Investigating the load–displacement restorative force model for steel slag selfstressing concrete–filled circular steel tubular columns

To investigate the seismic behavior of steel slag self-stressing concrete–filled circular steel tubular (SSSCFCST) columns, 14 specimens were designed, namely, 10 SSSCFCST columns and four ordinary steel slag (SS) concrete (SSC)–filled circular steel tubular (SSCFCST) columns. Comparative tests were conducted under low reversed cyclic loading considering various parameters, such as the axial compression ratio, diameter–thickness ratio, shear–span ratio, and expansion ratio of SSC. The failure process of the specimens was observed, and hysteretic and skeleton curves were obtained. Next, the influence of these parameters on the hysteretic behavior of the SSSCFCST columns was analyzed. The self stress of SS considerably increased the bearing capacity and ductility of the specimens. Results indicated that specimens with a shear–span ratio of 1.83 exhibited compression bending failure, whereas those with shear–span ratios of 0.91 or 1.37 exhibited drum-shaped cracking failure. However, shear–bond failure occurred in the nonloading direction. The stiffness of the falling section of the specimens decreased with increasing shear–span ratio. The hysteretic curves exhibited a weak pinch phenomenon, and their shapes evolved from a full shuttle shape to a bow shape during loading. The skeleton curves of the specimens were nearly complete, progressing through elastic, elastoplastic, and plastic stages. Based on the experimental study and considering the effects of the SSC expansion rate, shear–span ratio, diameter–thickness ratio, and axial compression ratio on the seismic behavior, a peak displacement coefficient of 0.91 was introduced through regression analysis. A simplified method for calculating load– displacement skeleton curves was proposed and loading and unloading rules for SSSCFCST columns were provided. The load– displacement restorative force model of the specimens was established. These findings can serve as a guide for further research and practical application of SSSCFCST columns.