• Steel and Composite Structures
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• 제13권5호
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• pp.451-471
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• 2012

Concrete filled steel tube (CFST) structures have been used widely in high-rise buildings and bridges due to the efficiency of structurally favourable interaction between the steel tube and the concrete core. In the current design codes only one loading condition in the column members is considered, i.e., the load is applied on the steel tube and concrete core at the same time. However, in engineering practice the tube structures may be subjected to various loading conditions such as loading on the concrete core only, preloading on the steel tube skeleton before filling of concrete core, and so on. In this research, a series of comparative experiments were carried out to study the structural performance of concrete filled circular steel tube columns subject to four concentric loading schemes. Then, a generalized prediction method is developed to evaluate the ultimate load capacity of CFST columns subject to various loading conditions. It is shown that the predictions by the proposed method agree well with test results.

• 복합신소재구조학회 논문집
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• 제6권2호
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• pp.32-39
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• 2015

So far, square concrete filled tubular(CFT) columns have been used in a limited width thickness ratio. The reason is that local buckling occurs in steel tube easily. Once the local buckling occurs, the confinement effect of steel tube on concrete disappears. In this study, we developed welded built-up square steel tube with reinforcement which are placed at the center of the tube width acts as an anchor. 3 specimens of slender welded built-up square CFT columns and 3 specimens of slender welded built-up square steel tube columns were manufactured with parameters of width(B) of steel tube, width thickness ratio(B/t). we conducted a experimental test on the 6 specimens under eccentric load, and evaluated the structural resistance and behavior of 6 specimens.

• Steel and Composite Structures
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• 제14권2호
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• pp.191-204
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• 2013

A hybrid double skin concrete filled (HDSCF) circular steel tube column is proposed in this study. The yield strength of the outer steel tube is larger than 690MPa and the inner tube has less strength. In order to achieve efficiency with the high strength outer tube, a feasibility study on reducing the thickness of the tube below the specified design codes for CFTs was conducted based on an experimental approach. The experiment also took variables such as thickness of the inner tube, hollow ratio, and strength of concrete into consideration to investigate the behavior of the HDSCF column. In order to estimate the applicability of design equations for CFTs to the HDSCF column, test results from CFT and HDSCF columns with design codes were compared. It was found that the axial compressive performance of the proposed HDSCF column is equivalent to that of the conventional CFT member irrespective of design variables. Furthermore, the design equation for a circular CFT given by EC4 is applicable to estimate the ultimate strength of the HDSCF circular steel tube column.

• Steel and Composite Structures
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• 제16권5호
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• pp.455-480
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• 2014

Sixteen concrete filled square CFRP-steel tubular (S-CFRP-CFST) stub columns under axial compression were experimentally investigated. The experimental results showed that the failure mode of the specimens is strength loss of the materials, and the confined concrete has good plasticity due to confinement of the CFRP-steel composite tube. The steel tube and CFRP can work concurrently. The load versus longitudinal strain curves of the specimens can be divided into 3 stages, i.e., elastic stage, elasto-plastic stage and softening stage. Analysis based on finite element method showed that the longitudinal stress of the steel tube keeps almost constant along axial direction, and the transverse stress at the corner of the concrete is the maximum. The confinement effect of the outer tube to the concrete is mainly focused on the corner. The confinements along the side of the cross-section and the height of the specimen are both non-uniform. The adhesive strength has little effect both on the load versus longitudinal strain curves and on the confinement force versus longitudinal strain curves. With the increasing of the initial stress in the steel tube, the load carrying capacity, the stiffness and the peak value of the average confinement force are all reduced. Equation for calculating the load carrying capacity of the composite stub columns is presented, and the estimated results agree well with the experimental results.

• 한국강구조학회 논문집
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• 제15권5호통권66호
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• pp.561-570
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• 2003

본 논문은 스테인리스강관과 일반구조용강관의 비교를 통한 스테인리스 강관의 건축구조용 강재로서 적용성 검토를 위해, 폭(지름)-두께비, 단면형상을 주요 변수로 한 소재의 인장강도실험과 단주의 압축강도실험을 실시하여 소재의 기계적 성질과 단주의 강도 및 거동을 파악한다. 실험결과, 스테인리스강관은일반구조용 강관에 비해 인장내력, 항복비, 연신율, 에너지흡수능력 등이 월등히 우수한 것으로 나타났다. 항복내력 또한 KS규격 항복강도 $2.1tf/cm^2$ 나 일본 스테인리스설계기준강도 $2.4tf/cm^2$ 을 충분히 만족한 값으로 일반구조용 강판보다 더 높은 값을 보였다. 스테인리스 각형강관은 일반구조용 각형강관에 비해 폭-두께비의 제한값을 초과하는 경우에도 국부좌굴에 의한 급격한 내력저하 없이 연성적인 거동을 보이나 소성가공에 의한 영향은 폭-두께비가 증가하면서 더 많이 받는 것으로 나타났으며, 스테인리스 원형강관은 일반구조용 원형강관보다 지름-두께비가 증가함에 따라 국부좌굴과 소성가공의 영향을 더 적게 받는 것으로 나타났다. 소성변형능력 또한 일반구조용 강관에 비해 스테인리스 강관이 우수하게 나타났다.

• Steel and Composite Structures
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• 제22권5호
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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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• 제13권5호
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• pp.423-436
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• 2012

In this study total of six buckling-restrained braces (BRBs) were manufactured using a square steel rod as a load-resisting core member and a hollow steel tube as restrainer to prevent global buckling of the core. The gap between the core and the tube was filled with steel rods as filler material. The performances of the proposed BRB from uniaxial and subassemblage tests were compared with those of the specimens filled with mortar. The test results showed that the performance of the BRB with discontinuous steel rods as filler material was not satisfactory, whereas the BRBs with continuous steel rods as filler material showed good performance when the external tubes were strong enough against buckling. It was observed that the buckling strength of the external tube of the BRBs filled with steel rods needs to be at least twice as high as that of the BRBs filled with mortar to ensure high cumulative plastic deformation of the BRB.

• 한국공간구조학회논문집
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• 제2권2호
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• pp.51-58
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• 2002

This paper is presented an experimental studies on bond stress between steel and concrete in concrete filled 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.

• 한국공간구조학회논문집
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• 제3권3호
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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.

• Computers and Concrete
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• 제15권2호
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• pp.141-166
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• 2015

In the present study, a Finite Element Model has been developed and used to study the effect of diameter to wall thickness ratio (D/t) of steel tube filled with concrete under axial loading on its behavior and load carrying capacity. The model is verified by comparing its findings with available experimental results. Influence of thickness and area of steel tube on strength, ductility, confinement and failure mode shapes has been studied. Strength enhancement factors, load factor, confinement contribution, percentage of steel and ductility index are defined and introduced for the assessment. A parametric study by varying length and thickness of tube has been carried out. Diameter of tube kept constant and equals to 140 mm while thickness has been varied between 1 mm and 6 mm. Equations were developed to find out the ultimate load and confined concrete strength of concrete. Variation of lateral confining pressure along the length of concrete cylinder was obtained and found that it varies along the length. The increase in length of tubes has a minimal effect on strength of tube but it affects the failure mode shapes. The findings indicate that optimum use of materials can be achieved by deciding the thickness of steel tube. A better ductility index can be obtained with the use of higher thickness of tube.