• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.523-532
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• 2010

Concrete-filled square steel tube (CFT) columns have inherently high fire resistance and load-bearing capacity. Nevertheless, it is sometimes necessary to improve their fire resistance using external fire protection. This paper presents the experimental results of the temperature distribution of CFT columns with fire protection. A fire load test was carried out by exposing small-scale specimens to heat in an electric furnace that was especially built for testing loaded columns. The temperature distribution of CFT columns under constant axial loads was determined, as were its significant parameters, such as the types of fire protection and thickness, the thickness of the square CFT, and the fire duration times. The results of this study showed the temperature distribution of each specimen of the electric furnace and the temperature distribution properties of concrete and steel. In addition, the axial displacement and local buckling behavior of CFT columns based on temperature changes was observed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.4024-4030
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• 2010

Axial load tests and cyclic load tests for FRP reinforced rectangular CFT columns were carried out The main parameters were width-thickness ratio of a steel tubeand FRP layer numbers for the axial load tests and were concrete strength and FRP layer numbers for cyclic load tests. The maximum strength and ductility capacity were compared between the current CFT columns and the FRP reinforced CFT columns. Finally, the axial design formulas were presented for the FRP reinforced CFT columns.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.471-479
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• 2002

In this paper, 18 square CFT columns filled with high-strength concrete were tested under concentric or eccentric axial loading. Two parameters of the experimental program included the buckling length-section depth ratio ($L_K$/D) and the eccentricity of the appled compressive load (e). In additon, mechanical properties such as the compressive concrete strength and compressive and tensile steel strength were measured and incorporated into the material models for the stress-strain relationships of concrete and steel. This model was used in an elasto-plastic analysis in order to predict the behavior of the slender CFT columns. Observtions of the failure mode during the tests under axial loadig were also presented. The strengths obtained from the analysis. Recommendations for Design, and Constructions of CFT structures were presented, as verified by the experimental results.

• Journal of Korean Society of Steel Construction
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• v.12 no.1 s.44
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• pp.9-16
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• 2000

The model of load-strain relations for CFT stub columns subjected to centrally compressive axial load is shown in this paper. The modified model of concrete and steel is obtained by using the experimental data and the formulas of that is based on the foreign researcher's result. The purpose of this paper is to suggest the basic data for evaluating the behavior of CFT stub columns to be variable to the strength of concrete and steel.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.311-320
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• 2009

This paper presents the experimental results of an experiment on the current rectangular CFT columns and rectangular CFT columns additionally confined by carbon fiber sheets(CFS) under axial loading. The main experimental parameters were the layer numbers of the CFS and the depth-to-thickness ratio. Nine specimens were prepared according to the experimental parameter plans, and axial compression tests were conducted. From the tests, the failure procedure, the load-axial deformation curve, the maximum axial strength, and the deformation capacity of the CFT columns and the confined CFT columns were compared. Finally, it was seen that the maximum axial strengths of the CFT increased more significantly than that of the current CFT columns because of delayed local buckling.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.289-298
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• 2015

The steel tube of Concrete-Filled Tube(CFT) confines the concrete and the concrete restrains the buckling of the tube, The objective of this study is to investigate the influences of the opening shape of the through diaphragm in case of the rectangular CFT column-to-beam connection through the structural experiment. The experiment results are compared with analysis results obtained by using the FEM program. These results are shown that strength of the rectangular CFT column-to-beam connection have similar structural performance regardless of the opening shape if opening areas of the through diaphragm are same. Also in case the connection area/shape of the through diaphragm and the flange of H-beam are similar, it was ascertained that the bending stress occurred at the beam can be transferred to the column through the diaphragm.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.95-102
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• 2011

The CFT columns used in thin-walled steel tubes can be more economical, because it was expected the increase of strength by restriction for the local buckling of steel tubes. The purpose of this paper is to review feasibility of existing design formula and verify the applicability limit of width-to-thickness ratio for increasing the strength of rectangular CFT columns. As the main parameters of experiments, width-to-thickness ratios of steel tube, height of rectangular concrete columns, and concrete filled or not. The strength of concrete are selected to 90MPa. From the test results, the confinement effect of steel tube on the compressive strength of infilled concrete is remarkably appeared in the thin-walled rectangular steel tube columns infilled wih high strength concrete. By the non-linear analysis, the axial strength from experiment result was given higher than analysis result for all CFT stub columns.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.443-450
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• 2012

In this study, This study investigates the axial load behavior of concrete-filled steel columns using seismic rectangular steel tube with the width-to-thickness and slenderness ratio. Due to cold-roll forming and cold-press forming of steel tube, the flat part and the corner part of the rectangular steel tubes are changed in the material properties compared to SN-steel plate. It was showed the tendency to increase yield strength, tensile strength and upper limit of yield ratio This phenomenon affects the nonlinear behavior after local buckling of the steel tube. Therefore, the coupon test was performed by the processing of rectangular steel tube, in order to assess forming performance. And a total of 6 CFT-columns were tested under monotonic loading condition. Main parameters were the width-thickness ratio and the slenderness ratio.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.537-544
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• 2009

The design standards, such as AISC-LRFD (2005) and KBC-2005, specify the maximum width-to-thickness ratio that can be used for computing the strength of the concrete-filled tube (CFT), and do not include any formula for computing the strength when the width-to-thickness ratio is over the limit. This paper proposes a strength equation for CFTs with a large width-to-thickness ratio by acknowledging the fact that the stiffened slender steel platehas substantial postbuckling strength, and that it therefore can be more economical to use it. The equation adopts the concept of effective width,which is very useful for plate analysis. By comparing the strengths of AISC2005, KBC2005, and the proposed method with the results of the experiment, where the width-to-thickness ratio was regarded as the main parameter, the applicability of the proposed method was verified.

• Journal of Korean Society of Steel Construction
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• v.28 no.2
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• pp.75-83
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• 2016

Existing tubes for concrete filled tubular structure are made through welding of four plates irrespective, but the production performance is poor and special welding technique is needed to weld the internal or through diaphragm. Accordingly, We developed a welded built-up square steel tube having a welding lines and a stiffeners at location out of stress concentration. The welded built-up square steel tube occurred a interference with stiffeners at the internal or through diaphragm, therefore researches of a external diaphragm for welded built-up square CFT column connections are needed for the purpose of avoidance of a interfere with stiffeners. In this study we suggest a design formulation for external diaphragm of the welded built-up square CFT external diaphragm connections. Four specimens were manufactured for a experimental test, then we analyzed the behaviors of the specimens.