Seismic performance of ultra-high performance concrete-filled FRP tube composite columns reinforced with SFCBs: Test and modeling

To reduce residual deformation and address corrosion issues, this paper introduces a novel type of composite columns, utilizing ultra-high performance concrete (UHPC)-filled fiber reinforced polymer (FRP) tubes (UHPCFFT) and reinforced with steel-FRP composite bars (SFCBs). The seismic performance of the proposed SFCBreinforced UHPC-FFT composite columns was evaluated through pseudo-static experiments and numerical analysis in comparison with those of traditional composite columns. Results indicated that the UHPC-FFT composite columns reinforced with SFCB exhibited larger energy dissipation compared with those reinforced with either steel or FRP bars. Increasing the axial compression ratio from 0.15 to 0.25 enhance load-bearing capacity but reduces ductility and energy dissipation. Increasing the yield strength of internal steel bar of SFCBs can improve the load-bearing capacity and deformation of the columns without affecting the ductility, initial stiffness, and stiffness degradation rate. Increasing the elastic modulus of out-wrapped FRP of SFCBs enhanced the seismic performance of UHPC-FFT composite columns but could lead to premature failure due to FRP rupture. It is recommended to set an elastic modulus for the outer FRP wrap at 55 GPa for optimal seismic performance in UHPC-FFT composite columns.