• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.13 no.4
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• pp.20-29
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• 2014

Density is applied both three major macroscopic traffic variables (traffic volume, speed, and density) and two measures of effectiveness (MOE) for level of service (LOS) on highway (density and V/C). Especially, it is known for the most accurate MOE on evaluating the LOS of highway. Despite such importance, there is a lack of study on density relatively than other variables for its difficulty of measurement. Existing density estimation methods have some limitations such as density values of same traffic flow vary with collecting time. In this study, we researched actual density measuring method with panoramic image, after each CCTV images in the Sapaesan Tunnel on Seoul Ring Expressway are matched into one panoramic image. Analysis through the Central Limit Theorem shows that density of 24 1 km-images, which means 24 second, applies traffic situation well. That is to say that reasonable density value regardless of collecting time, and practical density which represents actual traffic flow can be taken in case of measuring density by suggested collecting cycle.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.273-280
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• 2003

Tunneling in difficult geological conditions is often inevitable especially in urban areas. Ground improvement and reinforcement techniques are often required to guarantee safe tunnel excavations and/or to prevent damage to adjacent structures. The steel pipe-reinforced multi-step grouting method has been recently applied to tunnel sites in Korea as an auxiliary technique. In this study, the face stability with steel pipe-reinforced multi-step grouting was evaluated by simultaneously considering two factors: one is the effective stress acting on the tunnel face calculated by limit theorem and limit equilibrium method; the other is the seepage force obtained by means of numerical analysis. The study revealed that the influence of the steel pipe-reinforced multi-step grouting on the support pressure in dry condition is not significant while there is relatively a large amount of reduction in seepage forces by adopting the technique in saturated condition. The effect of the anisotropy of permeability on the seepage force acting on the tunnel face was also estimated by conducting the coupled analysis. It was found that a higher horizontal permeability compared with the vertical one causes reduction in the seepage force acting on the tunnel face.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.807-814
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• 1994

One case of pointwise limit design is performed for a hyperbolic paraboloid saddle shell(originally used by the Lin-Scordelis) to check the design strength against a consistent design loads, therefore, to verify the adequacy of current design practice for reinforced concrete shells. The design method which was based on stresses from membrane analysis in conjunction with pointwise limit state design equations shows a good performance, which means that the design method gives a lower bound on the ultimate load. This shows the adequacy of the current practice at least for this saddle shell case studied. To generalize the conclusion many more designs-analyses are performed with different shell configurations.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.515-527
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• 2020

This paper presents a stress field approach for the shear capacity of stirrup-reinforced concrete beams that explicitly incorporates the contribution of principal tensile stresses in concrete. This formulation represents an extension of the variable strut inclination method adopted in the Eurocode 2. In this model, the stress fields in web concrete consist of principal compressive stresses inclined at an angle θ combined with principal tensile stresses oriented along a direction orthogonal to the former (the latter being typically neglected in other formulations). Three different failure mechanisms are identified, from which the strut inclination angle and the corresponding shear strength are determined through equilibrium principles and the static theorem of limit analysis, similar to the EC-2 approach. It is demonstrated that incorporating the contribution of principal tensile stresses of concrete slightly increases the ultimate inclination angle of the compression struts as well as the shear capacity of reinforced concrete beams. The proposed stress field approach improves the prediction of the shear strength in comparison with the Eurocode 2 model, in terms of both accuracy (mean) and precision (CoV), as demonstrated by a broad comparison with more than 200 published experimental results from the literature.

• Geomechanics and Engineering
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• v.39 no.2
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• pp.171-179
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• 2024

Gravity wall combined with anchoring frame beam is widely adopted to support a high slope under complex geomorphic condition, in which the rigid gravity wall is adopted as a lower structure and the flexible anchoring frame beam serves as an upper structure. The seismic anchor force and the seismic active earth pressure are two essential issues for the seismic design of combined retaining structure in high seismic intensity area. In this study, an analytical model of combined retaining structure is established based on the upper bound theorem of limit analysis, and the formulas for seismic anchor force and seismic active earth pressure of combined retaining structure are derived. The results are optimized by using the global optimization algorithm. The proposed method is verified by a comparison with previous method. Moreover, the influence of main parameters on seismic anchor force and seismic active earth pressure is analyzed to facilitate the seismic design of such combined retaining structure.

• Journal of KSNVE
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• v.10 no.4
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• pp.648-654
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• 2000

A procedure to determine the realizable optimal positions of rigid supports is suggested to get a maximum fundamental natural frequency. a measured frequency response function based substructure-coupling technique is used to model the supported structure. The optimization procedure carries out the eigenvalue sensitivity analysis with respect to the stiffness of supports. As a result of such stiffness optimization, the optimal rigid-support positions are shown to be determined by choosing the position of the largest stiffness. The optimally determined support conditions are verified to satisfy the eigenvalue limit theorem. To demonstrate the effectiveness of the proposed method, the optimal support positions of a plate model are investigated. Experimental results indicate that the proposed method can effectively find out the optimal support conditions of the structure just based on the measured frequency response functions without any use of numerical model of the structure.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.569-575
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• 2018

The stability of shallow cavities with an arbitrary profile is a difficult issue in geotechnical engineering. This paper investigates this problem on the basis of the upper bound theorem of limit analysis and the Hoek-Brown failure criterion. The influence of pore pressure is taken into consideration by regarding it as an external force acting on rock skeleton. An objective function is constructed by equating the internal energy dissipation to the external force work. Then the Lagrange variation approach is used to solve this function. The validity of the proposed method is demonstrated by comparing the analytical solutions with the published research. The relations between shallow and deep cavity are revealed as well. The detaching curve of cavity roof with elliptical profile is obtained. In order to facilitate the application of engineering practice, the numerical results are tabulated, which play an important role in tunnel design and stability analysis of roof. The influential factors on potential collapse are taken into consideration. From the results, the impact of various factors on the extent of detaching is seen intuitively.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.5
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• pp.309-318
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• 1987

In the on-line security analysis of power system, Automatic Contingency Selection (ACS) is commonly used to reduce the number of contingency cases which will be evaluated in detail. This paper describes a fast and reliable ACS method which adopts DC load flow in conjunction with compensation theorem to improve execution time, and applies severity performance index, divided on each limit level for considering overload rate, to make reliable contingency ranking. The method has been tested in IEEE 25 bus system and KEPCO 130 bus actual power system. The results of these tests verify its superiority to both the execution time and reliability, and illustrate its effectiveness for the practical use.

• Journal of the Korean Statistical Society
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• v.24 no.1
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• pp.197-218
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• 1995

We first consider the random censorship model of survival analysis. Efron (1981) introduced two equivalent bootstrap methods for censored data. We propose a new bootstrap scheme, called Method 3, that acts conditionally on the censoring pattern when making inference about aspects of the unknown life-time distribution F. This article contains (a) a motivation for this refined bootstrap scheme ; (b) a proof that the bootstrapped Kaplan-Meier estimatro fo F formed by Method 3 has the same limiting distribution as the one by Efron's approach ; (c) description of and report on simulation studies assessing the small-sample performance of the Method 3 ; (d) an illustration on some Danish data. We also consider the model in which the survival times are censered by death times due to other caused and also by known fixed constants, and propose an appropriate bootstrap method for that model. This bootstrap method is a readily modified version of the Method 3.

• Journal of the Korean Geotechnical Society
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• v.17 no.3
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• pp.69-75
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• 2001

본 논문에서는 지하공동 위에 설치된 띠 기초의 지지력에 대하여 upper bound theory를 이용하여 연구하였다. 기초 크기, 공동의 크기 및 위치, 그리고 지반의 물성치의 영향에 관하여 고찰하였으며 10개의 파괴 형상에 대하여 분석을 수행하였다. 각각의 파괴형상은 지반의 물성치 및 기하학적인 형상에 관한 함수로 표현되어 컴퓨터 해석을 통한 최소화를 시행하였다. 최소화를 위한 프로그램은 Boland C++ Builder를 이용하여 작성한 후 PC에서 수행되었다. 10개의 파괴형상 중 최소의 기초 지지력을 작성된 컴퓨터 프로그램을 통하여 구하였고 이를 해당 기초의 극한 지지력으로 추정되었다. 본 연구의 결과를 종합 정리하여 지하공동 위에 위치한 띠 기조의 극한 지지력을 구할 수 있는 간단한 식을 제시하였다.