• 대한토목학회논문집
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• 제32권2A호
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• pp.75-83
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• 2012

본 연구에서는 콘크리트 부유구조체의 구조성능을 향상시키기 위한 부력 프리플랙션 효과에 대한 해석적 연구를 수행하였다. 부력 프리플랙션은 부유구조체를 구성하는 모듈들의 부분적 부력차이에 의해 부유구조체에 프리플랙션 효과가 도입되는 것을 뜻한다. 부력 프리프랙션 효과를 검증하기 위해, 실제 설계에서 도출된 콘크리트 부유구조체 단면을 바탕으로 전체 부유구조체 길이에서 부력 부리플랙션 효과를 발생시키는 변단면 중앙부의 길이 비를 매개변수로 설정한 해석적 연구를 수행하였다. 해석결과는 부력 프리플랙션에 의해 도입되는 콘크리트 부유구조체의 하부 슬래브 응력상태와 부상 변위량에 대해, 이를 부력 프리플랙션과 활하중의 하중단계별로 분석하여 부력 프리플랙션 효과가 콘크리트 부유구조체의 구조성능에 미치는 영향을 분석하였다. 연구결과, 전체 부유구조체 길이에 대한 중앙부 모듈의 길이 비가 작은 경우에도 상대적으로 큰 부력 프리플랙션 효과가 발생되는 것으로 나타났다. 부력 프리플랙션 효과는 중앙부 모듈의 길이 비에 따라 포물선의 형태를 나타내며, 중앙부 모듈의 길이 비 40~60%에서 최대의 효과가 도입되는 것으로 나타났다. 인접한 모듈들의 부력차이를 이용하는 부력 프리플랙션은 원리가 간단하여 적용이 간편하고, 부유구조체의 하부 슬래브에 효율적으로 사전 압축응력을 도입시킬 수 있는 것으로 나타났다. 이는 부유구조체의 하중지지능력 향상을 가져와 콘크리트 부유구조체의 구조성능 향상과 단면높이 슬림화에 기여할 수 있을 것으로 판단된다.

• Steel and Composite Structures
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• 제43권1호
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• pp.67-77
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• 2022

In the current study, ordinary design of Represstessed Pre-Flex (RPF) girder by classical beam theory and numerical model taking buckled shape into consideration were compared with field-survey data to find imperfections on the RPF girder before prestressing and after preflexion. It should be noted that the ordinary design do not consider deformed shape of steel girder in RPF beam. The deformed shapes of steel girder due to the incomplete fabrication that could be caused by self-weight, preflexion misalignment, existence of lateral bracing at mid-span and stiffness of reaction frame were found using a newly developed model which was verified against a deformation survey conducted on actual RPF girder in the field. The final observed deformed shapes of RPF after concrete shrinkage and before prestressing were classified into W, C and Unsymmetric shapes in regard to both survey and analytical results. The deformation survey showed negligible amount of unwanted deformation compared to the large size of the RPF girders. The shallower width of the bottom flange of steel girder caused amount of lateral torsional buckling under self-weight and preflexion thereby affecting the unwanted final overall shape of the RPF girders. However, it was found that the unwanted deformation of RPF girders by fabrication errors even though it is negligible compared to the size of the girder, caused unsymmetrical stress contours in concrete and additional tensile stress and raise some safety issues.

• Journal of Welding and Joining
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• 제22권2호
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• pp.33-37
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• 2004

Since the preflex beam is fabricated by welding, the pre-compressive stresses that should occur over the concrete pier are diminished by the welding residual stresses. For this reason distribution of welding residual stresses must be analyzed accurately and welding residual stresses should be relieved during the fabrication. In this study strain history, displacement of beam and re-distributed welding residual stresses by different loading conditions are measured and compared to choose more appropriate preflex condition.

• 한국산업융합학회 논문집
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• 제7권4호
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• pp.433-441
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• 2004

This paper presents a strategy for the quality assurance of the continuous preflex composite girder bridge through the camber management of the girder during construction. The construction stages which require welding, balanced preflexion loads at the ends, etc. may cause unexpected large deformation to the preflex girder. Furthermore, these defects can be detected by measurements and analyses of the girder behavior which is sometimes time consuming. In the present study, preflex girder's camber data at equally spaced nodes in each construction stage are obtained and analyzed for the quality control of thee span continuous preflex girder composite bridge.

• 수산해양기술연구
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• 제57권2호
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• pp.134-148
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• 2021

During the ichthyoplankton survey around the Chilsan Island (previously known as the biggest spawning ground of the Sciaenidae) in the southwestern sea of Korea from April to June in 2019 using ring nets, we collected a total of 12 individuals belonging to the family Sciaenidae. Using molecular methods, we identified five sciaenid species (Collichthys lucidus, Collichthys niveatus, Johnius grypotus, Nibea albiflora, and Pennahia argentata), and described and compared them on the basis of the preflexion larval stage. C. lucidus was well distinguished by the presence of occipital crests at preflexion stage. Although there were no occipital crests, preflexion larva of C. niveatus was distinguished by the absence of melanophore except for the upper part of the abdominal cavity. J. grypotus and N. albiflora were very similar morphologically, but were distinguished by myomere height (15.22-15.53% in J. grypotus vs. 11.66-12.78% in N. albiflora) in the percentage of notochord length, and eye diameter (32.58-33.37% in J. grypotus vs. 40.32-42.53% in N. albiflora) in the percentage of head length between specimens of similar size (J. grypotus: 3.22-3.23 mm, N. albiflora: 3.04-3.13 mm). P. argentata were distinguished by distribution of ventral caudal melanophore (one row of small spot in P. argentata vs. irregular patches on the central part of caudal in J. grypotus and N. albiflora). Comparative morphological studies using more diverse species must be conducted for more comprehensive understanding of the morphogenesis of Sciaenidae.

• Steel and Composite Structures
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• 제4권5호
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• pp.385-402
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• 2004

Nearly 400 composite railway bridge decks of a new kind belonging to the trough type with U-shaped cross section have been constructed in Belgium over the last fifteen years. The construction of these bridge decks is rather complex with the preflexion of precambered steel girders, the prestressing of a concrete slab and the addition of a 2nd phase concrete. Until now, they have been designed with a classical computation method using a pseudo-elastic analysis with modular ratios. Globally, they perform according to the expectations but variability has been observed between the measured and the computed camber of these bridge decks just after the transfer of prestressing and also at long-term. A statistical analysis of the variability of the relative difference between the measured camber and the computed camber is made for a sample of 36 bridge decks using no less than 10 variables. The most significant variables to explain this variability at prestressing are the ratio between the maximum tensile stress reached in the steel girders during the preflexion and the yield strength and the type of steel girder. For the same sample, the long-term camber under permanent loading is computed by two methods and compared with measurements taken one or two years after the construction. The camber computed by the step-by-step method shows a better agreement with the measured camber than the camber computed by the classical method. The purpose of the paper is to report on the statistical analysis which was used to determine the most significant parameters to consider in the modeling in order to improve the prediction of the behaviour of these composite railway bridge decks.

• 한국발생생물학회지:발생과생식
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• 제24권2호
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• pp.125-133
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• 2020

This study is intended to be used as the basic material for the taxonomic research by observing the stages of skeletal development of Luciogobius grandis larvae compared to the skeletal development patterns of the same fish family of Gobiidae. 3 days after hatching (DAH), the preflexion larvae was 4.01±0.11 mm (n=5) in average total length (TL) and the frontal began to ossify in the skull. 17 DAH, the advanced postflexion larvae was 5.37±0.05 mm (n=5) in average TL the supraoccipital and epiotic were ossified in the cranial bone. 36 DAH, the juvenile was 12.2±0.20 mm (n=5) in average TL and the urohyal was ossified in the hyoid arch. In addition to one hypural bone being ossified, the first, second, third and fourth were combined and were made three bone fragments and then, the bone ossification of all skeletons was completed.

• 한국해양공학회지
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• 제18권2호
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• pp.52-57
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• 2004

Preflex beam is a method of construction designed to hold the pre-compressive stresses over the concrete pier by the preflexion load. During the fabrication of the girder, welding causes residual stresses. The welding residual stresses must be relieved in order to generate the accurate compressive pre-stresses. In this study, to determine the thermal distribution characteristics on the girder by welding, both three-dimensional finite element analysis and two-dimensional finite element analysis, in a quasi-steady state, is carried out. After comparing each result between the three-dimensional analysis and the two-dimensional analysis, finite element analysis is carried out against the actual girder, and the welding thermal distribution characteristic over the preflex beam is analyzed. It is possible to provide the input data for the analysis of the welding residual stresses.

• 한국어류학회지
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• 제31권3호
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• pp.150-158
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• 2019

낙동강 하구역에 서식하는 문절망둑 자치어의 식성을 밝히기 위해 2011년 2월부터 4월까지 RN80 네트를 이용하여 채집하였고, 그 중 260개체를 해부현미경을 이용하여 장내용물 분석을 실시하였다. 분석결과 문절망둑 자치어는 요각류와 유종섬모충류를 주로 섭식하였고, 그 외에도 갯지렁이 유생, 거구목(편형동물), 이매패류 유생, 윤충류, 따개비 유생, 규조류 등을 섭식하였다. 문절망둑 자치어는 시간대별로 다른 섭식강도를 보였는데, 18~19시 사이에 가장 높은 섭식참여율 보였고, 개체당 먹이생물 개체수는 18~01시까지 높은 수준을 유지하였다. 성장에 따른 문절망둑 자치어의 식성변화를 평가하기 위해 발생단계(3단계: 전기, 중기, 후기자어) 별로 먹이생물을 분석한 결과, 전기자어 시기에는 유종섬모충류를 주로 섭식하였고, 중기자어기에는 요각류, 후기자어 시기에는 갯지렁이 유생을 주로 섭식하였다. 문절망둑 자치어의 먹이생물의 평균크기는 성장에 따라 유의하게 증가하였고, 개체당 평균먹이생물 평균 개체수와 평균 부피도 증가하는 경향을 보였다. 먹이생물의 다양성을 나타내는 먹이 섭식 폭 지수는 중기자어 시기까지는 증가하다가 후기자어에 들어 급격히 감소하였다.

• Fisheries and Aquatic Sciences
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• 제18권3호
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• pp.301-309
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• 2015

Chub mackerel, Scomber japonicus, larvae and juveniles were reared from hatching to 35 days after hatching (DAH), and the development of their digestive systems was histologically investigated. The larvae were initially fed on rotifers and Artemia nauplii starting around 19 DAH, and thereafter on Artemia nauplii, fish eggs, and a formulated feed mixture. The primitive digestive system differentiated at 3 DAH; the digestive tract was distinctively divided into the buccopharyngeal cavity, esophagus, stomach, air bladder, intestines, and rectum. The gastric gland and pyloric caeca first appeared at 5 and 7 DAH, respectively. The stomach was divided into cardiac, fundic, and pyloric regions in the preflexion phase. The number of gastric glands and pyloric caeca, as well as the volume of the gastric blind sac increased markedly, with development continuing into the juvenile stage. The precocious development of the digestive system during the larval period might be related to the early appearance of piscivory, which is able to support high growth potential. The organogenesis results obtained for this precocial species represent a useful tool to aid our understanding of the physiological requirements of larvae and juveniles to ensure optimal welfare and growth under aquaculture conditions, which will improve current rearing practices of this scombrid species.