Clarification on NBC 2005 - Rd Ro

[PAstructural08]

In the NBC it is unclear to me what to increase the seismic loads by....do you multiply the seismic loads by Rd (Ductility-Related Force Modification Factors) or by Ro (Overstrength-Related Force Modification Factors, or do you multiply Ro and Rd together and use that??

The wording in the NBC is confusing!

 

[JoshPlumSE]

I'm not all that familiar with the NBC. But, based on your descriptions, I would guess that you divide by Rd. That sounds equivalent to the R value in the US codes.

Then when you are designing critical items (connections and such), you would multiple by Ro. That sounds equivalent to the Omega overstrength factor in the US codes.

 

[PAstructural08]

That's what I thought as well.

In the NBC section 4.1.8.15(5) reads, "the design forces need not exceed the forces determined in accordance with Sentence 4.1.8.7(1), multiplied by RdRo."

Where sentence 4.1.8.7(1) just describes whether to use the static equivalent method or a dynamic anaylsis for seismic forces.

 

[PAstructural08]

Also Rd is the Ductility-Related Force Modification Factor...where as in the ASCE 7-05, R is the Response Modification Factor

 

[VoyageofDiscovery]

This RdRo is a product of the two, therefore use that.