on asset management of public facilities, as the importance of such management has been increasing. This basic study aims to present strategies for the practical use of public asset management, and seeks to propose efficient management and utilization measures from a cost perspective by comparing and analyzing the importance and impact relationship between cost items for public asset management. In this study, 19 sub-items and the top 4 items were chosen by deriving cost factors based on the previous literature. A survey was conducted, and the results of the survey were analyzed by using the Analytic Hierarchy Process(AHP) and Interpretive Structural Modeling (ISM) methods. The AHP was used to derive the priority between items, and ISM was used to identify major groups and mutual influences. As a result, those items showing both high priority and high importance, such as user cost, dismantling/disposal cost, replacement cost, maintenance/repair cost, etc. are determined as priority items to be considered for public asset management of public facilities. Also, it is necessary to minimize the impact on other items in public asset management by those items which are impacted less by other items but have significant impact on the items such as initial construction costs, conceptual design costs, construction costs, and supervision costs. It is expected that the results and analysis methods presented in this study can be used to provide strategies for asset management of public facilities.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.75-89
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• 2006

This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology of steel bridges considering time effect of bridge reliability under environmental stressors such as corrosion and heavy truck traffics. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure which depends upon the prior and updated load and resistance histories should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model considering corrosion initiation, corrosion rate, and repainting effect are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40 m+50 m+40 m=130 m), and various sensitivity analyses of types of steel, local corrosion environments, average daily traffic volume, and discount rates are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the number of truck traffics significantly influence the LCC-effective optimum design of steel bridges, and thus realized that these conditions should be considered as crucial parameters for the optimum LCC-effective design.

• Journal of Korea Water Resources Association
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• v.39 no.6 s.167
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• pp.545-552
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• 2006

The purpose of this study is to develop an optimal, long-term planning model for improvement of water distribution networks. The water distribution system is divided into sub-zones and the decision of improvement plan is made for each sub-zone. Costs for replacement, rehabilitation and repair, benefits including reduced pumping and leakage costs, and hydraulic reliability are considered to make optimal decision for improvement planning of water network. Harmony search algorithm is applied to optimize the system and hydraulic analysis model EPANET is interfaced with the optimal decision model to check the hydraulic reliability, The developed model is applied to actual water distribution system in Daegu-city, South Korea. The new model which use durability, conveyance and cost as a decision variable is different from existing methods which use only burying period and pipe type and can be used as optimal decision making system for water distribution network.

• Journal of Korean Society of Steel Construction
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• v.13 no.5
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• pp.477-492
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• 2001

About half of bridges in United States are considered to be deficient and therefore are in need of repair or replacement. Half of these are functionally obsolete, and others do not have required strength For these bridges repairs and replacements are needed To avoid the high cost of rehabilitation the bridge rating must corectly report the present load-carrying capacity Rating engineers use Allowable Stress Design(ASD) Load Factor Design(LFD), and Load Resistance Factor Design(LRFD) to evaluate the bridge load carrying capacity In this paper the load rating methods are introduced and bridge load test data are collected. The reasons that make the difference between test results and analytical results are explained for each bridge load test And load rating methods are applied to real bridge. The rating factors from each method are compared.