• Journal of Korean Institute of Industrial Engineers
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• v.25 no.4
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• pp.466-475
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• 1999

A backward Dynamic Programming(DP) model for the optimal facility replacement decision problem during a finite planning horizon is presented. Multiple alternative challengers to a current defender are considered. All facilities are assumed to have finite service lives. The objective of the DP model is to maximize the profit over a finite planning horizon. As for the cost elements, purchasing cost, maintenance costs and repair costs as well as salvage value are considered. The time to failure is assumed to follow a weibull distribution and the maximum likelihood estimation of Weibull parameters is used to evaluate the expected cost of repair. To evaluate the revenue, the rate of operation during a specified period is employed. The cash flow component of each challenger can vary independently according to the time of occurrence and the item can be extended easily. The effects of inflation and the time value of money are considered. The algorithm is illustrated with a numerical example. A MATLAB implementation of the model is used to identify the optimal sequence and timing of the replacement.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.29 no.3
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• pp.135-142
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• 2006

Engineers are always concerned with life cycle costs for making important economic decisions through engineering action like reliability of products. Decisions during the reliability growth development of products involve trade-offs between invested costs and its returns. In order to find minimal LCC containing the reliability improvement cost, production cost, repair and replacement costs, and holding cost of spare parts for failure items we suggest in this paper relationship between development cost and sustaining cost in values of growth parameter $\beta$ of AMSAA model. This model is applied to the reliability growth program based on AMSAA model during R&D phase, the warranty activities of items and the block replacement policy for maintenance of items in avionic equipment.

• IE interfaces
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• v.6 no.2
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• pp.37-51
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• 1993

This paper studies the economic replacement method for production facilities which requires huge investment but are necessary for higher productivity and competability of products. That is, the general models for the decision of economic life of properties which minimizes the total costs throughout the usage life(Life cycle costs) are generated. Main factors which make influences for the decision of econmic life can be divided by three. These are the change of salvage value, repair and maintenance costs, and availability of production facilities with the passage of usage time. In this paper, the real world data for these three factors are collected and analyzed for the extraction of representative standard forms with the passage of time. And general models for economic replacement methods and optimal usage terms are presented through tables with the combination of the standard forms of these three main factors.

• Clinics in Orthopedic Surgery
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• v.10 no.4
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• pp.398-406
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• 2018

Background: Hypoalbuminemia (serum albumin < 3.5 g/dL) is associated with increased morbidity and mortality in patients undergoing total hip arthroplasty (THA) and total knee arthroplasty (TKA). However, costs associated with hypoalbuminemia remain unknown. This study investigated the effect of serum albumin on direct treatment costs, length of stay (LOS), and readmissions for primary and revision THA and TKA patients. Methods: All adult patients at a single institution undergoing primary or revision THA or TKA between January 2014 and December 2016 were retrospectively reviewed. Patients were stratified by preoperative serum albumin level. The primary outcome was total direct costs at index hospitalization. Secondary outcomes included LOS and readmission within 30 days. Multivariable regressions were utilized to adjust for demographics and comorbidities. Results: Of 3,785 patients, 114 (3.0%) had hypoalbuminemia. After adjustment, hypoalbuminemia was associated with a 16.2% increase in costs (${\beta}=0.162$; 95% confidence interval [CI], 0.112 to 0.213; p < 0.001), representing an average cost increase of $3,383 (95% CI, $2,281 to $4,485) relative to costs for serum albumin > 4.5 g/dL. The increased total costs were significantly higher in revision ($4,322, p = 0.034) than in primary ($3,446, p < 0.001) procedures. In adjusted regression, each 1.0 g/dL increase in serum albumin yielded a 6.6% reduction in costs (${\beta}=-0.066$; 95% CI, -0.090 to -0.042]; p < 0.001), for average savings of $1,282 (95% CI, $759 to $1,806) per unit albumin. Adjusted regressions demonstrated that a 1-point increase in serum albumin reduced readmissions by 53% (odds ratio, 0.47; 95% CI, 0.31-0.73; p = 0.001) and LOS by 0.6 days (${\beta}=-0.60$; 95% CI, -0.76 to -0.44; p < 0.001). Conclusions: Hypoalbuminemia is associated with increased total direct costs, LOS, and readmissions following primary and revision THA and TKA. Future efforts to predict and address total costs should take into consideration the patient's preoperative serum albumin levels.

• Korean Journal of Construction Engineering and Management
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• v.17 no.2
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• pp.31-38
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• 2016

In a construction project, the portion for maintenance costs for a building is considerable compared to the initial construction cost. As such, Life Cycle Cost (LCC) analysis is being increasingly utilized to assess the design value of engineering work in Korea. Additionally, the Public Procurement Service in Korea announced that it will be mandatory for all domestic construction projects to adopt BIM. Furthermore, the paradigm for architectural design has shifted from 2D to 3D, and to BIM, which includes a data management system. Within this background, however, there is currently no adequate BIM-based LCC analysis software and the requirements of cost estimation for repair and replacement cost for a building is not completely adequate in BIM tools such as Revit and Archicad. Therefore, this study suggests a process of cost estimation for repair and replacement (R&R) cost based on IFC data. First, we analyzed existing R&R criteria and defined BIM-based requirements when calculating R&R costs. These requirements were extracted from relevant IFC data. Subsequently, this was saved to a database and a BIM-based database was built for R&R cost estimation. Finally, this database was connected with external databases such as R&R Criteria DB and Cost Information DB to calculate R&R costs. This process is expected to improve upon the traditional process of cost estimation of R&R cost by applying a BIM model. The proposed process can contribute to a further standardizing of BIM-based LCC analysis thru application to initial construction costs, energy costs, and other maintenance costs.

• Computers and Concrete
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• v.21 no.5
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• pp.531-538
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• 2018

The slag through sieve #4 replaced the natural fine aggregate in different proportions (0-50%) to make ready-mixed soil and slag (RMSAS). The fresh properties studied, and the concrete specimens were produced to test the hardened properties at different ages. Results showed that the workability of RMSAS decreases when the replacement increases. The unit weight increases with the replacement. The setting time extends when the replacement decreases and shortens when the replacement increases. The compressive strength, ultrasonic pulse velocity and hammer rebound value increase with the replacement. However, the high-replacement results decrease because of the expansion factor at late age. Resistivity is close and less than $20k{\Omega}-cm$. After the industrial of steelmaking by-products are processed properly, they can be used in civil engineering, not only as a substitute for natural resources and to reduce costs, but also to provide environmental protection.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.12
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• pp.913-917
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• 2009

Flash memories have asymmetric I/O costs for read and write in terms of latency and energy consumption. However, the ratio of these costs is dependent on the type of storage. Moreover, it is becoming more common to use two flash memories on a system as an internal memory and an external memory card. For this reason, buffer cache replacement algorithms should consider I/O costs of device as well as possibility of reference. This paper presents WWCLOCK(Write-Weighted CLOCK) algorithm which directly uses I/O costs of devices along with recency and frequency of cache blocks to selecting a victim to evict from the buffer cache. WWCLOCK can be used for wide range of storage devices with different I/O cost and for systems that are using two or more memory devices at the same time. In addition to this, it has low time and space complexity comparable to CLOCK algorithm. Trace-driven simulations show that the proposed algorithm reduces the total I/O time compared with LRU by 36.2% on average.

• The Journal of Engineering Geology
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• v.26 no.4
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• pp.485-495
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• 2016

To reinforce and improve the soft ground under a breakwater while using materials efficiently, the replacement ratio and leaving periods of surcharge load are optimized probabilistically. The results of Bayesian updating of the random variables using prior information decrease uncertainty by up to 39.8%, and using prior information with more samples results in a sharp decrease in uncertainty. Replacement ratios of 15%-40% are analyzed using First Order Reliability Method and Monte Carlo simulation to optimize the replacement ratio. The results show that replacement ratios of 20% and 25% are acceptable at the column jet grouting area and the granular compaction pile area, respectively. Life cycle costs are also compared to optimize the replacement ratios within allowable ranges. The results show that a range of 20%-30% is the most economical during the total life cycle. This means that initial construction cost, maintenance cost and failure loss cost are minimized during total life cycle. Probabilistic analysis for leaving periods of shows that three months acceptable. Design optimization with respect to life cycle cost is important to minimize maintenance costs and retain the performance of the structures for the required period. Therefore, more case studies that consider the maintenance costs of soil structures are necessary to establish relevant design codes.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.249-256
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• 1999

This study is intended to propose a systematic procedure for the development of the reliability-based seismic safety and cost-effective Performance criteria for design and upgrading of long span PC bridges. In the paper, a set of cost function models for life cycle cost analysis of bridges is proposed. The total life cycle cost functions consist of initial cost and direct/indirect damage costs considering repair/replacement costs, human losses and property damage costs, road user costs, and indirect regional economic losses. The damage costs are successfully expressed in terms of Park-Ang median global damage indices and damage probabilities. The proposed approach is successfully applied to model bridges in both regions of a moderate seismicity area like Seoul, Korea and a high one like Tokyo, Japan. It may be expected that the proposed approach can be effectively utilized for the development of cost-effective performance criteria for design and upgrading of various types of bridges as well as long span PC bridges.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2007.11a
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• pp.145-150
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• 2007

This study is a LCC case analysis on the school one of the BTL projects which is constructed by private organizations and rented to government. According to the RFP to make out documents, it is performed the case analysis based on the results of LCC calculation about maintenance & conservation costs; repairing costs and replacement costs. It is analyzed LCC on maintenance & conservation costs for 20 years(rent period) and 65 years(life cycle). As a result of LCC analysis, about more than 50% of total LCC are architectural works and the rest of them are machinery works, electric works, and civil works in the order. And it is also suggested some problems and their solutions to perform LCC analysis on the current BTL projects of school.