• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.253-256
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• 2005

We have constructed the Mount Fuji submillimeter-wave telescope at Nishiyasugawara (alt. 3725 m) near the summit of Mt. Fuji (alt. 3774 m). Thanks to the excellent condition of Mt. Fuji, we have successfully carried out the [CI] survey toward more than 40 square degrees of sky, including qrion MC, Taurus MC, Rosetta MC, DR 15, DR 21, NGC 1333, NGC 2264, W 3, W 44, W 51, L 134, p-Oph. Our [CI] survey have revealed that the [CI] 492 GHz emission widely extends to the molecular clouds. The spatial and velocity structures of the [CI] 492 GHz emission resemble those of 13CO J=l-0 in many molecular clouds, implying that [CI] 492 GHz and $^{13}CO$ J=1-0 are emitted from the same gas. The column density of $C^o$ linearly correlates with that of CO up to high Av, suggesting that $C^o$ exist in the deep interior of molecular clouds. In several regions, we have found that the distributions of $C^o$ and CO are different from each other. The $C^o$-rich area is found in the Hieles' cloud 2. The C+/CO/$C^o$ configuration is found in DR 15, p-Oph, M 17, Orion KL, and NGC 1333. These results indicate that an origin of $C^o$ is unrelated with the photodissociation process. We discuss the observed $C^o$ distributions in relation to the non-equilibrium chemistry.

• Ocean and Polar Research
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• v.35 no.2
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• pp.107-121
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• 2013

The underwater glider is an autonomous vehicle that can glide through the ocean interior by using a pair of wings attached to its body and can move up and down through the water column by changing its buoyancy. As of now, there are three widely-used gliders, namely, the Spray that was co-developed by Scripps Oceanographic Institution and Woods Hole Oceanographic Institution, the Slocum produced by the Webb Research Cooperation, and the Seaglider that was produced by the University of Washington. In this paper, I will introduce these three gliders and discuss the principles and procedures related to glider operation as well as the application and extendability of modern physical and bio-geochemical sensors to gliders. My experiences in developing a glider for measuring ocean turbulence and testing it 7 times during 12 days are shared in this paper. On the basis of my experiences and knowledge, different kinds of aspects that should be considered for successful glider operation are discussed. In addition, a suggestion is made as to what would be the ideal way to operate underwater gliders in the East/Japan Sea. At the end, the current status of active glider operation teams is presented and the efforts to proceed toward future gliders are briefly introduced.

• Structural Engineering and Mechanics
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• v.30 no.1
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• pp.1-20
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• 2008

The dynamic characteristics of the passive, semi-active, and active tuned-liquidcolumn dampers (or TLCDs) are studied in this paper. The design of the latter two are based on the first one. A water-head difference (or simply named as water head in this paper) of a passive TLCD is pre-set to form the so-called semi-active one in this paper. The pre-set of water head is released at a proper time instant during an earthquake excitation in order to enhance the vibration reduction of a structure. Two propellers are installed along a shaft inside and at the center of a passive TLCD to form an active one. These two propellers are driven by a servo-motor controlled by a computer to provide the control force. The seismic responses of a five-story shear building with a passive, semiactive, and active TLCDs are computed for demonstration and discussion. The responses of this building with a tuned mass damper (or TMD) are also included for comparison. The small-scale shaking-table experiments of a pendulum-like system with a passive or active TLCD to harmonic and seismic excitations are conducted for verification.

• Journal of the Korean housing association
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• v.26 no.5
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• pp.71-78
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• 2015

Currently, the Korean construction industry is shifting its interest to the overseas construction market because of a stagnating domestic market. In the meantime, the international housing construction market is expanding with respect to new city development projects that are supported by population growth and urban migration. Despite the Korean construction industry's expertise in new city development, technology, and systems for apartment supply, the share of Korean players in the international housing construction market is continuously decreasing. As a measure to overcome this situation, the authors of this study considered the paper "The Development of a Cost Effective, Long-life Housing Model and Construction of Testbed," which is currently in progress as a part of national project. Through literature review and interviews with experts, the authors determined that there are "column+minimum interior (infill)" apartments that are similar to the long-life housing in some areas of China, Southeast Asia, and Russia. Candidate countries expected to be feasible for the entry of long-life housing were selected by determining the top countries that have already entered the long-life housing market and analyzing those selections through additional specific techniques. The external environments of the selected countries were also analyzed. Please refer to the full paper for details.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.111-114
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• 2005

While the existing reinforced concrete flat plate(RC flat plate) has a lot of advantages including reduced building height, it has some weak points such as many steel bars and the brittle rupture by punching shear. Compared with the RC flat plate, the post-tensioned flat plate (PT flat plate) has not only the same merits, but it also makes longer span possible and induces slab-column connections to be failed with the ductile behavior rather than with the brittle behavior by means of post-tensioning. However, it is difficult to define the joint behavior of PT flat plate under vertical and lateral loads since there are limit experimental results. For this reason, the experimental study is undertaken to investigate the comparison of behavior of PT flat plate and RC flat plate, and how flat plate(Gravity Load Resisting System) is displaced as lateral loads, like the wind and the earthquake, are occur. The result of this experiment shows that PT flat plate is generally superior to RC flat plate in terms of controlling crack, postponing stiffness deterioration, energy dissipation, etc.

• International Journal of Concrete Structures and Materials
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• v.11 no.1
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• pp.161-169
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• 2017

Flat slab systems are vastly used in multi-story buildings because of their savings in story height and construction time, as well as for their flexibility in architectural remodeling. However, they frequently suffer brittle punching-shear failure around columns, especially when subjected to lateral loads. Therefore, seismic codes labeled flat slabs as non-ductile systems. This research goal is investigating some construction alternatives to enhance flat slab ductility and deformability. The alternatives are: adding different types of punching-shear reinforcement, using discreet fibers in concrete mixes, and increasing thickness of slab around columns. The experimental study included preparation and testing of seven half-scale interior slab-column connections up to failure. The first specimen is considered a reference, the second two specimens made of concrete mixes with different volumetric ratios of polymer fibers. Another three specimens reinforced with different types of punching-shear reinforcement, and the last specimen constructed with drop panel of inverted pyramidal shape. It is found that using the inverted pyramid-shape drop panel of specimen, increases the punching-shear capacity, and the initial and the post-cracking stiffnesses. The initial elastic stiffnesses are different for all specimens especially for the slab with closed stirrups where it is experienced the highest initial stiffness compared to the reference slab.

• Computers and Concrete
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• v.19 no.2
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• pp.191-201
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• 2017

External pre-stressing is often used in strengthening or retrofitting of steel-concrete composite beams. In this way, a proper numerical model should be able to trace the completely nonlinear response of these structures at service and ultimate loads. A three dimensional finite element model based on shell elements for representing the concrete slab and the steel beam are used in this work. Partial interaction at the slab-beam interface can be taken into account by using special beam-column elements as shear connectors. External pre-stressed tendons are modeled by using one-dimensional catenary elements. Contact elements are included in the analysis to represent the slipping at the tendon-deviator locations. Validation of the numerical model is established by simulating seven pre-stressed steel-concrete composite beams with experimental results. The model predictions agree well with the experimental results in terms of collapse loads, path failures and cracking lengths at negative moment regions due to service loads. Finally, the accuracy of some simplified formulas found in the specialized literature to predict cracking lengths at interior supports at service loading and for the evaluation of ultimate bending moments is also examined in this work.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.5
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• pp.201-211
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• 2021

The Ministry of the Interior and Safety in Korea developed seismic fragility function for various building types in 2009. Damage states for most building types were determined by structural analyses of sample models and foreign references because actual cases damaged by earthquakes rarely exist in Korea. Low-rise, piloti-type buildings showed severe damage by brittle failure in columns due to insufficient stirrup details in the 2017 Pohang earthquake. Therefore, it is necessary to improve damage state criteria for piloti-type buildings by consulting actual outcomes from the earthquake. An analytical approach was conducted by developing analysis models of sample buildings reflecting insufficient stirrup details of columns to accomplish the purpose. The result showed that current spectral displacements of damage states for piloti-type buildings might be too large to estimate actual fragility. When the brittle behavior observed in the earthquake is reflected in the analysis model, one-fourth through one-sixth of current spectral displacements of damage states may be appropriate for existing low-rise, piloti-type buildings.

• Journal of the Korean Society of Safety
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• v.37 no.4
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• pp.101-112
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• 2022

Expanding urbanization practices result in high numbers of buildings being developed in city centers. This high building concentration leads to an increased fire risk, resulting in higher casualty rates and increased economic damages compared to fires in the past. The purpose of this study was to analyze the structural behavior of fire-damaged reinforced concrete buildings using analytical methods and to suggest methods of improving fire resistance in the event of a fire. Damage levels were measured using commercial software to apply the finite element method, ABAQUS, and MIDAS GEN to the dataset. Load-deflection curves were calculated using the effective area and moment of inertia of the fire-damaged columns provided by ABAQUS. The results of this analysis indicate that fire-damaged beams with experience greater deflection from indoor fires than they will from outdoor fires. Fires that occurred on the middle floors were more dangerous than those occurring on higher floors, and eccentrically loaded columns experienced more damage than axially loaded columns. The results indicate that these methods accurately predict structural behaviors of fire damaged concrete columns by considering fire exposure area and eccentric loading.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.5
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• pp.257-266
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• 2024

Due to seismically deficient details, existing reinforced concrete structures have low lateral resistance capacities. Since these building structures suffer an increase in axial loads to the main structural element due to the green retrofit (e.g., energy equipment/device, roof garden) for CO₂ reduction and vertical extension, building capacities are reduced. This paper proposes a machine-learning-based methodology for allowable ranges of axial loading ratio to reinforced concrete columns using simple structural details. The methodology consists of a two-step procedure: (1) a machine-learning-based failure detection model and (2) column damage limits proposed by previous researchers. To demonstrate this proposed method, the existing building structure built in the 1990s was selected, and the allowable range for the target structure was computed for exterior and interior columns.