• Computers and Concrete
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• 제31권3호
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• pp.173-184
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• 2023

In this study, the flexural behaviors of one- and two-way reinforced concrete (RC) slabs strengthened with carbon-fiber-reinforced polymer (CFRP) strips under impact loads were investigated. The flexural strengthening of RC slabs under simulated static monotonic loads has been comprehensively studied. However, the flexural behavior of RC slabs strengthened with CFRP strips has not been investigated extensively, particularly those conducted numerically. Nonlinear three-dimensional finite element models were developed, executed, and verified against previous experimental results, producing satisfactory models with approximately 4% error. The models were extended to a parametric study, considering three geometric parameters: the slab rectangularity ratio, CFRP strip width, and CFRP strip configuration. Finally, the main results were used to derive a new formula for predicting the total deflection of RC slabs strengthened with CFRP strips under impact loads with an error of approximately 10%. The proposed equation reflected the slab rectangularity, CFRP strip width, equivalent slab stiffness, and dropped weight. Results indicated that the use of CFRP strips enhanced the overall impact performance, the wider the CFRP width, the better the enhancement. Moreover, the application of diagonally oriented CFRP strips diminished the cracking zone compared to straight strips. Additionally, the diagonal orientation of CFRP strips was more efficient for two-way slabs while the vertical orientation was found to be better in the case of one-way slabs.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.697-702
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• 1997

This study presents test results of RC beams strengthened by carbon fiber sheet (CFS) or carbon fiber reinforced plastics (CFRP) for increasing shear resistance. Fifteen specimens were tested, and the test was performed with different parameters including the type of strengthening materials (CFS, CFRP), shear-strengthening methods (wing type, jacket type, strip type), strip-spacing, strengthening direction of FRP. The results show that shear-damaged RC beams strengthened by either CFS or CFRP have more improved the shear capacity.

• 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.

• Steel and Composite Structures
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• 제15권6호
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• pp.605-621
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• 2013

CFRP strips are widely used nowadays for repair/strengthening or capacity increase purposes. Sharp bending at the ends of the CFRP strips is frequently encountered at these applications. In this study, Reinforced Concrete (RC) beam specimens that were produced with 10 MPa compression strength concrete were strengthened by using bonded CFRP strips with end anchorages to tension region. The parameters that were investigated in this study are the width of the strip, the number of applied fan anchorages and whether additional layer of CFRP patch is used or not at the strip ends. Specimens were strengthened with 100 mm wide CFRP strips with one or two anchorages at the ends. In addition CFRP patch with two and three anchorages at the ends were tested for investigating the effect of the patches. Specimens that were strengthened with three anchorages at the ends with patches were repeated with 60 and 80 mm wide CFRP strips. The most successful result was obtained from the specimen that was strengthened with 80 mm wide CFRP strips with 3 end anchorages and patches among the others at the experimental program. The numbers of anchorages that were applied to ends of CFRP strips were more effective than the width of the CFRP strips onto strength and stiffness of the specimens. Due to limited space at the ends of the strips at most three anchorages could be applied.

• 콘크리트학회논문집
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• 제20권3호
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• pp.299-305
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• 2008

본 연구는 탄소섬유판으로 보강된 철근콘크리트 부재의 전단거동 특성 및 파괴형상을 구명함에 그 목적이 있다. 이를 위하여 탄소섬유판의 형상, 섬유판 부착 간격 및 전단보강 철근량 등의 변수를 포함하는 실험 연구가 수행되었다. 본 실험 결과 탄소섬유판으로 보강된 철근콘크리트 부재의 전단 강성은 보강되지 않은 보에 비해 현저하게 개선되며 최대 전단강도 증진율은 100% 이상인 것으로 나타났다. 또한 탄소섬유판은 전단균열의 발생 및 진전을 억제하며, 적은 량의 탄소섬유판으로 보강했을 경우에도 전단강도의 증진 효과는 매우 좋은 것으로 나타났다. 본 연구에서는 탄소섬유판에 발생하는 변형률을 기본으로 하여 유효응력을 도출하였으며, 탄소섬유판으로 보강된 철근콘크리트 부재의 전단강도를 계산하였다. 이는 실험 결과와 잘 일치하는 것으로 나타났다.

• 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.

• 콘크리트학회지
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• 제10권4호
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• pp.101-111
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• 1998

본 논문의 목적은 전단내력이 부족한 R/C보에 CFS(Carbon Fiber Sheets), CFRP(Carbon Fiber Reinforced Plastic), GFRP(Glass Fiber Reinforced Plastics)를 이용해 전단보강을 할 경우에 보의 역학적 거동특성을 규명하기 위한 것이다. 본 논문의 목적을 달성하기 위하여 총 19개의 시험체가 제작되었으며, 실험변수로는 전단스팬비, 보강재료, 보강방법, 보강간격 및 방향을 산정하였다. 본 논문의 실험결과, FRP를 이용해 전단내력이 부족한 R/C보에 보강을 하였을 경우 약 50~70%정도의 보강효과를 나타내었다. 또한 소성이론에 근거한 철근콘크리트보의 전단강도 예측모델을 개발하였고 실험치와의 비교를 통해 개발된 모델의 적합성을 검증하였다.

• Structural Engineering and Mechanics
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• 제26권4호
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• pp.427-439
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• 2007

The exploitation of fibre reinforced polymer composites, as external reinforcement is an evergreen and well-known technique for improving the structural performance of reinforced concrete structures. The demand to use FRP composites in the civil engineering industry is mainly due to its high strength, light weight, and stiffness. This paper exemplifies the shear strength of partially precracked reinforced concrete rectangular beams repaired with externally bonded Bi-Directional Carbon Fibre Reinforced Polymer (CFRP) Fabrics strips. All specimens were cast in the laboratory environment without any internal shear reinforcement. The test parameters were longitudinal tensile reinforcement, shear span to effective depth ratio, spacing of CFRP strips, and orientation of CFRP reinforcement. It mainly focuses on the shear capacity and modes of failure of the CFRP strengthened shear beams. Results have shown that the CFRP repaired beams attained a shear enhancement of 32% and 107.64% greater than the control beams. This study underscores that the CFRP strip technique significantly enhanced the shear capacity of precracked reinforced concrete rectangular beams without any internal shear reinforcement.

• 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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• 제15권5호
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• pp.178-189
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• 2011

본 연구에서는 CFRP 표면부착 공법의 대안으로 최근에 관심을 끌고 있는 NSM(Near Surface Mounted)기법으로 전단 보강된 RC 부재의 전단강도를 평가하기 위한 실험과 해석을 수행하였다. 전단철근이 없는 7개의 실험체에 대해 4점 휨실험을 실시하였다. 실험변수로는 CFRP 스트립의 경사($45^{\circ}$, $90^{\circ}$)와 스트립의 간격(250mm, 200mm, 150mm, 100mm)이 고려되었다. 실험적 연구를 통해 NSM공법으로 전단 보강된 RC 부재의 전단강도와 파괴모드에 대한 각 실험변수의 영향을 평가하였다. 실험결과는 $45^{\circ}$ 경사로 스트립을 보강한 실험체들은 스트립의 파단으로 파괴된 반면, 수직으로 스트립을 보강한 실험체들은 스트립의 슬립으로 파괴됨을 보였다. 또한, $45^{\circ}$ 경사 스트립이 수직 스트립보다 전단저항력 증가시킬뿐만 아니라 파괴시의 처짐을 크게 증가시키는 것으로 나타났다. 추가적으로 RBSN 해석은 NSM기법으로 전단 보강된 RC 부재의 균열형상 및 하중-처짐관계를 적절하게 예측하였다.