RAM Concept assumes that unbonded post-tensioning stresses are not affected by service loading.

For ultimate strength considerations, RAM Concept treats unbonded tendons as partially bonded tendons:

fps = F(εpse + k Δεp ) ≤ flimit

where

fps	=	tendon stress at ultimate bending strength
F()	=	post-tensioning material stress strain curve (described above)
εpse	=	strain in tendon at effective prestress level
Δεp	=	change in strain in concrete adjacent to the tendon from effective prestress level to ultimate bending
k	=	strain reduction factor, taken as 0.1
flimit	=	limit stress as defined by the effective code

For ACI 318-99, f_limit is defined by equations 18-4 and 18-5. In the calculation of ρ _p used in the ACI equations, RAM Concept assumes the tendons are placed on the more beneficial side of the tendon centroid (the same limiting stress value is used for both positive and negative moment capacity calculations at each cross section).

For AS 3600-2001, f_limit is defined by section 8.1.6. In the calculation of b_efd_p used in the AS equations, RAM Concept assumes the tendons are placed on the more beneficial side of the tendon centroid (the same limiting stress value is used for both positive and negative moment capacity calculations at each cross section).