• Steel and Composite Structures
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• v.48 no.4
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• pp.461-474
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• 2023

Concrete-filled steel tubes are among the most efficient compressive structural members because the strength of the concrete is enhanced given that the surrounding steel tube confines the concrete laterally and the steel tube is restrained with regard to inward deformation due to the concrete existing inside. Accurate estimations of the ultimate compressive strength of CFT are important for efficient designs of CFT members. In this study, an analytical procedure that directly formulates the interaction between the concrete and steel tube by considering the nonlinear Poisson effect and stress-strain curve of the concrete including the confinement effect is proposed. The failure stress of concrete and von-Mises failure yield criterion of steel were used to consider multi-dimensional stresses. To verify the prediction capabilities of the proposed analytical procedure, 99 circular CFT experimental data instances from other studies were used for a comparison with AISC, Eurocode 4, and other researchers' predictions. From the comparison, it was revealed that the proposed procedure more accurately predicted the ultimate compressive strength of a circular CFT regardless of the range of the design variables, in this case the concrete compressive strength, yield strength of the steel tube and diameter relative to the thickness ratio of the tube.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.1
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• pp.109-116
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• 2012

This paper presents a study on the nonlinear behavior of an innovative bridge girder made from concrete-filled and tied tubular steel arch (CFTA) under static loading. Manufacturing of the CFTA girder may have defects which may highly affect the symmetry and performance of the structure. A simple method is proposed by using stiffness extracted from static test data to detect manufacturing defects of the CFTA girder. A three-dimensional finite element model was used in the numerical analysis in order to verify the method. The proposed method was experimentally validated through static tests of the CFTA girder. The application of the proposed method showed that it is effective in identifying invisible manufacturing defects of the CFTA girder, especially for mass production of a standard type in the factory.

• Steel and Composite Structures
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• v.50 no.2
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• pp.217-235
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• 2024

Concrete-filled steel tubes (CFSTs) nowadays are widely used as the main parts of momentous structures, and its connection has gained increasing attention as the complexity in configuration and load transfer mechanism. This paper proposes a novel CFST pier-to-footing incorporating tube-confined RC encasement. Such an innovative approach offers several benefits, including expedited on-site assembly, effective confinement, and collision resistance and corrosion resistance. The seismic behavior of such CFST pier-to-footing connection was studied by testing eight specimens under quasi-static cyclic lateral load. In the experimental research, the influences on the seismic behavior and the order of plastic hinge formation were discussed in detail by changing the footing height, axial compression ratio, number and length of anchored bars, and type of confining tube. All the specimens showed sufficient ductility and energy dissipation, without significant strength degradation. There is no obvious failure in the confined footing, while local buckling can be found in the critical section of the pier. It suggests that the footing provides satisfactory strength protection for the connection.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.2
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• pp.104-110
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• 1999

This study was performed to evaluate the properties of permeable polymer concrete with fly ash and CaCO3. The following conclusions are drawn. The static modulusof elasticity is in the range of 1.19 $\times$105 ~1.49$\times$105 kgf/$\textrm{cm}^2$, which is approximately 53 ~56% of that of the normal cement concrete. The oission's number of permeable polymer concrete is in the range of 3.95 ~6.53, which is less than that of the normal cement concrete. The dynamic modulus of elasticity is in the range of 1.29$\times$105 ~1.59$\times$105 kgf/$\textrm{cm}^2$, which is approximately less compared to that of the normal cement of the static modulus . Fly ash 50% and CaCO3 50% filled permeable polymer concrete has showed higher dynamic modulus. The water permeability is in therange of 3.971 ~4.393$\ell$ /$\textrm{cm}^2$/h, and it is largely dependent upon the mix design. These concrete can be used to the structures which need water permeability.

• International Journal of High-Rise Buildings
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• v.2 no.1
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• pp.39-48
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• 2013

The fire resistance performance of generic CFT columns has been verified through various tests and analyses and the columns are widely used for fire resistance designs abroad. In this study, 3 groups of specimens (Non-fire protection, reinforcement with steel fiber and fire resistance paint) are suggested in order to evaluate the fire resistance performance of interior anchor type concrete-filled steel tubular columns having efficient cross-sections through loaded heating tests. Axial deformation-time relationship and in-plane temperatures are compared to evaluate the fire resistance performance of the specimens associated with variables. Suggested from the fact that the interior anchors exposed to fire exert influence on fire resistance performance due to thermal expansion, the reinforcements using steel fiber and fire resistance paint are verified to mitigate contraction and improve fire resistance performance. The result obtained from the tests of interior anchor type concrete-filled tubular columns is expected to be used for effective fire resistance design in association with previously conducted studies.

• Steel and Composite Structures
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• v.6 no.4
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• pp.303-317
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• 2006

The connection with combined cross diaphragm is developed for the connection of square CFT column and steel beam and proposed to be used for the frame with asymmetric span length. The structural characteristics of this connection lie in the penetration of the beam flange in the direction of major axis through the column for the smooth flow of stress. The purpose of this study is to analyze the dynamic behavior and stress flow of suggested connection and to evaluate the resistance to shock of connection. Four T-type CFT column-to-beam specimens; two with combined cross diaphragm and the others with interior and through diaphragms, the existing connection types, were made for cyclic load test guided by the load program of ANSI/AISC SSPEC 2002. The results show that the proposed connection is more efficient than existing ones in terms of strength, stress flow and energy absorption and satisfies the seismic performance required in the region of weak/moderate earthquakes.

• Steel and Composite Structures
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• v.32 no.4
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• pp.521-536
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• 2019

The mechanical response of concrete-filled steel tubular (CFST) columns subjected to pure compression or uniaxial bending was studied in depth over the last decades. However, the available research results on CFST columns under biaxial bending are still scarce and the lack of experimental tests for this loading situation is evident. At the same time, the design provisions in Eurocode 4 Part 1.1 for verifying the stability of CFST columns under biaxial bending make use of a simplistic interaction curve, which needs to be revised. This paper presents the outcome of a numerical investigation on slender CFST columns subjected to biaxial bending. Eccentricities differing in minor and major axis, as well as varying end moment ratios are considered in the numerical model. A parametric study is conducted for assessing the current design guidelines of EN1994-1-1. Different aspect ratios, member slenderness, reinforcement ratios and load eccentricities are studied, covering both constant and variable bending moment distribution. The numerical results are subsequently compared to the design provisions of EN1994-1- 1, showing that the current interaction equation results overly conservative. An alternative interaction equation is developed by the authors, leading to a more accurate yet conservative proposal.

• Advances in Computational Design
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• v.8 no.2
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• pp.147-177
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• 2023

Elliptical concrete-filled steel tubular (CFST) column is widely used in modern structures for both aesthetical appeal and structural performance benefits. The ultimate axial load is a critical factor for designing the elliptical CFST short columns. However, there are complications of geometric and material interactions, which make a difficulty in determining a simple model for predicting the ultimate axial load of elliptical CFST short columns. This study aims to propose an efficient adaptive neuro-fuzzy inference system (ANFIS) model for predicting the ultimate axial load of elliptical CFST short columns. In the proposed method, the ANFIS model is used to establish a relationship between the ultimate axial load and geometric and material properties of elliptical CFST short columns. Accordingly, a total of 188 experimental and simulation datasets of elliptical CFST short columns are used to develop the ANFIS models. The performance of the proposed ANFIS model is compared with that of existing design formulas. The results show that the proposed ANFIS model is more accurate than existing empirical and theoretical formulas. Finally, an explicit formula and a Graphical User Interface (GUI) tool are developed to apply the proposed ANFIS model for practical use.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.458-461
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• 2004

The column for Steel Framed Reinforced Concrete Structure (SFRCS) and the column for Reinforced Concrete Structure (RCS) could be the most common building structure. The increasing of the need for massive space hasaffected the size of building components for supporting the massive structure. However, the changing of components size makes inefficient space of building. Hence. to meet the need for acquiring efficient space comparing the budget and cost the new structure method, Concrete Filled Tube Steel (CFT), was developed. CFT is the structure for which steel tube instead of other materials such as wood for holding concrete is used. The most benefit of this one is to help in reducing the size of the building components and local buckling because of tube steel holding concrete. For this reason, this research will examine the probability of applying CFT on construction sites by using the concrete $(800kg/cm^2)$ especially for CFT through the data from the real size mock-up.

• Steel and Composite Structures
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• v.37 no.1
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• pp.75-90
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• 2020

This paper introduces a new composite joint, which is the composite CFST beam- concrete column joint, and it is more convenient for transportation and erection than conventionally welded joints. The main components of this joint include steel H-beams welded with CFST beams, reinforced concrete columns, and reinforced concrete slabs. The steel H-beams and CFST beams are connected with a concrete slab using shear connectors to ensure composite action between them. An experimental investigation was conducted to evaluate the proposed composite joint performance. A three-dimensional (3D) finite element (FE) model was developed and analyzed for this joint using the ABAQUS/explicit. The FE model accuracy was validated by comparing its results with the relevant test results. Additionally, the parameters that consisted of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab were considered to investigate their influence on the proposed joint performance.