Seismic resistance of square concrete columns retrofitted with glass fiber-reinforced polymer

The capacity of key structural members, particularly columns, to absorb and dissipate energy without severe strength degradation dictates the survival of structures during a major, earthquake. Reinforced concrete columns with inadequate confinement do not possess the necessary ductility to dissipate sufficient seismic energy. This research evaluates the effectiveness of glass fiber-reinforced polymer (GFRP) wraps in strengthening deficient and repairing damaged square concrete columns. Each of the eight specimens tested, representing columns of buildings and bridges constructed before 1971, consisted of a 305 x 305 x 1473 mm column connected to a 508 x 762 x 813 mm stub. Specimens were tested under constant axial compression and cyclic lateral displacement excursions simulating earthquake loads. Test results reveal that retrofitting with GFRP wraps significantly enhanced ductility, energy dissipation ability, and shear and moment capacities of deficient columns. Cyclic behavior progressively improved as, the number of GFRP layers increased, causing both stiffness degradation and strength reduction rates to decrease. Improvements observed following GFRP repair of damaged columns depended mainly on the extent of damage sustained. GFRP-confined columns exceeded the performance of similar columns that contained transverse steel reinforcement in accordance with the seismic provisions of the current North American codes.