• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.101-102
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• 2017

This study was carried out as basic study to apply to construction site the HPC method which is being developed. The construction cost of HPC method was analyzed in comparison with conventional method (half slab method). With regard to research method, it was decided that data on construction work carried out by half slab method was analyzed. According to the results of study, in case of being applied to the construction work using a divided column, the number of columns was decreased. So, it was shown that member production cost, and transport and assemblage cost reduced. In case of being applied to construction work using an undivided column, the analysis showed that there was little difference in construction cost. Therefore, the analysis showed that, if HPC construction method was applied to large structure using a large column, the construction cost was reduced to some extent in comparison with conventional half slab method.

• The Journal of the Acoustical Society of Korea
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• v.17 no.4
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• pp.30-37
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• 1998

본 논문은 중공형 층상 복합체 멘드릴(mandrel)을 이용하여 기본 공진주파수가 15kHz이상이고, 우수한 감도 특성을 지닌 광섬유 하이드로폰의 최적 구조를 설계하는 것에 관한 것이다. 유한요소법을 이용하여 Al/foraming 및 Nylon/foaming층상 복합체의 공지주 파수를 분석하여 설계 변수의 범위를 결정하였고, 멘드릴 형상에 따른 광음향 감도 특성을 분석하여 최적구조를 결정하였다. 그 결과로 멘드릴의 외경이 감소할수록, 길이가 증가할수 록 감도가 향상되었다. AL 멘드릴의 경우, 내경/외경 비가 낮을수록, Nylon멘드릴의 경우 내경/외경 비가 높을수록 감도 증가를 위하여 효율적이다. 그리고 결정된 최적구조의 Al/foaming 및 Nylon/foaming멘드릴을 사용한 광섬유 하이드로폰의 감도는 각각 1rad./Pa 대비 약 82dB 및 85.7dB 정도 이었고, Al층상 복합체 보다는 Nylon층상 복합체를 이용하는 것이 고 감도의 광섬유 하이드로폰을 제조하는데 유리함을 알 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.430-439
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• 2019

In this study, a nonlinear impact analysis was performed to evaluate the safety and damage of an eco-pillar debris barrier with a hollow cross-section, which was proposed to improve constructability and economic efficiency. The construction of concrete eco-pillar debris barriers has increased recently. However, there are no design standards concerning debris barriers in Korea, and it is difficult to find a study on performance evaluations in extreme environments. Thus, an analysis of an eco-pillar debris barrier was done using the rock impact speed, which was estimated from the debris flow velocity. The diameters of rocks were determined by ETAG 27. The impact position, angles, and rock diameter were considered as variables. A concrete nonlinear material model was applied, and the estimation of damage was done by ABAQUS software. As a result, the damage ratio was found to be less than 1.0 at rock diameters of 0.3 m and 0.5 m, but it was 1.39 when the diameter was 0.7 m. This study could be used as basic data on impact force in the design of the cross section of an eco-pillar debris barrier.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.441-448
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• 2014

From several researches, recently, it was found that using hollowed precast concrete (HPC) column made more compact concrete casting in joint region possible than using normal solid PC (Precast concrete) column. Therefore, the rigidity of joints can be improved like those of monolithic reinforced concrete (RC). After filling the hollow with grout concrete, however, it is expected that the HPC column behaviors like composite structure since PC element and grout concrete have different materials as well as there is a contact surface between two elements. These may affect the structural behavior and strength of the composite column. A compressive strength test was performed for the HPC column with parameter of hollow ratio for the case with and without grout in the hollow and the result is presented in this paper. The hollow ratios in the test are 35, 50 and 59% of whole section of column. Concentrated axial force was applied to top of the specimens supported as pin connection for both ends. In addition, finite element (FE) analysis was performed to simulate the failure behavior of HPC column for axial compression. As a result, it was found that the hollow ratio did not affect the initial stiffness of HPC filled with grout regardless of the strength difference of HPC and grout. However the strength was increased inversely corresponding to the hollow ratio. The structural capacity of HPC without grout closely related to the hollow size. Especially, the local collapse governs the overall failure when the thickness of HPC is too thin. Based on these effect, a suitable equation was suggested for calculation of the compressive strength of HPC column with or without grout. FE analysis considering the contact surface between HPC and grout produced a good result matched to the test result.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.1
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• pp.596-602
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• 2018

Nanoimprint lithography (NIL) is an emerging technology that enables cost-effective and high-throughput nanofabrication. In ultraviolet (UV) NIL, low-cost and high-speed production can be achieved using a non-vacuum environment at room temperature and low pressure. However, there are problems with the formation of bubble defects in such an environment. This paper investigates the shape of the mold cavity and the bubble defect formation in UV NIL in a non-vacuum environment. The bubble defect formation was simulated using two-dimensional flow analysis and the VOF method for commonly used cavity mold shapes (rectangular, elliptical, and triangular). The characteristics of the resist flow front and various contact angles were also analyzed. The shape of the mold cavity had a very significant effect on the bubble defect formation. For all cavity shapes, a smaller contact angle with the mold and larger contact angle with the substrate decreased the possibility of bubble defect formation. The elliptical shape was the most effective for preventing bubble defect formation.

• Membrane Journal
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• v.15 no.2
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• pp.147-156
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• 2005

It is well-known that polyethersulfone (PES) has high $CO_2$ selectivity over $N_2\;(or\;CH_4)$ and excellent pressure resistance of $CO_2$ plasticization among muy commercialized engineering plastics[1-4]. Asymmetric PES hollow fiber membranes for flue gas separation were developed by dry-wet spinning technique. The dope solution consists of PES, NMP and acetone. Water and water/NMP mixtures are used in outer and inner coagulants, respectively. Gas permeation rate (i.e., permeance) and $CO_2/N_2$ selectivity were measured with pure gas, respectively and the micro-structure of hollow fiber membranes was characterized by scanning electron microscopy. The effects of polymer concentration, ratio of NMP to acetone, length of air gap, evaporation condition and silicone coating were investigated on the $CO_2/N_2$ separation properties of the hollow fibers. Optimized PES hollow fiber membranes exhibited high permeance of $25\~50$ GPU and $CO_2/N_2$ selectivity of $30\~40$ at room temperature and have the apparent skin layer thickness of about $0.1\;{\mu}m$. The developed PES hollow fiber membranes, would be a good candidate suitable for the flue gas separation process.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.7-15
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• 2021

In this study, we developed Void Plywood Slab (VPS) that improved the shape of existing hollow materials. Its performance was evaluated through one-way flexural and one-way shear tests using the developed VPS. As a result of the one-way flexural performance tests of VPS, the yield load value for FPS series(longitudinal direction specimens with hollow materials) was approximately 97.5% compared to FPS-00(without hollow materials) specimen. The tests showed that the yield load was not much different. In addition, FNS series(transverse direction specimens with hollow materials) also represented about 97% of FPS-00 specimen. The one-way flexural performance was shown to have little impact from void materials. Therefore, it is confirmed that the presented system is applicable to the VPS to the slab design. The results of the one-way shear performance tests of VPS showed that it was about 92% compared to the SS-00(without hollow materials) specimen. These results were somewhat insufficient for the SS-00 specimen. Shear strength equation is expressed as the sum of shear force by concrete and shear force by reinforcement. However, in the case of void slab, it is believed that the concrete section has been deleted by the void material. However, the strength of the structure applied to the shear design, as with the flexural design, is also applied to the design based on the yield load value.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.456-470
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• 2013

Hollow-fiber membranes, is one of the new technologies that is growing rapidly in the past few decades. In addition, separation membranes using polymer materials, have attracted attentions in various fields including gas separation, fuel cells, water treatment, wastewater treatment, and organic separation. Nanofiltration (NF) membranes having the separation characteristics in the intermediate range between ultrafiltration and reverse osmosis (RO) membranes for liquid separation, with relatively low investment cost and operating pressure lower than that of RO membranes, have high permeance and rejection performance of multivalent ions as well as organic compounds of molecular weight between $200{\sim}1000gmol^{-1}$. In this paper, we would like to review the research trends on the various structure control and characterization of NF hollow fiber membranes with respect to materials and the methods of preparation (phase inversion method and interfacial polymerization method). Currently, most of NF membranes have been manufactured by plate and frame types or spiral wound types. But hollow fiber types have delayed in commercial products, because of the weak strength when to produce on the basis of the existing materials, therefore the development of new materials or improvement of existing materials will be needed. If improving manufacturing technology is available, hollow fiber types will replace spiral wound types and gradually show a higher market share.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.41-54
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• 1999

Because of relatively heavy dead weight of concrete itself and unavoidable heat of massive concrete in bridge piers, circular hollow columns are widely used in Korean highway bridges. Since the occurrence of 1995 Kobe earthquake, there have been much concerns about seismic design for various infrastructures, inclusive of bridge structures. It is, however, understood that there are not much research works for nonlinear behavior of circular hollow columns subjected to eqrthquake motions. The objective of this experimental research is to investigate nonlinear behavior of circular hollow reinforced concrete bridge piers under the quasi-static cyclic load, and then to enhance their ductility by strengthening the plastic hinge region with glassfiber sheets. Particularly for this test, constant 10 cyclic loads have been repeatedly actuated to investigate the magnitude of strength degradation for the displacement ductility factor. Important test parameters are seismic design, confinement steel ratio, axial force and load pattern. It is observed from quasi-static tests for 7 bridge piers that the seismically designed columns and the retrofitted columns show better performance than the nonseismically designed colums, i.e. about 20% higher for energy dissipation capacity and about 70% higher for curvatures.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.215-222
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• 1995

Anisotropic pitch-based C-type and hollow carbon fibers can obtain wider shear stresses during the spinning and induce higher molecular orientation than that of round along the fiber axis. These fibers reinforced unidirectional epoxy composites were prepared by hot-press moulding method and perpendicular and parallel thermal conductivities of the composites were measured by a steady-state meth od. In the case of round carbon fibers reinforced epoxy composites(H-CF/EP), thermal anisotropic factor showed nearly 50, while those of H-CF/EP and C-CF/EP showed about 130 and 118, respectively. As a result, both H-CF/EP and C-CF/EP had an excellent directional thermal conductivity to distribute heat, above 200 %.