The strength reduction factor, also known as Φ (phi) factor, is used in reinforced concrete design & analysis. For different reinforced concrete members various values of Φ factors are used. The strength reduction factors for ACI code is provided at section 9.3.
Following are the reasons to use Φ (phi) factor:
- Possible variations in dimensions.
- Possible variations in material strength.
- Possible inaccuracies in the strength equations.
- To ensure a good level of safety of reinforced concrete structures.
The above mentioned variation may be raised due to various reasons including poor workmanship, lack of understanding, low strength material ingredients etc.