Structural Performance of Cold-Formed High-Strength Steel Circular Hollow Sections under Combined Compression and Bending

The ultimate strengths of cold-formed high-strength steel (CFHSS) circular hollow section (CHS) beam-columns have been experimentally and numerically studied in this investigation. The steel grades of CHS members were S700, S900, and S1100 with the nominal 0.2% proof stresses of 700, 900, and 1,100 MPa, respectively. In the experimental program, 32 CHS short beam-columns were axially compressed. The test results obtained in this study were used to develop an accurate finite-element (FE) model. The developed FE model precisely replicated the overall structural behavior of CHS beam-column test specimens. After validation, a detailed parametric study was conducted. The test results of CFHSS CHS long beam-columns reported in the literature were also included in this study. In the parametric study, 150 long and short beam-columns (LBC and SBC) were analyzed. The values of diameter-to-thickness ratio of CHS members varied from 9.7 to 108. The ultimate compression capacities of 190 test and numerical data were compared with the nominal compression capacities predicted from American, Australian, and European standards. The safety levels of design rules given in these standards were examined by performing a reliability analysis. It is shown that the American specification provided the closest, least scattered, and reliable predictions. On the contrary, the Australian standard provided very conservative, highly scattered, and unreliable predictions. In addition, the predictions from European code were also quite scattered and unreliable. Hence, it is proposed to use the American specification for the design of cold-formed steel CHS beam-columns with steel grades ranging from S700 to S1100.