Strength Reduction Factors ()

Strength Reduction factors are needed to take forces between ultimate (Mu) loading and nominal loading (Mn). They are a function of the net tensile strain.

Note: The strength reduction factor , will vary in respect to εt

ACI 318 Chapter 9[1]:

  • Compression
    • = 0.65
    • = 0.70 (Spiral reinforcement)
  • Tension
    • = 0.9
  • Shear
    • = 0.75

ACI 318 Appendix C[1]:

  • Compression
    • = 0.70
    • = 0.75 (Spiral reinforcement)
  • Tension
    • = 0.9
  • Shear
    • = 0.85

For transition regions (regions between tension and compression):

ACI 318 Chapter 9[1]:

  • Transition Region
    • = 0.48 + 83εt [ACI 9.3.2]
    • = 0.57 + 67εt (Spiral reinforcement) [ACI 9.3.2]

ACI 318 Appendix C[1]:

  • Transition Region
    • = 0.57 + 67εt [ACI C.3.2]
    • = 0.65 + εt (Spiral reinforcement) [ACI C.3.2]

Significance of the Strength Reduction Factor ()

As stated in the intro, the strength reduction factors are used to jump between Nominal Loads and Ultimate Loads.

Mn ≥ Mu
Vn ≥ Vu

References

  1. American Concrete Institute, "ACI 318-05", 2005

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