  An elasto-plastic model for concrete, based on a recently-proposed yield
surface and simple hardening laws, is formulated, implemented, numerically
tested and validated against available test results. The yield surface is
smooth and particularly suited to represent the behaviour of rock-like
materials, such as concrete, mortar, ceramic and rock. A new class of isotropic
hardening laws is proposed, which can be given both an incremental and the
corresponding finite form. These laws describe a smooth transition from linear
elastic to plastic behaviour, incorporating linear and nonlinear hardening, and
may approach the perfectly plastic limit in the latter case. The reliability of
the model is demonstrated by its capability of correctly describing the results
yielded by a number of well documented triaxial tests on concrete subjected to
various confinement levels. Thanks to its simplicity, the model turns out to be
very robust and well suited to be used in complex design situations, as those
involving dynamic loads.
