Axial compressive behaviour of high-strength steel spiral-confined square concrete-filled steel tubular columns

Abstract

The ductility of concrete-filled steel tubular (CFST) columns with square cross-sections is significantly lower than circular ones when subjected to large axial forces or when thin-walled steel tubes and high-strength concrete are employed. The additional confinement contribution of the internal steel spiral compensates for the shortcomings of the rapid reduction of the ductility and strength of square CFST columns. The axial compressive performance of high-strength steel (HSS) spiral-confined square CFST (HSS-CFST) columns was experimentally investigated to enhance this advantage. 20 HSS-CFST columns, five normal-strength steel spiral-confined CFST (NSS-CFST) columns, and four CFST columns without an internal steel spiral were tested under axial compression. It was found that the high strength characteristic of the internal HSS spiral was fully utilized, thereby alleviating the non-uniform confinement of the square steel tube and significantly enhancing the ductility and strength of CFST columns. The ultimate strength improvement induced by increasing the volume of HSS spiral is more pronounced than that caused by increasing the same volume in the outer steel tube. A strong interaction exists between the confinement contribution made by the internal steel spiral and that provided by the outer steel tube. A new ultimate axial load model was subsequently proposed based on the experimental findings of the author's own and those collected from the literature, which significantly extends the range of the parameter space and clearly illustrates the interaction between the steel tube and internal steel spiral.