yield strain

[martinmasanes]

Dear all:
Im usig a fiber model with steel02 material. The response of the elements (forceBeamColumn) is recorded with basicDeformation recorder.

What I want to know is how can I compute the yield strain (or an approximation to it) with the mentioned material model.

Im asking this because computing the obious ratio fy/E=420/200000=0.0021 doesn't seem to be correct. For example for a beam of 9108mm the corresponding yield deformtion should be 0.0021*9108mm=19.1mm, but it seems to be about 13mm or 14mm.

the parameters of the material model are:
fy=420MPa
E=200000MPa
b=0.0055
R0=20
CR1=0.925
CR2=0.15


THANKS!!!