• Magazine of the Korea Concrete Institute
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• v.10 no.3
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• pp.219-226
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• 1998

본 연구에서는 경량콘크리트보의 거동을 연구하는데 적용될 수 있는 비선형해석이 나타나있다. 콘크리트에 대한 2축 실험 자료를 사용하여 경량콘크리트의 구성모델을 만들었다. 구성모델에서 콘크리트의 비선형성은 주응력비에 따른 강도증감계수와 탄성계수의 변화에 따른 비선형저감계수를 사용하여 나타내었다. 유한요소 모델해석에서 콘크리트는 8절점을 가진 사각형요소로 하고 철근은 1차원 선형요소로 가정하여 해석하였다. 유한요소해석으로부터 얻어진 수치해석결과와 실험실에서 행한 실험결과를 비교하였다.

• Computational Structural Engineering
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• v.11 no.1
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• pp.179-190
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• 1998

A geometrically nonlinear finite element formulation of spatial cable networks is presented using two cable elements. Firstly, derivation procedures of tangent stiffness and mass matrices for the space truss element and the elastic catenary cable element are summarized. The load incremental method based on Newton-Raphson iteration method and the dynamic relaxation method are presented in order to determine the initial static state of cable nets subjected to self-weights and support motions. Furthermore, static non-linear analysis of cable structures under additional live loads are performed based on the initial configuration. Challenging example problems are presented and discussed in order to demonstrate the feasibility of the present finite element method and investigate static nonlinear behaviors of cable nets.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.70-72
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• 1999

일반적으로 비선형 정자계 문제를 해석하기 위해서 뉴튼-�N슨(Newton -Raphson : NR)법이 이용된다. 하지만 뉴튼-�N슨법의 경우 각 반복계산 때마다 새로운 선형 시스템의 해를 구하기 위해서 LU-decomposition과 같은 과정을 매 반복계산 때마다 시행해야 하므로 절점(node)의 수가 증가할 경우 계산시간이 증가한다는 단점이 있다. 이러한 단점을 보완하기 위해서 최근 TLM (Transmission Line Modeling)법이 새로운 반복계산법으로 비선형 유한 요소 해석에 적용되었으며 뉴튼-�N슨법에 비해 훨씬 우수한 특성을 보여주었다. 하지만 지금까지의 TLM법은 2차원의 정식화만 이루어졌고 3차원에는 적용되지 못한 것이 사실이다. 본 논문에서는 3차원의 비선형 정자계 문제에 TLM법을 적용할 수 있는 수식을 최초로 제안하며 3차원 코어(core)모델에 대해 TLM법을 적용하여 그 타당성을 검증하기로 한다. 또한 3차원 비선형 TLM법을 이용한 해석 결과가 뉴튼-�N슨법에 의한 결과와 완전히 일치하며 수렴 속도에 있어서도 훨씬 향상된 결과를 나타냄을 보이도록 하겠다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.533-539
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• 2009

In this study, the femur, the tibia, the articular cartilage and the menisci are three dimensionally reconstructed using MR images of healthy knee joint in full extension of 26-year-old male. Three dimensional finite element model of the knee joint is fabricated on the reconstructed model. Also, the FE models of ligaments and tendons are attached on the biologically suitable position of the FE model. Bones, articular cartilages and menisci are considered as homogeneous, isotropic and linear elastic materials, and ligaments and tendons are modeled as truss element and nonlinear elastic springs. The numerical results show the contact pressure and the von Mises stress distribution in the soft tissues such as articular cartilages and menisci which can be regarded as important parameters to estimate the failure of the tissues and the pain of the patients.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.3
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• pp.53-61
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• 1984

A nonlinear formulation of a beam finite element(NB6) on the total Lagrangian mode for the geometrically nonlinear analysis of two-dimensional elastic framed structures is presented. The NB6 beam element has been degenerated from the three-dimensional continuum by introducing the deep beam assumptions and consists of three reference nodes and three relative nodes. The element characteristics are derived by discretizing the beam equations of motion using the Galerkin weighted residual method and are reduced-integrated repeatedly for each loading step by the Newton-Raphson iteration techpique. Several numerical examples are given to demonstrate the accuracy and versatility of the proposed nonlinear NB6 beam element.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.100-107
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• 2018

The material and geometrical nonlinear finite elment analysis of UHPFRC 50M composite box girder was carried out. Constitute law in tension and compressive region of UHPFRC and HPC were modeled based on specimen test. The accuracy of nonlinear FEM analysis was verified by the experimental result of UHPFRC 50M composite girder. The UHPFRC 50M segmental composite box girder which has 1.5% steel fiber of volume fraction, 135MPa compressive strength and 18MPa tensile strength was tested. The post-tensioned UHPFRC composite girder consisted of three segment UHPFRC U-girder and High Strength Concrete reinforced slab. The parts of UHPFRC girder were modeled by 8nodes hexahedron elements and reinforcement bars and tendons were built by 2nodes linear elements by Midas FEA software. The constitutive laws of concrete materials were selected Multi-linear model both of tension and compression function under total strain crack model, which was included in classifying of smeared crack model. The nonlinearity of reinforcement elements and tendon was simulated by Von Mises criteria. The nonlinear static analysis was applied by incremental-iteration method with convergence criteria of Newton-Raphson. The validation of numerical analysis was verified by comparison with experimental result and numerical analysis result of load-deflection response, neutral axis coordinate change, and cracking pattern of girder. The load-deflection response was fitted very well with comparison to the experimental result. The finite element analysis is seen to satisfactorily predict flexural behavioral responses of post-tensioned, reinforced UHPFRC composite box girder.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.2
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• pp.19-25
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• 2004

The linear analysis for the balance of linear momentum of a structure is relatively easy to perform, but the error becomes large when the structure experiences large deformation. Therefore, the material and geometric nonlinearity need to be considered for the precise calculations in that case. The plastic flow of a ductile steel-like metal mainly transforms its dissipated mechanical energy into heat, which transfers under the first and second law of thermodynamics. This heat increases the temperature of the material and the strength of the material decreases accordingly, which affects mechanical behavior of the given structure. This paper presents a finite-strain thermo-elasto-plastic steel model. This model can handle large deformation and thermal load simultaneously, which is common during earthquake periods. Two 3-dimensional finite element analyses verify this formulation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.29-29
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• 1997

각광 받는 구조재료인 섬유강화 복합적층재에 대한 기계적 체결 거동은 본질적인 재료의 이방성에 의해서 파단강도가 파단 모우드와 매우 밀접한 관련을 갖는 것으로 알려져 있다. 따라서, 복합적층판 체결부의 정밀 구조 설계에서는 단순화에 따른 오차를 줄이고 정밀해에 의한 설계 및 해석이 요청된다. 특히, 층간응력 성분을 무시할 수 없는 두께를 갖는 복합적층 판의 기계적 체결부 해석이나 실제 구조물의 체결부에서 발생하는 굽힘이나 비틀림과 같은 하중 상태를 묘사하기 위해서도 정밀한 3차원 응력 해석은 필요하다. 하지만, 지금까지 기계적 체결부의 거동에 관한 연구는 층간응력 성분들을 어느정도 무시할 수 있는 얇은 평판에 대한 2차원 응력해석에 주로 국한되어 왔으며, 일부 수행된 체결부에 대한 3차원 응력 해석의 경우 여러 단점을 갖는 3차원 연속체 요소에 의한 유한요소 해석이 수행되었을 뿐이다.본 연구는 층간응력 성분들을 무시할 수 없는 두께를 갖는 복합적층판의 기계적 체결부 해석에 지금까지 사용되어온 3차원 연속체 요소에 의한 유한요소 방법이 갖는 단점들을 개선한 Layerwise 유한요소법을 이용하여 3차원 응력해석을 수행하였다. 특히, 선형상보성원리에 근거한 최적설계 기법을 응용하여, 기계적 체결시 핀과 적층판의 홀 사이에 발생하는 하중 전달 과정을 모사하고, 접촉력에 의한 홀 주위의 복잡하고 국부적인 응력 집중현상을 규명하여본다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.435-444
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• 2006

This paper investigates the effect of 3-dimensional FE models to evaluation results of jointed concrete pavements which is back-calculated by AREA method. Sensitivity of 3-dimensional FE models developed to simulate the behavior of real jointed concrete pavement are analyzed after compared with 2-dimensional FE models using ILLISLAB. In comparison with 2-dimensional models, influence of concrete contraction under loading plate and base layer on surface deflections is more than that of loading configuration. Deflections at 3-dimensional model between linear and nonlinear temperature distribution under same temperature difference are similar, but noticeable differences are investigated in low elastic modulus of foundations. Dynamic deflections under loading plate are larger than static deflections in high elastic modulus of foundation, but smaller in low elastic modulus. Lower dynamic modulus of subgrade reactions are backcalculated by dynamic deflections than by static deflections. But reverse trend is investigated in the backcalculated elastic modulus of concrete which describes trends of the field backcalculation values calculated from AREA method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.653-656
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• 2010

월성 1호기 격납건물에 대하여 극한내압하중에 대한 확률론적 취약도 평가를 수행하였다. 격납건물 성능의 불확실성은 가동중 검사 결과를 통해 얻어진 재료 물성치 중앙값과 텐던 긴장력 중앙값을 적용하여 고려하였다. 격납건물은 개구부를 고려하여 3차원 유한요소로 모델링하였으며, 확률론적 취약도 평가를 위하여 대규모의 비선형 유한요소 해석 모델을 적용하기에 적합한 효율적인 취약도 평가 기법을 개발하였다. 월성 1호기 격납건물에 대한 취약도 평가 결과, 벽체 중단부가 극한내압발생으로 인한 방사능물질 누출에 가장 취약한 것으로 나타났으며, 중앙값 성능은 약 55psi, 고신뢰도 저파괴 파괴확률값인 HCLPF(High Confidence Low Probability of Failure)는 약 29psi를 나타내었다.