• Structural Engineering and Mechanics
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• v.24 no.1
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• pp.1-18
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• 2006

Strengthening of existing old structures has traditionally been accomplished by using conventional materials and techniques, viz., externally bonded steel plates, steel or concrete jackets, etc. Alternatively, fibre reinforced polymer composite (FRPC) products started being used to overcome problems associated with conventional materials in the mid 1950s because of their favourable engineering properties. Effectiveness of FRPC materials has been demonstrated through extensive experimental research throughout the world in the last two decades. However there is a need to use refined analytical tools to simulate response of strengthened system. In this paper, an attempt has been made to develop a numerical model of strengthened reinforced concrete (RC) beams with FRPC laminates. Material models for RC beams strengthened with FRPC laminates are described and verified through a nonlinear finite element (FE) commercial code, with the help of available experimental data. Three dimensional (3D) FE analysis has been performed by assuming perfect bonding between concrete and FRPC laminate. A parametric study has also been performed to examine effects of various parameters like fibre type, stirrup's spacing, etc. on the strengthening system. Through numerical simulation, it has been shown that it is possible to predict accurately the flexural response of RC beams strengthened with FRPC laminates by selecting an appropriate material constitutive model. Comparisons are made between the available experimental results in literature and FE analysis results obtained by the present investigators using load-deflection and load-strain plots as well as ultimate load of the strengthened beams. Furthermore, evaluation of crack patterns from FE analysis and experimental failure modes are discussed at the end.

• Journal of Korean Society of Steel Construction
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• v.24 no.2
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• pp.175-188
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• 2012

A parametric study for varying the radii of curvature is performed with a curved tub girder bridge having three continuous spans. The bracing forces of top lateral bracings from the results of numerical equations are compared to those of 3-dimensional finite element analyses. New modifying factors applicable in computing the nominal member forces of top lateral bracings were suggested. The numerical equations were derived based on one girder system, and it is shown that the numerical equations exhibit some errors compared with 3D FEA results. The main reason for this phenomenon lies on the number of girders. The twin girder system has an external cross-beam between inner and outer girder. It also has larger lateral stiffness than the single girder system. Finally, the distributions by the torsion, bending, distortion, and lateral loading of the top lateral bracing forces were presented in this paper.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.357-365
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• 2011

The current trends in steel construction intend to use tapered sections to minimize as much as possible the use of excess material. This can be done by choosing the cross-sections to be as economical as possible, leaving the classical approach of using prismatic members. In addition, it is important to predict the buckling behavior of tapered member with large depth-to-thickness ratio in order to prevent the collapse of PEB system subjected to overloads. An experimental investigation of buckling behavior of tapered beam was presented. The primary test parameter was depth-to-thickness ratio and taper ratio. Using initial stiffness and load-carrying capacity proposed by current provision, the simple plastic hinge method using modified Yoda's model and finite element analysis, the prediction of a moment-rotation curve of linearly tapered member was presented. Moreover, comparisons between analytical and experimental data for moment-rotation curves were accomplished.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.1
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• pp.81-88
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• 2011

This paper presents a design of spiral antenna with broad bandwidth for non-linear junction detector(NLJD). An elliptical patch as radiating element located on center position of radiating surface, as well as the spiral elements on radiating surface was designed for broad bandwidth of spiral antenna. An antenna ground structure generating the multi resonance by spiral slit inserted on ground surface was also proposed. In order to realize high directivity and high gain of the proposed antenna, the cavity wall made of Fr4-epoxy and the metal cap were considered in design. As a result, the calculated gain of antenna with metal cap was improved about 3 dB with comparison of antenna without metal cap and the measured main beam directivity toward -z axis direction agreed well with calculation result. The measured axial ratio satisfied the circular polarization within -z axis ${\pm}45^{\circ}$ at design frequency bands and showed reasonable agreement with prediction.

• Journal of the Korea Institute of Military Science and Technology
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• v.1 no.1
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• pp.227-237
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• 1998

HgCdTe Is the most versatile material for the developing infrared devices. Not like III-V compound semiconductors or silicon-based photo-detecting materials, HgCdTe has unique characteristics such as adjustable bandgap, very high electron mobility, and large difference between electron and hole mobilities. Many research groups have been interested in this material since early 70's, but mainly due to its thermodynamic difficulties for preparing materials, no single growth technique is appreciated as a standard growth technique in this research field. Solid state recrystallization(SSR), travelling heater method(THM), and Bridgman growth are major techniques used to grow bulk HgCdTe material. Materials with high quality and purity can be grown using these bulk growth techniques, however, due to the large separation between solidus and liquidus line on the phase diagram, it is very difficult to grow large materials with minimun defects. Various epitaxial growth techniques were adopted to get large area HgCdTe and among them liquid phase epitaxy(LPE), metal organic chemical vapor deposition(MOCVD), and molecular beam epitaxy(MBE) are most frequently used techniques. There are also various types of photo-detectors utilizing HgCdTe materials, and photovoltaic and photoconductive devices are most interested types of detectors up to these days. For the larger may detectors, photovoltaic devices have some advantages over power-requiring photoconductive devices. In this paper we reported the main results on the HgCdTe growing and characterization including LPE and MOCVD, device fabrication and its characteristics such as single element and linear array($8{\times}1$ PC, $128{\times}1$ PV and 4120{\times}1$ PC). Also we included the results of the dewar manufacturing, assembling, and optical and environmental test of the detectors.

• Journal of architectural history
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• v.28 no.6
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• pp.43-54
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• 2019

The grade of East Asian architecture is generally classified by the size, the shape of the roof, and the type of bracket set. The craftsmanship of columns, beam, purlin, stylobate, column base stone and paintwork is also a contributing factor for such classifications. These classifications can be found not only in historical documents such as 「Oksajo(屋舍條)」 of 『Samguksagi(三國史記)』 but also in 「house details regulations of residential architecture(家舍規制)」 of Joseon Dynasty. However, there are differences in detailed designs among the same grade of architecture regardless of the classification. In this research, the Palace, the Royal Residence(宮家), and the Jaesil(齋室) are considered as the Palatial Buildings and Royal Residences. And the advanced architectural o details which appear only in the Royal Architectures are defined as the 'The Architectural Crafts as a Code of Manners'. The Architectural Crafts as a Code of Manners is detailed design, which can be seen as fabrication of materials and supplementary factors. The Architectural Crafts as a Code of Manners used in the Palatial Buildings and Royal Residences reveal the types and their historical changes. This research will present a basis for the repair and restoration of cultural heritages to be carried out in the future, and also prevent them from further damages, thus help to preserve the cultural heritages.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.259-279
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• 1999

Model tests on propped retaining walls were performed for the investigation of wall displacement, distribution of earth pressure, surface settlement and underground movement at various excavation stage in sand. The result of model tests on the trough of surface settlement showed considerable difference depending on the characteristic of wall stiffness, wall friction and soil condition. The location of maximum underground movement were found to be at range of 0.15H to 0. 1H(H: Final excavation depth). Effect of arching by the redistribution of earth pressure were closely related to the stiffness of wall as well as the soil condition. The wall displacement and earth pressure distribution were simulated by elasto - plastic beam analysis program and finite element method with GDHM model respectively. The result of elasto-plastic analysis showed some discrepancy on the wall displacement and earth pressure, but result of underground movement by FEM with various wall stiffness were in good agreement with the model tests.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.128-134
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• 2010

In this paper, a high-power 20-way stripline power divider with low insertion loss and low side lobe level is successfully designed, fabricated and measured as a feed network for an S-band linear array antenna having Dolph-Chebyshev current distribution which has a narrow beam width and very low side lobe level (SLL). The 20-way stripline power divider consists of an 8-way power divider, three 4-way power dividers and three ring hybrids. It utilizes a T-junction structure as a basic element for power dividing. Notches and modified input/output N-to-stripline transitions are used for improving insertion loss and return loss. The fabricated power divider shows insertion loss less than 0.3 ㏈ and rms phase mismatch less than 8o in the full bandwidth. A final 40-way power divider is synthesized by combining symmetrically two 20-way power dividers and is expected to have SLL over 40 dB, based on the measured results of the 20-way power divider.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1023-1031
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• 1994

The closed forms of consistent mass matrix with rotational inertia matrix are developed for free vibration analysis in space sutructures containing linearly tapered members with cross section of thin-walled I-sections. The exact displacement functions are used for formulating mass matrices. The very small slopes of the tapered member are used in usual practice, such that the series expansion forms of these are also developed to avoid numerical failure in vibration analysis. Significant improvements of accuracy and efficiency of free vibation analysis are achieved by using the mass matrices developed in this study. Frequencies of free vibation of tapered members are compared with solutions based upon stepped representation of beam element in the ANSYS. The mass matrices presented in this study can be used for the free vibration analysis of tapered and prismatic members.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1013-1021
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• 1994

The stiffness and mass matrices are developed for free torsional vibration analysis in linearly tapered thin-walled I-beams that takes into account the effect of warping torsion. The approximate shape functions are used for formulating stiffness and mass matrices. Significant improvements of accuracy and efficiency of free vibration analysis are achieved by using the stiffness and mass matrices developed in this study. Frequencies of free vibration of tapered members are compared with solutions based upon stepped representation of beam element and also are verified with model tests. The stiffness and mass matrices presented in this study can be used for the free vibration analysis of tapered and prismatic thin walled I-beams and space structures involving warping torsion.