Asymmetric bilinear curve - bl_asm

This is a curve frequently employed to model idealised asymmetric elastic-plastic behaviour. An isotropic hardening rule is adopted and six parameters need to be defined in order to fully characterise this response curve:

Initial stiffness in positive region (K0+)
The default value is 20000

Yield force in positive region (Fy+)
The default value is 1000

Post-yield hardening ratio in positive region (r+)
The default value is 0.005

Initial stiffness in negative region (K0-)
The default value is 10000

Yield force in negative region (Fy-)
The default value is -1500

Post-yield hardening ratio in negative region (r-)
The default value is 0.01

Notes

1. Stiffness values K0(+) and K0(-) must be positive.
2. The image above reflects those (relatively common) cases where the post-yield stiffness is not very high and the maximum force does not thus reach a value that is twice its yield counterpart, making the curve behaviour resemble that of a kinematic-hardening curve such as bl_kin. This however will not be the case on all instances, and hence an isotropic-hardening type of response (such as that shown clearly in here) should be expected.