Seismic Performance Assessment of GFRP-RC Circular Columns under High Torsion Combined with Bending and Shear Cyclic Loading

This study presents the results of an investigation into the seismic performance of six large-scale concrete circular columns reinforced with glass fiber–reinforced polymer (GFRP) reinforcement. Among these columns, one underwent concentric reversed cyclic lateral loading, causing bending and shear, while the remaining five columns experienced eccentric cyclic lateral loading, causing additional torsional stresses. The test variables included the torsion-to-bending moment ratio, transverse and longitudinal reinforcement ratios, and concrete compressive strength. The test results indicated that the concurrent cyclic torsion and lateral drift reversals significantly altered the behavior of concrete members in terms of mode of failure, lateral load resistance, drift capacity, and energy dissipation. It was found that adequately confined columns exhibited a notable reduction in concrete core deterioration, thereby preventing the decline in both bending and torsional strength. Furthermore, the paper examined the validity of the North American design provisions predicting the torsional strength of GFRP-reinforced concrete members subjected to combined seismic loading. Amendments to the GFRP tensile stress limits specified in these provisions were introduced, yielding better and safer predictions for the torque capacity of the tested columns.