• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.337-345
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• 2009

The purpose of this study is to investigate the shear strengthening effectiveness of the beams strengthened with near surface mounted (NSM) and external bonded (EB) CFRP strips. A total of nine concrete beams were made and tested. From this study, it was found that the shear stiffness and strength of the beams strengthened with NSM and EB strips were significantly improved compared to the control beam. Failure of the beam strengthened with NSM and EB strips was initiated by shear cracks, propagated diagonally to the adjacent epoxy grooves without crossing the epoxy and finally sudden diagonal crack connecting the point of application of load and flexural crack was occurred. For the beam strengthened combined with NSM and EB CFRP strips, the tensile strains in the NSM CFRP strips were observed in the range of 0.35% to 0.45% and strains with EB strips were measured about 0.3%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.171-180
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• 2008

The aim of this paper is to clarify the structural performance of RC beams strengthened with Carbon Fibre Reinforced Polymer(CFRP) plates using channel-type anchorage system. Twelve RC beams were specifically designed without and with a channel-type anchorage system, which was carefully detailed to enhance the benefits of the strengthening plates. All the twelve beams were identical in terms of their geometry but varied in their internal reinforcement, concrete strength. All the beams were tested under four point bending and extensively instrumented to monitor strains, cracking, load capacity and failure modes. The structural response of all the twelve beams is then critically analyzed in terms of deformability, strength and failure processes. It is shown that with a channel-type anchorage system, a brittle debonding failure of a strengthened beam can be transformed to an almost ductile failure with well-defined enhancement of structural performance in terms of both deformation and strength.

• Journal of Korean Association for Spatial Structures
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• v.5 no.4 s.18
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• pp.71-77
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• 2005

Bonded CFRP Plate method used murk in reinforcement method is very efficient for stress increment of reinforced members. But CFRP plate dosen't display enough its capacity and have the destruction characteristic of premature failure that reach failure by debond plate, because near-surface-bond using epoxy. Such destruction character of reinforced specimens take the influence at variables as steel reinforcement ratio, concrete strength, kind of reinforcement materials, reinforced length, property of epoxy used in binder and so on. In this study, performed experiment results are compared and considered on flexural performance of Near Surface Mounted Reinforcement used CFRP-Rod, as complement about structural behavior of RC beam reinforced flexural capacity in CFRP plate and premature failure of reinforcement material. Main variables of RC beam applied CFRP Plate external bond method are experimental variables as reinforcement length, reinforcement position (tension face and side face of beam) and existence of ironware in end parts. In case of CFRP-Rod, variable is reinforcement length.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.349-356
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• 2008

Recently FRP (Fiber Reinforcement Polymer) is widely used for the strengthening of damaged RC beams. Although many tests were carried out to verify flexural capacity of RC beams strengthened with FRP sheet or plate, the behavior of strengthened RC beams has not yet clearly verified. To investigate the strengthening efficiency of the Near Surface Mounted Reinforcement (NSMR) technique experimentally and analytically, a total of 7 specimens have been tested. The experimental results revealed that specimens strengthened with NSMR improved the flexural capacity of RC beams. Also, while the NSMR specimens utilized CFRP reinforcement efficiently compared to the EBR (Externally Bonded Reinforcement) specimen, the NSMR specimens still have debonding failure between epoxy and concrete interface. This study has proposed the model to predict failure modes and failure loads. Good agreement was obtained between the predicted and the experimental results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.311-314
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• 2011

최근 콘크리트 구조물의 안전성강화를 위해 탄소섬유 강화 플라스틱(CFRP) 보강 공법이 널리 사용되고 있지만 잘 알려진 바와 같이 CFRP 보강재와 콘크리트 표면사이의 부착면 탈락은 보강재 자체의 손상보다 발생할 확률이 높고 이러한 부착면 탈락은 보강의 효과를 무의미하게 만들기 때문에 구조물 전체의 파괴로 직결될 수 있다. 이에 본 연구에서는 CFRP 부착면 탈락손상을 실시간으로 검색하기 위해 압전센서를 사용하는 구조물 건전성 평가 기술을 적용하였다. 이의 검증을 위해 CFRP로 보강된 콘크리트 보를 제작하였고 3단계로 증가하는 부착면 탈락 손상을 발생시켰다. 손상 증가 단계마다 CFRP 표면에 배열된 압전센서로부터 임피던스와 유도초음파 신호를 계측하였고 손상에 따른 신호변화를 정량화하기 위해 손상지수인 RMSD를 계산하였다. 더 구체적인 부착면 탈락 손상위치 탐색을 위해서 두 가지 계측 기법으로부터 구해진 RMSD 값를 중첩시키는 Superposed RMSD 가 제안되었다. 구해진 Superposed RMSD 값을 사용하여 커브 피팅이 수행되었고 도출된 커브의 최고값에 해당하는 위치값을 찾아 실제 손상위치와 비교함으로써 제안된 기법의 가능성을 검증해 보았다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.155-163
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• 2008

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally bonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips. Specimens consist of 9 small-scaled specimens with the different post-tensioning level as a main test parameter. A control specimen and specimens with simply bonded CFRP strips have been manufactured to compare the structural performances of prestressed system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned CFRP strips reached the rupture strength of the CFRP strip. The cracking and yielding loads were also increased proportionally to the post-tensioning level, but the ultimate loads were nearly equal regardless of the post-tensioning level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.147-154
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• 2008

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally unbonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips using embedded or stud-type plate anchorages. Total 10 small-scaled specimens were manufactured with the different post-tensioning level and types of mechanical anchorage as a main test parameter. A control specimen and specimens with simply bonded CFRP strips were included to compare the structural performances of each system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned unbonded CFRP strips reached the rupture strength of the CFRP strip. Also, it was observed that the specimens with stud-type anchorage have equivalent strengthening performance compared with embedded-type anchorage.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.601-609
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• 2008

The purpose of this study is to investigate the flexural strengthening effectiveness for the beams combined reinforced with NSM CFRP strips and EBR CFRP strips. To accomplish this objective, a total of nine concrete T beams were tested. From this study, it is found that the flexural stiffness and strength of the beams combined reinforced with NSM and EBR strips were significantly improved compared to the beams strengthened only with NSM CFRP strip. The maximum increase of flexural strength was 347% compared to the beam without CFRP strip. Failure of the beam combined reinforced with NSM and EBR strips (T shape) is initiated by debonding of EBR strips attached on the bottom face, and it was succeeded a part of separatio-n of NSM strips along the longitudinal direction and secondly failure of NSM strips was occurred, eventually sudden explosive failure with the separation of concrete cover in the shear region. This result shows that the NSM and EBR strips have good combination to resist applied load and the combined reinforcement with NSM and EBR strips can redistribute appropriately the total stress subjected concrete beam to the EBR and NSM strips.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.181-192
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• 2007

The purpose of this study is to analyse and compare experimentally flexural behavior of RC beams strengthened with CFRP plates by different methods, and finally suggest the evaluation equations of flexural capacity of RC beams with the aim of application of prestressed CFRP strengthening. The experimental parameters are compressive strength, reinforcement ratio, prestressing level and strengthening methods. The non-prestressed specimens failed on account of separation of the plates from the beams due to premature de-bonding, while most of the prestressed specimens failed due to CFRP plate fracture. The evaluation equations of flexural capacity of RC beams is suggested and these equations have a good reliability in predicting flexural strength of RC beams.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.645-652
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• 2002

This paper presents the flexural behavior and strengthening effect of reinforced concrete beams bonded with carbon FRP plate. Parameters involved in this experimental study were plate bond length and sheet web anchorage length. Test beams were strengthened with FRP plate on the soffit and anchored with FRP sheet on the web. In general, strengthened beams with no web anchorage were failed by concrete cover failure along the longitudinal reinforcement. On the other hand, strengthened beams with web anchorage were finally failed by delamination shear failure within concrete after breaking of CFRP sheet wrapping around web. The ultimate load and deflection of strengthened beams increased with an increased bond length of FRP plate. Also, the ultimate load and deflection increased with an increased anchorage length of FRP sheet. Particularly, the strengthened beams with web anchorage maintained high ultimate load resisting capacity until very large deflection. The shape of strain distribution of CFRP plate along beam was very similar to that of bending moment diagram. Therefore, an assumption of constant shear stress in shear span could be possible in the analysis of delamination shear stress of concrete. In the case of full bond length, the ultimate resisting shear stress provided by concrete and FRP sheet Increased with an increase of web anchorage length. In the resisting shear force, a portion of the shear force was provided by FRP anchorage sheet.