• 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.39 no.2
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• pp.159-170
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• 2021

Concrete filled steel tubes (CFSTs) are extensively used in a variety of structures due to their structural and economic advantages over other types of structures. Considerable research has been conducted with regards to their short-term behaviour, and very limited studies have focused on their long-term behaviour. In this study, a series of tests were carried out on high strength squat (short) CFSTs and concrete cylinders under controlled conditions of temperature and humidity to better understand their time dependent behaviour. A number of parameters were investigated including the influence of steel and concrete bond, confinement, level of sustained load and sizes of specimens. The results revealed that creep strains increased by more than 40% if there was no bonding between steel tube and concrete core. As expected, creep and shrinkage of concrete inside a steel tube were significantly less than those developed in exposed concrete. At the end of a creep period of six months, all the specimens were tested to failure to observe the influence of sustained loads on the ultimate strength. It was found that creep does not have a major effect on the strength of short CFSTs in the specific experimental study conducted here, which was less than 2.5%.

• Steel and Composite Structures
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• v.14 no.5
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• pp.453-472
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• 2013

This paper presents the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened CFT (concrete-filled steel tubes) columns under axial loads. Circular and square specimens were selected to investigate the retrofitting effects of CFRP sheet on CFT columns. Test parameters are cross section of CFT, D/t (B/t) ratios, and the number of CFRP layers. The load and ductility capacities were evaluated for each specimen. Structural behavior comparisons of circular and rectangular section will be represented in the experimental result discussion section. Finally, ultimate load formula of CFRP strengthened CFT will be proposed to calculate the ultimate strength of CFRP strengthened circular CFT. The prediction values are in good agreement with the test results obtained in this study and in the literature.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.210-214
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• 1995

Research on concrete-filled steel columns has been conducted. It is also well known that the load and deformation capacity of concrete-filled steel columns are considerable larger than those of widely used reinforced concrete columns and steel encased concrete columns because the concrete core in the steel is confined laterally by the steel. But, most of these works focused on columns with strength enhancement by the confinement effect, so that no local buckling prevented by the concrete. columns because the concrete core in the steel is confined laterally by the steel. But, most of these works focused on columns with strength enhancement by the confinement effect, so that no local buckling prevented by the concrete. This paper, therefore, presents on the stress-strain relation of a concrete filled rectangular steel tube under axial compression. As the results, the axial load verse average axial strain relationship of concrete-filled rectangular steel columns were very stable. The small B/t ratios in concrete-filled rectangular steel columns aren't affected prevention of local buckling but strength enhancement by confinement effect.

• Steel and Composite Structures
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• v.33 no.6
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• pp.823-836
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• 2019

Spiral welded tubes (SWTs) are fabricated by helically bending a steel plate and welding the resulting abutting edges. The cost-effectiveness of concrete-filled steel tube (CFST) columns can be enhanced by utilising such SWTs rather than the more conventional longitudinal seam welded tubes. Even though the steel-concrete interface bond strength of such concrete-filled spiral-welded steel tubes (CF-SWSTs) is an important consideration in relation to ensuring composite behaviour of such elements, especially at connections, it has not been investigated in detail to date. CF-SWSTs warrant separate consideration of their bond behaviour to CFSTs of other tube types due to the distinct weld seam geometry and fabrication induced surface imperfection patterns of SWTs. To address this research gap, axial push-out tests on forty CF-SWSTs were carried out where the effects of tube material, outside diameter (D), outside diameter to wall thickness (D/t), length of the steel-concrete interface (L) and concrete strength grade (f'_c) were investigated. D, D/t and L/D values in the range 102-305 mm, 51-152.5 and 1.8-5.9 were considered while two nominal concrete grades, 20 MPa and 50 MPa, were used for the tests. The test results showed that the push-out bond strengths of CF-SWSTs of both mild-steel and stainless-steel were either similar to or greater than those of comparable CFSTs of other tube types. The bond strengths obtained experimentally for the tested CF-SWSTs, irrespective of the tube material type, were found to be well predicted by the guidelines contained in AISC-360.

• Steel and Composite Structures
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• v.47 no.5
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• pp.645-661
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• 2023

Concrete-filled steel tubular columns with double inner steel tubes (CFST-DIST) are a novel type of composite members developed from conventional concrete-filled steel tubular (CFST) columns. This paper investigates the structural performance of circular CFST-DIST stub columns using nonlinear finite element (FE) analysis. A numerical model was developed and verified against existing experimental test results. The validated model was then used to compare circular CFST-DIST stub columns' behavior with their concrete-filled double skin steel tubular (CFDST) and CFST counterparts. A parametric study was performed to ascertain the effects of geometric and material properties on the axial performance of CFST-DISTs. The FE results and the available test data were used to assess the accuracy of the European and American design regulations in predicting the axial compressive capacity of circular CFST-DIST stub columns. Finally, a new design model was recommended for estimating the compressive capacity of CFST-DISTs. Results clarified that circular CFST-DIST columns had the advantages of their CFST counterparts but with better ductility and strength-to-weight ratio. Besides, the investigated design codes led to conservative predictions of the compressive capacity of circular CFST-DIST columns.

• Steel and Composite Structures
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• v.36 no.5
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• pp.587-602
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• 2020

In recent years, the composite columns have been widely used in the structures. These columns are mainly used to construct the structures with a large span and high floor height. Concrete filled tubes (CFTs) are a type of composite column, which are popular nowadays due to their numerous benefits. The purpose of this study is to investigate such frames at elevated temperatures. The method used in this research is based on section 2.2 of Eurocode 4. First, for the verification purpose, a comparison was made between the experimental results and the numerical model of the concrete filled tube. Then a composite frame was analyzed under fire temperature with different parameters. The results showed that the failure time decreased with increasing the friction of different models. Moreover, investigation of the concrete moisture content revealed that an increase in the concrete moisture content from 3% to 10% led to extended failure time for different models. For instance, in the second frame model, the failure time has increased up to 8%.

• Steel and Composite Structures
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• v.47 no.5
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• pp.615-631
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• 2023

Steel corrosion induces structural deterioration of concrete-filled steel tubes (CFSTs), and any potential extreme action on a corroded CFST would pose a severe threat. This paper presents a comprehensive investigation on the lateral impact behaviour of CFSTs suffering from localised pitting corrosion damage. A refined finite element analysis model is developed for the simulation of locally corroded CFSTs subjected to lateral impact loads, which takes into account the strain rate effects on concrete and steel materials as well as the random nature of corrosion pits, i.e., the distribution patterns and the geometric characteristics. Full-range nonlinear analysis on the lateral impact behaviour in terms of loading and deforming time-history relations, nonlinear material stresses, composite actions, and energy dissipations are presented for CFSTs with no corrosion, uniform corrosion and pitting corrosion, respectively. Localised pitting corrosion is found to pose a more severe deterioration on the lateral impact behaviour of CFSTs due to the plastic deformation concentration, the weakened confinement and the reduction in energy absorption capacity of the steel tube. An extended parametric study is then carried out to identify the influence of the key parameters on the lateral impact behaviour of CFSTs with localised pitting corrosion. Finally, simplified design methods considering the features of pitting corrosion are proposed to predict the dynamic flexural capacity of locally pitted CFSTs subjected to lateral impact loads, and reasonable accuracy is obtained.

• Computers and Concrete
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• v.11 no.4
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• pp.291-304
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• 2013

By considering the creep characteristics of concrete core under eccentric compression, a creep model of concrete filled steel tubes (CFT) columns under eccentric compressive loads is proposed based on the concrete creep model B3. In this proposed model, a discrete element method is introduced to transform the eccentric loading into axial loading. The validity of the model is verified by comparing the predicting results with the published creep experiments results on CFT specimens under compressive loading, together with the predicting values based on other concrete creep models, such as ACI209, CEB90, GL2000 and elastic continuation and plastic flow theory. By using the proposed model, a parameters study is carried out to analysis the effects of practical design parameters, such as concrete mix (e.g. water to cement ratio, aggregate to cement ratio), steel ratio and eccentricity ratio, on the creep of CFT columns under eccentric compressive loading.

• Steel and Composite Structures
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• v.15 no.1
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• pp.41-55
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• 2013

This paper presents a numerical study of axially loaded concrete-filled steel tubular columns with "T" shaped cross section (CFTTS) based on the ABAQUS standard solver. Two types of columns with "T" shaped cross section, the common concrete-filled steel tubular columns with "T" shaped cross section (CCFTTS) and the double concrete-filled steel tubular columns with "T" shaped cross section (DCFTTS), are discussed. The failure modes, confining effects and load-displacement curves are analyzed. The numerical results indicate that both have the similar failure mode that the steel tubes are only outward buckling on all columns' faces. It is found that DCFTTS columns have higher axial capacities than CCFTTS ones duo to the steel tube of DCFTTS columns can plays more significant confining effect on concrete. A parametric study, including influence of tube thickness, concrete strength and friction coefficient of tube-concrete interface on the axial capacities is also carried out. Simplified formulae were also proposed based on this study.