Strength Of Concrete-filled Steel Tubular Columns Research Articles

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

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.

Comparison of ultimate strength results from ACI and Eurocode 4 for steel tubular columns filled with SCC

The Concrete Filled Steel Tubular (CFST) columns have several benefits in comparison to the ordinary steel or reinforced concrete ones. Therefore, they have become more commonly acknowledged in the structural applications. In this study, two design codes such as American Concrete Institute (ACI) and Eurocode 4 (EC4) were used for predicting the ultimate axial strength of CFST columns filled with self-compacting concrete (SCC). To evaluate the results, circular steel tube with different diameter to thickness (D/t) ratio of 30, 60, and 90 and steel yielding strength of 185, 275, and 450 MPa were considered as prediction parameters. The wall thickness and length to diameter (L/D) ratio of the steel tubes were kept constant. As an infill material for the steel tubes, 16 different SCC mixtures reported in the literature were studied and their compressive strength results were used to get the code predicted ultimate axial strength of the composite columns. The analysis of the results based on ACI and EC4 were performed and discussed comparatively.