• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2011년도 추계 학술논문 발표대회
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• pp.225-227
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• 2011

This study investigates the effect of crushed fine aggregate and chemical admixture (durability improvement agent, named DIA) on blast furnace slag-based brick. The control brick was made with recycled fine aggregate of 100% and, no cement was used. Test results showed that all specimens developed similar strength, except for the specimen without partial replacement of crushed fine aggregate at 3 days. However, it is interesting to note that this specimen without crushed fine aggregate resulted in the highest strength at 7 days. In addition, the DIA had a major effect on the absorption ratio of brick specimens. For the brick specimens with partial replacement of crushed fine aggregate with 10%, the addition of DIA with only 1% was enough to satisfy the code regulated by KS F 4004.

• 논리연구
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• 제15권3호
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• pp.307-322
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• 2012

프리드먼에 의해 제안된 "크루스칼 정리의 소형화 정리"가 2차 페아노 공리체계의 부분 시스템인 $(\prod_{2}^{1}-BI)_0$에서 증명될 수 없음을 증명한다. 또한 위 증명이 크루스칼 정리와 관련된 기존의 연구에서 알려진 중요한 정리들을 잘 조합함으로 해서 가능함을 보인다.

• 대한물리치료과학회지
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• 제18권2호
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• pp.41-49
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• 2011

Purpose: The purpose of this study is to acknowledge the effects that have the strength exercise done only on the neck extensor, only on the thoracic extensor, and both the neck and the thoracic extensor on forward head posture(FHP) and cervical range of motion. Also is to discover which of the exercise is the most effective. Method: This experiment will be done by selecting 40 people who have 16cm or more FHP and they will be divided into four groups: three experimental groups and a control group. The first experimental group will do only the neck extensor strength exercise(NESE). The second experimental group will do only the thoracic extensorstrength exercise(TESE) and the third experimental group will do both the NESE and the TESE. The experimental groups will make a day three times each ten sets of extensor isometric strength exercise but the time will be increased from 4 to 6 and8 seconds until it will be done the ten sets. Then after four weeks, they will be compared which had the best results for the FHP and the cervical range of motion. Result: After the experiment, it was compared the experimental groups with the control group. Every experimental group had an improvement on their FHP and cervical range of motion. However, the only NESE and the only TESE did not have a significantly difference(p>.05). Only the group who did both the NESE and the TESE had a sign ificantly improvement compared to the control group. Conclusion: 1. The only NESE and the only TESE seem that had a positive effect on FHP and cervical range of motion. However, it cannot be conclude that it is effective. 2. When both the NESE and the TESE are done, it is showed statistically a significant difference(p<.05) on FHP and cervical range of motion. The refore, it would be note worthy if this exercise is used to improve the FHP and the cervical range of motion.

• 한국구조물진단유지관리공학회 논문집
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• 제12권4호
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• pp.115-122
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• 2008

본 연구는 화재시 고강도 콘크리트의 폭렬발생에 대한 영향요인을 검토한 것으로써, 폭렬에 직접적인 상관관계에 있는 물-결합재비, 공기량 및 함수율 등을 PP섬유의 혼입률과 함께 변화시켜 실험을 실시하였다. 실험결과 유동특성은 섬유의 혼입률이 0.05 vol.% 증가함에 따라 약 11%정도 감소하는 것으로 나타났고, 공기량이 10%인 경우는 다량의 AE제 사용에 기인하여 섬유의 혼입률과 상관없이 거의 유사한 유동성을 나타냈다. 강도특성으로는 W/B 15, 25 및 35%일 경우 100, 80 및 60 MPa이상으로써 고강도 범위로 나타났으며, 공기량 변수의 경우는 H-air가 L-air에 비해 약 1/2배 정도로 낮게 나타났다. 폭렬특성으로는 KS F 2257-1에 규정되어 있는 표준가열곡선에 의해 1시간 내화시험을 실시한 결과, W/B는 고강도로 W/B가 낮을수록 심하게 발생하는데, 15%를 제외한 모든 경우에서 전반적으로 PP섬유의 혼입률 0.10 vol.%에서 폭렬이 방지되는 것으로 나타났고, 공기량을 10%로 많이 함유하는 시험체와 완전건조 시킨 시험체는 0.05 vol.% 혼입시에도 폭렬현상이 발생하지 않는 것으로 나타났다.

• Smart Structures and Systems
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• 제25권4호
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• pp.433-446
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• 2020

In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. A circular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

• 지질공학
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• 제22권3호
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• pp.353-363
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• 2012

울릉도는 강도가 약한 화산암과 강도는 높으나 수직절리가 잘 발달하는 조면암질암으로 구성되어 있으며, 이러한 지질학적 특성으로 인해 낙석이 빈번하게 발생하고 있어 일주도로의 이용에 큰 위험요소로 작용하고 있다. 본 연구에서는 낙석 재해위험도가 높은 울릉도 북동부의 약 3 km 구간을 대상으로 3종류의 낙석재해 위험도 평가법을 이용하여 낙석재해 위험도 평가를 수행하고 재해도를 작성하였다. 사용된 평가표는 일본 도로방재 총점검에서 적용된 낙석위험도 조사표, 일본 고속도로조사회의 낙석위험도 평가표, 그리고 미국연방도로국의 RHRS (Rockfall Hazard Rating System)이다. 도로사면의 지형 지질학적 조건을 고려하여 27개 구간을 설정하여 평가한 결과, 20개 사면(약 74%)에서 낙석재해 위험도가 높음과 보통으로 평가되었다. 이러한 조사결과를 바탕으로 낙석재해 위험도를 작성하였다.

• Geomechanics and Engineering
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• 제17권4호
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• pp.355-365
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• 2019

It is normal to observe the presence of numerous cracks in coal body. And it has significantly effective on the mechanical characteristics and realistic failure models of coal mass. Therefore, this paper is to investigate the influence of crack parameters on coal body by comprehensive using theoretical analysis, laboratory experiments and numerical simulation through prepared briquette specimens. Different from intact coal body possessing single peak in stress-strain curve, other specimens with crack angle can be illustrated to own double peaks. Moreover, the unconfined compressive strength (UCS) of specimens decreases and follow by increasing with the increase of crack angle. It seems to like a parabolic shape with an upward opening. And it can be demonstrated that the minimum UCS is obtained in crack angle $45^{\circ}$. In terms of failure types, it is interesting to note that there is a changing trend from tensile failure to tensile-shear mixing failure with tension dominant follow by shear dominant with the increase of crack angle. However, the changing characteristics of UCS and failure forms can be explained by elastic-plastic and fracture mechanics. Lastly, the results of numerical simulations are good consistent with the experimental results. It provides experimental and theoretical foundations to reveal fracture mechanism of coal body with non-penetrating single crack further.

• Structural Engineering and Mechanics
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• 제69권1호
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• pp.11-20
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• 2019

The biaxial failure mechanism of transversally bedding concrete layers was numerically simulated using a sophisticated two-dimensional discrete element method (DEM) implemented in the particle flow code (PFC2D). This numerical modelling code was first calibrated by uniaxial compression and Brazilian testing results to ensure the conformity of the simulated numerical model's response. Secondly, 21 rectangular models with dimension of $54mm{\times}108mm$ 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 were 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 noted 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.

• 대한금속재료학회지
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• 제46권12호
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• pp.780-787
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• 2008

For the advanced high strength steels (AHSS), high-manganese TWIP (twinning induced plasticity) steels exhibit high tensile strength (800-1000 MPa) and high elongation (50-60%). However, the TWIP steels need to be understood of delayed fracture following the cup drawing test. Among the factors to cause delayed fracture, i.e, martensite transformation, hydrogen embrittlement and residual stress, the effects of martensite transformation (${\gamma}{\rightarrow}{\varepsilon}$ or ${\gamma}{\rightarrow}{\alpha}^{\prime}$) were investigated on the delayed fracture phenomenon. Microstructural phase analysis was conducted for cold rolled (20, 60, 80% reduction ratio) steels and tensile deformed (20, 40, 60% strain) steels. For the Al-added TWIP steels, no martensite phase was found in the cold rolled and tensile deformed specimen. But, the TWIP steels with no Al addition indicated the martensite transformation. The cup drawing specimens showed the martensite transformation irrespective of the Al-addition to the TWIP steel. However, the TWIP steel with no Al exhibited the larger amount of martensite than the case of the TWIP steel with Al addition. For the reason, it was possible to conclude that the Al addition suppressed the martensite transformation in TWIP steels, therefore preventing the delayed fracture effectively. However, it was interesting to note that the mechanism of delayed fracture should be incorporated with hydrogen embrittlement and/or residual stress as well as the martensite transformation.

• 한국유체기계학회 논문집
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• 제15권4호
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• pp.50-54
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• 2012

Wind-power generation, which is recently drawing attention as one of renewable energies across the world, has been developed mainly by Europe. As the demand for the wind-power generation rose and the amount of wind-power generation increased, the studies on megawatt-class wind-power system have been active, and the use of composite with such properties as less weight, more strength, anti-corrosion and environment-friendliness has required gradually. In other word, wind turbine tower will be required to be lighter, more reliable and more consistent. Therefore it is necessary to lose weight of the wind turbine tower. This points squarely toward hybrid/composite tower production growing. It is important to note however that hybrid/composite tower production as it is today is flawed and that there are ways to improve greatly on the performance of these towers in manufacturing process and in their in-service performance. Through this, we have some detail on the current process and its advantage of cost and weight of towers.