• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.442-445
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• 1997

With increasing use of high strength concrete tied columns in structural engineering, it becomes necessary to examine the applicability of related sections of current design codes. High strength concrete has an advantage of strength capacity and stiffness especially for column elements. This paper presents an experimental study of high strength concrete tied columns subjected to eccentric loading. The main variables included in this test were concrete compressive strength, steel amount, eccentricity, and slenderness ratio. The concrete compressive strength varied from 34.9Mpa(356kg/$\textrm{cm}^2$ ) to 93.2Mpa(951kg/$\textrm{cm}^2$ ) and the longitudinal steel ratios were between 1.1% and 5.5%. The eccentricity was selected for the different failure modes, i.e., compression control, balanced point, and tension control. The slenderness ratio varied from 19 to 61. The column specimens with same slenderness ratio but with different concrete compressive strength were constructed and tested. The purpose of this paper is to show failure modes of high strength reinforced concrete columns.

• Steel and Composite Structures
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• v.10 no.6
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• pp.501-516
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• 2010

This paper is aiming to study the performances of reinforced high-strength concrete (HSC) short columns confined with aramid fibre-reinforced polymer (AFRP) sheets. An experimental program, which involved 45 confined columns and nine unconfined columns, was carried out in this study. All the columns were circular in cross section and tested under axial compressive load. The considered parameters included the concrete strength, amount of AFRP layers, and ratio of hoop reinforcements. Based on the experimental results, a prediction model for the axial stress-strain curves of the confined columns was proposed. It was observed from the experiment that there was a great increment in the compressive strength of the columns when the amount of AFRP layers increases, similar as the ultimate strain. However, these increments were reduced as the concrete strength increasing. Comparisons with other existing prediction models present that the proposed model can provide more accurate predictions.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.91-94
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• 2005

Experimental research was conducted to investigate the behavior of RC circular columns confined by high-strength ties. Large scale columns with concrete strength 34.1 and 65.3 MPa were tested under monotonically increasing concentric compression. The test parameters included the volumetric ratio, tie arrangement, tie yield strength, and concrete compressive strength. The results indicate that high-strength concrete columns can be confined to achieve inelastic deformations usually predicted for normal-strength concrete columns. This can be done by providing increasing volumetric ratio and tie yield strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.487-492
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• 2003

High-strength concrete(HSC) is a new construction material with enormous potential. Structures using high-strength concrete are to be coming more and more popular. But high-strength reinforced concrete columns show brittle behavior. It, therefore, is necessary to improve the ductility of HSC members. The purpose of this study is to investigate the ductility and strength of high-strength columns with variable lateral confinement under concentric axial load. Five HSC columns with compressive strength 68㎫ are designed with variable lateral confinements such as carbon fiber sheet(CFS), glass fiber sheet(GFS), and metal lath. Test results indicate that specimen confined by CFS show 11% higher maximum strength, 2.74 times ductility than A specimen using hoop. On comparing with the specimen A and B confined metal lath instead of hoop, strength decrease of 3%, and ductility increase of 1.21 times were observed.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.259-262
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• 2005

Numerous studies showed that safety and serviceability of many concrete infrastructures and buildings built in 1970's have capacity less than their design capacities and thereby require immediate retrofitting. Currently, these aged concrete structure are being repaired using many repair and strengthening methods developed in the past. Therefore, in this study, a repairing and strengthening method for retrofitting high strength concrete columns that can effectively improve the performance of high strength concrete columns is developed. The square high strength concrete column's cross-sectional shape is modified to octagonal shape by attaching precast members on the surface of the column. Then, the octagonal column surface is wrapped using Carbon Fiber Sheets (CFS). The method allowed the maximum usage of confinement effect of externally wrapped CFS, which resulted in improved strength and ductility of repaired high strength concrete columns.

• Advances in concrete construction
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• v.8 no.4
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• pp.257-267
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• 2019

This paper presents the results of cyclic loading tests on new high-strength concrete (HC) short columns. The seismic performance and deformation capacity of three reinforced high-strength concrete filled Polyvinyl Chloride tube (RHC-PVCT) short columns and one reinforced high-strength concrete (RHC), under pseudo-static tests (PSTs) with vertical axial force was evaluated. The main design parameters of the columns in the tests were the axial compression ratio, confinement type, concrete strength, height-diameter ratio of PVCT. The failure modes, hysteretic curves, skeleton curves of short columns were presented and analyzed. Placing PVCT in the RHC column could be remarkably improved the ultimate strength and energy dissipation of columns. However, no fiber element models have been formulated for computing the seismic responses of RHC-PVCT columns with PVT tubes filled with high-strength concrete. Nonlinear finite element method (FEM) was conducted to predict seismic behaviors. Finite element models were verified through a comparison of FEM results with experimental results. A parametric study was then performed using validated FEM models to investigate the effect of several parameters on the mechanical properties of RHC-PVCT short columns. The parameters study indicated that the concrete strength and the ratio of diameter to height affected the seismic performance of RHC-PVCT short column significantly.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.103-109
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• 2006

Spalling is defined as damages to concrete exposed to high temperature during fire, causing cracks and localized bursting of small pieces of concrete. As the concrete strength increases, the degree of damage caused by spalling becomes more serious due to impaired permeability. It is reported that polypropylene(PP) fiber has an important role in protecting concrete from spalling, and the optimum dosage of PP fiber is 0.2%. However, this study was conducted on non-reinforced concrete specimens. The high-temperature behavior of high-strength reinforced concrete columns with various concrete strength and various quantity of PP fibers is investigated in this study. The results revealed that the ratio of unstressed residual strength of columns increased as the concrete strength increased and as the quantity of PP fiber increased from 0% to 0.2%. However, the effect of PP fiber quantity on residual strength of column was barely above 0.2%.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.747-758
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• 2003

The moment-curvature envelope describes the changes in the flexural capacity with deformation during a nonlinear analysis. Therefore, the moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted providing the stress-strain relation for the concrete and steel are known. The moments and curvatures associated with increasing flexural deformations of the column may be computed for various column axial loads by incrementing the curvature and satisfying the requirements of strain compatibility and equilibrium of forces. Clearly it is important to have accurate information concerning the complete stress-strain curve of confined high-strength concrete in order to conduct reliable moment-curvature analysis that assesses the ductility available from high-strength concrete columns. However, it is not easy to explicitly characterize the mechanical behavior of confined high-strength concrete because of various parameter values, such as the confinement type of rectilinear ties, the compressive strength of concrete, the volumetric ratic and strength of rectangular ties. So a stress-strain model is developed which can simulate complete inelastic moment-curvature relations of high-strength concrete columns.

• Steel and Composite Structures
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• v.48 no.1
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• pp.89-102
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• 2023

This study investigates the eccentric performance of concrete-filled steel tubular (CFST) stub columns strengthened with steel tube and sandwiched concrete (STSC) jackets. It was revealed that the STSC jacketing method effectively weakened the cracking of concrete in CFST columns on the convex side and the crash on the concave side. Substantial increases in the eccentric bearing capacities were demonstrated after strengthening. A numerical study was further conducted. The decrease in diameter-to-thickness ratio and increase in strength of outer tube contributed to increase in peak load of all components, whereas the increase in sandwiched concrete strength resulted in load increase on itself and had negligible effects on other components. The parametric study showed the effect of inner concrete strength on columns' bearing capacity was magnified after strengthening, whereas that of inner tube thickness was reduced. Within the parameters investigated, high-strength concrete and high-strength steel can be applied without the concern of early abrupt failure of inner low-strength concrete or steel tube.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.923-928
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• 2002

Experimental and analytical study were conducted to develop the confined model of reinforced high strength concrete tied columns subjected to monotonically increasing concentric axial compression. Twenty-one large-scale columns(260$\times$260$\times$1200mm) used high strength concrete of 50 and 85MPa were fabricated to simulate an actual structural members size. Test results indicated that gains of strength and ductility of high strength concrete columns could be increased, if efficient arrangements and volumetric ratios of transverse reinforcements were provided. The proposed model satisfactorily predicted the experimental stress-strain curves for high strength concrete up to 100MPa.