Axial compressive behavior of FRP-confined recycled compound concrete–filled steel tube columns

This paper presents findings of our axial compressive loading experiments on fiber-reinforced polymer (FRP)–confined recycled compound concrete–filled steel tube (RCCFST) columns. A total of 11 specimens were used for the axial compressive loading experiments, and the main investigated parameters are the FRP layer quantity and the length-to-diameter ratio of the specimen. The effects of different parameters on the axial compressive behavior of FRP-confined RCCFST columns were first analyzed. Experimental results indicate that wrapping with FRP prevents failure due to steel tube buckling. Under the same length-to-diameter ratio, the axial load-carrying capacity increases with the number of FRP wrapping layers, with the increase ranging from 8.78% to 36.33% compared to the unwrapped specimens. The length-to-diameter ratio has a significant impact on the lateral deflection of the specimens, which increases as the length-to-diameter ratio increases. When the length-to-diameter ratio is 9, the maximum lateral deflection at the center of the specimen can reach 8.14 mm. Second, the stress–strain curve of the core concrete was obtained via the theoretical analysis of the test data, and it was compared with the simulation result based on the FRP-confined CFST (using ordinary concrete) stress–strain model developed by Teng et al. (2013), which validates applicability of the model. At last, a simple equation applicable to the slenderness limit of the FRP-confined RCCFST slender and short columns was proposed based on comprehensive parametric investigation. This equation provides valuable reference for the engineering applications and future research of this composite column.