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RE: Calculation of drift in Wood Frame Buildings

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Element 3 "Codes and Standards Element" report of the CUREE-Caltech
woodframe project addressed this issue.  Please see the following link for
the final draft of the Codes and Standards Report.  You'll want to download
topical discussion D (shearwalls).  D.6.2 has a one page discussion on the
requested topic.  Gypsum is mentioned in other portions of this topical
discussion, so a careful review is in order.

http://www.curee.org/projects/woodframe_project/element3/draft_d.html

It's about 150 pages or so (6.5Mbyte download), so you better have a fast
printer and a fast internet connection.

-----------------------------------------------------------------------
Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
P.O. Box 11700
Tacoma, WA 98411-0700
ph: 253/565-6600
fx: 253/565-7265
-----------------------------------------------------------------------

> -----Original Message-----
> From: Al Meyer [mailto:ameyer(--nospam--at)cagleyharman.com]
> Sent: Thursday, January 16, 2003 15:25
> To: SEAINT(--nospam--at)SEAINT.ORG
> Subject: Calculation of drift in Wood Frame Buildings
> 
> 
> List -
> 
> I know that in recent times we are trending away from the use 
> of gypsum
> sheathed shear walls based on their performance in recent 
> seismic events.
> The IBC 2000 does, however, provide values for shear 
> resistance for gypsum
> sheathed shear walls.
> 
> Essentially if your building is an SDC A you don't have to do a formal
> lateral analysis of the building, although a minimum force level and
> connection requirements still must be considered.  When a wood frame
> building is such that it is in an SDC of B or higher and it 
> does not meet
> the requirements for a simplified analysis (which allows 
> story drift to be
> be computed as 1% of the floor to floor height) or the requirements of
> section 2308, Conventional Light Frame Construction, it must 
> be analyzed as
> specified by the code.
> 
> In the past, wood sheathed diaphragms were generally 
> considered flexible,
> and Breyer's "Design of Wood Structures" textbook even states 
> this.  Now, a
> wood diaphragm may be flexible or rigid depending on its 
> deflection relative
> to its supporting shear walls.  Equations are available to 
> calculate the
> deflection of wood panel shear walls, but there is no 
> rational basis (per
> information I have read in NEHRP documents) for calculating 
> deflection of
> gypsum sheathed shearwalls.
> 
> While it seems logical that in many cases a wood diaphragm 
> would seem to be
> rigid relative to gypsum sheathed shear walls, I'm certain 
> that this isn't
> always the case.  How has anyone handled this issue other 
> than the obvious
> route of not using gypsum sheathed shearwalls?  I kn	ow that 
> buildings have
> been constructed all over the country which have used gypsum 
> shear walls but
> don't know how anyone else has handled drift calculations.  Thanks in
> advance for any input you can provide.
> 
> Albert J. Meyer, Jr., P.E.
> Cagley, Harman and Associates
> Structural Engineers / Parking Consultants
> 1015 West Ninth Avenue
> King of Prussia PA 19406-1222
> ameyer(--nospam--at)cagleyharman.com
> (610) 337-3360
> (610) 337-3359 Fax
> www.cagleyharman.com
> 
> 
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