• Structural Engineering and Mechanics
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• 제61권1호
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• pp.125-142
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• 2017

Extensive research work has been performed on shear strengthening of reinforced concrete (RC) beams retrofitted with externally bonded carbon fiber reinforced polymer (CFRP) in form of strips. However, most of this research work is experimental and very scarce studies are available on numerical modelling of such beams due to truly challenging nature of modelling concrete shear cracking and interfacial interaction between components of such beams. This paper presents an appropriate model for RC beam and to simulate its cracking without numerical computational difficulties, convergence and solution degradation problems. Modelling of steel and CFRP and their interfacial interaction with concrete are discussed. Finally, commercially available non-linear finite element software ABAQUS is used to validate the developed finite element model with key tests performed on full scale T-beams with and without CFRP retrofitting, taken from previous extensive research work. The modelling parameters for bonding behavior of CFRP with special anchors are also proposed. The results presented in this research work illustrate that appropriate modelling of bond behavior of all the three types of interfaces is important in order to correctly simulate the shear behavior of RC beams strengthened with CFRP.

• Advances in concrete construction
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• 제7권4호
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• pp.249-262
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• 2019

In this study, high strength aluminum alloys (AA) plates are proposed as a new construction material for strengthening reinforced concrete (RC) beams. The purpose of this investigation is to evaluate AA plate's suitability as externally bonded reinforcing (EBR) materials for retrofitting shear deficient beams. A total of twenty RC beams designed to fail in shear were strengthened with different spacing and orientations. The specimens were loaded with four-points loading till failure. The considered outcome parameters included load carrying capacity, deflection, strain in plates, and failure modes. The results of all tested beams showed an increase up to 37% in the load carrying capacity and also an increase in deflection compared to the control un-strengthened beams. This demonstrated the potential of adopting AA plates as EBR material. Finally, the shear contribution from the AA plates was predicted using the models available in the ACI440-08, TR55 and FIB14 design code for fiber reinforced polymer (FRP) plates. The predicted results were compared to experimental testing data with the ratio of the experimentally measured ultimate load to predicted load, range on the average, between 93% and 97%.

• Structural Engineering and Mechanics
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• 제51권3호
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• pp.413-431
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• 2014

By carrying out the experiment of eight pieces of brick masonry walls with pilaster strengthened by Glass fiber reinforced polymer (GFRP) and one piece of normal masonry wall with pilaster under low reversed cyclic loading, the failure characteristic of every wall is explained; Seismic performances such as hysteresis, stiffness and its degeneration, deformation, energy consumption and influence of some measures including strengthening means, reinforcement area proportion between GFRP and wall surface, "through-wall" anchor on reinforcement effects are studied. The test results showed that strengthening modes have little influence on stiffness, stiffness degeneration and deformation of the wall, but it is another thing for energy consumption of the wall; The ultimate load, deformation and energy consumption of the walls reinforced by glass fiber sheets was increased remarkably, rigidity and its degeneration was slower; Seismic performance of the wall which considers strengthening means, reinforcement area proportion between GFRP and wall surface, "through-wall" anchor at the same time is better than under the other conditions.

• 한국안전학회지
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• 제26권2호
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• pp.62-69
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• 2011

This paper presents a new simple two-dimensional frame finite element able to accurately estimate the load-carrying capacity of reinforced concrete beams flexurally strengthened externally bonded fiber reinforced polymer (FRP) strips and plates. The proposed analysis model considers distributed plasticity with layer-discretization of the cross-sections and the bond-slip behavior of epoxy layer. The proposed model is used to predict the load-carrying capacity and the applied load-midspan deflection response of RC beams subjected to bending loading. Numerical simulations and experimental measurements are compared based on numerous tests available in the literature and published by different authors. The numerically simulated response agree remarkably well with the corresponding experimental results. Thus, the proposed model is suitable for efficient and accurate modeling and analysis of flexural strengthening of RC beams with externally bonded FRP sheets/plates and for practical use in design-oriented parametric studies.

• Coupled systems mechanics
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• 제10권2호
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• pp.161-184
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• 2021

Strengthening of reinforced concrete beams with externally bonded fiber reinforced polymer plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites. This paper presents a simple uniaxial nonlinear analytical model that is able to accurately estimate the load carrying capacity and the behaviour of damaged RC continuous beams flexural strengthened with externally bonded prestressed composite plates on both of the upper and lower fibers, taking into account the thermal load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the damaged concrete beam, the FRP plate and the adhesive layer. The flexural analysis results and analytical predictions for the prestressed composite strengthened damaged RC continuous beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The use of composite materials increased the ultimate load capacity compared with the non strengthened beams. The major objective of the current model is to help engineers' model FRP strengthened RC continuous beams in a simple manner. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the FRP-damaged RC hybrid structures.

• 콘크리트학회논문집
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• 제17권6호
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• pp.903-910
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• 2005

최근 철근콘크리트 구조물의 보강 방법으로 고인장강도를 갖는 섬유복합체를 부재의 외부에 부착시켜 휨 내력을 증진시키는 부착식 보강공법이 널리 사용되고 있으나, 부착되는 섬유복합체의 박리에 의한 파괴강도를 예측하여 설계식에 반영하기 위한 연구는 미흡한 것이 사실이다. 보강재의 박리에 의한 파괴는 부재 전체의 취성적인 파괴를 유도하게 되므로, 부재의 보강설계를 위해서는 이에 대한 검토가 필수적으로 요구되어 진다. 본 연구에서는 보강재의 부착강도에 큰 영향을 미치는 유효부착길이의 개념을 도입하여, 기존 연구 결과로부터 부재의 부착강도를 좌우하게 되는 유효부착길이를 산정 하였으며, 이와 같은 유효부착길이에 의한 보강재의 박리하중을 산정할 수 있는 설계식을 제안하였다. 제안된 설계식은 기존 연구자들의 실험 연구결과와 비교하여 그 신뢰성을 검증하도록 하였으며, 기존 연구자들의 제안식과의 비교를 통하여 본 제안식의 타당성을 증명하였다.

• Steel and Composite Structures
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• 제4권5호
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• pp.333-353
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• 2004

Strength of reinforced concrete beams can easily be increased by the use of externally bonded CFRP composites. However, the mode of failure of CFRP strengthened beam is usually brittle due to tension-shear failure in the concrete substrate or bond failure near the CFRP-Concrete interface. In order to improve the ductility of CFRP strengthened concrete beams, critical variables need to be investigated. This experimental and analytical research focused on a series of reinforced concrete beams strengthened with CFRP composites to enhance the flexural capacity and ductility. The main variables were the amount of CFRP composites, the amount of longitudinal and shear reinforcement, and the effect of CFRP end diagonal anchorage system. Sixteen full-scale beams were investigated. A new design guideline was proposed according to the effects of the above-mentioned variables. The experimental and analytical results were found to be in good agreement.

• Computers and Concrete
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• 제8권2호
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• pp.193-206
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• 2011

The use of Carbon Fiber Reinforced Polymers (CFRP) to strengthen reinforced concrete beams under bending and shear has gained rapid growth in recent years. The performance of shear strengthened beams with externally bonded CFRP laminate or fabric strips is raising many concerns when the beam is loaded under cyclic loading. Such concerns warrant experimental, analytical and numerical investigation of such beams under cyclic loading. To date, limited investigations have been carried out to address this concern. This paper presents a numerical investigation by developing a nonlinear finite element (FE) model to study the response of a cantilever reinforced concrete T-beam strengthened in shear with side bonded CFRP fabric strips and subjected to cyclic loading. A detailed 3D nonlinear finite element model that takes into account the orthotropic nature of the polymer's fibers is developed. In order to simulate the bond between the CFRP sheets and concrete, a layer having the material properties of the adhesive epoxy resin is introduced in the model as an interface between the CFRP sheets and concrete surface. Appropriate numerical modeling strategies were used and the response envelope and the load-displacement hysteresis loops of the FE model were compared with the experimental response at all stages of the cyclic loading. It is observed that the responses of the FE beam model are in good agreement with those of the experimental test. A parametric study was conducted using the validated FE model to investigate the effect of spacing between CFRP sheets, number of CFRP layers, and fiber orientation on the overall performance of the T-beam. It is concluded that successful FE modeling provides a practical and economical tool to investigate the behavior of such strengthened beams when subjected to cyclic loading.

• 한국구조물진단유지관리공학회 논문집
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• 제12권6호
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• pp.155-163
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• 2008

본 연구에서는 외부 부착 프리스트레스트 탄소섬유판으로 보강된 RC보의 휨거동을 분석하기 위한 실험연구를 수행하였다. 실험체는 프리스트레스 양을 변수로 축소모형으로 제작되었다. 또한 프리스트레스의 도입에 따른 구조성능 비교를 위하여 기준실험체와 단순부착 실험체를 함께 제작하였다. 실험결과, 단순 부착 탄소섬유판으로 보강된 부재는 조기 박리에 의해 탄소섬유판 인장강도의 50% 이하에서 최종파괴되었다. 그러나, 프리스트레스를 도입하여 보강한 실험체는 모두 탄소섬유판의 파단하중까지 도달하였다. 또한 프리스트레스 보강량의 증가에 따라서 균열하중, 항복하중은 증가하며 최대하중은 프리스트레스 양과 관계없이 일정한 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.591-596
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• 2003

Many studies have dealt with strengthening by epoxy-bonded CFRP(Carbon Fiber Reinforced Polymer) composites. However, the effects of various influencing factors have not been clarified on the behavior of strengthened RC beams. This study was performed to verify the effects of strengthening due to various bond details of externally attached CFRP Composites. In this study, major test parameters include the bond type and the anchor type. The deflections, failure load, strain of reinforcing bar, concrete and CFRP are measured at each loading step. The failure mode and debonding loads(ultimate loads) are analysed from these measured data. According to the test results, all specimens are failed by intermediate flexural crack induced interfacial debonding.