• Steel and Composite Structures
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• v.10 no.5
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• pp.415-428
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• 2010

Proper material constitutive models for concrete-filled tube (CFT) columns of circular cross section and subjected to pure bending moment are proposed. These material models are implemented into the Abaqus finite element program and verified against experimental data. It has been shown that the steel tube does not provide good confining effect to the concrete core when the CFT columns is subjected to pure bending moment. When the diameter-to-thickness ratio of the CFT columns is small, the behavior of the CFT column is the same as the steel tube without a concrete core.

• Journal of Korean Society of Steel Construction
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• v.27 no.4
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• pp.399-410
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• 2015

Concrete filled steel tube(CFT) has outstanding deformation capacity and strength in comparison with reinforced concrete or steel tube. CFT drilled shaft, which is developed large shear force due to seismic load and soil liquefaction, is designed as large diameter. However, shear design equations of the current standards do not consider bond stress of CFT and it results in extremely conservative design. Currently, previous studies for improving shear equations scarcely exist and are impossible applied to large CFT drilled shafts since these studies focus on only small scale experimental research. In this study, eventually to propose improving shear equation of large diameter CFT, it is preliminary research to compare and investigate the previous studies and current standards.

• Steel and Composite Structures
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• v.26 no.4
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• pp.501-511
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• 2018

Concrete-filled steel tubular (CFT) columns are commonly used in engineering structures and always subjected to torsion in practice. This paper is thus devoted to investigate the mechanical behavior of circular CFT columns under pure torsion.3D finite element models based on reasonable material constitutive relation were established for analyzing the load-strain ($T-{\gamma}$) curves of circular CFT columns under pure torsion. The numerical simulation indicated that local bulking of the steel tube in CFT columns was prevented and the shear strength and ductility of the core concrete were significantly improved due to the confinement effect between the steel tube and the core concrete. Based on the results, formulas to predict the torsional ultimate bearing capacity of circular CFT columns were proposed with satisfactory correspondence with experimental results. Besides, formulas of composite shear stiffness and the overall process of the $T-{\gamma}$ relation of circular CFT columns under pure torsion were proposed.

• Journal of The Korean Digital Architecture Interior Association
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• v.11 no.2
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• pp.31-39
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• 2011

Concrete-filled steel tube(CFT) columns have become popular for building construction due to not only composite effect of steel tube and infilled concrete, but also more economical. The purpose of this paper is to propose the applicable boundary formula of width-to-thickness ratio for rectangular steel tube as using CFT column. A parametric study was performed taking width-to-thickness ratio of rectangular steel tube and compressive strength of concrete as the main parameter. The strength of concrete are selected to 30, 60, 90MPa. The non-linear analysis was adopted in order to take into account the effect of concrete strength. Finally, from the test and analysis results, the effect of increasing strength according to concrete strength and width-to-thickness of steel tube and plastic behavior of specimens were verified distinctly.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.1023-1028
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• 2003

The structure of Tower Palace III Sports Center building was designed as concrete Filled Steel Tube(CFT) Column and the filled-in concrete was designed as high compressive strength of 500kgf/$m_2$. The self compacting concrete(SCC, non-vibrating concrete) with 65$\pm$5cm flow must be applied to this case for filling the CFT by injecting the concrete from the column bottom. Laboratory tests and pilot productions of batcher plant were performed for optimum mix design and the full scale Mock-Up test was performed to check the appicability of the construction method. As a result, we observed that good quality SCC and the pressure change of concrete pump normally used domestically. Based on these results, we have constructed 20-40m height CFT columns successfully.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.451-458
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• 2012

The concrete-filled steel tube (CFT) that has an excellent performance can be more economically used when the steel tube has a large width-to-thickness ratio. However, the international provisions such as American Institute of Steel Construction (AISC) limit the use of a slender plate in CFT members, resulting in a less optimal use of CFT. This study verifies the post buckling strength of CFT columns through the experimental program for Hollow Steel Sections (HSS) and CFTs with a with-to-thickness ratio ranged 60 to 100. The study also proposes a relaxed limitations of with-to-thickness ratio compared to the one specified in the current standards.

• Steel and Composite Structures
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• v.22 no.5
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• pp.1141-1162
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• 2016

Concrete-filled double skin steel tube (CFDST) beam-columns are widely used in industrial plants, subways, high-rise buildings and arch bridges. The CFDST columns have the same advantages as traditional CFT members. Moreover, they have lighter weight, higher bending stiffness, better cyclic performance, and have higher fire resistance capacities than their CFT counterparts. The scope of this study is to develop finite element models that can predict accepted capacities of double skin concrete-filled tube columns under the combined effect of axial and bending actions. The analysis results were studied to determine the distribution of stresses among the different components and the effect of the concrete core on the outer and inner steel tube. The developed models are first verified against the available experimental data. Accordingly, an extensive parametric study was performed considering different key factors including load eccentricity, slenderness ratio, concrete compressive strength, and steel tube yield strength. The results of the performed parametric study are intended to supplement the experimental research and examine the accuracy of the available design formulas.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.439-454
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• 2011

A nonlinear analysis model for internally confined hollow concrete-filled tube (ICH CFT) columns was suggested and was verified by the test results obtained by the previous researchers. The suggested model considered the confining effect and nonlinearity of concrete. The verified results showed that the suggested model was reasonable and reliable for predicting the behavior of an ICH CFT column. Additionally, a simple parametric study was carried out. The strength of concrete, the hollow ratio of a column, and the thickness of an inner tube were selected as parameters affecting the behavior of an ICH CFT column. The analysis results showed that the concrete strength and the thickness of the inner tube affect the axial strength and moment capacity of the column while the hollow ratio affects only its axial strength.

• Steel and Composite Structures
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• v.11 no.5
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• pp.391-402
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• 2011

It is clear from the former researches on reinforced concrete filled steel tubular (RCFT) structures that RCFT structures have higher strength and deformation capacity than concrete filled steel tubular (CFT) structures. However, in the case of actual applications to large-scaled structures, the thin-walled steel tube must be used from the view point of economic condition. Therefore, in this study, compression tests of RCFT columns which were made by thin-walled steel tube or small load-sharing ratio in cooperation with high strength concrete were carried out, meanwhile corresponding tests of CFT, reinforced concrete (RC), pure concrete and steel tube columns were done to compare with RCFT. By the a series of comparison and analysis, characteristics of RCFT columns were clarified, and following conclusions were drawn: RCFT structures can effectively avoided from brittle failure by the using of reinforcement while CFT structures are damaged due to the brittle failure; with RCFT structures, excellent bearing capacity can be achieved in plastic zone by combining the thin-walled steel tube with high strength concrete and reinforcement. The smaller load-sharing ratio can made the reinforcement play full role; Combination of thin-walled steel tube with high strength concrete and reinforcement is effective way to construct large-scaled structures.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.153-154
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• 2022

When reinforcing an existing building with the Concrete Filled Tube(CFT) structure, it is impossible to form a diaphragm inside with the existing method. Therefore, in this study, a construction method was proposed so that the force could be transmitted using the friction force between the diaphragm and the concrete using a double diaphragm.