Prestressed reinforcement is modeled as using a power formula. The curve is defined by four parameters:

• E_ps = the elastic modulus at zero strain (from materials window)
• F_py = the "yield" stress of the reinforcement (from materials window)
• F_pu = the ultimate stress of the reinforcement (from materials window)
• γ_m = partial safety factor for materials

These four parameters are used to calculate the three parameters needed for the power formula, as described in Post-tensioning Material Stress-Strain Curves in "Section Design Notes". The three parameters are:

E_ps' = E_ps

F_py' = F_py/γ_m

F_pu' = F_pu/γ_m

For strength considerations, a γ_m of 1.05 is used (Amendment 1 and 2).

For strength considerations, a γ_m of 1.15 is used (Amendment 3).

For all other considerations (including accident strength) a γ_m of 1.0 is used.