What is the specific meaning of the parameters of Steel02, i

[bridger]

In the uniaxialMaterial Steel02, I know the cr1 and cr2 are the parameters that control the transition from elastic to plastic branches. And a1 – a4 are the parameters that define the isotropic hardening. But I want to know the specific meanings of these parameters, or the formula including these parameters to define the constitutive model of steel, or references that include these parameters?
Thank very much!

[vesna]

All formulas are contained in the source code:
http://opensees.berkeley.edu/WebSVN/lis ... f049a7b320