Confinement Model for Concrete Columns Reinforced with GFRP Spirals

Confinement of concrete using glass fiber-reinforced polymer (GFRP) spirals was evaluated using small-scale concrete cylindrical specimens with a 254-mm diameter and 762-mm height under concentric axial compression. The contribution of longitudinal GFRP bars to confinement was excluded by using wood dowels as longitudinal reinforcement to maintain a constant spiral pitch. Thus, concrete confinement was provided exclusively by the GFRP spiral. An ultimate hoop strain of 1.0 to 1.5% was achieved for the GFRP spirals of well-confined small-scale concrete specimens. Expressions were developed for the confined compressive strength and ultimate axial compressive strain of concrete confined with GFRP spirals. The resulting confinement model is compared with axial column tests of reinforced concrete columns with GFRP spirals and GFRP longitudinal bars from the present study and the literature. An expression is proposed for the ultimate axial compression capacity of concrete columns reinforced with GFRP spirals and GFRP longitudinal bars.