Unloading/reloading rules in Concrete02 ?

[tperea]

I was wondering if somebody knows what the rules are for the unloading/reloading stiffness in the Concrete02 material model. I think this cyclic model is not the one proposed by Karsan-Jirsa, which is used in concrete01 and concrete04, right?

I'd really appreciate if you can give me a reference. The OpenSees manual don't provide the details for this. The Concrete02 source code mentions an "EERC report (Fig. 2.11, equations 2.31, 2.32, 2.35)", with no more extra details.

I appreciate your attention.