• 한국지반공학회논문집
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• 제15권4호
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• pp.185-205
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• 1999

유류비축용 지하저장공동의 설계를 위하여 수압파쇄시험에 의한 현지암반내 초기응력 해석이 수행되었다. 부지 내 2개의 경사 시추공에 대해 수행된 금번 시험은 국내 기술진에 의한 지하비축기지 적용의 첫 사례이다. 또한, 경사공 해석기법을 처음으로 도입하여 수직공 해석기법에 의한 결과와 비교, 해석기법의 타당성을 검증함으로써 향후 수압파쇄시험의 적용범위 확대를 기대할 수 있었다. 특히 인근 지역이라도 지형적 또는 지질학적 특성에 따라 초기응력의 크기는 달라질 수 있음을 보여주었으며, 동일 시추공 내에서라도 구조선 등과 같은 뚜렷한 불연속면이 있을 경우초기응력의 방향이 심도에 따라 변화될 수 있음을 보여주었다.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.475-483
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• 2018

Square tubular columns are commonly used in moment resisting frames, while through-diaphragm connection is the most typical configuration detail to connect the H-shaped beam to the column. However, brittle fracture normally occurs at the complete joint penetration weld between the beam flange and the through-diaphragm due to the stress concentration caused by the geometrical discontinuity. Accordingly, three improved types of through-diaphragm are presented in this paper to provide smooth force flow path comparing to that of conventional connections. Tensile tests were conducted on four specimens and the results were analyzed in terms of failure modes, load-displacement response, yield and ultimate capacity, and initial stiffness. Furthermore, strain distributions on the through-diaphragm, the beam flange plate, and the column face were comprehensively evaluated and discussed. It was found that all the proposed three types of improved through-diaphragm connections were able to reduce the stress concentration in the welds between the beam flange and the through-diaphragm. Furthermore, the stress distribution in connection with longer tapered through-diaphragm was more uniform.

• 콘크리트학회논문집
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• 제11권6호
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• pp.35-46
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• 1999

The steel fiber reinforced concrete may affect substantially to the tension stiffening at post cracking behavior. Even if several tension stiffening models exist, they are for plain and normal strength concrete. Thus, the development of tension stiffening models for steel fibrous high strength RC members are necessary at this time when steel fiber reinforced and high strength concretes are common in use. This paper presents tension stiffening effects from experimental results on direct tension members with the main variables such as concrete strength, concrete cover depth, steel fiber quantity and aspect ratio. The comparison of existing models against experimental results indicated that linear reduced model closely estimated the test results at normal strength level but overestimated at high strength level. Discontinuity stress reduced model underestimated at both strength levels. These existing models were not valid enough in applying at steel fibrous high strength concrete because they couldn't consider the concrete strength nor section area. Thus, new tension stiffening models for high strength and steel fiber reinforced concrete were proposed from the analysis of experimental results, considering concrete strength, rebar diameter, concrete cover depth, and steel fiber reinforcement.

• 터널과지하공간
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• 제12권3호
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• pp.158-170
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• 2002

Shi가 개발한 불연속 변형 해석은 많은 발전이 있었지만 지금까지의 해석이 모두 평면변형률이나 평면응력을 가정한 이차원으로 이루어진 해석이다. 하지만 불연속면이 기본적으로 삼차원을 형성하므로 이차원으로 해석하는데는 한계가 있다. 삼차원의 불연속면이 안정성에 큰 영향을 미치는 사면, 지하 비축기지 등의 설계에서는 삼차원 해석에 대한 연구가 필요하다. 이에 이 연구에서는 기존 Shi가 개발한 이차원 불연속 변형 해석을 삼차원 불연속 변형 해석의 이론으로 확장하고 프로그램을 개발하여 실제 블록에 적용함으로써 개발된 이론과 프로그램의 타당성을 검증하였다. 개발한 프로그램을 이용하여 일정한 경사를 가진 블록의 미끄러짐과 쐐기의 미끄러짐을 해석하여 이론값과 정확히 일치하는 결과를 얻었다. 삼차원 이론확장과 검증을 바탕으로 향후 보다 많은 숫자의 블록에 적용하면서 해석을 할 것이다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1166-1171
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• 2008

Despite of the increasing number of the application of drilled shaft piles in construction site, most studies on pile capacity have been focused on the side shear resistance. But it is common that the drilled shaft is socketed on the rock so as to use its bearing resistance. The prediction of the end movement and characteristics of the bearing capacity of the pile is great important as well. Therefore, a series of scaled model tests were carried out in order to study the characteristics of the bearing capacity on rock mass. The material of the test block was cement mortar which was mixed with sand, cement and water, and the size of a test block size was $240{\times}240{\times}240mm$. The axial load was applied by a miniaturized pile of 45mm in diameter and flat jacks and steel plate were used for confinement to simulate the real underground loading conditions. The relation of load-displacement was measured in various different conditions of rock mass such as strength, discontinuity of the rock mass and in-situ stress, so q-w curves of the end of the pile were presented for each condition.

• Journal of Mechanical Science and Technology
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• 제14권2호
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• pp.197-206
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• 2000

A boundary integral equation method in the shape design sensitivity analysis is developed for the elasticity problems with axisymmetric non-homogeneous bodies. Functionals involving displacements and tractions at the zonal interface are considered. Sensitivity formula in terms of the interface shape variation is then derived by taking derivative of the boundary integral identity. Adjoint problem is defined such that displacement and traction discontinuity is imposed at the interface. Analytic example for a compound cylinder is taken to show the validity of the derived sensitivity formula. In the numerical implementation, solutions at the interface for the primal and adjoint system are used for the sensitivity. While the BEM is a natural tool for the solution, more generalization should be made since it should handle the jump conditions at the interface. Accuracy of the sensitivity is evaluated numerically by the same compound cylinder problem. The endosseous implant-bone interface problem is considered next as a practical application, in which the stress value is of great importance for successful osseointegration at the interface. As a preliminary step, a simple model with tapered cylinder is considered in this paper. Numerical accuracy is shown to be excellent which promises that the method can be used as an efficient and reliable tool in the optimization procedure for the implant design. Though only the axisymmetric problem is considered here, the method can be applied to general elasticity problems having interface.

• 한국정밀공학회지
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• 제10권4호
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• pp.109-117
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• 1993

Force balance method is employed to predict forging information such as forging load, tool pressure and normal stress at the surface of tangential velocity discontinuity. The incipient stages of deformation for the plane strain forging of rectangular billets in V-shaped dies of different semi-angles are analysed. To construct an approximate model for the analysis of deformation by the force balance method in the incipient deformation stages, slip-line field is used. When the deformation mode by slip-line method is the same as that by force balance method, the slip-line method and the force balance method give identical solutions. The effects of die angle, coefficient of friction, billet geometries and deforma- tion characteristics are also investigated. In order to verify the validity of force balance analysis, the rigid-plastic finite element simulation for the various forgig parameters are performed and performed and find to be in good agreement.

• 지질공학
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• 제4권2호
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• pp.139-151
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• 1994

암반은 서로 다른 입자 및 미소크랙과 같은 미소구조의 개별요소로 구성되어 있다. 이러한 미소구조에 대한 연구는 대심도 지하공간개발과 관련된 지질공학 및 토목공학분야등에 있어서의 관심이 증대되고 있다. 따라서, 단순한 연속체역학에 의한 접근보다는 구성입자들에 대한 역학적성질 및 개별구조요소등이 고려되어야 할 것이다. 그러나, 단순한 유크리드 공간에서 아들 구조를 표현하기는 매우 어렵다. 그래서 Mandelbrot에 의해 자연에 있어서 규칙성이 거의 없는 물체를 정량적으로 표현하기위한 Fractal이론이 개발되었다. 본 연구에는, 크랙의 진전과 응력의 관계를 평가하기위해 미소구조의 기하학적 성질이 Fractal차원에 의해 계산되었다. 암반의 역학적 성질을 평가함에 있어 그 구조의 복잡성을 Fractal이론에 의해 단순화 및 수치화시켜 균질화이론에 적용시키므로서 그 평가를 보다 용이하고 효과적으로 할 수 있다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.579-582
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• 2011

본 논문에서는 9 % Ni강 LNG 저장탱크 조사를 통해서 유한요소해석을 수행하여 구조건전성을 평가하였으며 실용에서 활용할 수 있는 자료를 제시하였다. 과거의 LNG 저장탱크의 설계는 2차원 선에서만 유한요소해석이 수행되었으나 보다 진보된 하드웨어와 소프트웨어의 발전으로 3차원 유한요소해석이 가능케 되었다. 본 연구에서는 9 % Ni 강 LNG 저장탱크 내조의 정적 구조 해석이 상용 유한 요소 해석 프로그램인 ABAQUS를 통해 수행되었다. LNG 저장 탱크 내조 시공 시 용접부 형상을 참고하여 용접부 모델을 고려한 해석을 각각 수행하였다. 용접부의 탄성계수의 변화를 통하여 최대응력과 최대변위를 계산하였다. 실제 LNG tank의 운용 시 발생하는 하중은 자중과, 수두 압과, 온도차에 의한 열응력이며 이들이 복합적으로 작용하였을 시, 용접선을 고려하지 않은 모델에 대해서는 최대응력이 207 MPa이며, 동일 조건에서 용접선을 포함한 모델에 대해 해석을 수행한 결과로서 최대응력이 그보다 약 100 MPa 정도 상승한 결과가 나타났다. 하중조건에서 온도차에 의한 열응력을 고려함과 고려하지 않음을 비교함으로서 실제 열응력에 대해서는 내조에 큰 영향을 미치지 않음을 확인하였다.

• Composites Research
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• 제28권4호
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• pp.182-190
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• 2015

The phenomenological evolution laws of damage can be defined either based on residual life or residual strength. The failure of a specimen can be defined immediately after or before fracture. The former is called in this paper by "failure defined by approach I" and the latter "failure defined by approach II." Usually at failure there is a discontinuity of loading variables and, because of this, damage at failure is discontinuous. Therefore the values of damage at failure by two different approaches are not the same. Based on this idea the sequence effects of the phenomenological evolution law of damage given by $dD/dN=g(D)f({\Phi})$ were studied. Thin-walled graphite/epoxy tubes consisting of four of $[{\pm}45]_s$ laminates were used for the experimental study of sequence effects and the effects of mean stress on fatigue life. It was found that the sequence effects in two step uniaxial fatigue for $[{\pm}45]_s$ graphite/epoxy tubular specimen showed that a high-low block loading sequence was less damaging than a low-high one.