A gradual spread inelasticity model for R/C beam-columns, accounting for flexure, shear and anchorage slip

A new beam-column model is developed for the seismic analysis of reinforced concrete (R/C) structures. This finite element consists of two interacting, gradual spread inelasticity sub-elements representing inelastic flexural and shear response and two rotational springs at the ends of the member to model anchorage slip effects. The flexural sub-element is able to capture gradual spread of flexural yielding in plastic hinge regions of R/C members. The shear sub-element interacts throughout the analysis with the flexural sub-element, in the location of the plastic hinge regions, in order to capture gradual spread of inelastic shear deformations as well as degradation of shear strength with curvature ductility demand based on an analytical procedure proposed herein. The skeleton curves and hysteretic behaviour in all three deformation mechanisms are determined on the basis of analytical procedures and hysteretic models found to match adequately the experimental results. Empirical formulae are proposed for the shear distortion at onset of stirrup yielding and onset of shear failure. The proposed element is implemented in the general finite element code for damage analysis of R/C structures IDARC and is validated against experimental results involving R/C column and frame specimens failing in shear subsequent to yielding in flexure. It is shown that the model can capture well the hysteretic response and predict reliably the type of failure of these specimens.