] [Thread] [Date] [Author]

["Haan, Scott M." <HaanSM(--nospam--at)ci.anchorage.ak.us>]

Chapter 16 of 2000 IBC does not say you can automatically take a 1.33
allowable stress increase for all materials when wind or seismic forces are
used, with the exception of foundation soil pressure per 1616.1.

IBC 1605.3.2 says to see the material's chapter for determing wind/seismic
allowable stress increases for "alternate basic load combinations".  IBC
1605.3.1.1 says that for the "basic load combinations" you can't use
wind/seismic increases except for wood load duration factors.  The idea for
wood in the IBC is to use the load duration factors out of NDS 2.3.2.3.

ACI 530-99 Section 2.1.1.2.3.2 says when you can use an 1.33 increase for
masonry and AISC ASD 89 Section A5.2 says when you can use an 1.33 increase
for steel.



-----Original Message-----
From: utej(--nospam--at)attbi.com [mailto:utej(--nospam--at)attbi.com]
Sent: Thursday, April 11, 2002 10:14 AM
To: seaint(--nospam--at)seaint.org
Subject: '97 UBC section 2316 comparision to 2000 IBC section 2306


The 2000 IBC section 2306 references the NDS for ASD 
design and I do not see any deletions or substitutions 
similar to the '97 UBC section 2316.2.  The '97 UBC 
section 2316.2 states that "When using Section 
1612.3.2....the 1/3 increase shall not be used 
concurrently with the Load Duration Factor, CD."  It 
also revises the NDS table 2.3.2 to use CD=1.33 for 
earthquake and 1.6 for wind for members and nailed and 
bolted connections exhibiting Mode III or IV behavior.

I could not find these deletions and substitutions in 
the 2000 IBC and in IBC section 1605.3.1.1 it states 
that "Increases in allowable stresses specified in the 
appropriate materials section of this code....shall not 
be used with the load combinations of 1605.3.1 except 
that a duration of load increase shall be permitted in 
accordance with Chapter 23."  There is no statements 
that I could find in the 2000 IBC that stated that one 
shall not take the 1.33 or 1.6 load duration factor 
increase in conjunction with the 1.33 stress increase 
such as the '97 UBC section 2316.2 states.

Are these purposeful omissions and modification of 
design requirements in the 2000 IBC compared to the 1997 
UBC or perhaps an oversight? 

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