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RE: ASCE 7-98 Kd Wind factor

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When taken literally, the code language makes it difficult to interpret the
provisions. I recommend reading commentary section C2.3.2 in ASCE 7-02. This
explains that the load factor for wind was increased in ASCE 7 from 1.3 to
1.6 when the directionality factor was introduced. Thus, when strength
design load combinations being used use a 1.6 load factor, it seems
reasonable to include the directionality factor. 

IBC Alternate allowable stress design load combinations require an
additional 1.3 factor when wind loads are calculated per ASCE 7. This seems
to be intended to allow the use of the directionality factor, using the 1.3
factor to offset its effects.  
 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com 
________________________________

	From: Jim Carey [mailto:jimcarey(--nospam--at)jgsteel.com] 
	Sent: Wednesday, October 06, 2004 9:07 AM
	To: seaint(--nospam--at)seaint.org
	Subject: Re: ASCE 7-98 Kd Wind factor
	
	If IBC is specified, which refers to ASCE 7 for wind design, the IBC
load combinations would seem to apply.  That would dictate the omission of
the Kd factor.  To compound the original question, is that the proper
approach?  Resulting wind loads are obviously higher, particularly when the
1.3 omega factor is included with the Alternate basic load combinations of
IBC 1605.3.2.

	> ASCE 7-98 added the directionality factor Kd.  The standard states
the Kd
	> factor is only to be used when sections 2.3 & 2.4 are used.
Sections 2.3
	> & 2.4 are the factored and allowable stress load combinations.
	>
	> Can anybody tell me when I wouldn't use section 2.3 or 2.4 for
design and
	> therefore can't use the Kd factor?
	>
	> Thanks.

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