SANISTEEL: Simple Anisotropic Steel Plasticity Model

A simple constitutive model for the inelastic response of steel under monotonic and random cyclic loading conditions is developed within the framework of bounding surface plasticity. The particular feature that distinguishes this model from other similar ones is the ability of the bounding surface formulation to describe in a very simple way the initial “plateau” type of perfectly plastic response that many kinds of structural steels exhibit upon initial yield in tension or compression, before hardening begins. The key constitutive element is to assume a fixed nonhardening bounding surface during the plateau response until a cumulative plastic strain threshold is reached, while the yield surface softens isotropically and hardens kinematically. In this way not only monotonic but also cyclic loading within the plateau range can be easily described. Three kinematic hardening rules for the bounding surface are explored. The development is focused on uniaxial loading conditions that are typical in many structural engineering applications employing a fiber-based discretization of the cross section. Several simulations to demonstrate the effectiveness of the proposed model are presented. Finally, its extension to a multiaxial stress generalization is concisely presented for future use.