• Journal of Korean Society of Steel Construction
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• v.24 no.1
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• pp.81-89
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• 2012

The concrete-filled tubular square column is superior to steel frame column in terms of fire resistance because of the thermal storage provided by the concrete. Studies have been conducted on CFT column reinforcement with steel bars or with the use of an internal tube to improve its structural load capacity and fire resistance. In fact, reinforced CFT columns have been increasingly used to deal with high axial force. The functional deterioration of columns due to fire damage needs to be measured precisely. In this study, the temperature distribution inside the columns in case of a fire was evaluated and the degree of deterioration in the load capacity of the concrete and reinforcing members associated with temperature distribution was identified in order to evaluate the overall residual strength of the columns.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.423-433
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• 2012

This paper summarizes full-scale gravity-load test results on CFT column-to-RC flat plate connections reinforced with shearhead. CFT construction has many structural and constructional advantages over conventional steel and RC column construction and is gaining wide acceptance. Meanwhile the use of RC flat plate system in the basement and residential floors of tall buildings is often mandatory to reduce story height and enable rapid construction in domestic practice. Combining CFT column and flat plate floor is expected to result in further rapid construction. However, the issues related to connecting CFT column to RC flat plate have not been fully addressed yet. Several promising connecting schemes by using steel shearhead were proposed and tested in this study. Test results showed that the proposed connection can exhibit the punching shear strength higher than RC flat plate counterparts. An empirical formula that can reasonably predicts the punching shear strength of the proposed connection was also proposed.

• Journal of Korean Association for Spatial Structures
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• v.6 no.3 s.21
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• pp.69-76
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• 2006

Concrete Filled Steel Tube (CFT) system is advantageous because it increases the load-carrying capacity without increasing the size of column. However CFT system has many benefits, it is not applied to field generally because of its heavyweight and difficulty of concrete filling method. As a solution to these problems, we proposed concrete filled steel tube column with hollow made by factory-manufactured PC method. The hollow concrete filled steel tube system is expected to obtain the high strength and high capacity of deformation despite it is a lightweight. This study deals with mechanical properties, strength and deformation, of hollow concrete filled steel tube subjected to axial load. 9 specimens were tested to examine mechanical properties closely, and the following results were obtained: All specimens basically showed higher initial rigidity and maximum strength with increased concrete filling rate. And most specimens showed almost linear behavior until around 80% of maximum strength regardless of filling rate, it is estimated that the elastic range is up to a half of the maximum strength which is the yield strength level.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.112-118
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• 2015

These days, there are lots of skyscrapers being constructed in downtown areas. However, it requires columns which have a way heavier load. and far more extensive cross sections of column as well. Therefore, it is hard to lay the foundation in downtown areas. This being the case, composite columns such as CFT column are primarily being used. However, CFT column is occurred of difficult beam-column connection development and lower performance since CFT column is closed cross-section. Especially, the result of the study concerning development of connection details with CFT column and exterior diaphragms are very low in current state. In this study, through developing CFT column-H shape steel beam applicating Y shape plate, set width and depth of Y shape plate which affect structural performance of connection details applicating Y shape plate as main variables, and evaluate structural performance through experiments. And also, design Y shape plate used at experiments as setting allowable stress for tension suggested at design criteria lower than axial force of tension side flange connected Y shape plate, through shape of destruction, verify the structural safety and performance of Y shape plate.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.461-470
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• 2009

A column resisting axial load and seismic load is one of the main members in a structural system. The heated column by event of a fire can lose its strength and it may damage its structural system or cause the collapse of the entire structural system. In this study, the fire resistance capacity of internally confined hollow concrete filled tube (ICH CFT) column was investigated. In an ICH CFT column, the yield strength of the external tube is important as a concrete filled tube (CFT) column because the external tube confines the filled concrete and the strength of the column depends on the confined effect. A study was performed by finite element analyses considering the confined effect and material nonlinearity as the temperature changes by the fire. The hollow ratio, the thickness of the external tube, and the strength of concrete were selected as the parameters for the analyses. The analyses were performed by using a commercial FEA program (ABAQUS) and nonlinear concrete model program. The analysis results showed that the hollow ratio and the strength of concrete mainly affect the fire resisting capacity of an ICH CFT column.

• Journal of the Korean Society for Advanced Composite Structures
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• v.2 no.1
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• pp.23-29
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• 2011

This study investigates the axial behavior of CFRP strengthened circular CFT columns and proposes the design formula of CFRP strengthened circular CFT columns. 10 specimens were prepared and axial loading test were conducted to investigate the retrofitting effects of CFRP composites on CFT columns. The main parameters are the number of FRP sheets and D/t ratio. Test results showed that the CFRP retrofitting enhanced the load bearing capacity of the circular CFT columns. Finally, A ACI 440 code applied ultimate axial strength formula is proposed to predict the ultimate strength of CFRP strengthened circular CFT columns. The proposed formula are good agreement with the test results.

• 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 the Earthquake Engineering Society of Korea
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• v.13 no.5
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• pp.61-71
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• 2009

This paper presents the results of an experiment comparing the current circular CFT columns and circular CFT columns that were additionally confined by carbon fiber sheets (CFS) under axial loading. The main experimental parameters are the numbers of CFS layers and the diameter-to-thickness ratio. 10 specimens were prepared according to the experimental parameter plans, and axial compression tests were conducted. From the tests, the failure procedure, load-axial deformation curve, maximum axial strength, and deformation capacity of the CFT columns and confined CFT columns were compared. The test results showed that the maximum axial strengths of CFT columns additionally confined by CFS are increased higher than those of the current CFT columns, and that local buckling can be delayed due to the confinement effect of CFS.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.655-663
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• 2008

In this research, the fire resistance of Concrete-Filled Circular Steel Tube Columns (CFT) was evaluated by numerical analysis. As the materials of CFT columns, the steel of SPSR 400 grade and the concrete of 27.5MPa, 37.8MPa strengths were used. Significant parameters,such as concrete strength, axial load, and cross-sectional dimensions were determined. To verify the accuracy of the numerical analysis,the analysis results were compared with the former experiment results. The effect of the fire resistance time, axial load ratio, cross-sectional dimensions and concrete strength was evaluated by comparison with the fire resistance of the square CFT columns. This research showed that the structural behavior and fire resistance from the findings of numerical parametric studies showed a similarity to that of the experimental results. Therefore, this numerical analysis is reasonable in estimating the fire resistance of the circular CFT column.

• Journal of Korean Society of Steel Construction
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• v.18 no.4
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• pp.491-502
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• 2006

This paper summarizes full-scale test results on CFT column-to- flat plate connections has gained wide acceptance subjected to gravity loading. CFT construction has gained wide acceptance in a relatively short time in domestic building construction practice due to its various structural and construction advantages. However, efficient details for CFT column to flat plate connections have not been proposed yet. Based on the strategies that maximize economical field construction, several connecting schemes were proposed and tested. Test results showed strength and connection stiffness exceeding those of R/C flat p late counterparts. A semi-analytical procedure is presented to model the behavior of CFT column-to-flat plate connections. The five parameters to model elastic to post-punching catenary action range are calibrated based on the limited test data of t to progressive collapse prevention design is also illustrated.