• 콘크리트학회논문집
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• 제14권2호
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• pp.199-206
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• 2002

The objective of this study is to investigate the seismic behavior and evaluate structural performance of columns in Ordinary Moment Resting Concrete Frames (OMRCF). For this purpose 3 story OMRCF building was designed and detailed in compliance to ACI 318 (1999). Only gravity load is considered for the design. It is important to note that details strongly relate to the structural performance. The 1st story columns in the 3 story building are considered in this study since 다lese columns shall resist the largest axial and lateral forces during an earthquate. Four test specimens were made for representing the upper part and lower part of exterior and interior columns. All specimens are two-third scale. Based on the test results this study estimates deformation, ductility, strength, and energy absorption capacities as well as plastic hinge length.

• KIEE International Transactions on Electrophysics and Applications
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• 제3C권3호
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• pp.86-90
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• 2003

This paper describes the electrical characteristics of Nomex paper employed as an insulating material for distribution transformers. The relative permittivities (dielectric constants) and tan$\delta$ (dielectric dissipation factors) were measured as dielectric characteristics and the partial discharge inception voltages (PDIVs) and breakdown voltages were also measured as electrical strength characteristics of Nomex paper. As a result, the permittivity and tan $\delta$ of Nomex paper demonstrated both temperature and frequency dependency. Of particular note, the permittivity of 0.18 mm Nomex paper was 2.4 according to the ASTM condition, The PDIVs and breakdown voltages were almost linearly increased with the thickness of Nomex paper. Furthermore, its electrical strength was superior to conventional Kraft paper.

• Structural Engineering and Mechanics
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• 제67권5호
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• pp.493-504
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• 2018

In this paper, the tensile failure behaviour of transversally bedding layers was numerically simulated by using particle flow code in two dimensions. Firstly, numerical model was calibrated by uniaxial, Brazilian and triaxial experimental results to ensure the conformity of the simulated numerical model's response. Secondly, 21 circular models with diameter of 54 mm were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$ and $90^{\circ}$ while the angle of second layer, with high mechanical properties, related to loading direction was $90^{\circ}$, $105^{\circ}$, $120^{\circ}$, $135^{\circ}$, $150^{\circ}$, $160^{\circ}$ and $180^{\circ}$. Is to be note that the angle between bedding layer was $90^{\circ}$ in all bedding configurations. Also, three different pairs of the thickness was chosen in models; i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that In all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Numbers of shear cracks are constant by increasing the bedding thickness. It's to be note that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.

• 콘크리트학회논문집
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• 제23권5호
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• pp.603-608
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• 2011

국내외적으로 수주량이 증가하고 있는 대형 구조물의 건설 시 보다 정밀한 시공 및 유지관리 기술이 요구 된다. 그 중 콘크리트의 강도는 대표적인 품질관리 변수 중 하나로, 정확한 강도 값의 측정 및 이력관리는 건설 프로세스에서의 공기단축을 통한 비용 절감 및 효율적인 시공관리를 위해 매우 중요한 요구 사항이다. 이에 이 논문에서는 유비쿼터스 시대에 적합한 건설시공기술로의 발전을 위해 최근 개발된 임베디드 자율 감지형 콘크리트 강도 모니터링 기술을 데이터베이스화하고 이를 QR(quick response)코드와 연동시키는 콘크리트 강도 라벨링 기술을 소개한다. 이를 통하여 콘크리트 구조물의 강도 이력 DB를 언제 어디서나 실시간으로 확인하고 이를 바탕으로 보다 정밀하고 경제적인 시공 및 유지관리할 수 있는 차세대 콘크리트 생애주기 품질관리 시스템으로의 실현 가능성에 대해 고찰해본다.

• 대한화학회지
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• 제54권1호
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• pp.105-109
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• 2010

Propylene glycol을 첨가제로 사용하여 HEMA (2-hydroxyethyl methacrylate)와 교차결합제인 EGDMA (ethylene glycol dimethacrylate) 그리고 개시제인 AIBN(azobisisobutyronitrile)을 사용하여 공중합 하였다. 생성된 고분자의 물리적 특성을 측정한 결과, 함수율 37.06~38.71%, 굴절률 1.492~1.432, 가시광선 투과율 89.4~91.5%, 인장강도 0.1416~0.2302 kgf 그리고 접촉각의 경우 $38.60{\sim}53.53^{\circ}$ 범위의 분포를 나타내었다. 따라서 propylene glycol을 첨가한 콘택트렌즈 재료의 경우, 기본적인 콘택트렌즈의 물성을 만족하였으며 함수율의 큰 변화를 나타내지 않으면서도 습윤성과 인장강도를 증가시키는 결과를 보여주었다.

• Smart Structures and Systems
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• 제22권5호
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• pp.611-620
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• 2018

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $25^{\circ}$. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results shows that when layer angle is less than $50^{\circ}$, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilize in failure process. Also the failure trace is very short. It's to be note that number of cracks decrease with increasing the layer thickness. The minimum shear test strength was occurred when layer angle is more than $50^{\circ}$. The maximum value occurred in $0^{\circ}$. Also, the shear test tensile strength was increased by increasing the layer thickness.

• 한국물환경학회지
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• 제36권3호
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• pp.185-193
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• 2020

Bimodal flocculation describes the aggregation and breakage processes of the flocculi (or primary particles) and the flocs in the water environment. Bimodal flocculation causes bimodal size distribution with the two separate peaks of the flocculi and the flocs. Extracellular polymeric substances and ionic species common in the water environment increase the occurrence of bimodal flocculation and flocculi-floc size distribution, under the flocculation mechanisms of electrostatic attraction and polymeric bridging. This study investigated bimodal flocculation and flocculi-floc size distribution, with respect to the extracellular polymeric substance concentration and ionic strength in the kaolinite-containing suspension. The batch flocculation tests comprising 0.12 g/L of kaolinite showed that the highest flocculation potential occurred at the lowest xanthan gum (as extracellular polymeric substances) concentration, under all the ionic strengths of 0.001, 0.01, and 0.1 M NaCl. Also, it was important to note that the higher ionic strength resulted in the higher flocculation potential, at all the xanthan gum concentrations. The bimodal flocculation and flocculi-floc size distribution became apparent in the experimental conditions, which had low and intermediate flocculation potential. Besides the polymeric bridging flocculation, steric stabilization increased the flocculi mass fraction against the floc mass fraction, thereby developing the bimodal size distribution.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.507-517
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• 2018

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly punch shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $25^{\circ}$. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results show that when layer angle is less than $50^{\circ}$, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilizes in failure process. Also, the failure trace is very short. It's to be note that number of cracks decrease with increasing the layer thickness. The minimum shear punch test strength was occurred when layer angle is more than $50^{\circ}$. The maximum value occurred in $0^{\circ}$. Also, the shear punch test tensile strength was increased by increasing the layer thickness.

• 콘크리트학회논문집
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• 제23권5호
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• pp.637-645
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• 2011

압축강도 50 MPa이 넘는 고강도 콘크리트가 화재에 취약하다는 것은 널리 알려진 사실이다. 그러나 화재 피해를 입은 고강도 콘크리트 구조 부재의 구조 성능 저감 정도를 정확하게 파악하기 위해서는 단순히 열역학적 거동만으로 파악하는 것이 아니라, 구조 거동에 대한 연구가 필요하다. 따라서 이 연구에서는 비재하 상태에서 고온에 일정시간 노출시킨 고강도 콘크리트 단주를 대상으로 하중 재하 실험을 수행하였다. 실험 변수로는 콘크리트 압축강도, 가열시간, 그리고 폴리프로필렌 섬유 혼입을 통한 폭렬 저감 공법 사용 유무가 있었으며, 실험의 결과로는 콘크리트 강도 및 가열 시간이 증가할수록 구조 성능은 저감되는 것으로 나타났다. 특히 폴리프로필렌 섬유를 혼입하여 폭렬이 저감 된 경우에도 구조 성능에는 변화가 없거나 오히려 감소하는 것으로 나타났다. 이 연구를 통하여 알아낸 바를 토대로 보다 안전하고 경제적인 내화 설계를 할 수 있으며, 또한 화재로 인한 고강도 콘크리트 구조물의 구조성능 저감 정도를 예측하는데 유용하게 활용될 수 있을 것이라고 사료된다.

• Geomechanics and Engineering
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• 제20권3호
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• pp.207-220
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• 2020

Clay soils have a big potential to become contaminated with the oil derivatives because they cover a vast area of the earth. The oil derivatives diffusion in the soil lead to soil contamination and changes the physical and mechanical properties of the soil specially clay soils. Soil stabilization by using new material is very important for geotechnical engineers in order to improve the engineering properties of the soil. The main subjects of this research are a- to investigate the effect of the cement and epoxy resin mixtures on the stabilization and on the mechanical parameters as well as the microstructural properties of clay soils contaminated with gasoline and kerosene, b- study on the phenomenon of clay concrete development. Practical engineering indexes such as Unconfined Compressive Strength (UCS), elastic modulus, toughness, elastic and plastic strains are all obtained during the course of experiments and are used to determine the optimum amount of additives (cement and epoxy resin) to reach a practical stabilization method. Microstructural tests were also conducted on the specimens to study the changes in the nature and texture of the soil. Results obtained indicated that by adding epoxy resin to the contaminated soil specimens, the strength and deformational properties are increased from 100 to 1500 times as that of original soils. Further, the UCS of some stabilized specimens reached 40 MPa which exceeded the strength of normal concrete. It is interesting to note that, in contrast to the normal concrete, the strength and deformational properties of such stabilized specimens (including UCS, toughness and strain at failure) are simultaneously increased which further indicate on suitability and applicability of the current stabilization method. It was also observed that increasing cement additive to the soil has negligible effect on the contaminated soils stabilized by epoxy resin. In addition, the epoxy resin showed a very good and satisfactory workability for the weakest and the most sensitive soils contaminated with oil derivatives.