Behaviour of circular concrete bridge columns internally reinforced with GFRP under reversed-cyclic loading including torsion

Abstract

This study investigates experimentally the behaviour of circular reinforced concrete (RC) bridge columns internally reinforced with glass-fiber-reinforced polymer (GFRP) bars and spirals under cyclic combined loading conditions of bending, shear, and torsion. The study involved testing four large-scale column-footing connections, including one steel and three GFRP-RC columns. The effects of the reinforcement type (GFRP and steel) and torsion-to-bending ratios (tm) (0, 0.2 and 0.4) on seismic indexes, such as mode of failure, deformation and twist capacity, hysteretic responses, energy dissipation, ultimate strength and stiffness were evaluated. The results showed that the mode of failure varied according to the tm. Under combined loading with a tm of 0.2, both GFRP-RC and its steel-RC counterpart specimen were able to sustain similar lateral load and torsional moment capacities. Moreover, under the effect of combined loadings, the GFRP-RC columns showed a stable seismic response with adequate deformability. The GFRP-RC columns exhibited a decrease in ultimate lateral load and displacement capacity with increasing tm, however, their torsional moment carrying capacity increased. All GFRP-RC columns met the ductility requirements of North American codes, while their torsional stiffness degraded faster than their bending stiffness under combined torsion and bending loadings.