• Steel and Composite Structures
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• 제25권3호
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• pp.375-388
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• 2017

This paper presents a combined experimental, numerical, and analytical study on elliptical concrete-filled steel tubular (E-CFT) and rebar-stiffened elliptical concrete-filled steel tubular (RE-CFT) subjected to axial loading. ABAQUS was used to establish 3D finite element (FE) models for the composite columns and the FE results agreed well with the experimental results. It was found that the ultimate load-bearing capacity of RE-CFT stub columns was 20% higher than that of the E-CFT stub columns. Such improvement was attributed to the reinforcement effects from the internal rebar-stiffeners, which effectively enhanced the confinement effect on the core concrete, thereby significantly improved both the ultimate bearing capacity and the ductility of the E-CFT columns. Based on the results, equations were also established in this paper to predict the bearing capacities of E-CFT and RE-CFT stub columns under axial loading. The predicted results agreed well with both experimental and numerical results, and had much higher accuracy than other available methods.

• Computers and Concrete
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• 제9권4호
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• pp.257-273
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• 2012

Based on the heterogeneous characterization of concrete at mesoscopic level, Realistic Failure Process Analysis ($RFPA^{3D}$) code is used to simulate the failure process of concrete-filled tubular (CFT) stub columns. The results obtained from the numerical simulations are firstly verified against the existing experimental results. An extensive parametric study is conducted to investigate the effects of different concrete strength on the behaviour and load-bearing capacity of the CFT stub columns. The strength of concrete considered in this study ranges from 30 to 110 MPa. Both the load-bearing capacity and load-displacement curves of CFT columns are evaluated. In particular, the crack propagation during the deformation and failure processes of the columns is predicted and the associated mechanisms related to the increased load-bearing capacity of the columns are clarified. The numerical results indicate that there are two mechanisms controlling the failure of the CFT columns. For the CFT columns with the lower concrete strength, they damage when the steel tube yields at first. By contrast, for the columns with high concrete strength it is the damage of concrete that controls the overall loading capacity of the CFT columns. The simulation results also demonstrate that $RFPA^{3D}$ is not only a useful and effective tool to simulate the concrete-filled steel tubular columns, but also a valuable reference for the practice of engineering design.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.213-216
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• 2008

강관의 내부에 콘크리트를 충전한 구조인 콘크리트 충전 강관 구조(Concrete Filled Steel Tubular Structure, CFT 구조)는 강재와 콘크리트의 단점을 상호 보완하고 장점을 극대화 할 수 있다는 이점이 있다. 이와 같은 CFT 거더의 장점을 살리면서 CFT 거더보다 더 뛰어난 경제적, 구조적 효율성을 얻기 위해 기존의 CFT 구조에 아치 형식과 프리스트레스를 도입한 신형식 거더인 CFTA(Concrete-Filled and Tied Tubular Arch) 거더에 대한 연구가 현재 진행 중이다. CFTA 거더의 가장 큰 특징은 아치형상과 외부로 노출되어 있는 텐던인데 현재 연구과정에서 지적되고 있는 문제점 중의 하나는 외부로 노출된 텐던의 안전성에 관한 문제이다. 따라서 본 논문에서는 외부로 노출되어 있는 텐던에 대한 안전성 평가를 수행하였다. 또한, collision numerical simulation을 사용하여 동적 충돌에 대한 해석도 수행하였다. 모델의 해석을 위해 유한요소 해석 결과의 신뢰성이 높고, 타 연구에서도 많이 사용되고 있는 ABAQUS 6.5-1을 이용하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.688-693
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• 2007

Nowadays various studies related with superstructure of bridges are developed and they pursuit more effective section of bridges superstructure, material and economical application of composite materials. CFT structure(Concrete Filled Steel Tubular Structure) is developed type of composite structure that concrete is filled with steel box, and the deformation of the member, stiffness and internal force will be improved by confinement effect of steel box and concrete. This paper introduces new type of girder, CFTA girder( Concrete- Filled and Tied Steel Tubular Arch Girder) which is combined with traditional CFT structure,arch effect and prestress through carrying out the structural analysis by computer programs. The computer programs which is used are ABAQCS and MIDAS, and the 12.2m girder which is applied same load and prestresses is analyzed and compared the results respectively.

• 한국구조물진단유지관리공학회 논문집
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• 제4권2호
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• pp.151-158
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• 2000

A study on the strength of steel tubular column filled with concrete under cocentrically compressed load is presented in this paper. This paper is structured as follows. The first section briefly discusses the M-N relationship formula derived for CFT, highlighting the additional moment effect. Next, the simple superposed method used to generate the strength formula of CFT loaded concentrically is described. In the final portion of this paper, the presented formula is compared to experimental data reported. The applicability of CFT strength formula presented here is limited somewhat by scope of concrete strength but can predict the strength of CFT simply and rapidly. The objective of this paper is to approach the strength of CFT theoretically and to examine the feasibility of presented formula.

• Steel and Composite Structures
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• 제12권6호
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• pp.523-540
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• 2012

It was clear from the former researches on reinforced concrete filled tubular steel (RCFT) structures that RCFT structures have different performance than concrete filled steel tubular (CFT) structures. However, despite of that, load-sharing ratio of RCFT is evaluating by the formula and range of CFT given by JSCE. Therefore, the aim of this investigation is to study the load-sharing ratio of RCFT columns subjected to axial compressive load by performing numerical simulations of RCFT columns with the nonlinear finite element analysis (FEA) program - ADINA. To achieve this goal, firstly proper material constitutive models for concrete, steel tube and reinforcement are proposed. Then axial compression tests of concrete, RC, CFT, and RCFT columns are carried out to verify proposed material constitutive models. Finally, by the plenty of numerical analysis with small-sized and big-sized columns, load-sharing ratio of RCFT columns was studied, the evaluation formulas and range were proposed, application of the formula was demonstrated, and following conclusions were drawn: The FEA model introduced in this paper can be applied to nonlinear analysis of RCFT columns with reliable results; the load-sharing ratio evaluation formula and range of CFT should not be applied to RCFT; The lower limit for the range of load-sharing ratio of RCFT can be smaller than that of CFT; the proposed formulas for load-sharing ratio of RCFT have practical mean in design of RCFT columns.

• Steel and Composite Structures
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• 제17권4호
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• pp.517-533
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• 2014

Experimental results of 39 specimens including concrete columns, RC columns, hollow steel tube columns, concrete filled steel tubular (CFT) columns, and reinforced concrete filled steel tubular (RCFT) columns are presented. Based on the experimental results, the load-carrying capacity, confined effect, ductility, and failure mode of test columns are investigated. The effects of the main factors such as width-thickness ratio (the ratio of external diameter and wall thickness for steel tubes), concrete strength, steel tube with or without rib, and arrangement of reinforcing bars on the mechanical characteristics of columns are discussed as well. The differences between CFT and RCFT are compared. As a result, it is thought that strength, rigidity and ductility of RCFT are improved; especially strength and ductility are improved after the peak of load-displacement curve.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.217-220
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• 2008

구조물의 시공에 있어 더욱 경제적이고 안정적인 결과를 얻기 위해 최근 전 세계적으로 고성능 콘크리트와 복합재료에 관한 연구가 활발히 이루어지고 있다. 그 중 하나로 대구경의 강관 내부를 콘크리트계 재료로 충전하여 충전재간의 상호 구속효과(Confinement effect)로 인해 부재의 변형성능과 강성 및 내력을 향상시키는 콘크리트 충전 강관구조(Concrete Filled Steel Tubular Structure, CFT구조)에 아치구조 효과와 강선 등을 이용한 프리스트레스 구조를 도입하여, 구조적, 경제적 효율성을 극대화 시킨 새로운 형식의 거더인 CFTA 거더(Concrete Filled and Tied Steel Tubular Arch 거더)가 있다. 본 연구에서는 구조해석 프로그램인 ABAQUS 6.5-1을 사용하여 CFTA 거더에 일반 콘크리트와 여러 강도의 고강도 콘크리트를 충전한 모델의 비선형 거동을 분석하고 각각의 결과를 비교 분석하였다.

• Steel and Composite Structures
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• 제16권6호
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• pp.639-655
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• 2014

The mechanical characteristic of reinforced concrete filled steel tubular (RCFT) structures are differed from that of concrete filled tubular steel (CFT) structures because the reinforcement in RCFT largely affects the performance of core concrete such as ductility, strength and toughness, and hence the performance of RCFT should be evaluated differently from CFT. To examine the effect axial reinforcement on bending performance, an investigation on RCFT beams with varying levels of axial reinforcement is performed by the means of numerical parametric study. According to the numerical simulation results with 13 different ratios of axial reinforcement, it is concluded that the reinforcement has obvious effect on bending capacity, and the neutral axis of RCFT is different from CFT, and an evaluation equation in which the effect of axial reinforcement is considered for ultimate bending strength of RCFT is proposed.

• Steel and Composite Structures
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• 제28권5호
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• pp.573-588
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• 2018

The objective of this paper is to investigate the mechanical performances of polygonal concrete-filled circular steel tubular (CFT) stub columns under axial loading through combined experimental and numerical study. A total of 32 specimens were designed to investigate the effect of the concrete strength and steel ratio on the compressive behavior of polygonal CFT stub columns. The ultimate bearing capacity, ductility and confinement effect were analyzed based on the experimental results and the failure modes were discussed in detail. Besides, ABAQUS was adopted to establish the three dimensional FE model. The composite action between the core concrete and steel tube was further discussed and clarified. It was found that the behavior of CFT stub column changes with the change of the cross-section, and the change is continuous. Finally, based on both experimental and numerical results, a unified formula was developed to estimate the ultimate bearing capacity of polygonal CFT stub columns according to the superposition principle with rational simplification. The predicted results showed satisfactory agreement with both experimental and FE results.