  This work focuses on the numerical modelling of confined concretes when
subjected to multiaxial loading accounting for a nonlinear material response.
Particularly, an improved return mapping procedure is here presented to cope
with the issue of singularities (corners) in the yield surface, able to catch
locally the optimal return point on the active yield surface. The algorithm is
applied to the Menetry and Willam's yield surface, with a plastic potential as
suggested by Grassl and the softening law proposed by Cervenka suitable for
concrete materials. The model capabilities to reproduce the confined behaviour
of concrete, as well as its post-peak behaviour, and to predict perfect
plasticity or softening are here discussed. The proposed approach can be
applied to any elastoplastic material with singular yield surface along the
hydrostatic axis.
