R factor for two different structural systems

[lesgiu]

Hello,

I'm doing the structural evaluation of a 3-story building that has in one direction only confined masonry. For earthquake loads the building doesn't comply with any requirement and we are adding concrete shear walls. During the evaluation I used an R factor of 3 but now that I have added new concrete shear walls I wonder if I can increase the R factor to 6? or should I keep it as R=3?

I would appreciate if you can give me your comments.

Thanks

 

[msquared48]

If you ignore the existing CMU, 6. Otherwise 3.

Mike McCann
MMC Engineering

 

[SteelPE]

If you are designing the system to comply with the increased R factor then you should use the increased R factor. I have a current project where the client wants to use 2 walls of an existing URM building in his new structure (due to permitting concerns). I utilizing braces for the LFRS of the new building. I am not relying on the existing URM and have told the client that the existing URM now need to be attached to the new structure as if was a facade and that is how I am looking at the URM section of the new building. Kind of cheap... but as far as I can tell allowed by the code.