• Title/Summary/Keyword: CFT Columns

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Finite element study the seismic behavior of connection to replace the continuity plates in (NFT/CFT) steel columns

  • Rezaifar, Omid;Younesi, Adel
    • Steel and Composite Structures
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    • v.21 no.1
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    • pp.73-91
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    • 2016
  • The use of box columns has been increased due to the rigidity in rigid orthogonal moment resisting frames. On the other hand, the installation and welding of necessary horizontal continuity plates inside the columns are both labor-consuming and costly tasks. Accordingly, in this paper, a new beam-to-box column connection by trapezoidal external stiffeners and horizontal bar mats is presented to provide seismic parameters. The proposed connection consists of eight external stiffeners in the level of beam flanges and five horizontal bar mats in Concrete Filled Tube (CFT) columns. The new connection effectively alleviates the stress concentration and moves the plastic hinge away from the column face by horizontal external stiffeners. In addition, the result shows that proposed connection has provided the required strength and rigidity of connection, so that the increased strength, 8.08% and rigidity, 3.01% are compared to connection with internal continuity plates, also the results indicate that this connection can offer appropriate ductility and energy dissipation capacity for its potential application in moment resisting frames in seismic region. As a result, the proposed connection can be a good alternative for connection with continuity plates.

An Analytical Investigation on the Ultimate Strength of Concrete-Filled Steel Tube Columns using Elasto-Plastic Large Deformation Analysis (탄소성 대변형 해석을 이용한 콘크리트 충전강관(CFT) 기둥의 극한강도에 관한 해석적 연구)

  • Jang, Gab-Chul;Chang, Kyong-Ho
    • Journal of Korean Association for Spatial Structures
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    • v.7 no.6
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    • pp.69-74
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    • 2007
  • Recently, to improve performance and strength of circular steel columns, application of concrete-filled steel tube(CFT) type are gradually increased. To accurately predict the plastic design of concrete-filled steel tube columns, a plasticity model is required which can be describe large deformation behavior of concretes and steels. In this study, elastic-plastic large deformation analysis is developed by using the plasticity model of structural steels, and accurate and validity of the developed program is verified by comparing between the experiment and the analysis for concrete-filled steel tube column. In concrete-filled steel tube columns, influence of initial deflection on ultimate strength behavior is investigated by using developed program.

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Analytical Model for CFTA Girder (CFTA 거더의 해석모델 개발)

  • Jeon, Jong-Su;Park, Seung-Jae;Kim, Yong-Jae;Park, Myoung-Gyun;Kim, Jung-Ho
    • Proceedings of the Korea Concrete Institute Conference
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    • 2009.05a
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    • pp.169-170
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    • 2009
  • CFT structure has many advantages compared with the ordinary structural member made of steel or reinforced concrete. Because of increases in ductility, stiffness and load carrying capacity of overall structure owing to confinement effect of steel box and concrete, CFT structure is widely used to columns. Recently, the utilization of CFT member has been expanded to bridge structure as a girder member. The purpose of this study is to develop the analytical model and propose design method for CFTA girder bridge consisting of CFT structure, arch shape and tendons.

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Design Equation for Square CFT Columns with Large Width-to-Thickness Ratio (폭두께비가 큰 각형CFT 단주의 설계식)

  • Kim, Sun Hee;Choi, Young Whan;Choi, Sung Mo
    • Journal of Korean Society of Steel Construction
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    • v.21 no.5
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    • pp.537-544
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    • 2009
  • The design standards, such as AISC-LRFD (2005) and KBC-2005, specify the maximum width-to-thickness ratio that can be used for computing the strength of the concrete-filled tube (CFT), and do not include any formula for computing the strength when the width-to-thickness ratio is over the limit. This paper proposes a strength equation for CFTs with a large width-to-thickness ratio by acknowledging the fact that the stiffened slender steel platehas substantial postbuckling strength, and that it therefore can be more economical to use it. The equation adopts the concept of effective width,which is very useful for plate analysis. By comparing the strengths of AISC2005, KBC2005, and the proposed method with the results of the experiment, where the width-to-thickness ratio was regarded as the main parameter, the applicability of the proposed method was verified.

Analysis of the Axial Force-Bending Moment Interaction for a CFT Column Considering the Confining Effect and the Material Nonlinearity of Concrete (콘크리트의 구속효과와 재료비선형을 고려한 내부 구속 CFT 기둥의 축력-모멘트 상호작용 분석)

  • Han Taek-Hee;Youm Eung-Jun;Yoon Ki-Yong;Lee Chang-Soo;Kang Jin-Ook;Kang Young-Jong
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2006.04a
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    • pp.141-148
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    • 2006
  • Concrete in a CFT(Concrete Filled Tube) column has enhanced strength and ductility because it is triaxially confined by a steel tube. But CFT columns are designed based on linear analyses by stress block method without the confining effect or the nonlinearity of the concrete. These make the significantly difference between the analysis results and the experimental results. Thus in this study, a nonlinear CFT column model was developed considering the confining effect on the concrete in a CFT column. This developed model was verified by experimental results from other researchers and compared with the results of various specifications. With the developed model, parametric studies were performed and the developed column model showed reasonable and accurate results.

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Long-Term Behavior of CFT Column under Central Axial Load (중심축 하중을 받는 CFT 기둥의 장기거동에 관한 연구)

  • 권승희;김진근
    • Journal of the Korea Concrete Institute
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    • v.13 no.1
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    • pp.77-85
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    • 2001
  • Concrete filled steel tubular (CFT) columns are becoming popular in structural applications. The increased popularity comes from their excellent structural properties such as high strength, high ductility, and large energy absorption capacity. However, the disadvantage feature of CFT column is the difficulty in predicting its time dependant characteristic (i.e., creep and shrinkage) of inner concrete. The time dependent behavior of CFT column can cause serious serviceability problems. Therefore, it is necessary to investigate the long term behavior of CFT column. This paper presents analytical and experimental studies on long-term behavior of CFT-column under a central axial loading. Two loading cases are considered in the research; (1) the load applied only at the inner core concrete of CFT-column and (2) the load applied simultaneously on both concrete and steel tube. Analysis method using the bond strength model is proposed and conclusions on long-term properties of CFT-column can be derived from the results.

Evaluation of Seismic Performance for an Internally Confined Hollow CFT Column (내부 구속 중공 CFT 기둥의 내진 성능 평가)

  • Han, Taek Hee;Kim, Sung Nam;Kang, Young Jong
    • Journal of Korean Society of Steel Construction
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    • v.19 no.1
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    • pp.53-65
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    • 2007
  • Column tests were performed for a new type of column, the internally confined hollow concrete filled tube column (ICH CFT column), to evaluate its seismic performance. The seismic performances for two types of ICH CFT columns and a general solid RC column were evaluated and compared by quasi-static tests. The displacements and the lateral loads of column specimens were measured during tests. Ductilities, absorbed energy, equivalent damping ratios, damage indices were calculated from recorded data. From the test results, the ICH CFT column shows superior seismic performances with double moment capacity and larger energy absorbing capacity over that of a solid RC column.

Axial Loading Behaviors of Square Concrete-Filled Tubular Columns with Large Width-to-Thickness Ratio Retrofitted using Carbon Fiber Reinforced Polymer Sheets(CFRP Sheets) (탄소섬유쉬트(CFRP Sheets)로 보강된 폭두께비가 큰 콘크리트 충전 각형강관 기둥의 중심축하중거동)

  • Park, Jai Woo;Yoo, Jung Han
    • Journal of Korean Society of Steel Construction
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    • v.26 no.3
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    • pp.169-176
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    • 2014
  • This paper presents the experimental results of behavior of square CFT columns with large the width-ro thickness ratio strengthened with carbon fiber reinforced polymers (CFRP) sheets subjected to concentrated axial loading. The main parameters were b/t ratio and the number of CFRP layers and 6 specimens were fabricated. The values of b/t were ranged from 60 to 100. From the tests, Maximum increase of 16% was also achieved in axial-load capacity with three transverse layered CFRP applied on four sides of steel tubes. The load capacity decreased up to 41% comparing with nominal load capacity of unstrengthened CFT column. However, for CFRP strengthened CFT, the load capacity decreased up to 32%. Finally, from the load-strain relationships, the local buckling occurred before yield point of steel tubes. Also, from the load-strain relationships, it was observed that local buckling were delayed on CFT columns by CFRP sheets retrofitting.

Proposal of Stress-Strain Relations Considering Confined Effects for Various Composite Columns (합성형태에 따른 콘크리트 구속효과를 고려한 응력-변형률 관계식의 제안)

  • Park, Kuk Dong;Hwang, Won Sub;Yoon, Hee Taek;Sun, Woo Hyun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.3A
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    • pp.265-275
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    • 2010
  • Concrete filled steel tube and concrete encased steel tube columns are expected to have confined effects of concrete by steel and reinforced effects of local buckling by concrete. On the basis of confined state concrete models of previous researches, stress-strain and load-displacement relations of RC, CFT and CET columns are analyzed by steel ratio. After comparing analysis results with experimental results, Modified stress-strain relations are derived through evaluation the influence upon confined effects of concrete in each cases. Also, the modified stress-strain models are carried out to be compared with specified strength of various countries.

Evaluation for fire resistance performance of high strength CFT with loading (재하하중에 따른 고강도 CFT의 내화성능 평가)

  • Hong, Seok-Beom;Yoo, Jo-hyeong;Kim, Woo-Jae;Lee, Ji-Hwan
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2013.11a
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    • pp.184-185
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    • 2013
  • Concrete filled steel Tube(CFT) columns have great strength but also fire resistance performance due to the heat storage effect of concrete. In this research, we focus on the fire performance of CFT using 100 MPa concrete without fire protection. We use steel fiber and nylon fiber for fire resistance. We perform the fire test of CFT specimen with loading 200, 300 and 400 ton. To investigate the effect of loading to fire resistance, we compare the fire resistance time according to the loading.

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