• Proceedings of the Korea Water Resources Association Conference
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• 1994.02a
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• pp.361-366
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• 1994

저수지 운영방안 정책결정에 있어 보다 효과적으로 적용할 수 있는 방법론의 개발이 여러측면에서 이루어져 왔다. 이중 동적계획기법의 Explicit 및 Implicit 해에 의한 최적운영방안의 검토가 한강수계의 충주댐을 대상으로 이루어졌다. 이들 방법은 한정된 과거 기록치로부터 합성유량을 발생하여 동적계획기법에 의한 충주댐 최적 운영모형에 적용하여 얻어진 상태변수 및 결정변수의 상관관계를 기준으로 도출한 운영율에 기초하여 모의운영모형을 개발할 수 있다. 개발된 모형중 Explicit 기법은 조건확율에 따른 전단계의 이산화된 유입량 조건별 운영단계의 월초저류량을 기준으로 월말 저류량은 결정하는 방법이며, Implicit 기법은 전단계 저류량 및 유입량, 운영단계 저류량 및 유입량을 대상으로 조합에 의한 회귀분석후 상관성이 우수한 운영율 방정식을 개발하게 된다. 본 연구에서는 이렇게 개발된 두가지 운영율을 기준으로 다목적 운영정책 결정을 위한 저수지 모의운영 모형을 개발하여 모형의 이행도를 평가하였다. Explicit 및 Implicit 기법에 기초한 모의모형의 평가방법은 모의치와 과거 운영실적을 비교하는 것으로 하고 Explicit 기법의 적용에서 홍수기 수문사상의 불확실성에 따른 저수지 운영 효율개선을 위하여 수정 방류량 결정방법을 도입하여 가장 적절한 저수지 운영모의모형 개발방법을 제시하고 있다.

• Magazine of the Korea Concrete Institute
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• v.6 no.2
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• pp.118-128
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• 1994

There have been conducted a lot of works on shear behavior of steel fiber reinforced concrete beams. Fiber reinforced concrete beams without shear reinforcement were tested to determine their cracking shear strengths and ultimate shear capacities. Results of tests on 14 reinforced concrete beams (including 11 containing steel fibers) are reported. Two parameters were varied in the study, namely, the volume fraction of fibers and shear span-to-depth ratio.The effects of fiber incorporation on failure modes, deflections, cracking shear strength, and ul~imate shear strength have been examined. Resistance to shear stresses have been found to be improved by the inclusion of fibers, The mode of failure changed from shear to flexure when the shear span-to-depth ratio exceeds 3.4. Based on these investigations, a method of computing the shear strength of steel fiber reinforced concrete beam is suggested. The comparisons between computed values and expenmentally observed values are shown to verify the proposed theoretical treatment and steel fibers efficiency.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.53-68
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• 1998

Microstructural and rock structural analyses on the deformed Cheongsan granite characterized by abundant K-feldspar megacrysts have been carried out to understand the temperature condition for the ductile shear deformation. In K-feldspar, microkinks, microfractures and core-and-mantle structures without the development of subgrains in outer core-zone are the most common microstructures observed. Myrmekites and flame perthites are developed at the strain-localized areas along the microfractured K-feldspar. In plagioclase, microfractures, deformation twins and kink bands are predominant. The deformation twins cut across the igneous zonation of the plagioclase. Patterns of c-axis fabrics of dynamically recrystallized new quartz grains display single girdle and type II crossed girdle where prism slip system is predominant. These characteristic microstructures produced during the ductile shearing suggest that the ductile shear deformation in the Cheongsan granite occurred under epidote-amphibolite conditions($400-500^{\circ}C$). Three main shear zones are recognized at outcrop scale: discrete shear zone with anastomosing high-strain domain, shear zone with pervasive S-C structure and shear zone with homogeneously foliated domain. Geometric features of these shear zones produced during the ductile shear deformation are controlled by amount of strain under the $400-500^{\circ}C$ deformation temperature.

• Journal of the Korean Geotechnical Society
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• v.32 no.5
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• pp.15-26
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• 2016

Dam and embankment are very important civil structures. Grouting is widely used to repair and maintain dam and embankment, and it is important to evaluate the effect of grouting for dam safety. The non-destructive method based on determination of wave velocity in the dam or embankment is effectively used to evaluate grouting effect because wave velocity is identical with stiffness and grouting increases local stiffness in a dam. In this paper, HWAW (Harmonic wavelet analysis of waves) method was applied to evaluate the grouting effect. HWAW method can determine two-dimensional shear wave velocity map with good spatial resolution and the shear velocity profile by the proposed method is sensitive to a variation of stiffness of target system. Through numerical simulation and field tests, the applicability of HWAW method in determining grouting effect is shown.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.27-33
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• 2011

In general, the shear strength of a clay specimen under the direct shear test and the triaxial compression test increases with an increase in the shear rate. This study investigates the effects of shear rate and silt content on the stress-strain behavior of remolded Gwangyang clay, by changing the shear rate and the silt content. Based on the results of the triaxial compression tests, the equi-strain line of remolded Gwangyang clay shows initially positive slope and then becomes flat at certain strain level. As the strain level where the equistrain becomes flat is different depending on the soil with different silt contents, this can be considered as the inherent property of soil.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.121-128
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• 2014

In this study, The purpose of this study is to experimentally investigate the shear behavior of reinforced flat plate embedded with GFRP(glass fiber reinforced polymer) plate with openings. The GFRP shear reinforcement is manufactured into a plate shape with several openings to ensure perfect integration with concrete. The test was performed on 7 specimens. the parameters include the type of reinforcement and amount of the shear reinforcement., From the test, we analysed the crack, failure mode, Strain, load-displacement graph. a calculation of the shear strength of reinforced flat plate with GFRP plate based on the ACI 318-11 was compared with the test results. The results of the experiment indicate that GFRP plate is successfully applied as a shear reinforcement in the flat plate under punching shear.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.6
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• pp.18-25
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• 2007

In a plastic metal forming of thermally rate-sensitive material, the localized shear band stems from evolution of a narrow region in which intensive plastic flow occurs. And it give rise to fatal fracture with plastic instability. The objectives of this study are to investigate the localization behavior by using numerical method and predict the failure for WHA(Tungsten Heavy Alloy). In this work, the implicit finite difference scheme is used because of the advantage about convergence and the numerical stability. This study is based on an analysed material with hardening as well as thermally softening behavior which includes isotropic strain hardening and observed the extension of localization within shear band according to material properties.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.201-207
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• 2006

Soil tests are generally conducted using a membrane to measure a pore water pressure. However, it has also been recognized that the membrane penetrates into the specimen by the change of the confining pressure, and it results in the erroneous measurement in the pore water pressure and the volumetric strain. This study examined the effectiveness of the correction equation of the membrane penetration on the basis of the experimental data acquired during the isotropic unloading and the cyclic shear process using the hollow cylindrical shear test equipment. The results showed that the membrane penetration by the correction equation could be overestimated when the mean effective stress was lower than 20kPa in this study. The limitations originated from the sudden increase near the zero effective stress, and in order to prevent the overestimation in low effective stress condition, the use of the constant a was proposed in this study. Furthermore, the correction equation for the membrane penetration had to be applied carefully when the initial relative density was high and the density changes were occurred by the relocation of the soil particle by the liquefaction.

• Journal of the Korean Geotechnical Society
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• v.20 no.1
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• pp.5-12
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• 2004

The purpose of this paper is to make an understanding of fundamental mechanism of shear behaviour between rock and concrete interfaces in the pile socketed into granite. The interface of pile socketed in rock can be modeled in laboratory tests by resolving the axi-symmetric pile situation into the two dimensional situation under CNS(constant normal stiffness) direct shear condition. In this paper, the granite core samples were used to simulate the interface condition of piles socketed in granite in our country. The samples were prepared in the laboratory to simulate field condition, roughness(angle and height), stress boundary condition, and then tested by CNS direct shear tests. This paper describes shearing behaviour of socket piles into domestic granite through the analysis of CNS test results. It was found out that the peak shear strength increases with the angle of asperity and CNS value, and also the dilation increases with the angle of asperity but decreases with the CNS value.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.342-346
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• 1998

최근의 자동차엔진에서 사용되는 윤활유에는 여러 가지 첨가물이 사용된다. 특히 고분자량 폴리머계의 점도 지수 향상제를 윤활유의 원유에 첨가함으로써 온도 증가에 따른 점도 불안정성을 방지하는 다등급 윤활유 성격을 얻을 수 있다. 그러나 이러한 고분자량 폴리머계의 첨가물은 고온의 엔진 운전 조건에서 윤활유의 점도 안정성을 보장해줌에도 불구하고 엔진 부품들의 정상적인 운동 속도에서도($1-^6 S^{-1}$) 고 전단 변형율 속도로 인하여 유막 감소 효과를 발생 시킨다. 또한 이 첨가제들은 엔진 부품의 마찰 표면에 큰 전단 응력을 지닌 끈끈한 형태의 경계막을 형성한다. 고분자량 폴리머계의 점도 지수 향상제에 대한 예기치 못한 영향은 유막 감소 효과로 인하여 엔진 부품간의 마모를 증가 시키고 점도의 감소로 마찰을 감소 시키는 반면 경계막으로 인하여 고체면이 보호를 받는데 있다. 이러한 유막 형성의 물리적인 개념에 대하여 고체면의 끈끈한 경계막의 존재 효과와 두 경계막 사이에서 일어나는 유막 감소 효과를 표현할 수 있는 현실적인 해석의 필요성이 제기된다. 본 연구는 최근에 많이 쓰이고 있는 점도 향상제가 첨가된 윤활유가 자동차 밸브 트레인 시스템에서 유막 형성에 미치는 영향을 마찰 효율과 마모 방지의 입장에서 고찰하였다.