Seismic and Additions to Existing Buildings
Seismic and Additions to Existing Buildings
(OP)
So if you are connecting an addition to an existing building what is the conscensus on the use of the Response Modification Factor and the system Overstrength Factor? By that I mean if the existing, older building, has different factors than the new addition what Factors would you use for the building as a whole, existing and addition as one building? It is the intent to not seismically separate the two.
Thanks
Thanks






RE: Seismic and Additions to Existing Buildings
The answers to your questions can be found in either IBC chapter 34 or the IEBC. This part of the code places limits on how much you can increase the "demand/capacity ratio" of members before you need to update the member/structure to comply with the existing building code.
RE: Seismic and Additions to Existing Buildings
ASCE 7-10 section 12.2.3.3 says you have to use the least value of R in any given direction. There is an exception for small structures with flexible diaphragms that you can design each line of resistance with its own R factor, but the diaphragm always must use the lower R.
As far as the Overstrength, use whichever goes with the R factor you are using. Since the diaphragm is always using the lower R, us the Ω that goes with it.
RE: Seismic and Additions to Existing Buildings
Once that is triggered, your question about R value goes away as it would now need to meet current code and the R value listed, for the whole thing.
This is why often many additions are added with a separation, especially if the existing structure has a rigid diaphragm, since adding elements could change the entire lateral distribution.. not just at your area of work.