• 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.

• Steel and Composite Structures
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• v.13 no.6
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• pp.587-606
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• 2012

Concrete-filled-steel-tubular (CFST) columns have been well proven to improve effectively the strength, stiffness and ductility of concrete members. However, the central part of concrete in CFST columns is not fully utilised under uni-axial compression, bending and torsion. It has small contribution to both flexural and torsion strength, while it can be replaced effectively by steel with smaller area to give similar load-carrying capacity. Also, the confining pressure in CFST columns builds up slowly because the initial elastic dilation of concrete is small before micro-crackings of concrete are developed. From these observations, it is convinced that the central concrete can be effectively replaced by another hollow steel tube with smaller area to form double-skinned concrete-filled-steel-tubular (CFDST) columns. In this study, a series of uni-axial compression tests were carried out on CFDST and CFST columns with and without external steel rings. From the test results, it was observed that on average that the stiffness and elastic strength of CFDST columns are about 25.8% and 33.4% respectively larger than CFST columns with similar equivalent area. The averaged axial load-carrying capacity of CFDST columns is 7.8% higher than CFST columns. Lastly, a theoretical model that takes into account the confining effects of steel tube and external rings for predicting the uni-axial load-carrying capacity of CFDST columns is developed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1051-1060
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• 2003

The heat and mass transfer on two kinds of tube surfaces (bare stainless steel tube and Teflon coated tube) in steam-air mixture flow are experimentally studied to obtain design data for the heat exchanger of the latent heat recovery from flue gas. In the test section, 3-tubes are horizontally installed, and steam-air mixture is vertically flowed from the top to the bottom. The pitch between tubes is 67mm, the out-diameter of tube is 25.4mm, and the thickness is 1.2mm ; blockage factor (cross sectional tube area over the cross sectional area of the test section) is about 0.38. All of sensors and measurement systems (RTD, pressure sensor, flow-meter, relative humidity sensor, etc.) are calibrated with certificated standard sensors and the uncertainty for the heat transfer measurement is surveyed to have the uncertainty within 7%. As experimental results, overall heat transfer coefficient of the Teflon (FEP) coated tube is degraded about 20% compared to bare stainless tube. The degradation of overall heat transfer coefficient of Teflon coated tube comes from the additional heat transfer resistance due to Teflon coating. Its magnitude of heat transfer resistance is comparable to the in-tube heat transfer resistance. Nusselt and Sherwood numbers on Teflon (FEP) coated surface and bare stainless steel surface are discussed in detail with the contact angles of the condensate.

• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.437-444
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• 2008

The use of imported structural steel tubes has been increased in domestic construction field because of its low price, but the mechanical properties of those steel tube are not verified exactly. This study includes coupon test and stub - column compression test on the structural steel tube. The compression test of stub - column was performed to characterize and quantify the material characteristic and strength of column compatibility, in which we compared the experiment formula and the abstract formula by the application of the LRFD standard formula and multiple column curve.

• Journal of Korean Society of Steel Construction
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• v.27 no.5
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• pp.435-445
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• 2015

Concrete filled steel tube(CFT), which has superior ductility and strength, is used for building column, bridge piers of ocean structure. Shear design equations of CFT existing in structural design provisions are excessively conservative. It has an effect on constructability and the economics of CFT. However, to suggest the reasonable shear design equation, experimental studies on the shear capacity of CFT have been rarely conducted. This study is analytical research to suggest improved shear design equations of large-diameter concrete-filled steel tubes. This analytical research was conducted to apply finite element analysis model of CFT based on the prior research. It was verified by comparison with prior test results. The verified model was used for parameter studies to estimate the influence of overhang length, concrete compressive strength and diameter-thickness ratio on shear strength.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.529-541
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• 2004

Concrete filled steel tube structures were recently used in constructing high-rise buildings due to their effectiveness. Studies on concrete filled steel tubes have been focused on the experiments of uni-axial compression and bending and eccentric compression. There were also a few studies that investigated CFT member behavior under combined compression and torsion. The behavior of a circular CFT column under combined torsion and compression was theoretically investigated, considering the confinement of steel tubes on the concrete, the softening of the concrete, and the spiral effect, which were the dominant factors that influenced compression and torsion strength. The biaxial stress effects due to diagonal cracking were also taken into account. By applying those factors to compatibility and equilibrium conditions, the basic equation was derived, and the equation could be used to incorporate the torsional behavior of the entire loading history of the CFT member.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.329-334
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• 2015

The aim of this paper is to determine the proper heat treatment temperature for SDSS tube production without ${\sigma}$-phase precipitation. When Mother steel tube was heat treated at $800^{\circ}C$ temperature, relatively a large amount of ${\sigma}$-phase precipitated and grain refinement of ferrite phase occurred simultaneously. However, in Pilgered and Drawn steel tubes, grain refinement of the ferrite phase did not occur and a small amount of ${\sigma}$-phase precipitated. For all three types of steel tubes, the pitting potential was reduced to 2/5 or less compared with the untreated one and corrosion also occurred in the salt spray test due to the precipitation of ${\sigma}$-phase. When heat treatment temperature was $900^{\circ}C$, grain refinement of the ferrite phase occurred and very little ${\sigma}$-phase precipitated in Pilgered and Drawn steel tubes. But when heat treatment was done at $1,000^{\circ}C$ temperature, all three types of steel tubes had a similar corrosion properties of that of untreated one and also corrosion did not occur in the salt spray test, as ${\sigma}$-phase did not precipitate. Therefore, the optimum heat treatment temperature range is determined to be more than $1000^{\circ}C$ for the SDSS at which corrosion does not occur.

• Proceedings of the KSR Conference
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• 2001.10a
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• pp.568-577
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• 2001

An important and cotinuing research effort has been concentrated to estimate safety for behavior of soil nearby construction site. This construction under ground would cause the soil to deform and vibrate at any direction. This paper presents to estimation of safety for movement and reliability for vibration due to steel tube jacked under ground.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.53-57
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• 2002

Brake tube is considered one of the most important parts in automobile. The shape of brake tube-end has a great influence on the function of brake, and the quality and productivity of brake tube have relation to die design. The forming process of brake tube-end is peformed by hydraulic press forming machine. In this paper, the forming processes of tube-end for automobile is analyzed and designed to make the optimal form of brake tube-end. Also, finite element analysis has been carried out using DEFORM-3D$\^$TM/ to predict the optimal shape of brake tube-end and the results obtained showed the optimal length between punch and chuck is 1.0 ∼ 1.2mm. The shape of tube-end is in good agreement with the finite element simulations and the experimental results.

• Steel and Composite Structures
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• v.17 no.1
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• pp.83-103
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• 2014

The objective of this research is to study the ultimate moment capacity of the connections between steel I-beams and concrete-filled steel tube columns using different stiffener configurations. The main parameters considered are column cross section shape, square or circular, and filling the column with concrete. This analytical study includes finite element models using ANSYS program taking geometric and material nonlinearities into consideration. These models are verified against the experimental results obtained from previous researches and current design guides. The results show that using proper stiffener configuration affects the stress distribution through the connection and increases the ultimate moment capacity of the connections. Also, circular column is advantageous than the square column for all stiffener configurations and dimensions.