Sectional strength design of l-shaped irregularly concrete-filled steel tube column under axial compression and any directional moment

Authors' previous research proposed a new kind of L-shaped irregularly concrete-filled steel tube column (LICFSTC) and conducted the experimental and numerical investigation into it under eccentric compression. In this paper, authors further study the sectional strength capacity of L-ICFSTC under axial compression and any directional moment and establish a complete set of design formulas for it. The FE model validated by the authors' previous experimental results is adopted to the parameter analysis of this study. The involved parameters include the length of two column limbs, the thickness of steel tube, the material strength and the axial compressive ratio, and consider the possibility of unequal length between two column limbs. Due to the irregularly-shaped section and two materials with different properties, the load-bearing behavior of L-ICFSTC is significantly related to the angle of moment, making its interaction curves and design formulas much more complex than current those of rectangular or circular CFST columns. Therefore, we start from the capacity of L-ICFSTC under pure unidirectional moment, and then study the capacity of L-ICFSTC under axial compression and unidirectional moment, and based on this, we finally obtain the capacity of L-ICFSTC under axial compression and any directional moments. The complete set of design formulas is established by theoretical analysis and fitting the N -M curves and Mx -My curves obtained by FE model. The formula results can agree well with the FE investigation results, demonstrating its applicability to the engineering design of L-ICFSTC.