• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.210-214
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• 1995

Research on concrete-filled steel columns has been conducted. It is also well known that the load and deformation capacity of concrete-filled steel columns are considerable larger than those of widely used reinforced concrete columns and steel encased concrete columns because the concrete core in the steel is confined laterally by the steel. But, most of these works focused on columns with strength enhancement by the confinement effect, so that no local buckling prevented by the concrete. columns because the concrete core in the steel is confined laterally by the steel. But, most of these works focused on columns with strength enhancement by the confinement effect, so that no local buckling prevented by the concrete. This paper, therefore, presents on the stress-strain relation of a concrete filled rectangular steel tube under axial compression. As the results, the axial load verse average axial strain relationship of concrete-filled rectangular steel columns were very stable. The small B/t ratios in concrete-filled rectangular steel columns aren't affected prevention of local buckling but strength enhancement by confinement effect.

• Steel and Composite Structures
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• v.19 no.6
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• pp.1511-1529
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• 2015

This article provides an analysis of the complex character of stress distribution in concrete in stub columns consisting of two HE160A steel sections held together with batten plates and filled with concrete. In such columns, evaluating the effect of concrete confinement and determining the extent of this confinement constitute a substantially complex problem. The issue was considered in close correspondence to rectangular cross section tubular elements filled with concrete, concrete-encased columns, as well as to steel-concrete columns in which reinforcement bars are connected with shackles. In the analysis of concrete confinement in two-chord columns, elements of computational methods developed for different types of composite cross sections were adopted. The achieved analytical results were compared with calculations based on test results.

• Steel and Composite Structures
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• v.13 no.6
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• pp.587-606
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• 2012

Concrete-filled-steel-tubular (CFST) columns have been well proven to improve effectively the strength, stiffness and ductility of concrete members. However, the central part of concrete in CFST columns is not fully utilised under uni-axial compression, bending and torsion. It has small contribution to both flexural and torsion strength, while it can be replaced effectively by steel with smaller area to give similar load-carrying capacity. Also, the confining pressure in CFST columns builds up slowly because the initial elastic dilation of concrete is small before micro-crackings of concrete are developed. From these observations, it is convinced that the central concrete can be effectively replaced by another hollow steel tube with smaller area to form double-skinned concrete-filled-steel-tubular (CFDST) columns. In this study, a series of uni-axial compression tests were carried out on CFDST and CFST columns with and without external steel rings. From the test results, it was observed that on average that the stiffness and elastic strength of CFDST columns are about 25.8% and 33.4% respectively larger than CFST columns with similar equivalent area. The averaged axial load-carrying capacity of CFDST columns is 7.8% higher than CFST columns. Lastly, a theoretical model that takes into account the confining effects of steel tube and external rings for predicting the uni-axial load-carrying capacity of CFDST columns is developed.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.401-407
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• 1997

Objectives of this study is to investigate experimentally the behaviors of high strength concrete columns made with Belite cement by comparing with those of normal concrete columns. For the Belite high strength concrete columns and normal concrete columns having different core sizes, lateral reinforcement ratios and spacings, the experiment are performed and the behaviors of the columns like the confining effect are analyzed and discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.585-590
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• 2001

The structural characteristics of concrete-filled glass fiber reinforced polymer tubes were studied. The concept of concrete-filled composite columns was introduced to overcome the corrosion problems associated with steel and concrete piles under severe environments. Other benefits of composite columns include low maintenance cost, high earthquake resistance, and long expected endurance period. Several experiments were conducted; 1) compression test for short-length composite columns, 2) uniaxial compression tests on a total of 7 columns with various slenderness ratios. Short-length columns give higher strength and ductility revealing high confinement action in concrete. Failure strengths, failure patterns, confinement effects, and stress-strains relations were analyzed for slender columns. Current study will show the feasibility of concrete-filled glass fiber reinforced polymer composite columns in corrosive environments, and will provide an experimental database for columns that are externally reinforced by multidirectional fibers.

• Steel and Composite Structures
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• v.4 no.1
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• pp.1-8
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• 2004

Tests on steel tubular columns of square, rectangular and circular section filled with normal and lightweight aggregate concrete were conducted to investigate the failure modes of such composite columns. Thirty-six full scale columns filled with lightweight and normal weight aggregate concrete, eighteen specimens for each, were tested under axial loads. Nine hollow steel sections of similar specimens were also tested and results were compared to those of filled sections. The test results were illustrated by a number of load-deflection and axial deformation curves. The results showed that both types of filled columns failed due to overall buckling, while hollow steel columns failed due to bulging at their ends (local buckling). According to the above-mentioned results, and due to low specific gravity and thermal conductivity of the lightweight concrete the further interest should be concentrated in replacing the normal concrete by the lightweight aggregate concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.399-404
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• 2000

This paper are the mechanical characteristics of eccentrically loaded normal strength and high strength reinforced concrete columns based on the test results. The columns are $120\times120$mmat the mid-section and are haunched at the ends to apply the eccentric loading and prevent premature failure. Variables are concrete strengths(361, 672, 974 kgf/$\textrm{cm}^2$), $\textrm{cm}^2$longitudinal reinforcement ratios (1.98, 3.54, 1 5.53%), spacing of lateral reinforcement (30, 60, 120mm), and eccentricities (24, 40mm). As a results, the main conclusions obtained from the comparison and analysis for the strength tendency, deformation and ductility of high strength reinforced concrete columns with variables are as follows; As the concrete compressive strength concrete and lateral reinforcement increases, the ductility index of high strength reinforced concrete columns decrease, but it increase with the increase of eccentricity and longitudinal reinforcement ratio. The confinement ratio must be greater than 20 percent in order for the level of ductility between high strength reinforced concrete columns and normal strength reinforced concrete columns to be almost equal.

• Steel and Composite Structures
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• v.22 no.1
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• pp.63-77
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• 2016

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

• Computers and Concrete
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• v.8 no.5
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• pp.597-616
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• 2011

With respect to rehabilitation, strengthening and retrofitting of existing and deteriorated columns in buildings and bridges, CFRP sheets have been found effective in enhancing the performance of existing RC columns by wrapping and bonding CFRP sheets externally around the concrete. Concrete columns and piers that are confined by both lateral steel reinforcement and CFRP are sometimes referred to as "hybrid" concrete columns. With the availability of experimental data on concrete columns confined by steel reinforcement and/or CFRP, the study presents modeling using artificial neural networks (ANNs) to predict the compressive strength of hybrid circular RC columns. The prediction of the ultimate confined compressive strength of RC columns is very important especially when this value is used in estimating the capacity of structures. The present ANN model used as parameters for the confining materials the lateral steel ratio (${\rho}_s$) and the FRP volumetric ratio (${\rho}_{FRP}$). The model gave good predictions for three types of confined columns: (a) columns confined with steel reinforcement only, (b) CFRP confined columns, and (c) hybrid columns confined by both steel and CFRP. The model may be used for predicting the compressive strength of existing circular RC columns confined with steel only that will be strengthened or retrofitted using CFRP.

• Steel and Composite Structures
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• v.15 no.1
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• pp.41-55
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• 2013

This paper presents a numerical study of axially loaded concrete-filled steel tubular columns with "T" shaped cross section (CFTTS) based on the ABAQUS standard solver. Two types of columns with "T" shaped cross section, the common concrete-filled steel tubular columns with "T" shaped cross section (CCFTTS) and the double concrete-filled steel tubular columns with "T" shaped cross section (DCFTTS), are discussed. The failure modes, confining effects and load-displacement curves are analyzed. The numerical results indicate that both have the similar failure mode that the steel tubes are only outward buckling on all columns' faces. It is found that DCFTTS columns have higher axial capacities than CCFTTS ones duo to the steel tube of DCFTTS columns can plays more significant confining effect on concrete. A parametric study, including influence of tube thickness, concrete strength and friction coefficient of tube-concrete interface on the axial capacities is also carried out. Simplified formulae were also proposed based on this study.