Do you perhaps mean post-yield stiffness ratio?
If it is that, a quick search in the sap2000 help (or on the internet), will probably give you something like this:
"The post-yield stiffness ratio applies for nonlinear analyses. It is the post-yield stiffness divided by the initial stiffness."
Should mention that this quote is taken for rubber isolators in SAP2000, so it probably does not apply to beams.