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RE: PEMB and AISC Seismic Provisions
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: PEMB and AISC Seismic Provisions
- From: Francois Rambau <Francois.Rambau(--nospam--at)StarBuildings.net>
- Date: Fri, 20 Dec 2002 08:34:14 -0600
2002 " accumulative supplement to the IBC" reduces
the height of ordinary braced frames
160 ft to 65 ft in seismic design categories D,E & F.(it also changes the
of ordinary braced frames to ordinary braced frames in light-frame
realize that the proper title should have been "cumulative" since it can only
deal with past revisions
claim no responsibility for the title and frankly this silly title should
be a warning about
of the validity of the changes made without industry
I would not freak out about losing the low building
exception. It looks like they made the code a whole lot
simpler. It basically tells you to design the frame for the
special load combinations and it gets rid of a bunch of other checks. It
does not say that you need to meet B/t ratios or have less than an 80% brace
stress ratio or have less than 70% of braces in tension or compression. You can still
have tension only braces.
Where it sticks you is requiring to meet the slenderness ratios for
chevrons even with special load combinations and making you design connections
for the nominal axial tension strength of the member.
What I am wondering is if the new edition of the IBC limits the
height of ordinary braced frames now?
Scott M. Haan P.E.
Public Works, Engineering Department
Fort Richardson, Alaska
1. Is it true that in the world of the
IBC and AISC seismic provisions, that the historic "low rise buildings"
exemption (Section 14.5 in the AISC Provisions Part 1) has been deleted in
its entirety by Supplement No. 2?
2. If the deletion of the "low rise"
exemption is true, or if it were deleted at the discretion of the
writer of a specific project criteria, is the PEMB industry
capable of meeting the letter of the AISC seismic provisions inclusive of
Supplements 1 and 2, the same as for other conventional SMF/OMF and
SCBF/OCBF steel-framed buildings?
Mark D. Anderson PE