Slender concrete columns reinforced with fiber reinforced polymer spirals

Corrosion in commonly used epoxy-coated steel reinforcing bars has raised concern with its use and has increased interest in the use of alternative reinforcement including fiber-reinforced polymer (FRP) bars. Glass FRP (GFRP) bars are a costcompetitive alternative in conditions where chloride-induced deterioration is an issue. There has been considerable research and code-writing effort towards using GFRP bars in construction of bridge deck and beam elements but these efforts are still somewhat limited with regards to the use of FRP bars in construction of column elements and particularly in the use of FRP-spiral confining hoops or spirals. Steel spiral reinforcement is commonly used in concrete columns for confinement and improvement of displacement ductility but little is known regarding the use of FRP-spiral reinforcement for confinement. The purpose of this research is to gain a better understanding of the behavior and performance of FRP reinforcement for short as well as slender concrete columns, particularly FRP-spiral confining reinforcement, to better determine its viability as a potential construction alternative. Tests were conducted on nine circular concrete columns reinforced with internal GFRP-spirals and either steel, GFRP or a combination of steel and GFRP longitudinal bars. Axial load tests were conducted on both slender and short columns with loads placed at two eccentricities to observe the mode of failure, load capacity, and general behavior associated with different geometric and loading conditions. The test data is analyzed and a confinement model based on plasticity theory is derived to describe the axial strength and stress-strain relationship for FRP-spiralconfined circular columns. The confinement model is used to predict the momentcurvature relationship for FRP-spiral-confined circular columns. An analytical buckling model is developed, based on a numerical integration method, to describe the loaddeflection behavior for slender FRP-spiral-confined circular columns. Axial load and bending moment interaction diagrams are produced for FRPspiral-confined slender columns. The analytical buckling model is also used in parametric studies of large-scale slender columns to compare steel with FRP spirals in addition to other comparisons between reinforcement configurations and concrete compressive strength.