Study of Biaxial Shear Failure Envelope of Reinforced Concrete Columns

Several scenarios can trigger bi-axial shear in reinforced concrete (RC) vertical members such as wind actions, earthquake, column loss induced by explosions and/or impacts. The majority of standard codes impose uniaxial shear verification of vertical members and neglect the interaction between shear forces and bending moments acting along the two principal directions of inertia of the transversal cross section. Moreover, bi-axial shear interaction curves proposed by codes are based on the fitting of experimental data conducted on heavily reinforced specimens. In this paper, the bi-axial shear failure envelope of existing RC columns, is investigated. A database previously published by Authors on experimental data on beams and columns tested under bi-axial loading is updated. Afterwards, the experimental shear resistances of the database's members subjected to both monotonic and cyclic loading are compared with analytical predictions. Three different formulations are adopted for the analytical calculation of the uniaxial shear resistance: (i) Model Code 2010, (ii) Eurocode 8 and (iii) the cyclic shear resistance recently proposed by Biskinis and Fardis. Such resistances are adopted to create the bi-axial shear failure envelope. Finally, the shape of the bi-axial shear failure envelope is critically analysed in order to select the formulation that provides the best fitting between experimental and analytical bi-axial shear resistances.