• 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.

• Journal of the Korean GEO-environmental Society
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• v.11 no.7
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• pp.57-63
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• 2010

The necessity of effective and economical improvement for soft ground is required more and more as mountains form 70% of country. The soft ground improvement methods for ocean development are sand compaction pile method, displacement method are applied to the soft ground improvement from ocean development pre-loading method, air pressure method, well point method, pack drain method, quicklime pile method etc. Among them, the sand compaction pile method, has many problems such as the economical problem on importing materials due to the lack of sand and destroying the nature while collecting sand. To replace the sand with other alternative materials, a study on the bottom ash compaction pile method because the bottom ash has the similar engineering properties with sand. Therefore, in this study, after compose the complex soil with a replacement rate of 10~80% and a large direct shear test, shear test, consolidation test with replacement rates of bottom ash are performed to estimate whether its shear and consolidation characteristics are suitable for the alternative material of compaction pile method. As a result of test, Shear Strength Parameters tend to be increased in accordance with the increase of replacement ratio of bottom compaction pile, and Settlement Reduction Factor and $t_{90}$ tend to be decreased.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.344-351
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• 2010

Slip along a frictional fracture can be approached as initiation and propagation of a mode II crack along its own plane. Fracture mechanics theories predict that under pure mode II loading initiation will occur when the energy release rate of the fracture attains a critical value ($G_{IIC}$), which is generally taken as a material property. For the past few years the rock mechanics group at Purdue University has investigated experimentally the dependence of $G_{IIC}$ on normal stress and on the frictional characteristics of a fracture. A number of experiments has been conducted first on acrylic, a material that, using photoelastic methods, allows visualization of the stress field ahead of the fracture tip; and later on gypsum, a rock model material with relatively low unconfined compression strength. The experimental investigation has been expanded to include other frictional materials with higher unconfined compression strength. Direct shear tests have been conducted on specimens made with cement paste. New observations together with previous experiments indicate that $G_{IIC}$ can only be considered a material property when the peak friction angle of the discontinuity is similar to the residual friction angle; otherwise the critical energy release rate increases with normal stress.

• Tunnel and Underground Space
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• v.28 no.6
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• pp.584-595
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• 2018

This study conducted direct shear test on about 290 sorts of materials such as sandy soil, clayey soil and gravely soil to present proper standard on shear strength of soil. Shear strength of soil in large scale tends to show that angle of internal friction increases as sand contents grow and it ranges $23.5^{\circ}{\sim}34.9^{\circ}C$ with cohesion of 2.0 kPa~15.7 kPa. Elastic modulus was visibly distinct by load, and which increased approximately 80% as vertical load grows. Angle of internal friction arranging $15.0^{\circ}{\sim}28.6^{\circ}$ on clayey soil decreased as clay contents rises and cohesion increase in regular scale. Elastic modulus tends to increase initial elastic modulus with almost same growing rate. While angle of internal friction on gravely soil indicates $29.9^{\circ}{\sim}36.7^{\circ}$ which hardly shows distinctive features. According to test in detail, cohesion of SW (well-graded sand), SP (poorly-graded sand), SC (clayey sand) and SM (silty sand) indicates value by 94%, 78% and 59% comparing to SC, SW and SP respectively. Angle of internal friction of ML (low-liquid limit silt) and CL (low-liquid limit clay) appears almost same features, and MH (high-liquid limit silt) despite of 88% value of ML. Cohesion among them varies with similar growing rate.

• Journal of the Korean GEO-environmental Society
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• v.12 no.5
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• pp.59-63
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• 2011

Ground dynamic parameter such as shear elastic modulus and damping ratio is a very important variable in design of ground-structure with repeated load and dynamic load. Shear elastic modulus and damping ratio on small strain below linear limit strain is constant regardless of strain. Shear elastic modulus as the maximum shear elastic modulus and damping ratio as the minimum damping ratio were considered. As a lot of experiment related to the maximum shear elastic modulus, which is in dynamic deformation characteristics, have been conducted, many factors including voiding ratio, over consolidation ratio(OCR), confining pressure, geology time, PI, and the number of load cycle affect to dynamic soil characteristic. However, the research of ground dynamic characteristic improved with grout is absent such as underground continuous wall construction, deep mixing method, umbrella arch method. In order to investigate the dynamic soil characteristics improved with grout, in this study, resonant column tests were performed with changing water content(20%, 25%, 30%) and injection ratio of grout(5%, 10%, 15%), cure time(7th day, 28th day) As a result, shear elastic modulus and damping ratio, which are ground dynamic parameter, are affected by the injection ratio of milk grout, cure time and water content.

• The Journal of the Convergence on Culture Technology
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• v.9 no.4
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• pp.331-335
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• 2023

As the viscosity of the blood increases, the blood becomes more sticky and difficult to flow, so the possibility of thrombosis increases and the probability of ischemic cerebral infarction increases. The importance of measuring blood viscosity has recently been emphasized for the prevention of circulatory system diseases, and the need for a viscometer capable of easily and accurately measuring blood viscosity has emerged. In this study, the measured values of a viscosity standard solution and an artificial blood by a parallel-plate viscometer ARS-Medi were compared with the those by Ares-G2 of TA instrument, which is internationally recognized for its accuracy and reliability. The viscosity of N44 standard solution, which is a Newtonian solution, was almost perfectly matched between the two instruments at all shear rates. In the case of an artificial blood, which is a non-Newtonian solution, the measured values between the two instruments showed a difference of about 10% at the lowest shear rate 1 rad/s; however, at a clinically significant shear rate of 10 rad/s or higher, the measured values between them were consistent within the error range. We expect that ARS-Medi, a newly developed parallel-plate viscometer for blood, using disposable plates, will be very useful in clinical practice as it improves the convenience and hygiene of blood viscosity measurement.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.874-882
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• 2002

Currently, deep beams are designed according to ACT 318-99 equations derived from experimental data for slender beams with normal-strength concrete. In addition, there is relatively limited information on high-strength concrete deep beams with shear reinforcement. The purpose of this experimental study is to investigate the shear behavior of high-strength concrete deep beams and to grasp the conservatism of ACI shear design provisions. Experimental results on the shear behavior of 22 deep beams under two equal symmetrically placed point loads are reported. compressive strength of concrete cylinder was 800kgf/$\textrm{cm}^2$, and main variables were vertical and horizontal shear reinforcement and shear span-to-overall depth ratio (а/h). Test results showed that for high-strength concrete deep beams with shear span-to-overall depth ratio exceeding 0.75, the vertical shear reinforcement more effectively resisted the shear load than horizontal shear reinforcement. In high-strength concrete deep beams, ACI shear design provisions tended to underestimate the effect of strut-tie action and vertical shear reinforcement and overestimate the ones of horizontal shear reinforcement. Based on the experimental results of high-strength concrete deep beams and shear friction theory, this study modified the equations on the shear capacity specified by the ACI provisions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.3
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• pp.596-601
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• 2009

In this study, the rate-sensitive constitutive model, which was developed in the previous paper of this journal, was validated using the experimental results obtained from the well-calibrated triaxial compression test conducted with the Boston blue clay. The validation was performed for the various cases of the strain rate of 0.05%/hr, 0.5%/hr, 5.0%/hr and OCR of 1, 2, 4, 8. The developed model was validated for the normally and slightly overconsolidated cases; however, the cases of heavily overconsolidation needs further research.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.299-305
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• 2008

The main goal of this study was to examine the shear behavior of reinforced concrete beams strengthened with CFRP strups. Seven rectangular beams were tested. The test variables were the configuration types, spacing length of CFRP strips and the amount of reinforced stirrups bars. From this experimental study, the shear capacity of beams strengthened with CFRP increased significantly compared to the beam without CFRP strip. Maximum increase of ultimate shear strength was found about 100% more than that of the beam without a CFRP strip and the CFRP strips attached in the shear region can resist the occurrence of the initial shear cracks and the propagation of major shear cracks. In this test, most of the shear strengthened beams failed suddenly due to the debonding of CFRP strips. A calculation of the shear strength of reinforced beams strengthened with CFRP strips based on the effective stresses was conducted and the comparisons were made with the test results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.189-196
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• 2018

Degraded shear performance of reinforced concrete members with recycled coarse aggregate (RCA) compared to flexural strength is a problem. To address this, steel fibers can be used as concrete reinforcement material. In this study, the strength and deformation characteristics of SFRC beams using RCA were to be determined by shear tests. Major experimental variables include the volume fraction of steel fiber (0, 0.5%, 1%), the replacement rate of RCA (0%, 100%), and the shear span ratio (a/d = 1, 2). As a result of the experiment, the shear strength of the specimen increased as the rate of mixing steel fiber increased. For specimens with RCA and 1% steel fiber, the maximum shear strengths increased by 1.77 - 6.25% compared to specimens with normal coarse aggregate (NCA). On the other hand, at 0-0.5% steel fiber, the shear strengths of RCA specimens were reduced by 24.2% to 49.2% compared to NCA specimens. This indicates that reinforcement with 1% volume fraction of steel fiber greatly contributes to preventing shear strength reduction due to the use of RCA.