To: "Alan Carr (E-mail)" <carr(--nospam--at)icbo.org>, "Lanny Flynn (E-mail)" <flynn(--nospam--at)aiscmail.com>, "Seaint list (E-mail)" <seaint(--nospam--at)seaint.org>, "IBC list (E-mail)" <IBC_IRC(--nospam--at)listbot.com>
Subject: 1997 AISC seismic - IBC seismic design category D - OBF brace co nnections - column strength
From: "Haan, Scott M." <HaanSM(--nospam--at)ci.anchorage.ak.us>
Date: Tue, 1 May 2001 07:10:50 -0800
1997 AISC Seismic Provisions Section 4.1 indicates orthogonal effects are
not required with special load combinations including OMEGAo*Qe.
IBC 1620.3.5 always requires orthogonal effects to be considered for Seismic
Design Category D. IBC 1617.1.2 does not say that orthogonal effects are
not required when considering the special load combinations in the IBC.
1997 UBC only required orthogonal effects for highly load columns at
intersecting lateral systems, non-parallel systems and torsional
irregularities and didn't say orthogonal effects did not need to be
considered with special load combinations for ASD steel design [it did for
It seems the intent of the IBC is to use the orthogonal effects with the
special load combinations in Seismic Design Category D. Is this an
oversight in the conversion to the IBC from the UBC, that the AISC
provisions were not amended? Should orthogonal effects be included in
special load combinations for columns, and brace connections in Seismic
Design Category D? For tension only braces?
Scott M Haan P.E.
Plan Review Engineer
Building Safety Division http://www.muni.org/building
Development Services Department
Municipality of Anchorage
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