Seismic Performance of Reinforced Concrete Bridge Columns Subjected to Combined Loading Including Torsion

Reinforced Concrete (RC) bridge columns could be subjected to combined flexural, axial, shear and torsional loading during earthquake excitations. This fact is particularly true for bridges that are skewed, curved, have unequal spans, or unequal column heights. In addition, multi-directional earthquake motions, significant vertical motions, and structural constraints due to stiff decking, movement of joints, abutment restraints, and soil conditions may also lead to combined loading effects. This combination of seismic loading can result in complex flexural and shear failure of these bridge columns. As part of a NEES-R funded study, a total of 14 columns are being tested under various loading conditions: cyclic bending, cyclic torsion, biaxial bending, and combined cyclic bending and torsion. This paper presents the results of the first three columns tested under pure cyclic bending, pure cyclic torsion, and combined cyclic bending and torsion respectively. The effects of combined loading on the hysteretic load-deformation response, reinforcement stress variations, and plastic hinge characteristics are discussed. Finite element models of the RC columns were developed and analyzed for different combinations of bending and torsion to guide the experimental study. The finite element predictions are compared with the experimental data and the results are discussed. Based on the test results, it is concluded that combined loading reduces the flexural and torsional capacity of a column and can also change the failure modes and deformation characteristics.