• Structural Engineering and Mechanics
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• 제9권5호
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• pp.491-504
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• 2000

A convenient method for enhancing the strength and stiffness of existing reinforced concrete beams is to bond adhesively steel plates to their tension faces. However, there is a limit to the applicability of tension face plating as the tension face plates are prone to premature debonding and, furthermore, the addition of the plate reduces the ductility of the beam. An alternative approach to tension face plating is to bond adhesively steel plates to the sides of reinforced concrete beams, as side plates are less prone to debonding and can allow the beam to remain ductile. Debonding at the ends of the side plates due to flexural forces, that is flexural peeling, is studied in this paper. A fundamental mathematical model for flexural peeling is developed, which is calibrated experimentally to produce design rules for preventing premature debonding of the plate-ends due to flexural forces. In the companion paper, the effect of shear forces on flexural peeling is quantified to produce design rules that are applied to the strengthening and stiffening of continuous reinforced concrete beams.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.335-338
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• 2003

Flexural test and parametric study by FEM analysis on 6.0m long reinforced concrete beams strengthened by GFRP are reported in these tests. The selected variables are strengthened plate length, plate thickness. The effects of these variables are discussed. The results generally indicate that the flexural strength of strengthened beams is increased. The results of FEM analysis show that the more strengthening GFRP is the more stress of GFRP is decrease when failure mode is peeling failure.

• 한국구조물진단유지관리공학회 논문집
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• 제2권2호
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• pp.195-201
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• 1998

The purpose of this study is to evaluate the flexural strengthening effects of RC beams reinforced with carbon fiber sheets (CFS) in variable of strengthening amount and anchorage length of CFS. This study can be summarized as follows ; The CFS shares the tensile stress such as rebar during loading test. Also, as the strengthening amount of CFS is increased, the maximum flexural strength of RC beams reinforced with CFS is increased. Therefore, it is confirmed that the CFS's strengthening method is very effective to improve the flexural strength of RC beams. The maximum flexural strength of RC beams with CFS is determined by bond failure between CFS and concrete surface. So, the evaluation of CFS's strengthening effect can be calculated using the tensile stress of CFS which is peeling. When the anchorage length of CFS is increased, the ductility of RC beams is increased because of delaying the peeling of CFS. But, in case of same anchorage length of CFS, when the strengthening amount of CFS is increased, the ductility is decreased. Therefore, it is considered that the anchorage of CFS in the end zone is necessary.

• Structural Engineering and Mechanics
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• 제9권5호
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• pp.505-518
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• 2000

A major cause of premature debonding of tension face plates is shear peeling (Jones et al. 1988, Swamy et al. 1989, Ziraba et al. 1994, Zhang et al. 1995), that is debonding at the plate ends that is associated with the formation of shear diagonal cracks that are caused by the action of vertical shear forces. It is shown in this paper how side plated beams are less prone to shear peeling than tension face plated beams, as the side plate automatically increases the resistance of the reinforced concrete beam to shear peeling. Tests are used to determine the increase in the shear peeling resistance that the side plates provide, and also the effect of vertical shear forces on the pure flexural peeling strength that was determined in the companion paper. Design rules are then developed to prevent premature debonding of the plate ends due to peeling and they are applied to the strengthening and stiffening of continuous reinforced concrete beams. It is shown how these design rules for side plated beams can be adapted to allow for propped and unpropped construction and the time effects of creep and shrinkage, and how side plates can be used in conjunction with tension face plates.

• 콘크리트학회논문집
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• 제16권6호
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• pp.867-873
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• 2004

It has been known that debonding failures between CFS(Carbon Fiber Sheet) and concrete in the strengthened RC beams are initiated by the peeling of the sheets in the region of combined large moment and shear forces, being accompanied by the large shear deformation after flexural cracks. These shear deformation effects are seldom occurred in small-scale model tests, but debondings due to the large shear deformation effects are often observed in a full-scale model tests. The premature debonding failure of CFS, therefore, must be avoided to confirm the design strength of full-scale RC beam in strengthening designs. The reinforcing details, so- called 'U-Shape fiber wrap at mid-span' which wrapped the RC flexural members around the webs and tension face at critical section with CFS additionally, were proposed in this study to prevent the debonding of CFS. Other reinforcing detail, so called 'U-Shape fiber wrap at beam end' were included in this tests and comparisons were made between them.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.579-584
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• 1998

The purpose of this study is to evaluate the flexural strengthening effects of RC beams reinforced with carbon fiber sheets (CFS) in variable of strengthening amount and anchorage length of CFS. This study can be summarized as follows. The CFS shares the tensile stress such as rebar during loading test. Also, as the strengthening amount of CFS is increased, the maximum flexural strength of RC beams reinforced with CFS is increased. Therefore, it is confirmed that the CFS's strengthening method is very effective to improve the flexural strength of RC beams. The maximum flexural strength of RC beams with CFS is determined by bond failure between CFS and concrete surface. So, the evaluation of CFS's strengthening effect can be calculated using the tensile stress of CFS which is peeling. When the anchorage length of CFS. But, in case of same anchorage length of CFS, when the strengthening amount of CFA is increased, the ductility is decreased. Therefore, it is considered that the anchorage of CFS in the end zone is necessary.

• 한국구조물진단유지관리공학회 논문집
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• 제2권2호
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• pp.202-208
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• 1998

To investigae the effect of anchorage type of carbon fiber sheet (CFS) on flexural behavior of RC beams, the loading test of RC beams reinforced with CFS was conducted in variable of anchorage Type such as bolting anchorage and U type anchorage using CFS. This study can be summarized as follows ; It is confirmed experimentally that the bolting anchorage and U type anchorage with CFS is very effective to delay the bond failure and prevent the peeling of CFS. Also, the anchorage type applied with this study is very effective to improve the ductility compared with the improving of maximum flexural strength of RC beams. It is believed that the anchorage type used this study must secure the ductile capacity of above 3 for the flexural strengthening of RC beams. In the future, it is required to obtain the data about anchorage type of CFS for utilization of field work as well as investigate the ductile capacity of conventional study of anchorage type

• Steel and Composite Structures
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• 제11권3호
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• pp.207-223
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• 2011

The results of an experimental investigation are presented in this paper for retrofitting of shear damaged reinforced concrete beams by using U shaped CFRP strips. The experimental program is consisted of seven shear deficient T cross sectioned 1/2 scale simply supported beam specimens. One beam was used as reference specimen, and the remaining six specimens were tested in two stages. At the first stage, specimens were shear damaged severely, and then were retrofitted by using CFRP strips with or without fan type anchorages. Finally, retrofitted beams were tested up to failure. Three different CFRP strip spacing were used such as 125 mm, 150 mm, and 200 mm. The effect of anchorages on shear strength and behavior of the retrofitted specimens is investigated. CFRP strips without anchorages improved the shear strength, but no flexural failure mode was observed. Specimens showed brittle shear failure due to peeling of CFRP strip from RC beam surface. Shear damaged specimens retrofitted with anchoraged CFRP strips showed improved shear strength and ductile flexural failure. Maximum strains at anchoraged strips were approximately 68% larger than that of strips without anchorages.

• 한국구조물진단유지관리공학회 논문집
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• 제3권3호
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• pp.245-251
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• 1999

이 연구는 탄소섬유판공법을 사용하여 보강된 철근콘크리트 슬래브에 집중하중 즉 같은 위치에서 휨모멘트와 전단력이 동시에 최대가 되는 경우에 대하여 탄소섬유판의 두께를 변수로 하여 슬래브의 구조적 거동을 실험하였다. 탄소섬유판의 두께에 따른 내력의 차이는 뚜렷이 나타나지 않았으며 이는 보강시험의 주된 파괴가 탄소섬유판의 파단이 아닌 하중점 주위에서의 휨-전단균열에서부터 층분리가 시작되기 때문이다. 그러므로 재하상태에 따른 설계방법을 다르게 할 필요가 있으며, 특히 같은 위치에서 휨 모멘트와 전단력이 최대가 되는 경우 탄소섬유판의 두께는 최대 0.6mm로 하고 무보강슬래브의 휨모멘트에 대한 보강된 슬래브의 휨모멘트는 1.5-2.0으로 제한하는 것이 바람직하다.

• 한국건설관리학회논문집
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• 제5권6호
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• pp.212-217
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• 2004

이 연구는 같은 위치에 힘모멘트와 전단력이 최대가 되는 철근콘크리트 보에 대하여 휨모멘트 보강을 실시하는 경우, 탄소 섬유판의 두께와 하중점 부위 및 탄소섬유판의 끝부분을 감싸는 탄소섬유쉬트의 겹수를 변수로 하여 보의 구조적 거동을 실험하였다. 탄소섬유판의 두께의 증가에 따라 내력이 증가하였으나 선형적으로 비례하지 않았으며, 하중점에 감싼 탄소섬유쉬트의 영향은 뚜렷하게 나타나지 않았다 이 는 보강시험의 주된 파괴가 탄소섬유판의 파단이 아닌 하중점 주위에서의 휭-전단균열에서부터 층분리가 시작되었고 하중점을 탄소섬유쉬트로 감싼 경우 휭-전단균열 탄소섬유쉬트의 바깥 부분으로 이동하기 때문이다. 또한 탄소섬유판 단부에 정착용으로 시공한 탄소섬유쉬트는 하중점에서 발생한 취성파괴로 인하여 큰 효과를 나타내지 못하였다. 그러므로 재하상태에 따른 설계방법을 다르게 할 필요가 있으며, 특히 같은 위치에서 휨모멘트와 전단력이 최대가 되는 경우 탄소섬유판의 유효 두께는 최대 0.6mm로 하고 무보강보의 휨모멘트에 대한 보강된 보의 휨모멘트 비는 1.5-2.0으로 제한하는 것이 바람직하며, 0.6mm이상의 탄소섬유판을 사용하기 위하여 탄소섬유쉬트로 하중점을 보강하는 경우 무보강보 휨모멘트의 1.5 배가 되는 위치이상 탄소섬유쉬트를 연장하는 것이 바람직하다.