• Geomechanics and Engineering
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• 제22권6호
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• pp.553-564
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• 2020

In this study, a simple numerical approach for a circular tunnel opening in strain-softening surrounding rock is proposed considering out-of-plane stress and seepage force based on Biot's effective stress principle. The plastic region of strain-softening surrounding rock was divided into a finite number of concentric rings, of which the thickness was determined by the internal equilibrium equation. The increments of stress and strain for each ring, starting from the elastic-plastic interface, were obtained by successively incorporating the effect of out-of-plane stress and Biot's effective stress principle. The initial value of the outmost ring was determined using equilibrium and compatibility equations. Based on the Mohr-Coulomb (M-C) and generalized Hoek-Brown (H-B) failure criteria, the stress-increment approach for solving stress, displacement, and plastic radius was improved by considering the effects of Biot's effective stress principle and the nonlinear degradation of strength and deformation parameters in plastic zone incorporating out-of-plane stress. The correctness of the proposed approach is validated by numerical simulation.

• Advances in materials Research
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• 제8권4호
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• pp.295-311
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• 2019

In this study, a three-dimensional Finite Element Model has been developed to estimate the size of the weakened zone in a bi-material a ceramic bonded to metal. The calculations results were compared to those obtained using Scanning Electron Microscope (SEM). In the case of elastic-plastic behaviour of the structure, it has been shown that the simulation results are coherent with the experimental findings. This indicates that Finite Element modeling allows an accurate prediction and estimation of the weakening effect of residual stresses on the bonding interface of Alumina. The obtained results show us that the three-dimensional numerical simulation used by the Finite Element Method, allows a good prediction of the weakened zone extent of a ceramic, which is bonded with a metal.

• Structural Engineering and Mechanics
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• 제44권3호
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• pp.289-303
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• 2012

Existing plane stress solutions for thin plates and disks have shown several qualitative features which are difficult to handle with the use of commercial numerical codes (non-existence of solutions, singular solutions, rapid growth of the plastic zone with a loading parameter). In order to understand the effect of temperature and pressure-dependency of the yield criterion on some of such features as well as on the distribution of residual stresses and strains, a semi-analytic solution for a thin hollow disk fixed to a rigid container and subject to thermal loading and subsequent unloading is derived. The material model is elastic-perfectly/plastic. The Drucker-Prager pressure-dependent yield criterion and the equation of incompressibity for plastic strains are adopted. The distribution of residual stresses and strains is illustrated for a wide range of the parameter which controls pressure-dependency of the yield criterion.

• 터널과지하공간
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• 제32권5호
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• pp.312-326
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• 2022

암반의 표준 파괴기준식의 하나로 인정받고 있는 일반화된 Hoek-Brown (GHB) 식은 암반공학적 활용에 특화되어 있으며 넓은 범위의 암반조건을 고려할 수 있다. 이에 따라 암반 구조물의 안정성 해석과정에서 GHB 식을 적극적으로 활용하기 위한 많은 연구 노력이 진행 중이다. 이 연구에서는 탄소성 해석법의 일종인 slip-line 해석법을 GHB 파괴기준식과 결합하여 원형터널 주변의 소성반경과 응력분포를 간편하게 계산할 수 있는 해석적 수식들을 유도하였다. 관련 수식 유도과정에서는 파괴 후 거동으로 완전 소성 거동을 가정하였고, 초기지압은 정수압 상태로 가정하였다. 이 연구를 통하여 소성반경은 터널 벽면과 탄성-소성 경계면에 대응되는 두 접선 마찰각을 이용하여 해석적으로 계산할 수 있음을 밝혔다. 또한 유도한 해석 식들을 이용하여 계산한 소성반경과 응력분포는 2008년에 발표된 Lee & Pietruszczak의 수치해석적 방법의 결과와 일치함을 보였다. 이 논문의 후반부에서는 유도한 해석 식을 활용하여 암반의 양호도가 소성영역의 크기, 응력분포, 접선마찰각의 변화에 미치는 영향을 분석하였다.

• Geomechanics and Engineering
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• 제7권2호
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• pp.165-181
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• 2014

In the past decade, different types of underreamed ground anchors have been developed for substructures requiring uplift resistance. This article introduces a new type of umbrella-shaped anchor. The uplift behavior of this ground anchor in clay is studied through a series of laboratory and field uplift tests. The test results show that the umbrella-shaped anchor has higher uplift capacity than conventional anchors. The failure mode of the umbrella-shaped anchor in a large embedment depth can be characterized by an arc failure surface and the dimension of the plastic zone depends on the anchor diameter. The anchor diameter and embedment depth have significant influence on the uplift behavior. A finite element model is established to simulate the pullout of the ground anchor. A parametric study using this model is conducted to study the effects of the elastic modulus, cohesion, and friction angle of soils on the load-displacement relationship of the ground anchor. It is found that the larger the elastic modulus and the shear strength parameters, the higher the uplift capacity of the ground anchor. It is suggested that in engineering design, the soil with stiffer modulus and higher shear strength should be selected as the bearing stratum of this type of anchor.

• 한국전산구조공학회논문집
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• 제27권3호
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• pp.191-198
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• 2014

본 논문에서는 노심용융사고 시 관통노즐이 제거된 원자로용기 하부헤드의 구조 건전성 평가를 수행하였다. 열응력, 노심용융물의 질량 그리고 내압조건의 해석결과를 고려할 때, 하부헤드의 열응력에 의한 영향이 가장 크게 나타났다. 손상 가능성은 파손기준에 따라 평가하였으며, 등가소성변형률이 임계변형률 파손기준보다 낮은 수준으로 평가되었다. 열-구조물 연성해석 결과 하부헤드의 두께 중간층에서 항복강도보다 낮은 응력이 발생한 탄성영역 구간을 확인하였다. 내압이 커지면서 탄성영역 범위가 점차 좁아지면서 탄성영역이 내벽으로 이동하는 결과를 확인하였고, 노심용융사고 시 구조적 건전성을 만족하는 것으로 평가되었다.

• 한국안전학회지
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• 제19권4호
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• pp.135-140
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• 2004

마모구조는 대략적으로 기계, 화학 및 열적 마모 등으로 구분되어 진다. 평면변형 유한요소법이 지속적인 칩 형성을 갖는 대각선 가공을 시뮬레이션 하기 위하여 새로운 재료의 응력 및 온도 필드와 같이 사용되었다. 작업소재의 변형은 등방성 변형 경화를 갖는 탄성-점소으으로 취급되며, 수치해석의 해는 소성 변형과 온도 필드의 결합을 설명하며, 온도 종속적인 재료 물성치로 취급된다. 이 논문에서 개발된 모델에서는 전단영역 주위의 변형률, 응력 및 온도 분포에 대한 구성모델의 불확실성의 영향들을 보여주며 예측된 전단영역의 응력, 변형률 및 온도의 평균값들은 기존의 실험 치와 비교해서 잘 맞는 것으로 사료된다.

• 한국농공학회지
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• 제41권6호
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• pp.64-74
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• 1999

The frequency of earthquake occurrence tends to increase in Korea. Therefore, the stability of pipeline, such as watersupply pipe, gas pipe, and oil pipe etc. across fault zones in Gyoung-sang landmass is very important, expecially , in metropolitan area. There were some examples of the construction of buried pipeline across fault zones in Korea. the interactiion between the buried pipeline across fault zones and the ground is considered. As well, in the interfaces of them, the direct shear numerical analysis model including elasto-plastic joint element is assumed that the retained dilatancy theory in them, otherwise. Also, the other elements are modeled the ground is nonlinear elastic coutinuaus beam, respectively. In this study, the maximum shear force point exist inside retaine zone(anchored zone) during shwar (as fault sliding), and the distribution of pipeline's behavior is all alike them of pipeline buried in ladnsliding grounds. Since the pipeline is not continuous beam but jointed by steel-pipe segments , practically, on acting of a large bending moment or a shear force, then, those are may be unstable. The reaearch on this point may be new approach.

• 터널과지하공간
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• 제1권2호
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• pp.181-203
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• 1991

The effects of geologic structures such as rock joins and bedding planes on the thermal conductivity of a discontinuous rock mass are studied. The expressions for the equivalent thermal conductivities of jointed rock masses are derived and found to be anisotropic. The degree of anisotropy depends primarily on the thermal properties contrast between the joint phase and surrounding intact rock, the joint density expressed as volume fraction and the inclination angle of the joint. Within the context of 2-dimensional finite element heat transfer scheme, the isotherms around a circular hole are analyzed for both the isotropic and anisotropic rock masses in 3 different thermal boundary conditions. i.e. temperature, heat flux and convection boundary conditions. The temperature in the stratified anisotripic rock mass is greatly influenced by the thermal properties of the rock formation in contact with the heat source. Using the excavation-temperature coupled elastic plastic finite element method, analyzed is the thermo-mechanical stability of a circular opening subjected to 10$0^{\circ}C$ at a depth of 527m. It is found that the thermal stress concentration was enough to deteriorate the stability and form a plastic yield zone around the opening, in contrast to the safety factor greater than 2 resulted form the excavation-only analysis.

• Geomechanics and Engineering
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• 제29권6호
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• pp.697-706
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• 2022

In order to explore the stable anchoring conditions of coal side under the mining disturbance of soft section coal pillar in Wangcun Coal Mine of Chenghe Mining Area, the distribution model of the anchoring support pressure at the coal pillar side was established, using the strain-softening characteristics of the coal to study the distribution law of anchoring coal side support pressure. The analytical solution for the reinforcement anchorage stress in the coal pillar side was derived with the inelastic state mechanical model. The results show that the deformation angle of the roadway side and roof increases with the roof subsidence due to the mining influence at the adjacent working face, the plastic deformation zone extends to the depth of the coal side, and the increase of anchorage stress can effectively control the roof subsidence and further deterioration of plastic zone. The roadway height and the peak support pressure have a certain influence on the anchorage stress, the required anchorage stress of the coal side rises with the roadway height and the peak support pressure. The required anchorage stress of the coal pillar side decreases as the cohesion between the coal seam and the roof and floor and the anchor length increases. Then, applied the research result to Wangcun coal mine in Chenghe mining area, the design of anchor cable reinforcement support was proposed for the section of coal pillars side that has been anchored and deformed, which achieved great results and effectively controlled the convergence and deformation of the side, providing a safety guarantee for the roadway excavation and mining.