Study on restoring force model of welded stud steel reinforced concrete column under different torque combinations

To investigate the restoring force model of welded stud steel-reinforced concrete (SSRC) columns subjected to combined torsion, quasi-static loading tests were conducted on eight X-shaped SSRC columns. The torsion-bending ratio, shear-span ratio, and different torque composite forms were varied as parameters. From the test data, the specimens' failure process and modes were observed and summarized. Furthermore, hysteretic performance indicators, including torque-torsion angle hysteretic curves, characteristic point parameters, and energy dissipation capacity, were analyzed for the SSRC columns. The results indicate that the torsion-bending ratio is the primary factor influencing the failure mode and hysteretic performance of the columns. An increase in the torsion-bending ratio within a reasonable range effectively improves the specimens' bearing capacity and energy dissipation capacity. However, exceeding this range adversely affects the columns' hysteretic performance.A trilinear skeleton curve model, suitable for SSRC columns, and the superposition principle were used to derive a calculation method for the skeleton curve of X-type SSRC columns under various torque combinations. The hysteretic rules of these columns were then simplified. A calculation formula for the unloading stiffness of both positive and negative hysteretic curves was obtained through curve fitting, leading to the development of a restoring force model for SSRC columns under diverse torque combinations. Calculated results showed excellent agreement with experimental data. Finally, a finite element model was developed, based on experimental results, to analyze the influence of the torsion-bending ratio on the hysteretic performance of SSRC columns under different torque combinations. The simulation results corroborated the impact of the torsion-bending ratio on the hysteretic performance, also exhibiting good agreement with experimental findings.