• 한국지반공학회논문집
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• 제21권8호
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• pp.37-43
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• 2005

암반의 거동을 예측하기 위해 1980년 발표된 Hoek-Brown 모델은 지속적인 개선과 더불어 수많은 문제들을 해결하기 위해 널리 사용되고 있다. 그러나 Hoek-Brown 모델의 유한요소법 등 수치해석에 대한 적용성에 관한 연구는 미미한 실정이다. 본 논문에서는 Hoek-Brown 모델을 일반적 소성론 절차에 따라 구성모델로 정식화하여 그 특징을 살펴보았고, 수치적 문제점을 유발하게 되는 항복면의 모서리부를 곡면으로 처리한 Rounded Hoek-Brown 모델을 제시하였다. 제안모델은 탄소성 구성모델로서의 요구조건들을 만족하며, 압축측에서 원래의 Hoek-Brown 모델과 동일한 항복면을 갖는다. 제안 모델을 일반적인 비선형 유한요소해석에 적용하기 위하여 제안 모델의 구성방정식을 수립하였다.

• 농업과학연구
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• 제13권2호
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• pp.255-264
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• 1986

수확시기(收穫時期)의 벼줄기에 대(對)한 역학적(力學的), 점탄성적(粘彈性的) 특성(特性)을 구명(究明)하기 위(爲)해 압축시(壓縮時) 최대압축하중(最大壓縮荷重), 이력현상(履歷現象), 가공경화현상(加工硬化現象) 및 점탄성(粘彈性) 거동(粘彈性)에 대(對)한 변형속도(變形速度), 초기하중(初期荷重)이 영향을 분석(分析)하며, 도해법(圖解法) 및 computer에 의(依)한 수치해법(數値解法)으로 하중이완(荷重弛緩)의 rheological model 을 제시(提示)코져 시험(試驗)한 결과(結果)는 다음과 같다. 1. 압축시험시(壓縮試驗時) 벼줄기의 최대압축하중(最大壓縮荷重)은 다수계(多收系) 품종(品種)보다 일반계(一般系)에서 큰 경향(傾向)이었다. 2. 동진벼의 부위별(部位別) 최대압축하중(最大壓縮荷重)은 4절간이 가장 컷고, 3절간, 1절간 하부(下部), 2절간, 1절간 상부(上部)의 순(順)으로 작았다. 3. 비례한도내(比例限度內)의 하중(荷重)으로 loading-unloading 할 때 일부의 잔유변형이 발생(發生)하여 탄소성(彈塑性) 변형(變形)을 일으켜 이력손실(履歷損失)을 가져왔다. 4. Loading-unloading cycle을 반부(反復)하면 소성변형(塑性變形)이 감소(減少)하여 가공경화현상(加工硬化現象)을 보였다. 5. 하중이완거동(荷重弛緩擧動)은 변형속도(變形速度)의 증가(增加)에 따라 이완속도(弛緩速度)가 빨라졌다. 6. Computer에 의(依)한 수치해법(數値解法)과 도해법(圖解法)으로 이완거동(弛緩擧動)을 분석(分析)한 결과(結果) 3개지수항(個指數項)으로 표시(表示)되고 일반화(一般化) Maxwell model로 나타내었다. 이 model의 rheology 방정식(方程式)은 다음과 같다. $$F(t)=C_1e^{{-t/{\tau}}_1}+C_2e^{{-t/{\tau}}_2}+C_3e^{{-t/{\tau}}_3}$$ 동진벼줄기의 함수율(含水率) 71.9%(w.b.), 초기하중(初期荷重) 45.5 N, 변형속도(變形速度) 38mm/min 일 때 하중이완(荷重弛緩) 방정식(方程式)은 다음과 같았다. $$F(t)=24.3e^{-t/1006}+7.6e^{-t/12.7}+13.6e^{-t/1.8}$$ 7. 초기변형(初期變形)이 클수록 하중이완(荷重弛緩)은 크게 일어났다.

• 한국강구조학회 논문집
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• 제22권4호
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• pp.377-388
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• 2010

HSB600 및 HSB800 고성능강재를 적용한 정모멘트부 강합성거더의 휨거동을 비선형 모멘트-곡률 해석법으로 분석하였다. 연성특성이 다른 3개의 대표적인 강합성거더 기본 단면을 선정하여 모멘트-곡률 해석법으로 모멘트-곡률 이력과 휨저항강도를 구하고 비선형 유한요소해석 프로그램 ABAQUS(2008)로 구한 결과와 비교하여 모멘트-곡률 해석 프로그램을 검증하였다. 비선형 유한요소해석 시에는 플랜지, 복부판 및 콘크리트 바닥판을 판요소로 모델링하여 3차원 강합성거더 유한요소모델을 적용했으며 초기변형과 단면의 잔류응력을 고려하여 해석하였다. 강합성거더 단면에서 콘크리트 바닥판의 28일 압축강도는 30~50MPa를 고려하였으며, 콘크리트 재료는 CEB-FIP(1990) 모델로, 일반 강재와 HSB600 및 HSB800 고성능 강재는 탄소성-변형경화 재료로 모델링하였다. 강합성단면의 연성비, 강거더의 강종, 콘크리트 바닥판의 압축강도, 소성중립축의 위치 등이 강합성거더의 연성특성 및 휨저항강도에 미치는 영향을 분석하였다.

• 산업기술연구
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• 제24권B호
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• pp.95-105
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• 2004

This paper is an experimental and numerical research works about the effects of the b earing capacity of sloped rubble mound on the density of rubble mound and the position of footing. Centrifuge model tests were performed to investigate the bearing capacity of rubble m ound by changing the density of rubble mound and the location of loading in forms of s trip loading to simulate the caisson. Materials of rubble mound used in the model tests were crushed rocks having similar value of uniformity coefficient to the value in field. Two different relative densities of 80% and 90% were prepared during tests. The dimens ions of centrifuge model were trapezoidal shape of model mound having the bottom wid th of mound, 30cm and height of mound, 10cm. Gravity level applied during the centrif uge test was 50G. Surcharge loading in the forms of strip loading was applied on the t op of the sloped model mound. Tests were carried out by changing the position of loadi ng. The rigid model footing was located in the center of top of the model rubble mound and the edge of model footing was at the crest of mound. Test results were analyzed by using the limit equilibrium methods proposed by Meyer hof(1957) and Bowles(1982) and the numerical approach with FLAC being available com mercially software. For the numerical estimations with FLAC, the rubble mound was si mulated with the constitutive relationship of Mohr-Coulomb elasto-plastic model.

• 산업기술연구
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• 제24권A호
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• pp.227-238
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• 2004

This paper is results of experimental and nunerical works on the behavior of the cut-and-cover tunnel. Centrifuge model tests were performed to simulate the behavior of the cut-and-cover tunnels having cross sections of national road and subway tunnels. Model experiments were carried out with changing the cut slope and the slope of filling ground surface. Displacements of tunnel lining resulted from artificially accelerated gravitational force up to 40g of covered material used in model tests, were measured during centrifuge model tests. In model tests, Jumunjin Standard Sand with the relative density of 80 % and the zinc plates were used for the covered material and the flexible tunnel lining, respectively. Basic soil property tests were performed to obtain it's the property of Jumumjin Standard Sand. Shear strength parameters of Jumunjin Standard Sand were obtained by performing the triaxial compression tests. Direct shear tests were also carried out to find the mechanical properties of the interface between the lining and the covered material. Numerical analysis with the commercially available program of FLAC were performed to compare with results of centrifuge model experiment In numerical modelling. Mohr-Coulomb elasto-plastic constitutive model was used to simulaye the behavoor of Jumunjin Standard Sand and the interface element between the lining and the covered material was implemented to simulate the interaction between them. Compared results between model tests and numerical estimation with respect to displacement of the lining showed in good agreements.

• 한국지반공학회논문집
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• 제18권4호
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• pp.215-228
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• 2002

동반논문(오세붕, 2002)에서는 전체 변형도 영역의 거동을 모델할 수 있는 GUX( 구성모델을 ABAQUS 코드(Hibbit 등, 2001)에 구현하였다. 먼저 정확도 해석을 통하여 동반논문에서 구현한 내재적 응력적분 기법이 해의 정확도를 확보함을 알 수 있었다. GUX 모델은 전응력 개념에 의거한 비등방경화 탄소성 구성모델이므로 완전 배수 또는 비배수 삼축시힘시 응력-변형도 관계를 입력하여 대상문제를 배수 및 비배수조건에 따라 해석할 수 있다. 본 연구에서는 연약지반 및 풍화토 지반상 성토시 안정성 문제와 지반-말뚝계의 축하중 재하시 거동에 대한 예제 해석을 수행하였다. 그리고 대변형 해석을 통하여 기하학적 비선형성을 고려하였고 전체 변형도 거동을 합리적으로 모델하는 GUX 모델을 이용한 결과를 Mises 모델 결과와 비교하였다.

• Geomechanics and Engineering
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• 제14권3호
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• pp.211-224
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• 2018

In this paper, a predictive method accounting for the scaling effects of rockfill materials in the numerical deformation analysis of rockfill dams is developed. It aims to take into consideration the differences of engineering properties of rockfill materials between in situ and laboratory conditions in the deformation analysis. The developed method is based on the modification of model parameters used in the chosen material model, which is, in this study, an elasto-plastic model with double yield surfaces, i.e., the modified Hardening Soil model. Datasets of experimental tests are collected from previous studies, and a new dataset of the Nam Ngum 2 dam project for investigating the scaling effects of rockfill materials, including particle size, particle gradation and density, is obtained. To quantitatively consider the influence of particle gradation, the coarse-to-fine content (C/F) concept is proposed in this study. The simple relations between the model parameters and particle size, C/F and density are formulated, which enable us to predict the mechanical properties of prototype materials from laboratory tests. Subsequently, a 3D finite element analysis of the Nam Ngum 2 concrete face slab rockfill dam at the end of the construction stage is carried out using two sets of model parameters (1) based on the laboratory tests and (2) in accordance with the proposed method. Comparisons of the computed results with dam monitoring data indicate that the proposed method can provide a simple but effective framework to take account of the scaling effect in dam deformation analysis.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권4호
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• pp.418-428
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• 2017

In offshore area, newly deposited Quaternary loose seabed soils are widely distributed. There are a great number of offshore structures has been built on them in the past, or will be built on them in the future due to the fact that there would be no very dense seabed soil foundation could be chosen at planed sites sometimes. However, loosely deposited seabed foundation would bring great risk to the service ability of offshore structures after construction. Currently, the understanding on wave-induced liquefaction mechanism in loose seabed foundation has been greatly improved; however, the recognition on the consolidation characteristics and settlement estimation of loose seabed foundation under offshore structures is still limited. In this study, taking a semi-coupled numerical model FSSI-CAS 2D as the tool, the consolidation and settlement of loosely deposited sandy seabed foundation under an offshore breakwater is investigated. The advanced soil constitutive model Pastor-Zienkiewics Mark III (PZIII) is used to describe the quasi-static behavior of loose sandy seabed soil. The computational results show that PZIII model is capable of being used for settlement estimation problem of loosely deposited sandy seabed foundation. For loose sandy seabed foundation, elastic deformation is the dominant component in consolidation process. It is suggested that general elastic model is acceptable for subsidence estimation of offshore structures on loose seabed foundation; however, Young's modulus E must be dependent on the confining effective stress, rather than a constant in computation.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.481-495
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• 2015

Many hydropower stations in southwest China are located in regions of brittle rock mass with high geo-stresses. Under these conditions deep fractured zones often occur in the sidewalls of the underground caverns of a power station. The theory and methods of fracture and damage mechanics are therefore adopted to study the phenomena. First a flexibility matrix is developed to describe initial geometric imperfections of a jointed rock mass. This model takes into account the area and orientation of the fractured surfaces of multiple joint sets, as well as spacing and density of joints. Using the assumption of the equivalent strain principle, a damage constitutive model is established based on the brittle fracture criterion. In addition the theory of fracture mechanics is applied to analyze the occurrence of secondary cracks during a cavern excavation. The failure criterion, for rock bridge coalescence and the damage evolution equation, has been derived and a new sub-program integrated into the FLAC-3D software. The model has then been applied to the stability analysis of an underground cavern group of a hydropower station in Sichuan province, China. The results of this method are compared with those obtained by using a conventional elasto-plastic model and splitting depth calculated by the splitting failure criterion proposed in a previous study. The results are also compared with the depth of the relaxation and fracture zone in the surrounding rock measured by field monitoring. The distribution of the splitting zone obtained both by the proposed model and by the field monitoring measurements are consistent to the validity of the theory developed herein.

• 한국지반공학회지:지반
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• 제8권2호
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• pp.45-58
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• 1992

지반재료의 탄소성 구성 모델은 유연성과 안정성을 동시에 만족하여야 공학적으로 의미를 가지며 실용적으로 사용될 수 있다. 본 연구에서는 안정성이 있는 계수를 사용하는 수정 Cam-clay 모델을 근간으로, 한계상태 간격비를 계수로 도입하여 더욱 유연성이 있는 모델을 제안하였다. 한계상태 간격비는 추가적인 실험없이 간편하게 구할 수 있으며 특히 비배수 전단거동에 대하여 실용적으로 사용될 수 있다. 제안된 모델은 비 배수전단 삼축압축시험에 대하여 응력경로 및 응 력-변형률관계를 수정 Cam-clay 모델에 비하여 매우 정확하게 예측할 수 있었다. 뿐만 아니라 전단변형률 속도, 크리프 및 응력이완의 영향을 고려할 수 있었다. 특히 실제의 상태경계면을 표현 탄성 -완전소성모델, 사용해야 삼축압축시험중 비 배수시험이 W W 삼축압축시험시 전단시험을 논문에서 해석한 점토질 지반의 거동에 대하여 관련유동칙을 따른다는 가정이 잘 적용되기 때문이라고 판단된다.