• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.111-117
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• 2009

Concrete columns reinforced with Fibre Reinforced Polymer (FRP) rebar have been increasingly used in civil engineering applications, while the research on fire resistance of such structural members is still very limited. In this paper, attempts are made to predict temperature distribution and mechanical performance of FRP rebar reinforced concrete columns in fire. The effect of concrete cover and section size on fire resistance time is studied by the finite element method. Based on a parametric study, a simple empirical formula to predict fire resistance time is proposed for possible adoption in fire resistance design.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.557-564
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• 1997

This research is aimed to evaluate the effects of repair conditions, axial load intensities and the enlargement of cross sections after strengthening with steel plate and on the structural behavior of the reinforced concrete columns subjected to axial and lateral loadings. 6 columns were tested under uniform axial compression and concentrated load at the midspan until failiure occurs. As test results, It has been found that the amount of grout bar and the condition of strengthening significantly affect the behavior or reinforced concrete column with steel plate and grout 4 bar (C-G4S2 serise) and enlarged reinforced concrete column with steel plate and grout 8 bar (C-G8S2 serise) are increased to 1000% and 1200% in comparison of those of unstrengthened reinforced concrete columns, respectively

• Computers and Concrete
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• v.15 no.1
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• pp.1-20
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• 2015

Many existing reinforced concrete (RC) columns in structures tend to become substandard RC ones due to updated standards or environmental changes. These substandard columns may alter the behaviors of the whole structure and therefore are in urgent need of seismic retrofitting. Owing to their superior advantages, carbon fiber reinforced polymer (CFRP) composites are widely used to retrofit RC columns. The applications mainly focus on various substandard RC columns, but few deals with substandard columns with deteriorated concrete, especially damaged by earthquake. The purpose of this paper is to investigate the seismic behaviors of CFRP reinforced partially deteriorated RC columns and to evaluate the effect of CFRP sheets on them. Six flexure-dominant columns were tested under a constant axial load and transverse cyclic displacements. It is found that the seismic behaviors of partially deteriorated columns can be recovered by wrapping CFRP sheets on them. Numerical analysis is then conducted using finite element methods and verified with experimental results. The effects of the axial load ratio, the ratio of the thickness of CFRP sheet to the column diameter, and the slenderness ratio on the seismic behaviors of CFRP reinforced RC columns are evaluated. Finally, a method is proposed to determine the required thickness of CFRP sheet.

• Steel and Composite Structures
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• v.27 no.1
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• pp.95-108
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• 2018

A new composite reinforced method, namely self-compacting concrete filled circular CFRP-steel jacketing, was proposed in this paper. Experimental tests on eight RC square short columns reinforced with the new composite reinforced method and four RC square short columns reinforced with CFS jackets were conducted to investigate their eccentrically compressive behaviour. Nine reinforced columns were subjected to eccentrically compressive loading, while three reinforced columns were subjected to axial compressive loading as reference. The parameters investigated herein were the eccentricity of the compressive loading and the layer of CFRP. Subsequently, the failure mode, ultimate load, deformation and strain of these reinforced columns were discussed. Their failure modes included the excessive bending deformation, serious buckling of steel jackets, crush of concrete and fracture of CFRP. Moreover, these reinforced columns exhibited a ductile failure globally. Both the eccentricity of the compressive loading and the layer of CFRP had a significant effect on the eccentrically compressive behaviour of reinforced columns. Finally, formulae for the evaluation of the ultimate load of reinforced columns were proposed. The theoretical formulae based on the ultimate equilibrium theory provided an effective, acceptable and safe method for designers to calculate the ultimate load of reinforced columns under eccentrically compressive loading.

• Structural Engineering and Mechanics
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• v.27 no.3
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• pp.293-310
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• 2007

Theoretical foundation for the buckling load determination in reinforced concrete columns is described and analytical solutions for buckling loads of the Euler-type straight reinforced concrete columns given. The buckling analysis of the limited set of restrained reinforced concrete columns is also included, and some conclusions regarding effects of material non-linearity and restrain stiffnesses on the buckling loads and the buckling lengths are presented. It is shown that the material non-linearity has a substantial effect on the buckling load of the restrained reinforced concrete columns. By contrast, the steel/concrete area ratio and the layout of reinforcing bars are less important. The influence on the effective buckling length is small.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.603-608
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• 1997

Studies on the second-order analysis of reinforced concrete columns have been chiefly dealt with symmetric section under uniaxial loading. In practical situations, however, columns are subjected to biaxial loadings. Therefore, for more accurate prediction of the behavior of concrete columns under biaxial loading, the interaction between bending moments of major and minor axes should be considered. Recently Kim & Lee proposed a numerical method of predicting the behavior of concrete columns under biaxial loading. In this paper, to investigate the behavior of concrete columns under biaxial loading and verify the validity of proposed method, a series of test were carried out for sixteen tied reinforced columns with 100${\times}$100mm square and 200${\times}$100mm rectangular sections under various loading conditions. The length of columns was 1,300mm and the concrete strength was 28MPa. The boundary conditions at the both ends were hinged and end eccentricities were equal(400mm). Proposed numerical analyses applied to the test piece were performed to predict behavior of concrete columns with square and rectangular sections under various loading conditions. Test results were also compared with those using the moment magnifier method in ACI code. The test results showed that the moment magnifier method is conservative.

• KIEAE Journal
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• v.8 no.3
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• pp.69-76
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• 2008

This is an experimental study on the maximum load value and structural behavior of reinforced concrete columns containing shells as a substitute fine aggregate of concrete, through making reinforced concrete test columns with shells. In this study, the main factors consist of the grain sizes and the percentage of substitution of shells to fine aggregate in two kinds of water cement ratio. The results of the study showed as followed. The maximum load value decreased with increased the rate of substitution about shells and as the grain size of shells became smaller, the load values of them were somewhat changed higher but it is important that we must consider absorption rate of shells sufficiently. If we have a proper water cement ratio in column productions containing the shells, we can meet the requirement of the percentage of substitution until 30%. The deflection and deformation properties of reinforced concrete columns with shells represented typical curves like that of normal reinforced concrete. But as the failture types, they are able to make some change without being out of the fundamental graph forms. After the analyzing structural behaviors and the properties of reinforced concrete test columns containing shells, the most excellent grain size of shells represented 3.0mm and less with taking uniformly, and the percentage of practicable substitution of them to fine aggregate was about 30%.

• KIEAE Journal
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• v.7 no.4
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• pp.105-111
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• 2007

As this study investigates the influence about type of transverse reinforcement, spacing of transverse reinforcement(s), volumetric ratios of transverse reinforcement(${\rho}s$) of ultra-high strength concrete columns. It try to offer to resonable basic data of the confined model for the ultra-high concrete of in reinforced concrete columns. Experimental tests with large scaled columns were conducted under concentric axial loads. The ultra-high strength concrete (100MPa) was used. From this test result, it evaluate influence of the strength enhancement and ductility enhancement, important variables about behavior of the confined concrete by confinement of ultra-high strength reinforced concrete.There are two ways to improve the confinement effect of high strength concrete columns through the increase of amounts and/or strength of transverse reinforcement.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.727-732
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• 2001

External Confinement of concrete in CFS enhances strength and ductility of concrete columns. This paper presents the test results on the study of reinforced concrete columns strengthened with carbon fiber sheets. The purpose of this research is to evaluate the CFS confinement characteristics of square reinforced concrete columns and the CFS efficiency. The tests were performed with different lateral reinforcement ratios, CFS reinforcement ratios and concrete strength. Test results were characterized according to maximum loads and lateral strain of CFS.

• KCI Concrete Journal
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• v.12 no.1
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• pp.23-34
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• 2000

Experiments were carried out to investigate the seismic behaviors, such as lateral strength, ductility and energy-dissipation capacity. of high-strength concrete (HSC) square short column confined in thin steel shell. The primary objective of the study was to investigate the suitability of using HSC square columns confined in thin steel shell in region of moderate-to-high seismic risk. A total of six columns, consisting of two ordinarily reinforced concrete square short columns and four reinforced concrete square short columns confined in thin steel shell was tested. Column specimens, short columns in a moment resisting frame with girder. were tested under a constant axial and reversed cyclic lateral loads. To design the specimens. transverse reinforcing methods, level of axial load applied, and the steel tube width-thickness ratio (D/t) were chosen as main parameters. Test results were also discussed and compared in the light of improvements in general behaviors, ductility, and energy-absorption capacities. Compared to conventionally reinforced concrete columns, the HSC columns confined in thin steel shell had similar load-displacement hysteretic behavior but exhibited greater energy-dissipation characteristics . It is concluded that, in strong earthquake areas, the transverse reinforcing method by using a thin steel shell (D/t=125) is quite effective to make HSC short columns with very strong and ductile.