• Journal of the Korean Society of Safety
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• v.27 no.3
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• pp.125-130
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• 2012

According to the Korea National Statistical Office data in 2010, the population over ages of 65 years would possess to 11.3% whole population of Korea in 2011 denoting Korea is already in the aging society. Old age is associated with inevitable time-dependent losses in physical capabilities. However the maintenance of physical capabilities is essential for continuing independence in old age. The work ability index(WAI) was constructed to reveal how well a worker is able to perform his work. This study focused on the discovery of an industrial and age-related influences on the work ability and job stress of workers in the shipbuilding, house managing, apartment construction industry. For this, the study conducted a job stress test using the Korean Occupational Stress Questionnaire Short Form, and employee performance evaluations using the Work Ability Index (WAI) of the Finnish Institute of Occupational Health (FIOH) on 3,228 workers in the shipbuilding, house managing and apartment construction industry. SPSS 12.0 K statistics program was used for statistics analysis and significance was verified with the Kruskal-Wallis test, a corporate body of nonparametric statistical analysis. As a result, employee performance had significant differences, depending on age, an industrial and years of service. The mean WAI score of the shipbuilding industry was lower than that of the other industry. Additionally, it was found that employee work ability decreased more as job stress increased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.2
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• pp.57-65
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• 2016

The suspension system of a subway vehicle is composed of $1^{st}$ and $2^{nd}$ springs. The suspension system is the most important parameter in determining the vibration ride comfort. If the $1^{st}$ suspension spring is designed as a spring with strong stiffness to improve the running stability at high speed, it causes vehicle vibrations. In this paper, by testing and analyzing changes of the characteristics of Chevron springs, which have been the primary suspension springs used for about 20 years, we study how changing the characteristics affects vehicle acceleration and ride comfort. The lateral and longitudinal vibrational ride comfort index levels were lower than the vertical ones. Therefore, as increasing the stiffness of Chevron springs has the greatest effect on the vertical vibrational ride comfort index level, a countermeasure for vertical vibration reduction is needed when the stiffness increases owing to aging. Finally, maintenance guidelines, including the replacement time for the Chevron rubber, were proposed based on these findings.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.162-162
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• 2019

Water Distribution Network (WDN) is a critical infrastructure to be maintained ensuring proper water supply to wide-spread consumers. The WDN consists of pipes, valves, pumps and tanks, and these elements interact each other to provide adequate system performance. If elements fail by internal or external interruptions, it may result in adverse impact to water service with different degree depending on the failed element. To determine an appropriate maintenance priority, the critical elements need to be identified and mapped in the network. In order to identify and prioritize the critical elements in WDN, an element-based simulation approach is proposed, in which all the elements composing the WDN are reviewed one at a time. The element-based criticality is measured using several resilience indexes that are newly developed in this study. The proposed resilience indexes are used to quantify the impacts of element failure to water service degradation. Here, three resilience indexes are developed, such as User Demand Severity, Economic Value Loss and Water Age Degradation, each of which intends to measure different aspects of consequences, such as social, economic, and water quality, respectively. For demonstration, the proposed approach is applied to a benchmark water network to identify and prioritize the critical elements.

• Geomechanics and Engineering
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• v.18 no.3
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• pp.299-313
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• 2019

This research investigated the nonlinear compressibility, permeability, the yielding due to structural degradation and their effects on consolidation behavior of structured soft soils. Based on oedometer and hydraulic conductivity test results of natural and reconstituted soft clays, linear log (1+e) ~ $log\;{\sigma}^{\prime}$ and log (1+e) ~ $log\;k_v$ relationships were developed to capture the variations in compressibility and permeability, and the yield stress ratio (YSR) was introduced to characterize the soil structure of natural soft clay. Semi-analytical solutions for one-dimensional consolidation of soft clay under time-dependent loading incorporating the effects of soil nonlinearity and soil structure were proposed. The semi-analytical solutions were verified against field measurements of a well-documented test embankment and they can give better accuracy in prediction of excess pore pressure compared to the predictions using the existing analytical solutions. Additionally, parametric studies were conducted to analyze the effects of YSR, compression index (${\lambda}_r$ and ${\lambda}_c$), and permeability index (${\eta}_k$) on the consolidation behavior of structured soft clays. The magnitude of the difference between degree of consolidation based on excess pore pressure ($U_p$) and that based on strain ($U_s$) depends on YSR. The parameter ${\lambda}_c/{\eta}_k$ plays a significant role in predicting consolidation behavior.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.12
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• pp.41-49
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• 2018

The current housing performance rating system displays the performance rating of the houses supplied by the housing construction company, approved by the Housing Law. This system is intended to provide accurate information to the consumers in the announcement of the tenant recruitment, thereby improving the quality of the housing. This system was revised in January 2005 and implemented from January 2006. It is obligatory for companies with a scale of more than 1,000 households (energy performance rating is over 300 households), but there is currently no content on the waterproofing field. Therefore, this study suggests the revision plan proposes the necessity of the inclusion of the performance grade for the waterproofing field which is not currently implemented in the apartment house performance rating system, and to understand how to secure an adequate living environment. As a result, according to survey results, the performance score based on the difficulty of the maintenance method according to future leaks was selected and the revised system was prepared. Based on this, the performance grade for the virtual apartment was evaluated, and the results show that the performance of various grades is presented accordingly.

• Structural Monitoring and Maintenance
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• v.7 no.4
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• pp.319-344
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• 2020

Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

• Geomechanics and Engineering
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• v.24 no.1
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• pp.43-55
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• 2021

Peatland is distributed in China widely, and organic matters in soil frequently induce problems in the construction and maintenance of highway engineering due to the high permeability and compressibility. In this paper, a selected site of Dali-Lijiang expressway was surveyed in China. A numerical model was built to predict the settlement of the foundation of the selected section employing the soft soil creep (SSC) model in PLAXIS 8.2. The model was subsequently verified by the result of field observance. Consequently, the parameters of 17 types of soils from different regions in China with organic contents varying from 1.1-74.9% were assigned to the numerical model to study the settlement characteristics. The calculated results showed that the duration of primary consolidation and proportion of primary settlement in the total settlement decreased with increasing organic content. Two empirical equations, for total consolidation settlement and secondary settlement, were proposed using multiple linear regression based on the calculated results from the numerical models. The analysis results of the significances of certain soil parameters demonstrated that the natural compression index, secondary compression index, cohesion and friction angle have significant linear relevance with both the total settlement and secondary settlement, while the initial coefficient of permeability exerts significant influence on the secondary settlement only.

• Journal of Korean society of Dental Hygiene
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• v.4 no.1
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• pp.31-48
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• 2004

Dental caries taking place with milk teeth affects eruption of permanent teeth adversely, and thus, it is very important to prevent dental caries from taking place with a child in maintaining his/her physical, mental and emotional health. In this study as conducted to obtain basic data to be required for development of a program for letting preschool children form a habitual life for oral health and right dietary life, a total 172 children aged 5 years and 6 years were selected from children who lived in Hwasung-si, Kyunggi-do and attended preschools (childrens houses) located there with the consent of their guardians. Then, the weight length index (WLI) and blood components of each child were analyzed, and each relation between the weight length index (WLI) and dental caries of milk teeth and between blood components and dental caries of milk teeth was comparatively examined, and thereby, the following results were obtained. When the dmf rate of each group according to the obesity was examined, it was found to be 87.50% in the under-weight group, 71.20% in the normal weight group and 83.87% in the overweight group. And when the dmft rate of each group was examined, it was found to be 48.43% in the under-weight group, 37.10% in the normal weight group and 47.17% in the overweight group. Also, when the dmft index of each group was examined, it was found to be 3.9 in the under-weight group, 3.0 in the normal weight group and 3.8 in the overweight group. That is to say, the under-weight group and the overweight group having an abnormal weight were found to be higher in all of the dmf rate, the dmft rate and the dmft index than the normal weight group. It could be, therefore, known that normal weight should be maintained in order to prevent dental caries of milk teeth. And, it is thought that a right dietary life habit ensuring intake of balanced nutrients should be formed for maintenance of a normal weight. As a result of examining the relation between nutrient components in blood and dental caries of milk teeth, in the case of children with no dental caries, inorganic nutrient components of blood had a tendency to be a little higher, but no statistical significance was observed therein. Meanwhile, it was found that there was a relation between blood type and the dmft index.

• Journal of the Korean Dietetic Association
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• v.8 no.2
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• pp.185-198
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• 2002

The purpose of this study was to compare food habits and nutrient intakes with body mass index of hypertensive patients commuting to a Local Health Center. A total of 85 patients were divided into two groups according to BMI. The non-obese group comprised 43 subjects with BMI below 25㎏/$m^2$ , while the obese group comprised 42 subjects with BMI above 25㎏/$m^2$ . All Subjects were interviewed for general characteristics, food habits, clinical characteristics, effort for health maintenance and the knowledge of hypertension and nutrition. Anthropometric assessments such as weight, height, waist-hip ratio and biochemical measurement of blood urea nitrogen, creatinine, triglyceride, total cholesterol, HDL-cholesterol and fasting blood glucose(FBG) were obtained from subjects. In general characteristics, smoking, drinking, exercise, and hypertension status were not significantly different between the two groups. Food habits and the means of daily energy and nutrients were not significantly different between the two groups. An analysis of the percentage of RDA(Recommended Dietary Allowances of Korea, 2000) consumed by patients showed that but for ascorbic acid and phosphorus, all nutrients were below the RDA. And intakes of vitamin $B_1$(P<0.001), vitamin $B_2$(P<0.01), niacin(P<0.001) of the obese group were significantly lower than that of the non-obese group. Blood urea nitrogen, creatinine, triglyceride, total cholesterol, HDL-cholesterol and fasting blood glucose were in the normal range and there was not a significant difference in the two groups. Therefore, more effective nutrition education programs about exercise, smoking, caloric intake, vitamins and minerals are required for hypertensive patients commuting to Local Health Center.

• Journal of Trauma and Injury
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• v.29 no.1
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• pp.14-21
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• 2016

Purpose: The purpose of this research was to analyze the results of the combined and posterior approaches for treating thoracolumbar and lumbar burst fractures and to find an adequate method of treatment. Methods: We retrospectively analyzed the cases of 46 patients with unstable thoracolumbar and lumbar burst fractures who had been surgically treated. All cases were divided into two groups based on the operation method used. Eleven patients had undergone the combined approach, while 35 patients had undergone the posterior approach. Radiological and clinical evaluations were performed before surgery, after surgery, and at the final follow-up. Results: The stenotic ratios of the area occupied by the retropulsed bony fragments to the estimated area of the original spinal canal were 68.2% and 45.6% for the combined and the posterior approaches, respectively. No significant differences in the neurological improvement or the corrected state of the sagittal index were noted, but the patients who had been treated with the combined approach group had better results than those who had been treated with the posterior approach group in terms of correction and maintenance of the sagittal index. The average kyphosis corrections at the final follow-up were 15.3 degrees for the patients in the combined approach group and 10.0 degrees for those in the posterior approach group. Surgical time and estimated blood loss were all significantly higher for patients in the combined approach group. Conclusion: The combined and the posterior approaches showed similar results in the improvements of the neurologic state and the corrected state of the sagittal index. However, use of the combined approach is recommended for patients with severe kyphosis and with severe canal encroachment.