Quadrilinear symmetric curve - quad_sym

This is a curve employed to model idealised quadrilinear behaviour. An isotropic hardening rule is adopted and five parameters need to be defined in order to fully characterise this response curve:

Yielding strength (Fy)
The default value is 500

Yielding displacement limit (dy)
The default value is 0.005

Ultimate Strength (Fu)
The default value is 550

Ultimate displacement capacity (du)
The default value is 0.02

Residual strength
The default value is 200