Reinforced concrete (RC) bridge columns can be subjected to flexural, axial, shearing, and torsional loading during earthquake excitations, resulting in complex failure modes. However, in spite of its explicit occurrence during earthquake excitations and significant effect on final failure modes, the torsional loading effect on the seismic performance of RC columns has not been studied in depth. In particular, understanding interacting behavior of each loading condition should be preceded to satisfy the increased demand for seismic design. In this context, this study aims at improving the knowledge of seismic performance of RC bridge columns under combined loading, including torsion through the experimental study carried out by Missouri University of Science and Technology. The experimental study focused on investigating the effect of different cross-sectional shapes (circle and square), hysteretic torsional and flexural response, damage distribution, and ductility characteristics with respect to various torsion-to-bending moment (T/M) ratios. Finally, interaction diagrams were established based on experimental results. Copyright © 2012, American Concrete Institute.