• Steel and Composite Structures
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• v.33 no.5
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• pp.629-640
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• 2019

This paper presents a theoretical and finite element (FE) study on the stress intensity factors of double-edged cracked steel beams strengthened with carbon fiber reinforced polymer (CFRP) plates. By simplifying the tension flange of the steel beam using a steel plate in tension, the solutions obtained for the stress intensity factors of the double-edged cracked steel plate strengthened with CFRP plates were used to evaluate those of the steel beam specimens. The correction factor α₁ was modified based on the transformed section method, and an additional correction factor φ was introduced into the expressions. Three-dimensional FE modeling was conducted to calculate the stress intensity factors. Numerous combinations of the specimen geometry, crack length, CFRP thickness and Young's modulus, adhesive thickness and shear modulus were analyzed. The numerical results were used to investigate the variations in the stress intensity factor and the additional correction factor φ. The proposed expressions are a function of applied stress, crack length, the ratio between the crack length and half the width of the tension flange, the stiffness ratio between the CFRP plate and tension flange, adhesive shear modulus and thickness. Finally, the proposed expressions were verified by comparing the theoretical and numerical results.

• Composites Research
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• v.36 no.1
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• pp.1-15
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• 2023

Demand for energy consumption reduction is increasing according to the development expectations of future mobility. Lightweight structural materials are known as a method to reduce greenhouse gas emissions and improve energy efficiency. In particular, fiber reinforced polymer composite (FRP) is attracting attention as a material that can replace existing metal alloys due to its excellent mechanical properties and light weight. In this paper, industrial applications and research trends of carbon fiber reinforced composites (CFRP, carbon FRP) and self-reinforced composites (SRC) were reviewed based on the reinforcement, polymer matrix, and manufacturing process. In order to overcome the expensive process cost and long manufacturing time of the epoxy resin-based autoclave method, which is mainly used in the aircraft field, mass production of CFRP-applied electric vehicles has been reported using a high-pressure resin transfer molding process including fast-curing epoxy. In addition, thermoplastic resin-based CFRP and interface enhancement methods to solve the recycling issue of carbon fiber composites were reviewed in terms of materials and processes. To form a perfect matrix-reinforcement interface, which is known as the major factor inducing the excellent mechanical properties of FRP, studies on SRC impregnated with the same matrix in polymer fibers have been reported. The physical and mechanical properties of SRC based on various thermoplastic polymers were reviewed in terms of polymer orientation and composite structure. In addition, a copolymer matrix strategy for extending the processing window of highly drawn polypropylene fiber-based SRC was discussed. The application of CFRP and SRC as lightweight structural materials can provide potential options for improving the energy efficiency of future mobility.

• Structural Engineering and Mechanics
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• v.53 no.6
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• pp.1067-1081
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• 2015

This study investigates structural and mechanical behaviors of RC (Reinforced concrete) beams strengthened with tapered CFRP (Carbon fiber reinforced polymer) sheets having various configurations. Toward this goal, experiments are performed on RC beams strengthened with four layers of CFRP sheets and each layer of the CFRP is prepared to have different length. Experimental results show that tapered CFRPs have better strengthening effect than non-tapered CFRP sheets and maximum loads of the beams with tapered CFRPs are governed by the length of first CFRP layer rather than total length of CFRP layers. In addition, analyses are performed using FE (Finite Element) models including cohesive elements to predict debonding behaviors between FRP and concrete elements. The predicted results from the FE models show good agreement with the experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.161-164
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• 2008

In recent years, carbon fiber-reinforced polymer (CFRP) has been widely used for repairing and/or strengthening structural elements in concrete. Not enough test data, however, are available to predict the long-term performance of the repaired and improved structures exposed to weathering. The objective of this research is to study the effect of freeze-thaw cycling on the behavior of reinforced concrete (RC) beams strengthened in shear with carbon fiber sheet. Six small-scale RC beams (100mm${\times]$100mm${\times]$400mm) were strengthened with CFRP in shear, subjected to up to 400 cycles freeze-thawing from -17${\sim}4^{\circ}C$, and tested to failure in four-point bending. Test result, there was no significant damage to carbon fiber sheet strengthened concrete beams had been suffered 30 cycles of freeze-thawing, and more over 60 cycles of freezing-thawing brought about a reduction in resistance of only 25% of the initial level.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.729-736
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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 resulted in large permanent deformations and structural collapse. In this study, experimental investigations into the performance of exterior reinforced concrete beam-column joints strengthened with the carbon fiber-reinforced polymer(CFRP) under cyclic loading were presented. The CFRP has been applied by choosing different combinations and locations to determine the effective way to improve structural performances of joints. Eight beam-column joints were tested to investigate behaviors of each specimen under cyclic load and to compare performances of seismic retrofit. According to the experimental study, the retrofit strengthened with the CFRP provides significant improvements of flexural capacity and ductility of beam-column joints originally built without seismic details.

• Steel and Composite Structures
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• v.32 no.1
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• pp.21-35
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• 2019

This study investigates the flexural behavior of steel-concrete composite beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. An innovative mechanical anchorage system was developed. The components of the system can be easily assembled on site before applying a prestressing force, and removed from the structures after strengthening is completed. A total of seven steel-concrete composite specimens including four simply supported beams strengthened at the positive moment region and three continuous beams strengthened at the negative moment region were tested statically until failure. Experimental results showed that the use of prestressed CFRP plates enhanced the flexural capacity and reduced the mid-span deflection of the beams. Furthermore, by prestressing the CFRP laminates, the material was used more efficiently, and the crack resistance of the continuous composite specimens at the central support was significantly improved after strengthening. Overall, the anchorage system proved to be practical and feasible for the strengthening of steel-concrete composite beams. The theoretical analysis of ultimate bearing capacity is reported, and good agreement between analytical values and experimental results is achieved.

• Steel and Composite Structures
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• v.4 no.5
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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.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.473-476
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• 2004

Carbon Fiber Reinforced Polymer(CFRP) composites are widely applied to strengthen deteriorated concrete structures. This paper presents the experimental results of the performance of reinforced concrete(RC) beams strengthened with Near Surface Mounted T-shape CFRP. Simple beams with 3m span length were tested to investigate the effect of CFRP reinforcement shapes on the flexural behavior of strengthened RC beams. The test results were analyzed with the special emphasis on the failure mode and the maximum load.

• 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/$cm^{2}$.

• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.29-34
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• 2006

Elastic modulus, tensile and bond capacities are important factors for developing an effective reinforcing action of a flexural member as a reinforcing material for concrete structures. Reinforcement must have enough bond capacity to prevent the relative slip between concrete and reinforcement. This paper presents an experimental study to clarify the bond capacity of prestressed carbon fiber reinforced polymer(CFRP) rod manufactured by an automatic assembly robot. The bond characteristics of CFRP rods with different pitch of helical wrapping were analyzed experimentally. As the result, all types of CFRP rods show a high initial stiffness and good ductility. The mechanical properties of helical wrapping of the CFRP rods have an important effect on the bond of these rods to concrete after the bond stress reached the yield point. The stress-slip relationship analyzed from the pull-out test of embedded cables within concrete was linear up to maximum bond capacity. The deformation within the range of maximum force seems very low and was reached after approximately 1 mm. The average bond capacity of CF20, CF30 and CF40 was about 12.06 MPa, 12.68 MPa and 12.30 MPa, respectively. It was found that helical wrapping was sufficient to yield bond strengths comparable to that of steel bars.