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RE: 1.7 allowable increase gone? 2003 IBC

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The 1.7 is intended to convert ASD to strength (or so I thought) for use in the Em combinations.  Are you allowed to divide Em by 1.4?  You couldn't before, maybe now you can.  That would make things more consistent.  Unfortunately I don't have the '03 code yet, but have a look.
 
Jake Watson, P.E.
Salt Lake City, UT
-----Original Message-----
From: Chad Druffel [mailto:CDruffel(--nospam--at)AHBL.com]
Sent: Friday, September 12, 2003 7:36 PM
To: seaint(--nospam--at)seaint.org
Subject: 1.7 allowable increase gone? 2003 IBC

List:
 
IBC Section 1617.1.1.2 indicates that an allowable stress increase of 1.7 can be used with the amplified seismic forces, which is not a change for me...great.  Except, this only applies when you are using the simplified analysis procedure, which is only allowed to be used for relatively small structures (and I'm assuming that the simplified analysis is overly conservative anyways, if this code follows how the 97 UBC worked).
 
When using the equivalent lateral force procedure, you are directed to ASCE 7-02, which in turn only permits the use of a 1.2 allowable increase for the amplified loads!  Is this correct?  I thought that it must be a typo so I searched for an errata to the 7-02, but nothing is out there.  This is a whopping 42% increase in force.  Does anyone have input?  Looks like I'm almost being forced to switch to strength design.
 
A conflict is that the seismic provisions for steel structures (AISC 341-02) specifically indicate that the 1.7 increase may be used.
 
This brings up an additional point.  What has happened to the 1/3 stress increase for steel design when used with non-amplified seismic or wind loads?  The 9th Addition AISC had it in there, but it was then removed by Supplement #1 (December 17, 2001), and instead put the responsibility on the applicable building code.  IBC 2003 does not reference a 1.33 allowable increase for steel design as far as I have seen (they in turn put the responsibility back on AISC), except in the case of the amplified seismic load.
 
 
 
Chad P. Druffel, P.E.