• Steel and Composite Structures
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• 제42권3호
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• pp.289-298
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• 2022

In the present study, structural behavior of steel beams strengthened with CFRP strips and cables was investigated by a series of experiments. For this purpose, two groups of experimental studies were carried out: one for the beam series strengthened only with CFRP strips and the other for the steel beam series strengthened with CFRP strips and prestressed wires. From this test, it is found that the flexural stiffness and strength of the steel beams strengthened with CFRP strips and cables were significantly improved comparing to the un-strengthened one. Three failure modes such as sudden de-bonding, splitting and rupturing of CFRP strips were observed. The ultimate tensile strains of attached CFRP strips on the steel beams were noticed in the range between 8,000με and 11,000με, and this result disclose the perfect composite reaction CFRP strips and steel beams.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.117-128
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• 2014

Numerous investigations of RC beams strengthened in shear with externally-bonded (EB) fibre-reinforced polymer (FRP) sheets, plates and strips have been successfully conducted in recent years. These valuable studies have highlighted a number of influencing parameters that are not captured by the design guidelines. The objective of this study was: (1) to highlight experimentally and analytically the influential parameters on the shear contribution of FRP to RC beams strengthened in shear using EB FRP sheets and strips; and (2) to develop a set of transparent, coherent, and evolutionary design equations to calculate the shear resistance of RC beams strengthened in shear. In the experimental part of this study, 12 tests were performed on 4,520-mm-long T-beams. The specimens were strengthened in shear using carbon FRP (CFRP) strips and sheets. The test variables were: (1) the presence or absence of internal transverse-steel reinforcement; (2) use of FRP sheets versus FRP strips; and (3) the axial rigidity of the EB FRP reinforcement. In the analytical part of this study, new design equations were proposed to consider the effect of transverse-steel in addition to other influential parameters on the shear contribution of FRP. The accuracy of the proposed equations has been verified in this study by predicting the FRP shear contribution of experimentally tested RC beams.

• Structural Engineering and Mechanics
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• 제47권1호
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• pp.75-98
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• 2013

This study focuses on shear strengthening performance of simply supported reinforced concrete (RC) T-beams bonded by glass fibre reinforced polymer (GFRP) strips in different configuration, orientations and transverse steel reinforcement in different spacing. Eighteen RC T-beams of 2.5 m span are tested. Nine beams are used as control beam. The stirrups are provided in three different spacing such as without stirrups and with stirrups at a spacing of 200 mm and 300 mm. Another nine beams are used as strengthened beams. GFRP strips are bonded in shear zone in U-shape and side shape with two types of orientation of the strip at $45^{\circ}$ and $90^{\circ}$ to the longitudinal axis of the beam for each type of stirrup spacing. The experimental result indicates that the beam strengthened with GFRP strips at $45^{\circ}$ orientation to the longitudinal axis of the beam are much more effective than $90^{\circ}$ orientation. Also as transverse steel increases, the effectiveness of the GFRP strips decreases.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.255-258
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• 2005

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally bonded prestressed CFRP (Carbon Fiber Reinforced Polymer) strips. A total of 7 specimens have been manufactured of which specimens strengthened with bonded CFRP strips considering the level of prestress as experimental variable, and a specimen with simply bonded CFRP strips. The following phenomena have been observed through the experimental results. The specimen with simply bonded CFRP strips failed below 50$\%$ of its tensile strength due to premature debonding. On the other hand, all the specimens strengthened with prestressed CFRP strips showed sufficient strengthening performance up to the ultimate rupture load of the CFRP strips. Also, it was observed that the cracking loads and yield loads of the strengthened beams were increased proportionally to the prestress level, but the maximum loads were nearly equal regardless of the prestress level.

• 대한토목학회논문집
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• 제28권2A호
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• pp.289-295
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• 2008

본 연구는 탄소섬유판으로 보강된 철근콘크리트 부재의 휨 거동특성 및 파괴양상을 규명하고 또한 탄소섬유판 부착탈락 거동을 규명함에 그 목적이 있다. 이를 위하여 탄소섬유판의 형상, 섬유판 부착길이, 부착면적 등의 다양한 변수를 포함하는 실험연구가 수행되었으며, 초기 부착균열이 발생되는 부착탈락 기구를 규명 하였다. 본 실험결과 탄소섬유판으로 보강된 철근콘크리트 부재의 휨 강성은 보강되지 않은 보에 비해 현저하게 개선되며 최대 극한강도 증진율은 120% 이상인 것으로 나타났다. 또한 탄소섬유판 탈락 시 측정된 탄소섬유판의 인장변형율은 탄소섬유판의 극한 변형율의 36%에 해당되는 것으로 나타났으며, 탄소섬유판의 부착길이가 충분 할수록 보는 휨 균열로 야기되는 탄소섬유판의 계면 부착탈락으로 파괴됨을 알 수 있었다. 탄소섬유판의 계면부착탈락은 휨을 받는 구역에서 시작되어 보의 양 끝단으로 급격하게 전파되는 취성적인 파괴를 유도하는 것으로 나타났다. 본 연구에서는 탄소섬유판의 유효응력에 근거하여 탄소섬유판으로 보강된 철근콘크리트 부재의 휨 강성을 계산하였으며, 이는 실험결과와 잘 일치하는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제64권1호
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• pp.135-143
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• 2017

To upgrade shear performance of reinforced concrete (RC) beams, and particularly of the segments under negative moment within continuous T-section beams, a series of original schemes has been proposed using carbon fibre-reinforced polymer (CFRP) U-shaped strips for shear-strengthening. The current work focuses on one of them, in which CFRP U-strips are wound around steel bars against the top of the flange of a T-beam and then spliced on its bottom face in addition to being bonded onto its sides. The test results showed that the proposed scheme successfully provided reliable anchorage for U-strips and prevented premature onset of shear failure due to FRP debonding. The governing shear mode of failure changed from peeling of CFRP to its fracture or crushing of concrete. The strengthened specimens displayed an average increase of about 60% in shear capacity over the unstrengthened control one. The specimen with a relatively high ratio and uniform distribution of CFRP reinforcement had a maximum increase of nearly 75% in strength as well as significantly improved ductility. The formulas by various codes or guidelines exhibited different accuracy in estimating FRP contribution to shear resistance of the segments that are subjected to negative moment and strengthened with well-anchored FRP U-strips within continuous T-beams. Further investigation is necessary to find a suitable approach to predicting load-carrying capacity of continuous beams shear strengthened in this way.

• 한국구조물진단유지관리공학회 논문집
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• 제12권6호
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• pp.89-96
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• 2008

본 연구에서는 탄소섬유판이 표면 매입된 철근 콘크리트 보의 휨 거동 효과를 고찰하였다. 이를 위하여, 탄소섬유판이 표면 매입된 T 형 철근 콘크리트 보를 제작하여 실험을 수행하였다. 본 연구 결과, 표면매입(NSM) 탄소섬유판으로 보강된 철근콘크리트 부재의 휨 강성 및 극한강도는 섬유판으로 보강되지 않은 보에 비하여 크게 증진되며, 그 최대 증가율은 보강되지 않은 부재의 경우보다 약 247%로 나타났다. 위 철근콘크리트 부재의 파괴는 부재 길이 방향으로 섬유 소선이 풀리는 표면매입 탄소 섬유판의 파괴로 시작되며, 탄소섬유판의 파단이 이어지는 2차 파괴가 발생하였다. 표면매입 탄소섬유판은 콘크리트와의 완정한 합성거동을 유도하여 따라서 탄소섬유판을 표면에 매입하는 방식은 노후 구조물 보강방식으로 매우 효과적인 것으로 판단된다.

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

• 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.

• International Journal of Concrete Structures and Materials
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• 제6권1호
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• pp.49-57
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• 2012

The main objectives of this research were to experimentally evaluate the impact of Carbon Fiber-Reinforced Polymers (CFRP) amount and strip spacing on the shear behavior of prestressed concrete (PC) beams and to evaluate the applicability of existing analytical models of Fiber-Reinforced Polymer (FRP) shear capacity to PC beams shear-strengthened with CFRP. The Ushaped CFRP strips with different spacing were applied externally to the test specimens in order to observe the overall behavior of the prestressed concrete I-beams and the mode of failure of the applied CFRP strips. Results obtained from the experimental program showed that the application of CFRP strips to prestressed concrete I-beams did in fact enhance the overall behavior of the specimens. The strengthened specimens responded with an increase in ductility and in shear capacity. However, it should be noted that the CFRP strips were not effective at all at spacing greater than half the effective depth of the specimen and that fracture of the strips was the dominant failure mechanism of CFRP. Further research is needed to confirm the conclusion derived from the experimental program.