• 한국공간구조학회논문집
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• 제6권3호
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• pp.69-76
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• 2006

콘크리트 충전 강관(Concrete Filled Steel Tube : CFT) 기둥은 내력 및 변형능력 등 구조적 성능이 뛰어남에도 불구하고 강관내부에 충전한 콘크리트의 재료분리저항성 및 유동성이 확보되는 고품질의 콘크리트가 요구되며, 또한, 다이어프램 하부의 충전 확인이 어렵다는 문제점을 안고 있다. 따라서 CFT기둥의 장점인 내력 및 시공성을 살리고, 현장 충전 공법에서의 단점을 극복하기 위하여 CFT부재의 PC화가 연구되어 왔다. 그러나 CFT부재의 PC화는 고중량물이기 때문에 운반과 양중능력의 확보 등 다른 문제를 낳게된다. 본 연구에서는 현장타설 CFT기둥의 단점과 공장생산 CFT기둥의 단점을 보완하기 위하여 새로운 형태인 중공 CFT 구조를 제안하고 중심축하중 하의 이력특성에 대한 기본적인 연구를 수행하였다. 이를 위하여 설정된 주된 실험변수는 CFT기둥의 충전율과 충전재의 강도이며, 특히 충전율은 0%, 30%, 50%, 80%, 100%를 설정하였다. 얻어진 결과는 기본적으로 항복강도레벨에 이르기까지 선형적인 거동을 나타내고 있으며, 내부 충전율이 증가함에 따라 강도, 강성 및 변형능력이 크게 나타나고 있다.

• 한국강구조학회 논문집
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• 제14권4호
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• pp.481-487
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• 2002

콘크리트충전 강관기둥의 외다이아프램 접합부형식에서, 철골보의 하중이 내부의 콘크리트로 전달되는 하중전달 메카니즘이 아직 명확하게 규명되지 않았다. 여기서 각 층에서 철골보의 전단력은 외부의 강관과 내부의 콘크리트 사이의 부착응력에 의해 전달된다고 본다. 따라서 본 연구는 콘크리트충전 강관기둥의 부착응력을 파악하기 위해, 콘크리트면에만 하중을 가하는 단순가력실험을 실시하였다. 콘크리트 종류, 강관의 형상/길이, 이음부의 유무/뒷댐재의 두께 등을 변수로 총 30개의 실험체를 제작하여 실험을 실시했으며, 각 변수에 따른 실험결과를 비교/분석하고자 했다.

• Steel and Composite Structures
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• 제17권1호
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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.

• Steel and Composite Structures
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• 제13권3호
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• pp.277-293
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• 2012

The interaction between steel tube and concrete core is the key design considerations for concrete-filled steel tube columns. In a concrete-filled steel tube (CFST) column, the steel tube provides confinement to the concrete core which permits the composite action among the steel tube and the concrete. Due to construction faults and plastic shrinkage of concrete, the debonding separation at the steel-concrete interface weakens the confinement effect, and hence affects the behaviour and bearing capacity of the composite member. This study investigates the axial loading behavior of the concrete filled circular steel tube columns with debonding separation. A three-dimensional nonlinear finite element model of CFST composite columns with introduced debonding gap was developed. The results from the finite element analysis captured successfully the experimental behaviours. The calibrated finite element models were then utilized to assess the influence of concrete strength, steel yield stress and the steel-concrete ratio on the debonding behaviour. The findings indicate a likely significant drop in the load carrying capacity with the increase of the size of the debonding gap. A design formula is proposed to reduce the load carrying capacity with the presence of debonding separation.

• Steel and Composite Structures
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• 제16권1호
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• pp.59-75
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• 2014

A new concrete confinement model is developed to predict the axial load versus displacement behavior of circular columns under concentric axial load. The new confinement model is proposed for concrete filled steel tube columns as well as circular reinforced concrete columns with steel tube jacketing. Existing confinement models were evaluated and improved using available experimental data from different sets of columns tested under similar loading conditions. The proposed model is based on commonly used confinement models with an emphasis on modifying the effective confining pressure coefficient utilizing the strength of the unconfined concrete and the steel tube, the length of the column, and the thickness of the steel tube. The proposed model predicts the ultimate axial strength and the corresponding strain with an acceptable degree of accuracy while also highlighting the importance of the manner in which the steel tube is used.

• 한국전산구조공학회논문집
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• 제33권3호
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• pp.153-158
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• 2020

본 논문에서는 부분 CFST (concrete-filled steel tube) 기둥에 대한 수치해석적 저항력 평가 방법에 대해 소개하고 있다. 기존 RC(reinforced concrete) 기둥에서 소성힌지가 발생할 것으로 예상되는 부분을 강관으로 보강함으로써 완전 CFST 기둥보다는 적은 재료를 사용하여 비슷한 휨 모멘트 저항력을 가지는 부분 CFST 기둥의 디자인 컨셉을 제시하였다. 부분 CFST 기둥에서 외부 강관과 내부 콘크리트 사이의 계면에서 거동을 수치해석적으로 모사하기 위해 개선된 부착슬립모델을 적용한 유한요소모델을 구축하고, 이중곡률 휨-압축시험결과와 비교를 통해 타당성을 검증하였다. 검증된 수치모델을 바탕으로 매개변수 연구를 통해서 P-M 상관도를 그려 단면 조건에 따른 최대 저항력을 평가하였다. 또한, 강관 두께별로 필요 보강길이를 산출하고, 보강 조건에 따른 부분 CFST 기둥에서의 파괴메커니즘을 분석하였다.

• 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.

• Earthquakes and Structures
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• 제3권6호
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• pp.889-910
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• 2012

Because of the heavy demand of confining steel to restore the column ductility in seismic regions, it is more efficient to confine these columns by hollow steel tube to form concrete-filled-steel-tube (CFST) column. Compared with transverse reinforcing steel, steel tube provides a stronger and more uniform confining pressure to the concrete core, and reduces the steel congestion problem for better concrete placing quality. However, a major shortcoming of CFST columns is the imperfect steel-concrete interface bonding occurred at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confining effect and decrease the elastic modulus. To resolve the problem, it is proposed in this study to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns with external steel rings and ties. From the results, it was found that: (1) Both rings and ties improved the stiffness of the CFST columns and (2) the rings improve significantly the axial strength of the CFST columns while the ties did not improve the axial strength. Lastly, a theoretical model for predicting the axial strength of confined CFST columns will be developed.

• KIEAE Journal
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• 제7권6호
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• pp.119-126
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• 2007

In the field of composite structures, the use of carbon tube for the confinement of concrete has been arisen since 1990's. However, experimental and analytical studies were limited to those of reinforced concrete and concrete filled steel tube. The carbon tube provides excellent confinement capabilities for concrete cores, enhancing compressive strength and ductility of concrete significantly. The carbon tube has high tensile strength, light weight, corrosion immunity and high fatigue strength properties. Since carbon fiber is an anisotropic material, carbon tube could be optimized by adjusting the fiber orientation, thickness and the number of different layers. In this study, both experimental and analytical studies of axial and lateral behavior of full-scale CFCT (Concrete Filled Carbon Tube) columns subjected to monotonic axial load were carried out using Drucker-Prager theory. And, based on comparison results between experiment results and analytical results, k factor estimation was proposed for effective analysis.

• 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.