Seismic vulnerability of r.c. circular bridge columns

The seismic response of highway viaducts with bearing-supported superstructures and characterized by structural regularity, essentially depends on the behaviour of its piers. Therefore, the vulnerability analysis of the most exposed column often coincides with that of the whole structure. This paper is focused on a simplified procedure that furnishes the expected damage vs ground acceleration for homogeneous families of piers, characterized by same design and site parameters. The procedure preliminarily analyzes different forms of column failures (flexural failure for inadequate confinement of the plastic hinge zone; flexural strength degradation in sections with lap-spliced reinforcement; shear failure; buckling of reinforcements). Subsequently, on the basis of a comparative analysis, the most probable condition of collapse is determined. The algorithm utilizes an approximated closed-form approach, properly obtained, in terms of longitudinal reinforcement, transverse confining steel, and base axial compression.