Seismic Behavior of High-Strength Concrete Columns Confined by Fiber-Reinforced Polymer Tubes

The use of high-strength concrete (HSC) in seismically active regions poses a major concern because of the brittle nature of material. The confinement requirements for HSC columns may be prohibitively stringent when ordinary grade transverse steel reinforcement is used. An alternative to conventional confinement reinforcement is the use of fiber-reinforced polymer (FRP) tubes in the form of stay-in-place formwork which can fulfill multiple functions of: (1) formwork; (2) confinement reinforcement; and (3) protective shell against corrosion, weathering and chemical attacks. The use of stay-in-place FRP formwork is investigated as concrete confinement reinforcement for HSC and normal strength concrete (NSC) columns with circular cross sections. Large-scale specimens with 270mm circular cross-sections and different concrete strengths were tested under constant axial compression and incrementally increasing lateral deformation reversals. FRP tubes were manufactured from carbon fiber sheets and epoxy resin. The results indicate that inelastic deformability of HSC and NSC columns can be improved significantly by using FRP tubes, beyond the performance level usually expected of comparable columns confined with conventional steel reinforcement.