I am modeling a Push-off shear transfer test specimen. This consists of two "blocks" of concrete connected along an interface with direct shear applied along the interface. I also modeled stirrups intersecting this interface as volume elements with a polygon shape and assigned the 3D von Mises material model to them. The model is producing results that agree with experimental results, but there is an issue with the steel von Mises behavior. I have entered a 0 value for the H parameter but my elements are clearly showing hardening when I process the stress/strain behavior. My understanding from all of your documentation is that the material should behave ideally plastic if I have H = 0. What could be causing these undesired results? And is it something that I could work around?