• Journal of the Korean Society for Railway
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• v.20 no.3
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• pp.329-338
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• 2017

A recent trend of technical development in auxiliary-power-supplies (APS) is to replace 60Hz low frequency transformers with isolated type dc/dc converters. This paper introduces the technical trend in APS structures and proposes a power converter circuit suitable for high-efficient and light-weight APS. By utilizing the resonant converter, which achieves ZCS, to reduce switching losses, various types of APS structures (1-stage and 2-stage) are reviewed, and they are verified by simulation. The full-bridge resonant LLC converter is designed with a 1-stage power converting structure; the resonant converter topology is designed with a 2-stage power converting structure that has a pre-regulator converter to compensate for the wide input voltage range. Both a step-down converter and a step-up converter are designed and compared for the pre-regulator in the 2-stage structure. Operational characteristics are compared with simulation results and loss analyses are presented to proposes appropriate system structure and topologies.

• Korean Journal of Construction Engineering and Management
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• v.24 no.6
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• pp.63-65
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• 2023

BIM and AR technologies have been assessed as a means of enhancing productivity within the construction industry, through the provision of effortless access to critical data on site, achieved via the projection of 3D models and associated information onto actual structures. However, most of the previous researches for applying AR technology in construction quality management has been performed for construction projects in general, resulting in only overall on-site management solutions. Also, a few previous researches for the application of AR in the quality management of specific elements like reinforcements focused only on simple projection, so conducting specific quality inspection was impossible. Hence, this study aimed to develop a practically applicable BIM-based AR quality management system targeted for reinforcements. For the development of this system, the reinforcement inspection items on the quality checklist used at railway construction sites were analyzed, and four types of AR functions that can effectively address these items were developed and installed. The validation result of the system for the actual railway bridge showed a degradation of projection stability. This problem was solved through model simplification and enhancement of the AR device's hardware performance, and then the normal operation of the system was validated. Subsequently, the final developed reinforcement quality inspection system was evaluated for practical applicability by on-site quality experts, and the efficiency of inspection would significantly increase when using the AR system compared to the current inspection method for reinforcements.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.3 s.22
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• pp.69-76
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• 2006

An hydraulic and hydrologic analysis procedure was proposed to reduce the inundation damage of highway in urban stream, that could contribute the EAP and Traffic control planning of Dongbu highway in the Jungrang stream basin which is one of the representative urban area in Korea. We performed the HEC-HMS runoff analysis, and the UNET unsteady flow modeling to decide the inundation reaches and their characteristics. The high inundation risk areas were of Emoon railway bridge and the Wollueng bridge, which are inundated in the case of 10 year and 20 year frequency flood respectively. We also analyze the inundation characteristics under the various conditions of the accumulation rainfall and the duration. Flood elevation at the Wolgye-1 bridge exceed over Risk Flood Water Level(EL.17.84 m) when the accumulation rainfall is over 250 mm and shorter duration than 7 hr. When neglecting backwater effect from the Han river, inundation risk are highly at the reach C2(Wolgye-1 br. ${\sim}$Jungrang br., left bank), C1(Wolgye-1 br. ${\sim}$Jungrang br., right bank), D(Jungrang br. ${\sim}$Gunja br.) in order, but when consider the effect, the inundation risk are higher than the others at the reach D2(Jungrang br. ${\sim}$Gunja br., left bank) and E(Gunja br. ${\sim}$Yongbi br.), which are located downstream near confluence.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.965-972
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• 2011

Unlike metallic materials, the importance of fatigue performance of concrete has been ignored. However, it is reported that environmental effects, if it cause deterioration, may increase the risk of fatigue failure under repeated loadings. In case of railroad bridges, the risk may increase due to highly periodic, repetitive, heavier nature of train load, which runs through the fixed passage called the track. Especially, when new material or structure is implemented for a main bridge member, experimental validation should be performed to avoid damage or failure due to unexpected behavior. In this paper, the fatigue performance of an IT girder is examined via a repeated loading test. The IT girder is a new type of a prestressed concrete (PSC) girder with two prestressed H-beams in the top of the girder, which provide additional sectional capacity, and it can be applied to the span longer than 30m which is a typical limit for a usual PSC girder. To obtain the fatigue performance, a 10m IT girder specimen is designed, and a repeated load test is performed by applying the cyclic load two million times. The fatigue performance of the girder is examined according to the Japanese and the CEB-FIB design codes. The fatigue test result shows that the IT girder satisfies both design codes.

• Geomechanics and Engineering
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• v.2 no.2
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• pp.125-140
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• 2010

Slope stability analysis of the right abutment of a railway bridge proposed at about 350 m above the ground level, crossing a river and connecting two huge hillocks in the Himalayas, India is presented in this paper. The site is located in a highly active seismic zone. The rock slopes are intensely jointed and the joint spacing and orientation are varying at different locations. Static slope stability of the rock slope is studied using equivalent continuum approach through the most commonly used commercial numerical tools like FLAC and SLOPE/W of GEOSTUDIO. The factor of safety for the slope under static conditions was 1.88 and it was reduced by 46% with the application of earthquake loads in pseudo-static analysis. The results obtained from the slope stability analyses confirmed the global stability of the slope. However, it is very likely that there could be possibility of wedge failures at some of the pier locations. This paper also presents the results from kinematics of right abutment slope for the wedge failure analysis based on stereographic projections. Based on the kinematics, it is recommended to flatten the slope from 50o to 43o to avoid wedge failures at all pier locations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.61-68
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• 1991

The system such as railway bridge can be modelled as the restrained beam with intermediate supports. This kind of structures are subject to the moving load, which has a great effect on dynamic stresses and can cause sever motions, especially at high velocities. Therefore, to analyze the dynamic characteristics of the system due to the moving load is very important. In this paper, the governing equation of motion of a restrained beam subjected to the moving load is derived by using the Hamilton's principle. The orthogonal polynomial functions, which are trial functions and satisfying the geometric and dynamic boundary conditions, are obtained through simple procedure. The dynamic response of the system subjected to the moving loads is obtained by using the Galerkin's method and the numerical time integration technique. The numerical tests for various constraint, velocity and boundary conditions were preformed. Furthermore, the effects of mass of the moving load are studied in detail.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.1
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• pp.125-136
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• 1984

In the weled structures, fatigue fracture mainly depends upon crack growth behavior. Specially anisotropy of crack growth orientation and welding direction become important factor of fracture in the welding jone. When fatigue stressed steel welded with nonfatigue stressed steel, at the low stress intensity factor range, residual stress become more important factor of growth behavior then properties of base metal but when the crack growth in the weld metal, toughness of weld metal become the most important factor. Especially nonhomgeniety of toughness for the weld metal make more scatter the relations of $da/dN-{\Delta}K$.

• Structural Engineering and Mechanics
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• v.52 no.1
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• pp.173-203
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• 2014

The cross-section warping due to the passage of high-speed trains can be a relevant issue to consider in the dynamic analysis of bridges due to (i) the usual layout of railway systems, resulting in eccentric moving loads; and (ii) the use of cross-sections prone to warping deformations. A thin-walled beam formulation for the dynamic analysis of bridges including the cross section warping is presented in this paper. Towards a numerical implementation of the beam formulation, a finite element with seven degrees of freedom is proposed. In order to easily consider the compatibility between elements, and since the coupling between flexural and torsional effects occurs in non-symmetric cross-sections due to dynamic effects, a single axis is considered for the element. The coupled flexural-torsional free vibration of thin-walled beams is analysed through the presented beam model, comparing the results with analytical solutions presented in the literature. The dynamic analysis due to an eccentric moving load, which results in a coupled flexural-torsional vibration, is considered in the literature by analytical solutions, being therefore of a limited applicability in practice engineering. In this paper, the dynamic response due to an eccentric moving load is obtained from the proposed finite element beam model that includes warping by a modal analysis.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2512-2518
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• 2014

The praseodymium-doped $TiO_2$ photocatalyst samples, which could degrade methyl orange under UV irradiation, were prepared by sol-microwave method for improving the photocatalytic activity of $TiO_2$. The resulting materials were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, Fourier transform infrared spectra (FTIR) and Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS). It was found Pr doping retarded the growth of crystalline size and the phase transformation from anatase to rutile, and narrowed the band gap energy. Praseodymium doping brought about remarkable improvement in the photoactivity. The optimal dopant amount of Pr was 2% by molar of cement and the calcination temperature was $500^{\circ}C$ for the best photocatalytic activity. The improvement of photocatalytic activity was ascribed to the occurrence of lattice distortion and the effective containment of the recombination of the electron-hole by $Pr^{3+}$.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1430-1436
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• 2010

Tubular member is hollow and is an excellent source of structural member with great buckling resistance and tortional resistance. With its development and simplicity in structure, steel tubular truss has the ability to be structured in long span bridges, without a stiffener. Recently, it has been used in many countries in Europe, Canada, Japan, and the US with the help of international committees such as CIDECT(International Committee for the Development and Study of Tubular Structures and International Institute of Welding). The most important problem when using the tubular member is the fact that it is difficult to test the fatigue stress determined by nominal stress, since geometrical stress concentration occurs due to the welded joint's nod of complexity. The purpose of this study is to compare and examine current theories and widely applied Hot Spot stress determinations through finite element analysis, which is about welded joints of steel tubular truss. We would like to suggest a way of design practice which involves a bridge plan with rarely domestically used steel tubular truss` basic research data as well as considering the future of tubular member.