Bonded Prestressed Reinforcement Behavior
Prestressed reinforcement is modeled as using a power formula. The curve is defined by four parameters:
- Eps = the elastic modulus at zero strain (from materials window)
- Fpy = the "yield" stress of the reinforcement (from materials window)
- Fpu = the ultimate stress of the reinforcement (from materials window)
- γm = 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:
Eps' = Eps
Fpy' = Fpy/γm
Fpu' = Fpu/γm
For strength considerations, a γm of 1.15 is used.
For all other considerations a γm of 1.0 is used.
This curve is similar but slightly different than the Stress Relieved Curve as shown in IS : 1343 - 1980 Figure 5A for normal prestressing materials, assuming this curve depicts strain percentage and not actual strains.