Deformation capacity of non-conforming r.c. columns under compressive axial load and biaxial bending

•Ultimate chord rotation capacity of existing r.c. columns biaxially loaded.•Theoretical rotation domains based on Load Contour method.•Practice-oriented approach for evaluating simplified rotation domains.

In a performance based approach, the knowledge of ultimate capacity of reinforced concrete (r.c.) columns subjected to simultaneous compressive axial load and biaxial bending becomes essential to correctly assess the seismic capacity of existing structures. In the present work, the reduction of ultimate deformation (i.e. rotational) capacity of r.c. members due to the two components of bending moment is analysed by using a specific simplified numerical model. The influence of axial load, geometry, amount of longitudinal reinforcement and mechanical properties on the ultimate chord rotation of r.c. columns is investigated on a dataset of 780 numerical tests on non-conforming columns with plain bars governed by flexural mode. Then, a practice-oriented formulation for the ultimate rotation domain, based on the Load Contour method extended to the chord rotations, is proposed and discussed.