• Computers and Concrete
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• 제7권5호
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• pp.437-453
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• 2010

CFRP has been widely used for strengthening reinforced concrete members in last decade. The strain transfer mechanism from concrete face to CFRP is a key factor for rigidity, ductility, energy dissipation and failure modes of concrete members. For these reasons, determination of the effective CFRP bonding length is the most crucial step to achieve effective and economical strengthening. In this paper, generalizations are made on effective bonding length by increasing the amount of test data. For this purpose, ANSYS software is employed, and an experimentally verified nonlinear finite element model is prepared. Special contact elements are utilized along the concrete-CFRP strip interface for investigating stress distribution, load-displacement behavior, and effective bonding length. Then results are compared with the experimental results. The finite element model found consistent results with the experimental findings.

• 한국구조물진단유지관리공학회 논문집
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• 제15권2호
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• pp.107-115
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• 2011

본 연구는 부착재료의 변화 및 동결융해에 따른 FRP-콘크리트구조물 경계면의 거동을 조사하였다. 실험 시 고려된 연구변수로는 부착경계면의 부착강도, 경계면 유효부착길이 등을 조사하였다. 경계면 부착재료에 따른 거동변화 실험체의 경우 FRP-구조물 부착경계면에 사용되는 에폭시의 종류를 각각 3가지로 분류하며 FRP-콘크리트간 다양한 부착길이를 고려하여 시편을 제작하였으며 동결융해에 따른 경계면 거동조사의 경우 0 cycle에서 300cycle까지 계속적으로 증가되는 주기에 대하여 실험체들을 제작, 장기거동 부착실험을 수행하였다. 본 실험결과, 적용 부착재료의 종류에 따라 최대 유효부착길이는 5~7% 차이가 있었으며 동결융해 주기증가에 따른 최대부착하중 및 유효부착길이의 경우 초기에 나타난 급격한 거동변화 이후 상대적으로 불규칙한 변화를 장기적으로 나타내었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.435-436
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• 2010

본 연구는 동결융해 및 부착재료의 변화에 따른 FRP-콘크리트 부착 경계면의 부착강도 및 유효부착길이의 변화를 조사하였으며, 본 연구 결과를 이용, 개선된 유효부착길이 관계식을 제안하였다.

• 한국철도학회논문집
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• 제12권5호
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• pp.641-648
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• 2009

최근 철도차량의 속도가 증가함에 따라 철도시설물에도 철근콘크리트 구조물이 많이 적용되고 있는 실정이다. 하지만 이러한 콘크리트 구조물은 공용년수의 증가에 따라 필연적으로 구조적인 보강이 요구된다. 강판보강법 및 섬유복합체(FRP)를 활용한 보강법 등이 가장 일반적으로 적용되는 실정이지만 각 공법마다 나름대로의 단점 역시 존재 한다. 최근 화재나 기타 환경적인 공격에 대하여 강한 내구성을 가진 재료의 개발이 요구되고 있으며 이에 따른 현무암으로부터 추출한 Basalt 섬유를 활용한 섬유보강재가 많은 관심을 받고 있다. 이에 본 연구에서는 Basalt 섬유쉬트를 보강재로 사용할 경우 중요한 특성인 콘크리트와의 부착특성에 관하여 연구를 수행하였다. 실험변수는 보강폭, 길이, 보강겹수를 포함한다. 실험결과, 파괴형태는 계면파괴, 섬유파단, 그리고 rip-off의 형태가 관측되었으며 보강길이보다는 보강폭이 보강강도에 더 많은 영향을 미치는 것으로 판단되었다. 또한 보강길이가 전부 유효하게 작용하지는 않았으며 이에 유효보강길이를 산정하고 이에 따른 부착강도를 산정하였다. 이를 다른 종류의 FRP재료를 활용한 경우에 유효 보강길이와 비교하여 Basalt 섬유쉬트의 부착특성을 분석하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권6호
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• pp.253-259
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• 2002

This paper deals with the effects of grounding conductors for metal oxide surge arresters. When surge arresters are improperly installed, the results can cause costly damage of electrical equipments. In particular, the route of surge arrester connection is very important because bends and links of leads increase the impedances to lightning surges and tend to nullify the effectiveness of a grounding conductor. Therefore, there is a need to know how effective installation of lightning surge arresters is made in order to control voltage and to absorb energy at high lightning currents. The effectiveness of a grounding conductor and 18 [㎸] metal oxide distribution line arresters was experimentally investigated under the lightning and oscillatory impulse voltages. Thus, the results are as follows; (1) The induced voltage of a grounding conductor is drastically not affected by length of a connecting line, but it is very sensitive to types of grounding conductor. (2) The coaxial cable having a low characteristic impedance is suitable as a grounding conductor. (3) It is also clear from these results that bonding the metal raceway enclosing the grounding conductor to the grounding electrode is very effective because of skin effect. (4) The induced voltages of grounding conductors for the oscillatory impulse voltages are approximately twice as large as those for the lightning impulse voltages.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.287-290
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• 2005

CFRP strips manufactured in factory are produced normally with smaller width and larger thickness than CFRP sheets. By this reason, bonding force between CFRP strips and concrete substrate is not sufficient to sustain tensile force in CFRP strips. Therefore premature debonding failure cannot be avoided when strengthening is done by simply bonding the CFRP strips. The flexural strength of RC beam strengthened with CFRP strips must be calculated based on the effective strain considering debonding failure. This paper presents test results of an experimental study conducted to evaluate the flexural strength on RC beams strengthened with CFRP strips. 7 specimens were tested with respect to bond length and amount of CFRP strips. From the test results, it was indicated that the strain of the CFRP strips achieved at debonding failure can be decreased less than 6,000$\mu$ depending on the amount of CFRP strips.

• 한국산학기술학회논문지
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• 제21권9호
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• pp.414-423
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• 2020

최근 콘크리트 구조물을 보강하는데 경량이며 높은 강도를 가지고 있는 FRP(Fiber Reinforced Polymer)시트의 사용이 증가하고 있는데 구조물 보강 설계 시 부착 강도가 매우 중요하다. 그래서 FRP시트와 콘크리트 사이의 부착 강도에 대한 정확한 수치 모델을 얻기 위하여 많은 연구자가 다양한 변수(콘크리트 압축강도 및 인장강도, 콘크리트와 FRP의 탄성계수, 콘크리트와 FRP의 폭과 두께, 파괴에너지, 부착 길이, 유효부착길이, 최대 부착 응력과 최대 슬립)를 가지고 실험과 해석 연구를 수행하여 왔다. 결과적으로 많은 모델이 도출되었으나 실무에 쉽게 사용될 수 있는 검증된 모델은 제시되지 않았다. 그래서 본 연구는 현재까지 제안된 23개의 모델(Khalifa 모델, Iso 모델, Maeda 모델, Chen 모델 등)로부터 부착 강도에 미치는 요인을 분석하고 188개의 시험체에 대한 부착 강도 실험값을 각 모델들의 수치 결과 값과 비교하여 수식이 간단하고 높은 정도를 가진 사용하기 쉬운 모델을 제시하고자 하였다. 결과적으로 부착 강도 모델로 Iso 모델과 Holzenkӓmpfer 모델의 유효부착길이에 근거한 실용성 있는 모델을 제안하였다.

• International Journal of Concrete Structures and Materials
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• 제1권1호
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• pp.37-43
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• 2007

This paper discusses the failure mode of reinforced concrete beams strengthened with composite materials based on six experimental set-ups to determine the FRP-to-concrete bond strength. Interfacial bond behavior between concrete and CFRP plates was discussed. Shear test were performed with different concrete compressive strengths (21 MPa and 28 MPa) and different bonding length (100 mm, 150 mm, 200 mm, and 250 mm). Shear test results indicate that the effective bond length (the bond length beyond which the ultimate load does not increase) was estimated as $196{\sim}204\;mm$ through linear regression analysis. Failure mode of specimens occurred due to debonding between concrete and CFRP plates. Maximum bond stress is calculated as about $3.0{\sim}3.3\;MPa$ from the relationships between bond stress and slip. Finally, the interfacial bond-slip model between CFRP plates and concrete, which is governed debonding failure, has been estimated from shear tests. Average bond stress was about $1.86{\sim}2.04\;MPa$, the volume of slip between CFRP plate and concrete was about $1.45{\sim}1.72\;mm$, and the fracture energy was found to be about $1.35{\sim}1.71\;N/mm$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.370-376
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• 2001

When an adhesive joint is exposed to high environmental temperature, the tensile load capability of the adhesive joint decreases because the elastic modulus and failure strength of structural adhesive decrease. The thermo-mechanical properties of structural adhesive can be improved by addition of fillers to the adhesive. In this paper, the elastic modulus and failure strength of adhesives as well as the tensile load capability of tubular single lap adhesive joints were experimentally and theoretically investigated with respect to the volume fraction of filler (alumina) and the environmental temperature. Also the tensile modulus of the fille containing epoxy adhesive was predicted using a new equation which considers filler shape, filler content and environmental temperature. The tensile load capability of the adhesive joint was predicted by using the effective strain obtained from the finite element analysis and a new failure model, from which the relation between the bonding length and the crack length was developed with respect to the volume fraction of filler.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.406-409
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• 2006

Serviceability resign is required to control the cracking at the joint of precast decks having longitudinal prestress in continuous composite bridges. Especially, details of twin girder bridges are complex not only due to main reinforcements and transverse prestress for the resign of long-span concrete slabs but also due to shear pockets for obtaining the composite action. This paper suggests the design guidelines for the magnitude of the effective prestress and for the selection of filling materials and their requirements in order to use precast decks for twin-girder continuous composite bridges. The necessary initial prestress was also evaluated through the long-term behavior analysis. From the analysis, existing design examples were revised and their effectiveness was estimated. When a filling material having bonding strength higher than the requirement is used in the region of high negative moment, uniform configuration of longitudinal prestressing steels along the whole span length of continuous composite bridges can be achieved resulting in simplification of details and enhancement of the construction costs.