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Shear Behavior of Reinforced Concrete Beams Strengthened with CFRP Strips (탄소섬유판 (CFRP Strip)으로 보강된 철근콘크리트 부재의 전단거동)

  • Lim, Dong-Hwan;Nam, Min-Hee
    • Journal of the Korea Concrete Institute
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    • v.20 no.3
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    • pp.299-305
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    • 2008
  • The main goal of this study was to examine the shear behavior of reinforced concrete beams strengthened with CFRP strups. Seven rectangular beams were tested. The test variables were the configuration types, spacing length of CFRP strips and the amount of reinforced stirrups bars. From this experimental study, the shear capacity of beams strengthened with CFRP increased significantly compared to the beam without CFRP strip. Maximum increase of ultimate shear strength was found about 100% more than that of the beam without a CFRP strip and the CFRP strips attached in the shear region can resist the occurrence of the initial shear cracks and the propagation of major shear cracks. In this test, most of the shear strengthened beams failed suddenly due to the debonding of CFRP strips. A calculation of the shear strength of reinforced beams strengthened with CFRP strips based on the effective stresses was conducted and the comparisons were made with the test results.

위성 Solar Array Regulator 모듈화를 위한 새로운 전원단 설계

  • Park, Sung-Woo;Park, Heei-Sung;Jang, Jin-Baek;Jang, Sung-Soo;Lee, Jong-In
    • Aerospace Engineering and Technology
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    • v.3 no.2
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    • pp.11-19
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    • 2004
  • A software-controlled unregulated bus system in which the main bus is directly connected to a battery and the duty-ratio for PWM switch is controlled by the on-board satellite software, is usually used for LEO satellites. This paper proposes a new power-stage circuit that can be available for modularization of a power regulator which is used at the software-controlled unregulated bus system satellite. And we analyze the proposed power-stage operation according to its operating modes and verify it by performing software simulation and hardware experiment using prototype. We construct a parallel-module converter which is composed of the proposed power-stage and perform experiment to verify modular characteristics of the proposed power-stage. Finally, we verify the usefulness of the proposed power-stage by comparing above results with those of a parallel-module converter made of conventional power-stage.

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Modeling of RC shear walls strengthened by FRP composites

  • Sakr, Mohammed A.;El-khoriby, Saher R.;Khalifa, Tarek M.;Nagib, Mohammed T.
    • Structural Engineering and Mechanics
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    • v.61 no.3
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    • pp.407-417
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    • 2017
  • RC shear walls are considered one of the main lateral resisting members in buildings. In recent years, FRP has been widely utilized in order to strengthen and retrofit concrete structures. A number of experimental studies used CFRP sheets as an external bracing system for retrofitting of RC shear walls. It has been found that the common mode of failure is the debonding of the CFRP-concrete adhesive material. In this study, behavior of RC shear wall was investigated with three different micro models. The analysis included 2D model using plane stress element, 3D model using shell element and 3D model using solid element. To allow for the debonding mode of failure, the adhesive layer was modeled using cohesive surface-to-surface interaction model at 3D analysis model and node-to-node interaction method using Cartesian elastic-plastic connector element at 2D analysis model. The FE model results are validated comparing the experimental results in the literature. It is shown that the proposed FE model can predict the modes of failure due to debonding of CFRP and behavior of CFRP strengthened RC shear wall reasonably well. Additionally, using 2D plane stress model, many parameters on the behavior of the cohesive surfaces are investigated such as fracture energy, interfacial shear stress, partial bonding, proposed CFRP anchor location and using different bracing of CFRP strips. Using two anchors near end of each diagonal CFRP strips delay the end debonding and increase the ductility for RC shear walls.

Numerical modeling of the aging effects of RC shear walls strengthened by CFRP plates: A comparison of results from different "code type" models

  • Yeghnem, Redha;Guerroudj, Hicham Zakaria;Amar, Lemya Hanifi Hachemi;Meftah, Sid Ahmed;Benyoucef, Samir;Tounsi, Abdelouahed;Bedia, El Abbas Adda
    • Computers and Concrete
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    • v.19 no.5
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    • pp.579-588
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    • 2017
  • Creep and shrinkage are the main types of volume change with time in concrete. These changes cause deflection, cracking and stresses that affect durability, serviceability, long-term reliability and structural integrity of civil engineering infrastructure. Although laboratory test may be undertaken to determine the deformation properties of concrete, these are time-consuming, often expensive and generally not a practical option. Therefore, relatively simple empirically design code models are relied to predict the creep strain. This paper reviews the accuracy of creep and shrinkage predictions of reinforced concrete (RC) shear walls structures strengthened with carbon fibre reinforced polymer (CFRP) plates, which is characterized by a widthwise varying fibre volume fraction. This review is yielded by three commonly used international "code type" models. The assessed are the: CEB-FIP MC 90 model, ACI 209 model and Bazant & Baweja (B3) model. The time-dependent behavior was investigated to analyze their seismic behavior. In the numerical formulation, the adherents and the adhesives are all modelled as shear wall elements, using the mixed finite element method. Several tests were used to demonstrate the accuracy and effectiveness of the proposed method. Numerical results from the present analysis are presented to illustrate the significance of the time-dependency of the lateral displacements and eigenfrequencies modes.

Study on the Characteristics of Korean Fashion Design -mainly on the works of fashion designers since 1980s- (한국적 패션디자인의 특성에 관한 연구 -1980년대 이후 한국패션디자이너의 작품을 중심으로-)

  • 김인경
    • Journal of the Korean Society of Clothing and Textiles
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    • v.19 no.3
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    • pp.536-547
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    • 1995
  • The modernization of the fashion design in our country, like our chaotic modern history, has not been easy for us to grasp its main stream because it lacked historical consciousness and sincere attitude of creating. In trying to find out designs very Korean, designers usually ignore the deeply rooted ideologies and modes of our own, and primarily depend on the scattered fragments of tradition, such as the curled line of the ancient roofs, folk jackets and skirts, and Talcum, our ethnic dance, sometimes making some patchwork like clothes they divan't really intend to make. In the world of modern design, especially of the fashion industrial design, designs more scientific, more rationale and more positively appealing to the consumers, not the unconscious and emotional ones, are being demanded. To win in the fierce competing world of design as well call this age an age of "Design War", it is desirable for us to create our peculiar designs by uniting the internationalism (universality) and nationalism (traditionalism) together under a single rigid purpose. Analyzing the designs mainly of Korean style fashion designers since the 1980s, 1 could see that Korean designs in the aspect of appearance have a strong tendency toward applying or reviving the traditional elements, thus are under a bias toward nationalism rather than in ternationalism. The idea of "very Korean" does not mean a mere harmony or negotiation of the traditional elements with modern ones. It is rather a concept from vivid historical experiences of the conflict between the purely Korean mental, cultural heritages and the demands in mod- eradiation. Therefore, based on this concept of "very Korean" we must create fashions completely Korean and modern at the same time.n and modern at the same time.

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On the Mechanism of Smooth Blasting on the Rock Containing Discontinuties (불연속면이 존재하는 암반에서의 Smooth Blasting의 기구)

  • 박홍민;이상은
    • Explosives and Blasting
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    • v.14 no.4
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    • pp.13-19
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    • 1996
  • Lately, the improtance of smooth blasting is increasing on every construction fields, suchas underground caves, tunnels, and roadconstruction, etc. The main purpose of smooth blasting is to prevent unnecessary cracks from the base rockwhich preserved permanently and is to gain the smooth fracture plane. So, in smooth blashing, explosives with low detonating velocity are generally used. But it is difficult to discuss general theory on the smooth blashing because the mechanical properties of pertienent rocks are difficult regionally. Accordingly basic reserches on the smooth blasting are demended. In this paper, the mechanisms of the smooth blasting on the rocks containing discontinuities were discussd. Firstly, the writer predicted the formation of fracture plane and unevenness using mathematical methodology, the next the model blast tests were conducted in order to simulate the crack propagation modes from the blast holes. Through the research, the following conclusions were obtained l)The blast test results were in reasonally good agreement with the theoretical prediction. 2)The degree of discontinuity has an influence on the fracture morphology.

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The KMTNet View of Variable Stars : Pulsation and Rotation of the EL CVn-type Eclipsing Binary J0247-25

  • Kim, Seung-Lee;Lee, Jae Woo;Lee, Chung-Uk;Lee, Yongseok;Lee, Dong-Joo;Hong, Kyeongsoo;Cha, Sang-Mok;Kim, Dong-Jin;Park, Byeong-Gon
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.1
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    • pp.41.2-41.2
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    • 2018
  • EL CVn-type eclipsing binaries are composed of a massive A-type main-sequence primary star and a hotter B-type secondary one. These are worthy of particular attention because the secondary stars are rare objects to be extremely low-mass white dwarf precursors (ELM proto-WD) with the mass of ${\leq}0.2M_{\odot}$, evolving to higher effective temperatures and higher surface gravities. A few of them were discovered to show multi-periodic pulsations in one or both components. We monitored one of these rare and interesting objects, J0247-25 (=1SWASP J024743.37-251549.2), at two KMTNet sites of SAAO in South Africa and SSO in Australia. The observations were performed with the KMTNet 1.6m telescopes and pre-science 4K CCD cameras during the system test run from July to November 2014. Using the photometric data obtained for a total of 23 nights, we constructed well-defined eclipsing light curves in B/V-bands and derived absolute parameters (mass and radius, etc.) of each binary component. After subtracting model eclipsing curves from the data, we detected seven frequencies with 33~53 cycles per day (c/d) and identified them to be Delta Sct-type pulsations originated from the A-type primary component. Five frequencies were turned out to be excited by rotational splitting of non-radial pressure modes, enabled us to investigate rotational properties. We could not detect any frequency higher than 100 c/d, implying that pulsation amplitudes of the proto-WD secondary decrease greatly.

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Rapid Cooling Performance Evaluation of a ZrCo bed for a Hydrogen Isotope Storage (수소동위원소 저장용 ZrCo용기의 급속 냉각 성능 평가)

  • Lee, Jungmin;Park, Jongchul;Koo, Daeseo;Chung, Dongyou;Yun, Sei-Hun;paek, Seungwoo;Chung, Hongsuk
    • Transactions of the Korean hydrogen and new energy society
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    • v.24 no.2
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    • pp.128-135
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    • 2013
  • The nuclear fuel cycle plant is composed of various subsystems such as a fuel storage and delivery system (SDS), a tokamak exhaust processing system, a hydrogen isotope separation system, and a tritium plant analytical system. Korea is sharing in the construction of the International Thermonuclear Experimental Reactor (ITER) fuel cycle plant with the EU, Japan, and the US, and is responsible for the development and supply of the SDS. Hydrogen isotopes are the main fuel for nuclear fusion reactors. Metal hydrides offer a safe and convenient method for hydrogen isotope storage. The storage of hydrogen isotopes is carried out by absorption and desorption in a metal hydride bed. These reactions require heat removal and supply respectively. Accordingly, the rapid storage and delivery of hydrogen isotopes are enabled by a rapid cooling and heating of the metal hydride bed. In this study, we designed and manufactured a vertical-type hydrogen isotope storage bed, which is used to enhance the cooling performance. We present the experimental details of the cooling performances of the bed using various cooling parameters. We also present the modeling results to estimate the heat transport phenomena. We compared the cooling performance of the bed by testing different cooling modes, such as an isolation mode, a natural convection mode, and an outer jacket helium circulation mode. We found that helium circulation mode is the most effective which was confirmed in our model calculations. Thus we can expect a more efficient bed design by employing a forced helium circulation method for new beds.

Vibration based damage detection in a scaled reinforced concrete building by FE model updating

  • Turker, Temel;Bayraktar, Alemdar
    • Computers and Concrete
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    • v.14 no.1
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    • pp.73-90
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    • 2014
  • The traditional destructive tests in damage detection require high cost, long consuming time, repairing of damaged members, etc. In addition to these, powerful equipments with advanced technology have motivated development of global vibration based damage detection methods. These methods base on observation of the changes in the structural dynamic properties and updating finite element models. The existence, location, severity and effect on the structural behavior of the damages can be identified by using these methods. The main idea in these methods is to minimize the differences between analytical and experimental natural frequencies. In this study, an application of damage detection using model updating method was presented on a one storey reinforced concrete (RC) building model. The model was designed to be 1/2 scale of a real building. The measurements on the model were performed by using ten uni-axial seismic accelerometers which were placed to the floor level. The presented damage identification procedure mainly consists of five steps: initial finite element modeling, testing of the undamaged model, finite element model calibration, testing of the damaged model, and damage detection with model updating. The elasticity modulus was selected as variable parameter for model calibration, while the inertia moment of section was selected for model updating. The first three modes were taken into consideration. The possible damaged members were estimated by considering the change ratio in the inertia moment. It was concluded that the finite element model calibration was required for structures to later evaluations such as damage, fatigue, etc. The presented model updating based procedure was very effective and useful for RC structures in the damage identification.

Three dimensional modelling of ancient colonnade structural systems subjected to harmonic and seismic loading

  • Sarhosis, V.;Asteris, P.G.;Mohebkhah, A.;Xiao, J.;Wang, T.
    • Structural Engineering and Mechanics
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    • v.60 no.4
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    • pp.633-653
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    • 2016
  • One of the major threats to the stability of classical columns and colonnades are earthquakes. The behavior of columns under high seismic excitation loads is non-linear and complex since rocking, wobbling and sliding failure modes can occur. Therefore, three dimensional simulation approaches are essential to investigate the in-plane and out-of-plane response of such structures during harmonic and seismic loading excitations. Using a software based on the Distinct Element Method (DEM) of analysis, a three dimensional numerical study has been performed to investigate the parameters affecting the seismic behaviour of colonnades' structural systems. A typical section of the two-storey colonnade of the Forum in Pompeii has been modelled and studied parametrically, in order to identify the main factors affecting the stability and to improve our understanding of the earthquake behaviour of such structures. The model is then used to compare the results between 2D and 3D simulations emphasizing the different response for the selected earthquake records. From the results analysis, it was found that the high-frequency motion requires large base acceleration amplitude to lead to the collapse of the colonnade in a shear-slip mode between the drums. However, low-frequency harmonic excitations are more prominent to cause structural collapse of the two-storey colonnade than the high-frequency ones with predominant rocking failure mode. Finally, the 2D analysis found to be unconservative since underestimates the displacement demands of the colonnade system when compared with the 3D analysis.