• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.161-171
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• 2001

점성토의 압밀거동은 투수성뿐만 아니라 변형 특성에 따라 크게 영향을 받으며, 변형 특성은 재하 방법에 따른 변형조건과 흙의 특성, 특히 이방성에 따라 다르게 나타난다. 이 논문에서는 점성토의 이방적 변형 특성이 압밀거동에 미치는 영향을 분석하기 위하여 다양한 변형 조건에 대한 압밀방정식과 압밀계수를 직교 이방성 탄성이론을 이용하여 유도하였다. 다양한 변형 조건에서 등방과 이방적 변형 특성하의 압밀계수를 평가하였으며, 그 결과 탄성계수의 이방성이 압밀계수에 미치는 영향이 매우 크고, 특히 수평방향의 변위가 허용되고, 수직방향의 변위가 구속될수록 크게 나타났다. 따라서 점성토 지반에 대한 하중 재하시 압밀소요시간의 정확한 예측을 위해서는 발생 가능한 변형 조건과 이방적 변형 특성에 대한 적절한 고려가 매우 중요함을 알 수 있었다.

• Korean Journal of Agricultural Science
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• v.14 no.2
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• pp.329-344
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• 1987

This paper described the behavior under repeated loading in triaxial compression test on clay. The experiment was conducted to investigate the influence of controlled various over-consolidation ratio and compaction energy, on the stress-strain behavior of clays. 1. The difference of deviator stress during repeated loading was greatly appeared at large strain. And pore water pressure was decreased at initial of unloading, but it was increased again before long. 2. The recoverable elastic strain (${{\Delta}{\varepsilon}e}$) and the slope of un-reloading were decreased with the increment of over-consolidation ratio (OCR). 3. The recoverable elastic strain (${{\Delta}{\varepsilon}e}$) was increased with the increment of strain rate but it was decreased with the increment of strain in strain rate tests. The slope of un-reloading (Eur) tends to increase with the increment of strain rate and it was decreased with the increment of strain. 4. The recoverable elastic strain was greatly increased with the increment of compaction energy and it slightly tends to decrease with the increment of strain on various compaction energy. The slope of un-reloading was not appeared markedly with increment of compaction energy but it tends to decrease with the increment of strain generally.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.4
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• pp.661-669
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• 1999

이 논문은 탄성지반위에 놓인 원호형 곡선보의 자유진동에 관한 연구이다. 회전관성 및 전단변형을 고려하여 두 개의 매개변수로 표현되는 탄성지반위에 놓인 원호형 곡선보의 자유진동을 지배하는 미분방정식을 유도하고, 이를 수치적분기법과 시행착오적 행렬값탐사법이 결합된 수치해석기법으로 해석하였다. 회전-회전, 회전-고정 및 고정-고정의 단부조건을 갖는 곡선보의 최저차모드 3개의 고유진동수를 산출하였다. 곡선보의 수평높이 지간길이비, Winkler 지반계수, 전단지반계수에 따른 고유진동수 변화를 분석하였으며, 회전관성 및 전단변형의 영향을 고찰하였다.

• Journal of the KSME
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• v.20 no.3
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• pp.211-217
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• 1980

탄성학문제의 엄밀해는 응력의 평형방정식과 변형의 적합조건식 또는 이들을 조합한 탄성의 기 초방정식을 만족하며, 주어진 경계조건을 만족하는 해를 구해야 하겠지만, 문제에 따라서는 그 엄밀해를 구하기가 곤란하거나 또는 아주 복잡하므로 엄밀해에 가까운 근사해를 구하는 것이 편리할 때가 있다. 본강좌에서는 극소 energy 정리와 ritz의 근사계산법을 결합하여 탄성문제의 근사해를 구하는 방법을 설명하고자 한다. 강좌의 처음에는 삼차원에서의 변형 energy와 외력의 일(work)을 유도하고, 이들 사이의 관계로부터 일반국소 energy 정리를 정의한 다음 이 정리가 실제문제에 어떻게 응용될 수 있는가를 보이는 응용예를 주로하여 진행해 보려한다. 이때의 응 용예로 서는 재료역학에서 이미 눈에 익은 기초적 문제를 주로 다루어 보려한다. 재료역학에서의 탄성문제의 해는 정정인 문제와 불정정인 문제를 따로 분류하며, 불정정인 문제의 해는 정역학의 평형방정식과 변형의 적합방정식을 연립으로 하여 해결하든가, 중첩법을 적용하므로서 일반적 으로 상당히 복잡한 해가 되는 것이 보통인데, 본강좌에서 기술하는 방법은 정정 불정정의 문 제를 구별할 필요가 없이 같은 방법이 적용되며 어떤 면에서는 불정정의 문제가 정정의 문제보다 그 해가 간편히 구해질 수 있다는 장점이 있는 것이다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.493-504
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• 2008

This paper presents a computation of nonlinear elastic strains that may occur in the leaflet of the Edwards MIRA mechanical heart valve by the applied high blood pressure using the finite element analysis methodology. By adopting numerical analysis techniques of the commercial finite element analysis code, NISA, structural analyses of the Edwards MIRA mechanical heart valve are performed for the slight variation of leaflet thickness to get the elastic strains occurring in the leaflet while the high blood fluid pressures are applied to the leaflet surface in order that the maximum stress occurring in the leaflet may be less than the yield stress of the leaflet material(Si-Alloyed PyC). And so, only the geometric non-linearity is assumed because large geometric nonlinear elastic strains are expected rather than material nonlinear strains due to the applied high blood pressure. Computed linear and nonlinear elastic strains are compared to make sure the non-linearity of the computed elastic strain. The comparison result shows that large elastic strains occur clearly in the very thin leaflets as high blood pressures are applied. However, only the linear elastic strains occur for low blood pressures, and also for thick leaflets even for the high blood pressures. Hence the nonlinear structural analysis is very required in the structural design of a mechanical heart valve.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.15-24
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• 2007

This paper will present a simple approach (or predicting layer deformation of unbound pavement materials with stress-dependent material properties. The approach is based on an uncoupled formulation in which the resilient and deformation response of unbound materials are considered separately. As a result, an uncoupled approach incorporating a resilient stiffness and Poisson's ratio model is able to simulate field measured deformation in pavement foundations. In addition, a sensitivity analysis is conducted to identify the significant factors in the stress-dependent modulus and Poison's ratio model. The predicted trends of deformation from this analysis are presented and discussed.

• Geotechnical Engineering
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• v.13 no.5
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• pp.89-100
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• 1997

It is very improtant to evaluate the reliable nonlinear deformational characteristics of soils not only in the analysis of geotechnical structures under working stress conditions but also for the soil dynamic problems. Field testings such as crosshole and pressuremeter tests can be used to determine the modulus of soils under in-situ conditions, but it is not possible to determine the modulus over the entire strain amplitude range. Laboratory methods such as resonant column 1 torsional shear test can be used to determine the modulus over the whole strain amplitude range, but it is very difficult to obtain the representative undisturbed samples on the sixte. For the reliable evaluation of nonlinear deformation characteristics of soils on a typical site, small strain modulus obtained from field testy and nomalized modulus reduction curve determined by laboratory bests need to be combined. In this paper, laboratory and Held testy were performed at a sixte which consisted of granite wearthered residual boils to evaluate the nonlinear deformational characteristics of coils such as the effects of strain amplitude, loading frequency, confining pressure and sample disturbance. It has been shorn that when the effects of these factors are properly taken into account, the stiffness values evaluated by various field and labrotary tests are comparable to each other fairly well. Finally, the procedure to evaluate the nonlinear deformstional characteristics of the sixte was proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.135-145
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• 2005

Geotechnical design routinely requires that in-situ strength, stiffness of the ground be determined. In the working stress conditions, the strain level in a ground experienced by existing structures and during construction is less than about 0.1%~1%. In order to analyze the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at small strains, needs to be developed. Cone pressuremeter tests were performed on the western off-shore region of korea, and analyzed using cavity expansion theory and curve fitting technique to obtain the shear modulus at small strain level of $10^{-1}%$. The value of $E_u/S_u$ ratio for the marine clay shows about 589 at the small strain. However the value of $E_u/S_u$ estimated by lab tests are much smaller values ranged from 81 to 91. It is indicated that the curve fitting technique from CPM tests results can be used to obtain the shear modulus at small strain.

• Journal of Korean Society of Steel Construction
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• v.17 no.1 s.74
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• pp.103-113
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• 2005

In the present study, the Direct Inelastic Design (DID) for steel structures developed in the previous study was improved to expand it applicability. The proposed design method can perform inelastic designs that address the design characteristics of steel structures: Group member design, discrete member sizes, variation of moment-carrying capacity according to axial force, connection types, and multiple design criteria and load conditions. The design procedure for the proposed method was established, and a computer program incorporating the design procedure was developed. The design results from the conventional elastic method and the DID were compared and verified by the existing computer program for nonlinear analysis. Compared with the conventional elastic design, the DID addressing the inelastic behavior reduced the total weight of steel members and enhanced the deformability of the structure. The proposed design method is convenient because it can directly perform inelastic design by using linear analysis for secant stiffness. Also, it can achieve structural safety and economical design by controlling deformations of the plastic hinges.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.257-262
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• 2008

Design and analysis of road subgrade system, which is exposed to repetitive loading condition, uses resilient modulus. The behavior of railway subgrade system will not be quite different from that of road system. Following this phenomenological feature of the subgrade system, this paper introduces the implementation of the resilient modulus based constitutive model on a commercial finite element software. The implementation of the resilient modulus models such as K-${\theta}$ and Uzan on a FE program has been conducted previously. These model assumes that the material state reaches to the nonlinear elastic condition and with further application of repetitive loads, the response of material is completed in elastic condition. According to the recent test results performed on cohesive subgrade soils, however, permanent deformation occurs with repetitive loads. With aids of previously suggested models the permanent deformation cannot be modeled. To overcome such limitation a plastic potential derived from the test results and simple failure criterion based constitutive model is developed. The comparison between the analysis and test results shows a good correlation.