For service conditions, RAM Concept assumes that unbonded tendon stresses are not affected by cross section strains.

For ultimate resistance moment calculations, RAM Concept ’s general approach to unbonded tendon stress-strain curves is detailed in "Unbonded Post-tensioning Stress-Strain Curves – Program Implementation" in Chapter 51, Section Design Notes .

For ACI 318-11, the maximum unbonded tendon stress, f_limit, is defined by equations 18-2 and 18-3. In the calculation of ρ_p, RAM Concept assumes that the tendons are placed on the more beneficial side of the cross section centroid (the same limiting stress value is used for both positive and negative moment capacity calculations at each cross section).