Bending restoring force model of angle-steel reinforced concrete columns under combined torsion

To explore the restoring force model of an angle steel truss reinforced concrete column (ASRC) under the combined action of compression, bending, shear, and torsion, nine ASRC columns under a combined torsion environment were tested and analyzed. This study observed and summarized the failure mode characteristics of different component columns, distinguished different failure modes, and analyzed the hysteresis curve and energy dissipation capacity of component columns. Then, a trilinear skeleton curve model suitable for ASRC columns is adopted, and the calculation method of skeleton curves in different stages under the combined action of compression, bending, shear, and torsion is given. Finally, the ASRC hysteresis rule is simplified, and fitting produces the formulae for positive and negative hysteresis curve unloading stiffness. The restoring force model of the ASRC column under coupled torsion is established, and the test results validate the restoring force model. The results show that the established restoring force model can predict the hysteretic behavior of ASRC under combined torsion. This research can be used as a theoretical foundation as well as an experimental reference for the technical use of ASRC.