Seismic Performance of Square RC Bridge Columns under Combined Loading Including Torsion with Low Shear

During earthquake excitations, reinforced concrete bridge columns can be subjected to a combination of axial load, shear force, flexural moments, and torsional moments. The torsional moment can be much more significant in columns of bridges that are skewed, curved, have unequal spans, or unequal column heights. Combined loading including torsion can result in complex flexural and shear failure of these bridge columns. This paper presents an experimental study on the seismic behavior of square reinforced concrete columns under combined cyclic flexural and torsional moments. The columns in this study were designed with anaspect ratio of six and tested under various loading conditions: cyclic flexural moment and shear force, cyclic pure torsion, and combined cyclic shear force, bending, and torsional moments. Test results reveal that (1) the flexural and torsional capacity is decreased due to the effect of combined loading, (2) the failure modes and deformation characteristics are changed, and (3) the damage zone tends to move upwards from the typical flexural plastic hinge zone due to the effect of additional torsional moment. The effects of combined loading on the hysteretic loading-displacement response, and damage characteristics are discussed.