• 콘크리트학회논문집
• /
• 제16권5호
• /
• pp.667-675
• /
• 2004

본 논문은 CFRP 격자 보강재로 보강한 콘크리트 슬래브의 파괴형태와 보강설계기준에 대한 연구이다. 실험 연구에서 채택한 시험변수로는 CFRP 격자 보강재의 양, 보강 모르타르의 깊이, 앵커핀의 유무, 압축부 보강 등이다. 연구에 의하면 CFRP 격자 섬유 보강량에 따라 파괴형태가 다르게 나타났는데 낮은 보강수준에서는 FRP 격자의 인장 파단파괴를 보였고 보통의 보강정도에서는 격자층 계면전단파괴가 발생하였다. 높은 보강량을 가진 슬래브에서는 사인장전단파괴 형태를 나타냈다. 보강 효과는 FRP 격자 보강재의 양이 증가할수록 증대하였으나 취성 전단파괴에 의해 연성은 감소되었다. 따라서 FRP 격자 보강량을 제한함으로써 갑자기 하중 지지력을 상실하는 전단파괴를 피할 수 있다. 파괴형태 중 CFRP 파단파괴가 바람직한데 그 이유는 섬유파단 후에도 극한상태에서 보강 전 슬래브의 하중지지력과 연성을 가지고 있기 때문이다. 마지막으로 본 논문은 CFRP 격자섬유보강설계기준과 과정을 제시하고 있다.

• 대한건축학회논문집:구조계
• /
• 제34권6호
• /
• pp.3-10
• /
• 2018

This paper described the shear strengthening effect by deviator location in pre-damaged reinforced concrete (RC) beams strengthened with externally post-tensioning steel rods. Three reinforced concrete beams as control beam and eight post-tensioned beams using external steel rods were tested to fail in shear. The externally post-tensioning material was a steel rod of 22 mm diameter, and it had a 655 MPa yield strength and an 805 MPa tensile strength. Specimens depend on multiple variables, such as the number of deviators, location of deviator, and load pattern. The pre-damaged loads up to about 2/3 of ultimate shear capacities were applied to specimens using displacement control and the diagonal shear crack just occurred at these loading levels. And then, the post-tensioning up to when a strain of steel rod reaches about $2000{\mu}{\varepsilon}$ was continuously applied to beam. A displacement control was changed to a load control during post-tensioning. The post-tensioning resulted in increase of load-carrying capacity and restoration of existing deflection. Also, it prevented the existing diagonal cracks from excessively growing. Two deviators effectively improved the load capacity when compared with in case of test which one deviator at mid-span installed. When deviators were located near region which the diagonal crack occurred on, the strengthening impact by post-tensioning was greater.

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

• 한국건축시공학회지
• /
• 제8권5호
• /
• pp.43-51
• /
• 2008

This study examines shear capacity performance and structural characteristics of reinforced concrete beam using carbon fiber sheet(CFS), g)ass fiber sheet(GFS), glass fiber steel plate(GSP) and carbon fiber bar CB) which are reinforcing materials for reinforced concrete beam in order to produce similar condition to repair and reinforce actual structure and aims to provide data available In designing and constructing reinforced concrete structures under the structural damage. This study obtains the following conclusions. After considering the shear experiment results. it was indicated that the CB reinforced test object was the best in the shear capacity improvement and ductility capacity as it was contained in the concrete and was all operated, Also, GFS reinforced test object indicated the reduced flexural capacity but good shear capacity. GSP reinforced test object had bigger reinforcing strength than other reinforcing test objects. On the other hand, it showed the lowest reinforcement effect as compared section thickness of reinforced material because it showed the bigger relativity a section thickness of reinforced material. If the adherence to the concrete is improved, it will seem to show bigger reinforcement effect.

• 한국구조물진단유지관리공학회 논문집
• /
• 제22권4호
• /
• pp.108-113
• /
• 2018

기존 구조물의 노후화로 인하여 보수 및 보강에 관한 연구는 활발히 이루어지고 있다. 탄소섬유를 사용한 외부 부착공법은 경제적이고 짧은 시간에 보강 작업이 이루어질 수 있기 때문에 널리 사용되고 있다. 일반적으로 탄소섬유를 사용한 전단 보강에는 일 방향 레이아웃이 많이 사용되고 있으며, 재료의 양, 섬유의 각도 그리고 간격 등에 관한 실험 연구가 많이 진행되었다. 하지만 예비 실험 결과를 통하여 이 방향 전단보강 레이아웃은 일 방향 전단보강보다 좀 더 효율적으로 부재를 구속하는 것을 확인하였다. 따라서, 유사한 재료의 양을 사용하여 일 방향과 이 방향 전단 보강 작업이 이루어진 후 실험을 통하여 두 보강작업의 효과가 검증되었다. 탄소섬유 보강 작업을 할 때는 탄소섬유의 부착파괴를 방지하기 위하여 탄소섬유 앵커가 설치되었다. 탄소섬유 앵커와 탄소섬유 레이아웃의 전단보강 효과는 실험 경간에 발생한 주인장 변형률의 분포를 통하여 검증되었다.

• Steel and Composite Structures
• /
• 제44권6호
• /
• pp.845-865
• /
• 2022

In this study, the performance of shear deficient reinforced concrete (RC) beams with rectangular cross-sections, which were externally bonded reinforced (EBR) with high strength CFRP and GFRP strips composite along shear spans, has been experimentally and analytically investigated under vertical load. In the study, the minimum CFRP and GFRP strips width over spacing were considered. The shear beam with turned end to a bending beam was investigated by applying different composite strips. Therefore various arising in each of strength, ductility, rigidity, and energy dissipation capacity were obtained. A total of 12 small-scaled experimental programs have been performed. Beam dimensions have been taken as 100×150×1000 mm. Four beams have been tested as unstrengthened samples. This paper focuses on the effect of minimum CFRP and GFRP strip width on behaviours of RC beams shear-strengthened with full-wrapping, U-wrapping, and U-wrapping+longitudinal bonding strips. Strengthened beams showed significant increments for flexural ductility, energy dissipation, and inelastic performance. The full wrapping strips applied against shear failure have increased the load-carrying capacity of samples 53%-63% interval rate. Although full wrapping is the best strengthening choice, the U-wrapping and U-wrapping+longitudinal strips of both CFRP and GFRP bonding increased the shear capacity by 53%~75% compared to the S2 sample. In terms of ductility, the best result has been obtained by the type of strengthening where the S5 beam was completely GFRP wrapped. The experimental results were also compared with the analytically given by ACI440.2R-17, TBEC-2019 and FIB-2001. Especially in U-wrapped beams, the estimation of FIB was determined to be 81%. The estimates of the other codes are far from meeting the experimental results; therefore, essential improvements should be applied to the codes, especially regarding CFRP and GFRP deformation and approaches for longitudinal strip connections. According to the test results, it is suggested that GFRP, which is at least as effective but cheaper than CFRP, may be preferred for strengthening applications.

• 콘크리트학회논문집
• /
• 제28권5호
• /
• pp.527-534
• /
• 2016

CFRP의 전단강도 기여분을 평가하고, 모어서클을 이용하여 전단거동 특성을 분석하기 위해 전단철근비가 서로 다른 보에 동일한 탄소섬유 전단보강 설계한 보 실험을 수행하였다. 취성특성을 가지는 CFRP의 전단기여분을 평가하기 위해서는 CFRP의 변형률을 평가해야 한다. 각 실험결과는 모어써클(Mohr's Circle)을 활용하여 전단변형률을 주인장변형률 및 균열각도의 변화와 연계하여 비교하였다. 전단철근비가 작은 경우 탄소섬유 자체의 전단강도 기여분 뿐만 아니라 탄소섬유에 의해 콘크리트 균열의 진전을 제어하여 균열에 의한 콘크리트의 성능저하를 최소화한다. 전단철근비가 큰 경우는 전단철근비가 작을 때 보다 탄소섬유 보강효과가 크지 않았다. 따라서 보강부재의 전단성능을 결정할 때 탄소섬유의 전단강도 기여분은 전단철근과의 상호작용을 고려할 수 있는 변형적합조건에 근거하여 평가되어야 한다.

• Steel and Composite Structures
• /
• 제45권4호
• /
• pp.591-603
• /
• 2022

The flexural strengthening of reinforced concrete beams by external bonding of composite materials has proved to be an efficient and practical technique. This paper presents a study on the flexural performance of reinforced concrete continuous beams with three spans (one span and two cantilevered) strengthened by bonding carbon fiber fabric (CFRP). The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened continuous beam, i.e., the continuous concrete beam, the FRP plate and the adhesive layer. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends. Remarkable effect of shear deformations of adherends has been noted in the results. The theoretical predictions are compared with other existing solutions that shows good agreement, and It shows the effectiveness of CFRP strips in enhancing shear capacity of continuous beam. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam.

• 한국공간구조학회논문집
• /
• 제5권2호
• /
• pp.65-71
• /
• 2005

최근 노후화된 철근콘크리트 구조물에 대한 FRP를 이용한 보강공법의 적용이 증가하고 있다. 하지만 휨 보강에 대해서는 연구로 인해 정량적인 평가로 인해 효율적인 설계가 가능하지만, 전단보강의 경우에는 파괴메카니즘을 완전히 규명하지 못하는 상태이다. 본 연구에서는 전단보강근이 있는 철근콘크리트보에 매립형 CFRP를 전단보강하여 보강효과를 파악하고자 실험을 수행한 후, 실험결과를 토대로 분석 및 고찰을 통해 정량적인 보강효과를 도출하고자 한다. 시험체 제작시 실험변수로는 전단보강근의 간격과 보강방향으로 하여 시험체를 10개 제작하여 실험을 수행하였다. 실험결과, 전단보강근 간격과 보강방향에 따라 CFRP의 보강효과는 다소 차이를 보였다.

• Steel and Composite Structures
• /
• 제50권2호
• /
• pp.183-199
• /
• 2024

In this paper, a closed-form rigorous solution for interfacial stress in continuous steel beam with variable section strengthened with bonded prestressed FRP plates and subjected to a uniformly distributed load is developed using linear elastic theory and including the variation of fiber volume fractions with a longitudinal orientation of the fibers of the FRP plates. The results show that there exists a high concentration of both shear and normal stress at the ends of the laminate, which might result in premature failure of the strengthening scheme at these locations. The theoretical predictions are compared with other existing solutions. Overall, the predictions of the different solutions agree closely with each other. A parametric study has been conducted to investigate the sensitivity of interface behavior to parameters such as laminate and adhesive stiffness, the thickness of the laminate and the fiber volume fractions where all were found to have a marked effect on the magnitude of maximum shear and normal stress in the composite member. This research gives a numerical precision in relating to the others studies which neglect the effect of prestressed plate and the shear lag impact. The physical and geometric properties of materials are taken into account, and that may play an important role in reducing the interfacial stresses magnitude.