Dear kanchana,
I.1. by saying that eq. 2.57 does not match with Fig. 2-21, do you just mean eps_c versus eps_c_p, or something else?
I.2. The references are included at the end of each ATENA Theory Chapter.
II.1. Fig. 2-4 is for SBETA, the figures in section 2.2.4 for the NLCementitious material model family.
II.2. Please note the material models are NOT based on stress-strain (except for the linear elastic parts), but crack opening and plastic displacement + crack band and crush band.
II.3. I understand you are interested in some specific region of the material model. Could you specify your interest such that we can answer (or direct you to the answer)?
II.4. You may be also interested in the utility New Material Driver, which is included in ATENA 5.7.0 (currently at beta testing stage, available to all users with valid maintenance upon request) and which allows you to apply any load history to a single material point, and plot the response.
Regards.