i make FEA for my master research in ANSYS PRO., i simulate a prestressed concrete beam with two precast units connected by contact element (CONTA.52). i used solid 65 for concrete modelling and link 8 for for prestressing steel with initial strain, i entered the stress strain curve for the concrete with linear isotropic, concrete and multilinear isotropic in five points as below:

strain=0.0004    stress = 12 Mpa

Strain = 0.001   stress = 30 Mpa

Strain = 0.0015   stress=37.5 Mpa

strain =0.002      stress = 40 Mpa

strain = 0.0003   stress = 40 MPa

i applied the load up to failure, then, i found that at the contact area, the strain =0.003 but the stress = 34 Mpa, however from the stress strain curve which i entered it must be = 40 Mpa.

i tried to change the stress strain curve to be the fc'=60 Mpa (just as a trial). and i applied the same load, i found that the strain at that load = 0.007 but the stress still = 34 Mpa at the same node

i hope if someone could help me to pass this problem

thanks