Help Needed with Material Model Arguments

[motalaat]

I am trying to use Steel02, and Concrete02 materials. Does anybody now what typical value to use for the "unloading stiffness ratio" for concrete. More importantly, any idea how the isotropic hardening model variables works? To be more speciific:

Let's consider similar hardening in compression and tension. We need to input a1=a3 and a2=a4 model parameters. Now, a1 is suposed to be "increase of yield envelope as proportion of yield strength after a plastic strain of a2*eps_y". Now, let us set our temporary coordinate origin at (f_y, eps_y), if we move forward one eps_y, the stress will rise up by SH*E_s*eps_y, where E_s is the elastic steel modulus. Now, according to that, and given these two points on te curve, and assuming full isotropic hardening, one has a following options.
1. a1 could be SH
2. a1 could be (1+SH)
3. a2 could be unity
4. a2 could be <1, where the elastic portion is subtracted from the additional eps_y we moved.


Additionally, are a1,..,a4 input as absolute values, or should one take care ofsigns himself? As an example, for a 100% or a 50% isotropic hardening as we know, what shoud be an example Tcl command?

Thanks for reading through

[jwaugh]

For the unloading slope ratio for concrete02 I use 0.1 in my analysis of walls, I don't know if that is right I found it somewhere and it seems to give a reasonable result.

For the strain hardening parameters I don't know, I don't use the isotropic strain hardening features in Steel02.