Seismic Performance of Square Concrete Columns Confined with Glass Fiber–Reinforced Polymer Ties

This paper assesses the seismic response of square concrete columns internally confined with glass fiber–reinforced polymers (GFRP). Tests were conducted under simulated earthquake loads on eight full-scale 305×305 mm columns reinforced with GFRP rectilinear ties and steel longitudinal bars. Shear versus deflection and moment versus curvature responses along with various ductility parameters were used to evaluate the performance of the columns. Results showed that the GFRP ties provide effective confinement to the concrete core until a rupture strain much larger than the steel yield strain. The influence of tie configuration on specimen behavior was found to be significant. An approximately 4% ultimate drift ratio was observed for properly confined columns tested under axial load of 42% of the column axial load capacity. The current design code provisions and guidelines for GFRP ties were found to be ambiguous and lacking in several aspects; suggestions are made for improvement.