• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.405-411
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• 2011

Using combinations of carbon and glass fiber composites normally used for strengthening of concrete structures, the hybrid effect from strengthening concrete structures using the composite is studied. To produce the hybrid effects, the specimens were made with optimum proportions of carbon fibers with glass fibers. Then, direct tensile tests were conducted on the hybrid FRP (fiber reinforced polymer) specimens. Unlike the woven fiber sheet currently used in construction sites, the FRP specimens have to be directly combined with the fibers, which make the work very complicated. Therefore, direct tensile test specimens manufacturing method based on the combination of high-tension carbon fibers and E-type glass fibers was proposed and the effects of hybridization is studied through the direct tensile test. By comparing the ductility index, the modulus of elasticity, and the stress-strain curves of the specimens, the most optimum glass to carbon fiber combination ratio for the hybrid FRP was found to be 9 to 1 with ductile K-type epoxy. The study results are discussed in detail in the paper.

• Journal of Korean Society of Disaster and Security
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• v.5 no.1
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• pp.43-47
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• 2012

The asset management of infra facilities is a total framework for finally supporting a safe and comfortable service, which includes functions of supporting evaluation of condition and performance of infrastructures, making the decision method of repair or rehabilitation of deteriorated facilities, and lengthening the life cycle of structure through the decision of adequate cost and time of repair or reinforcement. In the range of the asset management, organization, human, the target, and information & data of company are included. Therefore, in this paper, appling the method of asset management analysis to the infra structures, the process of the risk assesment using BRE (Business Risk Exposure) and the basis of consisting ORDM (Optimized Renewal Decision-Making) are expressed.

• Composites Research
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• v.18 no.5
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• pp.34-39
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• 2005

The relationship between strain and applied potential was derived for composite actuators consisting of single-wall carbon nanotubes (SWNTs) and conductive polymers (CPs). During deriving the relationship, an electrochemical ionic approach is utilized to formulate the electromechanical actuation of the composite film actuator. This relationship can give us a direct understanding of the actuation of a nanoactuator. The results show that the well-aligned SWNTs composite actuator can give good actuation responses and high actuating forces available. The actuation is found to be affected by both SWNTs and CPs components and the actuation of SWNTs component has two kinds of influences on that of the CPs component: reinforcement at the positive voltage and abatement at the negative voltage. Optimizations of SWNTs-CPs composite actuator may be achieved by using well-aligned nanotubes as well as choosing suitable electrolyte and input voltage range.

• The Journal of Korean Association of Computer Education
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• v.10 no.2
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• pp.9-16
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• 2007

The purpose of this research is to suggest effective teaching and learning method suitable for IT-gifted primary school students based on their learning style. This study investigated the means of identifying IT-gifted students by comparing IT-gifted's learning style with average student's. Grasha-Reichmann Student Learning Style Inventory was used, which was proved to identify gifted IT students with 66.45% accuracy. As a result, The learning style of IT-gifted was determined as independent, competitive, participant Therefore, self-directed learning methods seem to be suitable for IT-gifted. IT-gifted also need to have more opportunities to participate in learning activities and discussion with their peers.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.92-92
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• 2019

최근 기존의 격자방식의 해석 방법을 벗어나 해석 영역에 대한 분할을 별도로 고려치 않는 수치기법의 실무적 적용사례가 증가 하고 있으며, 이러한 방식중 SPH(Smoothed Particle Hydrodynamics) 방식이 근자에 수자원 분야에서도 도입되어 관수로 및 개수로 해석 또는 복합해석 등에 활용된 바 있다. 최초 도입된 무격자방식의 모형들은 주로 복잡한 형상을 지니는 유체기계 등에 활용성이 높았던 바, 큰 규모의 해석 도메인을 가지는 수자원 분야에서의 SPH의 실무적용 평가와 효율성의 확보를 위해서, 본 연구는 국내 댐을 시범 대상으로 하여 SPH 수치해석 툴을 적용하고자 하였다. 분석 대상댐은 국내 P댐으로서 관리수위의 변동은 크지 않으나, 댐 직상류의 만곡이 심하고 다수의 대규모 취수구를 가진 곳으로 상시 발전방류 및 수시 댐 수문방류에 의해 유체의 흐름이 2,3차원의 복잡성을 띄고있기 때문에, 3차원 전산유체역학 Tool의 적용이 적절한 것으로 판단하였다. 해석을 위해 하류경계조건을 댐축과 문비로 설정하였고 상류 1km까지를 해석의 도메인으로 설정하였다. 소요시간을 줄이기 위해 여러 번의 모의를 거쳐 입자의 평균 입경은 0.6m로 제안하고 시격은 1초 미만(평균 0.5초)로 설정하였다. 수문 및 발전방류는 해당댐의 1~2년 빈도 수준에 해당하는 $5,000m^3/s$ 이하의 유량을 기준으로 하여 모의를 수행하였다. 모의의 안정성을 확보한 이후에는 해당 댐지역의 하류영향을 고려한 문비제어를 반영한 다양한 방식의 수문운영 및 취수지점의 순간 수위 영향을 검토하였다. 그 결과로 본 모의에서는 특정한 수문의 운영 조건에서는 댐수위 계측지점과 인근 취수지점 간에도 0.2m 수준의 순간 수위차가 발생할 수 있음을 보였으며, 이는 경우에 따라 취수시설의 일시적 장애요소로 발생할 수 있음을 의미한다. 따라서, 현재의 취수구조물과 문비운영 특성에 따라 발생가능한 취수장애를 줄일 수 있는 운영조건의 탐색을 위해서 수치모의를 추가로 하였으며, 이 때 댐축 상류의 유속분포에 대한 추가 검토도 수행하였다. 다만, 댐에서 방류시 하류조건에 대한 검토는 추후 보강되어야 할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.845-849
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• 2005

도시지역 공간의 한정성으로 인해 하천연변의 저지대에 까지 토지이용도가 극대화되고 있다. 이러한 상황은 치수방재의 측면에서 과거와 같은 외수의 범람에 의한 홍수피해가 아닌 내수의 배수불량으로 의한 침수피해의 증가를 가져 왔다. 서울특별시의 경우 유수지 및 빗물펌프장의 보강을 통해 치수안전을 확보하고 있다 빗물펌프장 운영에서 가장 중요한 요소는 펌프의 가동과 배수문의 개폐을 통한 외수의 차단과 내수의 방류에 있다. 특히 배수문의 개폐시기가 적절치 않은 경우, 외수가 유수지로 들어와 펌프장의 기능을 저해 할 수 있다. 그러나 배수문의 개폐는 현재 자동화 되지 못하고 운영자에 의하여 경험적으로 운영되고 있다. 본 연구에서는 수리학적 홍수추적(Hydraulic Flood Routing)방법 중 FLDWAV모형을 사용하여 한강변에 위치한 빗물펌프장의 외수위를 모의 하였다. 모형의 모의 결과와 한강흐름의 실측치를 비교 검토하고, 이를 기초로 각 빗물펌프장의 배수문을 가동해야 하는 팔당댐 방류량과 도달시간을 구하고, 하류에 위치한 빗물펌프장의 황해의 조위 영향등을 분석, 운영자가 배수문 개폐시기를 예측하여 빗물펌프장의 운영 자료로 이용과 유수지$\cdot$펌프장 운영체계의 자동화에 기여하고자 한다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.241-248
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• 2008

The objective of sensitivity analyses is to identify critical variables of structural models and how their variability impacts mechanical response results. The sensitivity analyses have been used as significant basis data for practical applications of measuring and reinforcing fragile building structures. This study presents several sensitivity analysis methods for topological optimum designs of linear elastostatic structural systems. Numerical examples for structural analyses and topological optimum modeling demonstrate the reliability of sensitivities formulated in the present study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.1-14
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• 2010

Until now, the evaluation method of spalling depth using Martin et al. (1999)'s linear regression relations has long been known applicable. However, it is not likely that the proposed equation is applicable to the openings other than circular type and mostly overpredict the spalling depth in comparison with actual spalling cases. Moreover, the evaluation method to estimate the spalling width has not been presented yet; it is essential to evaluate the spalling width in addition to the spalling depth, because the shape of the spalled region influences the choice of suitable rock reinforcement. In this study, linear regression equations, in which normalized spalling depth ($d_f/W_D$) and normalized spalling width ($w_f/W_D$) are functions of three spalling evaluation indices, ${\sigma}_1/{\sigma}_c,\;D_{is}(={\sigma}_{max}/{\sigma}_c)$ and ${\sigma}_{dev}/{\sigma}_{cm}$, are established based on in-situ spalling observations and CWFS simulation results. Confidence intervals of 95% using the statistical inference theory are used in verifying the reliability of linear regression equations. Spalling depth ($d_f$) and spalling width ($w_f$) predicted from the proposed linear regression relations, which take three spalling evaluation indices into account, showed reasonable match with in-situ observations by adopting weighting factors considering the degree of variance of linear regression relations.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.19-42
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• 1999

In urban area, there are several major factors to be considered in tunnel design and construction. The first is to predict the magnitude and distribution of ground movements for particular ground conditions and construction procedures. The second is to assess the potential damage to nearby structures in response to the predicted ground movements. The third is to select the measures to be taken if a potential damage is foreseen. This study is concerned primarily with the first and second stages of the problem. Particularly, this paper is focused on the second stage to assess the potential damage to the nearby building with any type of geometries and locations above ground surface. In order to solve this problem, we introduced damage parameters(angular distortion, deflection ratio, maximum building settlements, maximum differential settlements, horizontal strain, etc.), and extended these parameters into 3-dimensional safety assessment. Also, to assess the safety of any walls existing in the building, we developed a 3-dimensional analysis program, and various parametric studies for the nearby building with any type of geometries and locations were presented. In addition to these parametric studies, we compared the results of the proposed techniques with some abroad case records for particular tunnels and adjacent buildings.

• Tunnel and Underground Space
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• v.17 no.5
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• pp.411-427
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• 2007

Reliability in tunnel analysis is necessary to accomplish technically sound design and economical construction. For this, a thorough understanding of the construction procedure including the ground-support interaction has to be obtained. This paper describes a proper modelling technique to simulate the behavior of the steel fiber reinforced shotcrete (SFRS) which maintain the supporting capability in post-failure regime. The additional supporting effect of the steel support was also verified by 3-D analyses and a new load distribution factor were proposed. The use of the plastic moment limit (PML) alone can eliminate the occurrence of the awkwardly high tensile stress in the shotcrete and can successfully model the post-peak ductile behavior of the SFRS. But with this method, moment is limited whenever the stress caused by moment reaches tensile strength of the shotcrete irrespective of the stress by axial force. Therefore, it was necessary to find a more comprehensive method which can reflect the influence of the moment and axial force. This can be accomplished by the proper use of "liner element" which is the built-in model in FLAC. In this model, the peak and residual strength as well as the uniaxial compressive strength of the SFRS can be specified. Analyses were conducted with these two models on the 2-lane road tunnels excavated in class IV and V rock mass and results were compared with the conventional elastic beam model. Results showed that both models can reflect the fracture toughness of the SFRS which could not be accomplished by the elastic beam model.