Effect of torsion on the flexural ductility of reinforced concrete bridge columns

Under earthquake loading, bridge superstructures will in general experience both translational and rotational motions. The rotational motions arise from a number of effects, including shaking response of asymmetrical structures, wave passage effects, and ground failure including fault-rupture at the bridge site. As a consequence, supporting columns may be subjected to significant torsion, which is often ignored in typical design practice. The degree to which torsion reduces bridge safety because of reduced lateral load strength or more importantly because of reduced deformation capacity, is unclear.;A research program is designed to investigate whether torsional response of RC bridge construction has a significant effect on the strength and deformability of the supporting bridge columns. Four one-third scale reinforced concrete bridge columns are tested in the laboratory under simulated seismic loading. Three circular columns and one oblong column are subjected to a compressive axial load and varying degrees of lateral and torsional loading, characterized by the imposed twist to drift ratio. Observed and measured behavior is strongly affected by the twist to drift ratio; deformation capacity is reduced by the associated twist.;Analytical models are developed to understand the effect of twist on column response. The degree of anticipated twist occurring in actual bridge structures is investigated using simplified bridge systems under a variety of loadings, including near-fault ground motions and ground motions across fault-rupture zones.;Design implications are addressed and a design procedure is proposed for enabling columns to achieve their estimated deformation capacity under simultaneous lateral and twisting deformations.