• Magazine of the Korea Concrete Institute
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• v.9 no.1
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• pp.195-206
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• 1997

비선형 layered 유한요소법과 비선형 프로그래밍 기법에 의하여 주어진 기존의 철근콘크리트 보의 휨강도 및 연성을 근사하게 나타낼 수 있는 강섬유고강 철근콘크리트 보(Reinforced Steel Fibrous Concrete Beam : RSFC Beam)의 인장 및 압축철근량, 강섬유의 혼입률 등을 산정하였다. 개발된 모델을 이용하여 콘트리트의 압축강도 및 철근비가 서로 다른 일반 철근콘크리트 보에 있어서 강섬유보강 콘크리트를 사용할 경우, 기존 철근을대체하는 강섬유의 량과 또한 이로 인한 인장 \ulcorner 압축 철근량의 변화량을 조사하였다. 기존 문헌에 나타난 강섬유보강 콘크리트보의 전간강도식을 이용하여 일반 철근콘크리트보와 비교하여 강섬유보강 철근콘크리트 보에서 증가될 수 있는 스터럽의 간격을 산정하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.100-107
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• 2018

The objective of this study is to assess the strengthening effects of fiber reinforced polymer(FRP) sheets such as Carbon fiber, Glass fiber, and PET(polyethylene terephthalate) on reinforced concrete flexural members. Variables of theoretical analysis are types of strengthening materials, material properties and amount of strengthening materials. A virtual flexural member without FRP sheets was created as a control specimen to understand the structural behavior of the non-strengthened specimen in terms of elastic and ultimate cross section. In total, 11 specimens including one non-strengthened and ten strengthened specimens were investigated. Various variables such as types of strengthening, strengthening properties, and amount of strengthening were studied to compare the behavior of the control specimen with those of strengthened specimens with regard to moment-curvature relationship. Results of theoretical analysis showed that the moment capacity of strengthened specimens was superior to that of the control specimen. However, the control specimen indicated the best ductility among all the specimens. As the amount of strengthening increased, flexural performance was improved. Furthermore, the results indicated that the ductile effect of members was affected by the ultimate strain of FRP sheets. The strengthening effect on the damaged member was similar to that on the non-damaged one since there was less than 10% difference in terms of flexural strength and ductility. Therefore, even if a damaged member is treated as non-damaged for analysis there is probably no noticeable difference.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.573-581
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• 2013

In this paper, an experimental investigation of bond properties between steel fiber reinforced concrete and glass fiber reinforced polymer reinforcements was performed. The experimental variables were diameter of reinforcements, volume fraction of steel fiber, cover thickness and compressive strength of concrete. Bond failure mainly occurred with splitting of concrete cover. Main factor for splitting of concrete is tension force occurred by the displacement difference between reinforcements and concrete. Therefore, in order to prevent the bond failure between reinforcements and concrete, capacity of tensile strength of concrete cover should be upgraded. As a results of test, volume fraction of steel fiber significantly increases the bond strength. Cover thickness changes the failure mode. Diameter of reinforcements also changes the failure mode. Generally, diameter of reinforcement also affects the bond properties but this effect is not significant as volume fraction of fiber. Increase of compressive strength increases the bond strength between concrete and reinforcement because compressive strength of concrete directly affects the tensile strength of concrete.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.867-874
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• 2003

섬유보강재를 이용한 성토제체의 설계에서 기존의 방법은 보강재의 변형을 무시하고 흙의 변형만을 중요시하고 있다. 보강재에 의해 보강된 성토제체의 파괴면에서 보강재와 흙의 거동은 초기응력단계에서는 일체거동현상을 나타내지만 응력의 증가에 따라 변형량에서 차이를 보인다. 이러한 문제는 토공구조물의 보강재를 설계하는데 있어서 중요한 요소로서 보강효과에 큰 영향을 미칠 수 있다. 본 연구에서는 연약지반 위에 PET Mat로 보강하여 축조한 성토제체에서 보강재와 흙의 응력 - 변형거동을 수치해석을 통하여 분석하였다. 연구결과, 파괴면에서 보강재의 변형은 보강재의 인장강도 크기에 따라 큰 차이를 보이고 있다. 외부하중에 의해 보강재에 발생하는 최대응력은 보강재의 항복인장강도를 초과하지 않으며, 보강재에 발생하는 응력이 성토체에서 발생하는 응력이상일 때 이상적인 것으로 나타났다. 또한 제체의 전단파괴에 대한 안전율은 보강재의 항복인장강도가 증가할수록 증가하는데 보강재와 흙의 변형이 일치되는 이후부터는 안전율의 증가율은 거의 미미한 것으로 나타났다.

• Magazine of the Korea Concrete Institute
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• v.3 no.4
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• pp.79-88
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• 1991

In this study, fracture tests were carried out in order to investigate the fracture behavior of SFRC(Steel Fiber Peinforced Concrete) with initial cracks. The relationships between loading. strain, mld-span deflections and CMOD(Crack Mouth Opening Displacement) of the beams were observed under the three point loading system. The effect of the fiber content and the initial crack ratio on the concrete fracture behavior were studied and the fracture toughness, the critical energy release ratio and the fracture energy were also calcul ated from the test results. From the test results, it was known that when the fiber contents are between 0.5% and 1.0%, and 1.5% the average fracture energy of SFRC specimens is about 7~10 times. and about 15 times better than that of the plam concrete specimens respectively.ively.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.113-120
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• 2005

The purpose of this study is to investigate the strength and ductility improvement of columns retrofitted by steel-fiber composite plate. Test specimens strengthened by three different materials - steel plate(SP), carbon fiber sheet(CF) and fiber-steel composite plate(CP) - were tested under cyclic lateral load with a constant axial load equal to $20\%$ of the axial compression capacity. The structural capacity of composite plate was good or better than that of other retrofitting materials. Test results from all retrofitted specimens showed that considerably higher retrofitting amount was required for strength enhancement. The ductility of retrofitted columns by composite plate was fairly improved. Also, energy ductility ratio was more effective than displacement ductility ratio for ductility estimation of retrofitted column.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.79-86
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• 2012

Though steel reinforcing bars are the most widely used tensile reinforcement, corrosion problems are encountered due to the exposure to aggressive environments. As an alternative material to steel, the fiber reinforced polymers have been used as reinforcement in concrete structures. However, bond strength of FRP rebar is relatively low compared to steel rebar. It has been reported that fibers in matrix can resist crack growth, propagation and finally result in an increase of toughness. In this study, high-strength concrete reinforced with structural fibers was produced to enhance interfacial bond behavior between FRP rebar and concrete matrix. The interfacial bond-behaviors were investigated from a direct pullout test. The test variables were surface conditions of GFRP bars and fiber types. Total of 54 pullout specimens with three different types of bars were cast for bond strength tests. The bond strength-slip responses and resistance of the bond failure were evaluated. The test results showed that the bond strength and toughness increased according to the increased fiber volume.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.530-539
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• 2002

In designing the boundary confinement of shear walls, the current design provisions and recommendations are empirical and prescriptive; they specify a certain confinement length and details, regardless of the actual requirement of ductility Therefore, they are inappropriate to the performance based-design. The purpose of the present study is to develop a ductility design method that Is applicable to the performance based-design of shear wall. For the purpose, experimental studies were performed to investigate variations in the ductility of shear walls with the length of the boundary confinement. Five specimens modeling the compressive zone of cross sections with different confinement area were tested against eccentric vertical load. Through the experimental studies, strength, ductility, and failure mode of the compression zone were investigated. In addition, nonlinear numerical analyses for the overall cross-sections of shear wall were performed to investigate variations of the stress and strain profiles with the length of compression zone. On the basis of the experimental and numerical studies, a ductility design method for shear wall was developed. By using the proposed design method, for a given ductility demand, the area of lateral confinement and corresponding reinforcement ratio can be precisely determined so that the ductile behavior and economical design are assured.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.1
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• pp.63-70
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• 2010

The purpose of this study is to investigate experimentally the behavior of unreinforced masonry RC frames strengthened by CFRP sheet under cyclic lateral loading. Four test specimens were constructed as one-story, one-bay, 1/2 scale unreinforced masonry infilled RC frames and differences in strength and stiffness were evaluated in specimens on which had been applied different retrofitting methods. Test results indicated that the CFRP sheets significantly increased the strength and stiffness of the specimens, and the specimens retrofitted in columns and masonry indicated the most adequate retrofitting methods.

• Geotechnical Engineering
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• v.14 no.5
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• pp.67-76
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• 1998

The commonly used method to secure the stability of reinforced retaining structure is the reinfocement of backfill with connection attached or unattached to the geogrid type wall. Laboratory model tests for both cartes were conducted to investigate the effectiveness of geogridreinforcement, length of reinforcement inclusion, failure envelop, and the relationships between the face wall displacement and vertical settlement. The bearing capacity of each case was also determined. According to the model test results, geogrid-reinforced rigid wall is very effective for increasing the bearing capacity and reducing the displacement of retaining wall. The observed sliding line of model test is similar to the theoretical one.