Behaviour and confinement-based direct design of concrete-filled cold-formed stiffened steel tubular short columns. (March 2023) - Huang, Wei-Feng
Abstract: The advantages of concrete-filled square steel tubular columns are currently being widely utilised in various applications, especially in marine and ocean structures. However, the use of slender cross-sectional tubes significantly reduces the concrete core confining effect due to the local buckling (LB) phenomenon of these tubes. Accordingly, welded stiffeners have been proposed to generate stiffened steel tubes to reduce the effect of LB. But due to welding, residual stress causes significant initial imperfections in the columns. This has resulted in the emergence of the concrete-filled cold-formed stiffened steel tubular (CFSST) columns that consist of cold-formed longitudinal stiffeners embedded in the concrete core. The literature shows that studies into the response of these columns are relatively limited. Accordingly, finite element (FE) modelling of CFSST columns with cold-formed steel tubes is used herein to increase the data bank of these columns. First, available test results on such columns using carbon steels were used to validate the FE models. Then, parametric studies were generated to suggest an innovative lateral confining pressure. These studies were also used to explore the effect of the depth-to-thickness ratio of the outer steel tube, concrete cylindrical strength and stiffener depth on the resistance and behaviour of the square CFSST columns with cold-formed steel tubes. It was found that increasing the cylindrical concrete strength is the most effective way to increase the ultimate strength of the columns, although it decreases the ductility of the columns. In addition, the strengths of CFSST short columns with cold-formed steel tubes were compared with the Japanese, British, European and Chinese codified strengths, which were found to provide conservative predictions. Finally, a new strength was provided for the CFSST short columns with cold-formed steel tubes based on a proposed linear law formula for the lateral confining pressure caused by the stiffened cold-formed tubes. Highlights: FE model for cold-formed stiffened CFST short columns under axial loading is presented. FE models of the stiffened CFSTs are validated against existing experimental results. Linear law formula for lateral confining pressure caused by stiffened tubes are proposed. Proposed design model is shown to predict well the strengths of the CFSST columns.