Search

This paper aims to investigate the material synergy and parameter optimization of circular ultra-high performance concrete (UHPC) filled steel tubes towards excellent axial bearing capacity and material utilization efficiency. 12 stub columns of UHPC-filled steel tubes (UCFST) were tested and analysed combined with 293 literature data sets under axial compression. The results show that increasing confinement index ξ and steel ratio α can enhance the ductility of the axial load-displacement curve and the failure mode of the column. Threshold values of ξ = 1.0 and α = 0.25 are proposed to distinguish the failure modes. Appropriately higher steel strength grade, lower D/t , larger α and ξ are recommended to ensure the good axial bearing capacity of the UCFST columns. To produce excellent material synergy and axial bearing capacity, the optimum steel and UHPC strength grades are recommended around C100 ∼ C160 and Q345 ∼ Q690 for the axially-loaded UCFST short columns, respectively. Furthermore, the optimum ranges of diameter-to-thickness ratio D / t , steel ratio α and confinement index ξ are <90·(235/ f y), 0.10–0.30, 0.7–2.0, respectively. The current normal CFST design codes are inappropriate for the UCFST columns due to the parameter values exceeding limit values. Therefore, a reliable analytical model is proposed and well validated to predict the axial bearing capacities of circular UCFST short columns. • 12 circular UCFST stub columns are tested and analysed combined with 293 literature data. • The material synergy and parameter optimization of the UCFST columns are explored. • The optimum ranges of material strength grades, D / t , α and ξ are proposed. • An analytical model is proposed to predict the axial bearing capacities of UCFST stub columns. [ABSTRACT FROM AUTHOR]

This paper proposes a novel concept of 'central angle' to extend cross-section design of round-ended rectangular concrete-filled steel tube (RRCFST). Axial compressive behaviour and confinement mechanism of RRCFST stub columns are experimentally and numerically researched, including effects of central angle θ of round ends, aspect ratio κ of middle rectangular part, cross-sectional type, steel wall-thickness t. The results show that local buckling and shear failure of core concrete usually occur. The θ and κ can clearly describe the cross-sectional geometrical characteristics of RRCFST sections, as well as unifying circular and rectangular CFST. When the θ gradually changes from 0 to 180°, the round-ended confinement increases but the corner confinement reduces continuously, which results in overall confinement effect and material efficiency followed by parabolic trends. A larger κ leads to a weaker overall confinement and material efficiency, due to relatively wider unconstrained or weak constrained zones. The optimized cross-sections with θ around 60° and relatively smaller κ are recommended to design RRCFST subjected to axial compression, which contribute to good overall confinement effect, high material efficiency, high axial bearing load and ductility. A new reliable predicting analytical model for axial ultimate bearing capacity of RRCFST is proposed and validated. [ABSTRACT FROM AUTHOR]