Performance and modeling of FRP-steel dually confined reinforced concrete under cyclic axial loading.

Fiber-reinforced polymer (FRP)-steel tubed reinforced concrete (FSTRC) columns present promising engineering applications due to the reasonable integration of three constituent materials. Compared with the numerous studies on their performance under monotonic loading, relatively few studies have focused on their cyclic axial behavior. Moreover, the available models for plain concrete solely confined by FRP might be incapable of estimating the confined concrete behavior in cyclically loaded FSTRC due to the possible effect induced by the steel reinforcement in concrete, the additional steel tube confinement, and the girth gaps at column ends. To this end, this paper investigated circular FSTRC stub columns under monotonic and cyclic axial loading. The test results confirmed that the inclusion of reinforcement had noticeable effects on the unloading path since the tensile axial stresses in longitudinal steel bars slowed down the stiffness degradation of the inner concrete during unloading. For envelope cycles, the increase of the additional steel confinement level had a negligible impact on the plastic strain and the stress deterioration of the inner concrete. A confinement model was developed to estimate the full-range behavior of the FRP-steel dually confined reinforced concrete under cyclic axial loading with favorable accuracy. [ABSTRACT FROM AUTHOR]