• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.319-332
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• 2004

Due to their high strength to weight ratios and excellent durability, fiber reinforced polymer(FRP) is widely used in construction industries. In this paper, a shape optimum design of FRP bridge decks haying pultruded cellular cross-section is presented. In the problem formulation, an objective function is selected to minimize the volumes. The cross-sectional dimensions and material properties of the deck of FRP bridges are used as the design variables. On the other hand, deflection limits in the design code, material failure criteria, buckling load, minimum height, and stress are selected as the design constraints to enhance the structural performance of FRP decks. In order to efficiently treat the optimization process, the cross-sectional shape of bridge decks is assumed to be a tube shape. The optimization process utilizes an improved Genetic Algorithms incorporating indexing technique. For the structural analysis using a three-dimensional finite element, a commercial package(ABAQUS) is used. Using a computer program coded for this study, an example problem is solved and the results are presented with sensitivity analysis. The bridge consists of a deck width of 12.14m and is supported by five 40m long steel girders spaced at 2.5m. The bridge is designed to carry a standard DB-24 truck loading according to the Standard Specifications for Highway Bridges in Korea. Based on the optimum design, viable cross-sectional dimensions for FRP decks, suitable for pultrusion process are proposed.

• Journal of Korea Water Resources Association
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• v.47 no.12
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• pp.1187-1198
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• 2014

Strong winds and heavy rainfall from tropical cyclones (TCs) that occur in the Northwestern Pacific cause significant human and material damage to the Korean peninsula and East Asia. Hence, it is important to establish early warning systems and conduct preparedness activities in advance of a TC. This study suggests a technique to extract the value of uniform TC-induced rainfall considering the TC track and TC size. To validate our technique, we compare it to existing TC rainfall techniques using the spatial domain. To determine the TC size required for extracting TC-induced rainfall, this research analyzed the mean of TC-induced rainfall by TC size (1973-2012). As a result of this analysis, the maximum amount of mean of TC-induced rainfall was found for a TC with a radius of 700 km. Other techniques have limitations which this new technique addresses; it can extract TC-induced rainfall in each administrative area and minimize systematic biases of other extraction methods. The result of this study can be utilized in the preparation of rainfall forecasts, designing hydraulic structures, and predicting landslide and debris flows using TC-induced rainfall and downpours.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.41-49
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• 2009

Cement concrete pavement has become more common in Korean highway systems. However, as its service period increases, there are some technical problems occurs and no clear solution is available primarily due to the lack of active researches. This research, hence, aims to develop a new mix proportion that may provide better strength and durability with extended service life. Based on a variety of literature reviews, the experimental variables were determined as unit cement content, S/a ratio and W/C ratio. From the experimental works, it is recommended to increase the unit cement content up to 375kg/$m^3$, 400kg/$m^3$ and 425kg/$m^3$. The target slump and air content were set 40mm and 5%, respectively. The maximum size of coarse aggregate was decided to be 25mm because of the easiness of supply in the field. The reduction of W/C ratio was necessarily required and decreased to 0.4 which was proven not to cause any mixing problem with the increased unit cement contents along with polycarbon-based high range water reducing agent. In addition, it was known that the S/a ratio could be reduced to 0.34. The lowered S/a might be possible because of the increased cement paste and hence increased cohesiveness and workability.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.35-43
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• 2016

With the development of construction technology, constructions of dam and levee (dike) as well as the environmental problems are becoming issues. Recently, many countries have tried to develop and used CSG (Cemented Sand and Gravel), which needs fewer requirements than others in aggregates, constructability and ground condition during the dam construction. Mixing up with small amount of cement, CSG is able to increase the strength and proceed accelerated construction without artificial gradation adjustment of riverbed aggregate and crushed rock on construction site. Thus, CSG can minimize environmental damage resulted from quarries mining and reduce cost of construction. Unlike heat of hydration condition that regular concrete usually met, CSG exposes to repeated dry-wet and freezing and thawing environment. Thus, consider the importance of structure of dam or levee, intensive study on the durability of CSG is needed. In this study, freezing and thawing experiment was carried out to evaluate the durability of CSG. In results, the durability factor of CSG is 30~40 or >40 when the amount of cement is $0.4{\sim}0.6kN/m^3$ or $0.8{\sim}1.0kN/m^3$, respectively. The unconfined compressive strength is reduced to 30~50% or 40~70% when the amount of cement is $0.4{\sim}0.6kN/m^3$ or $0.8{\sim}1.0kN/m^3$, respectively. Taken together, the strength and durability of CSG is reliable when the amount of cement is over $0.8kN/m^3$.

• Polymer(Korea)
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• v.35 no.5
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• pp.467-471
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• 2011

PET bottle is manufactured by blow molding the preform, which is molded by injection molding. The neck part of the preform of PET bottle for juice or grain-based beverage is crystallized before blowing to improve heat resistance at the entrance of the bottle. However, residual stress, developed during injection molding of preform, prevents the crystallization. In order to release the residual stress in the preform, the preform is annealed after the injection molding. If the residual stress is reduced by optimizing the injection molding conditions of preform the annealing time would be shortened. In this study, the optimum conditions for minimizing the residual stress and increasing dimensional accuracy of the injection molded preform are suggested through CAE analysis. In order to optimize the molding conditions, minimizing residual stress and shrinkage, computer simulations have been carried out with help of design of experiment scheduling. Injection temperature, initial packing pressure and filling time were selected for control parameters. Residual stress was affected by injection temperature and filling time. Shrinkage was affected by injection temperature. It was found that maximum residual stress, distribution of residual stress and shrinkage were decreased by 22%, 40% and 25%, respectively at an optimum molding condition compared with the results of previous molding condition.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.263-271
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• 2005

HPFRCC(High Performance Fiber Reinforced Cementitious Composite) is a class of FRCCs(Fiber Reinforced Cementitious Composites) that exhibit multiple cracking. Multiple cracking leads to improvement in properties such as ductility, toughness, fracture energy, strain hardening, strain capacity, and deformation capacity under tension, compression, and bending. These improved properties of HPFRCCs have triggered unique and versatile structural applications, including damage reduction, damage tolerance, energy absorption, crack distribution, deformation compatibility, and delamination resistance. These mechanical properties of HPFRCCs become different from the kinds and shapes of used fiber, and it is known that the effective size of fiber in macro crack is different from that in micro crack. This paper reports an experimental findings on the mechanical properties of HPFRCCs reinforced with the micro fiber(PP50, PVA100 and PVA200) and macro fiber(PVA660, SF500). Uniaxial compressive tests and three point bending tests are carried out in order to compare with the mechanical properties of HPFRCCs reinforced with micro fibers or hybrid fibers such as compressive strength, ultimate bending stress, toughness, deformation capacity and crack pattern under bending, etc.,

• Journal of Korean Society of Forest Science
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• v.99 no.4
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• pp.553-558
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• 2010

This study was conducted to clarify the differences in rodents population densities between natural restored and red pine silvicultured forests after forest fire in Samcheok, Gangwon Province, Korea from March to December 2008. One ha size of 3 study plots were set up in each natural restored and silvicultured stand. We trapped the small rodents during 4 consecutive nights every 2 months in each stand. Understory coverage and number of shrub stems were higher in silvicultured stand than in natural restored stand. Coverage of overstory, suboverstory and midstory, number of tree stem, woody seedling stems and dead wood, and amount of coarse woody debris were higher in natural restored stand than in silvicultured stand. Six hundred eighty eight individuals of four species, such as Apodemus agrarius, A. peninsulae, Eothenomys regulus and Tamias sibiricus were captured in our study. Number of captured small rodents were higher in natural restored stand than in silvicultured stand. Also, species compositions were differed in both stands. The captured number of A. agrarius and A. peninsulae were most highest in April and December. E. regulus were shown higher number of captured in April and June, and T. sibiricus were in June and October. Removal of coarse woody debris and silvicultural practice would not be good for the inhabitation of small rodents. For the conservation of small rodents diversity, management of understory and canopy would be needed in forest fired area.

• Restorative Dentistry and Endodontics
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• v.30 no.4
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• pp.335-343
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• 2005

Hemolytic property is a specific feature of bacteria to obtain iron which is essential for its survival in host tissues. Therefore, it is thought to be one of several factors of virulence. The purpose of this study was to investigate the hemolytic properties of Prevotella nigrescens isolated from the teeth diagnosed as pulp necrosis and apical periodontitis under the presence of hemolysin inhibitors such as $NaN_3$ and dithiothreitol. heat, various pH and cultural conditions. The results were as follows; 1. Clinically isolated P. nigrescens strains and standard P. nigrscens ATCC 33563 showed hemolytic activity. 2. P. nigrescens showed higher hemolytic activity against human erythrocytes than sheep or horse erythrocytes. 3. $NaN_3$ and dithiothreitol (DTT) reduced the hemolytic activity of P. nigrescens in a dose dependent manner (p<0.05). 4. Optimal pH for the maximum hemolytic activity of P. nigrescens was 4.0 and the hemolysin was stable under the $50^{\circ}C$, but the hemolytic activity was significantly decreased at $95^{\circ}C$. 5. P. nigrescens cultured in $10\%\;CO_2$ condition showed higher hemolytic activity than the bacteria cultured in the anaerobic condition.

• Journal of Korea Water Resources Association
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• v.40 no.1 s.174
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• pp.11-24
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• 2007

There exist various difficulties in runoff analysis due to many ungauged basins in Korea and the runoff phenomena is also more and more complicated by the change of geologic characteristics due to the urbanization. So, we use GIS technique which is widely used in hydrologic field and cell runoff concept for the fast and effective runoff simulation. This study uses the observations of 6 stage stations in Wi-Cheon watershed and simulates the watershed parameters by using WMS model. We construct DEM by the grids which are consisted based on the criteria of minimum area according to land use. The cell runoff is estimated by an average weighted method using mean annual streamflow and mean maximum daily streamflow obtained from six stage stations. The runoff ratio at arbitrary site is estimated by conducting the direction analysis of streamflow and by removing sinkhole. We compare the simulated and observed runoffs and know that the simulated runoff shows the valid results. So, we could use the geographical information and cell runoff concept for more fast and effective runoff simulation studies.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.371-371
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• 2019

우리나라는 홍수기(6~9월)에 집중되는 기상패턴과 하천 중하류부에 발달된 도시의 개발특성으로 인하여 가장 중요한 자연재해 중 하나로 홍수 및 도시침수가 거론되고 있다. 과거 집중호우로 침수 피해가 발생한 사례를 살펴보면, 피해가 발생하는 지역은 지방하천 및 소하천을 중심으로 형성된 도시지역이다. 중앙 지방 정부는 수차례 침수 피해를 겪으며 사후관리가 아닌 재난예방 및 사전관리 등의 방안 마련을 강조하고 있다. 하지만 기후변화에 의한 기상의 불확실성으로 치수 중심의 물관리 및 중 소하천의 하천 특성으로 여전히 홍수 발생에 대비할 수 있는 골든타임 확보 등에 어려움을 겪고 있다. 이러한 어려움을 극복하기 위해 사전 예방적 차원에서의 홍수대응 방안으로 중 소하천을 담당하는 지자체 중심의 홍수피해 저감 방안이 필요하다. 본 연구에서는 A 지자체를 대상으로 모니터링 대상 경계를 설정하여 우량 알람 기준을 예비알람, 주요 관측지점에 대해 강우에 따른 수위 상승 정도를 홍수대응 기준인 직접알람과 연계함으로써 예방적 재난대응 체계를 구축하였다. 모니터링 대상 지역은 해당 지자체를 포함하면서 유역 개념을 적용하여 만경강유역 전체로 설정하였다. 만경강 유역 내 유관기관(지자체, 환경부, K-water, 기상청 등)이 관할하는 우량국(41개소) 및 수위국(28개소), 저수용량이 30만톤 이상이 되는 농어촌공사 저수지(7개소)를 고려하여 홍수분석 모형(COSFIM)을 구축하였다. 해당 모형은 2018년 8월 호우사상에 대해 주요 수위관측 지점에서 $R^2$가 0.8 이상의 우수한 검증 결과를 보였다. 구축된 모형을 통해 예상강우량별 하천 내 수위지점별 최고수위, 최대유량, 도달시간 등 예상 조견표를 제시하여 호우 발생시 지자체 담당자가 참고할 수 있도록 제시하였다. 또한 수위지점별 홍수대응 기준은 평시, 관심, 주의, 경계, 심각 단계로 구분하여 담당자가 수위별 위험 정도를 인지할 수 있도록 지점별 도달되는 수위의 위험 정보를 알람기준으로 제시하였다. 홍수분석 모형은 상류에 위치한 주요시설물의 운영현황을 연계하고 있어 실제 강우 발생 시 기상예보를 고려하여 하천 내 수위관측 지점별 수위 상승 정도를 예상함으로써 사전에 홍수에 대비할 수 있는 단계별 시간 확보에 활용 가능하다. 향후 홍수대응기준은 하천 환경 변화를 반영하여 지속적인 보완이 필요하며 유관기관과의 수문자료 공유체계 확대로 예방적 차원의 홍수 대응 체계가 구축되어야 할 것이다.