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Seismic behavior of concrete bridge columns confined with fiber-reinforced polymer stay-in-place formwork

One of the applications of fiber-reinforced polymers in bridge construction is stay-in-place formwork. Fiber-reinforced polymer stay-in-place formwork, in the form of preformed tubes, provides easy form assembly, protection of steel reinforcement and concrete against corrosion and chemical attacks while also improving the strength and ductility of structural elements in earthquake resistant construction. Experimental research was conducted to investigate the seismic performance of fiber-reinforced polymer stay-in-place formwork for bridge columns. Tests of large-scale specimens were conducted under simulated seismic loading. The experimental program included circular and square columns confined with carbon fiber–reinforced polymer tubes. The results indicate that the use of carbon fiber–reinforced polymer tubes increases column inelastic deformability significantly. Bridge columns under low levels of axial compression exhibit inelastic drift capacities in excess of 4% before failing in flexural tension due to the rupturing of longitudinal reinforcement. These observations and experimental results were used to develop a displacement-based design procedure for concrete confinement for fiber-reinforced polymer–encased concrete columns. This article presents an overview of the experimental program and the design approach developed.