• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.2
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• pp.233-242
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• 2018

To overcome the low mechanical strength and corrosion behavior of a carbon steel canister at high temperature condition of a deep borehole, SiC ceramics were studied as an alternative material for the disposal canister. In this paper, a design concept for a SiC canister, along with an outer stainless steel container, was proposed, and its manufacturing feasibility was tested by fabricating several 1/3 scale canisters. The proposed canister can contain one PWR assembly. The outer container was also prepared for the string formation of SiC canisters. Thermal conductivity was measured for the SiC canister. The canister had a good thermal conductivity of above $70W{\cdot}m^{-1}{\cdot}K^{-1}$ at $100^{\circ}C$. The structural stability was checked under KURT environment, and it was found that the SiC ceramics did not exhibit any change for the 3 year corrosion test at $70^{\circ}C$. Therefore, it was concluded that SiC ceramics could be a good alternative to carbon steel in application to deep borehole disposal canisters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.35-44
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• 2020

The purpose of this study is to elaborate the request for proposal (RFP) for the localization parts development support project of core parts carried out by the Defense Agency for Technology and Quality. The RFP is the most important document throughout the localization parts project, including project announcement and developer selection, design and test of the development product, final evaluation, and standardization of the project. However, if the RFP is not established at the beginning of the project, there is an increased risk of business failure due to frequent changes by various reasons. In this study, we recognized the necessity of elaboration of RFP and applied the AHP method for quantitative elaboration. Eight requirements of the RFP related to the mechanical/electrical performance of localized development products and three elaboration methods for each requirement were designed in a hierarchical structure, and each weight was calculated by applying the 5-point scale AHP method. The AHP survey was conducted with 20 developers participating in the localization parts project, and the consistency ratio of the AHP survey result was less than 0.1. The elaboration method with the highest value among the calculated weights is classified, and the analysis results and future research directions of the elaboration method are presented.

• Journal of Korean Society of Steel Construction
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• v.20 no.4
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• pp.483-491
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• 2008

There has been much focus on the strong axis steel moment connections after the Northridge earthquake in 1994. However, research studieson the seismic behavior of weak axis moment connections could be hardly found despite the fact that these connection details have been frequently used as seismic details of MRF in Korea. Therefore, the objective of this research is to provide better knowledge on the seismic behavior of weak-axis steel moment connections, which can be widely applicable to many structures with similar characteristics. For this purpose, an experimental program was designed and performed with twotypes of weak-axis steel moment connections, namely the bracket type and WUF-B type, based on the survey of existing field data and literatures. Using the experimental results obtained from the quasi-static cyclic testing of these specimens, structural performances of the joints such as hysteretic curves, maximum strength capacities and the strain of reinforced bars were investigated. From the test results, the bracket-type connection was shown to have more than a 5% story drift capacity, compared with the WUF-B type connection's 4%. These specimens were also shown to have higher strength capacities than the nominal design strength. The bracket-type connection showed a slow strength degradation after maximum strength was researched. However,the WUF-B type connection showed a rapid strength degradation that caused brittle behavior.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.27-36
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• 2014

Due to the latitudinal location of Korea, the seasonally frozen ground has been focused on as research topics such as the frost heaving under the asphalt road rather than the permafrost ground. However, the recent construction of the second Korean Antarctic research station, the Jangbogo station and the participation on the development of the natural gas pipeline in Russia arouse the research interests on the behavior of the permafrost ground. At the design process of the geotechnical structures on the permafrost ground, the evaluation of the creep characteristics of the frozen soil is very crucial. Since the domestic specification on the frozen soil testing does not exist currently, it is necessary to evaluate the creep characteristics of frozen soils systematically with regard to the affecting factors. Therefore, the creep characteristics of the frozen specimens of dense Jumoonjin sand were evaluated under various loads at -5 and $-10^{\circ}C$. Based on the test results, as the load became close to the strength and the temperature became lower, the duration of the secondary creep became shorter and more distinct tertiary creep responses were observed.

• Therapeutic Science for Rehabilitation
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• v.8 no.4
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• pp.41-51
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• 2019

Objective : The purpose of this study was to investigate the effects of virtual reality-based activities of daily living (ADL) training on ADL and rehabilitative motivation in patients with traumatic brain injury. Methods : This study was performed using a pre-post design with seven traumatically brain injured patients. Subjects were subjected to virtual reality-based ADL training for 30 minutes a day, 2 to 3 times a week for 4 weeks. Evaluation was conducted before and after the intervention using the Korean Modified Barthel Index (K-MBI), Cognitive Functional Independence Measure (C-FIM), and Volitional Questionnaire (VQ). Changes before and after intervention were analyzed by Wilcoxon signed-rank test, and correlations were analyzed using Spearman's coefficient. Results : After intervention, patients with traumatic brain injury showed significant improvements in K-MBI (p<.05). There was no significant change in total C-FIM score and VQ score (p>.05). Total C-FIM score correlated significantly with VQ score (p<.05, r=.755). The social cognition domain of C-FIM had a significant correlation with VQ score (p<.05, r=826). Conclusions : Virtual reality-based ADL training can improve ADL performance, but further research is needed to determine whether improvements in social cognition and rehabilitative motivation are possible.

• The Journal of the Convergence on Culture Technology
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• v.5 no.4
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• pp.387-394
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• 2019

In this study, in order to evaluate the damage and deterioration of the track components of sleeper floating track (STEDEF), the field samples(specimens) were taken from the serviced line over 20 years old, and the track components were visually inspected, and investigated by laboratory tests and finite element analysis. As a result of visual inspection, the damage of the rail pad and fastener was slight, but the rubber boot was worn and torn at the edges of bottom. The resilience pads were clearly examined for thickness reduction and fatigue hardening layer. As a result of spring stiffness test of rail pad and resilience pad, the deterioration of rail pad was insignificant, but the deterioration of resilience pad exceeded design standard value. Therefore resilience pad was directly affected by train passing tonnage. As a result of comparing the deterioration state of the field sample and the numerical analysis result, the stress and displacement concentration position of the finite element model and the damage position of the field sample were coincident.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.738-746
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• 2019

Instead of hydraulic actuation systems, an electromechanical actuation system is more efficient in terms of weight, cost, and test evaluation in the thrust vector control of the 7-ton gimbal engine used in the Korea Space Launch Vehicle-II(KSLV-II) $3^{rd}$ stage. The electromechanical actuator is a kind of servo actuator with position feedback and uses a BLDC motor that can operate at high vacuum. In the case of the gimballed rocket engine, a synthetic resonance phenomenon may occur due to a combination of a vibration mode of the actuator itself, a bending mode of the launcher structure, and an inertial load of the gimbals engine. When the synthetic resonance occurs, the control of the rocket attitude becomes unstable. Therefore, the requirements for the stiffness have been applied in consideration of the gimbal engine characteristics, the support structure, and the actuating system. For the 7-ton gimbal engine of the KSLV-II $3^{rd}$ stage, the stiffness requirement of the actuation system is $3.94{\times}10^7N/m$, and the direct drive type electromechanical actuator is designed to satisfy this requirement. In this paper, an equivalent stiffness analysis model of a direct drive electromechanical actuator designed based on the stiffness requirements is proposed and verified by experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.83-91
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• 2021

In this study, to improve the connection performance between the existing reinforced concrete (R/C) frame and the strengthening member, we proposed a new H-section steel frame with elastic pad (HSFEP) system for seismic rehabilitation of existing medium-to-low-rise reinforced concrete (R/C) buildings. This HSFEP strengthening system exhibits an excellent connection performance because an elastic pad is installed between the existing structure and reinforcing frame. The method shows a strength design approach implemented via retrofitting, to easily increase the ultimate lateral load capacity of R/C buildings lacking seismic data, which exhibit shear failure mechanism. Two full-size two-story R/C frame specimens were designed based on an existing R/C building in Korea lacking seismic data, and then strengthened using the HSFEP system; thus, one control specimen and one specimen strengthened with the HSFEP system were used. Pseudodynamic tests were conducted to verify the effects of seismic retrofitting, and the earthquake response behavior with use of the proposed method, in terms of the maximum response strength, response displacement, and degree of earthquake damage compared with the control R/C frame. Test results revealed that the proposed HSFEP strengthening method, internally applied to the R/C frame, effectively increased the lateral ultimate strength, resulting in reduced response displacement of R/C structures under large scale earthquake conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.12-19
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• 2021

Recently, with frequent earthquakes around the world, research on seismic design and seismic reinforcement of reinforced concrete facilities has been actively conducted from earthquakes. In particular, columns, which are compressed members of reinforced concrete structures, are vulnerable to lateral forces caused by earthquakes, so an appropriate seismic reinforcement method is required. Therefore, this study intended to develop Velcro seismic reinforcement method that is quick and easy to construct. For the development of Velcro seismic reinforcement, the adhesion and tensile strength of the existing industrial velcro was improved. A direct tensile test was also conducted to compare the tensile performance of the newly-developed velcro seismic reinforcement to industrial one. In addition, numerical analysis was performed to predict the seismic performance of RC columns reinforced by industrial and newly-developed velcro. Based on the analysis results, the strength and ductility of the non-seismic and velcro-reinforced RC column were reviewed. The analysis confirmed that both the strength and ductility of non-seismic RC columns reinforced by industrial and newly-developed velcro increased, but the seismic performance of the newly-developed Velcro reinforcement is better than that of industrial velcro.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.75-82
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• 2021

The objective of this study is to examine the loss of prestressing stress in the developed prestressing reinforcing units using steel bar and pipe (SP). The main parameters were the reinforcing bar type, the magnitude of prestressed force, and prestressing method. The test results showed that the loss of prestressing stress for SP was highest in the initial prestressing step, which was higher for the compression introduction typed specimens than tension introduction typed specimens. The loss of prestressing stress of SP made with P800 was 1.6% for the compression introduction typed specimen with 0.8f_y, which was lowest than the other specimens. Meanwhile, the relaxation of SP with the respect to the time ranged between 0.4 and 1.9%, irrespective of SP material type, the magnitude of prestressed force, and prestressing method. These values were less than 2.5%, which is the maximum value for the relaxation of prestressed reinforcing steel bars in design codes. Consequently, considering the loss of stress developed in the initial prestressing step, the developed SP material type, prestressing introduction method, and magnitude are recommended to be P800, compression introduction type, and 0.8f_y.