• Steel and Composite Structures
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• 제20권2호
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• pp.357-378
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• 2016

The progressive collapse phenomenon in structures has been interested by civil engineers and the building standards organizations. This is particularly true for the tall and special buildings ever since local collapse of the Ronan Point tower in UK in 1968. When initial or secondary defects of main load carrying elements, overloads or unpredicted loads occur in the structure, a local collapse may be arise that could be distributed through entire structure and cause global collapse. One is not able to prevent the reason of failure as well as the prevention of propagation of the collapse. Also, one is not able to predict the start point of collapse. Therefore we should generalize design guides to whole or the part of structure based on the risk analysis and use of load carrying elements removal scenario. There are some new guides and criteria for elements and connections to be designed to resist progressive collapse. In this paper, codes and recommendations by various researchers are presented, classified and compared for steel structures. Two current design methods are described in this paper and some retrofitting methods are summarized. Finally a steel building with special moment resistant frame is analyzed as a case study based on two standards guidelines. This includes consideration of codes recommendations. It is shown that progressive collapse potential of the building depends on the removal scenario selection and type of analysis. Different results are obtained based on two guidelines.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.93-93
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• 2017

To develop rice cultivars with increased biomass and grain yield, superior lodging resistance is an essential trait. The new breeding approach can be adopted for the improvement of stem lodging resistance by enhancing culm strength. The resistance to breaking type lodging is attributed to bending moment of basal culm (M), which is composed of the section modulus (SM) and bending stress (BS). The resistance to the bending type lodging is attributed to flexural rigidity (FR) of stem, which is composed of the secondary moment of inertia (SMI) and Young's modulus (YM). Starch and cell wall components such as cellulose, hemicellulose and lignin also play a significant role in physical strength of culm, and thus affect lodging. Leaf Star has a superior lodging resistance due to its thick and stiff culm because of its high M and FR compared with Koshihikari. Furthermore, Leaf Star contains high densities of hemicellulose, cellulose and low lignin density in culm compared with Koshihikari. In this study, we performed QTL analysis for these traits associated with culm strength, using 94 recombinant inbred lines (RILs, $F_8$), derived from a cross between Leaf Star and Koshihikari. The SM in the RILs showed a continuous distribution. QTLs for SM were detected on chrs.2, 3 and 10. Leaf Star alleles increased SM on chrs. 2 and 3, but Koshihikari allele increased on chr.10. These QTLs overlapped with those QTLs identified using backcrossed inbred line derived from a cross between Chugoku 117 and Koshihikari, the parents of Leaf Star. The FR in Leaf Star was higher than that in Koshihikari due to the larger SMI and YM. 3 QTLs for SMI were detected on chrs.2, 3 and 10. Leaf Star alleles increased SMI on chrs.2 and 3, and Koshihikari alleles increased on chr.10. One QTL on chr.3 and two QTLs on chr.5 for hollocelulose content were detected with Leaf Star alleles contribution. Moreover, two QTLs were detected for hemicellulose density on chrs.3 and 5. Leaf Star allele increased hemicellulose density on chr.5, and Koshihikari allele increased on chr.3. Furthermore, two QTLs for cellulose density were detected on chr.5, and one QTL on chr.2. For starch content, one QTL on chr.3 and two QTLs on chr.5 with Leaf Star alleles contribution were detected. TULK-6 carrying a chromosome segment of Leaf Star on chr.5 in the Koshihikari genetic background showed higher densities of starch and hemicellulose than those in Koshihikari. These results suggest that the detected QTLs for culm strength could be utilized for the improvement of lodging resistance in rice by marker-assisted selection.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.133-133
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• 2017

Lodging is one of the important constraints in rice production. The lodging destroys the canopy structure, and sharply reduces the capacity of photosynthetic rate and dry matter production. In cereal crops, stem lodging can be classified into two types: stem breaking type and stem bending type. To improve stem lodging resistance, it is important to reveal strong culm traits of superior lodging resistant varieties. There are large varietal differences in parameters associated with the bending moment at breaking (M) and flexural rigidity (FR). The indica variety Takanari possesses large M due to its large section modulus (SM) despite of its small bending stress (BS), while Takanari also has large FR due to its large secondary moment of inertia (SMI) and Young's modulus (YM). To identify quantitative trait loci (QTLs) and the corresponding genes associated with the parameters for M ($=SM{\times}BS$) and FR ($=SM{\times}YM$) should enable to develop lodging resistant varieties, efficiently. In order to identify QTLs for cell wall materials such as cellulose, hemicellulose and lignin associated with BS and YM, a set of Chromosome Segment of Substitution Lines (CSSLs) consisted of 37 lines with chromosome segments of Koshihikari in the genetic background of Takanari were used. Takanari had large M and small BS as compared with Koshihikari. The QTLs for BS were estimated on chromosomes 3, 5, 6, 8, 9, 10, 11 and 12. Koshihikari alleles increased BS in these QTLs. Takanari had a large FR due to its large SMI and YM as compared with Koshihikari. The YM was increased by substitution of the Koshihikari chromosomal segments on chromosomes 2, 10 and 11. Other QTLs estimated on chromosomes 7 and 12 that Koshihikari alleles contributed to the decrease of YM. For lignin, only one major QTL for lignin density was detected on chromosome 11. Hollocellulose densities were increased by the substitution of Koshihikari segments on chromosomes 5 and 11. On the other hand, these were decreased on chromosomes 1 and 3 by substitution of Koshihikari segments. QTLs for cellulose density were estimated on chromosomes 1, 3 and 5 by substitution of Koshihikari segments. For hemicellulose, QTL on chromosome 3 showed that hemicellulose density decreased by the substitution of Koshihikari segment. However, hemicellulose densities on chromosomes 5, 8 and 11 showed the opposite effects. The QTLs for hemicellulose, cellulose, and hollocelulose densities identified on chromosome 5 overlapped with that for bending stress, indicating the positive effect of Koshihikari segment on increasing bending stress. These results suggest that some QTLs for the densities of cell wall materials contribute to increasing bending stress and Young's modulus, and could be utilized to improve the lodging resistance for both types of breaking and bending in rice varieties.

• 융합보안논문지
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• 제16권1호
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• pp.13-21
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• 2016

민간경비가 도입된 지 60여년이 지난 현재 민간경비와 관련된 국가공인 자격으로는 경비지도사와 신변보호사 자격제도가 있다. 본 연구에서는 2013년도부터 국가공인자격으로 실시 되어오고 있는 신변보호사 자격검정 사항 중에서 2차 실기시험제도의 문제점에 대하여 논의하였다. 현행 신변보호사 자격검정은 1차 학과시험과 2차 실기시험으로 분류하여 실시하고 있는 가운데 신변보호사의 자격 검증을 엄격히 하여 응시자에 대한 만족도와 대중의 신뢰도를 높여가야할 시기에 봉착하였다고 판단되어 신변보호사 실기시험제도의 문제점에 대한 개선방안을 다음과 같이 제시하였다. 첫째, 현재 단순하고 비교적 기초적인 실기시험 평가 항목의 난이도를 다양화 하여 구분하는 것이 필요하다. 둘째, 현재 실기시험 평가기술은 합기도의 기술분야에 치우쳐 있다고 볼 수 있어 각 무도분야의 실질적 활용가능성이 높은 기술을 복합적으로 접목시켜 다양화 하는 것이 필요하다. 셋째, 현재 일반화 되지 않은 실기시험 평가위원제도를 전문화된 실기시험 평가위원으로 선정할 수 있도록 기준안 마련이 필요하다. 넷째, 현재 실기시험 평가위원과 응시자의 관계에 있어 지인인 경우가 많아 객관성확보차원에서 제척제도를 신설하는 것이 필요하다. 이와 같이 신변보호사 자격검정 실기시험제도의 전문성을 고양시켜나가기 위해 관련기관의 제도적 개선이 시급히 이루어져야 할 것이다.

• 한국전산구조공학회논문집
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• 제23권3호
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• pp.303-314
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• 2010

이 논문에서는 외부강선으로 긴장된 PSC 거더의 비선형 해석방법에 대한 연구를 수행하였다. 외부강선은 정착부와 편향부에서만 부재와 일체로 거동을 하고 정착부-편향부, 편향부-편향부 사이에서 독립적인 거동을 보이는 특성으로 인해 구조물의 처짐이 증가할 경우 부재와 외부강선의 편심량이 감소하여 모멘트가 변화하는 2차 효과(secondary effect)가 발생한다. 또한 편향부에서 외부강선의 인장력 차이로 인해 슬립(slip)이 발생할 경우 외부강선의 인장력이 재분배되어 복잡한 비선형 거동을 보이게 된다. 이 논문에서는 정착부-편향부, 편향부-편향부 사이의 외부강선을 여러 개의 곡선요소로 모사하고, 편향부에서의 마찰력과 driving force(미끄러지는 힘)의 평형관계를 이용하여 외부강선의 인장력을 재분배함으로써 편향부에서의 슬립효과를 고려하였다. 이 논문에서 제시한 외부강선의 유한요소모델과 해석방법을 저자들이 개발한 시공단계를 고려한 PSC 뼈대의 비선형 해석 프로그램에 통합하고, 외부강선으로 긴장된 PSC 보의 해석에 적용하여 외부강선에 대한 유한요소모델 및 해석방법의 정당성과 적용성을 확인하였다. 또한 편향부의 수와 편향부에서의 마찰계수에 따른 극한거동을 검토해본 결과, 편향부의 수가 증가할수록 PSC 보의 항복하중과 극한하중은 증가하였으며, 편향부에서의 마찰계수에 따른 극한거동은 외부강선과 편향부 사이의 마찰력으로 인해 부재에 전달되는 모멘트의 영향에 따라 마찰계수가 적정한 값일 경우에 극한내력이 최대치를 보이는 것을 확인하였다.

• 한국산학기술학회논문지
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• 제20권5호
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• pp.569-576
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• 2019

PSC-Edge 거더 라멘교는 Edge 거더에 긴장력을 도입하고 정모멘트를 감소시켜 저형고와 장경간화가 가능한 교량이다. 본 교량은 가설벤트가 상부슬래브의 하부에 지지되고 Edge 거더부에 2차 강연선이 긴장된 후 거더 외측 면에 $45^{\circ}$방향의 사인장 균열이 발생하였다. 프리스트레스 정착부의 응력분포 및 파열균열의 양상에 관한 연구가 활발히 진행되었지만 기존 연구 결과는 본 구조물의 실제 형상과 경계조건이 상이하여 명백한 원인분석이 어려운 실정이다. 따라서 본 논문에서는 가설벤트의 경계조건을 추가로 고려된 3D Frame 해석을 수행하였으나 Edge 거더부에서 최대 압축응력이 발생하여 균열을 원인을 규명하기에는 한계가 있었다. 따라서 LUSAS 16.1을 사용한 3D Solid 해석을 수행하였으며 그 결과 Edge 거더의 하부와 상부슬래브의 경계부분에서 최대 주인장응력이 발생하였다. 최대 주인장응력과 방향여현을 사용하여 둔각부 Edge 거더 외측면의 소요 철근량을 분석한 결과 사용 철근량이 부족한 것으로 분석되었다. 따라서 추가 시공된 교량은 기존 교량보다 정착부의 철근량과 철근보강 범위를 확장시켰다. 그 결과 Edge 거더부의 균열은 더 이상 발생하지 않는 것으로 관찰되었다. 이와 유사한 PSC-Edge 거더 형식의 교량을 설계 및 시공할 때 본문에서 제안한 해석 및 보강방법을 적용하면 시공 중 발생하는 Edge 거더 외측면의 균열을 충분히 제어할 수 있을 것으로 기대된다.

• Structural Engineering and Mechanics
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• 제52권6호
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• pp.1069-1084
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• 2014

The long-term performance of plates resting on viscoelastic foundations is a major concern in the analysis of soil-structure interaction. As a powerful mathematical tool, fractional calculus may address these plate-on-foundation problems. In this paper, a fractionalized Zener model is proposed to study the time-dependent behavior of a uniformly loaded rectangular thin foundation plate. By use of the viscoelastic-elastic correspondence principle and the Laplace transforms, the analytical solutions were obtained in terms of the Mittag-Leffler function. Through the analysis of a numerical example, the calculated plate deflection, bending moment and foundation reaction were compared to those from ideal elastic and standard viscoelastic models. It is found that the upper and lower bound solutions of the plate response estimated by the proposed model can be determined using the elastic model. Based on a parametric study, the impacts of model parameters on the long-term performance of a foundation plate were systematically investigated. The results show that the two spring stiffnesses govern the upper and lower bound solutions of the plate response. By varying the values of the fractional differential order and the coefficient of viscosity, the time-dependent behavior of a foundation plate can be accurately captured. The fractional differential order seems to be dependent on the mechanical properties of the ground soil. A sandy foundation will have a small fractional differential order while in order to simulate the creeping of clay foundation, a larger fractional differential order value is needed. The fractionalized Zener model is capable of accounting for the primary and secondary consolidation processes of the foundation soil and can be used to predict the plate performance over many decades of time.

• 한국전산구조공학회논문집
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• 제29권5호
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• pp.413-419
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• 2016

지진시 사회 인프라시설물의 피해는 시설물 자체의 피해보다 사회 전반에 걸친 2차 피해를 야기한다. 그 중, 지하 공동구 구조물은 통신, 가스, 전기 등 사회의 라이프라인에 해당하여 지진에 대한 취약성을 정확히 평가하여야 할 필요가 있다. 따라서, 본 연구에서는 지하 공동구의 지진 발생 지반가속도에 따른 파괴가능성을 평가하였다. 평가를 위한 입력지반운동은 해외 실측 지진데이터와 한반도에서 발생가능한 인공지진파를 차용하였으며, 지진해석 방법은 응답변위법과 시간이력해석법을 사용하였다. 파괴여부를 판별하는 한계상태는 휨모멘트와 전단 파괴를 바탕으로 하였다. 취약도 함수 도출을 위한 방법은 최우도법이 사용되었으며, 그 분포함수는 대수정규분포로 가정하였다. 이는 지진시 지하 공동구 시설물의 피해 평가는 물론 지하 공동구 시설물의 내진설계를 위한 기초자료로 활용될 수 있다.

• 한국유체기계학회 논문집
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• 제10권6호
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• pp.32-37
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• 2007

Aerodynamic forces and moments have been used to control rocket propelled vehicles. If control is required at very low speed, Those systems only provide a limited capability because aerodynamic control force is proportional to the air density and low dynamic pressure. But thrust vector control(TVC) can overcome the disadvantages. TVC is the method which generates the side force and roll moment by controlling exhausted gas directly in a rocket nozzle. TVC is classified by mechanical and fluid dynamic methods. Mechanical methods can change the flow direction by several objects installed in a rocket nozzle exhaust such as tapered ramp tabs and jet vane. Fluid dynamic methods control the flight direction with the injection of secondary gaseous flows into the rocket nozzle. The tapered ramp tabs of mechanical methods are used in this paper. They installed at the rear in the rocket nozzle could be freely moved along axial and radial direction on the mounting ring to provide the mass flow rate which is injected from the rocket nozzle. In this paper, the conceptual design and the study on the tapered ramp tabs of the thurst vector control has been carried out using the supersonic cold flow system and schlieren system. This paper provides the thrust spoilage, three directional forces and moments and distribution of surface pressure on the region enclosed by the tapered ramp tabs.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.95-95
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• 2017

Lodging is a serious issue in rice production, because it drastically decreases the biomass production and grain yield. Since the Green Revolution, the lodging resistance has been increased by lowering the moment of above-ground parts due to the short culm by the semi-dwarf gene sd1. However, it has been pointed out that sd1 alone has suppressive effects for biomass production and yield. To increase rice yield, the long-culm and large panicle type varieties with a superior lodging resistance need to be developed. To improve the lodging resistance and yield of these type varieties, it would be effective to identify novel alleles for these traits underlying natural variations in rice and to pyramid these alleles to a single rice variety. In order to perform this strategy, we have developed new rice lines derived from crosses among varieties with superior alleles. At first, TULT-gh-5-5 was selected from a cross between strong culm and high biomass variety Leaf Star and high-yielding variety Takanari, and TUAT-32HB was selected from a cross between high-yielding variety Akenohoshi and Takanari. Then, we developed the super thick-culm and super grain-bearing line, LTAT-29 derived from a cross between TULT-gh-5-5 and TUAT-32HB. In the current study, to identify the QTLs and genes relating to the strong culm and the high yield of LTAT-29, we performed QTL analysis using SNPs markers with $F_2$ population derived from a cross between LTAT-29 and Takanari. LTAT-29 has never lodged throughout the growth period despite it had long culms and heavy panicles. LTAT-29 had a larger outer diameter of the culm and twice the size of the section modulus than Takanari. As a result, the bending moment at breaking of LTAT-29 was significantly larger than that of Takanari. Brown rice yield of LTAT-29 was $9.2t\;ha^{-1}$ about 10% higher than that of Takanari due to the larger number of spikelets per panicle. LTAT-29 had a greater number of secondary branches per panicle. In the $F_2$ population between LTAT-29 and Takanari, we found continuous frequency distributions in the section modulus and the spikelet number per panicle. Two QTLs increased the section modulus by the alleles of LTAT-29 were detected on Chr.1L and Chr.2L. One QTL increased the spikelet number per panicle of Takanari by the allele of LTAT-29 was detected on Chr.1L, and two QTLs increased the number of secondary branches per panicle by the alleles of LTAT-29 were detected on Chr.1L and Chr.4L. It was found that the alleles of these QTLs were the japonica type originated from Leaf Star or Akenohoshi. The novel QTLs for the traits related to super thick-culm and super grain-bearing and their combinations could be utilized for improving the lodging resistance and yield in rice varieties.