• 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.

• Journal of Korean Society of Rural Planning
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• v.19 no.4
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• pp.81-93
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• 2013

The selection of land for fishing village development project, and the standard used to classify fishing villages has been determined based on the guidelines developed by fishing village cooperatives. The approach fishing village cooperatives follows is likely to classify fishing villages without first reflecting on the overall development environment of the region, such as other industries and workers in the area. It also acts as a barrier for business promotion or evaluation, because the cooperatives do not match the administrative districts, which are the units of administration, and the main policy enforcement agent in regional development. Against this background, this study aimed to identify categories to situate the development direction, as well as the size and distribution of fishing villages based on eup, myeon, and dong administrative units as defined by the Fishing Villages and Fishery Harbors Act. This study was based on the Census of Agriculture, Forestry, and Fisheries of 2010, and analyzed 826 eups, myeon, and dongs with fishery households using the principal component analysis, and 2-Step cluster analysis methods. Therefore, 95% of the variance was explained using the covariance matrix for types of fishing villages, but it was analyzed as one component focusing on the number and ratio of fishery households, and used the cluster-type analysis, which focused on the sizes of fishing villages. The clusters were categorized into three types: (1) the development type based on the number of fishermen in the eups, myeons and dongs was analyzed as village size (682); (2) administrative district size (121); and (3) total eups, myeons and dongs (23), which revealed that the size of most fishing villages was small. We could explain 73% of the variance using the correlation coefficient matrix, which was divided into three types according to the three principal component scores, namely fishery household power, fishery industry power, and fishing village tourism power. Most fishing villages did not have a clear development direction because all business areas within the region were diversified, and 552 regions could be categorized under the harmonious development type, which is in need of balanced development. The fishery industry type typified by industrial strength included 159 regions in need of an approach based on industrialization of fishery product processing. Specialized production areas, which specialized in producing fishery products, were 115 regions with a high percentage of fishermen. The analysis results indicated that various situations in terms of size and development of fishing villages existed. However, because several regions exist in the form of small village units, it was necessary to approach the project in a manner that directed the diversification of regional development projects, such as places for local residents to relax or enjoy tourism experiences within the region, while considering the overall conditions of the relevant eups, myeons, and dongs. Reinforcement of individual support for fishermen based on the Fisheries Act must take precedence over providing support for fishermen through regional development. In addition, it is necessary to approach the development of fishing villages by focusing on industrializing the processing techniques of fishery products. Areas specialized in the production of fishery products are required to consider the facilities for fisheries production, and must make efforts to increase fishery resources, such as releasing fry.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.92-103
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• 2015

Development of new concrete bridge deck system with FRP plank using as a permanent formwork and the main tensile reinforcement recently has been actively conducted. Concurrent use as a reinforcing material and a permanent formwork, it is possible to reduce the construction time and construction costs than the usual concrete slab. In this study, an experiment was carried out for the bond stress between cast-in-place concrete and the type of FRP plank using as a permanent formwork. The interfacial fracture energy that can be one of the most important parameters were evaluated for adhesion performance and bond stress to know the characteristics of the failure mechanism of the adhesion surface. Interfacial fracture energy of normal concrete is 0.24kN/m of GF11 case, in the case of GF21, 0.43kN/m appears, in the case of CF11 and GF31, 0.44kN/m and 0.46kN/m respectively it appeared. In case of RFCON, 0.52kN/m appears from GF12, the CF12 and GF22, 0.51kN/m and 0.36kN/m appeared each case.

• Journal of the Korean Geosynthetics Society
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• v.6 no.1
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• pp.9-16
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• 2007

Geotextile is one of the most useful and effective polymer material in civil construction works and the main function of geotextile is separation, reinforcement, filtering and drainage. Recently, because of the shortage of natural rock, traditional forms of river and coastal structures have become very expensive to build and maintain. Therefore, the materials used in hydraulic and coastal structures are changing from the traditional rubble and concrete systems to the cheaper materials and systems. One of these alternatives employs geotextile tube technology in the construction of coastal and shore protection structures, such as embankment, see dyke, groins, jetties, detached breakwaters and so on. Geotextile tube technology has changed from being an alternative construction technique and, in fact, has advanced to become the most effective solution of choice. This paper presents case history of sea dyke filter construction using geotextile tube mattress and also, various issues related to the tube mattress design and construction technology.

• Journal of Digital Convergence
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• v.11 no.10
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• pp.537-547
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• 2013

A recent rapid change in society drives the colleges and universities into the unlimited competition for satisfying users' demand. The introduction of customized educational system is one of the survival strategies of university that reflected this characteristic. The result of a research on the customized curriculum of the dental hygiene study shows that the managers of dental hospitals and clinics think that the dental assistance field is dental hygienist's major task. On the other hand, though the dental hygienists think that the oral health education is the main task, they just comply with the intention of managers of the dental hospitals and clinics in reality. Hence, the reinforcement of the practicum in the industry field is required to meet the demand from the industry. And there is also a need to offer an opportunity of self-realization through work life by allowing dental hygienists to have stable status within dental hospitals and clinics with enhanced education and training on preventive dental treatment and oral health.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.47-55
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• 2006

Seismic performance and retrofit of reinforced concrete (RC) two-column piers widely used at roadway bridges in Korea was experimentally evaluated. Ten two-column piers that were 400 mm in diameter and 2,000 mm in height were constructed. These piers were subjected to hi-directional cyclic loadings under a constant axial load of $0.1f_{ck}A_g$. Test parameters were the confinement steel ratio, loading pattern, lap splice of longitudinal reinforcing bars, and retrofitting method. Specimens with lap-spliced longitudinal bars were retrofitted with steel jacket, pre-stressing steel wire, and steel band. Test result showed that while the specimens subjected to bi-directional lateral cyclic loadings which consisted of two main amplitudes in the transverse axis and two sub amplitudes in longitudinal axis, referred to as a T-series cyclic loadings, exhibited plastic hinges both at the top and bottom parts of the column, the specimens subjected to bi-directional lateral cyclic loadings in an opposite way, referred to as a L-series cyclic loadings, exhibited a plastic hinge only at the bottom of the column. The displacement ductility of the specimen under the T-series loadings was bigger than that of the specimen under the L-series loadings. Specimen retrofitted with pre-stressing steel wires exhibited poor ductility due to the upward shift of the plastic hinge region because of over-reinforcement, but specimens retrofitted with steel jacket and steel band showed the required displacement ductility. Steel band can be an effective retrofitting scheme to improve the seimsic performance of RC bridge piers, considering its practical construction.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.221-229
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• 2008

An improved unbonded-type column strengthening procedure using wire rope and T-shaped steel plate units was proposed. Eight strengthened columns and an unstrengthened control column were tested under concentric axial load. The main variables considered were the volume ratio of wire rope and the flange width and configuration of T-shaped steel plates. Axial load capacity and ductility ratio of columns tested were compared with predictions obtained from the equation specified in ACI 318-05 and those of conventionally tied columns tested by Chung et al., respectively. In addition, a mathematical model was proposed to evaluate the complete stress-strain relationship of concrete confined by the wire rope and T-plate units. Test results showed that the axial load capacity and ductility of columns increased with the increase of the volume ratio of wire rope and the flange width of T-plates. In particular, at the same lateral reinforcement index, a much higher ductility ratio was observed in the strengthened columns having the volume ratio of wire rope above 0.0039 than in the tied columns. A mathematical model for the stress-strain relationship of confined concrete using the proposed strengthening procedure is developed. The predicted stress-strain curves were in good agreement with test results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.130-137
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• 2017

The purpose of this study is to provide a reasonable analytical method for the reinforced concrete beams which shows failure mode of shear and flexure-shear by proposing a modified formulation to consider the effect of shear deformation on the beam-column fiber element based on the flexibility method and a new constitutive law of inelastic shear response history for the section. A total of 6 specimens of reinforced concrete beams which is designed to cause shear failure before yielding longitudinal reinforcement to investigate the influence of the main experimental variables on the shear behavior characteristics and the analysis was performed by using a non-linear finite element analysis program (RCAHEST) applying the newly modified constitutive equation by the authors. The failure mode and the overall behavior characteristics until fracture are predicted appropriately for all specimens and the results are expected to be useful enough for the 3 - D analysis to carry out reliable results of large-scale and complicated structures in the future.