• International Journal of Highway Engineering
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• v.6 no.2 s.20
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• pp.37-45
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• 2004

The asphalt concrete pavement takes various advantages of better riding quality, serviceability and easier maintenance. At the same time, it addresses a weak point of the premature failures due to rapid increasement of traffic volume, heavy vehicles and high temperature in summer. It increases the expenditure of maintenance and repair. In order to improve the performance of asphalt pavement avoiding this premature failure, the use reinforcements with geosynthetics have been considered. Geosynthetics are known as an effective reinforcement to restrain fatigue and reflective cracks in asphalt pavements. In this study, a comprehensive parametric study is conducted to capture the efficiency of geosynthetic-reinforcements using viscoelastic properties of the asphalt concrete(AC) layer. The investigated parameters were reinforcement location, AC layer thickness, temperature distribution across the AC layer and modulus of AC and base layer. As a result of observations, that reinforced asphalt concrete could be used effectively for improving resistance against fatigue cracks and permanent deformation. Especially, when a geogrid was placed at the interface between the asphaltic base and the subbase, tensile stress in the horizontal direction was significantly reduced.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.391-402
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• 1994

One of the most important design concept for reinforced concrete structures is to achieve a ductile failure mode, and also moment redistribution for economic design is possible in case that adequate ductility is provided. Flexural ductility index is, therefore, used as a reference for possibility of moment redistribution as well as for prediction of flexural behavior of designed R.C. structures. Ductility index equations, however, provide approximate values due to the linear concrete compressive stress assumption at the tension steel yielding state. Theoretically more exact ductility index is calculated by a numerical analysis with the realistic stress-strain curves for concrete and steel to be compared with the result from tire ductility index equations. Variation of ductility index for the selected variables and the reasonable maximum tension steel ratio for doubly reinforced section are investigated. A moment-curvature curve model is also proposed for future research on moment redistribution.

• Land and Housing Review
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• v.7 no.4
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• pp.261-269
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• 2016

Pipe-roof method is one of the mostly used method to prevent the ground subsidence during the tunnel construction. As pipe-roof method has made technical advancement and performance improvement, it suggested to utilize pipe-roof to a permanent support system rather than a temporal pre-reinforcing method. Therefore, in this study, pipe-roof method is numerically simulated using finite element method to evaluate effects of pipe-roof on behavior of ground and structure. Analyses are performed considering two major conditions that are with and without the application of pipe-roof and the shape of tunnel cross section. The results are presented with respect to variation of settlement and vertical stress distribution. Based on this results, it is found that ground settlement above the shallow tunnel can be considerably reduced by application of pipe-roof system. Also, the shape of tunnel cross section can influence on the mechanical behavior of ground and structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.81-84
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• 2008

The equation, specified in current bridge design code, for calculating the confining transverse reinforcement amount of RC bridge columns has been made to provide additional load-carrying strength for concentrically loaded columns equal to or slightly greater than the strength lost when the cover concrete spalls off. However, this equation does not directly consider ductile behavior, which is an important factor for the seismic behavior of bridge columns. Consequently, if the section area is relatively small or if the section area ratio becomes excessively large due to the concrete cover thickness increased for durability, too large an amount of transverse reinforcement, which could deteriorate the constructability and economy of piers, will be required. This study intends to analyze what effects the concrete cover thickness has on the equation for determining the confining transverse reinforcement amount.

• Journal of Life Science
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• v.18 no.9
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• pp.1225-1229
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• 2008

A total of 10 polymorphic microsatellite markers on bovine chromosome 5 were used for allelic association tests with phenotypic characteristics in Hanwoo. The data analyzed in this study were collected from 326 steers. Chi-square tests were performed to compare the frequencies of individual alleles between the high and the low breeding value groups. The following breeding values were analyzed for QTL effects. The frequency of allele 239 of DIK2828 showed a significant difference between the high and the low breeding value groups in the breeding value of marbling score (MSBV). The allele 279 of BMC1009 was found to show significant differences in allelic distribution for the breeding value of cold carcass weight (CWBV) and the breeding value of backfat thickness (BFBV) and allele 285 showed significant differences in allelic distribution for CWBV, BFBV, and MSBV. The allele 200 of DIK4329 showed significant differences in allelic distributions for the breeding values of longissimus muscle area (LMABV) and BFBV. In this study, we identified the QTL for carcass traits at around 20 (DIK2828), 41 (BMC1009) and 95 (DIK4329) cM in chromosome 5. The results provided a useful reference for further positional candidate gene research and marker-assisted selection for fat metabolism and carcass traits.

• Journal of Korean society of Dental Hygiene
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• v.21 no.6
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• pp.695-701
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• 2021

Objectives: This study aimed to determine the effect of COVID-19-induced household economic deterioration on gingival pain and bleeding. Methods: Data from the 16th Adolescent Health Behavior Survey 2020 were used. A total of 57,925 adolescents were included in this cross-sectional study. We evaluated the worsening of the COVID-19-induced household economic situation, gingival pain, and bleeding. All surveys were assessed in a subjective non-face-to-face online interview. Data were analyzed using descriptive statistics, chi-squared tests, and logistic regression. Results: The overall prevalence of gingival pain and bleeding symptoms in the study population was 19.2%. People with COVID-19 were more likely to suffer from gingival pain and gingival bleeding than those who did not have economic deterioration due to COVID-19. There was no economic deterioration due to COVID-19 (aOR=1.048, 95% CI=1.034-1.227) and worsened very much (aOR=1.358, 95% CI=1.164-1.585). Conclusions: There were more cases of gingival pain and gingival bleeding, which are early symptoms of periodontal disease, in patients with COVID-19 compared to cases without deterioration of the household economic situation due to COVID-19. It is necessary to measure and study gingival bleeding objectively rather than relying on self-reports.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.10a
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• pp.96-101
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• 1991

프리스트레스트 콘크리트 교량은 콘크리트와 PS 강재의 역학적 장점들을 십분 활용하여 경제적인 단면 구성이 가능한 반면, 서로 다른 두 재료의 복합적인 특성들 즉, 콘크리트의 크리이프 (creep), 건조수축 (shrinkage)과 PS 강재의 이완 (relaxation) 등과 같이 시간에 따라 변화하는 인자들로 인하여 복잡한 구조적 거동을 보여 해석상 어려움이 따른다. 이와같은 복합거동은 시공순서와 시공방법에 의해 시공중의 구조계와 지지조건 등이 변화하는 경우에는 더욱 복잡한 양상을 띄게 된다. 뿐만 아니라 박스 거더와 같은 박벽요소에서는 일반적인 보요소(beam element)로는 나타낼 수 없는 ？(warping)을 무시할 수 없으므로 ？ 자유도를 구현할 수 있는 특수한 기능의 구조해석용 프로그램의 개발이 절실히 요망된다. 그리고 시공단계별로 출력되는 많은 양의 수치결과들을 설계와 시공실무자에 지향된 형태로 조합, 변형시켜 그래픽 화면상에 나타내는 후처리 프로그램(Post-processor) 기능도 구조해석용 프로그램의 개발 못지않게 중요하다. 본 연구의 목적은 삼성종합건설과 서울대 토목공학과가 공동으로 ？(warping) 자유도를 포함한 7개의 자유도를 갖는 3차원 보요소를 사용하여 PS 콘크리트의 재료적 특성인 크리이프와 건조수축, 그리고 강재의 이완(relaxation)을 포함한 프리스트레싱력의 손실을 고려할 수 있고 시공 단계별 구조계의 변화 및 지지조건들의 다양한 변화를 효율적으로 모사할 수 있는 프로그램의 개발에 있다.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.84-84
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• 2011

터널화재의 위험요소에 대한 해석을 위해서는 실제 상황을 재현한 실대형 실험이 가장 유용하겠지만 현실적으로 시간적, 공간적, 경제적인 제약이 따르기 때문에 CFD Modeling 기술의 이용 및 검증이 필요하고, 실제 상황에 가까운 현상의 재현을 위해서는 시뮬레이션의 정확도에 대한 향상이 필수적이다. 또한, CFD Modeling을 터널화재에 적용할 때 시뮬레이션의 질에 영향을 미칠 수 있는 요소들에 대한 결정이 선행되어야 한다. 우선, 터널의 기하학적 구조와 경계조건의 확립이 필요한데 필요한 정보를 얻기 위해서 어느정도 길이의 터널이 적절한지에 대해 생각할 필요가 있으며, 단면변화에 대한 결정을 통해 모델링을 수행하여야 한다. 모델링 작업이 선행된 후에 화재의 위치, 성장률, 최대 크기, 환기시스템 사항 등의 고려가 필요한데 이러한 조건들은 CFD Modeling의 결과에 직접적인 영향을 주기 때문에 충분한 사전조사가 이루어져야 하고, 각 사항들의 변수를 고려하여 다양한 화재시나리오의 도출이 가능할 수 있다. 마지막으로, 화재에서 발생된 열중 약 30%가 복사에 의해 주위 벽으로 전달될 수 있고 열은 연기가 가득찬 영역내에서 재분배될 수 있는데, 열전달 및 연기의 유동 등에 관한 자료를 기초로 화재현상에 대한 분석이 가능하다. 이러한 과정들을 통해 실제 상황에 가까운 설계화재 시나리오를 예측할 수 있다. 본 연구에서는 우리나라 최장대터널인 죽령터널에 대해 합리적인 가정을 통한 설계화재 시나리오를 기초로 화재시뮬레이션은 FDS(Fire Dynamics Simulator) 프로그램을 사용하여 화재 및 연기의 이동 양상을 분석하고, 피난시뮬레이션은 SIMULEX 프로그램을 사용하여 피난시간을 예측 함으로써 터널화재의 CFD Modeling에 의한 피난안전성을 검토하고자 한다.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.185-188
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• 2008

Flat plate system has structural weakness such as punching shear. Punching shear resistance can be increase by using a lager column section and effective depth, higer concrete compressive strength, and more flexural reinforcement ratio. But using a shear reinforcement is most economical, enable, workable solution in flat plate. The slab with thickness smaller than 250mm can not perform effectively due to insufficient development length of shear reinforcement in the slab. In case of proposed reinforcements, since the shear reinforcements were installed between the top bar and the bottom bar, shear elements generated slip failure before they reached yield. strength. effect of anchorage strength were effective anchorage length, concrete strength, diameter of shear element and anchorage detail. considering effect of slab thickness and concrete strength, formula of K factor propose in thin flat plate slab. by considering effect of anchorage length and concrete strength, strength of shear reinforcement will be computed correctly in thin flat plate slab.

• Journal of the Korean Society of Radiology
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• v.12 no.2
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• pp.173-178
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• 2018

Lead is a very useful material in shielding radiation in hospitals. But lead is toxic. Therefore, there are many studies on substitutable materials, Typically, there are many studies using tungsten. In this study, we investigated the physical properties of lead and tungsten and the Half value layer. As a result, lead having higher atomic number showed higher cross - sectional area than tungsten. But, at the same size, the electron density of tungsten with a high density is about 1.7 times higher than that of lead. In MCNPX simulation, the shielding effect of tungsten is about 1.4 times higher than that of lead, It was confirmed that tungsten had better shielding efficiency than lead. However, considering the economic aspect, tungsten is a rare metal, which is about 25 times more expensive than lead, which is considered to be inappropriate as an alternative to lead.