• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.161-161
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• 2000

Ferromagnetic 3d 전이금속과 paramagnetic 5d 금속으로 이루어지진 Pt-Co 계는 자기이방적 (magnetic anisotropy) 성질로 인하여 많은 관심을 모으고 있는 계로서는 다층박막 및 합금박막에 대한 지기적 성질에 대한 많은 연구가 있어 왔다. 최근 sputtering method 에 의해 제작된 Pt-Co 합금박막에 대해 Ar 기체분압에 따라 보자력 (coercivity)이 변화되고 PMA (perpendicular magnetic anisotropy)를 갖는 것을 관측하였다. PMA의 근원은 주로 계면에서의 anisotropy 에너지와 관련이 있는 것으로 이해되기 때문에 합금박막의 경우는 PMA가 불가능한 것으로 여겨져 왔다. 그럼으로서 PMA에 대한 근원에 대한 명확한 해석이 필요하게 되었다. 또한 보자력(coercivity)은 불순물의 함량이 감소할수록, 그리고 내부적 변형이 제거될수록 감소하기 때문에, 계면 및 결정구조와 관련이 있는 것으로 알려져 있다. 이러한 자기적 특성을 관찰하고자 [Pt(51 )/Co(112 )]4, [Pt(90 )/Co(66 )]4, 그리고 [Pt(121 )/Co(30 )]4, 다층박막과 이들 박막을 80kV Ar+ 이온선 혼합후 박막의 결정성 변화를 관찰하기 위하여 GXRD (glancing x-ray diffraction) 스펙트럼을 얻어보았다. 그 결과 세 system 모두 disordered fcc 합금박막임을 확인하였다. fcc(111) 방향에 대한 평균 격자공간(lattice spacing)의 크기변화는 한층 당의 Co 두께가 두꺼울수록 거의 선형적으로 감소함을 볼수 있었다. MOKE 실험에 의하면, 이들 다층박막이나 합금박막의 경우 모두, in-plane 방향에 대해 자화 용이축(easy magnetization axis)을 가지고 있었다. 그리고 보자력의 크기에 있어서, 다층 박막의 경우에 있어서 Co 층에 두께 두꺼울수록 보자력의 크기가 감소하였지만 그림1에서와 같이 합금박막의 경우는 정반대로 Co층의 두께가 얇을수록 보자력의 크기가 감소함을 관찰하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.25-32
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• 2016

The pile-cap connection part which transfers foundation loads through pile body is critical element regarding flexural and shear force because the change of area, stress, and stiffness occurs in the this region suddenly. The purpose of this study is to investigate the structural behavior of pile-cap connection dependent on fabrication methods using conventional PHC pile and composite PHC pile. A series of test under cyclic lateral load was performed and the connection behavior was discussed. From the test results, it was found that the initial rotational stiffness of pile-cap connection was affected by the length of pile-head inserted in footing and the location of longitudinal reinforcing bars. The types of pile and location of longitudinal reinforcing bars governed the behavior of pile-cap connection regarding load-carrying capacity, ductility, and energy dissipation.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.103-111
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• 2008

Soils naturally contain grains of different minerals which may be dissolved under chemical or physical processes. The dissolution leads changes in microstructure of particulate media, such as an increase in local void or permeability, which affects the strength and deformation of soils. This study focuses on the small strain stiffness characteristics of vanishing mixtures, which consist of sand and salt particles at different volume fractions. Experiments are carried out in a conventional oedometer cell (Ko-loading) integrated with bender elements for the measurement of shear waves. Dissolutions of particles are implemented by saturating the mixtures at various confining stresses. Axial deformation and shear waves are recorded after each loading stage and during dissolution process. Experimental results show that after dissolution, the vertical strain and the void ratio increase, while the shear wave velocity and small strain shear modulus decrease. The decrease of the velocity results from the void ratio increase and particle contact decrease. The process monitoring during dissolution of the particles shows that the vertical strain dramatically increases at the beginning of the saturation process and converges after vanishing process finishes, and that the shear wave velocity decreases at the beginning and increases due to the particle reorientation. Specimens prepared by sand and salt particles are proved to be able to provide a valuable insight in macro structural behaviors of the vanishings mixtures.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.3-16
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• 1999

The objective of BMP( Barge Mounted Plant) project is to construct plants on mooring floating structures at sea. To analyze the pile behavior under mooring dolphins, generally, axial or lateral behavior of soil-pile system is evaluated by using a nonlinear subgrade reaction method which models the pile as a structural element and the soil as series of nonlinear springs along the depth. As a result, load-displacement curves at pile head can be solved by finite difference method and the equivalent stiffness of bottom boundaries of dolphin structure is evaluated. In this study off-shore site investigation was performed on the marine area of Koje Island and axial and lateral load transfer curves of the ground were modeled with depth. The subgrade reaction analysis was performed for piles under axial or lateral loadings, and the required penetration depth and section of the pile were determined. Subsequently, the spring boundaries under the dolphin structure could be modeled from the calculated load-displacement curve and then the dynamic response of the dolphin structure was analyzed reasonably by considering ground conditions. The analysis considering the stiffness of the soil-pile system has resulted in larger displacement amplitudes than those for rigid foundations. Furthermore, moment distributions of the casing were dependent on the soil-pile system so that deformable foundation induces the larger moment of top section of casing and the smaller moment of pile head.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.4 s.50
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• pp.15-24
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• 2006

This work reports the results of our study on the dynamic response of various buried pipelines depending on their boundary conditions. We have studied behavior of the buried pipelines both along the axial and the transverse direction. The buried pipelines are modeled as beams on elastic foundation while the seismic wave as a ground displacement in the form of a sinusoidal wave. The natural frequency, its mode, and the effect of parameters have been interpreted in terms of free vibration. In order to investigate the response on the ground wave, the resulting frequency and the mode shape obtained from the free vibration have been utilized to derive the mathematical formula for the forced vibration. The natural frequency varies most significantly by the soil stiffness and the length of the buried pipelines in the case of free vibration. The effects of the propagation direction and velocity and the frequency of ground wave on the dynamic responses of concrete, steel, and FRP pipes have been analyzed and then dynamic responses depending on the type of pipes have been compared. Through performing dynamic analyser for various boundary conditions and estimation of the location of maximum strain has been estimated for the type of pipes and boundary conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.439-452
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• 1994

A method to optimize the cost of R/C frames and an algorithm of the optimal limit state design for R/C frames subjected to dynamic loads are presented. The modal superposition method was used to find the dynamic responses of the frames. Each member of R/C frame is made up of more than two elements and the stiffness matrix and consistent mass matrix of three d.o.f in the node of each element was used to include axial, shear and flexural effects. The objective function to be minimized formulated the cost of materials, steel and concrete, and optimised to satisfy the behaviors of R/C frame and each constraint imposed by the limit state requirements. Both objective function and each constraint are derived in terms of design variables which include the effective depth, beam width, compression and tension steel area, and column shear steel area. A few applications are presented which demonstrate the feasibility, the validity and efficiency of the algorithm for automated optimum design of R/C frames where dynamic behavior is to be considered.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.1-8
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• 2001

Seismic design forces for bridge components may be determined by modifying elastic member forces of design earthquakes using appropriate response modification factors according to the national design code of bridges Modeling technique of pile foundation system is one of the important parameters which greatly affects the results in the process of the elastic seismic analysis of a bridge system with pile foundation. In this paper, a approximate and simplified modeling technique of a pile foundation system for the practical purposes is presented. The modeling technique is based on the stiffnesses of pile foundation during earthquake. The horizontal stiffnesses are determined from the resistance-deflection curves derived from the results of dynamic field tests using cyclic loads and the vertical stiffness includes the effects of the end bearing capacities and side friction of piles as well as the pile compliances under the expected vertical load level. The applicability of the proposed technique has been validated through the some example bridge analyses.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3C
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• pp.159-166
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• 2008

The stress-strain behavior of soils can usually be regarded as non-linear, while it is also known that the soil exhibits the linear-elastic behavior at pre-failure state (very small strain range, $<10^{-3}%$). This study aims to analyze the variation of anisotropic elastic shear moduli of granular soils in various stress conditions. The stress probe experiments with the triaxial testing device equipped with local strain gages and multi-directional bender elements were conducted. When the stress ratio exceeds the range between -0.5 and 1.5, the elastic shear stiffness in the axial direction deviates from the empirical correlation with current stresses, which indicates that the yielding of soils alters the internal pathway through which the elastic shear wave propagates. The experimental results show that the variation of elastic shear moduli in the horizontal direction closely relates to the volume change of soils.

• The Journal of Engineering Geology
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• v.8 no.1
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• pp.75-86
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• 1998

Eighteen oriented samples from the Jeongsun limestone of the Joseon Supergroup are collected. The orientations of C-axis of calcite and e twin plane, the average thickness, numbers of twins and the widths of calcite grains in 10 samples are measured. Then, the twin strain, mean width, intensity of twin and relative magnitude and orientations of principal stresses are calculated using Calcite Strain Gauge program. Twin strain, mean width and intensitv rainge between 0.801%~10.927%, $0.43{\mu\textrm{m}}~2.03{\mu\textrm{m}}$, and 33.5~113.4twim/mm, respectively. Metamorphic temperatures calculated from twin show below $70^{\circ}C$, indicating that twins were developed within 2.3km depth. In five samples, two events with different orientations of principal stress produced calcite twins, while only one event produced calcite twins in five samples. The direction of the maximum stress is almost horizontal and the minimum is almost vertical, indicating that the stress regirne is identical with thrust fault. E-W and NW-SE are the most dominant directions of comressive stress and N-S and NE-SW directions are also shown. Comparision between paleostress orientations measured in the study and others indicates that the maximum horizontal stress oriented to E-W may represent the paleostress of period either from the Silurian to the Triassic or from the Silulian to the Permian. Paleostress oriented to NW-SE may be the major direction of stress during the Daeho orogeny.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.129-138
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• 2012

This paper deals with geometrical non-linear analyses of the tapered variable-arc-length beam, subjected to the combined load with an end moment and a point load. The beam is supported by a hinged end and a frictionless sliding support so that the axial length of the deformed beam can be increased by its load. Cross sections of the beam whose flexural rigidities are functionally varied with the axial coordinate. The simultaneous differential equations governing the elastica of such beam are derived on the basis of the Bernoulli-Euler beam theory. These differential equations are numerically solved by the iteration technique for obtaining the elastica of the deformed beam. For validating theories developed herein, laboratory scaled experiments are conducted.