• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.1
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• pp.3-11
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• 2003

Face stability of a tunnel is a main concern during tunnel excavation. However, there has been only a few studies on this problem while a lot of researches on the support systems have been carried out. In addition, when tunneling is performed below the groundwater level, the groundwater flows into the tunnel so that the seepage forces generated on the tunnel face might give rise to a serious potential for the face instability. In this study, the face stability was evaluated by simultaneously considering two factors: one is the effective stress calculated by upper bound theorem; the other is the seepage forces acting on the tunnel face obtained by numerical analysis under the condition of steady-state groundwater flow. Tunneling in difficult geological conditions often requires auxiliary techniques to guarantee safe tunnel excavations and/or to prevent damage to structures and services around the tunnel. The steel pipe-reinforced multistep grouting has been recently applied to tunnel sites in Korea. Face stability of a tunnel with the steel pipe-reinforced multistep grouting was also analyzed in this study.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.369-379
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• 2012

The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.335-343
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• 2003

In the previous experimental study, it is verified that the ultimate strain of concrete (${\varepsilon}$$_{cu}$=0.003) and coefficient of equivalent stress block (${\beta}$$_1$) can be used for the analysis of RC beams under biaxial and uniaxial bending moment. However, the characteristics of stress distribution of non rectangular compressed area in the RC columns are different to those of rectangular compressed area. The properties of compressive stress distribution of concrete have minor effect on the pure bending moment such as beams, but for the columns subjected to combined axial load and biaxial bending moment, the properties of compressive stress distribution are influencing factors. Nevertheless, in ACI 318-99 code, the design tables for columns subjected to axial loads with bidirectional eccentricities are based on the parameters recommended for rectangular stress block(RSB) of rectangular compressed areas. In this study the characteristics of stress distribution through both angle and depth of neutral axis are observed and formulated rationally. And the modified parameters of rectangular stress block(MRSB) for non rectangular compressed area is proposed. And the computer program using MRSB for the biaxial bending analysis of RC columns is developed and the results of MRSB are compared to RSB and experimental results respectively.

• Journal of the Korean GEO-environmental Society
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• v.5 no.1
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• pp.55-64
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• 2004

Stone column is a soil improvement method and can be applicable for loose sand or weak cohesive soil. Since the lack of sand in korea, stone column seems one of the most adaptable approach for poor ground as a soil improvement technique. However, this method was not studied for practical application. In this paper, the most affective design parameters for the bearing capacity of stone column were studied. The parametric study of major design factors for single stone column was carried out under the bulging and general shear failure condition, respectively. Especially, a test result of single stone column by static load was compared with the bearing capacity values of suggested formulas. The analysis result showed that the ultimate bearing capacity by the formula was much less than the measured value by the static load test. Especially, the result of the parametric study under general shear failure condition showed that the bearing capacity has big difference between each suggested formulas with the variation of the major design parameters. Therefore, the result of this study can be appliable for the future stone column project.

• Journal of the Korean Data and Information Science Society
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• v.21 no.6
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• pp.1171-1180
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• 2010

It is well known that the asymptotic convergence rates of nonparametric regression estimator gets worse as the dimension of covariates gets larger. One possible way to overcome this problem is reducing the dimension of covariates by using single index models. Two coefficient estimation methods in single index models are introduced. One is semiparametric least square estimation method, which tries to find approximate solution by using iterative computation. The other one is weighted average derivative estimation method, which is non-iterative method. Both of these methods offer the parametric convergence rate to normal distribution. However, practical comparison of these two methods has not been done yet. In this article, we compare these methods by examining the variances of estimators in various models.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.5-12
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• 2005

In early days, to analyze the behavior of single pile under axial load, many assumptions were made and field tests were performed. But in recent days, the development of computers led the use of the numerical analysis resulting in more realistic and correct results. The numerical methods are classified into Load Transfer Method and Elastic Solid Approach. In this study a numerical program applying t-z model to Load Transfer Method suggested by Coyle & Reese was developed. And another finite difference program using matrix based on this load transfer was developed. As a result, it is found that the values of the F.D.M. were similar to the values measured in-situ.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.223-234
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• 1996

The purpose of this paper is to present an analysis method by using the finite element method which can exactly analyze load-deflection relationships, crack propagations. and stresses and strains of reinforcements, tendons, and concrete in behaviors of elastic. inelastic and ultimate ranges of reinforced and prestressed concrete slabs under monotonically increasing loads. For t h i s purpose, the m a t e r i a l and geometric nonlinearities are taken into account in this study. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearities of the structure. The material nonlinearities are taken into account by comprising the tension, compression. and shear models of cracked concrete and models for reinforcements and tendons in the concrete : and also a so-called smeared crack model is incorporated. The reinforcements and t,endons are assumed to be in a uniaxial stress state and are modelled as smeared layers of equivalent thickness. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzcd and compared with experimental results. As a result, this method can successfully predict the nonlinear and inelastic behaviors throughout the fracture of reinforced and prestressed concrete slabs.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.435-443
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• 2010

The current design practice of an electric transmission tower is based on the allowable stress design. Design strengths of the electric transmission tower's compression member are determined by buckling the strength of the member itself without considering joint strength. There is a possibility of a joint failure prior to the buckling of a member. Therefore, in this study, joint strength is calculated for various member forces, and the shape of joint and database of strength were established. These data was compared with the member strength obtained from previous research studies based on an equivalent nonlinear analysis technique. Finally, practical evaluation and design method to distinguish failure mode in an electric transmission tower member is proposed.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1018-1022
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• 2008

2007년 Intergovernmental Panel on Climate Change(IPCC) 4차보고서 이후로 지구 온난화에 대한 다양한 부분에 영향 분석 연구가 더욱 활발하게 진행되고 있으며, 그 가운데 수자원 즉 육상의 물 순환은 인간 활동과 생태계 전반에 대한 직접 영향으로 인해 기후변화 정책 수립 시 그 중요성이 더욱 부각되고 있다. 현재까지, 많은 연구에 있어서 Global Circulation Model (GCM)을 직접 축소기법을 이용한 후 이를 수문 모형에 입력하여 수자원 영향 분석을 실시해오고 있다. 국외를 중심으로 기존 GCM보다 해상도가 높은 Regional Climate Model(RCM)을 이용한 분석이 일부 시행되고 있으나, 국내에서는 자료의 가용 여부 및 적용성의 검토가 아직 미비한 실정이다. 이러한 관점에서 본 연구에서는 27km의 해상도를 갖는 기상청 RegCM3 RCM에서 도출된 10일 간격 기후변화 SRES 시나리오 자료에 대한 적합성을 평가하고자 한다. 적합성을 평가 하기위해서 국내 주요지점에 근접한 격자자료를 RCM으로부터 추출하고 이에 대한 수문학적 특성치 분석, 저빈도 분석(low frequency analysis), 극치사상의 분포형태 등을 실측 강수자료와 다양한 형태로 비교 검토하여 RCM 자료의 적합성을 평가하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1540-1544
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• 2008

최근 기후변화의 영향일 것으로 추정되는 이상가뭄의 발생빈도가 잦아지는 상황에서 이에 대한 대비책으로서 댐의 비상용량을 비상용수로 공급하는 방안이 조심스럽게 제기되고는 있으나 현재까지 국내에서는 비상용수에 대한 명확한 정의조차 제시되지 않는 등 다소 생소한 개념이라고 할 수 있다. 본 연구는 비상용수 공급의 국내 외 사례와 비상용수 공급편익 산정에 관한 국내 외 연구를 검토하여 댐에 의한 비상용수 공급의 가능성과 가치를 평가하는 것을 목적으로 한다. 비상용수의 수요는 정기적으로 발생하지 않는 특수한 경우이고 용수공급을 대체할 만한 대안이 거의 없는 극한 상황에서 발생한다. 그러므로 생 공용수의 편익산정 방법에 일반적으로 이용되는 대체시설비용법과 같은 편익산정 기법을 적용하는 것은 여의치 않을 것으로 판단된다. 그리하여 본 연구는 비상용량이 사용될 때의 갈수빈도와 갈수피해액의 관계를 설정하고 피해경감액을 추정함으로써 연평균 편익을 산출하는 방안을 검토하는 방안을 제안하고자 한다. 비상용수 공급편익의 합리적인 계량화하기 위해서는 적절한 이수안전도의 설정과 이에 따른 이수기능의 평가가 선행되어야 한다. 그러나 아직까지 갈수규모에 따른 비상용수 공급편익의 산정방법에 대한 명확한 기준이 마련되지 않은 실정이다. 따라서 향후 비상시 댐의 이수기능을 최대한 활용하고 이에 대한 올바른 가치평가를 위해서도 관련분야에 대한 기초연구가 시급히 이루어져야 할 것이다.