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RE: PEMB and AISC Seismic Provisions

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         2002 " accumulative supplement to the  IBC" reduces the height of ordinary braced frames
         from 160 ft to 65 ft in seismic design categories D,E & F.(it also changes the definition
          of ordinary braced frames to ordinary braced frames in light-frame construction)
         (I realize that the proper title should have been "cumulative" since it can only deal with past revisions
         but I claim no responsibility for the title and frankly this silly title should be a warning  about
         some of the validity of the changes made without industry participation )
         Francois Rambau
         Star Buildings Systems

 -----Original Message-----
From: Haan Scott M DPW CIVIL ENGR(n) [mailto:scott.haan(--nospam--at)]
Sent: Thursday, December 19, 2002 7:19 PM
To: seaint(--nospam--at)
Subject: RE: PEMB and AISC Seismic Provisions


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.
Civil Engineer
Public Works, Engineering Department
Fort Richardson, Alaska
phone: 907-384-3161
e-mail: scott.haan(--nospam--at)

-----Original Message-----
From: Mark D. Anderson PE [mailto:mark(--nospam--at)]
Sent: Thursday, December 19, 2002 1:19 PM
To: seaint(--nospam--at)
Subject: PEMB and AISC Seismic Provisions

Regarding PEMB,
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?
Thank you,
Mark D. Anderson  PE