• Title/Summary/Keyword: CFT Columns

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The behavior of lightweight aggregate concrete filled steel tube columns under eccentric loading

  • Elzien, Abdelgadir;Ji, Bohai;Fu, Zhongqiu;Hu, Zhengqing
    • Steel and Composite Structures
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    • v.11 no.6
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    • pp.469-488
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    • 2011
  • This paper consists of two parts; the first part describes the laboratory work concerning the behavior of lightweight aggregate concrete filled steel tubes (LACFT). Based on eccentricity tests, fifty-four specimens with different slenderness ratios (L/D= 3, 7, and 14) were tested. The main parameters varied in the test are: load eccentricity; steel ratio; and slenderness ratio. The standard load-strain curves of LACFT columns under eccentric loading were summarized and significant parameters affecting LACFT column's bearing capacity, failure mechanism and failure mode such as confinement effect and bond strength were all studied and analyzed through the comparison with predicted strength of concrete filled steel tube columns (CFT) using the existing codes such as AISC-LRFD (1999), CHN DBJ 13-51-2003 (2003) and CHN CECS 28:90 (1990). The second part of this paper presents the results of parametric study and introduces a practical and accurate method for determination of the maximum compressive strength of confined concrete core ($f_{max}$), In addition to, the study of the effect of aspect-ratio and length-width ratio on the yield stress of steel tubes ( $f_{sy}$) under biaxial state of stress in CFT columns and the effect of these two factors on the ultimate load carrying capacity of axially loaded CFT/LACFT columns.

Axial impact behavior of confined concrete filled square steel tubes using fiber reinforced polymer

  • Zhang, Yitian;Shan, Bo;Kang, Thomas H.K.;Xiao, Yan
    • Steel and Composite Structures
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    • v.38 no.2
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    • pp.165-176
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    • 2021
  • Existing research on confined concrete filled steel tubular (CCFT) columns has been mainly focused on static or cyclic loading. In this paper, square section CCFT and CFT columns were tested under both static and impact loading, using a 10,000 kN capacity compression test machine and a drop weight testing equipment. Research parameters included bonded and unbonded fiber reinforced polymer (FRP) wraps, with carbon, basalt and glass FRPs (or CFRP, BFRP, and GFRP), respectively. Time history curves for impact force and steel strain observed are discussed in detail. Experimental results show that the failure modes of specimens under impact testing were characterized by local buckling of the steel tube and cracking at the corners, for both CCFT and CFT columns, similar to those under static loading. For both static and impact loading, the FRP wraps could improve the behavior and increase the loading capacity. To analyze the dynamic behavior of the composite columns, a finite element, FE, model was established in LS-DYNA. A simplified method that is compared favorably with test results is also proposed to predict the impact load capacity of square CCFT columns.

Efficiency of stiffening plates in fabricated concrete-filled tubes under monotonic compression

  • Albareda-Valls, Albert;Carreras, Jordi Maristany
    • Steel and Composite Structures
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    • v.18 no.4
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    • pp.1023-1044
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    • 2015
  • Concrete-filled tubes (CFT), formed by an outer steel tube filled with plain or reinforced concrete inside, have been increasingly used these recent decades as columns or beam-columns, especially for tall buildings in seismic areas due to their excellent structural response. This improved behavior is derived from the effect of confinement provided by the tube, since the compressive strength of concrete increases when being subjected to hydrostatic pressure. In circular CFTs under compression, the whole tube is uniformly tensioned due to the radial expansion of concrete. Contrarily, in rectangular and square-shaped CFTs, the lateral flanges become subjected to in-plane bending derived from this volumetric expansion, and this fact implies a reduction of the confinement effect of the core. This study presents a numerical analysis of different configurations of CFT stub columns with inner stiffening plates, limited to the study of the influence of these plates on the compressive behavior without eccentricity. The final purpose is to evaluate the efficiency in terms of strength and ductility of introducing stiffeners into circular and square CFT sections under large deformation axial loading.

Structural Performance Evaluation to Centrally Compressed CFT Columns Using Seismic Rectangular Steel Tube (중심압축력을 받는 내진 건축구조용 각형강관 CFT 부재의 구조성능평가)

  • Shim, Hyun-Ju;Choi, Byong-Jeong;Lee, Eun-Taik
    • Journal of Korean Society of Steel Construction
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    • v.24 no.4
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    • pp.443-450
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    • 2012
  • In this study, This study investigates the axial load behavior of concrete-filled steel columns using seismic rectangular steel tube with the width-to-thickness and slenderness ratio. Due to cold-roll forming and cold-press forming of steel tube, the flat part and the corner part of the rectangular steel tubes are changed in the material properties compared to SN-steel plate. It was showed the tendency to increase yield strength, tensile strength and upper limit of yield ratio This phenomenon affects the nonlinear behavior after local buckling of the steel tube. Therefore, the coupon test was performed by the processing of rectangular steel tube, in order to assess forming performance. And a total of 6 CFT-columns were tested under monotonic loading condition. Main parameters were the width-thickness ratio and the slenderness ratio.

Axial Load Test on Rectangular CFT Columns using High-Strength Steel and Slender Section (세장 단면의 고강도 강관을 적용한 각형 CFT 기둥의 압축실험)

  • Lee, Ho Jun;Park, Hong Gun;Choi, In Rak
    • Journal of Korean Society of Steel Construction
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    • v.27 no.2
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    • pp.219-229
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    • 2015
  • An experimental study was performed for thin-walled rectangular concrete-filled tubular (CFT) columns. The present study mainly focused on evaluation of the axial load-carrying capacity of concrete-filled tubular columns using high-strength steel and slender section. The test parameters were width-to-thickness ratio, concrete strength, steel yield strength, and the use of stiffeners. Five specimens were tested under monotonic axial loading. Although elastic local buckling occurred in the slender-section specimens with high-strength steel, the specimens exhibited considerable post-buckling reserve. The test results also satisfied the predictions of a current design code. The specimens strengthened with vertical stiffeners exhibited improved strength and ductility when compared with the un-stiffened specimens.

An Experimental Study on Stength of Slender Square Tube Columns Filled with High Strength Concrete (고강도콘크리트충전 각형강관장주의 내력에 관한 실험적 연구)

  • Seo, Seong Yeon;Chung, Jin An
    • Journal of Korean Society of Steel Construction
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    • v.14 no.4
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    • pp.471-479
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    • 2002
  • In this paper, 18 square CFT columns filled with high-strength concrete were tested under concentric or eccentric axial loading. Two parameters of the experimental program included the buckling length-section depth ratio ($L_K$/D) and the eccentricity of the appled compressive load (e). In additon, mechanical properties such as the compressive concrete strength and compressive and tensile steel strength were measured and incorporated into the material models for the stress-strain relationships of concrete and steel. This model was used in an elasto-plastic analysis in order to predict the behavior of the slender CFT columns. Observtions of the failure mode during the tests under axial loadig were also presented. The strengths obtained from the analysis. Recommendations for Design, and Constructions of CFT structures were presented, as verified by the experimental results.

Development of Connection between CFT Prefounded Column and Slab (CFT 선기초기둥과 슬래브 접합부 개발)

  • Song, Jee-Yun;Rhim, Hong-Chul;Kim, Seung-Weon;Kim, Dong-Gun;Kang, Seung-Ryong;Jeong, Mee-Ra
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2008.11a
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    • pp.129-133
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    • 2008
  • For the construction of Top-Down structures, it is crucial to have a solid connection between prefounded columns and slabs. This paper presents a new construction method for the connection when using a circular Concrete Filled Tube (CFT) as a prefounded column as an alternative to currently using wide flange type columns. The development of shear studded jackets along with a shear band suitable for the circular shape of the column has been made. The details and mechanism of the connection is explained together with the results of experiments which verified the structural integrity of the connection.

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Practical Use of Self Compacting Concrete to be filled inside the Steel Tube Columns (무다짐 콘크리트를 이용한 높은 40m CFT 기둥의 시공)

  • 김규동;김한준;손유신;이승훈
    • Proceedings of the Korea Concrete Institute Conference
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    • 2003.05a
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    • pp.1023-1028
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    • 2003
  • The structure of Tower Palace III Sports Center building was designed as concrete Filled Steel Tube(CFT) Column and the filled-in concrete was designed as high compressive strength of 500kgf/$m_2$. The self compacting concrete(SCC, non-vibrating concrete) with 65$\pm$5cm flow must be applied to this case for filling the CFT by injecting the concrete from the column bottom. Laboratory tests and pilot productions of batcher plant were performed for optimum mix design and the full scale Mock-Up test was performed to check the appicability of the construction method. As a result, we observed that good quality SCC and the pressure change of concrete pump normally used domestically. Based on these results, we have constructed 20-40m height CFT columns successfully.

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Resistance and Flexure Behavior of Slender Welded Built-up Square CFT Column Using Internal Reinforced Steel Tube under Eccentric Loads (강관내부 보강재를 고려한 용접조립 각형 CFT 편심 장주의 내력 및 휨 거동)

  • Lee, Seong-Hui;Kim, Young-Ho;Choi, Sung-Mo
    • Journal of the Korean Society for Advanced Composite Structures
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    • v.6 no.2
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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.

Behavior of concrete-filled double skin steel tube beam-columns

  • Hassan, Maha M.;Mahmoud, Ahmed A.;Serror, Mohammed H.
    • Steel and Composite Structures
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    • v.22 no.5
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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.