Seismic performance of piers reinforced with GFRP/steel bars and double spiral stirrups

Conventional hybrid-reinforced piers have unresolved issues of seismic-induced shear failure and steel bar corrosion. To solve these problems, a corrosion-resist pier structure reinforced with GFRP/steel bars and double spiral stirrups is proposed. Eight piers were tested and compared under horizontal quasi-static reciprocating loading. The influence of parameters on the seismic performance of the piers was investigated, including the reinforcement configuration, spiral core diameter, core longitudinal bar diameter and shear span ratio. The test results show that all the specimens had a flexural failure. The double spiral stirrups configuration provides multiple confinements on concrete, improves the bearing and energy dissipation capacity of piers, and avoids the shear failure in piers. At the same time, corrosion of steel bars is prevented because the outer steel bars are replaced by GFRP bars. While the peak loads of the hybrid-reinforced piers were a little smaller than those of the steel-reinforced piers, their ductility, ultimate displacement and plastic hinge length improved significantly. A parameter analysis of finite element models was made to determine the influence of the spiral core diameter, core longitudinal bar diameter, concrete strength and outer GFRP longitudinal bar diameter on the peak load of the piers. The results show that increasing the outer and interior longitudinal bar diameters and spiral core diameter can improve the structural stiffness and bearing capacity of the piers effectively. This study provides reference for the safety design of bridge substructures under offshore earthquake actions.