Concrete LRFD Design

The ACI uses LRFD? Design. Below you will find the following factors needed to factor your loads when checking concrete design. They will vary dependent on what what section of the ACI 318 you decide to use (Chapter 9 or Appendix C).

Note: That you must remain consistent when choosing to use either Chapter 9 or Appendix C. Your Strength Reduction Factors, and numerous other factors change dependent on which method you choose.

Chapter 9[1]

Dead Load + Live Load

  • U = 1.4D
  • U = 1.2D+1.6L

...+Wind

  • U = 1.2D+1.6L+0.8W
  • U = 1.2D+L+1.6W
  • U = 0.9D+1.6W

...+Seismic

  • U = 1.2D+L+E
  • U = 0.9D+E

If Wind or Seismic are considered, the load factor on L (1.6,1, and 1 respectively) can be reduced to 0.5 for all structures except the following: garages, areas for public assembly, and areas where the live load exceeds 100 psf.

where:

U = Strength required to resist factored loads
D = Dead Load
L = Live Load
W = Wind Load
E = Seismic Load

Appendix C[1]

Dead Load + Live Load

  • U = 1.4D+1.7L

...+Wind (or Seismic)

  • U = 0.75(1.4D+1.7L)+(1.6W or E)
  • U = 0.9D+(1.6W or E)

References

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

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