Seismic Performance of Self-Centering Post-Tensioned Concrete Columns Reinforced with Steel-GFRP Bars and GFRP Spirals

A novel concept of hybrid reinforcement in the form of glass fiber-reinforced polymer (GFRP) longitudinal column bars combined with steel longitudinal column bars and high-strength post-tensioning all-threaded rods is investigated in this research to construct bridge columns for seismic regions. Two half-scale specimens were constructed using grouted ducts to connect the columns to the footings as an accelerated bridge construction method. The first column was reinforced with a combination of mild steel and GFRP longitudinal bars (hybrid column) and the second with all-mild steel longitudinal bars, and both columns were confined with a double layer of GFRP spirals; this arrangement improves column longevity since GFRP materials do not corrode. Both specimens utilized high-strength all-threaded rods for post-tensioning. Carbon fiber-reinforced polymer jackets were externally wrapped at the column bottom to confine the concrete in the plastic hinge region. The seismic behavior of both precast concrete specimens was assessed through quasi-static cyclic tests. Both columns exhibited satisfactory strength and deformability. The combination of post-tensioning bars with GFRP longitudinal bars improved the self-centering capability. The residual displacement of the hybrid column was decreased by 46% compared with the all-steel-reinforced column at 6.0% drift ratio. The elastic nature of the GFRP longitudinal bars provided substantial self-centering by reducing the residual displacement of the hybrid specimen thereby enhancing seismic resilience.