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Steel and Composite Structures
  Volume 33, Number 6, December25 2019, pages 849-864

Compressive and flexural behaviors of ultra-high strength concrete encased steel members
Yong Du, Ming-Xiang Xiong, Jian Zhu and J.Y. Richard Liew

    One way to achieve sustainable construction is to reduce concrete consumption by use of more sustainable and higher strength concrete. Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in the design of composite structures. Against such background, this paper investigates experimentally the mechanical properties of steel fibre-reinforced UHSC and then the structural behaviors of UHSC encased steel (CES) members under both concentric and eccentric compressions as well as pure bending. The effects of steel-fibre dosage and spacing of stirrups were studied, and the applicability of Eurocode 4 design approach was checked. The test results revealed that the strength of steel stirrups could not be fully utilized to provide confinement to the UHSC. The bond strength between UHSC and steel section was improved by adding the steel fibres into the UHSC. Reducing the spacing of stirrups or increasing the dosage of steel fibres was beneficial to prevent premature spalling of the concrete cover thus mobilize the steel section strength to achieve higher compressive capacity. Closer spacing of stirrups and adding 0.5% steel fibres in UHSC enhanced the post-peak ductility of CES columns. It is concluded that the code-specified reduction factors applied to the concrete strength and moment resistance can account for the loss of load capacity due to the premature spalling of concrete cover and partial yielding of the encased steel section.
Key Words
    concrete encased steel column; ultra-high strength concrete; steel fibres; compressive/flexural/beam-column behaviors; plastic design approach; ductility
(1) Yong Du, Jian Zhu:
College of Civil Engineering, Nanjing Tech University, Nanjing, China;
(2) Yong Du, Ming-Xiang Xiong, J.Y. Richard Liew:
Department of Civil and Environmental Engineering, National University of Singapore, 117576, Singapore;
(3) Ming-Xiang Xiong:
Protective Structures Centre, School of Civil Engineering, Guangzhou University, Guangzhou, China.

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