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Re: IBC special seismic load combinations for steel design

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While I can really answer your question (don't have the time to look at it
and then switch off the "brain power conservation mode" at the I am sure someone else with more brain power will respond),
I can ask a dumb question.  Are you using the 1997 AISC Seismic Provisions
WITH the 1999 Supplement No. 1?  This is actually what the 2000 IBC
references.  I don't know if the Supplement No. 1 deals with the sections
that you are dealing with since I cannot located my electronic copy of
Supplement No. 1 and AISC seems to have removed it from their web site.

HTH, but likely does not...


On Thu, 5 Apr 2001, Haan, Scott M. wrote:

> Hello everyone:
> IBC 1605.4 indicates the IBC  special seismic load combinations [combos with
> Em] are required where required by Sections 1613 through 1622 or by Chapters
> 18 through 23.  Chapter 22 does not specifically require the special load
> combinations.  IBC Section 2212.1.2 requires steel structures to be designed
> and detailed in with AISC Seismic Part I or Part III and there are no
> amendments to AISC Seismic.  AISC Seismic Part 1 Section 8.2 indicates to
> use the AISC "additional load combinations" for column design when
> Pu/[phi*Pn]>.4. 
> IBC 1617.1.2 special seismic load combinations Em include a vertical
> component of + - .2*SDS*D.  The AISC Seismic Part 1 Section 4.1 OMEGAo*Qe
> load combinations do not include the + - .2*SDS*D and the section indicates
> Qe is the horizontal seismic affect.  
> Is this an oversight that the IBC adoption of the AISC Seismic Provisions is
> not amended to specifically require the use the IBC special load
> combinations?  Why-why not? The IBC special load combinations require the
> additional .2*SDS*D vertical effect and this can be significant  for a
> multistory building.
> PS.  IBC 1605.1 indicates buildings need to be designed for the load
> combinations indicated in 1605.2 and 1605.3 and the load combinations in
> chapters 18 through 23.  IBC 1605.1 also indicates buildings need to be
> designed for the special seismic load combinations when required by Section
> 1620.1.7 or Section 1620.3.5.  This appears to be a misreference and it
> appears 1620.1.6, 1620.1.9 and 1620.3.4 are intended.
> Respectfully,
> Scott M Haan P.E. 
> Plan Review Engineer
> Building Safety Division
> Development Services Department
> Municipality of Anchorage
> phone:907-343-8183  fax:907-249-7399
> mailto:haansm(--nospam--at)