• 한국구조물진단유지관리공학회 논문집
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• 제1권1호
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• pp.89-96
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• 1997

The paper presents the results of experimental studies on two strengthening methods for reinforced concrete (RC) slabs. Bending tests on RC slabs have been carried out to investigate the influence of the increased thickness and externally bonded carbon fiber sheets. The interfaces of new and old concrete of increased thickness specimens have been chipped and treated with bonding agent. The conclusions have been reached as followings. (1) The behavior of specimens with chipped interface is good enough to calculate flexural strength of RC slabs for increased depth. (2) The flexural stiffness of increased depth specimen is severely increased and the deformation of RC slabs is controled. (3) The specimens with externally bonded carbon fiber sheets can be assumed to behave monolithically.

• 한국안전학회지
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• 제14권1호
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• pp.129-140
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• 1999

This study presents test results of RC beams strengthened by steel plates, carbon fiber sheets(CFS) and aramid fiber sheets(AFS) for increasing flexural and shear resistance. The test was performed with different parameters including the type of strengthening materials, flexural-strengthening methods and shear-strengthening methods. In case of flexural test, RC beams are initially loaded to 70% of the ultimate flexural capacity and in case of shear test loaded to 60 or 80 percent of the ultimate shear capacity and subsequently reinforced with steel plates, CFS and AFS. Experimental data on strength, steel strain, deflection, and mode of failure of the reinforced beams were obtained, and comparisons between the different shear reinforced schemes and the non-strengthened control beams were made. The test results showed that damaged RC beams strengthened by steel plates, CFS and AFS have more improved the flexural and shear capacity. For the beams with external reinforcement by steel plates, aramid fiber sheets and carbon fiber sheets increases in ultimate strength of 4 to 21, 17 to 43 and 26 to 36 percent were respectively achieved. Initial load had small effect on strength after reinforcement, but an important influence on deflection. One sheet reinforced was stronger than two sheets reinforced but less deflected than two sheets reinforced.

• 소성∙가공
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• 제24권4호
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• pp.241-247
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• 2015

In order to prevent shape defects such as fluting and stretcher strains during press forming of aged low carbon steel sheets, roller leveling conditions for reducing yield point elongation were studied. Yield point elongations of leveled sheets were determined as a function of leveling, which is defined as the plastic fraction or the ratio of plastically deformed part in sheet thickness section to the whole thickness of the sheet. By adjusting this plastic fraction during leveling to more than 78%, yield point elongation in the leveled sheets was reduced so no fluting occurred during subsequent tangential bending. Stretcher strains can be avoided by leveling the sheet to an 84% plastic fraction condition.

• 한국강구조학회 논문집
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• 제25권3호
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• pp.299-305
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• 2013

본 연구에서는 각형 중공강관(SHS) 장주기둥에 CFRP쉬트를 길이방향으로 보강하여 중심축하중 실험을 수행하였다. 총 3개의 장주실험체와 1개의 stub column 실험체를 제작하였으며, 실험변수는 CFRP 보강겹수이다. 실험결과 장주기둥에 대해 실험체 중간에서 전체좌굴이 발생하며 횡변위가 발생하여 파괴되었지만, CFRP쉬트의 보강을 통해 전체좌굴을 제어하며 횡변위로 인한 안정성을 확보하였다. 또한 CFRP쉬트의 보강으로 최대 22%의 내력이 상승하여 내력상승효과를 확인할 수 있었다.

• 한국농공학회논문집
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• 제48권1호
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• pp.61-68
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• 2006

The p-version nonlinear finite element model has been developed to analyze the nonlinear behavior of simply supported RC slabs strengthened with carbon fiber reinforced plastic sheets. The shape function is adopted with integral of Legendre polynomials. The compression model of concrete is based on the Kupfer's yield criterion, hardening rule, and crushing condition. The cracking behavior is modeled by a smeared crack model. In this study, the fixed crack approach is adopted as being geometrically fixed in direction once generated. Each steel layer has a uniaxial behavior resisting only the axial force in the bar direction. Identical behavior is assumed fur tension and compression of steel according to the elastic modulus. The carbon fiber reinforced plastic sheets are considered as reinforced layers of equivalent thickness with uniaxial strength and rigidity properties in the present model. It is shown that the proposed model is able to adequately predicte the displacement and ultimate load of nonlinear simply supported RC slabs by a patch with respect to reinforcement ratio, thickness and angles of CFRP sheets.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.601-606
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• 1998

In recent years, strengthening by steel plate, carbon fiber sheets, and carbon fiber laminate in spotlighted in order to repair and rehabilitation of R/C slabs. In this study, 3 method of rehabilitation are analyzed from the tests. Test parameters are the width of cracks, the method of repair and rehabilitation, the magnitude of pre-load. Deflection, failure load, strains of reinforcing bar, strains of sheet and plates are measured during tests. The failure mode and separption load analyzed from these measured data.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.691-696
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• 1997

In recent years, stengthening of beam by steel plate, carbon fiber sheets, and carbon fiber laminate is spotlighted in order to repair and rehabilitation of R/C structures. In this study, 3 method of rehabilitation technic are analyzed from the tests. Test parameters are the width of cracks, the method of repair and rehabilitation, the magnitude of existing load. Deflection, failure load, strains of reinforcing bar, strains of sheet and plates are measured during tests. The failure mode and ultimate load are analyzed from these measured data. Test result shows that the width of cracks and the magnitude of existing load do not make any difference of ultimate flexural capacity.

• 한국구조물진단유지관리공학회 논문집
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• 제21권5호
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• pp.163-169
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• 2017

비닐용기 등에 주로 사용되는 PET 섬유는 강도는 아주 작은 반면, 변형성능에는 아주 우수하기 때문에 지진 발생시 구조물의 대변형에 효과적으로 저항할 수 있는 보강재료로 사용가능하며, 일본에서는 이미 PET 섬유를 이용한 연구를 진행하고 있는 실정이다. 따라서 본 연구에서는 PET(polyethylene terephthalate) 섬유의 횡구속 효과를 파악하고, PET 섬유의 보강효과와 기존에 사용해왔던 탄소섬유시트 및 유리섬유시트의 보강효과를 비교함으로써 PET 섬유의 현장적용성 여부를 파악하기 위한 것이다. 이를 위해 무근 콘크리트 공시체에 탄소섬유시트와 유리섬유시트 및 PET 섬유 등으로 구분하고 각각에 대해 콘크리트 강도와 보강겹수를 달리하여 실험체 별로 각각 2개씩 동일하게 제작하여 실험을 실시하였다. 실험결과, 탄소섬유시트 및 유리섬유시트로 보강된 실험체는 기존연구결과들과 마찬가지로 시트가 파단된 후 급격한 내력저하로 최종파괴 되었다. 그러나 PET로 보강한 실험체들은 PET 섬유가 파단되지 않고 최대 강도 이후 급격한 내력저하 없이 서서히 감소되면서 최종파괴 되었다. 또한, 탄소섬유시트 및 유리섬유시트로 보강한 실험체에 비해 강도증진 효과는 크지 않았으나, 연성측면에서는 매우 우수하게 나타나 향후 보강재료로 사용할 수 있을 것으로 판단된다.

• 한국분말재료학회지
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• 제16권1호
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• pp.33-36
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• 2009

In order to increase the magnetic loss for electromagnetic(EM) wave absorption, the soft magnetic $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was used as the basic material in this study. The melt-spun strip was pulverized using an attrition mill, and the pulverized flake-shaped powder was crystallized at $540^{\circ}C$ for 1h to obtain the optimum grain size. The Fe-based powder was mixed with 2 wt% $BaTiO_3$, $0.3{\sim}0.6$ wt% carbon black, and polymer-based binders for the improvement of electromagnetic wave absorption properties. The mixture powders were tape-cast and dried to form the absorption sheets. After drying at $100^{\circ}C$ for 1h, the sheets of 0.5 mm in thickness were made by rolling at $60^{\circ}C$, and cut into toroidal shape to measure the absorption properties of samples. The characteristics including permittivity, permeability and power loss were measured using a Network Analyzer(N5230A). Consequently, the properties of electromagnetic wave absorber were improved with the addition of both $BaTiO_3$ and carbon black powder, which was caused by the increased dielectric loss of the additive powders.

• Steel and Composite Structures
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• 제32권5호
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• pp.595-610
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• 2019

This paper deals with the static and dynamic behavior of Functionally Graded Carbon Nanotubes (FG-CNT)-reinforced porous sandwich (PMPV) polymer plate. The model of nanocomposite plate is investigated within the first order shear deformation theory (FSDT). Two types of porous sandwich plates are supposed (sandwich with face sheets reinforced / homogeneous core and sandwich with homogeneous face sheets / reinforced core). Functionally graded Carbon Nanotubes (FG-CNT) and uniformly Carbon Nanotubes (UD-CNT) distributions of face sheets or core porous plates with uniaxially aligned single-walled carbon nanotubes are considered. The governing equations are derived by using Hamilton's principle. The solution for bending and vibration of such type's porous plates are obtained. The detailed mathematical derivations are provided and the solutions are compared to some cases in the literature. The effect of the several parameters of reinforced sandwich porous plates such as aspect ratios, volume fraction, types of reinforcement, number of modes and thickness of plate on the bending and vibration analyses are studied and discussed. On the question of porosity, this study found that there is a great influence of their variation on the static and vibration of porous sandwich plate.