Response Modification Coefficient
Response Modification Coefficient
(OP)
What would you classify the R value for a 4 story building, laterally supported utilizing X-braces? I am using the IBC 2000 code.
TIA,
Mark
TIA,
Mark
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Response Modification Coefficient
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RE: Response Modification Coefficient
RE: Response Modification Coefficient
If you have a steel framed building, in Table 1617.6, you would fall under "Building Frame Systems" (item 2).
Now, with X braces, you could either be type C, Special concentrically braced frames (R = 6); or type D, Ordinary Concentrically braced frames (R = 5)
The special frames require a higher degree of detailing vs. the ordinary.
RE: Response Modification Coefficient
RE: Response Modification Coefficient
Yes, Taro, the bracing is tension bracing on light gauge studs.
I also thought that R = 2 was the appropriate value. I just couldn't believe the seismic base shear would increase by 3!! After seeing some X-braces in the field, however, it does not seem like a bad idea at all. (Many braces were loose, poorly connected, etc...)
RE: Response Modification Coefficient
Can you have tension ONLY braces for seismic in this condition? I thought that a minimum percentage of braces have to be split between tension/compression.
RE: Response Modification Coefficient
Yes, the bracing is light gage flat strap bracing that carries tension only. That is why the R factor is so low. Better performance would be achieved by using structural panel sheathing (R=6).