Cyclic Performance of Square RC Bridge Columns Confined with Combined Steel and BFRP Ties

This paper proposes a confining combination of steel and innovative rectangular basalt fiber-reinforced polymer (BFRP) ties at the plastic hinge region on the seismic response of square reinforced concrete (RC) bridge columns. Six concrete specimens were constructed to test the bend parts' strength for comparison to the tested straight parts' strength. Seven square columns were constructed, considering the spacing between ties and axial load level as the parameters for experimental study. A lateral load versus drift ratio with ductility parameters was applied to assess the column performance. BFRP ties test results showed that BFRP ties had overcome the flaws of conventional pultruded FRP rod ties. The column test results showed enhancement in the columns' deformation ductility and deterioration stiffness even with increasing axial load level from 0.03 to 0.2 Po, indicating that the BFRP ties provided effective confinement, resulting in a delay of rebar buckling and an increased displacement ductility by more than 28%. BFRP ties with ρfw = 1.8% provide the same displacement ductility as a BFRP jacket with 0.666 mm thickness.