To: "Seaint list (E-mail)" <seaint(--nospam--at)seaint.org>
Subject: Re: IBC special seismic load combinations for steel design
From: Scott Maxwell <smaxwell(--nospam--at)engin.umich.edu>
Date: Thu, 5 Apr 2001 20:21:35 -0400 (EDT)
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
moment...plus 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
> 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.
> Scott M Haan P.E.
> Plan Review Engineer
> Building Safety Division http://www.muni.org/building
> Development Services Department
> Municipality of Anchorage
> phone:907-343-8183 fax:907-249-7399