• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.565-572
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• 2004

The mechanical behavior of concrete-filled glass fiber reinforced polymer columns is affected by various factors including concrete strength, stiffness of tube, end confinement effect, and slenderness ratio of members. In this research the behavior of slender columns was examined both experimentally and analytically. Experimental works include 1) compression test with 30cm long glass fiber composite columns under different end confinement conditions, 2) uni-axial compression test for 7 slender columns, which have various slenderness ratios. Short-length stocky columns gave high strength and ductility revealing high confinement action of FRP tubes. The strength increment and strain change were examined under different end confinement conditions. With slender columns, failure strengths, confinement effects, and stress-strains relations were examined. Through analytical work, effective length was computed and it was compared with the amount of reduction in column strength, which is required to predict design strength with slender specimens. This study shows the feasibility of slender concrete-filled glass fiber reinforced polymer composite columns.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.929-934
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• 2002

Eight full-scale columns were constructed and tested under monotonic axial compression loading to investigate the influence of headed bars on the confinement of the concrete. One column represented a column with no transverse reinforcement and another column had poor detailing and little confinement. A third column contained seismic hoops and crossties, which represented current detailing practice for significant confinement. A fourth column test is conducted to investigate the response with the seismic crossties replaced by headed bars. Two column specimens were constructed and tested with all of the transverse reinforcement provided by headed bars. These six specimens enabled an assesment of the effectiveness of headed bars in confining the concrete. It was found that the use of headed bars improved the confinement of the columns. Two additional specimens were constructed without any transverse reinforcement. These columns were later retrofitted, by drilling horizontal holes in the columns, adding special headed bars (one head fixed and the other head threaded) and then filling the drilled holes with epoxy. These retrofitted specimens with these added headed bars provided insight into the rehabilitation of older structures containing poorly detailed columns. All of the test specimens were instrumented to determine strain localization during failure and to monitor the strain in the longitudinal and transverse reinforcement.

• Structural Engineering and Mechanics
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• v.13 no.3
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• pp.313-328
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• 2002

Based on the orthotropic hypoelasticity formulation, a triaxial constitutive model of concrete is proposed. To account for increasing ductility in high confinement of concrete, the ductility enhancement is considered using so called the strain enhancement factor. It is also developed a three-dimensional finite element model for reinforced concrete structural members based on the proposed constitutive law of concrete with the smeared crack approach. The concrete confinement effects due to the beam-column joint are investigated through numerical examples for simple beam and structural beam member. Concrete at compression fibers in the vicinity of beam-column joint behaves dominant not only by the uniaxial compressive state but also by the biaxial and triaxial compressive states. For the reason of the severe confinement of concrete in the beam-column joint, the flexural critical cross-section is observed at a small distance away from the beam-column joint. These observations should be utilized for the economic design when the concrete structural members are subjected to high confinement due to the influence of beam-column joint.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3A
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• pp.189-196
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• 2012

In this paper, reinforced concrete columns test has been conducted under repeated lateral load reversals. The test columns have been reinforced with outside lateral confinement members in addition to transverse reinforcements. For this purpose, a strainless steel and a GFRP have been employed for the lateral confinement members. Primary parameters are types, thickness and spacing of the lateral confinement members. Experimental results reveal that columns reinforced with lateral confinement members exhibit improved ductility and energy dissipation capacity in comparison with those unreinforced. It is thus concluded that the present approach can be of a useful scheme for the seismic retrofitting of reinforced concrete columns.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.8-15
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• 2002

This paper presents a study carried out for the seismic capacity in reinforced concrete(RC) piers by the confinement effect of transverse reinforcement as such a hooked-tied, welded-tied and spiral reinforcement. In order to assess the seismic capacity with transverse reinforcement, experiment리 and analytical methods were adopted. A RC column survey was conducted based on eight one-fourth scale single circular column specimens designed and tested under slow horizontal cyclic loads. Two cases were analyzed. The confinement effect of concrete by transverse reinforcement is considered not in Case 1 but in Case 2. Also, we studied the propriety of making use of the method in which a carbon fiber rod replace spiral reinforcement in RC piers. In experimental tests, a welded-tied and spiral reinforcement has a good seismic capacity, but a carbon fiber rod presents low ductility in comparison with a hooked-tied reinforcement. In an analytical study, displacement ductility is approximate to the experimental result because of considering the confinement effect of the transverse reinforcement. Even if the confinement effect of the transverse reinforcement is considered, the analytical results for ductility of the specimens with welded-tied and spiral reinforcement show an excessive underestimation of the experimental results.

• Steel and Composite Structures
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• v.29 no.4
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• pp.465-481
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• 2018

The use of external carbon-fiber-reinforced polymer (CFRP) laminates is one of the most effective techniques existing for the confinement of circular concrete specimens. Currently, several researches have been made to develop models for predicting the ultimate conditions of this type of confinement. As most of the major existing models were developed based on limited experimental database. This paper presents the development of new confinement ultimate conditions, strength and strain models, for concrete cylinders confined with CFRP composites based on a statistical analysis of a large existing experimental database of 310 cylindrical concrete specimens wrapped with CFRP. The database is used to evaluate the performance of the proposed and major existing strength and strain models. Based on the two different statistical indices, the coefficient of determination ($R^2$) and the Root Mean Square Error (RMSE), the two proposed confinement ultimate conditions presents a good performance compared to the major existing models except the models of Lam and Teng (2003) and Youssef et al. (2007) which have relatively similar performance to the proposed models.

• Advances in concrete construction
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• v.14 no.2
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• pp.79-92
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• 2022

The amount and configuration of transverse reinforcement are known as critical parameters that significantly affect the lateral confinement of concrete, the ductility capacity, and the plastic hinge length of RC columns. Based on test results, this study investigated the effect of the three variables on structural indexes such as neutral axis depth, lateral expansion of concrete, and ductility capacity. Five reinforced concrete column specimens were tested under cyclic flexure and shear while simultaneously subjected to a constant axial load. The columns were reinforced by two types of reinforcing steel: rectangular hoops and spiral type reinforcing bars. The variables in the test program were the shape, diameter, and yield strength of transverse reinforcement. The interactive influence of the amount of transverse reinforcement on the structural indexes was evaluated. Test results showed that when amounts of transverse reinforcement were similar, and yield strength of transverse reinforcement was 600 MPa or less, the neutral axis depth of a column with spiral type reinforcing bars was reduced by 28% compared with that of a column reinforced by existing rectangular hoops at peak strength. While the diagonal elements of spiral-type reinforcing bars significantly contributed to the lateral confinement of concrete, the strain of diagonal elements decreased with increases of their yield strength. It was confirmed that shapes of transverse reinforcement significantly affected the lateral confinement of concrete adjacent to plastic hinges. Transverse reinforcement with a yield strength exceeding 600 MPa, however, increased the neutral axis depth of normal-strength concrete columns at peak strength, resulting in reductions in ductility and energy dissipation capacity.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.953-958
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• 2001

A retrofit method “Steel Ring Confinement Retrofit” was proposed and discussed on the material and member characteristics through experiments. Steel Ring Confinement Retrofit consist of confining steel ring and expansive concrete. The steel ring is set on the footing, surrounding the base of the pier. By placing expansive concrete between the pier and steel ring, chemical prestress is introduced in the members. Chemical prestressed ring concrete enlarge the pier section and enhance both the strength and ductility of the pier. It was confirmed that Various Ring Confinement Retrofit improved the strength of the pier up to 30% ~ 100% with experiments.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1203-1205
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• 2007

Confinement of charge carrier and exciton is the essential factor for enhancing the efficiency and stability of the electrophosphorescent devices. The interplay between the properties of emitters and other adjacent layers are studied based on the physical interpretation with difference of energy level, charge carrier mobility, and corresponding charge-trapping behavior.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.617-620
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• 2003

This paper presents the confinement effect of transverse reinforcement and cross-tie in hollow rectangular sectional columns. 20 analytical models with different amounts of transverse reinforcement and cross-tie in a plastic hinge region were analyzed by 3D nonlinear FEM. The analytical results show that the higher ductility can be achieved by the resonable combination of transverse re-bar and cross-tie providing sufficient lateral confinement.