Seismic Behavior of GFRP-RC Circular Bridge Columns under Eccentric Lateral Cyclic Loading: Influence of Transverse Reinforcement Ratio and Configuration

This study focused on evaluating the confinement requirements for glass fiber-reinforced polymer (GFRP) reinforcement in circular reinforced concrete (RC) columns subjected to seismic forces, including torsional effects. Seven large-scale GFRP-RC columns were tested under axial and quasi-static cyclic lateral loading. The test parameters included torsion-to-bending moment ratio (tm) and transverse reinforcement spacing and configuration (spiral and hoops). The experimental results revealed that introducing torsion to the loading scheme reduced the lateral load resistance and drift capacity of the columns. The study recommends adopting a spiral pitch equal to one-sixth of the effective core diameter, as per the Canadian provisions for FRP-RC structures. This spiral pitch significantly enhanced peak lateral load, torque, drift, and twist capacities while ensuring column stability at high drift ratios and preventing complex modes of failure under seismic loading, including torsion. The GFRP spirally reinforced columns consistently surpassed the drift threshold requirements specified by the Canadian provisions for FRP-RC structures. In contrast, hoop-reinforced columns failed at lower drifts, with a notable lap-splice failure observed in columns under tm of 0.4. It was concluded that using GFRP hoops with a lap splice length of 40 times the bar diameter is inadequate for columns subjected to seismic conditions with torsional effects.