• Steel and Composite Structures
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• v.32 no.1
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• pp.59-66
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• 2019

Hollow steel-reinforced concrete-filled GFRP tubular member is a new kind of composite members. Firstly set the mold in the GFRP tube (non-bearing component), then set the longitudinal reinforcements with stirrups (steel reinforcement cage) between the GFRP tube and the mold, and filled the concrete between them. Through the axial compression test of the hollow steel-reinforced concrete-filled GFRP tubular member, the working mechanism and failure modes of composite members were obtained. Based on the experiment, when the load reached the ranges of $55-70%P_u$ ($P_u-ultimate$ load), white cracks appeared on the surface of the GFRP tubes of specimens. At that time, the confinement effects of the GFRP tubes on core concrete were obvious. Keep loading, the ranges of white cracks were expanding, and the confinement effects increased proportionally. In addition, the damages of specimens, which were accompanied with great noise, were marked by fiber breaking and resin cracking on the surface of GFRP tubes, also accompanied with concrete crushing. The bearing capacity of the axially compressed components increased with the increase of reinforcement ratio, and decreased with the increase of hollow ratio. When the reinforcement ratio was increased from 0 to 4.30%, the bearing capacity was increased by about 23%. When the diameter of hollow part was decreased from 55mm to 0, the bearing capacity was increased by about 32%.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.3
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• pp.29-36
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• 2008

The TR-CFT(Transversely Reinforced Concrete Filled Steel Tube) column is proposed to control or at least delay the state of local buckling at the critical section by wrapping the CFT columns with a carbon fiber sheet. In this study, an equation to determine the flexural strength of TR-CFT is proposed. The ACI-318 code, in which the contribution of the confining effect in the concrete filled steel tube is not appropriately accounted for, may be conservative. Therefore, flexural strength design equations for CFT columns and TR-CFT columns are proposed based on the concrete strain-stress curve, which contributes to the confining effect. Finally, the predicted results for the CFT and TR-CFT columns are shown to be in good agreement with actual test results.

• Journal of Korean Association for Spatial Structures
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• v.3 no.3 s.9
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• pp.105-110
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• 2003

This paper is presented an experimental studies on bond stress between steel and concrete in concrete filled Rectangular steel tubes. In the actual building frames, vertical dead and live loads on beams are usually transferred to columns by beam-to-column connections. In case when concrete filled steel tubes are used as columns of an actual building frame which has a simple connection, shear forces in the beam ends are not directly transferred to the concrete core but directly to the steel tube. Provided that the bond effect between steel tube and concrete core should not be expected, none of the end shear in the beams would be transferred to the concrete core but only to the steel tube. Therefore, it is important to investigate the bond strength between steel tube and concrete core in the absence of shear connectors.

• Steel and Composite Structures
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• v.20 no.3
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• pp.571-597
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• 2016

A new unified design formula for calculating the composite compressive strength of the axially loaded circular concrete filled double steel tubular (CFDST) short and slender columns is presented in this paper. The formula is obtained from the analytic solution by using the limit equilibrium theory, the cylinder theory and the "Unified theory" under axial compression. Furthermore, the stability factor of CFDST slender columns is derived on the basis of the Perry-Robertson formula. This paper also reports the results of experiments and finite element analysis carried out on concrete filled double steel tubular columns, where the tested specimens include short and slender columns with different steel ratio and yield strength of inner tube; a new constitutive model for the concrete confined by both the outer and inner steel tube is proposed and incorporated in the finite element model developed. The comparisons among the finite element results, experimental results, and theoretical predictions show a good agreement in predicting the behavior and strength of the concrete filled steel tubular (CFST) columns with or without inner steel tubes. An important characteristic of the new formulas is that they provide a unified formulation for both the plain CFST and CFDST columns relating to the compressive strength or the stability bearing capacity and a set of design parameters.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.745-751
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• 2021

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-to-outer width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.

• Steel and Composite Structures
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• v.26 no.6
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• pp.705-717
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• 2018

This paper presents a numerical investigation on the mechanical performance of concrete-filled dual steel tubular columns of circular section subjected to concentric axial load. A three-dimensional numerical model is developed and validated against a series of experimental tests. A good agreement is obtained between the experimental and numerical results, both in the peak load value and in the ascending and descending branches of the load-displacement curves. By means of the numerical model, a parametric study is carried out to investigate the influence of the main parameters that determine the axial capacity of double-tube columns, such as the member slenderness, inner and outer steel tube thicknesses and the concrete grade - of both the outer concrete ring and inner core -, including ultra-high strength concrete. A total number of 163 numerical simulations are carried out, by combining the different parameters. Specific indexes are defined (Strength Index, Concrete-Steel Contribution Ratio, Inner Concrete Contribution Ratio) to help rating the relative mechanical performance of dual steel tubular columns as compared to conventional concrete-filled steel tubular columns, and practical design recommendations are subsequently given.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.511-516
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• 2008

Recently, many researchers are studying a high-strength concrete, composite materials and composite structures to build structures more economic and stable all over the world. For instance, there is CFTA(Concrete Filled and Tied Steel Tubular Arch) girder that applies an arch structure and a pre-stressed structure to CFT(Concrete Filled Steel Tubular) Structure to maximize the efficiency of structure and economic. In this study, linear-elastic behavior analysis of CFTA gider filled with high-strength concrete was performed by using ABAQUS 6.5-1 and also the result was analyzed.

• 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.

• Steel and Composite Structures
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• v.18 no.1
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• pp.213-233
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• 2015

A nonlinear finite element analysis (FEA) model is presented for simulating the behaviour of recycled aggregate concrete-filled steel tube (RACFST) beam-columns subjected to constant axial compressive load and cyclically increasing flexural loading. The FEA model was developed based on ABAQUS software package and a displacement-based approach was used. The proposed engineering stress versus engineering strain relationship of core concrete with the effect of recycled coarse aggregate (RCA) replacement ratio was adopted in the FEA model. The predicted results of the FEA model were compared with the experimental results of several RACFST as well as the corresponding concrete-filled steel tube (CFST) beam-columns under cyclic loading reported in the literature. The comparison results indicated that the proposed FEA model was capable of predicting the load versus deformation relationship, lateral bearing capacity and failure pattern of RACFST beam-columns with an acceptable accuracy. A parametric study was further carried out to investigate the effect of typical parameters on the mechanism of RACFST beam-columns subjected to cyclic loading.

• Steel and Composite Structures
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• v.4 no.3
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• pp.169-188
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• 2004

A mechanics model is developed in this paper for concrete-filled steel CHS (circular hollow section) beam-columns. A unified theory is described where a confinement factor (${\xi}$) is introduced to describe the composite action between the steel tube and the filled concrete. The predicted load versus deformation relationship is in good agreement with test results. The theoretical model was used to investigate the influence of important parameters that determine the ultimate strength of concrete-filled steel CHS beam-columns. The parametric and experimental studies provide information for the development of formulas for the calculation of the ultimate strength of the composite beam-columns. Comparisons are made with predicted beam-columns strengths using the existing codes, such as LRFD-AISC-1999, AIJ-1997, BS5400-1979 and EC4-1994.