Larry,
If you use the load combinations from IBC Section 1605.3.1 then a 1/3 increase in allowable stresses is not permitted. If you use the IBC load combinations from Section 1605.3.2 then you are allowed to use the 1/3 increases but ONLY if allowed by the material chapter. Unfortunately for steel neither the IBC nor AISC have the 1/3 increase factor anymore. I believe the only material left is masonry and in some cases geotechnical soil bearing.
Thomas Hunt, S.E.
Fluor
| Larry Hauer <lhauer@live.com> 04/21/2009 02:09 PM Please respond to seaint |
|
I am checking existing steel roof framing members for support of replaced roof top mechanical equipment. Obviously, I need to design per the '06 IBC/'07 CBC for seismic forces and will be using ASD equation 16-20 of the IBC/CBC. Based on Sec. 1605.3.1.1 it looks like a 1/3 increase in allowable stresses for the existing steel roof members is no longer allowed when considering seismic loads. Is this correct?
Thanks in advance,
Larry Hauer
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