• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.215-225
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• 2011

In general, the precast columns can obtain its homogeneous quality as they are produced in a factory with a hollow concrete block type by using high strength concrete, so that they can generate the reduction of dead load. Such a method of precast hollow concrete columns is already implemented in USA and Japan and used for connecting between blocks which use PC tendons. However, it is inevitable to have uneconomical construction with excessive cost in early stage when PC tendons are used. This study aims to develop an economical precast column with high quality and constructability which consists of only splice sleeve and general reinforcing bar without using PC tendons in order to reduce the construction period and cost. To achieve this goal, this study tested the performance of total 5 minimized models in the experiment with the variables such as hollowness, diameter of main reinforcement bar and cross-sectional size for the cross section of precast column by using grouting type splice sleeve which is a new type joint rebar. And it also verified the performance of column in the experiment for a large-sized model in order to overview its applicability by excluding large scale effect.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.6
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• pp.818-824
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• 2018

CFRP is often used as lightweight hull material for luxury yachts or special-service ships. An electric propulsion system is also eco-friendly, and has been trialled to equip a small vessel as its main propulsion. In this study, replacing the hull materials and propulsion system with CFRP and electric motors, we made an estimate of the effect of weight reduction and compared it to the original design, for this purpose a case study was conducted on a 45-ft yacht. When redesigning structures with CFRP, we applied the reinforcement content of the carbon fiber in the same way as the original (GC = 0.4), and when changing to the electric propulsion system, we designed motors and battery packs to achieve the same performance as the original. The result showed that CFRP and the electric propulsion system could make the structural and machinery weights 45 % and 58 % lighter, respectively. However, in terms of efficiency, it was confirmed that the electric propulsion system is practically inefficient because it requires a huge amount of battery packs for the same navigation range with diesel engines.

• The Journal of the Convergence on Culture Technology
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• v.6 no.3
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• pp.33-43
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• 2020

The purpose of this study is to investigate the level of payment of accommodation charge to hotel customers and to analyze the differences in hotel choice factors according to the level of payment(low, medium and high prices) to present marketing measures for attracting customers by hotel price range. To achieve the purpose of research, a survey was conducted on hotel customers from February 1, 2020 to April 30, 2020. A total of 350 questionnaires were distributed, eliminating 45 inappropriate copies for analysis, and finally utilizing 305 questionnaires for analysis. According to the analysis, among the basic factors, the biggest difference between groups was hotel size, breakfast menu, restaurants, and auxiliary facilities. It was analyzed that there are differences between groups in the amenity section in the room factor and outside tourism programs in the incidental factor. The main factors were analyzed as the most important factor, although there were no differences between groups. Based on this, the marketing plan is proposed as follows. Low-cost hotels are targeted at women in their 20s with high school diplomas, and it is recommended to have low-cost price policies and promotions. Mid-priced hotels are targeted at men in their 40s with college degrees, and they should strive to operate shuttle buses, promote room prices, and educate employees. In the case of high-priced hotels, it was analyzed that overall service reinforcement, employee education, and viral marketing are important, targeting high school graduates in their 20s.

• The Journal of Engineering Geology
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• v.17 no.2 s.52
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• pp.289-297
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• 2007

Slope failure that is occurred by rainfall generates a lot of property damages and loss of lives. Slope stability management and reinforcement countermeasure can be attained through continuous monitoring about various slope types that adjoin in human's life for reducing slope failure from natural and artificial cut slope hazards. The study area is rock slope that is consisted of gneiss, and large scale joint set is ranging by fault activity. This rock mass is exposed during long period and has lithological weathering property of weathered rock or soft rock. In-situ investigation carried out after divide by natural slope and cut slope. As a result, the natural slope appeared to high possibility of planar failure and wedge failure in few joint points that main joint set is formed. On the other hand, slope failure conformation in cut slope was superior only wedge failure occurrence possibility in eight joint points. In result of numerical analysis using SLIDE 2D, the minimum safety factor was analyzed slope stability for cut slope relatively low than natural slope in this study.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.49-59
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• 2013

Heavy rainfall intensity may cause shallow slope failures and debris flow by rill erosion and scour on land surface. The paper represents the difference between native soil (weathered soil) and reinforced soil, which is mixed by hardening agent with flyash as main material, for investigating experimental findings of rill erosion and erosion. Results obtained from artificial rainfall simulator show that erosion rate of reinforced soil mixed with hardening agent is reduced by 20% because an amount of eroded soil on slope surface is inversely proportional to the increase of soil strength. For example, rainfall of 45mm (at the elapsed time of 25mins in rainfall intensity of 110mm/hr) triggers rill erosion on native soil surface, but the rill erosion on reinforced soil surface does not even occur at 330mm rainfall (at the elapsed time of 3hrs in rainfall intensity of 110mm/hr). As a result of slope stability analysis, it was found that the construction method for reinforced soil surface would be more economical, easy and fast construction technology than conventional reinforcement method.

• Journal of the Korean Geosynthetics Society
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• v.4 no.4
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• pp.23-37
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• 2005

The factors affecting the long-term design strength of geogrid can be classified into factors on creep deformation, installation damage, temperature, chemical degradation and biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrid. Current practice in the design of a reinforced soil structures is to calculate the long-term design strength of a geosynthetic reinforcement damaged during installation by multiplying the two partial safety factors, $RF_{ID}$ and $RF_{CR}$. This method assumes that there is no evaluation of synergy effect between installation damage and creep deformation of geogrids. This paper describes the results of a series of experimental study, which are carried out to assess the combined effect of the installation damage and the creep deformation for the long-term design strength of geogrid reinforcements. A series of field tests was carried out to assess installation damage of various geogrids with respect to different fill materials, and then creep tests are conducted to evaluate the creep deformation of both undamaged and damaged geogrids. The results indicated that the tensile strength reduction factors, RF, considering the combined effect between the installation damage and the creep deformation is less than that calculated by the current design method.

• Composites Research
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• v.30 no.1
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• pp.46-51
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• 2017

Structural battery has been researched extensively to combine the functions of the battery and structure without gravimetric or volumetric increments compared to their individual components. The main idea is to employ carbon fabric as the reinforcement and electrode, glass fabric as the separator, and solid-state electrolyte which can transfer load. However, state-of-the-art solid-state electrolytes do not have sufficient load carrying functionality and exhibiting appropriate ion conductivity simultaneously. Therefore, in this research, a system which has both battery and load carrying capabilities using glass fabric separator and liquid electrolyte was devised and tested to investigate the potential and feasibility of this structural battery system and observe electric properties. It was observed that elongating separator decreased electrical behavior stability. A possible cause of this phenomenon was the elongated glass fabric separator inadequately preventing the penetration of small particles of the cathode material into the anode. This problem was verified additionally by using a commercial separator. The characteristic of the glass fabric and the interface between the electrode and glass fabric needed to be further studied for the realization of such a load carrying structural battery system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.75-82
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• 2007

As one of the main support systems, rock bolts play a crucial role in the reinforcement of tunnels. Numerical and experimental studies using a transmission method of ultrasonic guided waves are performed to evaluate the integrity of rock bolts encapsulated by grouting paste. Numerical simulations using "DISPERSE" are carried out for the selection of the optimal experimental setup, i.e. non-destructive testing (NDT) system of the rock bolt. Based on results of the numerical simulation, the calculated frequency range for NDT testing is between 20kHz and 70kHz with the first longitudinal L(1) mode. Laboratory transmission tests are performed by attaching the piezo electric sensor at the tip of the rock bolt before embedding. Both of analytical and experimental results show that the amplitude of signals as well as the wave velocity increases with increase in the defect ratio of grouting paste. The defect in grouting paste means that the space around the rock bolt is not fully filled with the grouting paste. Experimental results also show that the increase of the wave velocity is more sensitive to the defect ratio increase than that of the amplitude. This study demonstrates that the transmission technique of ultrasonic guided waves may be a valuable tool in the evaluation of the rock bolt integrity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.839-854
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• 2018

This study was performed to evaluate the performance of GFRP plate reinforced segments for TBM tunnel support. Recently, the SFRC segment has been applied to prevent local damage such as reduction of the amount of reinforcing bars of the segment, crack control and breakage. However, the steel fiber used in the SFRC segment has a problem of durability deterioration due to fiber corrosion. Compared with the RC segment, the maximum flexural load reduction of the SFRC segment hinders the broad application range of the TBM tunnel segment. Therefore, GFRP plate was considered as a stiffener for the maximum load increase of SFRC segment, and structural synthetic fiber without corrosive concern was used as a substitute for steel fiber. The flexural performance of the segment was evaluated by using the type of reinforcing fiber and GFRP plate thickness as the main parameters. As a result, the maximum load and the flexural toughness were increased by 21.78~23.03% and 0.5~7.96%, respectively, as compared with the segments reinforced with reinforcing fiber and GFRP plate of 3 mm thickness.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.428-436
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• 2020

The purpose of this study is to analyze the needs for developing a curriculum for strengthening the long-term care service expertise and job competency. Specifically, the researchers analyzed previous studies on national long-term care services and national policy data, and conducted focus group interviews with 14 experts from related agencies. Activity theory was applied as a framework for analysis and a questionnaire about the importance and difficulty of subjects from 25 long-term service employees was administered for validating the results of the qualitative data analysis. The upper part of the subject-goal-tool of the activity system was considered the main area of action, and the following rule-community-division was divided into contextual parts for action, and the implications for demand analysis and future operation of the online curriculum are summarized. In total, six courses were required for development. These courses could be applied to as a learner-centered flip learning for long-term care service workers and various educational methods of collective education and supplementary education have been proposed. Based on the study results, implications in the educational field for effective management of courses were suggested at the end of the study.