Performance of concrete columns longitudinally reinforced with steel and GFRP bars and confined with GFRP spirals and cross ties under reversed cyclic loading

This paper reports the comparative results of an experimental study performed on concrete columns reinforced entirely with glass fiber-reinforced polymer (GFRP) bars and with hybrid reinforcement (longitudinal steel bars and transverse GFRP spirals and cross ties) subjected to quasi-static cycling loading. Four full-scale bridge columns were constructed with longitudinal steel bars and confined with GFRP spirals and cross ties (hybrid-reinforced concrete columns). Four other columns were constructed solely with GFRP reinforcement (GFRP-reinforced concrete columns). The bridge columns had a cross section of 400 x 400 mm with a total height of 1850 mm. The columns were tested to failure under combined constant compressive axial load and quasi-static reversed lateral loading. The columns were investigated in terms of longitudinal bar type, longitudinal reinforcement ratio, and transverse reinforcement ratio. The results show that the longitudinal reinforcement type significantly affected column performance in terms of seismic parameters such as ductility and energy dissipation. The hybrid-reinforced concrete columns exhibited superior ductility and dissipated more energy than the GFRP-reinforced concrete columns. Furthermore, the GFRP-reinforced concrete columns experienced more gradual failure than the hybrid-reinforced concrete columns. Appropriately confined hybrid-reinforced concrete columns attained acceptable drift levels that meet the recommendations in most design codes. The transverse reinforcement ratio and longitudinal reinforcement ratio patently influenced column behavior. The lower elastic modulus of the GFRP bars compared to that of the steel bars had an impact on the theoretical lateral load capacity of the concrete columns.