• Steel and Composite Structures
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• v.16 no.5
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• pp.481-489
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• 2014

The function of carbon fibre reinforced polymer (CFRP) reinforcement in increasing the ductility of reinforced concrete (RC) deep beam is important in such shear-sensitive RC member. This paper aims to investigate the effect of CFRP-strengthening on the energy absorption of RC deep beams. Six ordinary RC deep beams and six CFRP-strengthened RC deep beams with shear span to the effective depth ratio of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were tested till failure in this research. An empirical relationship was established to obtain the energy absorption of CFRP-strengthened RC deep beams. The shear span to the effective depth ratio and growth of energy absorption of CFRP-strengthened deep beam were the significant factors to establish this relationship.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.106-109
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• 2006

It has been shown that many reinforced concrete(RC) structures designed without seismic details have experienced brittle shear failures in the beam-column joint area and may result in large permanent deformations and structural collapse. In this study, experimental investigations for RC beam-column joints strengthened with the carbon fiber-reinforced polymer(CFRP) under cyclic loadings were presented. The use of CFRP in the joint was varied to determine the effective way of improving the structural performances of RC joints. Ten RC beam-column joints were designed and tested with cyclic loadings. The experimental results showed that the use of CFRP in RC joints would be very effective solutions to improve the seismic performances of the non-seismic RC joints. All of the non-seismic design specimens strengthened with CFRP sheets showed the significant increase of strength and ductility.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.470-473
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• 2006

Past experiences from recent earthquakes indicate that shear failures of beam-column connections were one of the main reasons causing significant damages and collapses of RC structures subjected to earthquake loadings. Many researchers and engineers have conducted to propose an effective way to improve the joint shear strength of RC connections. This paper presents an analytical model for the RC exterior beam-column joints strengthened with CFRP sheets. In the analytical model, the effect of shear behavior of the RC beam-column joint, bond slip of the beam longitudinal reinforcements and CFRP sheets were considered and incorporated into the non-linear structural analysis program. Final analytical results were compared with those from the experiment of eight exterior RC beam-column specimens. The analytical results showed that the developed connection model is very useful to investigate the hysteretic joint behavior and overall load-displacement response of the RC beam-column connections strengthened with CFRP sheets.

• Advances in concrete construction
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• v.13 no.4
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• pp.307-313
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• 2022

This paper performs an experimental study on the flexural behavior of preloaded reinforced self-compacted concrete beams strengthened with carbon fiber reinforced polymers CFRP. A group of six preloaded strengthened beams was investigated along with one unstrengthened beam used as a reference beam RB. All beams have the same dimensions and reinforcement details: three beams are strengthened with CFRP laminates against flexural failure and three beams are strengthened with CFRP sheets. For simulating actual conditions, the beams are loaded before strengthening. Then, after strengthening, the beams are tested for flexural strength using 4-point loads where cracked and ultimate load and failure mode, along with load-deflection relation are recorded. To study the different configurations of strengthening, one layer, two layers, and U-wrap formation of laminates and sheets are considered. The results show that strengthing the RC beams using CFRP is an effective method to increase the beam's capacity by 47% up to 153% where deflection is reduced by 5%-80%. So, the beams strengthened with CFRP laminates have higher load capacity and lower ductility in comparison with the beams strengthened with CFRP sheets.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.997-1002
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• 2001

Tensile strength of CFRP (Carbon Fiber Reinforced Polymer) is approximately 10 times higher than that steel reinforcement, but the design strength of CFRP is normally reduced by the bond failure between RC and CFRP. Many researches have been carried out, concerned with bond behavior between RC and CFRP to prevent the unpredicted bond failure of RC beam strengthened by CFRP, but the national design code for design bond strength of CFRP hasn't been constructed. In this study, 3 beams specimen strengthened by CFRP under the variable of bonded length were tested to derive the design bond strength of CFRP to the RC flexural members. Also 2 beams specimen strengthened by CFRP were tested to inspect the construction environment effects such as mixing error of epoxy resin and the amount of primer epoxy resin. From the test results, It is concluded that the maximum design bond strength of CFRP to RC flexural member is considered to be $\tau_{a}$=8kgf/$cm^{2}$.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.279-282
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• 2005

This study investigates the flexural behavior and strengthening performance of RC beams strengthened by prestressed CFRP laminates through static bending tests. Tests on RC beams strengthened with prestressed CFRP laminates were carried out for both cases where the CFRP laminates were bonded or not and the corresponding effects on the strengthening performances of RC beams were examined. Experimental results revealed that RC beams strengthened with prestressed CFRP laminates presented increased crack load and yield load according to the level of prestress. Premature debonding occurred before the RC beam strengthened with bonded prestressed CFRP laminates reaches the maximum load, and the specimen presented similar behavior to the one exhibited by the specimen with unbonded laminates.

• Computers and Concrete
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• v.17 no.3
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• pp.407-421
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• 2016

This paper presents numerical modeling of the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened RC (reinforced concrete) beams under four-point bending. Simulation of debonding at the CFRP-concrete interface was focused, as it is the main failure mode of CFRP strengthened RC beams. Here, cohesive layer was employed to model the onset of debonding, which further helps to describe the post debonding behavior of the CFRP strengthened RC beam. In addition, the XFEM approach was applied to investigate the effects of crack localization on strain field on CFRP sheet and rebar. The strains obtained from the XFEM correlate better to the test results than that from CDP (concrete damaged plasticity) model. However, there is a large discrepancy between the experimental and simulated loaddisplacement relationships, which is due to the simplification of concrete constitutive law.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.549-555
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• 2002

Tensile strength of CFRP (Carbon Fiber Reinforced Polymer) is approximately 10 times higher than that of the steel reinforcement, but the design strength of CFRP is normally limited by unpredictable bond failure between RC and CFRP. Many researches concerned with bond behavior between RC and CFRP have been carried out to prevent the bond failure of RC beam strengthened by CFRP, but the national design code for design bond strength of CFRP has not been constructed. In this study, three beam specimens strengthened by CFRP under the parameters of bonded length were tested to derive the design bond strength of CFRP for the RC flexural members. Each bonded length was calculated based on the bond strength of JCI and CFRP manufacturing company. Also, another two beam specimens strengthened by CFRP were tested to inspect the construction environment effects such as mixing error of epoxy resin, and the amount of epoxy primer. From the test results, it is concluded that the maximum design bond strength of CFRP to RC flexural member is considered to be $\tau$a =8 kgf/㎠.

• Structural Engineering and Mechanics
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• v.44 no.6
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• pp.705-733
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• 2012

In this work, an experimental examination was carried out to study interfacial stresses developed at the junction zones between carbon fiber reinforced plastic (CFRP) fabrics (~1 mm thickness) and tensile concrete portion in CFRP retrofitted RC beams. In this respect, initially six similar RC beams of $150{\times}150{\times}1000mm$ dimensions were prepared. Three of which were strengthened with CFRP fabrics at the tensile side of the beams. Furthermore, a notch was cut at the center of the bottom surface for all of the studied beams. The notch was 15 mm deep and ran across the full width of tension side of the beams. The mentioned interfacial stresses could be calculated from strains measured using strain gauges mounted on the interface zone of the tensile concrete and the CFRP sheet. Based on the results obtained, it is shown that interfacial stresses developed between CFRP fabrics and RC beam had a noticeable effect on debonding failure mode of the latter. The load carrying capacity of CFRP strengthened RC specimens increased ~75% compared to that of the control RC beams. This was attributed to the enhancement of flexural mode of the former. Finally, finite element analysis was also utilized to verify the measured experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1003-1008
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• 2001

It is recently reported that bond failure can be initiated in the region where maximum bending moment and shear force is acted by accompanying shear deformation after flexural crack in full-scale RC beams strengthened by CFRP. Such a shear deformation effect causing bond failure is relatively little in the case of small-scale specimens. So, additional reinforcing details to the critical beam section where maximum moment and shear were acted is required to prevent the bond failure caused by the shear deformations. The U-type wrapping methods by CFRP to the critical beam section is proposed and tested in this paper. Also, the applicability of design bond strength derived from the tests of small-scale beam was investigated by the full-scale RC beam strengthened by CFRP.