• 아시안잔디학회지
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• 제20권2호
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• pp.203-211
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• 2006

본 연구는 천연잔디, 인조잔디 및 맨땅 축구장이 축구 경기력에 미치는 영향을 구명하고자 하였다. 천연잔디 축구장은 한지형 잔디(켄터키 블루그래스 80%+퍼레니얼 라이그래스 20%)와 중엽형 한국잔디로 조성된 축구장이며, 인조잔디 축구장은 코니그린 $DV5000^{TM}$으로 조성하였고 맨땅 축구장은 마사토로 조성되었다. 축구 경기력 분석을 위한 볼 구름거리(m)와 수직 볼리바운드(m)는 2005년과 2006년 건국대학교 스포츠과학타운에서 조사하였다. 본 실험에 사용된 공은 한국축구협회(Korea Football Association)에서 공인된 Hummel Air Vision #1을 사용하였고 공기압은 1.0 1bs를 유지하였다. 볼 구름거리는 맨땅 축구장(13.6m) > 인조잔디 축구장(11.4m) > 한지형 잔디축구장(7.8m) > 한국잔디 축구장(4.7m) 순으로 길었다. 또한 볼 구름거리는 잔디의 사용빈도가 적을수록, 잔디의 직립정도가 강할수록, 잔디의 밀도가 높을수록 짧아지는 경향이었다. 수직 볼리바운드 역시 맨땅 축구장(1.0m) > 인조잔디 축구장(0.98m) > 한지형 잔디 축구장(0.68m) > 한국잔디축구장(0.4m) 순으로 높았다. 수직 볼 리바운드는 잔디의 사용빈도가 적을수록, 잔디의 직립정도가 강할수록, 잔디의 밀도가 높을수록 낮아지는 경향이었다. 표준관리가 되는 한지형 잔디 축구장은 조성연수에 따른 볼 구름거리와 수직 볼 리바운드에 미치는 영향이 적었다. 반면 표준 관리가 하지 않은 한국잔디 축구장은 오래 될수록 볼 구름거리는 길어졌고 수직 볼 리바운드 역시 높았다.

• 산업기술연구
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• 제19권
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• pp.115-125
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• 1999

Current design and analyzing methods about soil nailing structures, developed on the basis of results obtained from experiments in laboratory or in field and numerical analyses, have applied different interaction mechanisms between the reinforced nails and the surrounding ground, and this different safety factors against failure have been obtained. They might be proper approached if the assumptions about rigidity of nails and ground conditions are met with actual conditions occurred in field. Otherwise, they would result in designing on analyzing in inappropriate ways so that it is needed to evaluate the validity of them. Therefore, overall behavior and failure mechanism about soil nailing system were investigated by performing numerical method. Using a finite element analysis, parametric studies were made to examine the importance of the various parameters and their effects on the soil nailing system. The numerical technique of FEM, implemented with Hyperbolic constitutive model, was also used to analyze the test results.

• Steel and Composite Structures
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• 제36권4호
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• pp.399-415
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• 2020

Responses of semi-rigid frames having different degrees of semi-rigidity obtained by the nonlinear static analysis (NSA) are evaluated at specific target displacements by comparing them with those obtained by the nonlinear time-history analysis (NTHA) for scaled earthquakes. The peak ground accelerations (PGA) of the earthquakes are scaled such that the obtained peak top story displacements match with the target displacements. Three different types of earthquakes are considered, namely, far-field and near-field earthquakes with directivity and fling-step effects. In order to make the study a comprehensive one, three degrees of semi-rigidity (one fully rigid and the other two semi-rigid), and two frames having different heights are considered. An ensemble of five-time histories of ground motion is included in each type of earthquake. A large number of responses are considered in the study. They include the peak top-story displacement, maximum inter-story drift ratio, peak base shear, total number of plastic hinges, and square root of sum of the squares (SRSS) of the maximum plastic hinge rotations. Results of the study indicate that the nonlinear static analysis provides a fairly good estimate of the peak values of top-story displacements, inter-story drift ratio (for shorter frame), peak base shear and number of plastic hinges; however, the SRSS of maximum plastic hinge rotations in semi-rigid frames are considerably more in the nonlinear static analysis as compared to the nonlinear time history analysis.

• Geomechanics and Engineering
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• 제12권3호
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• pp.417-439
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• 2017

The stone columns are increasingly being used as a soil improvement method for supporting a wide variety of structures (such as road embankment, buildings, storage tanks etc.) especially built on soft soil. Soil improvement by the stone column method overcomes the settlement problem and low stability. Nevertheless, stone column in very soft soils may not be functional due to insufficient lateral confinement. The required lateral confinement can be overcome by encasing the stone column with a suitable geosynthetic. Encasement of stone columns with geogrid is one of the ideal forms of improving the performance of stone columns. This paper presents the results of a series of experimental tests and numerical analysis to investigate the behavior of stone columns with and without geogrid encasement in soft clay deposits. A total of six small scale laboratory tests were carried out using circular footing with diameters of 0.05 m and 0.1 m. In addition, a well-known available software program called PLAXIS was used to numerical analysis, which was validated by the experimental tests. After good validation, detailed of parametric studies were performed. Different parameters such as bearing capacity of stone columns with and without geogrid encasement, stiffness of geogrid encasement, depth of encasement from ground level, diameter of stone columns, internal friction angle of crushed stone and lateral bulging of stone columns were analyzed. As a result of this study, stone column method can be used in the improvement of soft ground and clear development in the bearing capacity of the stone column occurs due to geogrid encasement. Moreover, the bearing capacity is effected from the diameter of the stone column, the angle of internal friction, rigidity of the encasement, and depth of encasement. Lateral bulging is minimized by geogrid encasement and effected from geogrid rigidity, depth of encasement and diameter of the stone column.

• 천문학회보
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• 제38권2호
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• pp.96.1-96.1
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• 2013

A Forbush decrease(FD) is a depression of cosmic ray intensity observed by ground-based neutron monitors(NMs). The cosmic ray intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection(ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of NM station. However, sometimes NMs of the almost same rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on cosmic ray intensity depression rate of FD event recorded at different NMs due to different ICME propagation direction as an additional parameter in the model explaining the cosmic ray modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We confirm that the asymmetric cosmic ray decreasing modulations of FD events are determined by the propagation directions of the associated ICMEs.

• 국제초고층학회논문집
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• 제7권3호
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• pp.255-264
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• 2018

This paper introduces three distinctive means for the use of a 189-meter high damped structure ensuring safety against earthquake: 1. Realization of L-shaped elevational structural planning: The bottom and top of the tower have belt trusses and hat trusses respectively to restrain the bending deformation. Furthermore, large-capacity oil dampers (damping force 6,000 kN) are installed in the middle part of the tower to restrain the higher-mode deformation. 2. Realization of L-shaped planar structural planning: We devised a means of matching the centers of gravity and rigidity by adjusting planar rigidity. Moreover, viscous damping devices are located at the edges of the L-shaped plan, where torsional deformation tends to be amplified. We call this the "Damping Tail" system. 3. Composite foundation to equalize deformations under different loading conditions: We studied the vertical and horizontal deformations using sway-rocking and 3D FEM models including the ground, and applied multi-stage diameter-enlarged piles to the tower and a mat foundation to the podium to keep the foundations from torsional deformations and ensure structural safety.

• 한국농공학회지
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• 제34권1호
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• pp.49-56
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• 1992

This study was carried out to investigate the mechanical behaviour of the plate on a Winkler's foundation according to the soil-structures relative stiffness and the applicability of the conventional analysis method. For the above purpose, Winkler's constant of 4, 15, 25 and 100kg/$cm^2$/cm was considered and the plate thickness of 20, 30, 50, 100 and 150cm was adopted. Results obtained from the numerical examples are summarized as follow: 1. The effects of elastic foundation is considerable for plates with small flexural rigidity. 2. As the Winkler's constant increases, the bending moment in the plate becomes localized near the loading point. 3. The stresses evaluated by the conventional method not correct even for rigid ground such as rock. 4. If the relative stiffness of the plate is very large, for example the plate thickness is larger than 100cm, the conventional analysis method can be justified for the design purposes. 5. On assumption the flexural rigidity of the plate is infinite, the interaction of soil and plate can be ignored in design consideration. The numerical examples in this paper show that when the plate thickness is more than 100cm, the effects of elastic foundation almost disappear. In practical design, soil-plate interaction should be taken into account, because the 100cm-thickness of the plate will not be practical value in usual sites.

• Earthquakes and Structures
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• 제7권1호
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• pp.39-55
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• 2014

A modified procedure is presented for assessing the seismic response of elastic non-proportionate multistory buildings. This procedure retains the simplicity of the methodology presented by the author in earlier papers, but it presents higher accuracy in buildings composed by very dissimilar types of bents. As a result, not only frequencies and peak values of base resultant forces are determined with higher accuracy, but also the location of the first mode center of rigidity (m1-CR). The closeness of m1-CR with the axis passing through the centers of floor masses (mass axis) implies a reduced rotational response and it is demonstrated that in elastic systemsa practically translational response is obtained when this point lies on the mass axis.Besides, when common types of buildings are detailed as planar structures under a code load, this response is maintained in the inelastic phase of their response as a result of the almost concurrent yielding of all the resisting bents. This property of m1-CR can be used by the practicing engineer as a guideline to form a structural configuration which will sustain minimum rotational response, simply by allocating the resisting elements in such a way that this point lies close to the mass axis. Inelastic multistory building structures, detailed as above, may be regarded as torsionally balanced multistory systems and this is demonstrated in eight story buildings, composed by dissimilar bents, under the ground motions of Kobe 1995 (component KJM000) and Friuli 1976 (component Tolmezzo E-W).

• 천문학회지
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• 제56권1호
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• pp.117-124
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• 2023

A Forbush decrease (FD) is a depression of cosmic ray (CR) intensity observed by ground-based neutron monitors (NMs). The CR intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection (ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of the NM station. However, sometimes NMs of almost the same cutoff rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on CR intensity modulation of FD event recorded at different NMs due to different ICME propagation directions as an additional parameter in the model explaining the CR modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We suggest the hypothesis that the asymmetric CR modulations of FD events are determined by the propagation directions of the associated ICMEs.

• 한국지반공학회논문집
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• 제19권6호
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• pp.189-206
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• 2003

터널시공 중, 터널자체의 안정성 확보와 주변지반 및 인접 구조물의 안정성 확보를 위한 체계화된 계측관리는 매우 중요한 사항이라고 할 수 있는데, 지반조건이 불리한 도심지 터널공사나 지반조건이 급격하고 빈번하게 변화하는 경우에 있어서는 그 중요성이 더욱 증대되는 것이 사실이다. 최근 오스트리아에서는, 임의 시점에 대한 절대변위를 계측하고 분석하는 기존의 방법 대신, Geodetic을 이용한 각 시공단계별 상대변위의 계측 및 분석방법이 널리 증가하고 있는데, 이를 통해 지반조건의 급격한 변화 예측 및 이에 상응하는 굴착방법과 지보방식의 변경등이 용이해지고 있다. 한편, 지반의 변위는 막장 굴착이 시공되기 이전부터 발행하기 시작하므로 막장 전방의 응력상태는 향후 변위 진행과정에 있어 매우 중요한 요소라 할 수 있다. 즉, 막장 전방의 강성이나 응력상태는 굴착 후의 장기적인 터널안정성 및 인접 구조물의 안정성 확보와 관련된 주요 변수라 할 수 있다. 본 논문에서는 이와 관련된 다양한 조건에 대한 3차원 변위해석을 실시하였으며, 그 결과를 통해 터널 굴착시의 수직변위 및 벡터회전, 막장면 변위 등의 변화를 살펴보았다.