A nonlocal damage model for mild steel under inelastic cyclic straining

A material model for mild construction steel is developed in order to analyse damage in 3D-steel structures under inelastic cyclic straining as it may occur during earthquakes. The constitutive equations consider viscoplastic material behavior, isotropic and kinematic hardening, softening, and isotropic ductile damage. For compression the evolution equation for ductile damage is disabled and the impact of damage on the material stiffness is reduced. The phenomenon of strain localization and its mesh-independent modelling is taken into account by a nonlocal implicit gradient enhanced extension provided by an additional partial differential equation for the nonlocal damage variable. The global structural stability is evaluated by a global damage indicator.