Seismic performance of reinforced concrete double-column piers in the longitudinal direction of the bridge under the combination of compression, bending, shear, torsion

To investigate the seismic performance of reinforced concrete (RC) double-column piers, particularly unequal-height double-column piers under the combination of compression, bending, shear and torsion in the longitudinal direction of the bridge, five 1:5 scale RC double-column pier specimens were designed and fabricated. The experimental parameters included the column height ratio and the applied displacement ratio by two actuators. The piers with different column height ratios were tested under the quasi-static loading with varying horizontal actuator displacement ratios in the longitudinal direction of the bridge. The results show that the increase of torsional effect by increasing the column height ratio and applied displacement ratio induced the change of failure mode of the test specimens from bending to bending-torsional failure and reduced the bending bearing capacity of double-column piers in the longitudinal direction of the bridge. With an increase in the applied displacement ratio, the torsional bearing capacity, torsional ductility, torsional stiffness, and torsional energy dissipation increased, while the bending bearing capacity and bending ductility and bending stiffness decreased. However, the bending energy dissipation did not decreased significantly (almost unchanged). Additionally, with an increase in the column height ratio, the bending bearing capacity, bending stiffness, and bending energy increased, while the torsional bearing capacity, bending and torsional ductility, torsional stiffness, and the torsional energy decreased, particularly when the column height ratio was greater than 4:3.