Axial compressive behaviors of H-shaped steel-reinforced geopolymer recycled aggregate concrete-filled GFRP tube columns

The geopolymer recycled aggregate concrete-filled glass fiber reinforced plastic (GFRP) tube (GRCFFT) column represents an eco-friendly composite solution; however, its initial compressive stiffness is inadequate, and its integration with other components presents challenges. H-shaped steel reinforcement was embedded into the GRCFFTs to address these issues, resulting in the development of the H-shaped steel-reinforced geopolymer recycled aggregate concrete-filled GFRP tube (SR-GRCFFT) column. This study investigated the effects of concrete core and GFRP tube parameters on the axial compression performance of SR-GRCFFT columns. The failure modes of the specimens, along with their load-displacement behavior and axial strain-hoop strain behavior, were analyzed. Furthermore, the enhancement effect of the H-shaped steel on the GRCFFT columns was quantified. The results indicated that the characteristics of the GFRP tube primarily dictated the failure modes exhibited by the SR-GRCFFT columns. Substituting 100 % RCA led to a 7.5 % decrease in bearing capacity, but adding 1.5 % steel fiber resulted in a 6.0 % increase. Notably, incorporating 6.45 % H-shaped steel improved the bearing capacity of the GRCFFTs by 23.9-40.6 % and enhanced the initial stiffness by 41.0-67.2 %. Furthermore, a synergistic effect was observed between the GFRP pipe and the H-shaped steel restraining the concrete. Finally, predictive models for the ultimate states of GRCFFTs were proposed, which considered the constrained stiffness ratio and a practical design formula for the bearing capacity of SR-GRCFFTs based on the superposition principle.