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RE: 94 UBC and Rigid Plywood Diaphragms??????

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This language is exactly as it appeared in section 1628.5 of 1994 UBC.

	-----Original Message-----
	From:	Cain, William [SMTP:bcain(--nospam--at)ebmud.com]
	Sent:	Monday, May 03, 1999 10:52 AM
	To:	'seaint(--nospam--at)seaint.org'
	Subject:	RE: 94 UBC and Rigid Plywood Diaphragms??????

	Thor-
	The pertinent section of the 1997 UBC reads:

	"Section 1930.6 Horizontal Distribution of Shear.  The design story
shear,
	Vx, in any story is the sum of the forces Ft and Fx above that
story.  Vx
	shall be distributed to the various elements of the vertical
	lateral-force-resisting system in proportion to their rigidities,
	considering the rigidity of the diaphragm.  Se Section 1633.2 for
rigid
	elements that are not intended to be part of the
lateral-force-resisting
	systems.

	Where diaphragms are not flexible, the mass at each level shall be
assumed
	to be displaced from the calculated center of mass in each direction
a
	distance equal to 5 percent of the building dimension at that level
	perpendicular to the direction of the force under consideration.
The effect
	of this displacement on the story shear distribution shall be
considered.

	Diaphragms shall be considered flexible for the purposes of
distribution of
	story shear and torsional moment when the maximum lateral
deformation is
	more than two times the average story drift of the associated story.
This
	may be determined by comparing the midpoint in-plane deflection of
the
	diaphragm itself under lateral load with the story drift of
adjoining
	vertical-resisting elements under equivalent tributary lateral
load."
	 
	Bill Cain, SE
	Oakland, CA


		-----Original Message-----
		From:	vicpeng [SMTP:vicpeng(--nospam--at)vtcg.com]
		Sent:	Monday, May 03, 1999 10:15 AM
		To:	seaint(--nospam--at)seaint.org
		Subject:	Re: 94 UBC and Rigid Plywood
Diaphragms??????

		I don't have a copy of the UBC.  Could someone send a copy
of that
	definition of rigid vs. flexible diaphragm?

		Thor Tandy  P.Eng  MCSCE
		Victoria BC
		Canada
		vicpeng(--nospam--at)vtcg.com <mailto:vicpeng(--nospam--at)vtcg.com> 

			-----Original Message-----
			From: Robert J Bossi, PE < rjbossi(--nospam--at)sonic.net
	<mailto:rjbossi(--nospam--at)sonic.net> >
			To: seaint(--nospam--at)seaint.org <mailto:seaint(--nospam--at)seaint.org>  <
	seaint(--nospam--at)seaint.org <mailto:seaint(--nospam--at)seaint.org> >
			Date: Monday, May 03, 1999 10:08 AM
			Subject: Re: 94 UBC and Rigid Plywood
Diaphragms??????
			
			
			Dennis: 

			I was surprised to find that the current definition
of
	flexible versus rigid diaphragm first appeared in the 1988 UBC
(2312(e)6 on
	page 148).