• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.275-281
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• 2011

When a flat bar type metal specimen for general tension test is subject to incremental uniaxial tension, a narrow plastic shear band, so called luders band, is generated at some instance. This band typically has an angle to the axis of specimen and many early researches have been done to investigate the condition and angle of this localized deformation phenomenon by many researchers. This study follows the procedure of Thomas(1961) under plane stress boundary condition. $J_2$ plasticity theory, balance of linear momentum, and constitutive equations are used to derive the angle of luders band under plain strain boundary condition. The result was confirmed by other angle based on acoustic tensor theory.

• Computational Structural Engineering
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• v.11 no.4
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• pp.187-196
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• 1998

불연속 갤러킨 정식화에 기초를 둔 시간적분법에 대하여 시간을 변수로 한 유한요소적 접근법을 시도하였다. 단일 형상함수와 두 형상함수 정식화에 대해 각각 선형, 이차 형상함수를 적용하여 모두 네 종류의 시간적분법을 유도하였으며, 각 방법에 대하여 시간시텝의 증가에 따른 변위와 속도의 관계를 나타내는 증폭행렬을 계산하였다. 유도된 방법들의 성능을 평가하기 위하여 부하가 갑자기 변화는 진동 문제를 해석하고 변위의 오차를 비교하였다. 네 가지의 방법에 대하여 국부 오차 추정치를 개발하였으며, 오차 추정치의 정확도를 수치예를 이용하여 평가하였다. 단일 형상함수 정식화에서 이차 형상함수를 이용한 오차 추정치가 실제 국부오차를 잘 나타내었으며 유도된 오차 추정치는 시간간격제어 기법에서 시간간격의 크기를 결정하는 척도로 이용 가능하다.

• Tunnel and Underground Space
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• v.5 no.1
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• pp.11-21
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• 1995

일반적으로 NATM공법에서 지보의 설계는 암반반응곡선의 개념을 통해 수행된다. 그러나 암반반응곡선은 암질이 좋고 과지압에 의한 문제가 심각하지 않은 지역에 적용되며, 따라서 주로 불연속면에 의해 암반의 거동이 영향을 받는 지역에서는 시공과정에 직접 적용하기가 힘들다. 본 연구에서는 암반 블록에 대한 블록반응곡선을 연구하여, 블록반응곡선상에서 지보를 설계하였다. 각각의 차분시각에서의 변위와 응력을 얻기위해서 개별요소 프로그램인 UDEC을 사용하였다. 블록은 Mohr-Coulomb 모델이며, 불연속면은 Barton-Bandis 모델이다. 블록과 불연속면의 물성은 실험실 실험을 통하여 구하였다. 블록반응곡선을 이용한 지보설계과정을 이해하기 위하여 간단한 모델분석을 실시하였다. 동일한 형상의 키블록이 공동의 천장, 측벽, 바닥에 존재할 경우, 각 블록의 안정성 판단 및 지보의 설계를 실시하였다. 또한 초기지압의 영향을 알아보기 위하여, 측압계수(K)를 달리하여 해석해보았다. 현재 건설중인 공동에 대한 안정성 판단 및 지보설계를 블록반응곡선을 이용하여 설계하였다.

• Tunnel and Underground Space
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• v.20 no.1
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• pp.28-38
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• 2010

In order to investigate the tendency of general displacements and behaviors with respect to each construction process as well as the applicability of numerical analysis schemes, this research has focused on not only analyzing a variety of field observations made in a NATM tunnel, such as displacement of top and side, stress of shotcrete and axial strength of rock bolt, but also carrying out a series of numerical analyses. It was established from the investigation that the 2-dimensional continuum numerical analysis was the one which could more accurately predict displacement of crown and side in the area of one step excavation (patten, P1-P3), while the 2-dimensional discontinuum analysis was the most suitable scheme to study that of two step excavation (patten, P4-P6). In addition, the 2-dimensional continuum analysis enabled to appropriately predict the axial strength of rock bolt and stress of shotcrete in all the area of the tunnel. Finally, it has been possible to conclude from the study that the 3-dimensional continuum analysis should be applied to inspect the behavior and tendency with respect to each stage of the construction as well as in the case of joints, such as large turnouts where relaxation loads in both of horizontal and vertical direction are piled up.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.303-312
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• 1991

This paper describes the general formulation for the in-plane flexural free vibration analysis of two layered structure by the transfer influence coefficient method. The structure is regared as a distributed mass system with lumped mass and inertia moments, massless linear and rotational springs, and joints elements of releases and rolls at which the displacements are discontinuous in each layer. The results of the simple numerical examples on a personal computer demonstrate the validity of the present method, that is, the numerical high accuracy, the high speed, the flexibility for programming of the present algorithm, compared with the transfer matrix method.

• Computational Structural Engineering
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• v.11 no.4
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• pp.155-168
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• 1998

보강된 판 및 쉘구조의 안정성 및 후좌굴을 포함하는 기하학적 비선형 해석을 수행하기 위하여, total Lagrangian formulation에 근거한 연속체의 증분평형방정식으로부터 변형된 쉘요소인 유한요소이론을 제시하였다. 쉘구조의 곡률이 불연속적으로 변하거나 쉘부재들이 유한한 각도로 만나는 보강된 판 및 쉘구조의 비선형 해석이 가능하도록 주부재와 보강재 간의 연결점에 대한 일반적인 변환관계를 제시하였으며 좌굴해석 및 기하학적 비선형해석의 경우에 해의 정확성 및 수렴성을 개선시키기 위하여 접선강도행렬 산정시 회전각의 2차항을 포함시켰다. 또한, shear locking 현상을 극복하기 위하여 감차적분을 적용하였고 쉘구조의 좌굴해석에서는 power method를 적용하여 해석의 효율을 높였으며, 후좌굴해석에서는 변위 및 하중증분법을 적절히 결합시켜 보강된 쉘구조의 후좌굴 거동추적이 용이하였다. 또한, 입력자료를 손쉽게 준비하고 좌굴모드 및 후좌굴거동을 효율적으로 분석하기 위하여 전, 후 처리 프로그램을 개발하였고 다양한 해석예제를 통하여 다른 문헌의 해석결과를 비교함으로써 본 연구에서 개발된 유한요소 해석프로그램의 타당성 및 정확성을 입증하였다.

• Explosives and Blasting
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• v.37 no.2
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• pp.14-21
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• 2019

Distinct element method is a powerful numerical tool for modelling the jointed rock masses. It is also a useful tool for modelling of later stage of blasting requiring large displacement. The distinct element method utilizes a rigid block idea in which the interacting force between distinct elements is calculated from contact displacement as elements penetrate slightly. The properties of joints defined as the boundaries of distinct elements are critical parameters to determine the block behavior, and affect the deformation and failure mode. However, regardless of real joint properties, joint stiffnesses have sometimes been selected without special concern just to prevent elements from penetrating too far into each other in some quasi-static problems. Depending on whether the main interest in the analysis is the prediction of the deformation with high precision, or the prediction of the block behaviour after failure, the input data such as joint stiffness may or may not have a significant effect on the results. The purpose of this study is to provide a sound understanding of the effect of the joint stiffness on the distinct element analysis results, and to help guide the selection of input data.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.366-377
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical mode1. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.

• Journal of the Korean Society for Railway
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• v.13 no.5
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• pp.521-527
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• 2010

The Paved Track is applied to reduce maintenance cost of conventional line. The Paved Track could be used in all types of lines including earthwork, bridge, tunnel and turnout sections. In case of earthwork section, the construction joint is the most critical factor to track durability. The construction joint does not affect to the track structure directly, but the gap due to discontinuity of slabs may affect to the long-term serviceability. To evaluate this problem, the accelerated track test has been performed on the construction joint and the middle part to of the real scale Paved Track. The purpose of this test is that evaluate the vulnerability of construction joint section comparing the trends of settlement and earth pressure under repeated loads of construction joint with those of the middle slab part.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.117-128
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical model. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.