Different R Values
Different R Values
(OP)
Hello everyone,
I have a hillside project that consists of wood framing over steel cantilever column system.
My question is this: can I use R=1.25 for the bottom part and R=6.5 for the upper part? should I do 2 stage analysis or use one of the R values for both levels?
Please see my sketch for better understanding. Thank you very much for your help.
I have a hillside project that consists of wood framing over steel cantilever column system.
My question is this: can I use R=1.25 for the bottom part and R=6.5 for the upper part? should I do 2 stage analysis or use one of the R values for both levels?
Please see my sketch for better understanding. Thank you very much for your help.
RE: Different R Values
You have to check ASCE 7 Section 12.2.3.1. And 12.2.3.2 for the dual stage.
However given that you have cantilever columns at the base, it is unlikely you will meet the requirements of section 12.2.3.2 and will be forced to use 12.2.3.1
Be aware of additional requirements for cantilever columns in section 12.2.5.2.
RE: Different R Values
RE: Different R Values
The way I have done this in the past is Run the model with R = 6.5 design the shear walls. Then run the model with R=1.5 and design the lower level. (Actually R=4 in my case, I'm not thrilled about cantilever columns in the case of the OP).
What is interesting to me is the Exception 3. It suggests that for a house all of 12.2.3.1 does not apply. But that doesn't really tell us how to select the R factor (omega and defl amp as well) for the vertical combination.
If one were gonna try to use this exception I lean towards designing the entire system for R = 1.5.
For the record I don't recommend WSW over Cantilever columns to start out with, and I would even less recommend using any exception to avoid the requirements of this vertical combination requirement 12.2.3.1
RE: Different R Values
RE: Different R Values