• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.861-874
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• 2019

A great interest in the seismic performance evaluation of small size tunnel structures such as utility tunnel has been taken since recent earthquakes at Pohang and Gyeongju in Korea. In this study, the three-dimensional dynamic analyses of vertical shaft and horizontal tunnel under seismic load were carried out using FLAC3D. Especially, parametric analyses was performed to investigate the effects of interfacial stiffness on interfacial behavior between soil and structure. The parametric analysis showed that the interfacial stiffness scarcely gave an effect on the global dynamic behavior of the structure, while had a significant effect on the local displacement behavior of the connections. The magnitude of the interfacial stiffness was inversely proportional to the displacement, while the magnitude of interface stiffness was proportional to the normal and shear stresses. The results of this study suggest the limitations of the existing empirical equations for interfacial stiffness and emphasize the need to develop new interfacial stiffness models.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.10
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• pp.549-555
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• 2017

The purpose of this study is to investigate how ozone-dissolution-tank structure affects micro-ozone-bubble distribution, energy consumption and water treatment efficiency. The partition walls inside the ozone-dissolution-tank generate pressure changes, shear forces, and swirling flows, which change the size of the bubble diameter. The size of the bubble diameter differs by 10.5% depending on the partition walls. Changes in ozone-bubble diameter are related to energy consumption. As the ozone-bubble becomes smaller, the bubble generation energy increases, but the ozone production energy decreases as the dissolution efficiency increases. Therefore, an ozone-dissolution-tank should be determined by means of an optimal condition producing a micro-ozone-bubble with a minimum sum of bubble generation energy and ozone production energy. The energy consumed to inject the same amount of ozone into the effluent differs by 2.5% depending on the partition walls. However, considering the water treatment efficiency, the conditions for selecting the ozone-dissolution-tank are variable. This is because the free radicals that increase as the ozone-bubble gets smaller are very efficient for water treatment. Even at the same ozone injection concentration, the water treatment efficiency differs by 10.4% according to the partition walls. Therefore, we have studied ozone-dissolution-tank structure which produces reasonable ozone-bubble considering water treatment efficiency and energy efficiency.

• Composites Research
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• v.29 no.2
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• pp.53-59
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• 2016

Aircraft wing structure is used as a fuel tank containing the fluid. Fuel tank and joint parts are consists of composite structure. Hydrodynamic Ram(HRAM) effect occurs when the high speed object pass through the aircraft wing or explosion and the high pressure are generated in the fuel tank by HRAM effect. High pressure can cause failure of the fuel tank and the joint parts as well as the aircraft wing structure. To ensure the aircraft survivability design, we shall examine the behavior of the joint parts in HRAM effect. In this study, static tensile tests were conducted on four kind of the composite T-Joints. The failure behavior of the composite T-joint was examined by strain gauges and high speed camera. We examine the validity of the Finite Element Modeling by comparing the results of FEA and static tensile tests. The failure stresses and failure pressure of the composite T-Joint were calculated by FEA.

• The Journal of the Petrological Society of Korea
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• v.22 no.4
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• pp.251-261
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• 2013

Hwagae area, which is situated in the southeastern part of the Jirisan province, Yeongnam massif, Korea, is mainly composed of Precambrian Jirisan metamorphic rock complex (JMRC). Lithofacies distribution of the Precambrian constituent rocks mainly shows NS-trending tight fold and EW-trending open fold. This paper researched deformational phased structural characteristics of JMRC based on the geometric and kinematic features and the forming sequence of multi-deformed rock structures, and suggests that the geological structure of this area was formed through at least three phases of ductile deformation. (1) Most of structural elements related to the $D_1$ deformation were recognized as $S_{0-1-2}$ composite foliation which was transposed by the $D_2$ deformation. (2) The $D_2$ deformation occurred under the EW-directed tectonic compression, and formed the NS-trending $F_2$ fold and $D_2$ ductile shear zone which is (sub)parallel to the axial plane of $F_2$ fold. (3) The $D_3$ deformation occurred under the NS-directed tectonic compression, and partially reoriented the pre-$D_3$ structural elements into ENE or WNW direction. It indicates that the distribution of Precambrian lithofacies showing NS and EW-trending folds in the Hwagae area is closely associated with the $D_2$ and $D_3$ deformations, respectively.

• Journal of the Korean Geosynthetics Society
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• v.8 no.2
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• pp.47-54
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• 2009

The ballast track, the most common type of conventional railroad track in Korea, is deteriorated by abrasion of ballast, it's penetration into roadbed, and rugged surface of roadbed caused by cyclic loading of train. Persistent occurrence of those phenomena lead to insufficient drain capacity, one of major factors in track design, and it increases pore water pressure and decreases of shear strength under rainfall condition leading to unstable roadbed. In this study, cylindrical model tests are executed for 3 types of geotextile applying cyclic loading in order to observe the characteristics of displacement and bearing capacity of geotextile, and undrained condition has been applied for 0 day, 3 days and 7 days to each geotextiles. The results showed that there was about 1% difference at the final displacement rates between reinforced soils and nature soils and the displacement of the ground surface increases along with the degrees of the saturation. And in case that water contents exceeds the threshold, it is also apparent that weight and tensile strength of geotextile influences displacement of the ground surface. And the larger weight of geotextile is, the smaller plastic displacement. It is evaluated that non-woven fabric comes into effect on reducing the bearing capacity but, the weight of geotextile has little influence on it.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.557-562
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• 2017

The microstructural evolution and modulation of mechanical properties were investigated for a $Ti_{65}Fe_{35}$ hypereutectic alloy by addition of $Bi_{53}In_{47}$ eutectic alloys. The microstructure of these alloys changed with the additional BiIn elements from a typical dendrite-eutectic composite to a bimodal eutectic structure with primary dendrite phases. In particular, the primary dendrite phase changed from a TiFe intermetallic compound into a ${\beta}$-Ti solid solution despite their higher Fe content. Compressive tests at room temperature demonstrated that the yield strength slightly decreased but the plasticity evidently increased with an increasing Bi-In content, which led to the formation of a bimodal eutectic structure (${\beta}$-Ti/TiFe + ${\beta}$-Ti/BiIn containing phase). Furthermore, the (Ti65Fe35)95(Bi53In47)5 alloy exhibited optimized mechanical properties with high strength (1319MPa) and reasonable plasticity (14.2 %). The results of this study indicate that the transition of the eutectic structure, the type of primary phases and the supersaturation in the ${\beta}$-Ti phase are crucial factors for controlling the mechanical properties of the ultrafine dendrite-eutectic composites.

• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.303-312
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• 2007

Steel box girder bridges are being commonly designed for medium-span bridges of span length. Composite truss bridges with steel diagonals instead of concrete webs can be an excellent design alternative, because it can reduce the dead weight of superstructures. One of the key issues in the design of composite truss bridges is the joint structureconnecting the diagonal steel members with the upper and lower concrete slabs. Because the connection has to carry concentrated combined loads and the design provisions for the joint are not clear, it is necessary to investigate the load transfer mechanism and the design methods for each limit state. There are various connection details according to the types of diagonal members. In this paper, the joint structure with group stud connectors welded on a gusset plate is used. Push-out tests for the group stud connectors of were performed. The test results showed that the current design codes on the ultimate strength ofthe stud connection can be used when the required minimum spacing of stud connectors is satisfied. Flexure-shear tests were conducted to verify the applicability of the design provisions for combined load effects to the strength of joint structures. To increase the pullout strength of the connection, bent studs were proposed and utilized for the edge studs in the group arrangement of the joint. The results showed that the details of the joint structure were enhanced. Thereafter, design guidelines were proposed.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.5
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• pp.233-238
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• 2010

The phase transformations and the shape memory effect in In-rich Pb alloys and In rich-Sn alloys have been studied by means of X-ray diffractometry supplemented by metallographic observations. The alloys containing 12~15 at.%Pb transform from the ${\alpha}_2$ (fct) phase to the ${\alpha}_1$ (fct) phase by way of an intermediate phase (m phase) on cooling. The results of X-ray diffraction show that the metastable intermediate phase is observed both on cooling and heating, and has a face-centered orthorhombic (fco) structure. It is concluded that the ${\alpha}_1{\rightleftarrows}{\alpha}_2$ transformation is expressed by the ${\alpha}_1{\rightleftarrows}m{\rightleftarrows}{\alpha}_2$ transformation both on usual cooling and heating with the rate more than $8{\times}10^{-3}$ K/s. The $m{\rightleftarrows}{\alpha}_2$ transformation takes place with a mechanism involving macroscopic shear and are of diffusionless (martensitic) type. The temperature hysteresis in the two transformations is 10~13 K between the heating and cooling transformations. The alloys containing 0~11 at.%Sn are -phase solid solutions with a face centered tetragonal structure (c/a > 1) at room temperature, the axial ratio increasing continuously with tin content. The In-(11~15) at.%Sn alloys are mixtures of ${\alpha}$ and ${\beta}$ phases, the ${\beta}$ phase having a f. c. tetragonal structure (c/a < 1). The alloys containing more than 15 at.%Sn are ${\beta}$-phase solid solutions. The In-(12.9~15.0) at.%Sn alloys show a shape memory effect only when quenched to the temperature of liquid nitrogen, although their effect becomes weak and finally disappears after keeping at room temperature for a long time. The ${\beta}{\rightarrow}{\alpha}^{\prime}$ phase transformation is of the diffusionless (martensitic) type, and takes place between 330 K at 12.9 at.%Sn and 150 K at 14.5 at.%Sn. The hysteresis of transformation temperatures on heating and cooling is considerably large (29~40 K), depending on the composition. Both In-Pb and In-Sn alloys showed distinct the shape memory effects.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.419-427
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• 2006

In this paper, an experimental real-time hybrid method, which implements the earthquake response control of a building structure with a TLD(Tuned Liquid Damper) by using only a TLD as an experimental part, is proposed and is experimentally verified through a shaking table test. In the proposed methodology, the whole building structure with a TLD is divided into the upper TLD and the lower structural parts as experimental and numerical substructures, respectively. The control force acting between their interface is measured with a shear-type load-cell which is mounted on the shaking table. The shaking table vibrates the upper experimental TLD with the response calculated from the numerical substructure, which is subjected to the excitations of the measured interface control force at its top story and an earthquake input at its base. The experimental results show that the conventional method, in which both a TLD and a building structure model are physically manufactured and are tested, can be replaced by the proposed methodology with a simple experimental installation and a good accuracy for evaluating the control performance of a TLD.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.60-66
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• 2012

This paper aims to constitute a feedback vibration control system using wireless sensor networks and experiment it on a model structure to verify its effectiveness. For the purpose, we set up a feedback vibration control system composed of a wireless input/output(I/O) sensor node based on bluetooth, a home-made shear type MR damper, a shaker which generates a constant size of sine wave, and a simple beam model structure. The vibration control experiment was performed by shaking the 1/4 point of beam with a shaker. At the moment of shaking, we controled the vibration with MR damper which was placed vertically on the center of beam. Simultaneously, by acquiring acceleration response at the 2/4 point of beam, we evaluated the effectiveness of control capability. The control command was set to send a voltage signal to MR damper when the acceleration response, acquired from the wireless I/O sensor node placed at the center of beam, was more than a certain amount. Although the realtime feedback vibration control system constituted in this paper is effective only within a limited command system, it has been proven that the system was able to effectively decrease the vibration of structure by generating a control command aimed for realtime purpose. The system also showed a possibility to be used as a structural response control system adapting a variety of semi-active control algorithm.