Cyclic axial compression behavior and modeling of FRP–steel double‐tube confined gangue aggregate concrete

Abstract FRP‐steel double‐tube confined gangue aggregate concrete column (DTC‐GAC) can not only effectively solve the mechanical defects of low strength, low stiffness and high brittleness of gangue aggregate concrete (GAC), but also effectively suppress the premature buckling deformation of steel tubes, improve the axial stiffness and confinement effect of components. To conduct a pre‐assessment of its seismic performance, the strength of GAC, the number of FRP layers, the relative diameter ratio, and the cyclic loading scheme were token as the test parameters, and the cyclic axial compression tests and theoretical research on DTC‐GAC were conducted. It was observed from the test results that the ultimate bearing capacity and ductility under cyclic axial compression were almost maintained at the same level as under monotonic loading. However, the hoop strain was found to be slightly higher compared with monotonic loading. Furthermore, the degradation of the specimen's bearing capacity was mainly attributed to the stress damage of GAC. The quantitative calculation methods for plastic strain and bearing capacity degradation of DTC‐GAC were established, and a predictive model for envelope cyclic axial compression was proposed. The axial force–strain envelope was predicted using its monotonic axial compression design model, while the unloading/reloading curves were predicted using a modified Lam–Teng model with the end slope E un,0 of the DTC‐GAC unloading curve was corrected to account for the influence of the steel tube.