• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.291-294
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• 2005

Presented are the results of recent tests on diagonal shear failure of reinforced concrete beams which are externally reinforced in the transverse direction by a unidirectional carbon fiber reinforced polymer, instead of the traditional steel stirrups. Three different series of the beams with different shear reinforcements, i.e. U-wrapping with carbon sheet, U-wrapping with carbon strips and full wrapping with carbon strips were tested. Those beams were geometrically similar, and the size range is 1:1.9:4. The failure of the beams are characterized by delamination, crushing of concrete and distributed shear cracks. It is found that the size effect is much weaker than that of the reference beams without CFRP. Therefore CFRP sheet may be used as the transverse reinforcement with a minor size effect. However, it is not clear that the same conclusion can be drawn in other sizes. Further researches are recommended.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.290-293
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• 2006

Glass fiber reinforced polymer (GFRP) bars gain increasingly more attention in the civil engineering community. GFRP reinforcement for concrete does not have the same shape as steel reinforcement. Therefore, the bond performance of FRP bars, unlike that of steel, is dependent on their design, manufacture and mechanical properties. It was tested in order to examine the bond behavior of GFRP bars under different compressive strength of concrete. Test results showed that the bond strength of GFRP increased with the compressive strength of concrete.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.5
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• pp.51-60
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• 2008

This study is to relate the bond characteristics of CFRP rebar in high strength concrete incorporated with silica fume(SF) and metakaolin(MK). An direct bond test were performed to evaluate the effect of SF and MK on bond properties of high-strength concrete and CFRP rebar. The high strength concrete mix included four SF and MK mixes with 0%, 5%, 10% and 15%. Results of bond performance experiment in relation to pullout vs slip behavior of FRP rebar and high strength showed better performance of SF than MK. Also, the results showed the improved bond strength as replacement ratio of SF and MK increased. The relative bond strength in which $1.3{\sim}3.2$ of estimated values were obtained.

• Structural Engineering and Mechanics
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• v.63 no.5
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• pp.629-637
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• 2017

Continuous concrete beams are commonly used as structural members in the reinforced concrete constructions. The use of fiber reinforced polymer (FRP) bars provide attractive solutions for these structures particularly for gaining corrosion resistance. This paper presents experimental results of eight two-span continuous concrete beams; two of them reinforced with pure glass fiber reinforced polymer (GFRP) bars and six of them reinforced with combinations of GFRP and steel bars. The continuous beams were tested under monotonically applied loading condition. The experimental load-deflection behavior and failure mode of the continuous beams were examined. In addition, the continuous beams were analyzed with a numerical method to predict the load-deflection curves and to compare them with the experimental results. Results show that there is a good agreement between the experimental and the theoretical load-deflection curves of continuous beams reinforced with pure GFRP bars and combinations of GFRP and steel bars.

• Steel and Composite Structures
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• v.20 no.2
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• pp.413-429
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• 2016

A theoretical method to predict the interfacial stresses in the adhesive layer of reinforced concrete beams strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) plate is presented. The analysis provides efficient calculations for both shear and normal interfacial stresses in reinforced concrete beams strengthened with composite plates, and accounts for various effects of Poisson's ratio and Young's modulus of adhesive. Such interfacial stresses play a fundamental role in the mechanics of plated beams, because they can produce a sudden and premature failure. The analysis is based on equilibrium and deformations compatibility approach developed by Tounsi. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the reinforced concrete beam and bonded plate. The paper is concluded with a summary and recommendations for the design of the strengthened beam.

• Journal of the Korean Ceramic Society
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• v.47 no.4
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• pp.276-282
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• 2010

There are the impregnating layer formation by surface protective materials or impregnants and the adhesion method by polymer, FRP sheet or steel plate in the surface protective method of concrete structure. The surface impregnation method by impregnants improves the durability of concrete structure by modifying the structure of the concrete surface and also have a merit that can be shortly applied in place without the decrease of concrete surface appearance and is easily applied again. This study is interested in manufacturing the concrete surface impregnants including lithium and potassium silicate for the repair of the exposed concrete and the color concrete requiring the advanced function in view of the concrete appearance. The durability and porosity properties was tested for the review of application. The result of this study show that the effective content of silicate ranges 5 to 20% and the separate application of the first impregnant and the second impregnant is effective for the optimum performance. The adhesion in tension is slightly increased but the reinforcement of concrete substrate is slight. So, the concrete impregnant of this study is more desirable for the improvement of durability rather than the reinforcement.

• Advances in concrete construction
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• v.5 no.5
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• pp.539-561
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• 2017

In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium -level, high -level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.45-51
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• 2013

Short beam tests of GFRP and CFRP specimens exposed to high temperature were conducted to measure the inter-laminar shear strength. For the phase I test, the exposure time and temperature were varied to measure reduction in the strength due to the applied conditions. As a results, the critical temperature was found to $270^{\circ}C$ for the both FRP reinforcements. The high temperature, which causes 50% loss of inter-laminar shear strength, is defined as the critical temperature in this study. It should be noted that the critical temperature for the inter-laminar shear strength is mainly dependent on resin properties not on fiber type. In the phase II test, the effect of exposure time was investigated at intervals of 0.25hour for the critical temperature. All test results demonstrate that the exposure time effect is not significant compared to the maximum exposure temperature, but it is not negligible and, moreover, is significant at the critical temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.474-480
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• 2018

FRP is a new material that is lightweight, has high strength and high durability, and is emerging as a third construction material in many countries. The composite material panel targeted in this study was a curved member and is the most frequently used arch-shaped member of a structures, such as tunnels. Composite curved panels can be produced in high quality and large quantities through automation operations. On the other hand, the frequency of application is low, and the design criteria and experimental data are lacking. Therefore, this study examined the mechanical performance of the member unit first to verify its performance as structural members of the FRP curved panel. For this purpose, tensile, compression, and connection performance tests were carried out. The tensile tests showed greater tensile strength of specimens with larger curvature, and the compression tests showed that the composite section of a composite material has greater compressive strength than the concrete section. Finally, the test of the performance of the connection showed that the attachment performance of the connection was more than equal to that of the FRP composite material panel.

• Structural Engineering and Mechanics
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• v.24 no.4
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• pp.429-446
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• 2006

Experimental investigation was conducted to evaluate the seismic ductility of earthquake-experienced concrete columns with an aspect ratio of 2.5. Eight circular concrete columns with a diameter of 600 mm were constructed with three test parameters: confinement ratio, lap-splice of longitudinal bars, and retrofitting with Fiber Reinforced Polymer (FRP) materials. The objective of this research is to examine the seismic performance of RC bridge piers subjected to a Quasi static test (QST), which were preliminary tested under a series of artificial earthquake motions referred to as a Pseudo dynamic test (PDT). The seismic enhancement effect of FRP wrap was also investigated on these RC bridge piers. Six specimens were loaded to induce probable damage by four series of artificial earthquakes, which were developed to be compatible with earthquakes in the Korean peninsula by the Korea Highway Corporation (KHC). Directly after the PDT, six earthquake-experienced columns were subjected to inelastic cyclic loading under a constant axial load of $0.1{f_c}^{\prime}A_g$. Two other reference specimens without the PDT were also subjected to similar quasi-static loads. Test results showed that specimens pre-damaged by moderate artificial earthquakes generally demonstrated good residual seismic performance, which was similar to the corresponding reference specimen. Moreover, RC bridge specimens retrofitted with wrapping fiber composites in the potential plastic hinge region exhibited enhanced flexural ductility.