• Composites Research
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• v.12 no.4
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• pp.62-70
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• 1999

It was well recognized that damages associated mainly with the aging of civil infrastructrues were one of very serious problems for assurance of safety and reliability. In recent, carbon fiber sheet(CFS) has been widely used for reinforcement and rehabitation of damaged concrete beam. However, the fundamental mechanism of load transfer and its load-resistant for carbon fiber sheet reinforced concrete are not fully understood. In this study, three point bend test has been carried out to understand the damage progress and micro-failure mechanism of CFS reinforced concretes. For these purposes, four kinds of specimens are used, that is, concrete, respectively. Acoustic Emission(AE) technique was used to evaluate the characteristics of damage progress and failure mechanism of specimens. In addititon, two-dimensional AE source location was also performed to monitor crack initiation and propagation processes for four types of these specimens.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.119-126
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• 2006

This paper presents the results of a test program for flexural strengthening characteristics of continuous unidirectional carbon-fiber sheets bonded or/and developed to reinforced concrete (RC) beams. A total of six $150mm{\times}250mm{\times}2000mm$ concrete beams were tested. Various sheet development locations were studied to determine their effects on the ultimate flexural strength of the beams. From the test, it was found that the strength increases remarkably with the development of sheets at shear bar. Among the various location, multi-developed sheet provided the most effective strengthening for concrete beam. Beam strengthened using this scheme showed 53% increase in flexural capacity as compared to the control beam without any strengthening.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.183-193
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• 2006

This study deals with the response of reinforced concrete beams strengthened with carbon fiber sheets. Test beams are subjected to static loading and repeated loading. Based on the static test results of the RC beams strengthened with carbon fiber sheets, repeated loading tests are performed. The variables of repeated loading test are composed of the number of carbon fiber sheets, the existence of U-shaped band at the end for anchoring, and loading rate of repeated loading, etc. Test results show the flexural behavior, the characteristics of strength, the characteristics of ductility, the change of flexural rigidity, and the amount of energy loss of RC beams under monotonic incremental loading and repeated loading. The failure strain of carbon fiber sheets is also estimated under repeated loading. From the experimental results, this work presents a basis of the data needed to analyze and design the static and dynamic flexural response of RC beams strengthened with carbon fiber sheets.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.221-228
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• 2010

External bonding of carbon fiber reinforced polymer (CFRP) sheets has been widely accepted as a popular method for strengthening of deteriorated RC structures. The long-term behavior of CFRP-strengthened RC structure is often affected by that of the interface between CFRP sheets and concrete. This study aims at applying a viscoelastic model to describe the creep behaviour of the adhesive layer bonding CFRP sheet to concrete, the CFRP-concrete interface. Reviews of available models on concrete creep behavior have been first carried out and then new FE analysis model is proposed. The proposed FE analysis model based on the maxwell model has been verified by previous experimental results. It is shown that the creep effect of interfacial adhesive layer is very important on the long-term behavior of concrete structures strengthened with CFRP.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.109-118
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• 2008

Carbon fiber reinforced polymer(CFRP) can be bonded to the soffit of a concrete beam as a means of repairing and strengthening the beam. In such beams, materials, concrete and carbon fiber sheets, are different in coefficient of thermal expansion. Consequently, interfacial shear stresses can be increased and debonding failure may occur at the plate ends due to temperature rising. This paper presents a method of approximate closed-form solutions for the interfacial shear stresses and conducts a beam test to compare the numerical results. In case of temperature rising over $30^{\circ}C$, interfacial stress of 0.91MPa is occurred at the end of sheet. Therefore, using carbon fiber sheet for strengthening the concrete beam, it is necessary to consider the thermal effects and to evaluate the long time behavior of the concrete beam by temperature change.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.163-169
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• 2017

Although the strength of polyethylene terephthalate (PET) fibers which are generally used to make plastic bottles is low, the deformability of PET fibers is substantially high. Due to these material characteristics, a PET fiber can be used as a reliable strengthening material to resist a large deformation caused by earthquake and research pertinent to application of PET fibers is actively conducted in Japan. Therefore, in this study, experiments have been carried out to investigate the lateral confinement effect of PET fibers and to assess the applicability of PET fibers to construction fields by comparing the strengthening effect of PET fibers to that of carbon and glass fiber sheets. For this purpose, concrete cylinder specimens with parameters of different concrete strength and strengthening layers of carbon fiber sheets, glass fiber sheets, and PET fibers were respectively tested using two sets of cylinders for each parameter. As a result, specimens strengthened with carbon fiber sheets and glass fiber sheets failed due to sudden decrease of strength as with existing studies. However, specimens with PET fibers reached their maximum strength and then failed after gradual decrease strength without failure of PET fibers. In addition, although the strength of specimens with PET fibers did not significantly increase in comparison with that of specimens with carbon fiber sheets and glass fiber sheets, specimens with PET fibers indicated considerable deformability. Thus, a PET fiber can be considered as an effective strengthening material.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1997.11a
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• pp.165-169
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• 1997

기존 구조물의 보강을 하는 데는 휨모멘트 및 전단력에 대하여 충분한 보강 효과를 가지는 것과 함께 시공성을 만족해야만 한다. 현재 연속 섬유시트 중 아라미드섬유시트(AFS) 및 탄소섬유시트(CFS)는 기존구조물의 보강재로 사용한 사례가 증가하고 있으나 합리적인 보강설계방법이 확립되어 있지 않은 현 시점에서는 적절한 보강이 이루어지지 않는 경우가 많다 AFS 및 CFS에 의해 RC보의 적절한 보강을 위해서는 AFS 및 CFS를 이용한 기존 콘크리트 구조물의 보강설계방법의 구축이 급선무이다. (중략)

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.5
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• pp.567-576
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• 2023

In general, RC beam members are designed as flexural members, considering only the bending load. However, in actual buildings, axial and bending load are simultaneously applied due to the continuity between members. As a result, the bending strength of the RC beam member increases, but the displacement decreases, and cracks are mainly concentrated in the center of the beam. Therefore, in this study, the bending performance of both normal and strengthened RC beam using carbon fiber sheets subjected to combined axial and bending load was experimentally evaluated. The carbon fiber sheets were wrapped around the middle of the specimens, and axial and bending load were applied simultaneously to the beams. The magnitude of the axial force and the effects of carbon fiber sheet reinforcement on the deformed shape, bending strength, deflection, and ductility of the RC beams were analyzed. The results show that as the applied axial force increased, the maximum bending strength increased, but the ductility decreased 64%. The bending strength of the strengthened beams increased up to 27%, the maximum deflection decreased around 8% and the ductility increased by up to 43%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.109-116
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• 2008

In order to test the adhesive capacity of carbon fiber sheet, a static loading method for bending-behavior-type beam specimens, cut in half was developed and test was conducted with compressive strength of concrete set as the test parameter. The tests were performed to prescribe adhesive shear strength based upon the result of shear failure as well as verification of testing method. First of all, the test method proved to be reliable in determining the adhesive shear strength. The test result also exhibited two types of variations in adhesive shear strength. Among two types of variations, average and minimum values for adhesive shear strength, relatively stable results, 3.41MPa and 2.11MPa, respectively. Particularity in the adhesive shear strength with respect to compressive shear strength was not found.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.115-123
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• 2007

For investigating self-diagnosis applicability, a method based on monitoring the changes in the electrical resistance of carbon fiber reinforced concrete has been tested. Then after examining change in the value of electrical resistance at each flexural weight-stage of carbon fiber in CFGFRP (carbon fiber and glass fiber reinforcing plastic) with new type rib and carbon sheet for concrete reinforcing, the correlations of electrical resistance and load as a function of strain, deflection were analyzed. As the results, it is clarified that when carbon fiber rod, rib and sheet fracture, the electrical resistance of it increase largely, and specially in case of CFGFRP, afterwards glass fiber tows can be resist the load due to the presence of the hybrid (carbon and glass) reinforced fiber. Therefore, it can be recognized that reinforcing bar and new type rib of CFGFRP and sheet of CF could be applied for self-diagnosis of fracture in reinforced FRP concrete.