Curvature ductility of biaxially loaded reinforced concrete short columns

Modern structural design codes strongly rely on the dissipative capacity of structural elements to resist the relevant seismic actions at ultimate limit state. The full exploitation of dissipative capacities can, however, be achieved only in presence of adequate local and global ductility. Local ductility in cast-in situ and precast reinforced concrete buildings refers to curvature ductility of the critical part of the structural elements where plastic hinges are expected to occur. Bidirectionality of the seismic action is taken into account by the standards, in a more or less conventional manner, for the evaluation of stresses on the structure. Nevertheless, there are no specific indications of how to take biaxial bending into account in verifying the curvature ductility of reinforced concrete short columns. On the basis of this observation, a specific parametric investigation was planned and performed, with different values of angle between neutral axis and section principal axis, longitudinal reinforcement ratio, transverse reinforcement ratio, normalized axial force and section aspect ratio. Its results allowed for verification of the influence of bending moment directionality and of other parameters on the deformation capacities of reinforced concrete short columns beyond their own elastic limits.