Due to the good axial bearing capacity, energy dissipation capacity and fire resistance capacity, concrete-filled steel tubular (CFST) columns have been widely utilized as vertical members in buildings. When used in super-high-rise buildings, CFST columns usually have large areas. However, some problems may appear in these mega-columns. On one hand, the hydration heat of massive concrete in a mega-column is a difficult problem to solve. On the other hand, the thickness of the steel plate is large, and the requirement of the lamellar tearing resistance capacity of the steel is high. This requires controlling the ratio of different elements in the steel, which increases the cost.

There is a type of new CFST column called the multicell CFST (MCFST) column. Compared with the cross section of normal single-cell CFST columns, the cross section of the MCFST column is separated into several cells by internal steel plates, allowing the hydration heat to be effectively released. Because the number of walls in the steel tube increases in the multicell CFST column, the thickness of every wall decreases.

Multicell concrete-filled steel tubulars (MCFSTs) have been widely utilized in super-high-rise buildings. In this study, in order to explore the behavior of multicell concrete-filled steel tubulars under cyclic loads, Professor CAO Wanlin and his team from the FACTE proposed a kind of hexagonal six-cell CFST columns, and an experimental study was conducted under lateral cyclic loads. The parameters included 3 loading directions (strong axis, 45 degrees, and weak axis), 2 axial loads (750 kN and 1500 kN), and 2 types of cross-sectional structures (angle steel-reinforced type and basic type). Analysis was conducted on bearing capacity, the failure mode, ductility, residual deformation, accumulated energy dissipation and strain development.

The experimental results indicate that the angle steel can decrease the residual deformation and improve the accumulated energy dissipation and bearing capacity of samples. With the loading directions changing from the strong axis to the weak axis, the accumulated energy dissipation and bearing capacity decreased. The influence of the axial load ratio was related to the loading direction. A calculation model using the fiber-based method was established considering the differences among the different cells. According to the calculation results of this method, the limit axial load ratio decreased with the loading directions changing from the strong axis to the weak axis. The stress-strain relationships of plain concrete and confined concrete based on single-cell CFSTs were conservative in predicting the F-Δ curves, and the error increased with an increasing axial load ratio, while the separation model showed the best agreement. This paper is expected to provide theoretical basis and technical support for further research and application of multicell concrete-filled steel tubulars. The results have been published recently in Engineering Structures.

The first author of this project is Dr YIN Fei of BJUT. The work was done in collaboration with Prof.CAO Wanlin and DONG Hongying of FACTE BJUT.