• Steel and Composite Structures
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• 제21권5호
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• pp.1157-1182
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• 2016

A newly puzzle shape of crestbond rib shear connector is a type of ductile perfobond rib shear connector. This shear connector has some advantages, including relatively easy rebar installation and cutting, as well as the higher shear resistance strength. Thus, this study proposed a newly puzzle shape of crestbond rib with a "${\mho}$" shape, and its shear resistance behaviors and shear strengths were examined using push-out tests. Five main parameters were considered in the push-out specimens to evaluate the effects of shear resistance parameters such as the dimensions of the crestbond rib, transverse rebars in the crestbond dowel, concrete strength, rebar strength, and dowel action on the shear strength. The shear loading test results were used to compare the changes in the shear behaviors, failure modes, and shear strengths. It was found that the concrete strength and number of transverse rebars in the crestbond rib were significantly related to its shear resistance. After the initial bearing resistance behavior of the concrete dowel, a relative slip occurred in all the specimens. However, its rigid behavior to shear loading decreased the ductility of the shear connection. The cross-sectional area of the crestbond rib was also shown to have a minor effect on the shear resistance of the crestbond rib shear connector. The failure mechanism of the crestbond rib shear connector was complex, and included compression, shear, and tension. As a failure mode, a crack was initiated in the middle of the concrete slab in a vertical direction, and propagated with increasing shear load. Then, horizontal cracks occurred and propagated to the front and rear faces of the specimens. Based on the results of this study, a design shear strength equation was proposed and compared with previously suggested equations.

• 한국정밀공학회지
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• 제17권1호
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• pp.209-215
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• 2000

Precision forging technology that can control flow velocity of workpiece have been developed to minimize the amounts of machining. To get the uniform rib length, flow velocity distribution is needed to be estimated and controlled. Computer-aided design is known for very effective to estimate the deformation behavior and design the die for controlling the flow velocity. In this study, die design to control the deformation velocity are investigated using the DEFORM-2D about rib-web shape parts. Also we can get uniform rib length by enforcing the back pressure at end section of rib. The applied load of back pressure farming is lower than that of conventional forging. These results are analysed and confirmed by the experiment.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1351-1359
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• 2003

This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.627-630
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• 2003

This work presents a numerical procedure to optimize the shape of three-dimensional channel with angled ribs mounted on one of the walls to enhance turbulent heat transfer. The response surface method is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. SST turbulence model is used as a turbulence closure. The width-to-height ratio of the rib, rib height-to-channel height ratio, pitch-to-rib height ratio and attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with weighting factor. D-optimal experimental design method is used to determine the data points. Optimum shapes of the channel have been obtained for the weighting factors in the range from 0.0 to 1.0.

• 한국구조물진단유지관리공학회 논문집
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• 제18권2호
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• pp.38-46
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• 2014

기존의 많은 연구자들이 철근과 콘크리트 사이의 부착특성에 영향을 주는 다양한 변수에 대하여 연구해왔으며, 특히 최근에는 고강도철근의 등장과 더불어 부착강도의 증진을 위한 연구가 다수 진행 중이다. 철근과 콘크리트 사이의 부착특성은 두 이질재료 사이의 계면조건이 중요한 역할을 하게 되는데, 이 중에서 특히 철근의 마디형상은 계면조건에 가장 큰 영향을 미치게 된다. 본 연구에서는 철근과 콘크리트 사이의 부착거동을 분석할 수 있는 상용 비선형 유한요소프로그램을 사용하여 철근의 마디형상에 따른 부착특성에 대하여 연구하였다. 해석에 사용된 부착모델은 2차원 평면응력요소를 사용하였으며, 주요 해석변수로는 마디각, 마디높이, 마디간격 및 마디면적비이다. 해석결과, 마디각은 30~60도인 범위에서 부착력이 우수한 것으로 나타났으며, 마디높이는 일정구간까지는 부착강도가 증가하나 철근직경의 12%를 초과하면 전단파괴를 유발하여 오히려 부착강도가 감소되고, 마디간격에 대한 효과는 상대적으로 크지 않은 것으로 나타났다. 마디의 높이와 간격을 하나의 지표로 제시할 수 있는 마디면적비는 부착강도의 변화를 효과적으로 나타낼 수 있는 것으로 분석되었으며, 마디면적비는 0.15 이하에서 최대의 효율을 나타내는 것으로 분석되었다. 특히 대형마디(교차마디형상)를 가진 철근인 경우, 타 변수보다 우수한 효율을 나타내어 부착강도 증진효과가 커지는 것으로 평가되었다.

• 콘크리트학회논문집
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• 제23권3호
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• pp.393-400
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• 2011

최근 구조물 설계개념의 변화로 사용응력 수준이 높아지고, 시공 및 경제성의 이유로 고강도 재료의 활용이 증가되고 있다. 그러나 고강도 철근을 사용하면 정착 및 이음 길이가 증가하게 되어 시공성이 저하되고 상세 설계의 어려움을 유발할 수 있다. 이에 따라 이 연구에서는 고강도 철근의 정착 및 이음 길이를 단축시키기 위하여 철근 마디형상의 변화가 부착 성능에 미치는 효과를 분석하도록 하였다. 기존 철근을 포함하여 마디의 형상을 개선한 총 5개의 단순보형 실험체를 제작하여 실험하였으며, 각 실험체는 경간 중앙부에서 겹침 이음되어 부착 파괴를 유도하도록 설계하였다. 실험의 결과는 부착강도, 하중-처짐 관계 및 균열의 관점에서 분석하였으며, 기존 연구자들의 부착강도 관련 설계 및 제안식과 비교 분석하였다. 실험 결과 마디면적비가 증가된 철근은 보통 철근보다 약 11%의 부착강도 향상을 나타내었으며, 마디면적비가 같더라도 높고 낮은 마디를 혼합한 경우에는 23%의 강도 증가를 나타내었다. 또한, 부재의 처짐, 균열의 개수 및 균열폭 등 사용성 관점에서 살펴볼 때, 개선된 형태의 철근은 보통 철근과 유사한 거동을 나타내어 현장적용에 큰 문제가 없을 것으로 분석되었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.735-740
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• 2003

In this study, a numerical optimization to find the optimal shape of streamwise periodic ribs mounted on both of the principal walls is performed to enhance turbulent heat transfer in a rectangular channel. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model and is implemented using response surface method. The width-to-height ratio of a rib, rib height-to-channel height ratio, rib pitch to rib height ratio and distance between opposite ribs to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been investigated for the range of 0.0 to 0.1 of weighting factor.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.280-287
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside the rib-roughened cooling passage of the gas turbine blades. A square duct with rectangular ribs is used and $\wedge-$ and V-shape ribs with $60^{\circ}$ attack angle are installed on the test plate surfaces. Naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall and the vortices near the side-wall. The local heat transfer and the secondary flow in the duct are changed largely according to the rib orientation. A square duct with $\wedge$ and V-shape ribs has two pairs of secondary flow because of the rib arrangement. So, the duct has complex heat/mass transfer distribution. The average heat/mass transfer coefficient and pressure drop of $\wedge-$ and V-shape ribs are higher than those with $90^{\circ}$ and $60^{\circ}$ attack angles. The average heat/mass transfer coefficient on the $\wedge-shape$ ribs is higher than that on the V-shape ribs. Also, the uniformity of heat/mass transfer coefficient on discrete ribs is higher than that on continuous rib.

• 한국유체기계학회 논문집
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• 제10권2호
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• pp.7-15
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• 2007

A numerical procedure for optimizing the shape of three-dimensional channel with V-shaped ribs extruded on both walls has been carried out to enhance the turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Wavier-stoked analysis. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show good agreements with experimental data. The objective function is defined as a linear combination of heat transfer and friction loss-related terms with a weighting factor. Three dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, and the attack angle of the rib are chosen as design variables. Nineteen training points obtained by D-optimal designs for three design variables construct a reliable response surface. In the sensitivity analysis, it is found that the objective function is most sensitive to the ratio of rib height-to-channel height ratio. And, optimal values of design variables have been obtained in a range of the weighting factor.

• 대한수의학회지
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• 제36권2호
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• pp.289-296
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• 1996

A case of schistosomus reflexes in Korean native female calf was observed macroscopically and radiographically. The results were summarized as follows. 1. The abdominal visceral organs were exposed. 2. The vertebral column bent laterally to the left, and the sacrum approached to the cranium by reflected caudal lumber vertebrae, presenting S-shaped lateral twisting of the vertebrae. 3. The right ribs reflected laterally and dorso-cranially from the 7th rib to 13th rib. The left ribs bent caudally from 8th rib to 13th rib. 4. The length of rudimentary 6th right rib was one half of normal size and the 7th right rib was one third. 5. The sternum was bifid split from the fourth sternebra through the xyphoid cartilage. 6. The diaphragm was intact and thoracic cavity was reduced in size. The lung and heart severely deformed in shape and size. 7. The liver markedly deformed in shape and thickness. 8. The pelvic cavity was reduced in size by compression laterally to the left. 9. The uterus horn, ovary, urinary bladder, and urethra were severely deformed in the shape and position.