Experimental Study of Deformation Processes in Reinforced Concrete Beams Strengthened with a Carbon Fiber Sheet (original) (raw)
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Frattura ed Integrità Strutturale, 2016
Technology of strengthening reinforced concrete structures with composite materials has found wide application. The effectiveness of strengthening of concrete structures with externally bonded reinforcement is supported by a great deal of experimental evidence. However, the problem of serviceability of such structures has not been adequately explored. The present work describes the results of experimental studies on the loadcarrying capacity of concrete beams strengthened with carbon fiber reinforced plastic (CFRP). Special emphasis is placed on studying the debonding of the strengthening layer from the concrete surface and analyzing its influence on the load-carrying capacity of beams. Infrared thermography is used to detect the first signs of debonding and to assess the debond growth rate.
Delamination of carbon-fiber strengthening layer from concrete beam during def.PDF
Technology of strengthening reinforced concrete structures with composite materials has found wide application. The effectiveness of strengthening of concrete structures with externally bonded reinforcement is supported by a great deal of experimental evidence. However, the problem of serviceability of such structures has not been adequately explored. The present work describes the results of experimental studies on the loadcarrying capacity of concrete beams strengthened with carbon fiber reinforced plastic (CFRP). Special emphasis is placed on studying the debonding of the strengthening layer from the concrete surface and analyzing its influence on the load-carrying capacity of beams. Infrared thermography is used to detect the first signs of debonding and to assess the debond growth rate.
Use of carbon fiber laminates for strengthening reinforced concrete beams in bending
The use of Fiber Reinforced Polymer (FRP) is becoming a widely accepted solution for repairing and strengthening ageing in the field of civil engineering around the world. In the present paper, experimental study designed to investigate the flexural behavior of reinforced concrete beams strengthened with CFRP laminates attached to the bottom of the beams by epoxy adhesive subjected to transverse loading. A total of five beams having different CFRP laminates configurations were tested to failure in four-point bending over a clear span 1900mm. Four beams were strengthened by changing the levels of CFRP laminates whereas the last one was not strengthened with FRP and considered as a control beam. Test results showed that the addition of CFRP sheets to the tension surface of the beams demonstrated significantly improvement in stiffness and ultimate capacity of beams. The response of control and strengthened beams were compared and efficiency and effectiveness of different CFRP configurations were evaluated. It was observed that tension side bonding of CFRP sheets with U-shaped end anchorages is very efficient in flexural strengthening. The paper also highlighted the beams failure modes due to the different level of strengthening scheme.
Materials
This study investigates the mechanical behavior of steel fiber-reinforced concrete (SFRC) beams internally reinforced with steel bars and externally bonded with carbon fiber-reinforced polymer (CFRP) sheets fixed by adhesive and hybrid jointing techniques. In particular, attention is paid to the load resistance and failure modes of composite beams. The steel fibers were used to avoiding the rip-off failure of the concrete cover. The CFRP sheets were fixed to the concrete surface by epoxy adhesive as well as combined with various configurations of small-diameter steel pins for mechanical fastening to form a hybrid connection. Such hybrid jointing techniques were found to be particularly advantageous in avoiding brittle debonding failure, by promoting progressive failure within the hybrid joints. The use of CFRP sheets was also effective in suppressing the localization of the discrete cracks. The development of the crack pattern was monitored using the digital image correlation method. As revealed from the image analyses, with an appropriate layout of the steel pins, brittle failure of the concrete-carbon fiber interface could be effectively prevented. Inverse analysis of the moment-curvature diagrams was conducted, and it was found that a simplified tension-stiffening model with a constant residual stress level at 90% of the strength of the SFRC is adequate for numerically simulating the deformation behavior of beams up to the debonding of the CFRP sheets.
International Journal of Structural and Civil Engineering Research
The objective of this research work is to reinforced concrete beams with Carbon Fiber Reinforced Polymers (CFRP) and subject them to a flexural test. For this purpose, two concrete mix designs of 210 and 280Kgf/cm2 were made and CFRP was applied to them. A total of 12 specimens were made for each mix design and reinforced with 1/4", 3/8" and 8mm steels. It was concluded that the addition of CFRP as well as the stressing of different steel diameters improved the reinforced concrete beams in terms of flexural strength, cracking pattern, stiffness and ductility of all beams, compared to the beams without CFRP and steel reinforcement.
Deformation adjustment of concrete beams laminated with carbon fiber mats
Construction and Building Materials, 2007
A carbon fiber mat is a sheet composed of intercrossing short carbon fibers, which has more stable and lower electrical resistivity compared with dispersed short carbon fiber mixed in cement. Thereby carbon fiber mats can be used in cement and then make cement structures exhibit obvious electro-thermal effect. In this paper, Electro-thermal properties of carbon fiber mats and an elementary strengthening experiments against deformation of carbon fiber mat cement laminated beams were researched. Firstly, electro-thermal properties of carbon fiber mats were studied. Secondly, carbon fiber mat laminated beams are designed and experiments were conducted to get temperature and deformation responses driven by the electro-thermal effects of the carbon fiber mat cement laminated beams. Finally, some experiments of deformation adjustment were done according to the above experimental results. The results show that deformation of concrete beams upon loads can be reduced even removed, and the beams can be strengthened against deformation.
An Experimental Study on Mechanical Properties of Carbon Fiber Reinforced Concrete
Fibers have the characteristics to enhance the endurance of concrete..One of them is carbon fiber. These carbon fibers have superb mechanical properties and may be utilized more effectively. This study is focused towards analyzing the variation in strength of carbon fiber concrete at variable fiber contents and to establish it with that of conventional concrete. The mechanical properties analyzed are compressive strength, tensile strength and flexural strength of carbon fiber concrete at (0.3%, 0.6%,0. 9%,1%, 1.2%) percentages by volume of concrete. Result data clearly shows percentage increase in compressive strength, split tensile strength and flexural strength for M25 grade of concrete in 7 days and 28 days with respect to the variation in % addition of carbon fibers. Maximum increase in strength was achieved at 1% addition of fiber content and it can be considered as optimum dosage.
Flexural strengthening of reinforced concrete beams by continuous fiber sheets
Transactions of the Japan …, 2000
The most common method used to strengthening, rehabilitation or repairing of reinforced concrete (RC) members is to use external carbon fiber reinforced polymer (CFRP) sheets. CFRP can greatly improve the flexural and shear capacity of deteriorated members and therefore extends their useful life. The main problem of external CFRP is the debonding of the sheets from the concrete surface at some point of loading, which negatively affects the efficiency of strengthening and may consequently lead to an unanticipated failure of the strengthened members. The major reason for this early debonding is likely due to the low accuracy of the preparation and the high stress concentration at the flat contact area exists between CFRP sheets and the concrete. The problem has been extensively discussed in the literature and some CFRP application techniques such as "Externally Bonded Reinforcement on Grooves (EBROG)" and "Externally Bonded Reinforcement in Grooves (EBRIG)" have been proposed as alternatives to the conventional application methods. Although some research has been carried out, there have been few experimental investigations that provided quantitative discussion of the efficiency of the new developed techniques. This research was aimed to experimentally assess the efficiency of grooving techniques and to provide a quantitative data regarding the behaviour of bonding between CFRP and concrete. The effects of shape and direction of the grooves and CFRP layers on the load carrying capacity, mid-span deflection and failure mode of thirteen RC beams have been investigated and discussed. In general, CFRP has significantly improved the flexural capacity of strengthened beams especially when grooving technique has been employed.
2007
The basic aim of this paper is to present a preliminary study of the behavior of concrete beams under compression and a flexural stresses, both reinforced with carbon fibers. In each research, theoretical formulations, experimental results and numerical methodology using the finite element methods are presented. To simulate numerically the rupture of the concrete speciments, the adequate parameters are considered to define the rupture surface of the Drucker-Prager criterion for structural concrete elements in higher tensions. For the flexural beam simulation, the Willam-Warnke criterion is applied. In the end of this paper numerical results are presented to conclude this research.