• 한국터널지하공간학회 논문집
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• 제3권2호
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• pp.3-12
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• 2001

본 논문은 절리암반 터널의 안정성 해석을 위한 2차원 개별요소모델링방법에 대한 개선방안을 제안하였다. 먼저, 절리군과 터널의 상대방위를 고려하여 터널단면상에서 불연속거동이 가능한 절리군을 구별하는 기준을 제시하였다. 이 기준에 따라 불연속거동이 가능한 절리군은 개별요소(암석블록)의 변이 되도록 하고 그 외 절리군은 암석블록의 탄성특성을 보정하는 방법을 제시하였다. 또한, 주어진 절리의 기하학적 특성에 대해서 절리의 방위편차와 유한길이를 고려한 복잡한 모델과 절리의 평균방위와 무한길이를 고려한 단순한 모델의 특성을 분석하였다. 그 결과, 후자의 모델이 일관성 있는 터널의 국부적 파괴양상과 명료한 암반의 불연속거동을 보여줌으로써 터널설계목적에 적절함을 확인하였다.

• 지질공학
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• 제15권3호
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• pp.257-268
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• 2005

일반적으로 현지 암반은 강도의 변화가 심 한 다양한 불연속면들을 포함하여 불균질하고 불연속성 을 나타낸다. 절리, 단층, 균열, 층리와 같은 불연속면들은 암반의 강도와 변형특성을 좌우하는 중요한 요인이다. 결과적으로, 지하공동의 안정성은 무결암의 역학적 특성뿐만 아니 라, 공동의 기하학적 형상과 관련하여 불연속면들의 공간적 분포와 역학적 특성에 크게 영 향을 받는다. 따라서 지하심부의 응력 조건에서의 공동설계를 위해서는 불연속 암반의 거동에 대한 정확한 이해가 필수적이다. 암반역 학 분야의 발전에 의하여 등방성 암반에서 의지 하공동 설계를 위한 기준이 제시되고 있으나, 불연속성 암반의 변형 거동은 불명확성 이 여전히 존재한다. 본 연구에서는 연속체절 리모델을 적용하여 불연속성 암반내의 지하공동 주변의 소성영역의 크기, 응력분포 및 변형거동에 대하여 매개변수의 변화에 따른 영향을 고찰하였다. Mohr-Coulomb 파괴 이론에 의한 탄소성 유한차분법을 적용하였으며, 비조합 유동법칙과 완전소성 물질거 동을 가정하였다.

• 소성∙가공
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• 제5권4호
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• pp.327-336
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• 1996

The effect of dynamic strain aging on high temperature deformation behaviour of the A-Mg alloy was investigated by strain rate change tests and stress relaxation tests between 20$0^{\circ}C$and 50$0^{\circ}C$. Yield point, short stress transient and periodic discontinuities on the stress-strain curve were considered as an evidence of the effect of dynamic strain aging. With this criterion two distinct strain rate-temperature regimes could be manifested. Dynamic strain aging was considered to be effective in the high temperature-low strain rate regime, whereas dynamic recovery was a dominant deformation mechanism in the low temperature-high strain rate regime. It was found that dynamic strain aging in the high temperature deformation was governed by the mechcanism of diffusion-controlled, viscous dislocation movement.

• 터널과지하공간
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• 제2권1호
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• pp.152-163
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• 1992

The study of rock mass behaviour through a numerical analysis is important for the design, construction and maintenance of large rock caverns. The objectives of the numerical analysis are to design reasonably and construct safely the underground structures, to maintain them soundly after construction and to extend them securely for a desired period of time. Methods of numerical analyses included in this case study are the finite element method, the boundary element method, and the distinct element method. The numerical models are purely elastic, elastoplastic, visco-elastic, visco-plastic, easto-visco-plastic and jointed-discontinuous materials. The results of this case study indicate that the rock mass behaviour could be predicted exactly through continuous comparisons of the numerical results with the in-situ measurements.

• Advances in Computational Design
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• 제1권1호
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• pp.61-77
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• 2016

Seismic performance of structures depends on the force flow mechanism inside the structure. Discontinuity regions, like beam-column joints, are often affected during earthquake event due to the complex and discontinuous load paths. The evaluation of shear strength and identification of failure mode of the joint region are helpful to (i) define the strength hierarchy of the beam-column sub-assemblage, (ii) quantify the influence of different parameters on the behaviour of beam-column joint and, (iii) develop suitable and adequate strengthening scheme for the joints, if required, to obtain the desired strength hierarchy. In view of this, it is very important to estimate the joint shear strength and identify the failure modes of the joint region as it is the most critical part in any beam-column sub-assemblage. One of the most effective models is softened strut and tie model which was developed by incorporating force equilibrium, strain compatibility and constitutive laws of cracked reinforced concrete. In this study, softened strut and tie model, which incorporates force equilibrium equations, compatibility conditions and material constitutive relation of the cracked concrete, are used to simulate the shear strength behaviour and to identify failure mechanisms of the beam-column joints. The observations of the present study will be helpful to arrive at the design strategy of the joints to ensure the desired failure mechanism and strength hierarchy to achieve sustainability of structural systems under seismic loading.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.96-103
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• 2010

This paper presents of effect of tunneling on pile group of being operated bridge using Three-dimensional numerical modeling to study the effect of coordination of tunneling location under discontinuous group pile. In order to find idealistic tunneling location that causes settlement, change of stress on the piles and movement of soil at a minimum, a fully coupled 3D finite element model is adopted. The study contains pile settlement, axial force on each piles in the group, axial displacement of piles and soil behaviour caused by tunneling. Based on the result some insights into the pile behavior due to tunneling obtained from numerical analysis were mentioned and discussed.

• Corrosion Science and Technology
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• 제15권4호
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• pp.159-165
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• 2016

An attempt has been made to understand the influence of retrogression and re-aging (RRA) on the exfoliation corrosion behaviour of AA 7085 alloy in comparison with the peak aged condition (PA). Immersion tests using ASTM G34 and studies involving electrochemical impedance spectroscopy showed that the RRA treated alloy provided higher resistance to exfoliation corrosion than the PA treated alloy. The improved resistance was attributed to the enhanced Cu content and the discontinuous nature of the grain boundary precipitate, which was revealed through transmission electron microscopy.

• 한국안전학회지
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• 제18권3호
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• pp.46-53
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• 2003

For the tensile tests of the F.E.M., microvoids are created by the boundary separation process at the martensite boundary or neighborhood and at inclusions within the fracture. to grow to the ductile dimple fracture. For the case of the M.E.F., microvoids created at the discontinuities of the martensite phase which exists at the grain boundary of the primary ferrite are grown to coalescence with the cleavage cracks induced at the interior of the ferrite, which as a result show the discontinuous brittle fracture behavior. In spite of their similar tensile strengths, the fatigue limit and the notch sensitivity of the M. E.F. is superior to those of the F.E.M., The M.E.F. is much more insensitive to notch than F.E.M. from the stress concentration factor($\alpha$).

• 터널과지하공간
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• 제4권2호
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• pp.102-118
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• 1994

Thermomechanical analysis is conducted on the radioactive repository in deep rock mass considering the in-situ stress, excavation and thermal loading of a radioactive waste. Thermomechanical properties of a discontinuous rock mass are estimated by a theoretical method so called sequential analysis. Using the estimated properties as input for finite element analysis, the influence on temperature distribution and thermal stress is analyzed within the scope of 2-dimensional steady state and transient heat transfer and coupled thermal elastic plastic behaviour. Granitic rock mass is taken for this analysis. The analysis is done for two different rock mass conditions, i.e. continuous-homogeneous and highly jointed conditions, for the purpose of comparison. In the case of steady state, the extent of disturbed zone around the storage tunnel due to the heat production of the spent-fuel canister varies depending on the thermomechanical properties of the rock mass. In the case of transient analyses, the response of the jointed rock mass to the thermal loading after radioactive waste disposal varies significantly with time, resulting in dramatic changes in the both size and location of disturbed zone.

• 터널과지하공간
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• 제11권4호
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• pp.344-351
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• 2001

발파를 이용한 터널굴착에 있어서, 장약량 산정이나 터널 주변 암반 및 구조물웨 대한 영향 평가 등은 주로 간단한 경험식에 의해 이루어져 왔다. 또한 지금까지 발파의 충격에너지를 고려한 지하구조물의 동해석 연구는 매우 빈약한 실정이라 할 수 있다. 따라서 본 연구에서는 발파하중을 받는 불연속체 지하구조물의 비선형 거동을 평가하기 위하여 2차원 개별요소법의 수치모델기법을 개발하였고, 실제문제에의 적용성을 검토하기 위하여 제방하부에 위치한 터널발파의 수치해석을 통하여 시간별 지하 및 지상 구조물의 변위 및 입자속도의 전파과정을 살펴보았다. 해석결과 본 연구에서 제안한 발파하중의 모형이 실제 문제에 적용될 수 있었고, 이를 개별요소해석에 적용함으로써 발파지역 주변의 구조물의 안정성을 검토할 수 있었다.