• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.553-556
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• 2008

본 연구는 보통포틀랜드 시멘트(이하 OPC)의 제조공정 중 입도 분급에 의해 포집된 조립시멘트(역송분, 이하 RCC)와 저발열 혼화재료인 플라이애시(이하 FA)를 조합 치환하여 사용한 콘크리트의 기초적 특성에 대해 검토하고자 하였다. 실험은 W/B 50% 1수준에 대하여 OPC를 100% 사용한 것을Plain으로 하고, RCC를 0, 10, 20, 30%의 4수준, 혼화재로 FA를 0, 10, 20, 30%의 4수준으로 치환하여총 16배치를 계획 하였다. 실험결과로 유동성의 경우는 RCC를 치환하였을 때 증가하였으며, FA의 치환율이 증가 함에 따라 저하하는 경향을 나타냈다. 간이 단열에 의한 온도 상승량은 RCC 및 FA의치환율이 증가할수록 낮아졌고, FA를 조합하여 사용한 경우는 온도 상승을 저하시키는데 보다 효과적인 것을 알 수 있었으며, RCC30, FA30의 경우는 온도저감효과가 가장 뛰어난 것으로 나타났다. 초기강도는 RCC 및 FA의 치환율이 증가 할수록 저하하였고, 28일에서의 Plain에 대한 강도 발현율은RCC 치환율 별 FA10%에서 Plain에 비해 약 88%${\sim}$98%정도로 비교적 우수한 성능을 나타냈다.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.1041-1050
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• 2001

Control of bone cement volume (PMMA) may be critical for preventing complications in vertebroplasty, the percutaneous injection of PMMA into vertebra. The purpose of this study was to predict the optimal volume of PMMA injection based on CT images. For this, correlation between PMMA volume and textural features of CT images was examined before and after surgery to evaluate the appropriate PMMA amount. The gray level run length analysis was used to determine the textural features of the trabecular bone. Extimation of PMMA volume was done using 3D visualization with semi-automatic segmentation on postoperative CT images. Then, finite element (FE) models were constructed based on the CT image data of patients and PMMA volume. Appropriate material properties for the trabecular bone were assigned by converting BMD to elastic modulus. Structural reinforcement due to the changes in PMMA volume and BMD was assessed in terms of axial displacement of the superior endplate. A strong correlation was found between the injected PMMA volume and the area of the intertrabecular space and that of trabecular bone calculated from the CT images (r=0.90 and -0.90, respectively). FE results suggested that vertebroplasty could effectively reinforce the osteoporotic vertebra regardless of BMD or PMMA volume. Effectiveness of additional PMMA injection tended to decrease. For patients with BMD well lower than 50mg/ml, injection of up to 30% volume of the vertebral body is recommended. However, less than 30% is recommended otherwise to avoid any complications from excessive PMMA because the strength has already reached the normal level.

• Steel and Composite Structures
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• 제22권5호
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• pp.1085-1114
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• 2016

This paper investigates the transverse impact response for ultra lightweight cement composite (ULCC) filled pipe-in-pipe structures through a parametric study using both a validated finite element procedure and a validated theoretical model. The parametric study explores the effect of the impact loading conditions (including the impact velocity and the indenter shape), the geometric properties (including the pipe length and the dimensions of the three material layers) as well as the material properties (including the material properties of the steel pipes and the filler materials) on the impact response of the pipe-in-pipe composite structures. The global impact responses predicted by the FE procedure and by the theoretical model agree with each other closely. The parametric study using the theoretical approach indicates the close relationships among the global impact responses (including the maximum impact force and the maximum global displacement) in specimens with the equivalent thicknesses, proposed in the theoretical model, for the pipe-in-pipe composite structures. In the pipe-in-pipe composite structure, the inner steel pipe, together with the outer steel pipe, imposes a strong confinement on the infilled cement composite and enhances significantly the composite action, leading to improved impact resistance, small global and local deformations.

• 한국지반공학회논문집
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• 제29권11호
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• pp.29-47
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• 2013

본 연구에서는 항만구조물 기초지반에 소일-시멘트 파일을 이용한 말뚝식 지반개량을 적용한 90개 단면에 대해 안정검토를 수행하였고, 수치해석을 포함한 모든 항목에서 안정한 단면별 최소치환율을 결정하였으며, 원심모형실험을 통해 수치해석 결과의 신뢰성을 검증하였다. 연구결과, 기초지반이 매우 연약($s_u$ =15kPa이하)한 경우에는 말뚝식 지반개량이 부적합하고, 항만구조물의 말뚝식 지반개량에는 기초지반과 개량체의 강성비(n)가 최대 50~75이하이고 개량체 강도가 2~3MPa인 소일-시멘트 파일공법이 가장 적합하며, 최소치환율 지배인자가 허용수평변위이므로 말뚝식 지반개량을 설계할 때는 반드시 수평변위를 검토해야 하는 것으로 나타났다.

• Smart Structures and Systems
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• 제25권1호
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• pp.97-104
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• 2020

Due to the superior properties of nanoparticles, using them has been increased in concrete production technology. In this study, the effect of zinc oxide (ZnO) nanoparticles on the mechanical and smart properties of concrete was studied. At the first, the ZnO nanoparticles are dispersed in water using shaker, magnetic stirrer and ultrasonic devices. The nanoparticles with 3.5, 0.25, 0.75, and 1.0 volume percent are added to the concrete mixture and replaced by the appropriate amount of cement to compare with the control sample without any additives. In order to study the mechanical and smart properties of the concrete, the cubic samples for determining the compressive strength and cylindrical samples for determining tensile strength with different amounts of ZnO nanoparticles are produced and tested. The most important finding of this paper is about the smartness of the concrete due to the piezoelectric properties of the ZnO nanoparticles. In other words, the concrete in this study can produce the voltage when subjected to mechanical load and vice versa it can induce the mechanical displacement when subjected to external voltage. The experimental results show that the best volume percent for ZnO nanoparticles in 28-day samples is 0.5%. In other words, adding 0.5% ZnO nanoparticles to the concrete instead of cement leads to increases of 18.70% and 3.77% in the compressive and tensile strengths, respectively. In addition, it shows the best direct and reverse piezoelectric properties. It is also worth to mention that adding 3.5% zinc oxide nanoparticles, the setting of cement is stopped in the concrete mixture.

• 한국재난정보학회 논문집
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• 제13권3호
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• pp.348-357
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• 2017

본 연구에서는 생갯벌을 잔골재 대신 치환한 모르타르의 물리적 특성에 대한 실험을 진행하여 벽돌로써의 활용 가능성을 분석하였다. 플로우 측정결과 시멘트와 잔골재의 배합비가 높을수록 플로우 값이 증가하였으며, 생갯벌의 치환율이 감소할수록 플로우값이 감소하는 것으로 나타났다. 염화물 함유량 측정결과 생갯벌의 치환율이 감소할수록 염화물 함유량 또한 감소하는 것으로 나타났다. 압축강도 측정결과, 대부분의 배합비에서 생갯벌의 치환율이 감소할수록 압축강도는 반비례하여 증가하는 것으로 나타났다. 인장강도 측정결과, 압축강도와 비슷한 경향을 나타냈다. 그리고 생갯벌 치환율이 감소할수록 강도가 증가하는 것으로 나타났다.

• Geomechanics and Engineering
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• 제21권4호
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• pp.357-369
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• 2020

Different from the conventional planar fracture and simplified Newton model, for power-law slurries with a lower water-cement ratio commonly used in grouting engineering, flow model in geological rough fractures is built based on ten standard profiles from Barton (1977) in this study. The numerical algorithm is validated by experimental results. The flow mechanism, grout superiority, and water plugging of pseudo plastic slurry are revealed. The representations of hydraulic grouting properties for JRCs are obtained. The results show that effective plugging is based on the mechanical mechanisms of the fluctuant structural surface and higher viscosity at the middle of the fissure. The formulas of grouting parameters are always variable with the roughness and shear movement, which play a key role in grouting. The roughness can only be neglected after reaching a threshold. Grouting pressure increases with increasing roughness and has variable responses for different apertures within standard profiles. The whole process can be divided into three stationary zones and three transition zones, and there is a mutation region (10 < JRCs < 14) in smaller geological fractures. The fitting equations of different JRCs are obtained of power-law models satisfying the condition of -2 < coefficient < 0. The effects of small apertures and moderate to larger roughness (JRCs > 10.8) on the permeability of surfaces cannot be underestimated. The determination of grouting parameters depends on the slurry groutability in terms of its weakest link with discontinuous streamlines. For grouting water plugging, the water-cement ratio, grouting pressure and grouting additives should be determined by combining the flow conditions and the apparent widths of the main fracture and rough surface. This study provides a calculation method of grouting parameters for variable cement-based slurries. And the findings can help for better understanding of fluid flow and diffusion in geological fractures.

• Archives of Plastic Surgery
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• 제50권3호
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• pp.248-253
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• 2023

Metal fixation systems for cranial bone flaps cut by a drill are convenient devices for cranioplasty, but cause several complications. We use modified craniotomy using a fine diamond-coated threadwire saw (diamond T-saw) to reduce the bone defect, and osteoplasty calcium phosphate cement without metal fixation. We report our outcomes and tips of this method. A total of 78 consecutive patients underwent elective frontotemporal craniotomy for clipping of unruptured intracranial aneurysms between 2015 and 2019. The follow-up periods ranged from 13 to 66 months. The bone fixation state was evaluated by bone computed tomography (CT) and three-dimensional CT (3D-CT). The diamond T-saw could minimize the bone defect. Only one wound infection occurred within 1 week postoperatively, and no late infection. No pain, palpable/cosmetically noticeable displacement of the bone flap, fluid accumulations, or other complications were observed. The condition of bone fixation and the cosmetic efficacy were thoroughly satisfactory for all patients, and bone CT and 3D-CT demonstrated that good bone fusion. No complication typical of metal fixation occurred. Our method is technically easy and safety, and achieved good mid-term bone flap fixation in the mid-term course, so has potential for bone fixation without the use of metal plates.

• 한국지반공학회논문집
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• 제35권11호
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• pp.15-23
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• 2019

본 연구에서는 수치해석을 이용해 격벽형 중력식 2열 합성소일벽(BSCW) 공법의 변위에 대해 분석하고 고찰하였다. 수치해석 모델은 BSCW 앞면 중심부의 현장 변위 데이터를 통하여 검증되었고 세 가지 다른 점토지반(soft, medium, stiff)의 점착력 및 탄성계수에 대한 매개변수 해석을 수행하였다. 또한 Jumbo Special Pattern 공법을 이용한 저면 시멘트 칼럼의 Center-To-Center 간격에 대한 매개변수 해석도 수행하였다. 매개변수 해석 결과, BSCW의 변위는 연약 점토 지반에서 가장 크게 나타났고, 낮은 탄성계수를 가진 지반인 경우 낮은 Center-to-Center 간격이 요구되었다.

• Transactions on Electrical and Electronic Materials
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• 제9권4호
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• pp.143-146
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• 2008

In this study the thermal impact characteristics by forest fire are extensively investigated using temperature controlled ovens. The test conditions for thermal impact damage are simulated according to the characteristics of natural forest fire. The test pieces are suspension porcelain insulators made by KRI in 2005 for transmission lines. In the thermal impact cycle tests with $300\;^{\circ}C$ thermal impact gradient (-70 to $230\;^{\circ}C$), cycling in 10 minute periods, no critical failures occurred in the test samples even with long cycle times. But in tests with thermal impact gradient from room temperature to $200-600\;^{\circ}C$, cycling in 10 to 30 minute periods, there were critical failures of the porcelain insulators according to the thermal impact gradient and quenching method. In the case of thermal impact by forest fire, it was found of that duration time is more important than the cycling time, and the initiation temperature of porcelain insulator failures is about $300\;^{\circ}C$, in the case of water quenching, many cracks and fracture of the porcelain occurred. It was found that the thermal impact failure is closely related to the displacement in the cement by thermal stress as confirmed by simulation. It was estimated that the initiation displacement by the thermal impact of $300\;^{\circ}C$ is about 0.1 %. Above 1% displacement, it is expected that the most porcelain insulators would fail.