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Incheon, South Korea

Kim J.-K.,Steel Structure Research Division | Kwak H.-G.,Korea Advanced Institute of Science and Technology | Kwak J.-H.,Korea Advanced Institute of Science and Technology
Steel and Composite Structures | Year: 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. Source

Lee C.-H.,Seoul National University | Han K.-H.,Seoul National University | Uang C.-M.,University of California at San Diego | Kim D.-K.,Seoul National University | And 2 more authors.
Journal of Structural Engineering (United States) | Year: 2013

Flexural tests on full-scale I-shaped beams, built up from high-strength steels (HSB800 and HSA800) with a nominal tensile strength of 800 MPa, were carried out to study the effect of flange slenderness on flexural strength and rotation capacity. The primary objective was to investigate the appropriateness of extrapolating current stability criteria (originally developed for ordinary steel) to high-strength steel. For comparison purposes, specimens with ordinary steel (SM490) were also tested and showed sufficient flexural strength and rotation capacity in accordance with the AISC specification. The performance of high-strength steel specimens was also very satisfactory from the strength, but not from the rotation capacity, perspective. The inferior rotation capacity of high-strength steel beams was shown to be directly attributable to the absence of a distinct yield plateau and the high yield ratio of the material. When a higher rotation capacity is required as in plastic design, the testing clearly showed that high-strength steel beams were vulnerable to brittle fracture when full-height transverse stiffeners were welded to the tension flange in the plastic hinge region. Residual stress measurements reconfirmed that the magnitude of the residual stress is almost independent of the yield stress of the base metal. © 2013 American Society of Civil Engineers. Source

Kim C.-E.,RandD Team | Ahn H.-Y.,SamhyunPF. | Lee P.-G.,Steel Structure Research Division | Shim C.-S.,Chung - Ang University
Composite Construction in Steel and Concrete VII - Proceedings of the 2013 International Conference on Composite Construction in Steel and Concrete | Year: 2013

Concrete filled tubular structures have advantages to overcome stability of thin plates and to increase stiffness. A hybrid bridge combining common steel box girders and truss girders was suggested to increase the span length of steel-concrete composite bridges. In negative moment regions, a truss girder has lower chords of concrete filled rectangular steel box section to increase flexural stiffness. A bridge model with span length of 30m was fabricated and static tests were performed to assess the effect of composite chords on the flexural behavior of the girder. Depth of the girder varies from 2.0 m to 3.0 m. Significant reduction of stresses in lower steel chord was observed and measured deflections showed a good agreement with calculated values considering the contribution of infilled concrete. Cracking and crack width of the upper concrete slab were observed and indirect crack control by longitudinal reinforcing bars can be used for the design. © ASCE. Source

Chung K.-S.,Steel Structure Research Division | Kim J.-H.,Steel Structure Research Division | Yoo J.-H.,Seoul National University of Science and Technology
Steel and Composite Structures | Year: 2013

The concrete-filled steel tube (CFT) columns have several benefits of high load-bearing capacity, inherent ductility and toughness because of the confinement effect of the steel tube on concrete and the restraining effect of the concrete on local buckling of steel tube. However, the experimental research into the behavior of square CFT columns consisting of high-strength steel and high-strength concrete is limited. Six full scale CFT specimens were tested under flexural moment. The CFT columns consisted of high-strength steel tubes (fy=325MPa, 555MPa, 900MPa) and high-strength concrete (fck=80MPa and 120MPa). The ultimate capacity of high strength square CFT columns was compared with AISC-LRFD design code. Also, this study was focused on investigating the effect of high-strength materials on the structural behavior and the mathematical models of the steel tube and concrete. Nonlinear fiber element analyses were conducted based on the material model considering the cyclic bending behavior of high-strength CFT members. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results. Source

Chung K.-S.,Steel Structure Research Division | Kim J.-H.,Steel Structure Research Division | Yoo J.-H.,Seoul National University of Science and Technology
International Journal of Steel Structures | Year: 2012

This study aimed at predicting the structural behavior of high-strength square CFT (concrete-filled steel tube) columns. First, the material models of the existing steel tube and concrete were compared, and a nonlinear fiber element analysis method was proposed. To verify the proposed fiber element analysis method, the behavior of CFT columns made from high-strength materials was investigated experimentally. CFT members consisted of high-strength steel tubes (yield strength; f y=913 MPa) and high-strength concrete (f ck=91.3 MPa). The moment-rotation relationships for hollow and concrete-filled steel tubes were compared. In addition, the P-M interaction diagrams for the experiment result and AISC-LRFD code provisions were compared. Finally, the result of the fiber element analyses was compared with the test results. © KSSC and Springer 2012. Source

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