Plastic curve - plst

This is a curve frequently employed to model idealised rigid-plastic behaviour, sliding bearings, FPS (friction pendulum system) isolating devices, hydraulic or lead-extrusion dampers, and so on. A kinematic hardening rule is adopted. Two parameters need to be defined in order to fully characterise this response curve:

Initial force (F0)
The default value is 10000

Post-yield stiffness (K0)
The default value is 5

Note: Unloading and reloading stiffness is taken as infinite, which means that, if a sufficiently small analysis time-step is used, then the unloading/reloading branches of this response curve result practically vertical. With large time-steps, on the other hand, a finite unloading/reloading stiffness is obtained through the ratio 2F0/Δt.